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International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information andCommunications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 49 Transient Stability Investigations of the Wind-Diesel Hybrid Power Systems Pawan Sharma Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi India E-mail- [email protected] Abstract This paper presents automatic reactive power control of the isolated wind-diesel hybrid power systems. The synchronous generator (SG) is used for power generation from diesel and the induction generator (IG) is used for electric power generation from wind turbine. To minimize the gap between reactive power generation and demand, the variable sources of reactive power is used such as static synchronous compensator (STATCOM). The mathematical model of the STATCOM based on reactive power flow equations is developed with the wind-diesel hybrid power system. The examples of the wind-diesel hybrid power systems considered in the paper are multi-wind/single diesel, and single wind/multi- diesel. The study is based on small signal analysis by considering IEEE type-1 excitation system for the synchronous generator. The paper also shows the dynamic performance of the hybrid system for 1% step change in reactive power load without any change in input wind power i. e. constant slip, and for 1% step change in reactive power load with 1% step increase in input wind power i. e. variable slip. Keywords: Induction generator, synchronous generator, wind-diesel hybrid power system, STATCOM.. 1. Introduction There has been a continuous enhancement of power generation from renewable energy sources in recent years. The reasons for renewable energy sources getting more and more popular are that they are clean sources of energy, able to replenished quickly, sustainable, and eco-friendly. The only disadvantage is that they are intermittent in nature. To enhance the capacity and reliability of the power supply of local grids, the renewable energy sources like solar, wind, mini/micro hydro, etc. are integrated with diesel system. This combination of conventional and non-conventional energy sources is called as isolated hybrid power system [1]-[3]. Normally, synchronous generators and induction generators are chosen with diesel generators and wind turbines respectively [3]. Reduction in unit cost, ruggedness, brushless (in squirrel cage construction), absence of separate DC source for excitation, easy maintenance, self protection against severe overloads and short circuits etc, are the main advantages of an IG [4]-[7], but they require reactive power for their operation. Due to the mismatch between generation and consumption of reactive power, more voltage fluctuations at generator terminal occur in an isolated system which reduces the stability and quality of the supply. The problem becomes more complicated in hybrid system having both induction and synchronous generators. Many papers have appeared in the literature, which suggest different methods using fixed capacitors bank for providing the reactive power under steady state conditions [5]. As induction generator reactive power demand varies, the fixed capacitors are International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 50 unable to provide adequate amount of reactive power support to isolated power system under varying input wind power and load conditions [6]. Various Flexible AC transmission system (FACTS) devices are available which can supply fast and continuous reactive power [9]-[11]. For standalone applications, effective capacitive VAR controller has become central to the success of the induction generator system. Switched capacitors, static VAR compensator (SVC) and static synchronous compensator (STATCOM) can provide the reactive power. A switched capacitor scheme is cheaper, but it regulates the terminal voltage in discrete steps. Large values of capacitors and reactors are required in SVC scheme [9]. STATCOM employs a voltage source converter (VSC) that internally generates inductive/capacitive reactive power which has the advantages over the SVC scheme [9]. The different isolated hybrid power systems considered in the paper are multi-wind/single diesel, and single wind/multi- diesel. Multi-wind/single diesel systems attenuate the effect of power fluctuations produced by the turbulence of the wind. In fact, it is estimated that the variability of the power should decrease by the square root of the number of wind turbines [1]. Thus the need for short-term storage would decrease when the wind generation capacity is made up of more than one machine. Single wind/ multi-diesel systems allow a variety of possible operation and control strategies. Typically the most efficient diesel generators are allowed to run at their rated output. Load fluctuations are supplied by one of the less efficient diesel generators, which are allowed to cycle up and down. Diesel grid of Block Island, USA [1] is such type of an example. First the system state equations are derived from real and reactive power balance equations of the system. A voltage deviation signal is used by STATCOM controller to eliminate the reactive power mismatch in the system. Also the voltage deviation signal is used by excitation system of the synchronous generator to eliminate the voltage deviation. The integral square error (ISE) criterion is used to evaluate the optimum gain settings of the controller parameters. Finally, the transient responses of the hybrid systems are also shown for IG coupled with wind turbine. 2. Mathematical Modeling of Wind-Diesel Hybrid Power System A wind-diesel hybrid power system with STATCOM considered for study is shown in Fig.1. The real and reactive power balance equations of the system under steady state conditions are given by IG SG L P P P + = (1) SG com L IG Q Q Q Q + = + (2) L L P jQ + IG Q IG P Figure 1. Single Line Diagram of the Wind-Diesel Hybrid Power System International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 51 Due to disturbance in load reactive power L Q ∆ , the system voltage may change which results an incremental change in reactive power of other components. The net reactive power surplus is SG com L IG Q Q Q Q ∆ + ∆ − ∆ − ∆ and it will change the system bus voltage which will govern by the following transfer function equation [8]: | | ( ) ( ) ( ) - ( ) - ( ) 1 V SG com L IG V K V s Q s Q s Q s Q s sT ∆ = ∆ + ∆ ∆ ∆ + , (3) where, V K and V T are the system gain and time constant. All the connected loads experience an increase with the increase in voltage due to load voltage characteristics as shown below L V Q D V ∂ = ∂ (4) The composite loads can be expressed in exponential voltage form as 1 q L Q c V = (5) The load voltage characteristics V D can be found empirically as 0 0 . L L V Q Q D q V V ∆ = = ∆ (6) In equation (3) 1 / V V K D = and V T is the time constant of the system which is proportional to the ratio of electromagnetic energy stored in the winding to the reactive power absorbed by the system. An IEEE type-1 excitation control system as shown in Fig. 2 is considered for the synchronous generator of the hybrid system with saturation neglected, therefore the state transfer equations [8] are 1 ( ) ( ) fd a E E E s V s K sT ∆ = ∆ + (7) ( ) ( ) ( ) ( ) 1 A F a fd f A F K K V s V s E s V s sT T | | ∆ = −∆ − ∆ + ∆ | + \ ¹ (8) 1 ( ) . ( ) 1 F f fd F A K V s E s T sT ∆ = ∆ + (9) The small change in voltage behind transient reactance ( ) q E s ′ ∆ by solving the flux linkage equation [3] for small perturbation is given below 1 2 1 ( ) ( ) ( ) (1 ) q fd G E s K E s K V s sT ′ ( ∆ = ∆ + ∆ ¸ ¸ + (10) where 1 ' / d d K X X = (11) ( ) 2 ' cos / ' d d d K X X X δ = − ( ¸ ¸ (12) and ' ' / G do d d T T X X = (13) International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 52 1 E E K sT + ( ) fd E s ∆ ( ) a V s ∆ ( ) V s ∆ ( ) V s ( ) ref V s Figure 2. IEEE Type-1 Excitation Control System The small change in synchronous generator reactive power in terms of state variables is given by [8] 3 4 ( ) ( ) ( ) SG q Q s K E s K V s ′ ∆ = ∆ + ∆ (14) where 3 cos / ' d K V X δ = (15) and | | 4 ' ' cos 2 / d K E V X δ = − (16) Similarly ( ) IG Q s ∆ can be expressed in terms of system state variables as given below. For small perturbations, the reactive power absorbed by induction generator, IG Q ∆ , in terms of generator terminal voltage, and generator parameters can be written as [8] 5 ( ) ( ) IG Q s K V s ∆ = ∆ (17) where ( ) 2 2 5 K 2 / eq y eq VX R X = + (18) Y P eq R R R = + (19) 2 ' (1 ) P r R s s = − (20) Similarly, for variable slip conditions, the reactive power absorbed by induction generator, IG Q ∆ , in terms of generator terminal voltage, slip and generator parameters can be written as [8] 6 7 ( ) ( ) ( ) IG IW Q s K P s K V s ∆ = ∆ + ∆ (21) where ( ) { } 2 2 6 / - / 2 eq p Y eq Y K X R R X R = + ( ¸ ¸ (22) International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 53 { } 2 2 2 2 7 2 / ( ) / [ - ( ) / -{( ) / 2 } Y eq eq p eq P Y eq Y K V R X X R X R R X R ( = + + ¸ ¸ (23) The STATCOM is based on a solid state synchronous voltage source that is analogous to an ideal synchronous machine which generates a balanced set of three sinusoidal voltages, at the fundamental frequency, with rapidly controllable amplitude and phase angle. The configuration of a STATCOM is shown in Fig. 3. It consists of a voltage source converter (VSC), a coupling transformer, and a d. c. capacitor as shown in Fig. 3(a). The real current of the STATCOM is negligible and is assumed to be zero. Control of reactive current is possible by variation of δ andα as shown in Fig. 3 (b). Here δ is the phase angle of the system bus voltage, V where STATCOM is connected and α is the angle of the fundamental output voltage, dc kV of the STATCOM [12]. The magnitude of the fundamental component of the converter output voltage is dc kV , where dc V represent the voltage across the capacitor. The reactive power injection to the system bus has the form: [12], 2 - cos( - ) sin( - ) com dc dc dc Q kV B kV VB kV VG α δ α δ = + (24) The system bus voltage V is taken as reference voltage, therefore the angle δ is zero. Also G is negligible as G jB + represent the step down transformer admittance. Therefore, considering the value of G andδ to be zero, equation (24) can be written as 2 - cos com dc dc Q kV B kV VB α = (25) The flow of reactive power depends upon the variables V and α , therefore for small perturbation the linearized STATCOM equation can be com Q Q ∆Q = ∆α+ ∆V α V ∂ ∂ ∂ ∂ (26) Substituting the value of partial derivatives from equation (25) in equation (26), we get 8 9 ( ) ( ) ( ) com Q s K s K V s α ∆ = ∆ + ∆ (27) 8 dc K kV VB Sinα = (28) dc V (a) (b) Figure 3. STATCOM Configuration (a) Schematic Diagram (b) Equivalent Circuit V S C A . C . d c k V α ∠ V δ ∠ G j B + International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 54 9 - cos dc K kV B α = (29) where, 6 k= . 6 p π and p is the pulse number of the inverter with modulation index unity [12]. A simulation model of the system has been developed as shown in Fig. 4 (Matlab/Simulink). The dotted line blocks are shown when variable slip is considered. The constants, shown in Fig. 4, are given in the Appendix. The constant 5 K in eq. (12) is replaced by 51 K , and 52 K in the case of multi-wind/ single diesel system as induction generators are used with two wind sources. The constant 6 K in eq. (16) is replaced by 61 K , and 62 K and 7 K in eq. (16) is by 71 K and 72 K in the case of multiple wind/single diesel system shown in Fig. 4(a) as IGs are used with multi-wind sources. In case of single wind/multi-diesel system, the constants 1 K , 2 K , 3 K ,and 4 K in eq. (10) and 11 for 1 SG is replaced by 11 21 , K K , 31 K and 41 K respectively, and for 2 SG , is replaced by 12 22 , K K , 32 K , and 42 K , respectively as shown in Fig. 4 (b) 3. Transient Response of the Hybrid Power Systems The computer simulation of the wind-diesel hybrid systems have been carried out and the transient/dynamic performance is presented in this section. Two examples of the wind-diesel hybrid system as multi-wind/single diesel, single wind/multi-diesel have been investigated. The data of the wind-diesel hybrid power systems are given in the Appendix. The proportional and integral gains, P K and I K of the STATCOM were optimized using Integral Square Error (ISE) technique and the values of the gains are given in Table 1. Table 1 Optimized gain values of the PI controller Hybrid Power systems data Constant Slip Variable Slip P K I K P K I K Multi-Wind/Single diesel system 44 6818 41 6491 Single Wind /Multi-diesel system 108 14800 101 14687 The dynamic performances for 1% step increase in load, L Q ∆ without any change in input wind power, IW P ∆ , for multi-wind/single diesel system are shown in Fig. 5 and dynamic performances for 1% step increase in load, L Q ∆ with 1% step increase in input wind power, IW P ∆ , for multi-wind/single diesel system are shown in Fig. 6. The dynamic performances for 1% step increase in load, L Q ∆ without any change in input wind power, IW P ∆ , for single wind/multiple diesel system are shown in Fig. 7 and dynamic performances for 1% step increase in load, L Q ∆ with 1% step increase in input wind power, IW P ∆ , for single wind/multiple diesel system are shown in Fig. 8. International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 55 ( ) V s ∆ ( ) V s ∆ ( ) L Q s ∆ ( ) com Q s ∆ ( ) IW P s ∆ ( ) IW P s ∆ ( ) fd E s ∆ ' ( ) q E s ∆ 8 K 9 K 71 K 61 K 62 K 72 K ( ) SG Q s ∆ ( ) IG Q s ∆ 51 K 52 K ( ) IG Q s ∆ (a) ( ) V s ∆ ( ) V s ∆ ( ) L Q s ∆ ( ) c o m Q s ∆ ( ) SG Q s ∆ ( ) IG Q s ∆ 8 K 9 K ( ) IW P s ∆ 6 K 7 K 5 K (b) Figure 4. Transfer Function Block Diagram of the Systems (a) Multi-wind/ Single-diesel System (b) Single-wind/Multi-diesel International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 56 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -8 -6 -4 -2 0 2 4 x 10 -4 (a) (b) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -5 -4 -3 -2 -1 0 1 2 3 x 10 -5 (c) (d) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 0.005 0.01 0.015 (e) Figure 5.Transient responses of the multi-wind/single diesel hybrid power system for a 1% step increase load, and without any increase in input wind power showing time vs (a) V ∆ , (b) 1 IG Q ∆ , (c) 2 IG Q ∆ ,(d) SG Q ∆ , and (e) com Q ∆ 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -5 -4 -3 -2 -1 0 1 2 3 x 10 -5 ∆ V i n p u ∆ Q I G 1 i n p . u . Time in sec Time in sec ∆ Q I G 2 i n p . u . ∆ Q S G i n p u Time in sec Time in sec 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -4 -3 -2 -1 0 1 2 3 4 5 x 10 -3 Time in sec ∆ Q c o m i n p u International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 57 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -8 -6 -4 -2 0 2 4 x 10 -4 (a) (b) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 x 10 -4 (c) (d) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 (e) Figure 6. Transient responses of the multi-wind/single diesel hybrid power system for a 1% step increase load, and 1 % increase in input wind power showing time vs (a) V ∆ , (b) 1 IG Q ∆ , (c) 2 IG Q ∆ ,(d) SG Q ∆ , and (e) com Q ∆ 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 x 10 -4 ∆ V i n p u ∆ Q I G 1 i n p . u . Time in sec Time in sec ∆ Q c o m i n p u Time in sec 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -4 -2 0 2 4 6 x 10 -3 ∆ Q I G 2 i n p . u . ∆ Q S G i n p u Time in sec Time in sec Time in sec International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 58 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -5 -4 -3 -2 -1 0 1 2 3 4 x 10 -4 (a) (b) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -3 -2 -1 0 1 2 3 4 x 10 -3 (c) (d) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 0.005 0.01 0.015 (e) Figure 7. Transient responses of the single wind/multiple diesel hybrid power system for a 1% step increase load, and no increase in input wind power showing time vs (a) V ∆ , (b) IG Q ∆ , (c) 1 SG Q ∆ ,(d) 2 SG Q ∆ , and (e) com Q ∆ 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -3 -2 -1 0 1 2 3 4 x 10 -3 Time in sec Time in sec ∆ Q S G 1 i n p . u . ∆ Q S G 1 2 i n p . u . ∆ Q C o m i n p . u . Time in sec 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x 10 -5 ∆ V i n p u ∆ Q I G i n p u Time in sec Time in sec International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 59 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -6 -4 -2 0 2 4 x 10 -4 (a) (b) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -3 -2 -1 0 1 2 3 4 x 10 -3 (c) (d) 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 0.005 0.01 0.015 (e) Figure 8. Transient responses of the single wind/multiple diesel hybrid power system for a 1% step increase load, and with 1% step increase in input wind power showing time vs (a) V ∆ , (b) IG Q ∆ , (c) 1 SG Q ∆ ,(d) 2 SG Q ∆ , and (e) com Q ∆ Time in sec 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -3 -2 -1 0 1 2 3 4 x 10 -3 ∆ Q S G 1 i n p . u . ∆ Q S G 1 2 i n p . u . Time in sec Time in sec ∆ Q C o m i n p . u . Time in sec 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -2 -1 0 1 2 3 4 x 10 -5 ∆ V i n p u ∆ Q I G i n p u Time in sec International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 60 From Fig. 5-8, it is observed that the STATCOM provides the reactive power required by the load and the induction generator or induction generators under steady state condition, but initially the synchronous generator or synchronous generators is able to meet total demand. It has also been found that the increase in input wind power result in increased fluctuations in IG Q ∆ , without effecting the settling time of the transient responses as shown in Fig. 5 (b), 5(c), 6(b), 6(c), 7(b), 8(b). In the case of multi-wind/single diesel system, the STATCOM under steady state condition provides reactive required by the load and induction generator or induction generators due to 1% step increase in input wind power as shown in Fig. 6. In case of single wind / multi-diesel system, there is no change in the settling time of the responses, but initially both the synchronous generators satisfy the reactive power requirement by sharing according to their size and finally STATCOM provides the required power under steady state condition as shown in Fig. 8. 4. Conclusions The reactive power control of the isolated wind-diesel hybrid power systems has been presented in this paper. Induction generator or induction generators has been considered for electric power generation from wind turbine and STATCOM for providing variable reactive power required by the system. The examples of the wind-diesel hybrid power systems considered in this paper are multi-wind/single diesel, and single wind/multi-diesel. A complete dynamic model of the system has been derived to study the effect of load disturbances and input wind power disturbances. In the case of multi-wind/single diesel system, the STATCOM under steady state condition provides reactive required by the load and the induction generator or induction generators due to the change in the slip. The deviations in SG ∆V,∆Q become zero under steady state conditions. In case of single wind/multi-diesel system, there is no change in the settling time of the responses, but initially both the synchronous generator and synchronous generators satisfy the reactive power requirement by sharing according to their size and finally STATCOM provides the required power under steady state condition. Nomenclature M E = Electromagnetic energy stored in the IG. M E ∆ = Small change in the stored electromagnetic energy of IG. fd E ∆ , q E ∆ , ' q E ∆ = Small change in the voltages of the exciter, internal armature under steady state, and transient conditions, respectively. , , A E F K K K = Voltage regulator, exciter, stabilizer gain constants, respectively. , P I K K = Proportional and integral controller gains of the STATCOM regulator, respectively. IG P , IG Q = Real and reactive power generated by the IG. SG P , SG Q = Real and reactive power generated by diesel set with synchronous generator. L P , L Q = Real and reactive power of the load. com Q , Reactive power generated by compensator. V ∆ = Incremental change in the voltage. α ∆ = Incremental change in the phase angle of STATCOM. International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 61 s = Slip of IG. ' do T = Direct-axis open-circuit transient time constant. V = System terminal voltage. , , a f V V V ∆ ∆ ∆ = Small changes in system terminal voltage, amplifier output voltage, and exciter feedback voltage, respectively. , ' d d X X = Direct-axis reactance of synchronous generator under steady-state and transient- state conditions, respectively. Appendix The data of the proposed hybrid power systems are given below: S. No. Systems Wind 1 (kW) Wind 2 (kW) Diesel1 (kW) Diesel2 (kW) Load in kW 1. Multi-Wind/Single diesel system 150 50 150 - 150+50+100=300 2. Single Wind /Multi- diesel system 150 - 150 75 150+100+50=300 The data of the systems are as follows: System Parameter Multi-Wind/Single diesel system Single Wind / Multi-diesel system Synchronous Generators SG P (p.u. kW) SG Q (p.u. kVAR) q E (p.u.) ' q E (p.u.) δ (degree) ' d X (p.u.) d X (p.u.) ' do T (seconds) SG 0.3333 0.161 1.12418 0.9804 17.24 0.15 1.0 5.0 SG1 SG2 0.3333 0.161 1.12418 0.9804 17.24 0.15 1.0 5.0 0.16667 0.0181 1.10826 1.01 6.91 0.12 1.0 5.0 Induction Generators IG P (p.u. kW) , IG Q (p.u. kVAR) η (%) 1 2 ' r r = (p.u.) 1 2 ' x x = (p.u.) s (%) IG1 IG2 IG 0.5 0.242161 90 0.19 0.56 -3.5 0.6 0.2906 90 0.19 0.56 -3.5 0.16666 0.08072 90 0.55 1.6 -3.4 Load L P (p.u. kW) 1.0 1.0 International Journal International Journal International Journal International Journal of of of of Energy, Energy, Energy, Energy, Information Information Information Information and Communication and Communication and Communication and Communications ss s Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, ,, , 20 20 20 2010 10 10 10 62 L Q (p.u. kVAR) Power Factor 0.75 0.8 0.75 0.8 IEEE Type-1 Excitation System A K E K F K A T (seconds) F S , E T (seconds) 40 1.0 0.5 0.05 0, 0.55 40 1.0 0.5 0.05 0, 0.55 STATCOM 1 T (ms) T α (ms) d T (ms) 10-50 0.2-0.3 1.67 10-50 0.2-0.3 1.67 Reactive Power Data com Q (p.u. kVAR) α (degree) 0.91736 53.32 0.81206 53.2 The data of generation capacity, the excitation control, and load and STATCOM model are given below, Base power=250 kVA, Base Voltage=400 V. References [1] Ray Hunter, George Elliot, Wind-Diesel Systems; A guide to the technology and its implementation, Cambridge University Press, 1994. [2] H. Nacfaire, Wind-Diesel and Wind Autonomous Energy Systems, Elsevier Applied Science, London, 1989. [3] A.A.F. A1-Adem, Load-frequency control of stand-alone hybrid power systems based on renewable energy sources , Ph. D Thesis, Centre for Energy Studies, Indian Institute of Technology, Delhi (India), 1996 [4] R.C. Bansal, T.S. Bhatti, D. P. Kothari, A bibliographical survey on induction generators for application of non-conventional energy systems, IEEE Transactions on Energy Conversion. 18, (2003) 433-439. [5] R. A. David, Induction generator/synchronous condenser system for wind turbine power. Proceeding of IEE. 126 (1979) 69-74. [6] R.C. Bansal, Three phase self-excited induction generators: an overview, IEEE Transactions on Energy Conversion. 20, 2 (2005)292-299. [7] R.C. Bansal, T.S. Bhatti, V. Kumar, Reactive power control of autonomous wind-diesel hybrid power systems using ANN. Proceedings of the IEEE Power Engineering Conference, (2007) 982-987 [8] R.C. Bansal ‘Automatic reactive power control of autonomous hybrid power system’ Ph.D. Thesis, Centre for Energy Studies, Indian Institute of Technology, Delhi, 2002. [9] K. R. Padiyar, FACTS Controllers in Power Transmission and Distribution, New Age International Publishers, 2008. [10] NG Hingorani, L Gyugyi, Understanding FACTs: Concepts and technology of Flexible AC Transmission Systems. New York: IEEE Power Eng. Soc., 2000. [11] Kalyan K. Sen, Mey Ling Sen. Introduction to FACT controllers: theory, modeling and applications. Willey & Sons Publication. [12] Kouadri B, Tahir Y. Power flow and transient stability modeling of a 12-pulse Statcom. Journal of Cybernetic and Informatics, 7 (2008) 9-25. International Journal International Journal International Journal International Journal of of of of Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Energy, Information and Communications Vol. Vol. Vol. Vol. 1 11 1, , , , Issue Issue Issue Issue 1 11 1, , , , November November November November, 2 , 2 , 2 , 2010 010 010 010 63 Authors Pawan Sharma received the A. M. I. E. degree from Institution of Engineers, India, in 2005, the M. Tech degree from National Institute of Technology, India, in 2008 and at present pursuing PhD from the Indian Institute of Technology Delhi. His research interests include automatic generation control, reactive power control, hybrid power systems, and wind and small hydro systems. Switched capacitors. The real and reactive power balance equations of the system under steady state conditions are given by PIG + PSG = PL QSG + Qcom = QL + QIG PIG QIG (1) (2) PL + jQL Figure 1. Diesel grid of Block Island. Thus the need for short-term storage would decrease when the wind generation capacity is made up of more than one machine. A switched capacitor scheme is cheaper. effective capacitive VAR controller has become central to the success of the induction generator system. The different isolated hybrid power systems considered in the paper are multi-wind/single diesel. For standalone applications. Large values of capacitors and reactors are required in SVC scheme [9]. In fact.diesel. Single Line Diagram of the Wind-Diesel Hybrid Power System 50 . Typically the most efficient diesel generators are allowed to run at their rated output. 1. static VAR compensator (SVC) and static synchronous compensator (STATCOM) can provide the reactive power. 2010 Vol. The integral square error (ISE) criterion is used to evaluate the optimum gain settings of the controller parameters. but it regulates the terminal voltage in discrete steps. the transient responses of the hybrid systems are also shown for IG coupled with wind turbine. which are allowed to cycle up and down. 2. November. First the system state equations are derived from real and reactive power balance equations of the system. A voltage deviation signal is used by STATCOM controller to eliminate the reactive power mismatch in the system. and single wind/multi. Multi-wind/single diesel systems attenuate the effect of power fluctuations produced by the turbulence of the wind. Single wind/ multi-diesel systems allow a variety of possible operation and control strategies. USA [1] is such type of an example. Finally.Communications International Journal of Energy. Mathematical Modeling of Wind-Diesel Hybrid Power System A wind-diesel hybrid power system with STATCOM considered for study is shown in Fig. 2010 unable to provide adequate amount of reactive power support to isolated power system under varying input wind power and load conditions [6]. Information and Communications November. it is estimated that the variability of the power should decrease by the square root of the number of wind turbines [1].1. Also the voltage deviation signal is used by excitation system of the synchronous generator to eliminate the voltage deviation. Issue 1. Load fluctuations are supplied by one of the less efficient diesel generators. STATCOM employs a voltage source converter (VSC) that internally generates inductive/capacitive reactive power which has the advantages over the SVC scheme [9]. Various Flexible AC transmission system (FACTS) devices are available which can supply fast and continuous reactive power [9]-[11]. therefore the state transfer equations [8] are ∆E fd ( s ) = 1 ∆Va ( s ) K E + sTE (7)  KA  KF ∆E fd ( s ) + ∆V f ( s )  (8)  −∆V ( s ) − 1 + sTA  TF  K 1 ∆V f ( s ) = F . 2 is considered for the synchronous generator of the hybrid system with saturation neglected. 2010 Vol. Information and Communications November. ∆E fd ( s ) (9) TF 1 + sTA ′ The small change in voltage behind transient reactance ∆Eq ( s ) by solving the flux linkage ∆Va ( s ) = equation [3] for small perturbation is given below ′ ∆Eq ( s ) = where 1  K1∆E fd ( s ) + K 2 ∆V ( s )   (1 + sTG )  K1 = X 'd / X d (10) (11) (12) (13) K 2 = ( X d − X 'd ) cos δ  / X 'd   and TG = T 'do X 'd / X d 51 . Issue 1. November. 2010 Due to disturbance in load reactive power ∆QL . the system voltage may change which results an incremental change in reactive power of other components. An IEEE type-1 excitation control system as shown in Fig. 1 + sTV (3) where. 1.∆QL (s) . All the connected loads experience an increase with the increase in voltage due to load voltage characteristics as shown below DV = ∂QL ∂V q (4) The composite loads can be expressed in exponential voltage form as Q L = c 1V DV = (5) The load voltage characteristics DV can be found empirically as ∆QL Q0 = q. KV and TV are the system gain and time constant. L0 ∆V V (6) In equation (3) K V = 1 / DV and TV is the time constant of the system which is proportional to the ratio of electromagnetic energy stored in the winding to the reactive power absorbed by the system.∆QIG (s)] .International Journal of Energy. The net reactive power surplus is ∆QSG + ∆Qcom − ∆QL − ∆QIG and it will change the system bus voltage which will govern by the following transfer function equation [8]: ∆V ( s ) = KV [ ∆QSG ( s) + ∆Qcom ( s) . the reactive power absorbed by induction generator. November. ∆QIG . in terms of generator terminal voltage. slip and generator parameters can be written as [8] ∆QIG ( s ) = K 6 ∆PIW ( s ) + K 7 ∆V ( s ) (21) where K6 = X eq / Rp  {( R 2 Y + X 2 eq ) / 2 R }  Y (22) 52 .Communications International Journal of Energy. for variable slip conditions. For small perturbations. 2010 Vol. IEEE Type-1 Excitation Control System The small change in synchronous generator reactive power in terms of state variables is given by [8] ′ ∆QSG ( s ) = K 3 ∆Eq ( s ) + K 4 ∆V ( s ) where (14) (15) K 3 = V cos δ / X 'd and K 4 = [ E 'cos δ − 2V ] / X ' d (16) Similarly ∆QIG ( s ) can be expressed in terms of system state variables as given below. ∆QIG . the reactive power absorbed by induction generator. 2010 Vref ( s ) V ( s) ∆V ( s ) ∆Va ( s ) ∆E fd ( s ) 1 K E + sTE Figure 2. 1. Issue 1. in terms of generator terminal voltage. and generator parameters can be written as [8] ∆QIG ( s ) = K 5 ∆V ( s ) where (17) (18) (19) (20) K 5 = 2VX eq / ( R 2 y + X 2 eq ) RY = RP + Req RP = r '2 (1 − s ) s Similarly. Information and Communications November. therefore for small perturbation the linearized STATCOM equation can be ∆Q com = ∂Q ∂Q ∆α+ ∆V ∂α ∂V (26) Substituting the value of partial derivatives from equation (25) in equation (26). considering the value of G and δ to be zero. at the fundamental frequency. The configuration of a STATCOM is shown in Fig. where Vdc represent the voltage across the capacitor. 2 Qcom = kVdc B . It consists of a voltage source converter (VSC).C . Control of reactive current is possible by variation of δ and α as shown in Fig. (a) (b) Figure 3.kVdcVB cos α (25) The flow of reactive power depends upon the variables V and α . 2010 2 2 2 2 K 7 =  2V / ( RY + X eq )  / [ X eq . 1. Here δ is the phase angle of the system bus voltage. a coupling transformer. c. we get ∆Qcom ( s ) = K8 ∆α ( s ) + K 9 ∆V ( s ) K 8 = kVdcVB Sinα (27) (28) V ∠δ G + jB k Vdc ∠ α VSC Vdc A . Therefore. STATCOM Configuration (a) Schematic Diagram (b) Equivalent Circuit 53 . kVdc of the STATCOM [12]. The reactive power injection to the system bus has the form: [12]. therefore the angle δ is zero. V where STATCOM is connected and α is the angle of the fundamental output voltage.International Journal of Energy. 2010 Vol. 3.δ ) (24) The system bus voltage V is taken as reference voltage.kVdcVB cos(α . November. The real current of the STATCOM is negligible and is assumed to be zero. and a d. Also G is negligible as G + jB represent the step down transformer admittance. 3(a).{( R p X eq ) / RP -{( RY + X eq ) / 2 RY }}   (23) The STATCOM is based on a solid state synchronous voltage source that is analogous to an ideal synchronous machine which generates a balanced set of three sinusoidal voltages. with rapidly controllable amplitude and phase angle. capacitor as shown in Fig. 3 (b). The magnitude of the fundamental component of the converter output voltage is kVdc .δ ) + kVdcVG sin(α . Information and Communications November. equation (24) can be written as 2 Qcom = kVdc B . Issue 1. the constants K1 . K 32 . ∆PIW . The dynamic performances for 1% step increase in load. for single wind/multiple diesel system are shown in Fig. 1. respectively as shown in Fig. 4(a) as IGs are used with multi-wind sources. and K 62 and K 7 in eq.and K 4 in eq. ∆PIW . 2010 K 9 = -kVdc B cos α 6 π (29) where. 8. (16) is replaced by K 61 . 4 (b) 3. K 31 and K 41 respectively. is replaced by K12 . K 22 . The constants. ∆QL with 1% step increase in input wind power. A simulation model of the system has been developed as shown in Fig. are given in the Appendix. single wind/multi-diesel have been investigated. for single wind/multiple diesel system are shown in Fig. 6 and p is the pulse number of the inverter with modulation index unity [12]. The constant K5 in eq. k= p . In case of single wind/multi-diesel system. 6. The proportional and integral gains. K 2 . (10) and 11 for SG1 is replaced by K11 . The constant K 6 in eq. The dotted line blocks are shown when variable slip is considered. ∆PIW . (12) is replaced by K 51 . 2010 Vol. K 21 . for multi-wind/single diesel system are shown in Fig. and for SG2 . shown in Fig. 54 . for multi-wind/single diesel system are shown in Fig. Two examples of the wind-diesel hybrid system as multi-wind/single diesel. 5 and dynamic performances for 1% step increase in load. November. 4. Issue 1. The data of the wind-diesel hybrid power systems are given in the Appendix. ∆QL without any change in input wind power. Table 1 Optimized gain values of the PI controller Hybrid Power systems data Constant Slip Variable Slip KP Multi-Wind/Single diesel system Single Wind /Multi-diesel system 44 108 KI 6818 14800 KP 41 101 KI 6491 14687 The dynamic performances for 1% step increase in load. Information and Communications November. and K 52 in the case of multi-wind/ single diesel system as induction generators are used with two wind sources. (16) is by K 71 and K 72 in the case of multiple wind/single diesel system shown in Fig. 7 and dynamic performances for 1% step increase in load. K3 . ∆PIW . K P and K I of the STATCOM were optimized using Integral Square Error (ISE) technique and the values of the gains are given in Table 1.Communications International Journal of Energy. Transient Response of the Hybrid Power Systems The computer simulation of the wind-diesel hybrid systems have been carried out and the transient/dynamic performance is presented in this section. ∆QL with 1% step increase in input wind power. ∆QL without any change in input wind power. 4 (Matlab/Simulink). and K 42 . 1. Information and Communications November.International Journal of Energy. 2010 Vol. Transfer Function Block Diagram of the Systems (a) Multi-wind/ Single-diesel System (b) Single-wind/Multi-diesel 55 . 2010 ∆V ( s ) K8 K9 ∆ L(s) Q ∆Qcom ( s ) ∆Q (s) IG K 51 K 52 ∆QSG ( s ) ∆QIG ( s ) K 72 K 62 ∆V ( s ) ∆ IW(s) P K 71 ∆PIW ( s ) K 61 ∆ 'q (s) E ∆ fd (s) E (a) K8 ∆Q (s) L K9 ∆V(s) ∆ com(s) Q ∆QSG (s) ∆V(s) ∆QIG ( s ) K5 K7 ∆P (s) IW K6 (b) Figure 4. Issue 1. November. 002 0.008 0.01 -5 0 0. 2010 Vol.009 0.006 0. November.001 0.001 0.004 0.006 0. Information and Communications November.u.001 0.003 0. (c) ∆QIG 2 . and without any increase in input wind power showing time vs (a) ∆V .005 0.01 Time in sec (e) Figure 5.009 0.(d) ∆QSG .008 0. 2010 4 2 x 10 -4 3 2 1 x 10 -5 0 ∆QIG 1 in p.005 0.007 0.005 0 0 0.01 Time in sec Time in sec (a) 3 2 1 x 10 -5 (b) 5 4 3 2 x 10 -3 ∆QIG 2 in p.01 0 -1 -2 -3 1 0 -1 -2 -4 -3 -5 0 -4 0 0.007 0.009 0.015 (d) ∆Qcom in pu 0.004 0.009 0.005 0.008 0.002 0.u.004 0.01 0.005 0. ∆QSG in pu 0.Communications International Journal of Energy.004 0.006 0.003 0.003 0.003 0. 0 -1 -2 -3 ∆V in pu -2 -4 -6 -8 0 -4 0.003 0. 1.008 0.004 0.009 0. and (e) ∆Qcom 56 . (b) ∆QIG1 .006 0.01 Time in sec Time in sec (c) 0.002 0.007 0.Transient responses of the multi-wind/single diesel hybrid power system for a 1% step increase load. Issue 1.005 0.001 0.002 0.008 0.002 0.007 0.006 0.007 0.001 0. 014 0.u.008 0.002 0 0 0.008 0.5 2 1.01 (d) ∆Qcom in pu 0.003 0. (b) ∆QIG1 .006 0.5 2 0 Time in sec -2 -1 -1. Information and Communications November. Issue 1.003 0. 0.004 0. and (e) ∆Qcom 57 .(d) ∆QSG .009 0.002 0.007 0.009 0.u.5 x 10 ∆QIG 1 in p.005 0.001 0.001 0.008 0.01 0 1 0.003 0.001 0. Transient responses of the multi-wind/single diesel hybrid power system for a 1% step increase load.009 0.002 0. 2010 -4 4 2 x 10 -4 2.009 0.007 0.5 0 -0.008 0. ∆QSG in pu 1 0.002 0.006 0.004 0.5 ∆V in pu -2 -4 -6 -8 0 -1 -1.001 0.5 0 0.004 0.012 0.004 0.005 0. 1.5 0 -0.004 0.009 0.005 0.008 0.007 0. (c) ∆QIG 2 . November.003 0.International Journal of Energy.01 Time in sec Time in sec (c) 0.01 Time in sec Time in sec (a) 2.5 0 0.004 0.007 0.003 0.002 0.005 0.007 0.005 0.01 -4 0 0.006 0. 2010 Vol. and 1 % increase in input wind power showing time vs (a) ∆V .5 x 10 -4 (b) 6 x 10 -3 4 ∆QIG 2 in p.008 0.01 Time in sec (e) Figure 6.5 2 1.006 0.006 0.006 0.001 0.002 0. Communications International Journal of Energy.5 -1 -1.008 0.006 0.5 -2 -2.009 0.01 ∆QCom in p.009 0. 0.006 0.5 0 0.005 0.002 0.01 Time in sec (e) Figure 7.006 0. Information and Communications November.001 0.007 0.007 0.009 0.004 0.5 0 -0.009 0.004 0.007 0.004 0.003 0.004 0.002 0.u. and (e) ∆Qcom 58 .u.007 0.001 0.008 0.01 Time in sec Time in sec (c) 0.008 0. Transient responses of the single wind/multiple diesel hybrid power system for a 1% step increase load.001 0.008 0.003 0. and no increase in input wind power showing time vs (a) ∆V . 1 0 -1 -2 -3 0 ∆QSG12 in p.01 ∆V in pu Time in sec Time in sec (a) 4 3 2 x 10 -3 (b) 4 3 2 x 10 -3 ∆QSG1 in p.002 0.003 0. (b) ∆QIG . Issue 1.01 ∆QIG in pu 1 0.005 0.002 0.001 0. 2010 4 3 2 x 10 -4 2 1.004 0.002 0.003 0.01 1 0 -1 -2 -3 0 0.005 0.u.003 0.008 0.009 0. (c) ∆QSG1 .006 0.001 0. November.(d) ∆QSG 2 . 1.005 0 0 0.5 1 x 10 -5 0 -1 -2 -3 -4 -5 0 0. 0.007 0.005 0. 2010 Vol.006 0.005 0.015 (d) 0. 007 0.006 0. Time in sec 1 0 -1 -2 -3 0 0. and (e) ∆Qcom 59 .005 0.005 0.u.004 0.002 0. 2010 Vol.01 ∆QSG12 in p. 1.009 0.002 0.01 Time in sec (c) 0. Information and Communications November.002 0.008 0.006 0.(d) ∆QSG 2 .007 0. (c) ∆QSG1 .009 0.001 0. 2010 4 x 10 -4 4 3 2 x 10 -5 2 ∆V in pu ∆QIG in pu 0 1 0 -1 -2 -4 -6 0 0.003 0.001 0.003 0.009 0.007 0. and with 1% step increase in input wind power showing time vs (a) ∆V . (b) ∆QIG .004 0.01 Time in sec (a) 4 3 2 x 10 -3 (b) 4 3 2 x 10 -3 ∆QSG 1 in p. Transient responses of the single wind/multiple diesel hybrid power system for a 1% step increase load. November.u.008 0.u.01 0. 0.005 0.003 0.003 0.01 Time in sec (e) Figure 8.001 0.006 0.005 0.004 0.001 0.007 0.004 0. 1 0 -1 -2 -3 0 0.006 0.006 0.005 0.004 0.01 Time in sec -2 0 0.008 0.002 0.008 0.003 0.009 0. Issue 1.International Journal of Energy.009 0.008 0.005 0 0 0.001 0.002 0.007 0.015 (d) ∆QCom in p. PL . it is observed that the STATCOM provides the reactive power required by the load and the induction generator or induction generators under steady state condition. respectively. ∆EM = Small change in the stored electromagnetic energy of IG. and transient conditions. In case of single wind / multi-diesel system. ∆V = Incremental change in the voltage. 6. QSG = Real and reactive power generated by diesel set with synchronous generator. the STATCOM under steady state condition provides reactive required by the load and induction generator or induction generators due to 1% step increase in input wind power as shown in Fig. Issue 1. 8(b). The examples of the wind-diesel hybrid power systems considered in this paper are multi-wind/single diesel. 60 .Communications International Journal of Energy.∆QSG become zero under steady state conditions. 1. QL = Real and reactive power of the load. In the case of multi-wind/single diesel system. K P . PIG . 5-8. ∆α = Incremental change in the phase angle of STATCOM. Nomenclature EM = Electromagnetic energy stored in the IG. but initially the synchronous generator or synchronous generators is able to meet total demand. Induction generator or induction generators has been considered for electric power generation from wind turbine and STATCOM for providing variable reactive power required by the system. 2010 From Fig. A complete dynamic model of the system has been derived to study the effect of load disturbances and input wind power disturbances. 6(b). respectively. It has also been found that the increase in input wind power result in increased fluctuations in ∆QIG . K F = Voltage regulator. 2010 Vol. QIG = Real and reactive power generated by the IG. Information and Communications November. The deviations in ∆V. K A . there is no change in the settling time of the responses. PSG . 6(c). In case of single wind/multi-diesel system. 5(c). In the case of multi-wind/single diesel system. Conclusions The reactive power control of the isolated wind-diesel hybrid power systems has been presented in this paper. K E . stabilizer gain constants. without effecting the settling time of the transient responses as shown in Fig. the STATCOM under steady state condition provides reactive required by the load and the induction generator or induction generators due to the change in the slip. but initially both the synchronous generators satisfy the reactive power requirement by sharing according to their size and finally STATCOM provides the required power under steady state condition as shown in Fig. internal armature under steady state. 4. K I = Proportional and integral controller gains of the STATCOM regulator. respectively. 5 (b). but initially both the synchronous generator and synchronous generators satisfy the reactive power requirement by sharing according to their size and finally STATCOM provides the required power under steady state condition. 7(b). 8. ∆Eq . Reactive power generated by compensator. ∆E 'q = Small change in the voltages of the exciter. Qcom . November. and single wind/multi-diesel. there is no change in the settling time of the responses. exciter. ∆E fd . kW) QSG (p.15 0.u. kW) 61 .4 Single Wind / Multi-diesel system SG1 SG2 0. 2010 Vol.5 1. V = System terminal voltage.3333 0.08072 90 0. X 'd = Direct-axis reactance of synchronous generator under steady-state and transientstate conditions.u.55 1. 2010 s = Slip of IG.u.International Journal of Energy.12 1.161 0.) E 'q (p. No.5 1. T 'do = Direct-axis open-circuit transient time constant. ∆V f = Small changes in system terminal voltage.0 IG2 0. 1.10826 0.u.2906 90 0.9804 1. ∆V . respectively.16667 0.0 5.0 Induction Generators PIG (p.6 -3.56 -3.u.) x1 = x '2 (p. kVAR) Eq (p. kW) QIG.01 17. respectively.diesel system Wind 1 (kW) 150 150 Wind 2 (kW) 50 Diesel1 (kW) 150 150 Diesel2 (kW) 75 Load in kW 150+50+100=300 150+100+50=300 The data of the systems are as follows: System Parameter Synchronous Generators PSG (p.0 1.u. Issue 1.) δ (degree) X 'd (p.u. Information and Communications November.) T 'do (seconds) Multi-Wind/Single diesel system SG 0.19 0. 1. (p.12418 0. Appendix The data of the proposed hybrid power systems are given below: S.19 0.u.0181 1.0 IG1 0.u.9804 17.0 5.15 1. kVAR) η (%) r1 = r '2 (p.91 0.56 -3. Systems Multi-Wind/Single diesel system Single Wind /Multi.) s (%) PL Load (p.u.0 IG 0.6 0.5 0.u. amplifier output voltage.161 1. ∆Va . November.16666 0.0 5. 2.) X d (p. and exciter feedback voltage.24 0.24 6. X d .3333 0.242161 90 0.12418 1. References [1] Ray Hunter. 126 (1979) 69-74. Information and Communications November. the excitation control. FACTS Controllers in Power Transmission and Distribution. kVAR) Power Factor 0. Mey Ling Sen. modeling and applications. 0. Thesis. Journal of Cybernetic and Informatics. Bansal.91736 53.C. D Thesis. IEEE Transactions on Energy Conversion. Understanding FACTs: Concepts and technology of Flexible AC Transmission Systems.3 1.S. Wind-Diesel and Wind Autonomous Energy Systems. 1. Kothari..C. Delhi. P.0 0.55 10-50 0. Bansal. Soc. Base Voltage=400 V. [6] R. Issue 1.3 1.8 IEEE Type-1 Excitation System KA KE KF TA (seconds) S F . Base power=250 kVA. Load-frequency control of stand-alone hybrid power systems based on renewable energy sources . 62 . A bibliographical survey on induction generators for application of non-conventional energy systems. 1996 [4] R.75 0. 2008.05 0.A. Proceeding of IEE. Reactive power control of autonomous wind-diesel hybrid power systems using ANN. [3] A. Wind-Diesel Systems. [5] R. L Gyugyi. kVAR) α (degree) The data of generation capacity. TE (seconds) 40 1. Delhi (India). Indian Institute of Technology.Communications International Journal of Energy. Sen. 2002. David. Indian Institute of Technology. R.2-0. [12] Kouadri B. [9] K. Induction generator/synchronous condenser system for wind turbine power.75 0.u. 2010 QL (p. London.D. [2] H. (2003) 433-439. T. [11] Kalyan K.S.05 0. Tahir Y.81206 53. [7] R. 18. T. George Elliot. and load and STATCOM model are given below. Ph. A guide to the technology and its implementation. Nacfaire.5 0. (2007) 982-987 [8] R. Centre for Energy Studies. [10] NG Hingorani. Introduction to FACT controllers: theory.8 0. Centre for Energy Studies. 0. 20. Proceedings of the IEEE Power Engineering Conference.u.67 0. 2000. A.32 40 1. Padiyar.2 STATCOM T1 (ms) Tα (ms) Td (ms) Reactive Power Data Qcom (p. A1-Adem. New York: IEEE Power Eng. New Age International Publishers. IEEE Transactions on Energy Conversion. Bansal. D.C. Willey & Sons Publication. November. 1989.F.C. Elsevier Applied Science. 2 (2005)292-299.55 10-50 0.2-0.0 0. Three phase self-excited induction generators: an overview. Cambridge University Press.5 0.67 0. Bhatti. 7 (2008) 9-25. Kumar. Bhatti. Bansal ‘Automatic reactive power control of autonomous hybrid power system’ Ph. 2010 Vol. 1994. Power flow and transient stability modeling of a 12-pulse Statcom. V. M. Information and Communications November. in 2008 and at present pursuing PhD from the Indian Institute of Technology Delhi.International Journal of Energy. November. hybrid power systems. reactive power control. 1. India. 2010 Authors Pawan Sharma received the A. I. 2010 Vol. 63 . the M. and wind and small hydro systems. in 2005. Issue 1. India. His research interests include automatic generation control. Tech degree from National Institute of Technology. degree from Institution of Engineers. E.