Neural-Network-Based Integrated Electronic Load ... - IEEE Xplore

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Neural-Network-Based Integrated Electronic Load Controller for Isolated Asynchronous Generators in Small Hydro Generation Bhim Singh, Fellow, IEEE, and V. Rajagopal

Abstract—This paper deals with a neural-network (NN)-based integrated electronic load controller (IELC) for an isolated asynchronous generator (IAG) driven by a constant-power small hydro uncontrolled turbine feeding three-phase four-wire loads. The proposed IELC utilizes an NN based on the least mean-square algorithm known as adaptive linear element to extract the fundamental component of load currents to control the voltage and the frequency of an IAG with load balancing in an integrated manner. The IELC is realized using zigzag/three single-phase transformers and a six-leg insulated-gate bipolar-transistor-based currentcontrolled voltage-source converter, a chopper switch, and an auxiliary load on its dc bus. The proposed IELC, with the generating system, is modeled and simulated in MATLAB environment using Simulink and Simpower System toolboxes. The simulated results are validated with test results on a developed prototype to demonstrate the effectiveness of IELC for the control of an IAG feeding three-phase four-wire linear/nonlinear balanced/ unbalanced loads with neutral-current compensation. Index Terms—Adaptive linear element (adaline), integrated electronic load controller (IELC), isolated asynchronous generator (IAG), small hydro generation, small hydropower generation, voltage and frequency control, voltage-source converter (VSC).

I. I NTRODUCTION

B

ECAUSE of increasing concerns for the growing demand of electrical energy and the fast depletion of fossil fuels, the need for low-cost stand-alone generating plants becomes inevitable in remote locations. Electricity generation from locally available small hydro heads, wind, and solar-energy sources is an alternate solution for environment-friendly energy generation [1]–[3]. The reduction in cost may be obtained by utilizing run-of-the-river schemes and an integrated electronic load controller (IELC) to regulate the inherent voltage and frequency in isolated asynchronous generators (IAGs) for small hydro applications [4]–[6]. The asynchronous generators are preferred as compared with synchronous generators due to the advantages of low cost, ruggedness, brushless-rotor construction with least maintenance, and no requirement for a dc supply. As the asynchronous machine is isolated, its reactive power is supplied by Manuscript received September 7, 2009; revised February 3, 2010 and July 5, 2010; accepted November 19, 2010. Date of publication December 23, 2010; date of current version August 12, 2011. The authors are with the Department of Electrical Engineering, Indian Institute of Technology–Delhi, New Delhi 110016, India (e-mail: bhimsinghr@ gmail.com; [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2010.2102313

a voltampere reactive (VAR) generating unit connected across its terminals, which is generally met by capacitor banks. The rating of a capacitor bank is so selected that when driven at rated speed, it should produce the rated voltage at no load [7]. Major setbacks of such stand-alone small hydroelectric power generation systems are the regulation of terminal voltage and frequency under load perturbations compared with any other conventional generators, along with power-quality problems [8]. Therefore, the use of an IELC with a suitable control scheme becomes necessary for an uncontrolled small hydroturbine-driven generator for power generation [9]–[11]. In this paper, the control strategy is a neural-network (NN)based least mean square (LMS) known as adaptive linear element (adaline) algorithm [12]–[14] of an IELC, which has capability of controlling the voltage and its frequency in an integrated manner [15]–[17]. The adaline is used to extract the positive-sequence fundamental-frequency component of the load currents to estimate the reference source currents through tracking of the unit vectors together with tuning of the weights. The dc-bus voltage of the voltage-source converter (VSC) of IELC with this type of control strategy is less sensitive to load fluctuations. IELC is used to control the active power (indirectly, to control the frequency) and the reactive power (to control the terminal voltage) of the IAG, and the six-leg VSC also acts as a harmonic eliminator and a load balancer [18]. A set of zigzag three single-phase transformers is used to adjust the voltage to bring the dc-link voltage to an optimum level. The advantage of using the zigzag transformer is to mitigate the zero-sequence currents and triplen harmonics in the primary winding itself, thus reducing the rating of the devices of the VSC. The reduction in the kilovoltampere rating of the VSC is on the order of 14% as compared with three singlephase VSC topology without the zigzag transformer, and its neutral terminal is used for nonlinear and linear unbalanced loads where the neutral current is compensated in the primary windings of the zigzag/three single-phase transformers, keeping the secondary windings free from zero-sequence currents and triplen-harmonic currents [18]. A unipolar switching is used in case of the six-leg VSC (consisting of three H-bridge VSCs), which has the advantage of effecting the doubling of the switching frequency of a pulsewidth modulation (PWM) voltage as compared with bipolar switching, which is used in a three-phase three-leg VSC for any given switching frequency. In a four-leg VSC topology, the fourth-leg rating is observed on the order of 150% of the other three legs

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SINGH AND RAJAGOPAL: NN-BASED IELC FOR IAGs IN SMALL HYDRO GENERATION

Fig. 1.

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Schematic diagram of IAG with IELC (consisting of six-leg VSC, auxiliary load, and zigzag/single-phase transformer).

with nonlinear loads, and the overall VSC rating is larger compared with this proposed topology due to the flow of zero-sequence currents and triplen-harmonic currents into the VSC. In a three-leg VSC with midpoint-capacitor topology, the balancing of the voltages of the capacitors is a complicated task. Additional PWM circuit, voltage sensor, current sensor, and analog-to-digital converter channels are required in the four-leg VSC topology and the three-leg VSC with midpoint-capacitor topology. II. S YSTEM C ONFIGURATION AND P RINCIPLE OF O PERATION The complete stand-alone system with an asynchronous generator, an excitation capacitor, linear and nonlinear consumer loads, and the proposed IELC is shown in Fig. 1. The proposed IELC is an arrangement of six-leg insulated-gate bipolarjunction-transistor-based VSC along with a dc-bus capacitor, a chopper switch, and an auxiliary load on its dc link. The IELC is connected at the point of common coupling (PCC) through the interfacing inductors. The dc-bus capacitor is used to reduce the voltage ripples and provides a self-supporting dc bus for the VSC. A three-phase star-connected capacitor bank is used for the VAR requirement of the IAG, and the value of this capacitor bank is selected to generate the rated voltage at no load. The IAG generates constant power, and when consumer-load power changes, the dc chopper of the IELC consumes the difference in the active power (i.e., the generator and the load) by the auxiliary load. The IELC regulates the terminal voltage due to changes in consumer loads. Thus, the voltage and the frequency of an IAG system are not affected and remain constant during frequent changes in the consumer loads.

Fig. 2 shows the NN-based control strategy of an IELC with the constant excitation capacitor of the IAG driven by uncontrolled small hydroturbine. This NN-based control strategy uses LMS algorithm and is also known as an adaline algorithm for the control of the IELC, which performs the estimation of reference source currents. The estimation of reference source currents is carried out using an adaline, which is a simple and fast method of fundamental load-current extraction. Six adalines are used to extract the three-phase positive-sequence fundamental-frequency active and reactive component of the load currents. The adaline algorithm with an online calculation of weights responds well for severe load changes [12]–[14]. The p−q and synchronous reference frame (SRF) theories need reasonable transformations and computations compared with this adaline-based technique. The other advantage of using an adaline-based technique is that it does not need low-pass filters, thus further reducing the computational burden. The proposed controller is simpler than the p−q and SRF techniques. III. C ONTROL S TRATEGY Fig. 1 shows the adaline-based control algorithm of the proposed IELC to regulate the frequency and voltage of the IAG. The basic equations of this control algorithm are given as follows. A. In-Phase Component of Reference Source Currents Because the three-phase voltages at the IAG terminals (va , vb , and vc ) are considered sinusoidal, their amplitude is computed as 1/2   . (1) Vt = (2/3) va2 + vb2 + vc2

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Fig. 2. Adaline control algorithm.

The unit vector in phase with va , vb , and vc are derived as uap = va /Vt

ubp = vb /Vt

ucp = vc /Vt .

Therefore, the average weight of the fundamental reference active-power component of the source current is given as (2)

The error in the dc-bus voltage of the VSC (Vdcer(n) ) of IELC at nth sampling instant is ∗ − Vdc(n) Vdcer(n) = Vdc(n)

(3)

∗ where Vdc(n) is the reference dc voltage and Vdc(n) is the sensed dc-link voltage of the VSC. The output of the proportional–integral (PI) controller for maintaining the dc-bus voltage of the VSC of the IELC at the nth sampling instant is expressed as

Wp (n) = {Wloss (n) + Wap (n) + Wbp (n) + Wcp (n)} /3. (5) The extraction of the weights of the fundamental activepower component of the load currents is based on LMS algorithm and its training through adaline. The weights of the active-power component of the three-phase load currents are estimated as Wap (n + 1) = Wap (n) + η {iLa (n) − Wap (n)uap (n)} uap (n) (6)

  Wloss(n)= Wloss(n−1) +Kpd Vdcer(n) Vdcer(n−1) +Kid Vdcer(n) (4)

Wbp (n + 1)

where Wloss(n) is considered as part of the active-power component of the source current. Kpd and Kid are the proportional and integral gain constants of the dc-bus PI voltage controller.

Wcp (n + 1)

= Wbp (n) + η {iLb (n) − Wbp (n)ubp (n)} ubp (n)

(7)

= Wcp (n) + η {iLc (n) − Wcp (n)ucp (n)} ucp (n). (8)

SINGH AND RAJAGOPAL: NN-BASED IELC FOR IAGs IN SMALL HYDRO GENERATION

η is the convergence factor, and it decides the rate of convergence and accuracy of estimation. The η value is so selected to make a tradeoff between the accuracy and the rate of convergence. The weight of the active-power component of the three-phase load currents are extracted using adaline in each phase. The observed practical value of η varies between 0.01 and 1.0. The three-phase fundamental reference active-power component of the source currents are computed as i∗sap = Wp uap

i∗sbp = Wp ubp

i∗scp = Wp ucp .

(9)

B. Quadrature Component of Reference Source Currents The unit vectors in quadrature with va , vb , and vc may be derived using a quadrature transformation of the in-phase unit vectors uap , ubp , and ucp as √ √ uaq = − ubp / 3 + ucp / 3 (10) √ √ ubq = 3 uap /2 + (ubp − ucp )/2 3 (11) √ √ ucq = − 3 uap /2 + (ubp − ucp )/2 3. (12) The amplitude of the IAG terminal voltage and its reference value (Vtref ) are fed to a PI voltage controller. The voltage error Ver is the amplitude of the ac voltage at the nth sampling instant Ver(n) = Vtref(n) − Vt(n) .

(13)

∗ The output of the PI controller (Wqv(n) ) for maintaining the amplitude of the ac terminal voltage to a constant value at the nth sampling instant is expressed as   Wqv(n) = Wqv(n−1) + kpa Ve(n) − Ve(n−1) + kia Ve(n) (14)

where Kpa and Kia are the proportional and integral gain constants of the PI controller, Ver(n) and Ver(n−1) are the voltage errors in the nth and (n − 1)th instants, and Wqv(n−1) is the amplitude of the quadrature component of the reference fundamental current at (n − 1)th instant. The weights of the reactive-power component of the threephase load currents are estimated as Waq (n + 1) = Waq (n)+η {iLa (n)−Waq (n)uaq (n)} uaq (n)

The three-phase fundamental reference reactive-power components of the currents of IAG are given as i∗saq = Wq uaq

i∗sbq = Wq ubq

i∗scq = Wq ucq .

(19)

C. Reference Source Currents The total reference source currents are the sum of the inphase and the quadrature components of the reference source currents as i∗sa = i∗saq + i∗sap

(20)

i∗sb = i∗sbq + i∗sbp

(21)

i∗sc

(22)

= i∗scq

+

i∗scp .

These reference source currents (i∗sa , i∗sb , and i∗sc ) are compared with the sensed source currents (isa , isb , and isc ). The current errors are computed as isaerr = i∗sa − isa

(23)

isberr = i∗sb

(24)

− isb

iscerr = i∗sc − isc .

(25)

These currents errors are amplified using the proportional controller by a gain “K” and which is given as Vcca = K isaerr

(26)

Vccb = K isberr

(27)

Vccc = K iscerr .

(28)

These amplified current-error signals (Vcca , Vccb , Vccc ) are compared with fixed-frequency (10-kHz) triangular wave to generate unipolar PWM switching signals to generate the gating signals for the six-leg VSC (each phase consists of three H-bridge VSCs) of the IELC. For switching on the H-bridge VSC of phase “a,” the basic logic is   Vcca > Vtri (upper device of the left leg of phase a on) Vcca ≤ Vtri (lower device of the left leg of phase a on) (29)   −Vcca > Vtri (upper device of the right leg of phase a on) −Vcca ≤ Vtri (lower device of the right leg of phase a on) (30)

(15)

(16)

where Vtri is taken as the instantaneous value of the fixedfrequency triangular wave, and a similar logic is applied to generate the gating signals for the other two phases.

(17)

D. Chopper PWM Controller

Wbq (n+1) = Wbq (n)+η {iLb (n)−Wbq (n)ubq (n)} ubq (n)

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Wcq (n+1) = Wcq (n)+η {iLc (n)−Wcq (n)ucq (n)} ucq (n).

Therefore, the average weight of the fundamental reference reactive components of the generator currents is given as Wq (n) = [Wqv (n) − {Waq (n) + Wbq (n) + Wcq (n)}] /3. (18)

The frequency error of the IAG voltage is defined as ∗ fer (n) = f(n) − f(n)

(31)

where f ∗ is the reference frequency (50 Hz in the present system) and “f ” is the frequency of the voltage of the IAG. The

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Fig. 3. Extracted signals of the adaline control algorithm.

instantaneous value of f is estimated using the phase-locked loop over the ac terminal voltages (va , vb , and vc ), as shown in Fig. 2. At the nth sampling instant, the output of the frequency PI controller is   Vcf (n) = Vcf (n−1) + Kpf fre(n) − fre(n−1) + Kif fre(n) . (32) This output of the frequency controller Vcf (n) is compared with the fixed-frequency triangular carrier wave (3 kHz in this case) to generate the gating signal of the insulated-gate bipolartransistor (IGBT) of the chopper of IELC. IV. MATLAB-BASED M ODELING A Simulink model of the asynchronous-generator system is developed, and it consists of an asynchronous machine with a capacitor bank, IELC, and consumer loads. The modeling of the IAG is carried out using a 3.7-kW 230-V 50-Hz Y-connected asynchronous machine and a 4-kvar starconnected excitation capacitor bank. The IELC is an arrangement of zigzag/three single-phase transformers and six-leg IGBT-based current-controlled VSC connected through interfacing inductors, a chopper switch, and an auxiliary load on its dc bus. The linear and nonlinear consumer loads and the singlephase loads are considered here to demonstrate the effectiveness of the IELC. Simulation is carried out in discrete mode at 10 × 10−6 step size with ode23tb (stiff/TR-BDF-2) solver. Zigzag/three single-phase transformers are used for the neutralcurrent compensation and to adjust the dc-bus voltage of the

IELC to an optimum level, which is shown in Fig. 1. Therefore, a set of three single-phase multiwinding transformers of voltage rating 80 V/80 V/80 V is selected to meet the required zigzag/three single-phase transformers. V. H ARDWARE I MPLEMENTATION A prototype 3.7-kW 230-V 50-Hz Y-connected asynchronous machine IAG system with IELC is developed in the laboratory. A combination of single-phase diode rectifier with an inductive filter and a resistive load on the dc link are used as nonlinear consumer loads to demonstrate the effectiveness of IELC. Five current sensors are used to sense the load currents (iLa , iLb , and iLc ,) and sense the source currents of two phases (iSa and iSb ). The third phase source current (isc ) is calculated considering a zero source neutral current. Three voltage sensors are used to sense the ac phase voltages (va and vb ) and the dc-link voltage (vdc ). A dSPACE DSP is used to generate switching signals for the IGBTs of the IELC. The switching signals are fed to the gate driver’s circuit, which finally provides gate signals for the IGBT module of the IELC and the chopper switch on the dc link. The control algorithm is run at fixed step size of 70 μs inside the processor. The six-leg IGBT-based VSC is used as IELC for a 3.7-kW 230-V 50-Hz Y-connected asynchronous machine at PCC through the zigzag/three singlephase transformers and filtering inductors. The dc-bus capacitor used is 1650 μF, and the dc-bus voltage is regulated at 200 V. The auxiliary load resistance is selected as 10 Ω for dissipating the excess power. Test results are recorded using a power analyzer (Fluke 43B make). The IAG system data are given in the Appendix.

SINGH AND RAJAGOPAL: NN-BASED IELC FOR IAGs IN SMALL HYDRO GENERATION

Fig. 4.

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Performance of IAG system feeding a three-phase four-wire linear loads.

VI. S IMULATION R ESULTS AND D ISCUSSION The performance of the proposed IELC with NN-based adaline control algorithm is studied for a constant-power input uncontrolled small hydroturbine-driven IAG feeding linear/nonlinear balanced/unbalanced three-phase four-wire loads. Fig. 3 shows the performance of the proposed NN-based adaline control algorithm. Fig. 4 shows its performance on the IAG system with unbalanced linear loads. Figs. 5 and 6 show its performance with unbalanced nonlinear loads. Figs. 4 and 5 show the waveforms of the IAG terminal voltages (vabc ), source currents (isabc ), capacitor-bank current (iccabc ), load currents (iLa , iLb , and iLc ), compensator primary currents (iconp ), compensator secondary currents (icons ), zigzag transformer neutral

current (iT R ), load neutral current (iln ), amplitude of the IAG terminal voltage (vt ), reference and dc bus voltages (vdcref and vdc ), IAG speed (ωg ), reference and sensed frequencies (f ), and powers for the source (PG ), auxiliary load (PA ), and consumer loads (PL ) during different load conditions. Fig. 3 shows the waveforms of the IAG terminal voltages (vabc ), inphase unit templates (uabcp ), quadrature unit templates (uabcq ), load currents (iLa , iLb , and iLc ), average of in-phase weights (Wp ), average of quadrature weights (Wq ), in-phase reference source currents (isabcp ), quadrature reference source currents (isabcq ), and reference source currents (i∗sabc ), demonstrating the extraction of the fundamental load currents using the adaline algorithm.

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Fig. 5. Performance of IAG system feeding a three-phase four-wire nonlinear loads.

A. Performance of IAG With IELC at Balanced/Unbalanced Linear Loads Fig. 4 shows the performance of the IELC under the application of balanced/unbalanced linear loads on the IAG system driven by a constant-power uncontrolled small hydroturbine. All three single-phase loads of 1 kW each are applied to the IAG terminals. At 2 s, one phase load is removed, and the IAG starts diverting the excess amount of active power into the auxiliary load of the IELC. At 2.2 s, the removed phase load is applied back to the system, and now, the IAG is feeding increased active power to the loads. The zigzag transformer has the unbalanced currents, and it provides the neutral-current compensation through circulating current in the primary wind-

ings, while the stable neutral terminal and secondary windings are free from circulating currents.

B. Performance of IAG With IELC at Balanced/Unbalanced Nonlinear Loads Fig. 5 shows the performance of the IELC under the application of balanced/unbalanced nonlinear loads on the IAG system driven by constant-power uncontrolled small hydroturbine. At 1.9 s, all three single-phase loads of 1 kW each are fed by IAG. The IELC is consuming extra active power. At 2 s, one phase load is removed, and the IAG diverts the excess amount of active power to the IELC auxiliary load.

SINGH AND RAJAGOPAL: NN-BASED IELC FOR IAGs IN SMALL HYDRO GENERATION

Fig. 6.

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Harmonic spectra of (a) generator voltage (Va ), (b) generator current (isa ), and (c) load current (ilb ) under balanced nonlinear condition.

At 2.2 s, the removed phase load is applied back to the system. The IAG is feeding increased power from the auxiliary load of the IELC to the consumer loads. The transformer primary winding is having the unbalanced currents, providing the path to the load neutral current with the stable neutral terminal, leaving the secondary windings free from the load neutral currents. The rating of the transformer primary winding is observed as 5.35 kVA, and the secondary winding is found to be of 4.6-kVA rating, and there is a reduction of 14% in the secondary-winding kilovoltampere rating of the transformer in this IELC compared with the star/three single-phasetransformer-based VSC configuration of IELC. Fig. 6(a) shows the source-voltage waveform and its harmonic spectrum, which has a total harmonic distortion (THD) of 1.36%. Fig. 6(b) shows the source-current waveform and harmonic spectrum, and the THD is 3.10%. Fig. 5(c) shows the nonlinear loadcurrent waveform and its harmonic spectrum which has a THD of 46.81%. The THD of the terminal voltage and current of the generator is well within 5%, the limit imposed by the IEEE-519 standard.

VII. E XPERIMENTAL R ESULTS AND D ISCUSSION The performance of the proposed IAG system is extensively tested with IELC for the voltage and frequency control along with power-quality improvement with nonlinear loads. The salient points of the test results, shown in Figs. 7 and 8, are discussed in the following.

A. Performance of IAG With Balanced Nonlinear Loads Fig. 7 shows the performance of the IAG system with IELC under balanced nonlinear single-phase loads. Fig. 7(a)–(c) shows the PCC terminal voltage with three-phase generator currents. Fig. 7(d)–(f) shows the PCC terminal voltage with three-phase capacitor currents. Fig. 7(g)–(i) shows the PCC terminal voltage with three-phase source currents. Fig. 7(j)–(l) shows the PCC terminal voltage with three-phase load currents.

Fig. 7(m)–(o) shows the PCC terminal voltage with three-phase primary-winding-side compensator currents. Fig. 7(p) shows the secondary-winding-side compensator current. The absence of zero-sequence currents and triplen-harmonic currents may easily be observed from these primary- and secondary-winding current waveforms. Fig. 7(q) shows the dc-bus voltage with the dc chopper current due to the consumed active power into the auxiliary load, and it is observed that the dc-bus voltage is stable within the limits of 200 V. Fig. 7(r) shows the load neutral current, which is the same as seen in the simulation. Fig. 7(s) shows the PCC terminal voltage waveform and its harmonic spectrum, which has a THD of 1.2%. Fig. 7(t) shows the harmonic spectrum and the THD of the generator current waveform, which is 3.2%. Fig. 7(u) shows the nonlinear load-current waveform and its harmonic spectrum, which has a THD of 41.8%. It is observed that the load currents are highly nonlinear in nature, but the generator currents are balanced and harmonic-free, and the THD of the generator terminal voltage and current is well within the limit imposed by the IEEE-519 standard of 5%. Fig. 7(v)–(x) shows the generator power, consumer-load power, and auxiliary load power. This shows that the summation of the load power and the auxiliary load power is equal to the generator power. The frequency of the generator voltage is maintained constant. B. Performance of IAG With Unbalanced Nonlinear Loads Fig. 8 shows the performance of the IAG system with IELC under unbalanced nonlinear two-phase loads. Fig. 8(a)–(c) shows the PCC terminal voltage with three-phase generator currents. Fig. 8(d)–(f) shows the PCC terminal voltage with threephase capacitor currents. Fig. 8(g)–(i) shows the PCC terminal voltage with three-phase source currents. Fig. 8(j) shows the PCC terminal voltage with phase a load current which is open circuited. Fig. 8(k) and (l) shows the PCC terminal voltage with b- and c-phase load currents. Fig. 8(m) shows the PCC terminal voltage with phase a primary compensator current which is injecting higher current into the system. Fig. 8(n) and (o) shows the PCC terminal voltage with b- and c-phase primary

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Fig. 7. Performance of IAG with IELC. (a) iga . (b) igb . (c) igc . (d) icca . (e) iccb . (f) iccc . (g) isa . (h) isb . (i) isc . (j) iLa . (k) iLb . (l) iLc . (m) iconpa . (n) iconpb . (o) iconpc . (p) iconsa . (q) vdc with ich . (r) iLn . (s) THD and harmonic spectrum of the generator terminal voltage. (t) THD and harmonic spectrum of the generator current. (u) THD and harmonic spectrum of the load current. (v) Power of the generator (PG ). (w) Power of the load (PL ). (x) Power of the auxiliary load (PA ).

Fig. 8. Performance of IAG with IELC. (a) iga . (b) igb . (c) igc . (d) icca . (e) iccb . (f) iccc . (g) isa . (h) isb . (i) isc . (j) iLa . (k) iLb . (l) iLc . (m) iconpa . (n) iconpb . (o) iconpc . (p) iLn . (q) vdc with ich . (r) Power of the generator (PG ). (s) THD and harmonic spectrum of the generator terminal voltage. (t) THD and harmonic spectrum of the generator current. (u) THD and harmonic spectrum of the load current.

SINGH AND RAJAGOPAL: NN-BASED IELC FOR IAGs IN SMALL HYDRO GENERATION

compensator currents which are injecting normal currents into the system. Fig. 8(p) shows the load neutral current, which has a higher value than the balanced-load condition discussed earlier. Fig. 8(q) shows the dc-bus voltage with the dc chopper current, which has a larger value, demonstrating the consumption of an active power by the auxiliary load, and it is also observed that the dc-bus voltage is still in the stable range. Fig. 8(r) shows the active power of the source, which is the same as in the balanced load operation. Fig. 8(s) shows the PCC terminal voltage waveform and its harmonic spectrum, which has a THD of 2.4%. Fig. 8(t) shows the harmonic spectrum and the THD of the generator current waveform, which is 4.7%. Fig. 8(u) shows the nonlinear load-current waveform and its harmonic spectrum which has a THD of 41.8%. In this two-phase unbalanced load condition, the powerquality aspects are maintained according to the IEEE-519 standard.

VIII. C ONCLUSION A stand-alone uncontrolled hydroturbine-driven asynchronous generator has been modeled, and its performance has been simulated with an adaline-based control algorithm of an IELC. It has also been experimentally validated on a developed prototype of an IAG system. The performance of the IAG has been studied under different loading conditions to demonstrate the capability of the proposed IELC with NN-based control algorithm. It was observed that the IELC results in a satisfactory performance under different loading conditions along with the frequency and its voltage control, load balancing, and harmonic elimination of three-phase four-wire loads. This type of controller was found to be simple, easy to control, and less sensitive to load perturbations.

A PPENDIX A. Parameters of 3.7-kW 230-V 50-Hz Y-Connected Four-Pole Asynchronous Machine Rs = 0.3939 Ω, Rr = 0.4791 Ω, Xlr = 0.6335 Ω, Xls = 0.7898 Ω, Xm = 24.08114 Ω

B. Controller Parameters Lf = 2.5 mH, Cdc = 1650 μF, and Rd = 10 Ω. DC-bus voltage of VSC: 200 V AC voltage PI controller: Kpa = 0.3, Kia = 0.3 DC voltage PI controller Kpd = 0.12, Kid = 0.15 Frequency PI controller Kpf = 0.1, Kif = 0.1 Convergence factor η = 0.1, K = 1

C. Prime Mover Characteristics for Simulation Tshaft = (K1 − K2 ωm ); K1 = 1470, K2 = 8.5. Prime Mover for Hardware Implementation 415-V 3.7-kW 50-Hz induction machine drive

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D. IELC Processor Processor: dSPACE DS 1104 R&D controller board with TMS320F240 slave DSP.

E. Parameters of IELC Hardware IGBT three-leg with IGBT chopper on dc bus module: SKM 100 GB128DN Zigzag/star transformer: Three single-phase transformers of rating 80 V/80 V/80 V.

R EFERENCES [1] J. B. Ekanayake, “Induction generators for small hydro schemes,” Power Eng. J., vol. 16, no. 2, pp. 61–67, Apr. 2002. [2] J. M. Elder, J. T. Boys, and J. L. Woodward, “Self-excited induction machine as a low cost generator,” Proc. Inst. Elect. Eng., vol. 131, pt. C, no. 2, pp. 33–40, Mar. 1984. [3] S. Rajakaruna and N. N. Maw, “Unregulated performance of an induction generator in an isolated micro hydro power plant,” in Proc. 7th IPEC, Nov. 29–Dec. 2, 2005, pp. 1–6. [4] J. Bjornstedt and O. Samuelsson, “Voltage and frequency control for island operated induction generators,” in Proc. IET CIRED Smart Grids Distrib. Conf., 2008, pp. 1–4. [5] G. Dastagir and L. A. C. Lopes, “Voltage and frequency regulation of a stand-alone self-excited induction generator,” in Proc. IEEE Elect. Power Conf., Montreal, QC, Canada, Oct. 2007, pp. 502–506. [6] F. Profumo, B. Colombo, and F. Mocci, “A frequency controller for induction generators in stand-by mini hydro power plants,” in Proc. IEEE Elect. Mach. Drives Conf., Sep. 1989, pp. 256–260. [7] Y. Zidani and M. Naciri, “A numerical analytical approach for the optimal capacitor used for the self excited induction generator,” in Proc. Power Electron. Spec. Conf., Jun. 2001, vol. 1, pp. 216–220. [8] B. Singh, G. K. Kasal, and S. Gairola, “Power quality improvement in conventional electronic load controller for an isolated power generation,” IEEE Trans. Energy Convers., vol. 23, no. 3, pp. 764–773, Sep. 2008. [9] W. Jun and Y. Bo, “A novel electronic load controller: Theory and implementation,” in Proc. ICEMS, 2001, vol. 2, pp. 1276–1278. [10] J. M. Ramirez and M. E. Torres, “An electronic load controller for the self-excited induction generator,” IEEE Trans. Energy Convers., vol. 22, no. 2, pp. 546–548, Jun. 2007. [11] K. H. Youssef, M. A. Wahba, H. A. Yousef, and O. A. Sebakhy, “A new method for voltage and frequency control of stand-alone self-excited induction generator using PWM converter with variable DC link voltage,” in Proc. IEEE Amer. Control Conf., 2008, pp. 2486–2491. [12] B. Singh and J. Solanki, “An implementation of an adaptive control algorithm for a three-phase shunt active filter,” IEEE Trans. Ind. Electron., vol. 56, no. 8, pp. 2811–2820, Aug. 2009. [13] A. Bhattacharya and C. Chakraborty, “Adaline controlled 3-phase 3-wire shunt active power filter with enhanced performance using the capacitor voltage feedback,” in Proc. ICIT, Feb. 10–13, 2009, pp. 1–6. [14] B. Singh and J. Solanki, “Load compensation for diesel generator based isolated generation system employing DSTATCOM,” IEEE Trans. Ind. Appl., vol. 47, no. 1, pp. 238–244, Jan.–Feb. 2011. [15] G. K. Kasal and B. Singh, “Decoupled voltage and frequency controller for isolated asynchronous generators feeding three-phase fourwire loads,” IEEE Trans. Power Del., vol. 23, no. 2, pp. 966–973, Apr. 2008. [16] I. Serban, C. P. Ion, C. Marinescu, and M. N. Cirstea, “Electronic load controller for stand-alone generating units with renewable energy sources,” in Proc. IEEE IECON, Paris, France, Nov. 2006, pp. 4309–4312. [17] B. Singh, S. S. Murthy, and S. Gupta, “A stand-alone generating system using self-excited induction generators in the extraction of petroleum products,” IEEE Trans. Ind. Appl., vol. 46, no. 1, pp. 94–101, Jan./Feb. 2010. [18] B. Singh, P. Jayaprakash, T. R. Somayajulu, and D. P. Kothari, “Reduced rating VSC with a zig-zag transformer for current compensation in a threephase four-wire distribution system,” IEEE Trans. Power Del., vol. 24, no. 1, pp. 249–259, Jan. 2009.

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Bhim Singh (SM’99–F’10) was born in Rahamapur, India, in 1956. He received the B.E. degree in electrical engineering from the University of Roorkee, Roorkee, India, in 1977 and the M.Tech. and Ph.D. degrees in electrical engineering from the Indian Institute of Technology (IIT)–Delhi, New Delhi, India, in 1979 and 1983, respectively. In 1983, he was with the Department of Electrical Engineering, University of Roorkee, as a Lecturer, and in 1988, he became a Reader. In December 1990, he was with the Department of Electrical Engineering, IIT–Delhi, as an Assistant Professor and became an Associate Professor in 1994 and a Professor in 1997. His current research interests include power electronics, electrical machines and drives, active filters, flexible ac transmission system, high-voltage dc, and power quality. Dr. Singh was the recipient of the Khosla Research Prize from the University of Roorkee in 1991, the JC Bose and Bimal K Bose Awards from the Institution of Electronics and Telecommunication Engineers (IETE) for his contribution in the field of Power Electronics in 2000, the Maharashtra State National Award from the Indian Society for Technical Education (ISTE) in recognition of his outstanding research work in the area of Power Quality in 2006, and the IEEE Power Engineering Society, Delhi Chapter Outstanding Engineer Award in 2006. He has been the General Chair of the IEEE International Conference on Power Electronics, Drives, and Energy Systems 2006 held in New Delhi. He is a Fellow of the Indian National Academy of Engineering, the National Academy of Science, India, the Institution of Engineers (India), and IETE. He is a Life Member of ISTE, the System Society of India, and the National Institution of Quality and Reliability.

V. Rajagopal was born in Kazipet, Warangal, India, in 1969. He received the AMIE degree in electrical engineering from The Institution of Engineers (India), Kolkata, India, in 1999 and the M.Tech. degree in power electronics and drives from Uttar Pradesh Technical University, Uttar Pradesh, India, in 2004. He is currently working toward the Ph.D. degree at the Department of Electrical Engineering, Indian Institute of Technology–Delhi, India. His area of interest includes power electronics and drives, renewable energy generation and applications, custom power devices, flexible ac transmission system, and power quality. Mr. Rajagopal is a Life Member of the Indian Society for Technical Education.