This paper offers an alternative technique, namely, Improved Electronic Load Controller (IELC), which is proposal to improve power quality, maintaining voltage at frequency desired level for rural electrification. The design and development of IELC are considered as microhydroenergy system. The proposed work aims to concentrate on the new schemes for rural electrification with the help of different kinds of hybrid energy systems. The objective of the proposed scheme is to maintain the speed of generation against fluctuating rural demand. The Electronic Load Controller (ELC) is used to connect and disconnect the dump load during the operation of the system, and which absorbs the load when consumer are not in active will enhance the lifestyle of the rural population and improve the living standards. Hydroelectricity is a promising option for electrification of remote villages in India. The conventional methods are not suitable to act as standalone system. Hence, the designing of a proper ELC is essential. The improved electronic load control performance tested with simulation at validated through hardware setup.
The small scale microhydropower stations combine the advantages of hydropower with those of decentralized power generation without any disadvantages of large scale installations. Small scale hydropower has the advantages like economic distribution of energy, less environmental impacts compared with large hydrosystems, independence from imported fuels, and no need for expensive maintenance. Small scale hydropower can be used as decentralized energy systems for rural electrification.
Bassett and Potter have proposed a three-phase cage Induction Machine (IM) as a self-excited generator connected to the AC side of a voltage source. The generator is supposed to be driven by a low head unregulated shaft of microsystem. These systems intended to be applied in rural plants as a low-cost source of high quality AC sinusoidal regulated voltage with constant frequency [
Arrillaga and Watson proposed a static power conversion method from a Self-Excited Induction Generator [
Murthy et al. have proposed a simple and economical method for controlling a Self-Excited Induction Generator (SEIG) for standalone microhydropower generation [
Bhattacharya and Woodward have analyzed the performance of excitation balancing of Self-Excited Induction Generators (SEIG) supplying unbalanced loads. The additional drawbacks of SEIG are poor voltage regulation and require adjustable reactive power with varying load to maintain constant terminal voltage [
Bim et al. analyzed the performance of a voltage compensation based voltage regulator for Self-Excited Induction Generators (SEIG) supplying nonlinear loads [
Levy has presented importance of an Electronic Load Controller (ELC) for three-phase Self-Excited Induction Generators. The proposed generator was able to generate constant voltage and frequency, only if electrical load is maintained constant [
Wang and Su provided a comprehensive review of effect of long shunt and short shunt connections on permanent magnet generators, induction generators, synchronous generators, and doubly fed induction generators [
Rai et al. have presented the dynamic and steady state performance of a standalone Self-Excited Induction Generator with fuzzy logic controller (SEIG) using passive elements [
Singh et al. have presented a system based on a Self-Excited Induction Generator with shunt electronic converter to feed isolated three-phase and single phase linear or nonlinear loads [
Singh et al. have presented an Electronic Load Controller (IELC) based voltage and frequency regulator for an isolated asynchronous generator and demonstrated the improvements in the performance of Self-Excited Induction Generator [
Kuo and Wang have proposed the analysis of isolated self-induction generator feeding a rectifier load [
Wildi has proposed the voltage and frequency control of an autonomous Induction Generator (IG). A Voltage Source Inverter (VSI) with a Dump Load (DL) circuit is employed in its DC side. The IG frequency is controlled by keeping the VSI synchronous frequency constant [
Bansal has presented an overview about several solutions for standalone three-phase self-excited generators. A hybrid excited synchronous generator based on the two different types of excitation field is proposed [
Singh et al. have demonstrated the behavior of an Electronic Load Controller for Self-Excited Induction Generator under unbalanced grid voltage conditions. The phenomena are first analyzed theoretically as a function of the stator active and reactive instantaneous power exchange by the stator of the SEIG and the Grid Side Converter (GSC) [
Baroudi et al. have proposed new methods for power converter topologies consisting of a three-phase Self-Excited Induction Generator (SEIG) with STATCOM for feeding dynamic induction motor loads [
Mahato et al. analyzed the transient performance of a single phase self-regulated induction generator using a three-phase machine [
Singh [
Yokesh et al. (2010) proposed a voltage regulation scheme for Self-Excited Induction Generator for industry applications and analyzed the system with the help of different voltage and load conditions.
This paper considers a microhydrosystem at standalone mode. The microhydrosystems are consisting of a generating station, whose output power is less than 100 KW capacity. A squirrel cage induction motor can be used as a generator and capacitor bank of suitable rating is connected in both shunt or series and combination of both. It is required for supplying the VAR by the generator and the loads. The rotor is rotated at speed above the synchronous speed of the motor. The output voltage and frequency will be maintained within limits, under full load condition. When the consumer load is reduced, the excess load is consumed by the Improved Electronic Load Controller. The overall functional block diagram is shown in Figure
Block diagram of the proposed Improved Electronic Load Controller for microhydrosystem.
The microhydroenergy sources are available in plenty of places and usually seen in hilly areas where water flows as small rivers or streams. The schematic arrangement of microhydrosystem is shown in Figure
A typical microhydrosystem structure.
The power generation of the proposed microhydrosystem is expressed in
In standalone microhydrosystem, An IELC is a solid state electronic device designed to regulate output power of a microhydropower system and also to regulate voltage to a desired level. The output voltage and frequency will be during full load condition and full load is considered throughout the operation of the consumer load. Support the load reduced and then the excess load is consumed by the Improved Electronic Load Controller (IELC):
The converting three-phase induction motor into a three-phase induction generator various designs are available. Here, the three-phase motor with three excitation capacitors for three-phase output can be used for this purpose as shown in Figure
Three excitation capacitors for three-phase output.
Normal single phase induction motors cannot be used as Self-Excited Single Phase Induction Generators (SEIG) because the modifications or additions are required to act as SEIG. Single phase induction machines of integral kW ratings are costwise high, which is compared with three-phase induction machine of equivalent size. It has been found that three-phase SEIG can be used for supplying single phase loads.
The motor is chosen taking into consideration the power output and the voltage rating. The rating of the machine is shown in Table
Induction Machine ratings.
Parameter | Specification |
---|---|
Motor type | Squirrel cage induction motor |
Phase | 3 phases |
Line voltage | 230 V |
Rated speed | 1485 RPM |
Horsepower | 1 H.P |
The rating of the excitation capacitor is selected to produce the rated voltage at full load. The rating of the capacitor is chosen as per
The voltage rating of the uncontrolled rectifier and chopper switch will be the same and dependent on the Root Mean Square (RMS) value of the AC input voltage and average value of the output DC voltage. The ratings of the various components of the proposed ELC are given as follows:
An overvoltage of 10% of the rated voltage is considered for transient conditions; hence the RMSAC input voltage which will be with a peak value is calculated using
This peak voltage will appear across the components of ELC during the operation of the system. The current rating of the uncontrolled rectifier and chopper switch is decided by the active component of input AC current and calculated using
The three-phase uncontrolled rectifier draws approximately quasi-square current with the distortion factor of (
The Crest Factor (CF) of the AC current drawn by an uncontrolled rectifier with a capacitive filter varies from 1.4 to 2.0; hence, the AC input peak current may be calculated using
So the maximum voltage and peak current in the uncontrolled rectifier are 357.8 volts and 3.941 amperes, respectively. The rating of an uncontrolled rectifier and chopper switch is 600 V and 5 A, higher than the calculated values, respectively. The rating of dump load resistance is calculated by using
From this relation, the value of
The value of the DC link capacitance of the ELC is selected on the basis of the ripple factor. The relation between the values of DC link capacitance and Ripple Factor (RF) for a three-phase uncontrolled rectifier is given by
Normally, 5% ripple factor is permitted in the average value of DC link voltage. The capacitance is calculated using the previous formula and hence the value of the capacitance is given by
The entire ratings of the components of proposed ELC are given in Table
Ratings of the components of proposed ELC.
Power rating of motor (W) | Voltage rating of rectifier (V) | Current rating of rectifier (A) | Voltage rating of chopper switch (V) | Current rating of chopper switch (A) | Rating of dump load ( |
Rating of DC filtering capacitor ( |
|
||||||
750 | 600 | 5 | 600 | 5 | 125 | 200 |
The various blocks of the simulation circuits of the entire system are given in Figures
Main block of the proposed system.
Load bank.
IELC block.
Figure
Figure
The output waveforms are shown in Figures
(a) Simulation waveforms of output voltage. (b) Output RMS voltage. (c) Output current. (d) Frequency. (e) Speed.
(a) Active power of load. (b) Reactive power of load. (c) Active power of ELC. (d) Reactive power of ELC.
The simulation output reveals that the voltage and frequency remain constant for varying load conditions. Figure
The IELC is bringing the regulation of voltage and maintaining the SEIG speed at a constant value. The constant value of speed is achieved by SEIG; this is because IELC current increases and decreased against the load deviation. The active load power, reactive load power, the active power, and reactive power are illustrated in Figure
Figure
From the results, the simultaneous performance of proposed system shows that the microhydroschemes combined with improved load controller are produced. The good is shown. The constant power and sustainable power for rural electrification are added advantage in connection with the hardware implementation which is done based on simulation performance.
Hardware experimental setup.
The generator was tested without connecting the ELC and control circuit by connecting three 20 microfarad capacitors in star across the stator output. The test results are tabulated in Table
Test results of generator.
Load | Speed (RPM) | Phase voltage (V) | Frequency (Hz) |
---|---|---|---|
No load | 1505 | 475 | 49.9 |
205 ohms per phase in star | 1430 | 255 | 47 |
The hardware experimental results are obtained using GwINSTEK Digital Storage Oscilloscope (DSO). Figure
CCP1 pin output of PIC.
Figure
Optocoupler output.
Figure
Gate emitter voltage of IGBT.
Figure
Voltages across 50 ohm resistor with snubber.
Figure
Voltage across 50 ohm resistor without snubber.
The proposed microhydrosystem was designed and implemented with the IELC. The simulation results revealed that the voltage and frequency remain within limits during the load changes. The hardware experimental setup was fabricated by using a DC motor as the prime mover. The IELC and control circuits were designed and fabricated. The hardware experimental setup was first tested by giving 15 V regulated power supply instead of the rectified output supply from the generator. Then, it was tested with the output voltage of the induction generator through the diode rectifier. The IELC was operating properly by consuming the excess voltage during the load level which is below the nominal level. The IELC system is cost-effective and is easily constructible in rural areas. Compared to existing methods of ELC, the IELC gives prominent merits. The voltage and frequency maintained constancy through the operation. So power quality is improved.
The authors declare that there is no conflict of interests regarding the publication of this paper.