simulation of advanced elc with synchronous generator … · issn (print): 2278-8948, volume-2,...

ISSN (Print): 2278-8948, Volume-2, Issue-1, 20123

55

Simulation of Advanced ELC with Synchronous Generator for Micro Hydro-

power Station

ANKITA GUPTA1

Alternate Hydro Energy Centre

Indian Institute of Technology, Roorkee, India

Email: [email protected]

Abstract- This paper presents an analysis and design of an

Electronic Load Controller (ELC) for standalone synchronous

generator suitable for micro hydropower stations. ELC is

basically used to maintain the constant power at the generator

terminals, which in turn helps to maintain the system frequency

constant. The designed ELC consists of a controlled bridge

rectifier-chopper system feeding a resistive dump load whose

power consumption is varied through the duty cycle of the

chopper. Proper design of rectifier, chopper and dump load is

very important for trouble free operation of ELC. The ELC is

designed and simulated in MATLAB using Simulink. This

scheme can be efficiently used in micro hydropower stations.

Index Terms - Electronic Load Controller; Synchronous

Generator; Micro Hydropower Station.

I. INTRODUCTION

Micro hydropower stations are emerging as a major

renewable energy resource today as they do not encounter

the problems of population displacement and environmental

problems associated with the large hydropower plants. They

have been playing a great role to provide electricity to

remote area especially in developing countries. Micro

hydropower stations are defined as hydro electric system

upto 100 kW power range.

Almost all of the micro hydropower stations are based

on run-off-river type. The operating point of the generator is

fixed such that it gives constant rated output at the rated

conditions of voltage, current and speed, but the consumer

load may vary. When the consumer load on the generator

decreases, the turbine begins to accelerate and increases

generated frequency. Similarly, an increase in consumer

load on the generator causes deceleration in the turbine

speed and the frequency decreases [1]. Now the variation in

the consumer load connected is neutralized by the controller

diverting the extra power to a dump load. ELC regulates the

voltage and frequency of the generator through monitoring

of consumer load variation and automatically dissipating

any surplus power produced by the generator in additional

load known as dump load, so that, the total output power of

generator remains equal to its rated power.

Synchronous generator has some advantages over

induction generator for such systems.

Synchronous generators can run isolated from the grid

and produce power since excitation is not grid-dependent.

Also, synchronous generators are readily available in

market, no excitation capacitors are required to provide

reactive power, highly efficient, having in-built AVR for

voltage regulation and using synchronous generator with

ELC we can achieve good frequency regulation.

Literature has revealed that lots of work is done on

ELC with asynchronous generator [2-7]. This paper

therefore deals with the unexplored and relevant topic of

Development of ELC for micro hydropower station using

Synchronous generator of 50kW. The designed system

consists of hydro turbine, exciter, synchronous generator,

consumer load and ELC. In this case it is 50kW generator

driven by a hydro turbine. The voltage output of the

generator is regulated by AVR. The ELC is controlled

rectifier type with chopper controlled dump load. Here

IGBT is used as chopper. The system is designed in

MATLAB Simulink and the results are analyzed.

II. DEVELOPED SCHEME

A schematic diagram of the developed ELC system

with synchronous generator is shown in “Fig. 1”. The

system consists of 3-phase synchronous generator of 50kW

driven by a constant hydro turbine. Since the input to the

hydro turbine (i.e. Head and discharge) is assumed to be

constant, so the output of hydro turbine is nearly constant,

output power of the Synchronous generator must be held

constant at all loads. Any decrease in load may accelerate

the machine and raise the frequency levels to high value.

The power in surplus of the consumer load is dumped in the

resistive dump load through an ELC connected at the

terminals of the synchronous generator.

The ELC consists of a controlled bridge rectifier in

series with IGBT chopper and dump load (resistors). The

duty cycle of the chopper is adjusted so that the output

power of the generator remains constant.

ELC reacts so fast to load change which is not even

noticeable unless a very large load is applied. The advantage

of ELC is that, it is reliable and not having any moving part,

so virtually maintenance free.

mailto:[email protected]

International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)


56

Fig 1: Schematic Diagram of Developed ELC Scheme

III. PRINCIPLE OF OPERATION

The Synchronous generator–ELC system consists of a three-

phase delta-connected generator driven by a micro hydro

turbine and an ELC. Since the input power is nearly

constant, the output power of the SEIG is held constant at

varying consumer loads. The power in surplus of the

consumer load is dumped in a dump load through the ELC.

Thus, Synchronous Generator feeds two loads in parallel

such that the total power is constant, that is,

PG = PC + PD

where, PG = Generated power of the generator (which

should be kept constant),

PC = Consumer load power, and

PD = Dump load power

The power dissipated in the dump load can be used for

battery charging, water heating, cooking, etc.

IV. DESIGN OF ELC FOR SIMULATION

A number of Electronic Load Controller circuits are

developed based on various methods, to dissipate the power

in dump load, to obtain the balancing between the hydro

turbine input and the generator output [1]. With the

variation of consumer load the load controller has to change

the effective dump load resistance, so that,

PG = PC + PD (1)

where,

PG = Output power of synchronous generator

PC = Consumer load power

PD = Dump load power

The power in dump load depends on the duty cycle of the

chopper and is given as:

2( )dc

D

D

S VP

R

(2)

where,

S = Duty cycle of chopper

Vdc = DC output voltage of thyristor bridge rectifier

RD = Dump load resistance

The rating of dump load resistance is given by: 2( )dc

D

G

VR

P

(3)

The model of the 50 kW synchronous generator is

designed for simulation. The calculation is based on

assumption and it can be used to analyze the system and to

understand the effect of using ELC on the micro

hydropower plant. The model was designed to control the

frequency of the system but the voltage is controlled by

Automatic voltage regulator (AVR).

A. Generator Parameters

For simulation, the 3 phase synchronous generator

model of 50 kW, 400 V, 50 Hz, 4-pole is considered. The

generator is Salient pole type. The speed of synchronous

generator is calculated as below:

1201500

fN rpm

p

(4)

where,

N = synchronous speed of generator

f = frequency of generated voltage

p = no. of poles

B. Design of ELC

The rating of bridge rectifier and chopper switch

depends on the rated voltage and power of the synchronous

generator. The DC output voltage of controlled bridge

rectifier is given as below:

3 3cosm

dc

VV

(5)

where,

α = firing angle

Vm = Input voltage at ELC terminal

The maximum value of Vdc occurs when α=0, and is given

as,

3 3 mdc

VV

(6)

VVdc 59.66440033

(7)



57

ELC current is given as,

Gdc

dc

PI

V

(8)

AIdc 57.7559.661

50000 (9)

The dump load resistance is calculated as : 2 2( ) (661.59)

8.75450000

dcD

gen

VR

P

(10)

C. Design of DC Filter capacitor

When the AC signal passed through rectifier it would

become an uneven DC. A filtering section is used to smooth

out this uneven DC signal. Filters filter unwanted AC in the

output of a rectifier. The Ripple factor for C- filter is given

by:

1

4 3 L

rfCR

(11)

Where,

r = Ripple factor of C- filter

f = frequency (in Hz)

RL = Resistance of dump load (in Ohm)

or,

1

4 3 D

CfR r

(12)

Assume, the ripple factor is 15%,

312.1994 10

4 3 50 8.75 0.15C F

(13)

V. SIMULINK MODEL OF DESIGNED SCHEME

The imulink model of the designed scheme is as shown

in Fig 2. In this scheme, the ELC consists of a three-phase

controlled bridge rectifier and an IGBT chopper. The AC

voltage is rectified by means of a controlled bridge rectifier.

An electrolytic capacitor is connected across the bridge

rectifier to filter out the ripples. The dump load in series

with the chopper switch is connected across the DC link.

The dump load is designed such that, when the duty cycle of

the chopper is unity, it should consume the rated output

power of the generator.

The output power of the synchronous generator is kept

constant by the ELC.

The change in speed of generator (change in frequency)

corresponding to the change of load is measured. This is

compared with a reference frequency, which is taken as

proportional to the rated frequency of the generator. A

controller is used to process the error between feedback and

reference frequency signals. The error frequency is fed to a

controller as shown in “Fig. 2”.

The output of the controller is compared with a saw-

tooth carrier waveform to result in a PWM signal to alter the

duty cycle of the chopper.

The saw-tooth waveform is defined as [7]:

mst

p

A t V

T

(14)

where,

Am= amplitude of the saw-tooth carrier waveform

t = time in m-sec

Tp= time period of the saw-tooth PWM carrier wave

The controller output is compared with the saw-tooth

carrier waveform and output is fed to the gate of the chopper

switch (IGBT). The switching logic is as follows:

If Vst > Vo, then S=1

If Vst < Vo, then S=0

Where, S is the switching function used for generating the

gating pulse of IGBT of the chopper of ELC.

Figure 2: Simulink model of Designed scheme

D. Cases consider for analysis of designed scheme

For analysis of ELC with synchronous generator, we

considered three cases with synchronous generator of output

power 50kW and varying consumer load demand as shown

in table 1.



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TABLE 1: DIFFERENT CASES FOR SIMULINK MODEL ANALYSIS

Case No. Consumer load in kW

1 50

2 30

3 40

VI. RESULTS AND DISCUSSUION

The simulation circuit is simulated in MATLAB

Simulink, after simulation we get the results as shown in

“Fig 3, 4 and 5”, case 1, 2 and 3 respectively. The

oscilloscope output shows the Excitation Voltage, Rotor

Speed (in pu), Mechanical Power Output of Turbine, 3-

Phase Current output of generator, Error in Frequency and

Power outputs for all the three mentioned cases.

A. CASE 1: Generator output is 50kW and Consumer load

demand is 50kW

Figure 3(a): Excitation voltage

Figure 3(b): Rotor Speed of Synchronous Generator (in pu)

Figure 3(c): Mechanical Power Output of hydro turbine

Figure3 (d): 3-Phase Current Output of Generator

Figure 3 (e): Error in Frequency

Figure 3(f): Output power of generator and power across

consumer load and dump load (PG = PC + PD)

B. CASE 2: Generator output is 50kW and Consumer load

demand is 30kW

Figure 4(a): Excitation voltage





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Figure 4(d): 3-Phase Current Output of Generator

Figure 4(e): Error in Frequency

Figure (f): Output power of generator and power across


C. CASE 3: Generator output is 50kW and Consumer load

demand is 40kW

Figure 5 (a): Excitation voltage



Figure 5(d): 3-Phase Current Output of Generator

Figure 5(e): Error Frequency

Figure 5(f): Output power of generator and power across




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VII. CONCLUSION

An Electronic Load Controller with synchronous

generator using a three-phase controlled bridge rectifier and

IGBT as chopper converter has been modeled in MATLAB

Simulink, for controlling the frequency of micro hydro

turbine under varying load conditions. The controller is

modeled and the results are analyzed after simulation. The

designed ELC is achieving its objective to control the

frequency. This ELC can be fabricated and used efficiently

in any micro hydropower plant.

REFERENCES

[1] B. Singh, S.S.Murthy, M.Goel and A.K.Tandon, “A

Steady State Analysis on Voltage and Frequency Control of Self-Excited Induction Generator in Micro-Hydro System”, International conference on power electronics, Drives and Energy Systems, pp.1-6, 2006

[2] S.S.Murthy, B.Singh, A.Kulkarni, R.Sivarajan and S.Gupta, “Field Experience on A Novel Pico Hydel System using SEIG and ELC”, IEEE Conference, Vol. 2, pp.842-847, 2003

[2] B.Singh, S.S.Murthy and S.Gupta, “Analysis and Design of Electronic Load Controller for Self-Excited Induction Generators”, IEEE Transactions on Energy Conversion, Vol. 21, pp.285-293, 2006.

[3] M.Ramirez, “An Electronic Load Controller for the Self-Excited Induction Generator”, IEEE Transactions on energy conversion, Vol .22, No. 2, pp.546-548, 2007.

[4] B.Singh, G.K.Kasal and S.Gairola, “Power Quality Improvement in Conventional Electronic Load Controller for an Isolated Power Generation”, IEEE Transactions on Energy Conversion, Vol. 23, No. 3, pp. 764-773, 2008.

[5] B.Singh and V.Rajagopal, “Electronic Load Controller for Islanded Asynchronous Generator in Pico Hydro Power Generation”, Conference paper Electrical, Indian Institute of Technology Roorkee, 2010.

[6] B.Singh, S.S.Murthy and S.Gupta, “Transient Analysis of Self-Excited Induction Generator with Electronic Load Controller (ELC) Supplying Static and Dynamic Loads”, IEEE Transactions on Industry Applications, Vol. 41, No.5, pp.1194-1204, 2005.

simulation of advanced elc with synchronous generator … · issn (print): 2278-8948, volume-2,...

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