2011 Sofian Fufdffdfdzzy-libre

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2011 International Conference on Electrical Engineering and Informatics

17-19 July 2011, Bandung, Indonesia

Design of Electronic Load Controller for a Self

Excited Induction Generator Using Fuzzy LogicMethod Based MicrocontrollerYahya Sofian

#1*, Munawar Iyas

*2

#Department of Electrical Engineering,Bandung State Polytechnic, Bandung, Indonesia

*School of Electrical Engineering & Informatics, Bandung Institute of Technology, Bandung, Indonesia

[email protected]@lskk.ee.itb.ac.id

Abstract The self-excited induction generators (SEIGs) areconsidered to be well suited for generating electricity by means of

conventional energy sources and for supplying electrical energy

in remote and rural areas. Induction generators have manyadvantages such as cost, reduced maintenance, rugged, and

simple construction, brushless rotor (squirrel cage). A three-

phase induction generator can be operated on a C-2C connection

for supplying single phase loads. The main disadvantage of SEIG

has is that it poor voltage regulation, and its value depends on

the prime mover speed, capacitance, load current and power

factor of the load. The electronic load controller (ELC) can be

used for maintaining constant voltage and frequency of SEIG

with variable consumer load driven by constant primer mover.

This paper presents the design and implementation of a digitally

controlled ELC using fuzzy logic method based microcontroller

for an SEIG feeding single-phase load. The ELC consist of a

rectifier, MOSFET as a chopper switch, ATMega32 micro-

controller, voltage sensor, opto-coupler, and resistive dump loadin which power consumption was varied through the duty cycle

of the chopper. However an ELC consist of electronics system, in

general, has complex nonlinear model with parameter variation

problem, and the control need to be very fast. The fuzzy logic

based controller gives nonlinear control with fast response and

virtually no overshoot. The proposed ELC has been tested by

step change in the consumer load. The simulated perfomance of

the controller is supplmented by experimental results.

Keywords Electronic load controller (ELC), Self excited

induction generator (SEIG), Fuzzy logic, Microcontroller

I. INTRODUCTIONRecently, most of the electricity is generated making use offossil fuels (coal, oil, and natural gas). These fossil fuels are

limited and will run out in the future. Fossil fuels are a non-

renewable energy source and they have continuously degraded

the environmental conditions. In such a situation researchers

are forced to make effort to make use of new and renewableenergy sources in an economical and safe way. Among

electrical generation using the renewable sources, micro-

hydro generation systems are an attractive alternative for

remote locations where an electrical grid is not available.

Furthermore, it is important to that such systems must be

consider economical, robust and require minimal maintenance

and are likely to be managed by un-skilled operators, because

they are usually installed remote from any maintenance

facilities.The squirrel cage induction machine with capacitive self-

excitation, known as self-excited induction generators (SEIGs)

are considered as an alternative to the well-developed

synchronous generators. Induction generators are widely used

for micro-hydro powered electric generation, especially in

remote and isolated areas, because they do not need an

external power supply to produce the excitation magnetic field.

Furthermore, induction generators have more advantages such

as low cost, reduced maintenance, rugged and simple

construction, brushless rotor (squirrel cage), good over-speed

capability, and inherent protrction against short circuit [4].

Keeping the voltage and frequency of SEIG constant in spite

of the change in load, can be done by regulating thecapacitance value or by controlling the speed of the prime

movers. One alternative for supplying single phase loads

widely used in remote and rural areas is using three-phase

induction generator. It is used to supply the single phase loads

by using the connection C-2C. If the induction generator is

used to supply single phase with a constant load, the ELC

could be applied to maintain constant power output SEIG, for

this purpose the dump load must be connected in parallel with

the consumer load so that the total power load is generated by

the SEIG is constant. The amount of power that flowing intothe dump load is controlled by the electronic load controller

(ELC) [1-6].

Various controllers for SEIG have been reported in literature.T.Chandra Sekhar et al. [9] proposed different voltage

regulation schemes such as power electronic controller,

electronic load controller and magnetic amplifier (saturablecore reactor). Bhim Singh et al [7] has been developed an

ELC for two winding single phase SEIG. Juan M.Ramirez et

al [3] proposed an ELC with antiparallel insulated-gate bipolar

transistor (IGBT) switches are used to control dump load

connection and disconnection. D.K.Palwalia et al [2] present

design and implementation of Digital Signal Processor (DSP)based induction generator controller (IGC) for single phase

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978-1-4577-0751-3/11/$26.00 2011 IEEE


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SEIG. Sarsing Gao et al [1] present analysis and the design of

a microcontroller (PIC 18F252) based SEIG-ELC. A PIcontroller is used to provide proper control without steady

state errors or instability.

This paper present the design and implementation of

Electronic Load Controller (ELC) for a Self Excited Induction

Generator (SEIG). The SEIG using three phase induction

generator as a single phase SEIG feeding single phase loads.

The control technique to be used fuzzy based ATMega32microcontroller. The mains reasons of using fuzzy logic

controller to gives nonlinear control with fast response and

virtually no overshoot. The proposed ELC will be tested under

single phase resistive load.

II. SYSTEMDESCRIPTIONThe proposed as schematic diagram of ELC for SEIG using

fuzzy logic method based microcontroller is shown in Fig 1

and Fig 2 for supplying single phase loads. The ELC is

designed to operate an a delta connected three phase induction

machine with specification as follow 0.18 kW, 220 V, 1,67 A,4 pole, 50 Hz, 1370 rpm. Two capacitors are connected C-2C

as shown in Fig 1, for facilities the single phase load of a three

phase induction generator. The ELC consists of a uncontrolled

rectifier with parallel-resonant filters, MOSFET, ATMega32

microcontroller, voltage sensor, opto-coupler, and a series

dump load (resistor). The proposed uncontrolled single phasediode rectifier is shown in Fig 2, in which conversion of ac

power (from generator) to dc power. This rectifier with

parallel-resonant filter topology yields increased input power

factor and power density as compared with the conventional

diode rectifier [14]. A MOSFET is used as a chopper switch.

When gate pulse to MOSFET is high, the current flowsthrough the dump load and the power is consumed. A fuzzy

logic controller was applied to ELC, the controller regulates

the pulse width or duty cycle of chopper is decided by

difference of power generation to consumer load. The

ATMega32 microcontroller is used for generation of suitablepulse width in accordance with consumer load. Since the

speed and hence the frequency is constant, the output power

remains constant when the voltage is maintained at the rated

value.

III.IMPLEMENTATIONThe SEIG is connected in delta connection and excitationcapacitors are connected in a C-2C configuration. Excitation

capacitance has to provide required voltage on load at the

operating speed for the given induction machine operating asa SEIG such that it generates rated terminal voltage at full

load. The output power of the SEIG is held constant at varying

consumers loads. In order to keep SEIG output power constant,a dump load is connected in parallel with the consumer load

so the total generated power is held constant, that is

cdout PPP += where Pout is the generated power of the generator (which

should be kept constant), Pc is the consumer load power, and

Pd is dump load power.

Fig. 1 Three-phase SEIG with ELC feeding single phase load

Fig.2 ELC consists of uncontrolled rectifier

The AC voltage from SEIG terminal rectified by means of an

uncontrolled rectifier with parallel-resonant filter. The dump

load is designed so that when the duty cycle of the switch is

unity, an operating power of 0.12 kW diverted to dump load.

The terminal voltage for feedback is sensed with voltage

transducer to achieve a DC value proportional to SEIG output

voltage. This analog voltage is given to ADC input of the

ATMega32 microcontroller. The sensed voltage is compared

with reference, which is taken as proportional to the rated

terminal voltage of the SEIG and may be altered whenrequired. The microcontroller is programmed in such a way

that the feedback voltage is compared with a reference value

of 220 V for every 50 milliseconds and an error signal isgenerated. A fuzzy logic controller is used to gives nonlinear

control with fast response and virtually no overshoot. The

signal of PWM is fed to opto-coupler, which function as

insulation of the power circuit and the control circuit. The

signal drives the MOSFET switch an appropiate duty cycle.

The design aspects of single phase ELC are described insubsequent sections.

A.Rectifier CircuitThe diode rectifier is designed using a single phase bridge

parallel-resonant filter, the rectifier which will be designed

has the following specifications:

Vrms220Ei = Watt150Pr=

Hz50Frek = %5Ripple =


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Fig.3 Rectifier with parallel-resonant filter topology

A based on the calculation of the following component values

obtained [14]:

Lr= 0,319 H ; Cr = 3,52 uF ; C0= 58,39 uF

B. Specifications MOSFET and Dummy LoadThe voltage rating of the uncontrolled rectifier and the

chopper switch (MOSFET) is calculated based on rms value

ac input voltage (VL) to the diode bridge and the average

value of dc voltage. The average value of the output dc

calculated based on the following equation:

V198220x9,0V9,0V22

V LLdc ===

=

With estimates of 10% more voltage than the voltage ratingfor the transient state, the rms voltage to 242 V (220 +22) andthe peak voltage is thus, calculated as :

V2,342242x2Vdc ==

Current rating of single phase uncontrolled rectifier and thechopper switch is calculated as :

A68,0220

150

V

PI

Lac ===

A51,19,0/)2x68,0(9,0/)2xI(I acpeak ===

From the calculation above, the maximum voltage is 342.2 Vand maximum current 1.51 A.

The rating of dump load resistance, Rdis calculated as:

=== 36,261150

)198(

P

)V(R

22dc

D

C. Opto-coupler Circuit

The opto-coupler circuit that also functions as a gate driverusing the TLP 250.

Fig.4 Opto-coupler circuit with TLP 250

D.Fuzzy Logic ControllerA fuzzy logic controller consists of four main components asfuzzification, rule base, inference mechanism anddefuzzification. The fuzzification converts its inputs intofuzzy values with membership functions in the form oftriangle, trapezoid, bell or other appropriate forms expressedby the fuzzy linguistic variables. The rule base contains the

experts linguistic descriptions expressed in the form oflogical implications such as IF x is positive THEN y is big.The inference mechanism evaluates fuzzy information to

activate and apply control rules. The defuzzification that usesmethods such as centre of gravity, maximum and weightedmean converts the inference mechanism into the crisp valuesapplied to the actual system.

The proposed schematic of an ELC is shown in Fig. 2.There are two inputs and one output of the fuzzy controller.The first input is the error between reference value that isdesired output value and generator output value. The second

input is the derivative of the error. The inputs are given by:

e(k) = r(k) y(k)e(k) = e(k) e(k-1)

The design of the fuzzy controller depends on informationabout the system behavior or experience of a human expert.The fuzzification stage is determined by the choice of the

range, shape and number of the membership functions. Theinput membership functions for the error and the delta error tothe fuzzy controller, the positioning universe was divided intoseven domains which are negative big (NB), negative medium

(NM), negative small (NS), zero (Z), positive small (PS),positive medium (PM), and positive big (PB). The outputmembership functions are chosen to be nonuniformlydistributed seven singletons functions. The output

membership function processed by the fuzzy logic algorithmproduces the PWM singletons taken as output assignments forthe control dump load.


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Fig.5 Membership functions of error and the delta error

Fig.6 Membership functions output

The set of rules for fuzzy controller is shown in Table I.

Table I. Fuzzy Associative Memories (FAM)

E.Design of Fuzzy Logic ProgramThe software used to program ATMega32 microcontroller is

CodeVisionAVR by using C language. The program hasdesigned based on the flow chart as shown in the figure 7.

IV.EXPERIMENTAL RESULTSExperimentation has carried out on a three-phase SEIG-ELCsystem feeding a single-phase load with ATMega32microcontroller has been developed and tested in laboratoryunder various operating conditions. A single phase 0.18 kW,220 V, 1.67 A, 4 pole, 50 Hz, 1370 rpm squirrel cageinduction machine is used as a single phase self-excited

induction generator. The SEIG is driven by 220 V, 1.5 kW,1500 rpm shunt wound DC machine used as a prime mover.To generate 0.12 kW at 220 V and rated speed, 20F and

10F capacitors of 400 V are connected as C1and C2 acrossthe delta winding terminals of the SEIG.

Fig. 7 Flow chart of fuzzy logic program

The controller is designed to keep the operating point atthese conditions. The dump load is set as 0.12 kW in order to

consume the entire consumer load when the chopper dutycycle is 100% i.e., when the consumer load is zero.First test is experiment open loop transient response of thegenerator without load. The results are shown in Fig 8, the

generator is rotated by prime movers with a constant speed1510 rpm. The second test is still in open loop condition by

giving the load directly to the generator at a certain power

value, with initial voltage generator always at 231 volts.

Fig 8. Open loop transient response of generator

Error

dError NB NM NS Z PS PM PB

NB PB PB PM PS PS Z NS

NM PB PM PM PS Z NS NM

NS PB PM PS Z Z NS NM

Z PB PM PS Z NS NM NB

PS PM PS Z Z NS NM NB

PM PM PS Z NS NM NM NB

PB PS Z NS NS NM NB NB


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Fig 9. Graph of V = f(Pload) direct load open loop

Fig 9 is shows the graph based on the results of experimentalby giving direct loads. Fig 10 is shows the open loop transient

response when a load generator 80 watt (66.66%) is givendirectly. The graph and open loop transient response of thetest generator with direct loading shows that the direct voltagedrops quickly when the load is given.

Fig 10. Open loop transient response when a load generator 80

watt (66.66%) is given directly

Closed loop response experiment is conducted to test theperformance of a induction genenerator controlled usingfuzzy logic method based ATMega 32 microcontroller. Closedloop response testing with different loading conditions, i.e thedirect loading and gradual loading. Set point on a closed looptesting is 228 volts, 3.63% of the planned reference voltage of220 volts.

Fig 11. The generator transient response, when tested with aload of 112 watts (93.3%).

Fig 11 shows the generator transient response, when testedwith a load of 112 watts (93.3%). The generator is only able to

survive on the voltage 228 volts for 4 seconds, after which itshows an unstable response that resulted in loss of voltagegenerator.The test of load adding gradually has performed in the rangeof 0 to 122 watt of power. Fig 12 shows the voltage responsewhen given a load of 122 watts (101.6%), the settling time is

5.5 seconds with 212 volt voltage value, -7.01% steady stateerror, and error -3.63% against the reference voltage.

Fig 12. Close loop transient response of load 122 watt(101.6%) adding gradually

V. CONCLUSIONSBased on the design and testing electronic load controller for a

self excited induction generator using fuzzy logic methodbased microcontroller has obtained conclusions. When testingthe generator without controller with the single phase loadsdirectly, the generator is only able to loaded 67 watt with 147volt terminal voltage and frequency of 42.7 Hz. While withload gradual, the same generator could only load 67 watt with

167 volt terminal voltage and frequency of 42.9 Hz. The ELCof self excited induction generator can supply the single phaseresistive loads up to 122 watts or 66.77% of the rating as themotor, with 3.63% voltage regulation, frequency error of -2.6% to -3.6%, voltage THD average of 2.28%, and unity

power factor.

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