S. Ünal, M. Özdemir, S. Sünter,  Voltage and Frequency Control of a Single-Phase Self-Excited Asynchronous Generator
International Aegean Conference on Electrical Machines and Power Electronics (ACEMP), 0
stanbul-Turkey, May, 2004, pp.509-514.
Voltage and Frequency Control of a Single-Phase Self-Excited
Asynchronous Generator
Sencer Ünal Mehmet Özdemir Sedat Sünter
Department of Electrical and Electronic Engineering,
F1
rat University
Elaz1

, 23119 Turkey
Email:[e-mail] Tel : [phone] Fax : [phone]
Abstract In order to run a single-phase asynchronous machine
as a self-excited generator the machine must be
In this paper, voltage and frequency control of a driven by another driver and a condenser, which will
single-phase self-excited asynchronous generator provide a required magnetizing current, must be
driven by a dc machine with variable speed has been connected across the terminals. When the machine is
proposed. Here, an IGBT based single-phase PWM excited at the required speed, remnant magnetization
inverter controlled by a PIC microprocessor was in the rotor will induce a small emf in the stator
used to adjust the output frequency of a single-phase windings. The condenser at the terminals of
self-excited asynchronous generator. PIC generator causes a continuous increase in the
microprocessor produces SPWM signals by induced voltage and hence produced voltage until
implementing the asymmetrical regular-sampled the generator reaches to saturation due to magnetic
sine-PWM technique and then frequency of the saturation of the machine [4]. The speed of the drive
output voltage is adjusted by controlling IGBT system and value of the condensers connected to the
devices in the inverter. generator affect the self excitation time of the
Condenser group is controlled by PIC controller to generator, the produced voltage and its frequency. In
keep the output voltage of the generator constant at addition, the load to be connected to the terminals of
variable operating conditions. In this method, the the generator, depending on the load characteristic,
microprocessor samples the voltage data from the dc will also change the magnetizing current of the
link and then turns the condenser on or off into the generator and hence the terminal voltage will also be
system depending on variations in the voltage. In affected. The main purpose of this kind of systems is
this way the dc link voltage is kept constant. to produce and keep constant voltage and frequency
The complete system has been simulated by using if there is a change in the speed of the drive system
Matlab/Simulink package program. Comparison of and loading conditions.
the simulation and experimental results has shown Many researches are being carried on keeping the
the satisfactory operation of the single-phase self- voltage and frequency level of the generator constant
excited asynchronous generator. [5-7]. In these studies, systems such as bipolar PWM
inverters and battery groups are used. Whilst the
auxiliary winding of the single phase asynchronous
1 Introduction
generator is supplied by a dc-ac inverter fed by a
battery group, the main winding is connected to the
Recently increase in energy demand and limited load terminals in parallel with exciting condenser. If
energy sources in the world caused the researchers the load requirement is bigger than the power
to make effort to provide new and renewable energy provided by the drive system, the remaining power
sources for the usage in an economical and safe way. needed by the generator is provided by the battery
The use of the asynchronous generators which can group. If the power of the drive system is bigger
produce electricity in variable speeds has become a than the load requirement, the excess power charges
proper way for the renewable energy sources such as the battery group. Reactive power required by the
wind, natural gas and rivers with low flow. In generator is provided by the inverter and condenser
addition rapid developments in power electronics connected in parallel to the load terminals. In this
and microprocessors have made the use of way, voltage and frequency regulations are achieved
asynchronous generators more popular in this by active and reactive power control at variable load
application. Especially, load sharing can be conditions [5-6]. However, this method requires a
performed easily by using them in single or three- fixed battery group and it can only be applied into
phase micro-grid systems with the aid of power the single phase asynchronous machines having two
electronic circuit arrangements such as inverters and windings. In addition, here it is not clear how the
converters [1, 2, 3]. frequency regulation is performed. Apart from this
method, voltage regulation of the single-phase
S. Ünal, M. Özdemir, S. Sünter,  Voltage and Frequency Control of a Single-Phase Self-Excited Asynchronous Generator
International Aegean Conference on Electrical Machines and Power Electronics (ACEMP), 0
stanbul-Turkey, May, 2004, pp.509-514.
asynchronous generator can be obtained by using
passive components such as serial capacitors, a
saturable core reactor and a constant voltage
transformer [7]. However, it will be very difficult to
provide frequency regulation by only using these
components.
In this study, a circuit arrangement has been
designed to prevent the probable changes in the
terminal voltage and frequency of a single-phase
self-excited asynchronous generator, and a
simulation model based on Matlab/Simulink
program has been presented to study the transient
and steady state behaviors of this arrangement. In
Figure 2 Asymmetrical regular sampled PWM.
the proposed system, frequency of the generator is
regulated by a PWM inverter controlled by a PIC
In this method two counters are used to generate the
microprocessor and the generator voltage is
PWM signal. The first counter continuously counts
regulated by controlling the exciting condenser
the time which is equivalent to the half-switching
connected in parallel to the condenser group, which
period. When the counter times out, it produces an
is also controlled by a PIC microprocessor. The
interrupt signal and begins to time the same period
accuracy of the system is demonstrated by a
repetitively. The second counter counts the
comparison of the results taken from the simulation
switching period. When the counting is completed,
and the experimental setup at the variable load
an interrupt signal is produced which ensures that
conditions.
the PWM signal is logically reversed. Both counters
start to count simultaneously. In every half-
switching period the time, t is computed to be used
2 The System Description
in the next period. The time, t counted at the positive
alternation of the carrying wave is calculated as;
Ts
t = .(1- M.sin Ét ) (1)
k
4
The time, t counted at the negative alternation of the
carrying wave is calculated as;
Ts
t = .(1 + M.sin Ét ) (2)
k +1
4
Figure 1 Block diagram of the system.
Where TS is the switching period and M is the
The block diagram of the system is shown in Fig.1.
modulation index. This PWM signal is generated by
As seen in the diagram, the required driving power
PIC16F877 microprocessor and applied to the
is provided by a dc shunt machine in order to run the
inverter switches. In this way the frequency of the
single-phase asynchronous machine as generator.
inverter output voltage is kept constant.
To control the frequency of the voltage waveform
It is necessary to produce a delay between drive
produced by the generator a single-phase PWM
signals to avoid short circuit in the inverter. This has
inverter is used. Here, the produced voltage by the
been done by introducing a delay time between the
generator is rectified with a bridge rectifier and
incoming and outgoing switches at switching instant.
filtered by a condenser in order to remove voltage
In addition there is an R-C snubber circuit to
ripples. Then, this dc voltage is input to the inverter.
The inverter has been designed by using 2MBI75N- decrease the switching loses and voltage spikes at
turn-off. This circuit has some disadvantages over
60 IGBT switch modules and EXB840 driver
the other snubber circuits, but it was preferred to
modules. Asymmetrical regular sampled PWM
decrease the complexity of the circuit.
technique is used to generate PWM signals for the
In the circuit which is designed to keep the
IGBT switches.
PWM strategy is based on the comparison of a high- amplitude of the voltage constant generated by the
asynchronous generator at variable loading
frequency triangular carrier wave with a reference
conditions, the condenser group connected for
sine wave as shown in Fig.2. In asymmetrical
excitation is controlled by a PIC 16F877
regular sampled PWM reference sine modulation
microprocessor. A look-up table containing the
signal is sampled at every half-switching period and
voltage-condenser values is used in the
a pulse is produced at each switching period.
S. Ünal, M. Özdemir, S. Sünter,  Voltage and Frequency Control of a Single-Phase Self-Excited Asynchronous Generator
International Aegean Conference on Electrical Machines and Power Electronics (ACEMP), 0
stanbul-Turkey, May, 2004, pp.509-514.
microprocessor. Then, dc voltage information
dÉr
j = Tmec - Tem (6)
measured in the dc link at the output of the rectifier
dt
circuit is input to the analog-digital converter (ADC)
of the PIC microprocessor. The voltage information
in the ADC of the PIC microprocessor is evaluated
with respect to the look-up table and then the
required capacity value is obtained. According to
this value, an appropriate capacity value of the
condenser group is switched on by means of PIC
controlled relays. In this way, the generator voltage
is either kept constant or ensured to be close to the
required value under variable load conditions.
3 Mathematical Model of the Machine
In this study d-q model of a single phase
asynchronous generator has been used. By using this
model, it is easy to investigate the self exciting and
other behaviors of the generator in transient and
steady-state.
Figure 3 Equivalent circuit of a single-phase machine.
Although the equivalent circuit of a single-phase
asynchronous generator shows similarity to the
4 Simulink Modeling of the System
single-phase asynchronous motor there are some
differences between these two models. Instead of the
supply voltage in the equivalent circuit of
Simulation model for the frequency and voltage
asynchronous motor, the asynchronous generator has
control of the single-phase self excited asynchronous
excitation condensers and load in its structure. In
generator has been obtained by using
addition the movement equations of the motor and
Simulink/Matlab 6.5 package program. The
generator are also different.
Simulink model of the system is shown in Fig.4
The q-d stator and rotor winding voltages can be
written as;
dqs
Vqs = R Iqs +
qs
dt
dqs'
Vds' = R Ids' +
ds
dt
(3)
d¸r dqr's
's
Vqr's = R Iqr's - dr's +
r
dt dt
d¸r ddr's
'
Vdr's = R Idr's + qr's +
r
dt dt
Where the flux linkages are;
qs = LlqsIqs + Lmq (Iqs + Iqr's )
Figure 4 Simulink model of the complete system.
ds' = Llds'Ids' + Lmd (Ids' + Idr's )
(4)
Here, the simulation of a single phase asynchronous
qr's = Llr'Iqr's + Lmq (Iqs + Iqr's )
generator has been done by considering the
mathematical model of the generator given in
dr's = Llr'Idr's + Lmd (Ids + Idr's )
Section 3. In order to have the asynchronous
generator self-excited, there must be a remnant
The developed torque and motor motion equations
magnetization in the machine. This is represented in
are given;
the model by adding a constant magnetization value
P
Tem = (qr 'sIdr 's - dr 'sIqr 's ) (5) corresponding to the remnant value. As a result, self
2
excitation process is observed in the model.
S. Ünal, M. Özdemir, S. Sünter,  Voltage and Frequency Control of a Single-Phase Self-Excited Asynchronous Generator
International Aegean Conference on Electrical Machines and Power Electronics (ACEMP), 0
stanbul-Turkey, May, 2004, pp.509-514.
In the simulation the generator voltage is input to a
rectifier model in which its output feeds the single-
phase inverter model. Output of the inverter model is
connected to a resistor load bank. The load
resistance is taken on and off by a controlled switch
model. The control signals for the inverter switches
are obtained using the PWM strategy as explained in
Section 2. The condenser group required for exciting
the asynchronous generator is controlled with
respect to the voltage information sampled from the
rectifier output. Here, the proper capacity value is
found by using this voltage information.
5 Experimental and Simulation Results
In this section experimental and simulation results of
the condenser and inverter controlled single-phase
asynchronous generator are given for variable load
conditions.
The results in Fig.6 throughout Fig.8 show the
inverter output voltage without controlling the
condenser group for the variable load condition.
Fig.9 and Fig.10 illustrate the inverter output voltage
waveforms with controlled condenser group.
Figure 6 Transient output voltage of the inverter (loaded
with 100&!) (a) Simulation, (b) Experimental.
The simulation and experimental output voltage
waveforms of the inverter in steady-state are shown
in Fig.5 (a) and (b), respectively where the
asynchronous generator is unloaded and excited by a
240 µF condenser group. Similar results to Fig.5
have been obtained and illustrated in Fig.7 except
for a resistive load of 100&!. Careful examination of
these two results show that when the generator is
loaded the voltage level drops due to the
uncontrolled condenser group but the frequency
remains at constant value because of the inverter
control. The results in Fig 6 show the voltage drop at
the instant which the load is applied. Fig 8 gives the
voltage increase at the instant which the load is
removed.
Experimental and simulation results are given in
Fig.9 and Fig.10 for the system operation using the
controlled condenser group to prevent fluctuations in
the terminal voltages of the generator. In Fig 9, it
can be seen that the inverter voltage reaches
approximately to its original level when value of the
exciting condenser is increased to 137 µF in addition
to 240 µF after the 100&! load is taken on.
Figure 5 Output voltage of the inverter (unloaded) (a)
Simulation, (b) Experimental.
S. Ünal, M. Özdemir, S. Sünter,  Voltage and Frequency Control of a Single-Phase Self-Excited Asynchronous Generator
International Aegean Conference on Electrical Machines and Power Electronics (ACEMP), 0
stanbul-Turkey, May, 2004, pp.509-514.
Figure 8 Transient output voltage of the inverter
(unloaded) (a) Simulation, (b) Experimental.
Figure 7 Steady-state output voltage of the inverter
(loaded with 100&!) (a) Simulation, (b) Experimental.
Figure 9 Transient output voltage of the inverter
controlled by a condenser group (loaded with 100&!) (a)
Simulation, (b) Experimental.
S. Ünal, M. Özdemir, S. Sünter,  Voltage and Frequency Control of a Single-Phase Self-Excited Asynchronous Generator
International Aegean Conference on Electrical Machines and Power Electronics (ACEMP), 0
stanbul-Turkey, May, 2004, pp.509-514.
References
[1] B. Singh, L.B. Shilpakar, S.S. Murthy, A.K.
Tiwari,  Improved Steady State and Transient
Performance With Optimum Excitation of
Single-Phase Self-Excited Induction
Generator , Electric Machines and Power
Systems, 2000, 28:591-604.
[2] B. Singh, L.B. Shilpkar,  Steady-State Analysis
of Single-Phase Self-Excited Induction
Generator , IEE Proc.-Gener. Transm. Distrib.,
Vol. 146, No. 5, September 1999, p.421-427.
[3] E. Suarez, G. Bortolotto,  Voltage-Frequency of
a Self Excited Induction Generator , IEEE
Transactions on Energy Conversion, Vol. 14,
No. 3, September 1999, p.394-401.
[4] Y.N. Anagreh, I.M. Al-Refae e,  Teaching The
Self-Excited Induction Generator Using
Matlab , International Journal of Electrical
Engineering Education, Vol. 40, Is. 1, July
2003, p.55-65.
[5] O. Ojo, O. Omozusi, A. Ginart, B. Gonoh,  The
Operation of a Stand-Alone, Single-Phase
Induction Generator Using a Single-Phase,
Pulse-Width Modulated Inverter With a Battery
Supply , IEEE Transactions on Energy
Conversion, Vol. 14, No. 3, September 1999,
p.526-531.
[6] O. Ojo, O. Omozusi, A.A. Jimoh,  The
Figure 10 Transient output voltage of the inverter
Operation of an Inverter-Assisted Single-Phase
controlled by a condenser group (loaded with 200&!) (a)
Simulation, (b) Experimental. Induction Generator , IEEE Transactions on
Industrial Electronics, Vol. 47, Is. 3, June 2000,
Similar results are shown in Fig 10 for a load of p. 632-640.
[7] H.C. Rai, A.K. Tandan,  Voltage Regulation of
200&!. Here, a capacitor value of 91µF in addition to
Self Excited Induction Generator Using Passive
the constant exciting condenser of 240 µF is
Elements , 6th International Conf. on Electrical
switched on by the PIC controller when a load of
Machines and Drives, 1993, p. 240-245.
200&! is taken on. As a result the inverter output
voltage rises to its almost original value.
Appendix
6 Conclusions
Ratings of the single-phase 50 Hz, 220 V, 1.1 kW, 4
pole split-phase asynchronous machine is:
In this study the voltage and frequency control of a
Rqs=2.2&!, Llqs=1.3mH, Rds=7.62&!, Llds=6.3mH,
self-excited single-phase asynchronous generator
Rqr=1.3&!, Rdr=3.5&!, Llqr=Lldr=2.8mH,
has been for variable load conditions. A simulation
Lmq=0.485mH, J=0.00875kgm2, C=240µF.
model of the system using Simulink/Matlab program
has been obtained. The experimental setup has been
designed and results have been compared to their
simulation corresponding. The results have shown
that in variable loading conditions, the voltage and
frequency of the generator were kept constant by
controlling the condenser group and the inverter
output frequency, respectively.