This paper deals with the voltage control of self-excited induction generators. It
cover a large number of problem including mathematical model of stator and
rotor circuits, connections of loads to SEIG, operating algorithm of TRIAC,
Voltage Sensor and Logic Control Unit and others. Also this article includes results
of experiments and graphics of transient processes of the system technological
generators with self-excitation (SEIG) from capacitor bank are widely spread in
modern stand-alone electric power systems. But voltage control and
stabilization in such systems is not a simple task. In existing systems of
voltage control [1,2] different approaches are used,
from relay-switched capacitor banks to STATCOM  and inverters. These systems
have both advantages and disadvantages, but are often not-suitable for a wide
power-range and can not be multipurpose for high power induction generators (50
kW or higher). Therefore it is necessary to develop a system that will be
suitable to use both for low-power stand-alone generators, and for large power
generating plants, and which will provide a reliable and smooth voltage
regulation. Such system should also provide the self-excitation of an induction
generator at different loads.
One example of a system that meets the requirements set is
offered on, Fig.1 shows the functional diagram of such
Fig.1 Functional diagram of voltage
control system of SEIG
The voltage control system consists of SEIG, the six
blocks of three-phase capacitors, one of them is static and permanently
connected to the stator windings for self-excitation and others are connected
through TRIAC keys. TRIACs are controlled by using
Phase TRIAC Control blocks (PTC) depending on the current state of TRIAC key
and control signals coming from the Logic Control Unit. The Logic Control Unit
generates control signals which are in varying sequences (a total of 32 levels
of control) connect the AC capacitors on the generator bus, thus regulating the
reactive current or SEIG, depending on the load or velocity of the prime mover.
Formation pulse control is based on information received from the Voltage
Sensor. The operating algorithm of Voltage Sensor and Logic Control Unit
stabilizes the output voltage of SEIG by changing the load.
A standard mathematical model of induction generator
stator and rotor circuits in the arbitrary coordinate frame is described by two
nonlinear vector differential equations [2, 3]
where , , –
vectors of stator and
rotor flux linkages, , – vectors of stator and rotor currents, – a vector of stator voltage, і – are the resistances of stator and rotor, – number of pole pairs, – angular rotor velocity, і –the angular velocity of arbitrary coordinate frame F-G.
The resistive loads which are
connected in parallel with capacitors to the stator windings are shown in Fіg 2.
For equivalent replacement capacitors
triangle on the star enough to triple their capacity . Then the fragment of
generator phase equivalent circuit of the capacitor and the load will look like
in Fig. 3. Index "A" marked projection vectors corresponding to the
axis A in the fixed coordinate system A-B of stator. Then according to first Kirchhoff’s law
where , , vectors of currents in the fixed
coordinate system A-B of stator.
Since,, then the coordinate
where - is the vector of stator in the
fixed coordinate system A-B, - load resistance, С – value of capacitor.
The experimental verification of designed operating
algorithm and the voltage control system was performed on existing laboratory
stand for the study of operation of SEIG . It consists of three-phase
induction motor (AИPM63B4Y3, with rated values 370W, 380V, 50 Hz, and 1450 rpm) which was
used for experiments as SEIG. The following parameters of the generator were
determined experimentally =27 Щ, =17.9 Щ, =0.08266 H, =2, =1.03115 H, =0.6345 H. The SEIG was
coupled to another induction motor (4AM80B3Y3, with rated values 2.2KW, 380V,
50 Hz, and 2800 rpm) controlled through the frequency converter ABB ACS140
feeding the stator winding. The higher value of the motor’s power and the slip
compensation function in the ACS140 provided velocity stabilization at desired
levels during experiments. The load was Y-connected. Collection of the
experimental data was performed using ACS140’s monitoring system and a system
for tests of electric drives providing voltage and current measurements with
visualization compatible with MATLAB.
– Self-excitation of the SEIG under the rated load value
Fig. 5 –
Transients of voltage magnitude
Figure 4 describes the process of self-excitation of the SEIG
under the rated load value. At the time 0s. the generator is not connected to the circuit and the
capacitors. At the time 1s. It was connected to the
circuit and the capacitor bank and the self-excitation happens. The value
of generated voltage is stabilized on 380 V. The capacitance of the bank
was calculated using equations from .
Figure 5 presents the transients of voltage magnitude. At
time since 0s till 1с , the value of the load connected to the SEIG is 75%
from the rated value. But since time 1с the load increases to the rated value, the generated voltage sags, therefore the system of
voltage control activates and at time 1,5s the voltage is stabilized on 380 V
by increasing the capacity of
Conclusion. The voltage control system which
uses the proposed algorithm for switching the capacitors is workable. The
accuracy of voltage stabilization can be improved by increasing the number of
levels of the TRIAC-switched capacitor bank. Performance of the system allows
its use in stand-alone power systems with SEIGs to
support sustainable voltage value for consumers
1. Chauhan, Y.K.; Jain, S.K.; Singh, B.,
"A Prospective on Voltage Regulation of Self-Excited Induction Generators
for Industry Applications," Industry Applications, IEEE Transactions on,
vol.46, no.2, 2010. pp.720-730.
2. M. Bodson
& O. Kiselychnyk, “Nonlinear dynamic model and
stability analysis of self-excited induction generators,” Proc. of the American
Control Conference, San Francisco, CA, pp. 4574-4579, 2011.
3. M. Bodson
& O. Kiselychnyk, “On the triggering of
self-excitation in induction generators,” Proc. of the 20th International
Symposium on Power Electronics, Electrical Drives, Automation and Motion (Speedam 2010), Pisa, Italy, pp. 866-871, 2010.
4. Пушкар М.В.
Експериментальна установка для дослідження асинхронних генераторів з
самозбудженням / Пушкар М.В., Савич О.Ю., Кіселичник О.І., // Електромеханічні та енергетичні
системи, методи моделювання та оптимізації. Збірник наукових праць Х
Міжнародної науково-технічної конференції молодих учених і спеціалістів у місті
Кременчук 28-29 березня 2012 р. - Кременчук, КрНУ,
2012. - с. 159-160.