2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 230 -
Microcontroller-Based Self-Excited Induction
Generators Controller for Pico-hydro System
U. Boonbumroong* and P. Sripadungtham**
*Pilot Plant Development and Training Institute,
King Mongkut’s University of Technology T
honburi,
(Thailand)
**Department of Electrical Engineering, Faculty of Engineering, Kasetsart University,
(Thailand)
Abstract
--This
paper
presents
the
design
and
implementation of a microcontroller-based induction
generators controller (IGC) for three-phase, self-excited
induction generators (SEIG) supplying single phase loads.
This system is suitable for stand-alone hydro generation
systems with constant input power. The generated voltage
and frequency of these machines varies with the loads
applied. The prototype of a simple and cheap IGC, which
can operate almost unattended in remote and hilly regions,
needs to be developed. The proposed IGC consists of an
uncontrolled rectifier and chopper with a series dump load.
The core of this IGC is an ATmega 328 AVR
microcontroller, which implements PID control algorithms.
In this paper, steady state and transient behavior of the
developed prototype IGC at different operating conditions
is investigated
Index Terms
—
microcontroller, induction generators
controller (IGC), pico hydro power generation, self-excited
induction generator (SEIG).
I.
I
NTRODUCTION
Rural electrification is a key element in rural
development and can bring concrete social and economic
benefits to local populations. However, grid power is
unavailable in several areas, especially those in remote
areas and inaccessible locations of developing countries.
The lack of convenient, affordable and reliable electricity
hampers development efforts, and limits the ability of
locals to develop their communities. Renewable energy
resources such as wind, hydro, and solar have been
available for a long time although, so far, they have not
been adequately utilized as a result of more attractive but
pollution-generating fossil fuels.
In remote locations or hilly areas, electrical energy
from local sources such as hydro can be inexpensive to
generate compared to grid connection. Conventional
hydro power systems have a mechanical or hydraulic
speed governor, which in some cases controls the water
supply via a spear valve, or acts upon a deflector that
moves the jet away from the turbine. Some systems even
have the speed governor act on a mechanical brake.
These systems usually work reasonably well, but
governors are expensive and require careful maintenance,
making the micro-hydro system more expensive and less
reliable [1]. The uncontrolled pico-hydro turbines driving
self-excited induction generators may be one of the most
suitable options. However, a major drawback of the
SEIG is poor voltage regulation. The generated voltage
depends upon the speed, capacitance, load power and
power factor of the load [2]. Furthermore, input power
remains constant with an unregulated pico-hydro turbine,
but output power is not constant due to the changing load
requirements of consumer demand/usage. Nevertheless,
this characteristic can be resolved with a controllable
dump load connected in parallel with the consumer load,
such that the total generated power is held constant [3].
The function of a controller is to keep the voltage at the
SEIG terminals constant. Where the machine delivers a
fixed amount of power, the amount of power to be
supplied to the dump load is decided by an IGC. A
controller can be used to switch-in or switch-out a dump
load whenever the main load decreases or increases,
respectively.
There are different types of IGC. Some are purely
electrical and some make use of power electronic
switching devices [4-5]. One of the purely electrical
types is the binary weighted-switched resistors IGC. The
total resistive load is divided into a different number of
elements in which the system is bulky, and less reliable.
The second type is the phase angle control-based type;
the principle of phase angle control of back-to-back-
connected thyristors is delayed from 0 to 180 degrees as
the consumer load is changed from zero to full load. In
addition, it requires complicated driver circuits. The third
type is controlled rectifier feeding dump loads, of which
the most common. The firing angle is changed from 0 to
180 degrees for single-phase and 0 to 120 for three-
phase, to cover the full range of consumer loads from 0
to 100%. In this scheme, six thyristors and their driving
circuits are required. Hence, it is a complicated set-up.
The fourth type of uncontrolled rectifier with a chopper-
controlled dump load uses the pulse width modulation for
the chopper operation. The duty cycle of the pulse is
controlled from 0 to 100%; the power is controlled over
the entire range. The PWM for such a chopper can be
generated by comparing the error signal generated by
comparing a reference signal. The controller consists of
an uncontrolled rectifier with a chopper and a self-
commutating device such as a power MOSFET or IGBT
in series with a dump load. In this scheme, only one
switching device and its driving circuit are required.
Thus, the scheme is very simple, cheap, rugged, and
reliable. Only one dump load is required and, hence, it is
inexpensive and compact. Therefore, it is considered as
the most suitable scheme for a pico-hydro power system.
This paper details the design and implementation of a
microcontroller-based IGC for SEIG feeding single-
phase loads. The control is realized by means of an
