05-03-2013, 04:38 PM
A Voltage Controller in Photo-Voltaic System without Battery Storage for Stand-Alone Applications
A Voltage Controller in Photo.pdf (Size: 323.38 KB / Downloads: 50)
Abstract —
The paper proposes the new voltage controller in
photo-voltaic system for Stand-Alone Applications without
battery energy storage. The output of the PV array is
unregulated DC supply due to change in weather conditions. The
maximum power is tracked with respect to temperature and
irradiance levels by using DC-DC converter. The perturbation
and observes algorithm is applied for maximum power point
tracking (MPPT) purpose. This algorithm is selected due to its
ability to withstand against any parameter variation and having
high efficiency. The output of DC-DC converter is converted to
AC voltage by using inverter. The AC output voltage and
frequency are regulated. A closed loop voltage control for
inverter is done by using unipolar sine wave pulse width
modulation (SPWM). The regulated AC voltage is fed to AC
standalone loads or grid integration. The overall system is
designed, developed and validated by using MATLABSIMULINK.
The simulation results demonstrate the effective
working of MPPT algorithm and voltage controller with SPWM
technique for inverter in AC standalone load applications.
INTRODUCTION
The natural resources, which have been used for power
generation, are dwindling fast and the energy became very
expensive. So the entire world is looking for another option to
generate electrical energy. Among various renewable energy
systems, photovoltaic power generation systems (PV systems)
are expected to play an important role as a clean electricity
power source in meeting future electricity demands. Photo
voltaic systems are used in many applications such as solar
heaters, water pumping, battery charging, power supply to
home, swimming-pool heating systems etc.
Due to the nonlinear relationship between the current and
the voltage of the photovoltaic cell, it can be observed that
there is a unique maximum power point (MPP) at a particular
environment, and this peak power point keeps changing with
solar illumination and ambient temperature. An important
consideration in achieving high efficiency in PV power
generation system is to match the PV source and load
impedance properly for any weather conditions, thus obtaining
maximum power generation. The technique is employed by
tracking the maximum power point which is called as
maximum power point tracking (MPPT). In recent years, a
large number of techniques have been proposed for maximum
power point tracking (MPPT), such as the constant voltage
tracking (CVT), the incremental conductance (INC) method,
the perturb-and-observe (P&O or hill-climbing) method, and so
on. At last, these algorithms modify the actual voltage in order
to increase the power output.
Perturbation and Observation (P&O) method has a simple
feedback structure and fewer measured parameters. It operates
by periodically perturbing (i.e. incrementing or decreasing) the
array terminal voltage and comparing the PV output power
with that of the previous perturbation cycle. If the perturbation
leads to an increase (decrease) in array power, the subsequent
perturbation is made in the same (opposite) direction. In this
manner, the peak power tracker continuously seeks the peak
power condition. MPP is tracked by using DC-DC converters.
Much attention has been given to the single ended primary
inductor converter (SEPIC) topology recently because output
voltage may be either higher or lower than input voltage .The
output is also not inverted as is the case in a fly back or Cuk
topology. The input and output voltages are DC isolated by a
coupling capacitor and the converter works with constant
frequency PWM.
PROPOSED SYSTEM CONFIGURATION
The block diagram of the proposed solar energy conversion
scheme is shown in Fig. 1. It consists of PV array driven by
SEPIC converter interfaced to the stand-alone load through a
single phase Inverter. The output Power of the SEPIC
converter is varied due to temperature and irradiations. Hence,
the Maximum power is tracked and extracted from the PV
array and transferred to the stand-alone load through single
phase Inverter. The controller generates the gating pulses for
the SEPIC and Inverter to extract maximum power and to
maintain desired ac output voltage and frequency across load
terminals.
RESULTS AND DISCUSSIONS
The simulation results of the proposed scheme such as
active power fed to load, load voltage and load current, DC link
voltage and current are shown in figures. Three similar solar
panel with open circuit voltage Voc = 21.2V and Isc 5.17A are
connected in series which triples the Voltage keeping current
same. The change in climatic conditions affects the inverter
voltage and current. The maximum power rating of each panel
is 80W, as the panels are connected in series maximum power
will be 240W. The main objective is to extract the maximum
power. SEPIC converter specifications are tabulated below:
CONCLUSION
The development of a method for the mathematical
modeling of photovoltaic array has been analyzed. When the
PV array is used as a source of power supply to stand alone
loads, it is necessary to use the MPPT to get the maximum
power point from the PV array and implemented with
MATLAB/SIMULINK for simulation. The MPPT is
implemented by using a SEPIC-Converter, which is designed
to operate under continuous conduction mode. The
perturbation and observe Algorithm is used as the control
algorithm for the MPPT. From results of simulation, it can be
seen that the P&O MPPT algorithm which is able to improve
the dynamic and steady state performance of the PV system.
At the same time, output results of inverter with SPWM
control strategy have better voltage control and simulation
results of system demonstrate that the PV system has the fast
and effective response under changing irradiance levels. So
the PV generation system based P&O MPPT method and
SPWM control for single-phase voltage source PWM inverter
is feasible and effective.