Simulation Study on Current Control Techniques for Single Phase Grid Connected Inverter Systems

Abstract

In general, the reliability of power supply to load can be increased by grid connected inverter systems. But harmonics produced in the inverter, may lead to the harmonic injection in to the grid and this can cause non linearity in grid current which will produce undesirable effects like high Total harmonic distortion (THD) and low grid power factor. These unwanted effects can be reduced by current control techniques where the controller controls the inverter switching that indirectly controls the grid current.

The current control technique used in this work is based on the error between the actual grid current and a reference grid current trajectory. The error value is confined in a hysteresis band which is bounded between two limits. Hence, it is called Hysteresis current control. This current controller makes use of relay that switches only when the input given to it reaches the extreme value. In this hysteresis current control, the input given to relay is error value which is the difference between the actual and a reference grid current. The relay output triggers the inverter switches. Here, the switching frequency depends on the relay output which depend son hysteresis band. Thus, a proper selection of band is required to minimise switching loss. In this method, the grid voltage is used to generate the reference sinusoidal signal which after multiplication with a proper factor generates reference current signal. The reference current is compared to actual grid current which in turn forces the grid current to be in phase with grid voltage. In other words, the controller forces power consumption from the grid to be in unity power factor condition. In one way, the reactive power of the system is controlled.

In this project, another type of current controller is used. It is called adaptive hysteresis controller that can work in a similar manner. In this method, the factor used for reference current generation depends on load. In this method, a new switching technique is used to ensure the prevention of short circuit between inverter DC power supply terminals. The comparative analysis is made between conventional and adaptive hysteresis current controllers through its implementation in MATLAB SIMULINK and simulation results are compared.