Improvement of the Three-Phase Multifunctional Converter of the Photoelectric System with a Storage Battery for a Local Object with Connection to a Grid

Abstract

The improvement of a three-phase multifunctional converter with the function of an active filter for a photoelectric system with a storage battery for a local object with connection to a grid is considered. Principles for regulating the generation of photovoltaic batteries, the illumination of which can be different, with using a common controller with the introduction of an individual of current limit, which is determined in accordance with the measured value of the short-circuit current of each photovoltaic battery; principles of implementing an autonomous mode with regulation of the load voltage of the object, which allows for the close values of the load power and the current value of the maximum power of photovoltaic batteries to provide an increase in the energy accumulated in the battery has been developed. The output filter is improved, which will provide value $\mathrm{THD} i_{g} \leq 5 \%$ for while reduce almost 2 times the capacitance of the filter capacitor and reduce the PWM frequency to 9 kHz. A variant of the unit control system is proposed, which has a variable structure using the internal current control loop of a grid inverter and three voltage controllers to stabilize the voltage at the inverter input. The choice of controller is carried out by the control unit, taking into account the limitation of energy generation at the grid and the degree of battery charge. In stand-alone mode, the structure and settings of the current control loop are changed. Only a proportional link is used and to reduce energy losses in the inverter, the PWM frequency is reduced to 4 kHz at $\mathrm{THD} u_{L} \leq 5 \%$. It was found that to eliminate the DC component in the grid phase currents with an unbalanced load, the capacitance of the capacitors at the inverter input should be increased while the coefficient of the proportional link of the voltage controllers is reduced. The simulation results of the photoelectric system confirm the efficiency of the proposed solutions.