Improvement of the current control loop of the single-phase multifunctional grid-tied inverter of photovoltaic system

Resumen

Improvement of the current control loop of the multifunctional grid-tied inverter of the local object electrical power system is considered. The purpose is ensuring compliance with the quality standards of the grid current in the whole range of its values when connecting the load to the AC distribution grid and the converter unit of the photovoltaic system. The use of relay current controller with combining of unipolar and bipolar modulation in combination with a modified algorithm of switching the inverter switches is proposed. It is shown that at a non-linear load, the jump-like change of the derivative of the inverter reference current leads to a sharp change in the switching frequency of the switches. This leads to the appearance of ?splashes? in the grid current, which worsens its harmonic composition at small current values.In the nonlinear reactor with an increase in the inverter current, the ?splash? is also caused by changes in the switching frequency of the switches. This takes place in the areas of current growth (fall) due to a change in the reactor inductance. The dependence of the given deviation for the relay controller is established. In the case of a linear reactor, this provides a practically constant switching frequency for the inverter switches. It is proposed to take into account the derivative of the inverter current in the deviation reference of the relay controller. This eliminates an abrupt change in switches switching frequency. The necessity of taking into account the non-sinusoidal grid voltage during the determination of the voltage value at the inverter input is shown. It is proposed to reduce the capacitance of the filter capacitor at the point of common coupling and use of capacitor current coupling. This will improve the quality of the grid current at the non-sinusoidal voltage of the grid. The structure of the current control loop with a relay current controller with the combined modulation and regulation of the reference value of the controller deviation is proposed. Regulation is carried out in accordance with the reference value of the amplitude and the derivative of the inverter current. A mathematical model of the system ?grid ? grid inverter ? load? with a block of determination of power losses in the switches and a nonlinear reactor is developed