Introduction of On Grid Inverter

On grid inverter system converts the direct current emitted by solar photovoltaic array into alternating current with the same frequency and phase as the voltage of public grid, so the system can not only meet the demand of local load but also send electricity to public grid. Generally, the public power grid system can be regarded as an AC voltage source with infinite capacity. When the power generation of the solar photovoltaic array in the grid-connected solar photovoltaic power generation system is less than the electricity consumption of the local load, the insufficient part of the local load power is supplied by the public power grid; When the power generation of photovoltaic cell array is greater than the electricity consumption of local load, the solar photovoltaic system will transfer the excess electric energy to the public grid to realize grid-connected power generation.

Composition of On Grid Photovoltaic Power Generation System

On grid photovoltaic power generation system generally consists of solar cell photovoltaic array, MPPT control, DC/DC converter, driving circuit and controller, in which the converter can convert the direct current generated by the solar cell photovoltaic array into sinusoidal alternating current and merge it into the public power grid. The controller mainly controls the waveform and power of the grid-connected current of the inverter and the tracking of the maximum power point of the photovoltaic cells, so that the power transmitted to the power grid matches the maximum power generated by the solar photovoltaic cell array.

Control Mode of Grid-Connected Photovoltaic Power Generation System

If the output of on grid inverter is controlled by voltage, it is equivalent to the voltage source running in parallel with the voltage source; If the output of on grid inverter is controlled by current, it is equivalent to the parallel operation of current source and voltage source. When the inverter adopts current control, it only needs to control the output current of the inverter to track the grid voltage, and control the output current to have the same frequency and phase with the grid voltage, so that the power factor of the system is 1. At present, on grid inverters generally adopt the control mode of voltage source input and current source output. The inverter of photovoltaic grid-connected system usually adopts current control mode, so that the whole system is actually a system with voltage source and current source connected in parallel.

The main control goal of on grid inverter operation is to ensure that the output current of inverter has the same frequency and phase with the voltage of public grid, and it can also track the voltage of grid in real time to realize maximum power tracking control. Phase-locked control technology is adopted to realize the phase synchronization between the grid-connected current output by the solar photovoltaic power generation grid-connected system and the voltage of the public grid, so as to ensure that the power factor of the system output is 1. When the on grid inverter is running, it is necessary to control the total distortion of the grid-connected current to be low, so as to reduce the harmonic influence on the power grid and maximize the active power output of the grid-connected system.