Current injection-type photovoltaic grid-connected system

The invention discloses a current injection-type photovoltaic grid-connected system, which has the function of purifying a power grid. By using a sufficient voltage difference with DC voltage at a photovoltaic cell side greater than a voltage amplitude at a power grid side, the required current of the photovoltaic cell is forced to be injected to the power grid, and the output power is equal to the product of power grid voltage and injected current; the above required current comprises two parts: the first is AC which is active current generated when a power grid voltage waveform is directly taken for real-time SPWM sine wave pulse width modulation processing, and the second is power grid compensation current with the same magnitude as the active current in the power grid and with the opposite direction; in the case of photovoltaic grid connection, the photovoltaic cell charges a battery, when the energy of the photovoltaic cell is insufficient, the battery performs power supply and grid connection, and the g