Control circuit for stand-alone /grid-connected dual-mode inverter and switching technology thereof
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The invention discloses a control circuit for a stand-alone /grid-connected dual-mode inverter and a switching technology thereof. During grid-connected operation, a current loop PI (Proportional-Integral) control mode with power grid voltage feed-forward is adopted to enable grid connected current to have the same amplitude, frequency and phase with the voltage of a power grid. During stand-alone operation, a voltage loop PI control mode with feed-forward is adopted to control the amplitude and the frequency of a voltage output by a target to the inverter to meet load requirements. A dual-mode control strategy is realized by a method combining software and hardware. A micro-controller provides a carrier wave clock signal, a reference sine wave data table and a software phase locking control and mode selecting signal, and the control circuit comprises a triangular carrier wave generation circuit, a reference sine wave generation circuit, a current and voltage feedback link, a dead zone setting circuit and a single frequency doubling SPWM (Sinusoidal Pulse Width Modulation) circuit. The method provided by the invention has the advantages that the design difficulty of the inverter is lowered, the software of the microprocessor is simple to program, the delay of the control link is short, the seamless smooth switching between the stand-alone and grid-connected dual modes can be realized, and the work is stable and reliable.