Abstract: A method for distributing unbalanced and harmonic power among a plurality of inverters connected in parallel and operating in an islanded state, by respectively injecting an small-AC-signal in each inverter, including: sampling an output voltage and an output current of each inverter, extracting a fundamental positive sequence component, a fundamental negative sequence component, at least one major order of harmonic component from the current, and current components of the small-AC-signal; calculating an active power and a reactive power of the inverter, calculating the unbalanced and harmonic power; calculating a frequency and an amplitude of a fundamental positive sequence reference voltage, calculating a frequency reference value of the small-AC-signal; calculating a virtual impedance; calculating a voltage drop of the virtual impedance; generating a total reference voltage; and regulating the output voltage of the inverter to follow the total reference voltage.

Abstract: A method and an apparatus for decoupling output power of an inverter are provided. The method comprises: obtaining voltage amplitude instruction E* and voltage phase instruction ?* according to an output voltage and an output current of the inverter; obtaining an amplitude feedforward amount Eff and a phase feedforward amount ?ff according to an amplitude U of a grid voltage of the power grid, an amplitude E of the output voltage of the inverter, and a phase difference ? between the output voltage of the inverter[0] and the grid voltage; obtaining a reference voltage amplitude Eref according to the voltage amplitude instruction E* and the amplitude feedforward amount Eff, and obtaining a reference voltage phase ?ref according to the voltage phase instruction ?* and the phase feedforward amount ?ff; and regulating the output power of the inverter using the reference voltage amplitude Eref and the reference voltage phase ?ref.

Abstract: The present invention discloses a secondary control method and apparatus of parallel inverters in a micro grid, comprising: generating frequency and amplitude of fundamental voltage in the voltage instruction of inverter by droop control according to output voltage and output current of inverter to obtain a fundamental voltage instruction value; extracting voltage values and current values of a first and second AC signals from output voltage and output current of inverter, generating frequency instruction values of the first and second AC signals by droop control to obtain voltage instruction values of the first and second AC signals; regulating the output voltage of inverter according to the voltage instruction value of the first AC signal, the voltage instruction value of the second AC signal and the fundamental voltage instruction value.

Abstract: The present invention discloses a secondary control method and apparatus of parallel inverters in a micro grid, comprising: generating frequency and amplitude of fundamental voltage in the voltage instruction of inverter by droop control according to output voltage and output current of inverter to obtain a fundamental voltage instruction value; extracting voltage values and current values of a first and second AC signals from output voltage and output current of inverter, generating frequency instruction values of the first and second AC signals by droop control to obtain voltage instruction values of the first and second AC signals; regulating the output voltage of inverter according to the voltage instruction value of the first AC signal, the voltage instruction value of the second AC signal and the fundamental voltage instruction value.

Abstract: A method and an apparatus for decoupling output power of an inverter are provided. The method comprises: obtaining voltage amplitude instruction E* and voltage phase instruction ?* according to an output voltage and an output current of the inverter; obtaining an amplitude feedforward amount Eff and a phase feedforward amount ?ff according to an amplitude U of a grid voltage of the power grid, an amplitude E of the output voltage of the inverter, and a phase difference ? between the output voltage of the inverter[0] and the grid voltage; obtaining a reference voltage amplitude Eref according to the voltage amplitude instruction E* and the amplitude feedforward amount Eff, and obtaining a reference voltage phase ?ref according to the voltage phase instruction ?* and the phase feedforward amount ?ff; and regulating the output power of the inverter using the reference voltage amplitude Eref and the reference voltage phase ?ref.