Power compensation method for unbalanced direct power control of voltage controlled grid-connected inverter

Abstract

The invention discloses a power compensation method for unbalanced direct power control of a voltage controlled grid-connected inverter, which is suitable for direct power control (the conventional direct power control) without synchronous speed rotational coordinate transformation. The method comprises the following steps of extracting negative sequence voltage signals and positive sequence current signals by collecting voltage and current signals of a three-phase electric network; and computing compensation items of active and reactive power according to selected control targets. In the method of the invention, the compensation items of active and reactive power are injected in the power reference signals of the conventional direct power control according to required control targets so as to respectively eliminate negative sequence current, double frequency fluctuation of the active power and double frequency fluctuation of the reactive power in the electric network, caused by unbalanced voltage in the electric network, and fit different application situations. The invention has the advantages of enhancing the capabilities of control and uninterrupted operation of the voltage controlled grid-connected inverter when the electric network is in an unbalanced fault.

Description

technical field [0001] The invention relates to a voltage-type inverter PWM control technology in the field of power electronics, in particular to a power compensation method for a voltage-type grid-connected inverter to enhance direct power control under the condition of grid voltage asymmetry. Background technique [0002] With its excellent input and output characteristics, voltage-type PWM inverters are widely used in wind power generation, photovoltaic power generation and other new energy generation, as well as high-voltage direct current transmission and other fields. Vector control (VC) and direct power control (DPC) are the main control strategies of voltage source PWM inverter. The research on the direct power control of the voltage source PWM inverter under normal power grid conditions has been relatively complete. However, since the areas rich in wind energy and solar energy are mostly remote and far away from the core large power grid, the power grid is relativ...

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Problems solved by technology

Although the positive and negative sequence currents of the VSC are expressed as direct currents in the positive and negative synchronous speed coordinate systems respectively, two PIs can be used to track without static error, but this control needs to extract the positive and negative sequence currents in the control inner loop. components, which will greatly limit the control bandwidth of the system and affect the dynamic and stable response of the system

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