Load impedance estimation and repetitive control method capable of allowing inductance variation for inverter

A load impedance estimation and repetitive control method capable of allowing inductance variation for inverter, comprising steps of:

• (1) providing a three-phase four-wire inverter connecting to at least one load, wherein the three-phase four-wire inverter has a R-phase output inductor, an S-phase output inductor, a T-phase output inductor, a N-phase balance inductor, a R-phase output capacitor, an S-phase output capacitor, and a T-phase output capacitor;
• (2) deriving a first matrix equation for presenting the voltage variation of the R-phase output inductor, the S-phase output inductor, the T-phase output inductor by using Kirchhoff's current law and voltage law;
• (3) measuring a R-phase output voltage, an S-phase output voltage and a T-phase output voltage of the three-phase four-wire inverter for obtaining a signal waveform diagram, and then partitioning the signal waveform diagram into a plurality of phase voltage regions according to the zero voltage crossing points of the R-phase output voltage, the S-phase output voltage and the T-phase output voltage;
• (4) modulating a switching periodic signal waveform diagram of a R-phase switching member set, an S-phase switching member set, a T-phase switching member set, and a N-phase switching member set in the three-phase four-wire inverter through a Two Phase Modulation way, so as to make the switching periodic signal waveform diagram show centrally symmetrical;
• (5) deriving a plurality of switching duty cycle matrix equations for each of the phase voltage regions through the first matrix equation, and then integrating all the switching duty cycle matrix equations to a second matrix equation;
• (6) providing an equivalent RLC load for the at least one load, and then sampling a total current variation of the equivalent RLC load for three periods by using a controller;
• (7) deriving a total current variation matrix equation according to the total current variation obtained by the step (6) and Kirchhoff's current law;
• (8) using the total current variation matrix equation to estimate a specific resistance, a specific inductance and a specific capacitance for a parallel resistor, a parallel inductor and a parallel capacitor in the equivalent RLC load, respectively;
• (9) substituting the specific resistance, the specific inductance and the specific capacitance into the second matrix equation, so as to obtain a next-period switching duty cycle for the R-phase switching member set, the S-phase switching member set, the T-phase switching member set, and the N-phase switching member set;
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• (10) the R-phase switching member set, the S-phase switching member set, the T-phase switching member set, and the N-phase switching member set executing switching operations based on the next-period switching duty cycle, such that the three-phase four-wire inverter outputs an output voltage steadily.