Grid-connected inverter of combination of LCL and multiple LC branches and current control method

Abstract

The invention discloses a grid-connected inverter of combination of LCL and multiple LC branches. The inverter comprises a PWM inverter, a LCL-LC filter, two current transformers used for monitoring a grid-connected current, a current control loop and a PWM driving circuit, wherein the current control loop is used for grid-connected control and contains current weight calculation, current error calculation and proportional-integral control. The PWM inverter is connected to the LCL-LC filter. The LCL-LC filter is connected to the current control loop. The current control loop is connected to the PWM driving circuit. The PWM driving circuit is connected to the PWM inverter. The two current transformers measure an intermediate current which flows through a C branch and a LC series resonance branch and a current flowing through network side series inductors respectively. The intermediate current is added to the current according to a certain weight coefficient and the sum is served as a feedback control signal of an inverter output current. The feedback control signal is compared to a current instruction signal so as to acquire an error value. An output signal after the obtained error value passes through a PI regulator is served as an inverter PWM modulating signal so as to control an output current waveform and an amplitude of a LCL-LC grid-connected inverter.

Description

technical field [0001] The invention relates to the technical field of grid converter control, in particular to a grid-connected inverter combined with LCL and multiple LC branches and a current control method. Background technique [0002] Common LCL-LC grid-connected inverter, its circuit is as follows figure 1 with figure 2 As shown, usually includes PWM inverter, LCL-LC filter for grid-connected operation, current transformer for grid-connected current measurement, current weighting calculation and current error calculation and scaling for grid-connected control Integral regulation of the current control loop, PWM drive circuit. [0003] The PWM inverter adopts four insulated gate bipolar transistors, which are connected in parallel after two in series, for example figure 1 with figure 2 shown, the first IGBT S 1 and a second IGBT S 2 Composing the first series circuit, the third insulated gate bipolar transistor S 3 and the fourth IGBT S 4 Form the second seri...

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Problems solved by technology

However, since the filter of the LCL-LC structure is a high-order system, the filter has a large gain peak near the corner frequency. In order to ensure the stability of the control system, the gain of the PI regulator is limited and the value is small, so that The open-loop gain of the system in the low frequency band is small, which reduces the resistance of the grid-connected inverter to output current steady-state errors and harmonic interference, and is also easily affected by grid voltage distortion

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