Control method of cascaded h-bridge inverter and control device of cascaded h-bridge inverter

Abstract

The invention discloses a control method and device for a cascade H bridge inverter. The method comprises the following steps: sampling direct-current capacitor voltage and grid current of each H bridge of the cascade H bridge inverter; respectively calculating the difference between the direct-current capacitor voltage of each H bridge and the MPPT (Maximum Power Point Tracking) given voltage, and sequencing the differences from small to large; preliminarily judging the quantity and areas of zero-state H bridges, quantity and areas of to-be-charged H bridges, quantity and areas of to-be-discharged H bridges and quantity and areas of H bridges outputting PWM (Pulse Width Modulation) wave, and recording coordinates of two endpoints of the zero-state H bridges; dividing an area of modulated wave output by a current loop, and generating a switching mode distribution table; calculating the maximum of the quantity of zero-state H bridges in a certain area; substituting the maximum into the switching mode distribution table; and modulating the H bridge inverter according to the switching mode distribution table. The technical solution reduces the voltage fluctuation of the direct-current side, and improves the stability of a system.

Description

technical field [0001] The invention relates to the technical field of inverters, in particular to a control method for a cascaded H-bridge inverter and a control device for the cascaded H-bridge inverter. Background technique [0002] System structure reference of cascaded H-bridge inverter figure 1 as shown, figure 1 Medium PV 1 ~PV n For photovoltaic panels, Vdc 1 ~Vdc n is the DC side voltage, i s is the grid current. When uneven illumination or other conditions lead to a serious drop in the power of photovoltaic panels in some areas, the AC side current i of the cascaded H-bridge inverter s The power of the H-bridge powered by photovoltaic panels in other normal areas is almost unchanged. The H-bridges powered by these normal area PV panels will have too much modulation when modulated. If the cascaded H-bridge inverter adopts the traditional SPWM modulation method, the modulation degree of some H-bridges is greater than 1, which will cause the entire system to ...

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Problems solved by technology

[0008] However, there are uncertainties in the above technical solutions, because the charge and discharge state of each H-bridge is not really its own needs, but is subject to how to raise the PWM wave to the area K, and some power modules may already be higher than The given voltage of MPPT needs to be discharged, but due to system control, it may be assigned to continue charging, refer to Figure 4 , citing a situation when K=2, where "+1" means the H-bridge output +Vdc, "-1" means the output -Vdc, the H-bridge whose voltage difference is less than 0 needs to be charged, and the voltage difference is greater than The H bridge that is 0 needs to be discharged

The actual DC side capacitor voltage of the H-bridge corresponding to the voltage difference Verr2 and Verr3 is higher than the given voltage of MPPT. It should be discharged, but because the system must raise the PWM to area 2, it has to be charged, which causes the mixed Under the modulation method, the DC side voltage fluctuates greatly

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