Control method for expanding the stable operating range of cascaded h-bridge photovoltaic grid-connected inverters

Abstract

The invention discloses a control method for expanding the stable running range of a cascaded H-bridge photovoltaic grid-connected inverter. The method comprises the following steps of detecting output voltages and currents of all photovoltaic cell modules, a power grid voltage and a power grid current on line; judging whether the system can stably run or not according to the size of an effective value of the power grid current and the size of critical current of an inverter during unit power factor running; calculating an angle of the power grid current advancing the power grid voltage when the system cannot stably run, and compensating reactive power; and judging whether a power factor of the system is lower than 0.9 or not, maintaining the power factor to be 0.9 if the power factor is lower than 0.9, enabling the photovoltaic module with relatively large output power to exit from maximum power point running so as to balance power among the modules. By the method, the stable running range of the cascaded H-bridge photovoltaic inverter can be effectively expanded, and moreover, not too low power generation quantity and power factor of the system can be ensured.

Description

technical field [0001] The invention belongs to photovoltaic power generation technology in the field of electrical engineering, and more specifically relates to a cascaded photovoltaic grid-connected inverter and a method for controlling power imbalance thereof. Background technique [0002] Compared with two-level and three-level inverters, multi-level inverters have the advantages of less stress on switching devices, high system efficiency, and small filter volume. Since the multi-level inverter was proposed, there have been many topologies, and there are mainly three types: diode clamping type, flying capacitor type and cascaded H-bridge type. Among all the multi-level topologies, when outputting the same number of levels, the cascaded H-bridge inverter uses the fewest components and the simplest layout. In addition, the DC side of each power unit of the cascaded H-bridge inverter can be independently powered by a photovoltaic module, which makes MPPT control of a singl...

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Problems solved by technology

[0011] The problem to be solved by the present invention is to overcome the limitations of the above-mentioned solutions, aiming at the problem of overmodulation caused by the power imbalance of the cascaded H-bridge photovoltaic inverter, a method of expanding the stable operation range of the cascaded H-bridge photovoltaic grid-connected inverter is proposed control method

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