Starting method of multi-branch two-stage three-phase photovoltaic grid-connected inverter

Abstract

The invention discloses a starting method of a multi-branch two-stage three-phase photovoltaic grid-connected inverter and belongs to the technical filed of photovoltaic grid-connected inverter control. A converter connected with a starting power supply changes from ring opening to duty ratio slow starting, a constant-voltage tracking method is used to find the maximum power point, the maximum power point is tracked through a perturbation and observation method, and other convertors and the inverter starts slow starting when direct-current bus voltage is larger than starting voltage of the inverter. By the method, instant impact current of Boost converter starting and inverter grid connection can be restrained, dynamic features of maximum power point tracking during starting can be improved, stableness of the direct-current bus voltage can be guaranteed, and bus overvoltage or undervoltage can be prevented.

Description

technical field [0001] The invention discloses a starting method of a multi-branch two-stage three-phase photovoltaic grid-connected inverter, and belongs to the technical field of photovoltaic grid-connected inverter control. Background technique [0002] With the increasingly serious energy crisis and environmental pollution, the development and utilization of new energy sources are paid more and more attention by people. Solar energy is a non-polluting, renewable and widely distributed green energy, and photovoltaic grid-connected power generation is one of its main forms of utilization. There are three main application forms of photovoltaic grid-connected power generation: photovoltaic power station, photovoltaic building system and micro-inverter. The application occasion of this patent is the photovoltaic building system. This system usually uses multiple solar panels connected in series to form a photovoltaic string branch. Each string of photovoltaic strings is boos...

AI Technical Summary

Problems solved by technology

[0003] The following problems exist when the multi-branch two-stage three-phase grid-connected inverter is started: 1. Since the DC bus voltage has not yet been established, the energy storage inductor core of the Boost converter cannot be demagnetized, resulting in saturation of the inductor core and resulting in shock 2. Since the inverter has not been started, the output voltage of the photovoltaic panel is open circuit voltage when it is turned on, and does not work at the maximum power point. If the high-precision disturbance observation method is directly used to achieve maximum power point tracking, it is difficult to guarantee The rapidity of maximum power point tracking; 3. After the Boost converter is started, if the inverter is not started in time to release the energy accumulated in the DC bus capacitor, the DC bus voltage will be too high and the device will be damaged; 4. Due to the grid voltage The phase and amplitude difference from the inverter output voltage, the inverter will generate an inrush current at the moment of grid connection

The disadvantage of this method is that: No. 1 and No. 1 Boost converters use a relatively small constant duty ratio open-loop operation, and there will be no inrush current in the Boost converter during the constant duty ratio operation after starting up, and the bus voltage can also be established. , but when the No. 1 Boost converter switches from the open-loop operation mode to the disturbance-and-observation operation mode, there is a jump in the duty cycle, which will also cause an inrush current; 2. The direct operation of the disturbance-and-observation method cannot guarantee the fast Work at the maximum power point; 3. The three-phase grid-connected inverters start slowly at the same time, which can only ensure that the one-phase inverter starts slowly at the zero-crossing point of the voltage, and the other two-phase grid-connected inverters do not start slowly at the zero-crossing point of the voltage , resulting in an inrush current

Images