Voltage equalizing control method for cascaded two-stage inverter

Abstract

The invention discloses a voltage equalizing control method for a cascaded two-stage inverter. The voltage equalizing control method for a cascaded two-stage inverter includes the steps: performing fine adjustment on the duty ratio through error per unit correction to perform voltage stabilization control, on the basis of a cascaded two-stage inverter model, for a DC bus voltage drift problem caused by uneven illumination; obtaining the fine adjustment amount of the duty ratio through a series of adjustment of a PI adjustor after error voltage per unit for each module, and realizing voltage equalizing control of the DC bus by adjusting the duty ratio of each module; and providing a specific implementation mode for fine adjustment of the duty ratio through carrier phase shift modulation, and establishing a 3-cell cascaded two-stage inverter models in the MATLAB / Simulink software. The simulation results show that the control strategy of the voltage equalizing control method for a cascaded two-stage inverter can achieve stable tracking under the condition of uneven illumination and suppress bus voltage drift.

Description

technical field [0001] The invention relates to the technical field of inverter voltage equalization control, and more specifically relates to a voltage equalization control method for cascaded two-stage inverters. Background technique [0002] The output of photovoltaic cells is greatly affected by temperature, light intensity and its own parameters. In traditional centralized photovoltaic power generation systems, each photovoltaic array cannot achieve individual control of maximum power point tracking (MPPT), making power generation Efficiency is greatly reduced. Compared with the traditional inverter, the cascaded inverter has the characteristics of easy modularization, low output voltage harmonic content, large capacity and high efficiency. The cascaded inverter is applied to the high-power photovoltaic grid-connected power generation system. It can reduce system harmonics, reduce the switching stress of power tubes, and increase the output voltage level, so it has bec...

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Problems solved by technology

In the 19th issue of "Power System Automation" in 2016, "Voltage Equalization Strategy Applicable to Modular Cascaded Photovoltaic Power Generation DC Grid-connected System" under the assumption that the system is stable, the input power of the module and the duty cycle of the switch tube of the subsequent unit are analyzed The relationship between ratios, using a control strategy combining power proportion feedforward and PI limiting and fine-tuning the duty cycle, so as to achieve the stability of the capacitor voltage, but this strategy is only applicable to the case where the input power of each module is the same; the 10th issue of 2015 In "High Voltage Technology", "Photovoltaic Smart Grid-connected System Based on Module Cascade Topology" takes into account the difference in the output power of photovoltaic modules, and changes the switching status of photovoltaic modules according to the DC voltage of each module, and changes the DC side capacitance in real time. The charging and discharging state of each photovoltaic module keeps the DC capacitor voltage stable. This control method is simple and easy to implement, but it cannot guarantee that the switching frequency of each H-bridge is consistent.

In the 12th issue of "Power Electronics Technology" in 2016, "Research and Implementation of Voltage Equalization Control Method for Cascaded H-bridge Converters" aimed at the problem of unbalanced capacitor voltage in chain topology, proposed an upper layer voltage equalization control method with superimposed vectors , by analyzing the dynamic balance equation of the DC side voltage, a double closed-loop voltage control strategy combining chain voltage equalization and outer loop control is adopted, but the dynamic response speed of the grid side current under chain voltage equalization control is slow and the robustness is poor ; "Cascaded photovoltaic power generation system with synchronous motor characteristics" in "Proceedings of the Chinese Society for Electrical Engineering" in the second issue of 2017, based on the study of the grid-connected control strategy of virtual motor control, a cascaded photovoltaic power generation system with synchronous motor characteristics is proposed. The combined photovoltaic power generation system can stabilize the impact of photovoltaic random power fluctuations on the grid, respond to grid frequency changes, maintain system stability, and maintain overall power balance. However, the control structure is relatively complicated, and at the same time, many parameters are involved, which reduces the dynamic performance of the system.

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