Single-phase non-isolated photovoltaic grid-connected inverter and control method

Abstract

The invention discloses a single-phase non-isolated photovoltaic grid-connected inverter and a control method. The photovoltaic grid-connected inverter mainly comprises a half-bridge circuit, a full-bridge circuit and a control circuit, wherein the control circuit controls the half-bridge circuit and the full-bridge circuit, so that the half-bridge circuit can be modulated in a high-frequency sinusoidal pulse width modulation (SPWM) mode to output half-sinusoidal current, and the full-bridge circuit can commutate in an industrial-frequency mode to commutate the half-sinusoidal current output by the half-bridge circuit and output sinusoidal current required for grid connection. The photovoltaic grid-connected inverter can ensure that the problem of common-mode current in the non-isolated grid-connected inverter circuit is effectively solved, the distortion of the current at the zero crossing point is reduced and the high-frequency switching loss in the circuit is low at any time.

Description

technical field [0001] The invention relates to the technical field of photovoltaic grid-connected inverters, in particular to a single-phase non-isolated photovoltaic grid-connected inverter and a control method. Background technique [0002] Isolated photovoltaic grid-connected inverters with power frequency or high-frequency transformers are often used in photovoltaic grid-connected systems, which ensures electrical isolation between the grid and the photovoltaic system, thereby providing personal protection and avoiding contact between the photovoltaic system and the ground. leakage current. However, if a power frequency transformer is used, it is bulky, heavy and expensive; if a high frequency transformer is used, the power conversion circuit will be divided into several stages, which complicates the control and reduces the efficiency of the system. [0003] In order to overcome the shortcomings of the above-mentioned isolated grid-connected system with transformer, a ...

AI Technical Summary

Problems solved by technology

The disadvantages of this photovoltaic grid-connected inverter include: (1) The full-bridge circuit adopts high-frequency unipolar modulation, and as in "Study on Common Mode Current Suppression of Single-phase Non-isolated Photovoltaic Grid-connected Inverter" ( Sun Longlin et al., pointed out in the 11th Academic Annual Conference of the Power Electronics Society of the Chinese Electrotechnical Society), the common-mode voltage generated by the full-bridge topology using unipolar modulation excites the common-mode current generated by the common-mode resonant circuit will reach Amperes and increases linearly with the increase of switching frequency, that is to say, the unipolar modulation itself inevitably produces a large common-mode current (the common-mode voltage excitation of the full-bridge topology with bipolar modulation The common mode current generated is only milliamp level), especially in the case of high switching frequency; (2) There are two switching tubes working in the high frequency state at the same time during the entire switching cycle, so the high frequency switching in the circuit Greater loss

Images