Low-leakage-current photovoltaic inverter

Abstract

The invention provides a low-leakage-current photovoltaic inverter. The low-leakage-current photovoltaic inverter is mainly composed of a direct current-alternating current inverter circuit and a controller. A direct-current input anode or cathode is directly connected with an alternating-current output or a live wire or a zero wire of a public power grid, so that the leakage current of the inverter is reduced or even eliminated, and the PID effect of the component is relieved. In the direct current-alternating current inverter circuit, a low-cost and low-speed power switch tube can be used for a power frequency bridge arm, a high-speed power switch tube can be used for a high-frequency bridge arm, and a commutation inductor is used between the high-frequency bridge arms to avoid the direct connection risk of the bridge arms. The controller samples alternating current and direct current voltage and current signals, correspondingly adjusts input voltage and output current, achieves charging and discharging balance of the switched capacitor, and reduces alternating current output direct current components. A unipolar modulation strategy is adopted, and inversion midpoint output voltage is three-level and can be output in a reactive power mode. The inverter has the unique advantages of high efficiency, high reliability, low / no leakage current, reactive power output and the like, and can be widely applied to various one-way and two-way direct-current and alternating-current power converters.

Description

technical field [0001] The invention relates to the field of photovoltaic technology, in particular to a photovoltaic inverter with low leakage current. Background technique [0002] Photovoltaic modules are generally grounded through an aluminum frame to improve safety, but in rainy or humid environments, the parasitic capacitance to ground will reach 50nF ~ 1uF / kWp. In the transformerless non-isolated photovoltaic power generation system, the inverter is connected to the photovoltaic module and the AC grid, and generates common-mode resonance to the ground parasitic capacitance, output filter and AC grid line impedance, and the voltage across the parasitic capacitance excites the resonant circuit to generate leakage current. The voltage across the parasitic capacitance comes from the dynamic change of the high-frequency voltage between the inverter AC output zero line or neutral line (N) and the negative pole of the photovoltaic module, and the amplitude is proportional to...

AI Technical Summary

Problems solved by technology

Its improved type (Common-Ground-Type Transformerless Inverters for Single-Phase Solar Photovoltaic Systems, IEEE Industrial Electronics 2018, Vol. 65, No. 3) uses sine wave positive half-cycle freewheeling for additional charging, resulting in excessive voltage changes across the switched capacitor. And there are practical problems such as charging and discharging imbalance

[0005] Metal Oxide Semiconductor Field Effect Transistor (MOSFET) switching speed is faster to further increase the switching frequency, but because of its poor body diode reverse recovery characteristics, there is a risk of bridge arm shoot-through and reduce the reliability of the inverter. Therefore, the above inverters Insulated gate bipolar transistors (IGBTs) must be used when the inverter is connected to the grid to generate reactive power.

High-efficiency topological structures such as H5, HERIC, Karschny, etc. are all patented in European and American countries, which has caused serious technical barriers to the promotion and application of new energy power generation in China

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