Gird-connected current low-frequency harmonic suppression method of cascaded H-bridge medium-voltage converter

Abstract

The invention provides a grid-connected current low-frequency harmonic suppression method of a cascaded H-bridge medium-voltage converter. The method is applied to a grid-connected converter. The grid-connected converter comprises a plurality of three-phase voltage source-type pulse width modulation (PWM) sub-converters. The method comprises the step of introducing a second-order frequency conversion trapper into a voltage ring control loop of the three-phase voltage source-type PWM sub-converters to suppress low-frequency harmonics introduced by voltage fluctuation of a DC bus. The influence of the voltage fluctuation of the DC bus of a power module on the grid-connected current is prevented by changing the voltage ring control loop on the condition that a cascaded H-bridge medium-voltage converter system topological structure is not changed, and the quality of the grid-connected current is improved.

Description

technical field [0001] The invention relates to the technical field of converter control, in particular to a method for suppressing low-frequency harmonics of grid-connected current of cascaded H-bridge medium-voltage converters. Background technique [0002] The cascaded H-bridge converter has been popularized and applied in the field of medium voltage variable frequency drive due to its modular design and the characteristics of large-scale production. The grid side of the traditional cascaded H-bridge converter adopts the diode uncontrolled rectification method, and the energy can only flow in one direction, which limits its application range. In order to realize the four-quadrant operation of the converter, the diodes in the converter topology are replaced by insulated gate bipolar transistors (Insulated Gate Bipolar Transistor, IGBT) to form a cascaded H Bridge converter, also known as energy-fed cascaded H-bridge converter, such as figure 1 shown. [0003] Each phase...

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Problems solved by technology

The first solution is to reduce the bus voltage fluctuation amplitude and suppress its influence by increasing the DC bus capacitance, but this method will lead to a decrease in system dynamic performance and an increase in system cost and volume

The second solution is to use an active filter method, and connect a high-voltage capacitor in parallel with a Buck / Boost circuit next to the supporting capacitor to form a double frequency path. This solution increases the system switching device to increase the loss and increase the system hardware cost.

The third solution is to adjust the parameters of the grid-side control proportional-integral (PI) regulator or add a low-pass filter in the feedback link of the grid-side control system, so that the bandwidth of the grid-side converter control system is lower than the fluctuating voltage frequency. When the fluctuating voltage frequency is low, the bandwidth of the control system needs to be lower, which will lead to a decrease in the dynamic performance of the system

The fourth option is to add a notch filter to the control system, but this fixed-parameter notch filter can only filter out fluctuations of a certain fixed frequency, which is not suitable for medium-voltage converters with fluctuating frequency changes

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