Method for evaluating degree of parallel SVG (H-bridge cascade) higher harmonic circulating current

Abstract

The invention provides a method for evaluating the degree of parallel SVG (H-bridge cascade) higher harmonic circulating current, belongs to the technical field of power quality analysis and control, and aims to provide a circulating current access and static equivalent model according to the harmonic circulating current problem generated after parallel connection of SVG with a cascade H-bridge cascade structure and provide a method for evaluating the degree of parallel SVG (H-bridge cascade) higher harmonic circulating current based on indirect detection technology. The method comprises the following steps: constructing a model; analyzing the circulating current rate of two 2-cascade parallel SVG; simplifying calculation; calculating an actual circulating current rate equation; fitting each set of correction factor discrete values by utilizing a least square method in frequency bands; further pushing out a circulating current general formula; and calculating the criterion condition of the actual circulating current degree. The method can be used for indirectly and quantitatively analyzing the parallel SVG circulating current phenomenon by a simple linear mode, thereby laying a technical foundation for future detection analysis and inhibition work of higher harmonic circulating current among SVG.

Description

technical field [0001] The invention belongs to the technical field of power quality analysis and control. Background technique [0002] The cascaded H-bridge static var generator (static var generator, SVG) has many advantages such as fast adjustment speed, good dynamic performance, strong overload capacity, small size, and easy expansion. The capacity to compensate reactive power when power fluctuates has also been widely used. However, studies have shown that parallel SVGs have the following problems in actual engineering: because the triangular carrier phases are not exactly the same, the delay time of the switch is different, and the parameters of the inverter are different, etc., eventually leading to such as figure 1 The switches 11 and 12 are in the same phase, and the switches at the same position of the same valve group are not turned on and off at the same time, so the phases of the trigger pulses of the converters will not be exactly the same, which will cause a...

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Problems solved by technology

However, studies have shown that parallel SVGs have the following problems in actual engineering: because the triangular carrier phases are not exactly the same, the delay time of the switch is different, and the parameters of the inverter are different, etc., eventually leading to such as figure 1 The switches 11 and 12 are in the same phase, and the switches at the same position of the same valve group are not turned on and off at the same time, so the phases of the trigger pulses of the converters will not be exactly the same, which will cause a deviation in the phase of the SPWM wave output by the parallel SVGs, and generate high voltage between parallel SVGs. frequency potential

And because the transformer has an obvious suppression effect on high-order harmonics, the high-order harmonic currents generated will flow between the parallel SVGs, resulting in a large number of high-order harmonic circulation phenomena

[0003] This will not only cause overheating of the converter unit module, affect the effect of reactive power compensation, and increase the instability of the system, but also cause overshooting of the control system when it is more serious, and cause one-way charging or discharging between the DC capacitors of the SVG valve groups. Eventually the circuit breaker tripped due to a DC voltage imbalance

This kind of harmonic circulation is random and the frequency is changeable, so it makes it difficult to implement direct detection and quantitative analysis on site. It is difficult to eliminate and suppress these high-order harmonic circulation at the existing technical level

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