Control system for reducing voltage unbalancedness of direct current bus series capacitor of energy storage system bidirectional converter

Abstract

The invention relates to a control system for reducing the voltage unbalancedness of a direct current bus series capacitor of an energy storage system bidirectional converter. By aiming at the problem that the voltage unbalancedness of the direct current bus series capacitor can be possibly generated after the energy storage system bidirectional converter operates for a long time, voltage balance compensation control strategies are adopted for guaranteeing the long-period, safe and stable operation of the energy storage system bidirectional converter. Through the adoption of the method, the voltage unbalancedness of the series capacitor can be effectively reduced, the free maintenance of the converter is enhanced, the uninterrupted operation capability of the converter is improved, and obvious economic benefits are realized.

Description

technical field [0001] The invention belongs to the technical field of energy storage systems, in particular to the technical field of bidirectional converter control of energy storage systems. Background technique [0002] At present, electrolytic capacitors are widely used in the DC bus of bidirectional converters in energy storage systems. The electrolytic capacitor used in the mainstream two-level bidirectional converter of the energy storage system generally has a withstand voltage rating of 450V, while the output voltage of the three-phase full-bridge uncontrolled rectification of the 380V AC grid is at least 540V, so the DC bus of the bidirectional converter Generally, two sets of electrolytic capacitors are connected in series, and the voltage balance of the series connected electrolytic capacitors is maintained through a certain high-precision, high-resistance grading resistor. [0003] However, in the long-term operation of the bidirectional converter, due to the ...

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Problems solved by technology

[0003] However, in the long-term operation of the bidirectional converter, due to the difference in the capacity of the electrolytic capacitors and the influence of the equivalent series resistance inside the electrolytic capacitors, the voltage imbalance between the two series of electrolytic capacitors will inevitably occur only through the parallel connection of voltage equalizing resistors. Further aggravate the attenuation of the capacity of the two sets of electrolytic capacitors in series, reduce the service life of the electrolytic capacitors, and cause the output harmonics of the bidirectional converter to increase, the voltage and current control performance to decline, and even reduce the service life of the bidirectional converter

Traditional bidirectional converters for energy storage systems, such as image 3 As shown, including the DC bus voltage control module, three-phase AC current control module, and PWM inverter module, it can only realize the control of the grid-connected three-phase current amplitude and phase

And only connect voltage equalizing resistors in parallel at both ends of the series capacitors, there is no effective control on the balance of the voltage of the series capacitors, the capacitor voltage balance effect is not good, and the life of the series capacitors will be reduced when the converter runs for a long time

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