A control method for a DC microgrid bidirectional ac/dc converter parallel system

Abstract

The invention discloses a bidirectional AC / DC converter parallel system control method for a DC microgrid, and the method comprises the steps: secondary ripple inhibition, low-voltage deviation current-sharing control and voltage and current double-closed-loop control. Through the introduction of a second-order band-stop filter, the method achieves the effective filtering of the secondary ripple components in the current and voltage of the DC grid, and prevents the feedback introduced to a control loop from causing the grid-connected current distortion. The mean current of a DC line is fed back as a global variable in the low-voltage deviation current-sharing control, and an integration link is introduced, thereby achieving the precise distribution of power of each converter without the impact from the line parameters. The deviation of a DC bus voltage is reduced through the introduction of the mean output voltage PI (Proportional-Integral) control. A voltage outer loop in the voltage and current double-closed-loop control employs PI control, thereby guaranteeing the no-static-error tracking of a DC voltage. A current inner loop employs quasi-proportional resonant control, thereby achieving the better tracking control of a fundamental wave sine current.

Description

technical field [0001] The invention belongs to the field of DC micro-grid DC busbar voltage control, and relates to a control method for a parallel system of bidirectional AC / DC converters in a DC micro-grid. Background technique [0002] The promotion of distributed energy generation and the increasing proportion of DC loads in terminal power consumption have promoted the rapid development of DC microgrids. The bidirectional AC-DC grid-connected converter is the grid-connected interface unit of the DC microgrid, which plays a key role in controlling the energy flow of the DC bus and the large grid, maintaining the stability of the DC bus voltage and improving the operating efficiency of the system. The parallel structure of multiple bidirectional AC-DC grid-connected converters in the DC microgrid system can improve system redundancy, reliability and scalability. However, due to differences in line resistance, converter closed-loop parameters, and sensor errors, the outpu...

AI Technical Summary

Problems solved by technology

However, due to differences in line resistance, converter closed-loop parameters, and sensor errors, the output current of each converter is uneven, and in severe cases, the power flow direction of each converter will be inconsistent, resulting in the capacity of multiple converters not being fully utilized and reducing system operating efficiency. , and even endanger the safety of the device

[0003] The power sharing of multiple converters connected in parallel in a DC microgrid often adopts the conventional droop control technology, but there is a contradiction between the power sharing accuracy of the multi-converters and the DC bus voltage adjustment rate in the conventional droop control, and the power sharing accuracy of the converters It is difficult to achieve better results at the same time as the adjustment rate of the DC bus voltage

Adaptive droop control technology can also be used for power sharing, and an index for evaluating current sharing and output power loss is introduced. The optimal droop coefficient can be calculated in real time through this index, and a better current sharing effect can be obtained, but this The method requires high real-time processing performance of the processor

At present, there is still a control method that uses split positive and negative voltage regulators to ensure that the power flow direction of each converter is consistent, but this method easily leads to long-term full-load operation of the converter with a small DC bus voltage sampling coefficient, which affects the operating life of the entire parallel system.

[0004] In addition, the bidirectional AC / DC grid-connected converters in the low-voltage DC microgrid mostly use a single-phase full-bridge circuit topology, which will cause secondary ripples in the voltage in the DC microgrid and the DC line current

The secondary ripple is easily introduced into the control loop through feedback, resulting in severe distortion of the grid-connected current

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