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High-frequency oscillation suppression method of flexible direct-current power transmission system

A power transmission system, flexible DC technology, applied in AC network circuits, reducing/preventing power oscillations, electrical components, etc., can solve problems such as unfavorable grid economy, increase power loss, affect control system performance, etc., to reduce high-frequency oscillations the effect of risk

Active Publication Date: 2021-07-23
ZHEJIANG UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In terms of hardware, a passive filtering device is added at the grid-connected point. This method increases the construction investment cost of the system and the power loss during normal operation, which is not conducive to improving the economy of the power grid; Additional damping control strategy, for example, during the commissioning of the South Channel of the Chongqing-Hubei Project, a 1.82kHz oscillation appeared on the Hubei side, and the oscillation disappeared after a first-order low-pass filter with a bandwidth of 400Hz was used in the voltage feedforward link. To a certain extent, the risk of high-frequency oscillation in the system is reduced, but the high-frequency oscillation of 695 Hz still occurs when the same solution is used on the Chongqing side
In general, most of the current additional control strategies cannot adapt to the changing working conditions of the system, and may affect the performance of the control system

Method used

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  • High-frequency oscillation suppression method of flexible direct-current power transmission system
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  • High-frequency oscillation suppression method of flexible direct-current power transmission system

Examples

Experimental program
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Effect test

Embodiment 1

[0055] This embodiment is described by taking the flexible direct current transmission system as an MMC-HVDC power transmission system as an example, and the converter described in this embodiment refers to a modular multilevel converter, that is, MMC.

[0056] figure 1 in, u s , i and i cir are the AC bus voltage, AC current and the circulating current of the MMC in the abc coordinate system sampled by one voltage sensor and two current sensors respectively, u dq i dq i cirdq are the AC voltage, AC current and the circulating current of the MMC in the dq coordinate system obtained through Park transformation, i dqref is the reference command value of active and reactive current, u cdq and i cirdq The bridge arm reference voltage of the MMC is obtained from the output of the inner loop fundamental frequency current controller and the circulating current suppression controller, u dc is the DC voltage. In this embodiment, a Smith estimator is added to the inner-loop fund...

Embodiment 2

[0062] This embodiment is described by taking the flexible direct current transmission system as an example of a VSC-HVDC power transmission system, and the converter described in this embodiment refers to a voltage source converter, that is, a VSC.

[0063] figure 1 in, u s , i and i cir are respectively the AC bus voltage, AC current and VSC circulating current in the abc coordinate system obtained by sampling with one voltage sensor and two current sensors, u dq i dq i cirdq are the AC voltage, AC current and the circulating current of VSC in the dq coordinate system obtained through Park transformation, i dqref is the reference command value of active and reactive current, u cdq and i cirdq The bridge arm reference voltage of VSC is obtained from the output of the inner-loop fundamental frequency current controller and the circulating current suppression controller respectively, u dc is the DC voltage. In this embodiment, a Smith estimator is added to the inner-loo...

Embodiment 3

[0070] This embodiment is described by taking the flexible direct current transmission system as an MMC-HVDC power transmission system as an example, and the converter described in this embodiment refers to a modular multilevel converter, that is, MMC.

[0071] figure 1 in, u s , i and i cirare the AC bus voltage, AC current and the circulating current of the MMC in the abc coordinate system sampled by one voltage sensor and two current sensors respectively, u dq i dq i cirdq are the AC voltage, AC current and the circulating current of the MMC in the dq coordinate system obtained through Park transformation, i dqref is the reference command value of active and reactive current, u cdq and i cirdq The bridge arm reference voltage of the MMC is obtained from the output of the inner loop fundamental frequency current controller and the circulating current suppression controller, u dc is the DC voltage. In this embodiment, a Smith estimator is added to the inner-loop funda...

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Abstract

The invention discloses a high-frequency oscillation suppression method for a flexible direct-current power transmission system. The method comprises the following steps: S11, sampling to obtain an alternating-current side current signal under a dq rotating coordinate system of a converter; S12, performing subtraction on the active and reactive current reference instruction values and an alternating current side current signal under the dq rotating coordinate system of the converter to obtain a current modulation signal, and obtaining a voltage modulation signal uc (s) of the current period through a PI controller; S13, sampling to obtain an alternating current side voltage signal us of the converter in the dq rotating coordinate system, and performing addition and subtraction operation on us and uc (s) to obtain a comprehensive internal potential modulation signal E (s) of the period; S14, using a Smith predictor to take uc (s) and a compensated comprehensive internal potential modulation signal E (s) ', acquiring an estimated voltage modulation signal us' through additive operation, and processing the us' through the Smith predictor to obtain a voltage increment signal delta u (s); and S15, performing addition and subtraction operation on the delta u (s) and the E (s) to obtain a compensated comprehensive internal potential modulation signal E (s) ', and inputting the compensated comprehensive internal potential modulation signal E (s)' to a pulse modulator. According to the invention, high-frequency oscillation can be effectively suppressed.

Description

technical field [0001] The invention relates to the technical field of flexible direct current transmission, in particular to a high-frequency oscillation suppression method for a flexible direct current transmission system. Background technique [0002] Flexible DC transmission system has broad application prospects in the occasions of renewable energy grid connection, asynchronous AC system interconnection, passive network power supply, and power supply and distribution of large urban load centers. It is one of the important directions for the development of modern power systems. Currently, there are two mainstream flexible direct current transmission systems: two-level and three-level VSC-HVDC (full name is high-voltage direct current based on voltage source converter) and MMC-HVDC (full name is high-voltage direct current based on modular multilevel converter). DC). The stability characteristics of the grid have undergone profound changes, and high-frequency oscillation...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/24
CPCH02J3/241
Inventor 胡鹏飞刘思奇梁一桥江道灼
Owner ZHEJIANG UNIV
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