A Circulating Current Suppression Method Applied to Flexible DC Transmission System
A technology of circulating current suppression and power transmission system, applied in the direction of DC network circuit devices, electrical components, circuit devices, etc., can solve the problems of complex methods and difficult adjustment of controller parameters, and achieve the effect of reducing losses
Inactive Publication Date: 2015-08-05
STATE GRID CORP OF CHINA +2
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[0004] In the process of analyzing the operation mechanism of the flexible direct current transmission system, many researchers pointed out the mechanism of circulation generation and the method of elimination. In the patent "a three-phase modular multilevel circulator circulation suppression method" By performing dq transformation on the double frequency circulating current and giving an additional set value through decoupling control, the suppression of the double frequency current is realized. However, this method is only applicable to steady-state conditions; Tang Guangfu et al. Valve current control method of modular multi-level circulator" controls the low-frequency oscillation and double frequency components separately, but this method is complicated and the controller parameters are not easy to adjust
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[0018] The present invention will be described in further detail below in conjunction with the accompanying drawings.
[0019] The flexible DC transmission system consists of three-phase six bridge arms, and each bridge arm is composed of coupled or uncoupled inductors and several identical sub-modules SM cascaded. Each sub-module consists of two IGBTs, two reverse diodes and a DC capacitor, the structure is as follows figure 1 As shown, DC current and upper and lower bridge arm current (Ipa, Ipb, Ipc, Ina, Inc, Inc), voltage (Upa, Upb, Upc, Una, Unc, Unc) as figure 1 shown. Among them, j=a, b, c represent abc three phases respectively, p represents the upper bridge arm, n represents the lower bridge arm, Id and Vd are the DC bus current and voltage.
[0020] The circulation suppression method is as follows:
[0021] Measure the current of each bridge arm and calculate the internal circulating current Idiffj of each phase: the internal circulating current of each phase is o...
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The invention relates to a circulation inhibition method applied to a flexible direct current power transmission system. A detected bridge arm current signal is used for passing through a PI controller and then undergoing per-unit process so as to obtain an additional control signal used for inhibiting circulation. The additional control signal is superimposed on an existing voltage reference signal and undergoes pulse width modulation so as to obtain trigger control signals of all bridge arms of a circulator, and therefore bridge arm voltage is close to a bridge arm voltage reference value. With the circulation inhibition method, circulation can be inhabited at a much low level under the condition that bridge arm inductance is not increased, in addition, calculation is simple with the method, and engineering realization is easy.
Description
technical field [0001] The invention relates to the field of power electronics and user electric power, in particular to a novel circulating current suppression method applied to a flexible direct current transmission system. Background technique [0002] Compared with the traditional flexible DC transmission system (based on IGBT series technology), the flexible DC transmission system based on modular multilevel circulator (MMC) has attracted much attention in recent years because of its simple structure and easy engineering implementation. Wide attention of experts and scholars at home and abroad. [0003] An important feature of the MMC topology is that the energy storage capacitors are placed in series sub-modules. This brings a series of problems. For example, due to the existence of the bridge arm current, the capacitor voltage of each sub-module changes all the time. How to keep the capacitor voltage of each sub-module stable becomes a technical difficulty. In additi...
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IPC IPC(8): H02J1/00
Inventor 张群王柏恒马仪成陈朋赵倩
Owner STATE GRID CORP OF CHINA