Inter-phase voltage-sharing control method for DC bus of cascaded star-connected static synchronous compensator (STATCOM)

Abstract

The invention discloses an inter-phase voltage-sharing control method for a DC bus of a cascaded star-connected static synchronous compensator (STATCOM). The voltage-sharing control method comprises the following steps of regulating a d-axis component of a modulation wave output from a current ring according to the deviation between DC voltages of a phase A and a phase B and a reference value; converting dq-abc conversion on the modulation, wherein a negative-sequence component is overlaid with the modulation wave, so that the output of the STATCOM generates the negative-sequence voltage. The negative-sequence voltage is used for generating a negative-sequence current, the negative-sequence voltage, the negative-sequence current, positive-sequence current and positive-sequence voltage are separately used for changing allocation of three-phase power flow, and the balance among three phase DC voltages is achieved. In the voltage-sharing method proposed by the invention, a mode of overlaying the negative-sequence modulation wave is simple and is easy to implement, the stability of the current ring is not affected, meanwhile, the introduced modulation wave zero-sequence component is also removed, over-modulation caused by the zero-sequence component is avoided, and the reliability of STATCOM running is improved.

Description

technical field [0001] The invention belongs to the field of reactive power compensation for power grids, and in particular relates to a control method for phase-to-phase voltage equalization of cascaded star-connected STATCOM direct current busbars. Background technique [0002] With the continuous development of the national economy, industrial and agricultural production and life have higher and higher requirements for the quality and reliability of electric energy. Various impulsive reactive loads in the power system (such as asynchronous motors, electric arc furnaces, rolling mills, etc.) will cause grid voltage fluctuations, flicker and power factor reduction. In order to improve voltage quality, reactive power compensation technology is widely used. Static synchronous compensator (STATCOM), as a new generation of reactive power compensation device, has attracted more and more attention due to its advantages of fast adjustment speed, small size and low cost. [0003] ...

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Problems solved by technology

Betz, R.E. etc. in "SymmetryCompensationusingaH-BridgeMultilevelSTATCOMwithZeroSequenceInjection."IndustryApplicationsConference, 2006.41stIASAnualMeeting.ConferenceRecordofthe2006IEEEIEEE, 2006: 1724-1731."In "SymmetryCompensationusingaH-BridgeMultilevelSTATCOMwithZeroSequenceInjection."IndustryApplicationsConference, 2006.41stIASAnualMeeting.ConferenceRecordofthe2006IEEEIEEE, 2006: 1724-1731. , when the three-phase loss difference is relatively large or the grid voltage imbalance is large, the DC voltage needs a wide margin to prevent over-modulation

Ji Zhendong et al. put forward a proposal in "Zero-sequence and negative-sequence voltage injection DC-side voltage balance control of cascaded grid-connected inverters [J]. Chinese Journal of Electrical Engineering, 2013, 21 (21): 9-17." A method based on negative-sequence voltage injection, which involves inverse trigonometric function calculations, complex calculations, and requires an additional voltage detection device to detect the STATCOM output voltage

Lee, Chia-tse et al. proposed a method based on negative-sequence current injection in "AveragePowerBalancingControlofaSTATCOMBasedontheCascadedH-BridgePWMConvenerWithStarConfiguration." This method involves inverse matrix calculations in the process of obtaining a given negative-sequence current, which consumes a lot of resources for the controller

People such as Han, Chong propose the voltage equalization method of independent fine-tuning three-phase d-axis modulation wave in AGeneralizedControlStrategyofPer-PhaseDCVoltageBalancingforCascadedMultilevelConverter-basedSTATCOM."PowerElectronicsSpecialistsConference, 2007.PESC2007.IEEEIEEE, 2007: 1746-1752. There is a coupling relationship between them, which reduces the steady-state performance of the current loop

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