Einzeltreffer — DigiBib

Provided is a control method for a parallel MMC unit of a LCC-MMC hybrid cascade converter station. The control strategy includes: 1) numbering all MMC units connected in parallel in a MMC valve manifold; (2) for a MMC unit using a constant direct-current voltage control manner, calculating a direct-current instruction value of the MMC unit according to a direct-current measurement value; (3) for a MMC unit using a constant active power control manner, calculating an active power instruction value of the MMC unit according to the rated capacity of the MMC unit and a direct-current instruction value of a system rectifier station; (4) for the MMC unit using the constant direct-current voltage control manner, correcting a direct-current voltage instruction value of the MMC unit by using the direct-current instruction value and the direct-current measurement value, and controlling the MMC unit according to the corrected direct-current voltage instruction value.

Titel:	CONTROL METHOD FOR A PARALLEL MMC UNIT OF A LCC-MMC HYBRID CASCADE CONVERTER STATION
Link:	View record in USPTO Patent Applications (Volltext)
Veröffentlichung:	2021
Medientyp:	Patent
Sonstiges:	Nachgewiesen in: USPTO Patent Applications Sprachen: English Document Number: 20210143754 Publication Date: May 13, 2021 Appl. No: 17/061343 Application Filed: October 01, 2020 Claim: 1. A control method for a parallel Modular Multilevel Converter (MMC) unit of a Line Commutated Converter (LCC)-MMC hybrid cascade converter station, comprising following steps: (1) numbering all MMC units connected in parallel in a MMC valve manifold of a converter station according to a control manner and a rated capacity of each MMC unit of the MMC units; (2) for a MMC unit using a constant direct-current voltage control manner, calculating a direct-current instruction value of the MMC unit according to a direct-current measurement value; (3) for a MMC unit using a constant active power control manner, calculating an active power instruction value of the MMC unit according to the rated capacity of the MMC unit and a direct-current instruction value of a system rectifier station; (4) for the MMC unit using the constant direct-current voltage control manner, correcting a direct-current voltage instruction value of the MMC unit by using the direct-current instruction value and the direct-current measurement value, and further controlling the MMC unit according to the corrected direct-current voltage instruction value; and (5) for the MMC unit using the constant active power control manner, controlling the MMC unit according to the active power instruction value. Claim: 2. The control method of claim 1, wherein a specific implementation process of the step (1) is as follows: firstly, dividing all MMC units in the MMC valve manifold into two types, that is, MMC units controlled in the constant direct-current voltage control manner and counted to be N1, and MMC units controlled in the constant active power control manner and counted to be N2; and numbering the MMC units controlled in the constant direct-current voltage control manner from 1 to N1 according to an order of rated capacities from small to large, and numbering the MMC units controlled by the constant active power from N1+1 to N1+N2 according to an order of rated capacities from small to large. Claim: 3. The control method of claim 1, wherein in the step (2), the direct-current instruction value of the MMC unit is calculated by using a following formula: [mathematical expression included] wherein idcref_k is a direct-current instruction value of a k-th MMC unit in the MMC valve manifold, Sk is a rated capacity of the k-th MMC unit, Si is a rated capacity of an i-th MMC unit, idci and idcba_i are a direct-current measured value and a direct-current reference value of the i-th MMC unit respectively, idcba_k is a direct-current reference value of the k-th MMC unit, i and k are natural numbers, 1≤i≤N1, 1≤k≤N1, and N1 is a number of MMC units controlled in the constant direct-current voltage control manner in the MMC valve manifold. Claim: 4. The control method of claim 1, wherein in the step (3), the active power instruction value of the MMC unit is calculated by using a following formula; [mathematical expression included] wherein Pref_r is an active power instruction value of an r-th MMC unit in the MMC valve manifold, iba_rec and iref_rec are a direct-current instruction value and a direct-current reference value of a rectifier station respectively, Sr is a rated capacity of the r-th MMC unit, Sj is a rated capacity of a j-th MMC unit, idcba_r is a direct-current reference value of the r-th MMC unit, N1 is a number of MMC units controlled in the constant direct-current voltage control manner in the MMC valve manifold, N2 is a number of MMC units controlled in the constant active power control manner in the MMC manifold, r and j are natural numbers, 1≤j≤N1+N2, and N1+1≤r≤N1+N2. Claim: 5. The control method of claim 1, wherein a specific implementation process of the step (4) is as follows: firstly, subtracting a direct-current instruction value idcref_k from a direct-current measurement value idck of a k-th MMC unit to obtain a corresponding current error value; then, introducing the current error value into a proportional control stage and an amplitude limiting stage in turn to obtain a direct-current voltage correct value of the k-th MMC unit; and finally, adding the direct-current voltage correct value to an original direct-current voltage instruction value of the k-th MMC unit to obtain a corrected direct-current voltage instruction value, and controlling the k-th MMC unit in the constant direct-current voltage control manner according to the corrected direct-current voltage instruction value, wherein 1≤k≤N1, and N1 is a number of MMC units controlled in the constant direct-current voltage control manner in the MMC valve manifold. Claim: 6. The control method of claim 5, wherein a proportional coefficient of the proportional control stage is set to 0.1, and a maximum output limit value and a minimum output limit value of the amplitude limiting stage are set to 0.1 p.u. and −0.1 p.u. respectively. Claim: 7. The control method of claim 1, wherein for the LCC-MMC hybrid cascade converter station, the control strategy is capable of implementing a function of simultaneously controlling a direct-current voltage by a plurality of MMC units, and playing a certain guiding role in the design of future engineering. Claim: 8. The control method of claim 1, wherein according to the control strategy, active power of a MMC unit for controlling active power is calculated, and a direct-current voltage instruction value correction stage is added in a constant direct-current voltage MMC unit, a direct-current is reasonably distributed in the MMC units connected in parallel. Current International Class: 02; 02; 02; 02

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CONTROL METHOD FOR A PARALLEL MMC UNIT OF A LCC-MMC HYBRID CASCADE CONVERTER STATION