COORDINATED CONTROL METHOD AND DEVICE FOR SERIES VOLTAGE SOURCE CONVERTER VALVE GROUP

Abstract

A coordinated control method for series voltage source converter valve groups comprises: allocating a total direct-current voltage reference value or a total active power reference value at the end where a direct-current electrode series voltage source converter valve group is located according to the total number of voltage source converter valve groups in series; for a direct-current voltage control end, controlling the direct-current voltage of each valve group according to the assigned direct-current voltage reference value for each valve group; for an active power control end, controlling the active power of each valve group according to the assigned active power reference value for each valve group and based on adding the active power compensation amount of the valve group which has voltage equalization effects on the valve group. Correspondingly, also providing a coordinated control device for series voltage source converter valve groups. The direct-current voltage equalization of each valve group in operation of the direct-current voltage control end or the active power control end of the series voltage source converter valve group is achieved.

Claims

1. A coordinated control method for series voltage source converter valve groups, the series voltage source converter valve group formed by connecting two or more voltage source converter valve groups in series, the series voltage source converter valve group is able to be configured at a DC voltage control end or an active power control end of any DC electrode in a DC transmission system, characterized in that, the control method including following steps for the series voltage source converter valve groups configured at the DC voltage control end of the DC electrode: Step a1, obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located according to a DC voltage control target of the DC electrode, allocating the total DC voltage reference value U.sub.dcref according to a total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value, where $U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$  i∈(1, . . . , N), N is a positive integer; Step a2, obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups; Step a3, using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group; Step a4: for each operating valve group of the series voltage source converter valve groups, calculating a difference between the DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group, and then inputting the difference into a DC voltage control outer loop of this valve group, so as to perform closed-loop control of the DC voltage of this valve group, the control method including following steps for the series voltage source converter valve groups configured at the active power control end of the DC electrode: Step b1, obtaining a total active power reference value P.sub.ref at the end where the series voltage source converter valve group is located according to an active power control target of the DC electrode, allocating the total active power reference value P.sub.ref according to the total number N of voltage source converter valve groups in series, and then obtaining an active power reference value P.sub.Vref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total active power reference value, where the $P_{\mathrm{Vref}-i}=\frac{P_{\mathrm{ref}}}{N},$  i∈(1, . . . , N), N is a positive integer; Step b2, obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located, allocating the total DC voltage reference value U.sub.dcref according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value U.sub.dcref, where $U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$  i∈(1, . . . , N), N is a positive integer; step b3, obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups; step b4, using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group; step b5, for each operating valve group of the series voltage source converter valve groups, obtaining an active power compensation amount ΔP.sub.V-i of the valve group which has voltage-equalization effect for the valve group, and adding the active power compensation amount ΔP.sub.V-i of the valve group and the active power reference value P.sub.Vref-i of the valve group to obtain a value, and then inputting the value into the active power control outer loop of the valve group so as to control the active power of this valve group.

2. The coordinated control method for series voltage source converter valve groups according to claim 1, characterized in that: for the series voltage source converter valve group configured at the active power control end of DC electrode, in the step b5, specific steps of obtaining an active power compensation amount ΔP.sub.V-i of the valve group for each operating valve group, which has voltage-equalization effect for the valve group, including: Step c1, calculating a difference between DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group to obtain a DC voltage deviation ΔU.sub.dV-i of this valve group; Step c2, inputting the DC voltage deviation ΔU.sub.dV-i of this valve group into a valve group voltage-equalizing compensator of this valve group, and calculating the DC voltage deviation ΔU.sub.dV-i of this valve group in the valve group voltage-equalizing compensator of this valve group by using proportional or integral or proportional plus integral method to obtain the active power compensation amount ΔP.sub.V-i of the valve group.

3. The coordinated control method for series voltage source converter valve groups according to claim 1, characterized in that, for the series voltage source converter valve group configured at the DC voltage control end of DC electrode, simultaneously applying the current inner loop limit of one operating valve group to other operating valve groups to maintain the DC voltage balance between each operating valve group if the output of the DC voltage control outer loop of this operating valve group is limited by a current inner loop limit.

4. The coordinated control method for series voltage source converter valve groups according to claim 1, characterized in that, for the series voltage source converter valve group configured at the active power control end of DC electrode, simultaneously applying the current inner loop limit of one operating valve group to other operating valve groups to maintain the DC voltage balance between each operating valve group if the output of the active power control outer loop of this operating valve group is limited by a current inner loop limit.

5. A coordinated control device for series voltage source converter valve groups, the series voltage source converter valve group formed by connecting two or more voltage source converter valve groups in series, the series voltage source converter valve group are able to be configured at a DC voltage control end or active power control end of any DC electrode of a DC power transmission system, characterized in that the device comprising: a discrimination unit, an acquisition and distribution unit, a DC voltage control unit and an active power control unit, wherein: the discrimination unit configured for determining whether the end where the series voltage source converter valve group is located is a DC voltage control end based on the operating status of the DC electrode; the acquisition and distribution unit configured for obtaining a total DC voltage reference value U.sub.dcref, a total active power reference value P.sub.ref, a DC voltage measured value U.sub.dV-i of each valve group among operating valve groups etc. based on the operating status of the DC electrode, and allocating the total DC voltage reference value U.sub.dcref and the total active power reference value P.sub.ref according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group and the active power reference value P.sub.Vref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value; the DC voltage control unit configured for controlling the DC voltage of the valve group based on the DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups at the DC voltage control end of DC electrode, and realizing the control for the DC voltage of the DC electrode and the DC voltage balance for each operating valve group; the active power control unit configured for controlling the active power of the valve group based on an active power reference value P.sub.Vref-i of the valve group and an active power compensation amount ΔP.sub.V-i of the valve group for each operating valve group in the series voltage source converter valve groups at the active power control end of DC electrode, and realizing the control for the active power of the DC electrode and the DC voltage balance for each operating valve group; the DC voltage control unit comprising the following subunits: a calculation subunit of DC voltage reference value of the valve group for DC voltage control, configured for obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located according to a DC voltage control target of the DC electrode, allocating the total DC voltage reference value according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value, where $U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$ i∈(1, . . . , N), N is a positive integer; a receiving subunit of DC voltage measured value of the valve group for DC voltage control, configured for obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups; a calculation subunit of DC bias of the valve group for DC voltage control, configured for using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group; a control subunit of the valve group for DC voltage control, configured for calculating a difference between the DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups, and inputting the difference into a DC voltage control outer loop of this valve group, so as to perform closed-loop control of the DC voltage of this valve group, the active power control unit including the following subunits: a calculation subunit of active power reference value of the valve group for active power control, configured for obtaining a total active power reference value P.sub.ref at the end where the series voltage source converter valve group is located according to an active power control target of the DC electrode, allocating the total active power reference value according to the total number N of voltage source converter valve groups in series, and obtaining an active power reference value P.sub.Vref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total active power reference value, where $P_{\mathrm{Vref}-i}=\frac{P_{\mathrm{ref}}}{N},$ i∈(1, . . . , N), N is a positive integer; a calculation subunit of DC voltage reference value of the valve group for active power control, configured for obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located, allocating the total DC voltage reference value according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value, where $U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$ i∈(1, . . . , N), N is a positive integer; a receiving subunit of DC voltage measured value of the valve group for active power control, configured for obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups; a calculation subunit of DC bias of the valve group for active power control, configured for using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group; a control subunit of valve group for active power control, configured for obtaining an active power compensation amount ΔP.sub.V-i of the valve group which has voltage-equalization effect for the valve group for each operating valve group of the series voltage source converter valve groups, and adding the active power compensation amount ΔP.sub.V-i of the valve group and the active power reference value P.sub.Vref-i of the valve group to obtain a value, and inputting the value into active power control outer loop of the valve group so as to control the active power of this valve group.

6. The coordinated control device for series voltage source converter valve groups according to claim 5, characterized in that, in the control subunit of valve group for active power control, specific steps of obtaining an active power compensation amount ΔP.sub.V-i of the valve group for each operating valve group, which has voltage-equalization effect for the valve group, including: Step c1, calculating a difference between DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group to obtain a DC voltage deviation ΔU.sub.dV-i of this valve group; Step c2, inputting the DC voltage deviation ΔU.sub.dV-i of this valve group into a valve group voltage-equalizing compensator of this valve group, and calculating the DC voltage deviation ΔU.sub.dV-i of this valve group in the valve group voltage-equalizing compensator of this valve group by using proportional or integral or proportional plus integral method to obtain the active power compensation amount ΔP.sub.V-i of the valve group.

7. The coordinated control device for series voltage source converter valve groups according to claim 5, characterized in that: in the DC voltage control unit, simultaneously applying the current inner loop limit of one operating valve group to other operating valve groups to maintain the DC voltage balance between each operating valve group if the output of the DC voltage control outer loop of this operating valve group is limited by a current inner loop limit.

8. The coordinated control device for series voltage source converter valve groups according to claim 5, characterized in that: in the active power control unit, simultaneously applying the current inner loop limit of one operating valve group to other operating valve groups to maintain the DC voltage balance between each operating valve group if the output of the active power control outer loop of this operating valve group is limited by a current inner loop limit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a schematic diagram of a topology of series voltage source converter valve groups according to the present invention;

[0047] FIG. 2 is a flowchart of a coordinated control method for series voltage source converter valve groups provided by the present invention,

[0048] FIG. 3 is a schematic diagram of a coordinated control strategy of series voltage source converter valve groups configured at DC voltage control end of DC electrode provided by the present invention;

[0049] FIG. 4 is a schematic diagram of a coordinated control strategy of series voltage source converter valve groups configured at active power control end of DC electrode provided by the present invention;

[0050] FIG. 5 is a structural block diagram of a coordination control device of series voltage source converter valve groups provided by the present invention.

DESCRIPTION OF EMBODIMENTS

[0051] The technical solutions of the present invention will be described in detail below with reference to the drawings and specific embodiments.

[0052] The present invention provides a coordinated control method for series voltage source converter valve groups, and a coordinated control device for series voltage source converter valve groups, which are used to achieve the DC voltage balance of each voltage source converter valve group when two or more voltage source converter valve groups operating in series are used in DC electrode of the DC power transmission system, so as to meet the operation requirements of a series hybrid DC power transmission system or a series flexible DC power transmission system. The topological schematic diagram of the series voltage source converter valve groups is shown in FIG. 1. The series voltage source converter valve groups can be configured at either the DC voltage control end or the active power control end of any DC electrode of a DC transmission system.

[0053] In order to achieve the above objective, the technical solution of the present invention is to provide a coordinated control method of series voltage source converter valve groups, as shown in FIG. 2:

[0054] As for the series voltage source converter valve groups configured at the DC voltage control end of DC electrode, the method includes the following implementation steps:

[0055] Step a1, obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located according to a DC voltage control target of the DC electrode, allocating the total DC voltage reference value according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value, where

[00007]$U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$

i∈(1, . . . , N), N is a positive integer;

[0056] The DC voltage control target of the DC electrode is generally the DC voltage reference value of the rectifier station set by the operator. When the end w here the series voltage source converter valve group is located is a rectifier station, the total DC voltage reference value U.sub.dcref is equal to the DC voltage reference value of the rectifier station set by the operator; when the end where the series voltage source converter valve group is located is an inverter station, the total DC voltage reference value U.sub.dcref is equal to the DC voltage reference value of the rectifier station set by the operator minus the DC line voltage drop.

[0057] Step a2 obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source convener valve groups,

[0058] For a voltage source converter valve group, its operating characteristics are shown in equation (1):

[00008]$\begin{array}{cc}\{\begin{array}{c}{u}_{\mathrm{pj}}=\frac{1}{2}{U}_{\mathrm{dV}}-u_{\mathrm{vjref}}\\ u_{\mathrm{nj}}=\frac{1}{2}{U}_{\mathrm{dV}}-u_{\mathrm{vjref}}\end{array}& \left(1\right)\end{array}$

[0059] wherein, u.sub.pj and u.sub.nj are the upper bridge arm voltage and lower bridge arm voltage of the voltage source converter j (j=a, b, c) phase, ½U.sub.dV is the bridge arm voltage DC bias, u.sub.vjref is the AC voltage reference wave of j phase.

[0060] The control of the voltage source converter valve groups is realized by controlling the voltage of the upper and lower bridge arms of each phase. As can be seen from equation (1), the bridge arm voltage includes two parts: the DC bias and the AC voltage reference wave. Therefore, a control strategy shown in FIG. 3 can be used, including the following steps:

[0061] Step a3, using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group;

[0062] Step a4: for each operating valve group of the series voltage source converter valve groups, calculating a difference between the DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group and inputting the difference into a DC voltage control outer loop of this valve group, so as to perform closed-loop control of the DC voltage of this valve group.

[0063] The control of the DC voltage of the valve group can be achieved by using the bridge arm voltage DC bias of this valve group described in step a3 and the AC voltage reference wave of the valve group described in step a4 to control the bridge arm voltage of the upper and lower bridge arms of the phases of the valve group; by using the above control strategy, each operating valve group in the series voltage source converter valve groups can achieve balanced control of the DC voltage for each operating valve group at the DC voltage control end.

[0064] The control method includes the following steps for the series voltage source converter valve groups configured at the active power control end of the DC electrode.

[0065] Step b1, obtaining a total active power reference value P.sub.ref at the end where the series voltage source converter valve group is located according to an active power control target of the DC electrode, allocating the total active power reference value according to the total number N of voltage source converter valve groups in series, and obtaining an active power reference value P.sub.Vref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total active power reference value, where

[00009]$P_{\mathrm{Vref}-i}=\frac{P_{\mathrm{ref}}}{N},$

i∈(1, . . . , N), N is a positive integer;

[0066] Step b2, obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located, allocating the total DC voltage reference value according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter value group after evenly allocating the total DC voltage reference value, where

[00010]$U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$

i∈(1, . . . , N), N is a positive integer;

[0067] Step b3, obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups.

[0068] The coordinated control strategy shown in FIG. 4 is adopted, which specifically includes:

[0069] Step b4: using of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group;

[0070] Step b5: for each operating valve group of the series voltage source converter valve groups, obtaining an active power compensation amount ΔP.sub.V-i of the valve group which has voltage-equalization effect for the valve group, and adding the active power compensation amount ΔP.sub.V-i of the valve group and the active power reference value P.sub.Vref-i of the valve group to obtain a value, and inputting the value into active power control outer loop of the valve group so as to control the active power of this valve group;

[0071] The control of active power of this valve group can be achieved by using the DC bias of the bridge arm voltage of the valve group described in step b4 and the AC voltage reference wave of the valve group described in step b5 to control the bridge arm voltage of the upper and lower bridge arms of each phase of the valve group.

[0072] For the series voltage source converter valve group configured at the active power control end of the DC electrode, the steps of obtaining an active power compensation amount ΔP.sub.V-i of the valve group for each operating valve group, which has voltage-equalization effect for the valve group, including:

[0073] Step c1: calculating a difference between DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group to obtain a DC voltage deviation ΔU.sub.dV-i of this valve group;

[0074] Step c2, inputting the DC voltage deviation ΔU.sub.dV-i of this valve group into a valve group voltage-equalizing compensator of this valve group, and calculating the DC voltage deviation ΔU.sub.dV-i of this valve group in the valve group voltage-equalizing compensator of this valve group by using proportional or integral or proportional plus integral method to obtain the active power compensation amount ΔP.sub.V-i of the valve group.

[0075] By superimposing the active power compensation amount ΔP.sub.V-i of the valve group on the basis of the active power reference value P.sub.Vref-i of the valve group, the active power output of the valve group can be dynamically adjusted, which can indirectly achieve the control of the DC voltage of the valve group. The control strategy described above can realize the balanced control of the DC voltage for each operating valve group at the active power control end.

[0076] For series voltage source converter valve groups configured at the DC voltage control end of DC electrode, when the output of the DC voltage control outer loop of one operating valve group is limited by the inner loop current limit caused by the reduced inner loop current limit I.sub.dmax, the DC voltage of this valve group deviates from the reference value of the DC voltage of the valve group due to the limited power output. To this end, the current inner loop limit of the valve group will be simultaneously applied to other operating valve groups to maintain the DC voltage equalization.

[0077] For series voltage source converter valve groups configured at the active power control end of a DC electrode, when the output of the active power control outer loop of one operating valve group is limited by the inner loop current limit caused by the reduced inner loop current limit I.sub.dmax, the DC voltage of this valve group deviates from the reference value of the DC voltage of the valve group due to the limited power output. To this end, the current inner loop limit of the valve group will be simultaneously applied to other operating valve groups to maintain the DC voltage equalization.

[0078] The present invention also provides a coordinated control device for series voltage source converter valve groups, as shown in FIG. 5, which includes a discrimination unit, an acquisition and distribution unit, a DC voltage control unit and an active power control unit, wherein:

[0079] The discrimination unit is configured for determining whether the end where the series voltage source converter valve group is located is a DC voltage control end based on the operating status of the DC electrode;

[0080] The acquisition and distribution unit is configured for obtaining a total DC voltage reference value U.sub.dcref, a total active power reference value P.sub.ref, a DC voltage measured value U.sub.dV-i of each valve group among operating valve groups etc. based on the operating status of the DC electrode, and allocating the total DC voltage reference value U.sub.dcref and the total active power reference value P.sub.ref according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group and the active power reference value P.sub.Vref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value;

[0081] The DC voltage control unit is configured for controlling the DC voltage of the valve group based on the DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups at the DC voltage control end of DC electrode, and realizing the control for the DC voltage of the DC electrode and the DC voltage balance for each operating valve group.

[0082] The active power control unit is configured for controlling the active power of the valve group based on an active power reference value P.sub.Vref-i of the valve group and an active power compensation amount ΔP.sub.V-i of the valve group for each operating valve group in the series voltage source converter valve groups at the active power control end of DC electrode, and realizing the control for the active power of the DC electrode and the DC voltage balance for each operating valve group.

[0083] The DC voltage control unit includes the following subunits:

[0084] a calculation subunit of DC voltage reference value of the valve group for DC voltage control, configured for obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located according to a DC voltage control target of the DC electrode, allocating the total DC voltage reference value according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total DC voltage reference value, where

[00011]$U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$

i∈(1, . . . , N), N is a positive integer;

[0085] a receiving subunit of DC voltage measured value of the valve group for DC voltage control, configured for obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups;

[0086] a calculation subunit of DC bias of the valve group for DC voltage control, configured for using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this valve group;

[0087] a control subunit of the valve group for DC voltage control, configured for calculating a difference between the DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups, and inputting the difference into a DC voltage control outer loop of this valve group, so as to perform closed-loop control of the DC voltage of this valve group.

[0088] The active power control unit includes the following subunits:

[0089] a calculation subunit of active power reference value of the valve group for active power control, configured for obtaining a total active power reference value P.sub.ref at the end where the series voltage source converter valve group is located according to an active power control target of the DC electrode, allocating the total active power reference value according to the total number N of voltage source converter valve groups in series, and obtaining an active power reference value P.sub.Vref-i of the valve group for each operating voltage source converter valve group after evenly allocating the total active power reference value, where

[00012]$U_{\mathrm{dVref}-i}=\frac{u_{\mathrm{dcref}}}{N},$

i∈(1, . . . , N), N is a positive integer;

[0090] a calculation subunit of DC voltage reference value of the valve group for active power control, configured for obtaining a total DC voltage reference value U.sub.dcref at the end where the series voltage source converter valve group is located, allocating the total DC voltage reference value according to the total number N of voltage source converter valve groups in series, and obtaining a DC voltage reference value U.sub.dVref-i of the valve group after evenly allocating the total DC voltage reference value among operating voltage source converter valve groups, where

[00013]$U_{\mathrm{dVref}-i}=\frac{U_{\mathrm{dcref}}}{N},$

i∈(1, . . . , N), N is a positive integer;

[0091] a receiving subunit of DC voltage measured value of the valve group for active power control, configured for obtaining a DC voltage measured value U.sub.dV-i of the valve group for each operating valve group in the series voltage source converter valve groups.

[0092] a calculation subunit of DC bias of the valve group for active power control configured for using ½ of the DC voltage reference value U.sub.dVref-i of the valve group for each operating valve group in the series voltage source converter valve groups as a bridge arm voltage DC bias of this value group;

[0093] a control subunit of valve group for active power control, configured for obtaining an active power compensation amount ΔP.sub.V-i of the valve group which has voltage-equalization effect for the valve group for each operating valve group of the series voltage source converter valve groups, and adding the active power compensation amount ΔP.sub.V-i of the valve group and the active power reference value P.sub.Vref-i of the valve group to obtain a value, and inputting the value into active power control outer loop of the valve group so as to control the active power of this valve group.

[0094] In the control subunit of valve group for active power control, specific steps of obtaining an active power compensation amount ΔP.sub.V-i of the valve group for each operating valve group, which has voltage-equalization effect for the valve group, include:

[0095] Step c1, calculating a difference between DC voltage reference value U.sub.dVref-i of the valve group and the DC voltage measured value U.sub.dV-i of the valve group to obtain a DC voltage deviation ΔU.sub.dV-i of this valve group;

[0096] Step c2, inputting the DC voltage deviation ΔU.sub.dV-i of this valve group into a valve group voltage-equalizing compensator of this valve group, and calculating the DC voltage deviation ΔU.sub.dV-i of this valve group in the valve group voltage-equalizing compensator of this valve group by using proportional or integral or proportional plus integral method to obtain the active power compensation amount ΔP.sub.V-i of the valve group.

[0097] In the DC voltage control unit, when the output of the DC voltage control outer loop of one operating valve group is limited by a current inner loop limit, the current inner loop limit of the valve group is simultaneously applied to other operating valve groups to maintain the DC voltage balance between each operating valve group.

[0098] In the active power control unit, when the output of the active power control outer loop of one operating valve group is limited by a current inner loop limit, the current inner loop limit of the valve group is simultaneously applied to the other operation valve groups to maintain the DC voltage balance between each operating valve group.

[0099] The above embodiments are only for explaining the technical idea of the present invention, and the scope of protection of the present invention is not limited thereto. Any modification made based on the technical idea according to the technical idea of the present invention falls within the protection scope of the present invention.