CN109713707B - Method for reducing voltage fluctuation of MMC sub-module under unbalanced power grid voltage - Google Patents
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Abstract
The invention provides a method for reducing fluctuation of Modular Multilevel Converter (MMC) sub-module capacitor voltage under unbalanced power grid voltage. According to the technical scheme provided by the invention, the third harmonic voltage injection amount is introduced, so that the problem that the voltage fluctuation of the sub-module capacitor is increased when the voltage of the power grid is unbalanced is solved, and the problem that the conventional method for reducing the voltage fluctuation of the sub-module is not suitable for the unbalanced condition of the voltage of the power grid. The characteristics of economy and control flexibility are considered, the fluctuation degree of the sub-module capacitor voltage can be greatly reduced on the premise of keeping the direct-current bus voltage and the transmission power unchanged, the requirement on the capacitance value of the sub-module capacitor is further reduced, the size and the cost of the sub-module capacitor are reduced, and the modular multilevel converter is light.
Description
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to a method for reducing fluctuation of capacitance and voltage of an MMC sub-module under unbalanced power grid voltage.
Background
Flexible direct current transmission (VSC-HVDC) is a new generation of direct current transmission technology following alternating current transmission, conventional direct current transmission. The flexible direct current transmission technology has the characteristics of independent active and reactive power adjustment, strong weak power grid access and low voltage ride through capability, low alternating current filtering, reactive power compensation requirements and the like. The flexible direct current transmission is important equipment for constructing an intelligent power grid, compared with the traditional mode, the flexible direct current transmission has stronger technical advantages in aspects of island power supply, capacity increasing transformation of an urban power distribution network, alternating current system interconnection, large-scale wind power plant grid connection and the like, and is a strategic choice for changing the development pattern of a large power grid. The Modular Multilevel Converter (MMC) has the advantages of modularization, low switching frequency, low harmonic content, convenience in redundant configuration and the like, and has a wider application scene compared with a thyristor-based power grid commutation converter and a traditional two-level voltage source converter.
However, as a core device of a flexible direct current transmission system, the MMC still has many restriction bottlenecks at present. The modularized distributed arrangement also brings the problems of large voltage fluctuation of the sub-module capacitor and the like. The alternating-current side output voltage is deviated due to the influence of the capacitance voltage fluctuation and the interphase circulating current interactive coupling, the output harmonic content is increased, and meanwhile, the operation reliability of a direct-current system is reduced due to the large module capacitance voltage fluctuation amplitude.
The capacitors of the MMC are the largest volume devices in the sub-module, accounting for more than 60% of the total volume of the sub-module. Although increasing the sub-module capacitance can reduce the capacitance voltage fluctuation, if only relying on this method, the capacitor size and cost will increase continuously, and the economy is poor. Therefore, a method for reducing the sub-module capacitance voltage fluctuation by the MMC is explored, so that the requirement on the sub-module capacitance value is reduced, the light design of the converter is realized, and the method has important engineering significance.
The three-phase voltage unbalance situation often appears in the actual power grid operation, and the negative sequence voltage that produces this moment can cause MMC output power's fluctuation and output current's unbalance, also can aggravate the fluctuation of MMC internal module voltage and bridge arm electric current simultaneously. The conventional submodule voltage fluctuation suppression method is not suitable for the submodule voltage fluctuation condition under the condition of power grid voltage unbalance.
Disclosure of Invention
In order to overcome the defect that the conventional submodule voltage fluctuation suppression method is not suitable for the submodule voltage fluctuation condition under the condition of unbalanced power grid voltage, the invention provides a method for reducing the voltage fluctuation of an MMC submodule under the unbalanced power grid voltage, wherein when the alternating current power grid voltage is asymmetric, the three-phase third harmonic voltage correction quantity is respectively determined; determining the modulation wave voltage of the MMC under the unbalanced power grid voltage through the third harmonic voltage correction; determining the proportion of improving the amplitude of the valve side alternating voltage according to the voltage peak value of the modulation wave of the MMC; and finally, the sub-module capacitor voltage fluctuation of the MMC under the unbalanced power grid voltage is reduced by injecting third harmonic voltage correction and correspondingly increasing the valve side alternating voltage.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
the invention provides a method for reducing voltage fluctuation of an MMC sub-module under unbalanced power grid voltage, which comprises the following steps:
when the voltage of the alternating current power grid is asymmetric, determining three-phase third harmonic voltage correction quantities respectively;
determining the modulation wave voltage of the MMC under the unbalanced power grid voltage through the third harmonic voltage correction;
determining the proportion of improving the amplitude of the valve side alternating voltage according to the voltage peak value of the modulation wave of the MMC;
and the sub-module capacitor voltage fluctuation of the MMC under the unbalanced power grid voltage is reduced by injecting third harmonic voltage correction and correspondingly increasing the valve side alternating voltage.
Taking phase a as an example, the bridge arm voltage and the bridge arm current when the MMC is stable under the unbalanced grid voltage are represented as follows:
the upper and lower bridge arm currents are respectively expressed as:
wherein I + Is a positive sequence alternating current amplitude, I - Is the amplitude of the negative sequence alternating current, beta + And beta - The phase angles of the positive and negative sequence alternating currents are respectively. I is dca The dc current component in the a-phase leg current is represented.
Considering the third harmonic injection voltage, the bridge arm modulation voltage is expressed as:
wherein m is + And m - Positive and negative sequence voltage modulation ratios, alpha + And alpha - The phase angles of the positive and negative sequence alternating voltages are respectively.
For the injected third harmonic voltage, a represents the magnitude of the injection amplitude (in the third harmonic voltage generally injected under balanced grid voltage, a is 1), and θ is the phase angle of the injection amount. Upper and lower bridge arm injectionThe quantity is equal in size and opposite in direction, and the direct current voltage can be guaranteed not to contain the frequency tripling voltage component.
The third harmonic injection voltage correction is determined according to the following formula:
the injected third harmonic voltage is:
wherein the injection amplitude parameter and phase angle are expressed as:
wherein, A ═ m + cosα + +m - cosα - ；B＝m + sinα + +m - sinα - ；
The determining the modulation wave voltage of the MMC through the third harmonic voltage correction comprises the following steps:
1. determining the current reference value output by the positive sequence outer loop power controller according to the following formula:
wherein i d_ref D-axis current reference, i, representing the output of the outer loop power controller q_ref Representing a Q-axis current reference value output by the outer loop power controller, P representing active power output by the MMC, Q representing reactive power output by the MMC, P ref Active power reference, Q, representing MMC output ref Reference value of reactive power, k, representing MMC output 1 、k 3 Denotes the proportionality coefficient, k 2 、k 4 Representing integral coefficient；
2. When the voltage of the power grid is unbalanced, negative sequence current can be generated. To suppress the negative-sequence current, prevent the power electronics from over-current, the negative-sequence current reference value is determined as follows:
3. according to i + d_ref And i + q_ref And determining the voltage reference value output by the positive sequence inner loop current controller according to the following formula:
wherein e is d_ref + A positive sequence d-axis voltage reference, e, representing the output of the positive sequence inner loop current controller q_ref + Representing the positive sequence q-axis voltage reference, u, output by the positive sequence inner loop current controller sd + Represents the positive sequence AC network side voltage of d-axis, u sq + Representing the positive sequence ac network side voltage of q axis, i d + Representing positive sequence d-axis actual current, i q + Representing positive sequence q-axis actual current, k 5 、k 7 Denotes the proportionality coefficient, k 6 、k 8 Representing an integral coefficient;
4. according to i d_ref - And i q_ref - And determining the voltage reference value output by the negative-sequence current controller according to the following formula:
wherein e is d_ref - Reference value of negative sequence d-axis voltage, e, representing output of negative sequence current controller q_ref - Representing negative sequence q-axis voltage reference, u, of the negative sequence current controller output sd - Representing the negative sequence ac network side voltage of d-axis, u sq - Representing negative sequence ac of q-axisNetwork side voltage, i d - Representing the negative sequence d-axis actual current, i q - Representing negative sequence q-axis actual current, k 9 、k 11 Denotes the proportionality coefficient, k 10 、k 12 Represents an integral coefficient;
5. e is to be d_ref + 、e q_ref + Carrying out dq/abc conversion to obtain three-phase positive sequence virtual electromotive force; e is to be d_ref - 、e q_ref - And carrying out dq/abc conversion to obtain three-phase negative sequence virtual electromotive force.
6. Correction amount Deltau according to third harmonic voltage 3 And three-phase positive-sequence and negative-sequence virtual electromotive force, and determining the modulation wave voltage of the MMC according to the following formula:
wherein u is pj_ref Indicating modulated wave voltage, u, of upper bridge arm in MMC nj_ref Representing modulated wave voltage of lower arm in MMC j_ref + Representing a three-phase positive sequence virtual electromotive force, e j_ref - Representing a three-phase negative sequence virtual electromotive force.
The ratio of improving the valve side alternating voltage amplitude is determined according to the modulation wave voltage peak value of the MMC, and the method comprises the following steps:
if the operating condition before the voltage unbalance occurs is taken as the standard (that is, the number of the submodules required by each bridge arm is the same as that before the voltage unbalance occurs), the alternating-current voltage can be increased to about:
if the voltage unbalance working condition is voltage drop, the voltage modulation voltage peak value can be improved to the level before the voltage drop; if the voltage unbalance working condition is that one-phase voltage is increased, the peak value of the modulation voltage can be reduced through third harmonic injection, so that the problems of insufficient number of sub-modules and reduced margin caused by voltage increase are solved.
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
in the method for reducing the voltage fluctuation of the MMC sub-module under the unbalanced power grid voltage, when the alternating current power grid voltage is asymmetric, three-phase third harmonic voltage correction quantities are respectively determined; determining the modulation wave voltage of the MMC under the unbalanced power grid voltage through the third harmonic voltage correction; determining the proportion of improving the amplitude of the valve side alternating voltage according to the voltage peak value of the modulation wave of the MMC; and finally, the sub-module capacitor voltage fluctuation of the MMC under the unbalanced power grid voltage is reduced by injecting third harmonic voltage correction and correspondingly increasing the valve side alternating voltage. The method provided by the invention can effectively reduce the sub-module capacitance voltage fluctuation under the unbalanced power grid voltage, inhibit the sub-module capacitance voltage fluctuation increase caused by the unbalanced power grid voltage, improve the reliability of the MMC system, reduce the requirement on the sub-module capacitance value, and is beneficial to realizing the lightening of the MMC.
The method for reducing the voltage fluctuation of the MMC sub-module under the unbalanced power grid voltage fills the technical blank of the method for inhibiting the voltage fluctuation of the capacitor of the MMC sub-module under the unbalanced power grid voltage, can be combined with a circulation current inhibition scheme for use, minimizes the circulation current of the MMC system while reducing the voltage fluctuation of the capacitor of the sub-module, improves the reliability of the MMC system and reduces the loss of the MMC system.
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FIG. 1 is a flow chart of a method for reducing voltage fluctuation of an MMC sub-module under an unbalanced power grid voltage in an embodiment of the present invention;
FIG. 2 is a diagram illustrating a third harmonic voltage correction amount determination process according to an embodiment of the present invention;
FIG. 3 is a diagram of a three-phase positive and negative sequence virtual electromotive force determination process in an embodiment of the present invention;
FIG. 4 is a flow chart of obtaining a modulation voltage by a third harmonic voltage correction amount and three-phase positive sequence virtual electromotive force and negative sequence electromotive force according to an embodiment of the present invention;
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The embodiment of the invention provides a method for reducing voltage fluctuation of an MMC sub-module under unbalanced power grid voltage, a specific flow chart is shown as figure 1, and the specific process is as follows:
s101: when the voltage of the alternating current power grid is asymmetric, determining three-phase third harmonic voltage correction quantities respectively;
s102: determining the modulation wave voltage of the MMC under the unbalanced power grid voltage through the third harmonic voltage correction;
s103: determining the proportion of improving the amplitude of the valve side alternating voltage according to the voltage peak value of the modulation wave of the MMC;
s104: and the sub-module capacitor voltage fluctuation of the MMC under the unbalanced power grid voltage is reduced by injecting third harmonic voltage correction and correspondingly increasing the valve side alternating voltage.
The MMC comprises three phase units, each phase unit comprises an upper bridge arm and a lower bridge arm, and the number of the sub-modules in the upper bridge arm and the number of the sub-modules in the lower bridge arm are equal.
Taking the phase a as an example, the bridge arm voltage and the bridge arm current when the MMC is stable under the unbalanced network voltage are represented as follows:
the upper and lower bridge arm currents are respectively expressed as:
wherein I + For positive sequence AC current amplitude, I - Amplitude of negative-sequence alternating current, beta + And beta - The phase angles of the positive and negative sequence alternating currents are respectively. I is dca The dc current component in the a-phase leg current is represented.
Considering the third harmonic injection voltage, the bridge arm modulation voltage is expressed as:
wherein m is + And m - Positive and negative sequence voltage modulation ratios, alpha, respectively + And alpha-are the phase angles of the positive and negative sequence alternating voltages, respectively.
For the injected third harmonic voltage, a represents the magnitude of the injection amplitude (in the third harmonic voltage generally injected under balanced grid voltage, a is 1), and θ is the phase angle of the injection amount. The injection quantities of the upper bridge arm and the lower bridge arm are equal in size and opposite in direction, and the direct current voltage can be guaranteed not to contain a frequency tripling voltage component.
In S101, the third harmonic voltage correction amount determining process is as shown in fig. 2, and the third harmonic voltage correction amount is determined according to the following equation:
the injected third harmonic voltage is:
wherein the injection amplitude parameter and phase angle are expressed as:
wherein, A ═ m + cosα + +m - cosα - ；B＝m + sinα + +m - sinα - ；
In S102, the modulated wave voltage of the MMC is obtained from the third harmonic voltage correction amount of the three phases obtained in S101 and the positive and negative sequence virtual electromotive forces of the three phases. Fig. 3 shows a process diagram of determining the three-phase positive and negative sequence virtual electromotive force, and fig. 4 shows a flow diagram of obtaining the modulation voltage through the third harmonic voltage correction amount and the three-phase positive and negative sequence virtual electromotive forces. The specific process of determining the three-phase positive and negative sequence virtual electromotive force is as follows:
1. determining the current reference value output by the positive sequence outer loop power controller according to the following formula:
wherein i d_ref D-axis current reference, i, representing the output of the outer loop power controller q_ref Representing a Q-axis current reference value output by the outer loop power controller, P representing active power output by the MMC, Q representing reactive power output by the MMC, P ref Active power reference, Q, representing MMC output ref Reference value of reactive power, k, representing MMC output 1 、k 3 Denotes the proportionality coefficient, k 2 、k 4 Represents an integral coefficient;
2. when the voltage of the power grid is unbalanced, negative sequence current can be generated. To suppress the negative-sequence current, prevent the power electronics from over-current, the negative-sequence current reference value is determined as follows:
3. according to i + d_ref And i + q_ref And determining the voltage reference value output by the positive sequence inner loop current controller according to the following formula:
wherein e is d_ref + A positive sequence d-axis voltage reference, e, representing the output of the positive sequence inner loop current controller q_ref + To representPositive sequence q-axis voltage reference value, u, output by the positive sequence inner loop current controller sd + Representing the d-axis positive sequence AC network side voltage, u sq + Representing the positive sequence ac network side voltage of q-axis, i d + Representing positive sequence d-axis actual current, i q + Representing positive sequence q-axis actual current, k 5 、k 7 Denotes the proportionality coefficient, k 6 、k 8 Represents an integral coefficient;
4. according to i d_ref - And i q_ref - And determining the voltage reference value output by the negative-sequence current controller according to the following formula:
wherein e is d_ref - Negative sequence d-axis voltage reference, e, representing the negative sequence current controller output q_ref - Representing negative sequence q-axis voltage reference, u, of the negative sequence current controller output sd - Representing the d-axis negative sequence AC network side voltage, u sq - Representing the negative sequence ac network side voltage of q axis, i d - Representing the negative sequence d-axis actual current, i q - Representing the negative-sequence q-axis actual current, k 9 、k 11 Denotes the proportionality coefficient, k 10 、k 12 Represents an integral coefficient;
5. e is to be d_ref + 、e q_ref + Carrying out dq/abc conversion to obtain three-phase positive sequence virtual electromotive force; e is to be d_ref - 、e q_ref - And carrying out dq/abc conversion to obtain three-phase negative sequence virtual electromotive force.
The specific process of determining the modulation wave voltage of the MMC through the third harmonic voltage correction quantity is as follows:
correction amount Deltau according to third harmonic voltage 3 And three-phase positive-sequence and negative-sequence virtual electromotive force, and determining the modulation wave voltage of the MMC according to the following formula:
wherein u is pj_ref Indicating the modulated wave voltage, u, of the upper bridge arm in an MMC nj_ref Representing modulated wave voltage of lower arm in MMC j_ref + Representing a three-phase positive sequence virtual electromotive force, e j_ref - Representing a three-phase negative sequence virtual electromotive force.
The specific process of determining the proportion for increasing the valve-side ac voltage amplitude according to the peak value of the modulation wave voltage of the MMC in S103 is as follows:
if the operating condition before the voltage unbalance occurs is taken as the standard (that is, the number of the submodules required by each bridge arm is the same as that before the voltage unbalance occurs), the alternating-current voltage can be increased to about:
if the voltage unbalance working condition is voltage drop, the voltage modulation voltage peak value can be increased to the level before the voltage drop; if the voltage unbalance working condition is that one-phase voltage is increased, the peak value of the modulation voltage can be reduced through third harmonic injection, so that the problems of insufficient number of sub-modules and reduced margin caused by voltage increase are solved.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person of ordinary skill in the art can make modifications or equivalents to the specific embodiments of the present invention with reference to the above embodiments, and such modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims of the present invention as set forth in the claims.
Claims (2)
1. A method for reducing fluctuation of capacitor voltage of a Modular Multilevel Converter (MMC) submodule under unbalanced grid voltage is characterized by comprising the following steps of:
when the voltage of the alternating current power grid is asymmetric, determining three-phase third harmonic voltage correction quantities respectively;
determining the modulation wave voltage of the MMC under the unbalanced power grid voltage through the third harmonic voltage correction;
determining the proportion of improving the valve side alternating voltage amplitude according to the modulation wave voltage peak value of the MMC;
by injecting third harmonic voltage correction and correspondingly increasing the valve side alternating voltage, the aim of reducing the voltage fluctuation of the sub-module capacitor of the MMC under the unbalanced power grid voltage is fulfilled;
taking phase a as an example, the bridge arm voltage and the bridge arm current when the MMC is stable under the unbalanced network voltage are represented as follows:
the upper and lower bridge arm currents are respectively expressed as:
in which I + For positive sequence AC current amplitude, I - Is the amplitude of the negative sequence alternating current, beta + And beta - Phase angle, I, of positive and negative sequence alternating current, respectively dca Representing a direct current component in the a-phase bridge arm current;
considering the third harmonic injection voltage, the bridge arm modulation voltage is expressed as:
wherein m is + And m - Positive and negative sequence voltage modulation ratios, alpha + And alpha - The phase angles of the positive sequence alternating voltage and the negative sequence alternating voltage are respectively;
for the third harmonic voltage to be injected, a represents the injection amplitude, in the third harmonic voltage generally injected under the balanced grid voltage, a is 1, theta is the phase angle of the injection amount, the injection amounts of the upper and lower bridge arms are equal in size and opposite in direction, and the direct current voltage can be ensured not to contain a triple frequency voltage component;
the third harmonic injection voltage correction is determined as follows:
the injected third harmonic voltage is:
wherein the injection amplitude parameter and phase angle are expressed as:
wherein, A ═ m + cosα + +m - cosα - ；B＝m + sinα + +m - sinα - ；
The proportion of improving the amplitude of the alternating voltage at the valve side is determined according to the voltage peak value of the modulation wave of the MMC, if the working condition before the voltage is unbalanced is taken as a standard, namely the number of the sub-modules required by each bridge arm is the same as that before the voltage is unbalanced, the alternating voltage can be improved to about:
if the voltage unbalance working condition is voltage drop, the voltage modulation voltage peak value can be improved to the level before the voltage drop; if the voltage unbalance working condition is that one-phase voltage is increased, the peak value of the modulation voltage can be reduced through third harmonic injection, so that the problems of insufficient number of sub-modules and reduced margin caused by voltage increase are solved.
2. The method for reducing the ripple of the capacitance voltage of the MMC sub-module under the unbalanced network voltage according to claim 1, wherein the determining the modulation wave voltage of the MMC through a third harmonic voltage modifier comprises:
determining the current reference value output by the positive sequence outer loop power controller according to the following formula:
wherein i d_ref D-axis current reference, i, representing the output of the outer loop power controller q_ref Representing a Q-axis current reference value output by the outer loop power controller, P representing active power output by the MMC, Q representing reactive power output by the MMC, P ref Active power reference, Q, representing MMC output ref Reference value of reactive power, k, representing MMC output 1 、k 3 Denotes the proportionality coefficient, k 2 、k 4 Represents an integral coefficient;
when the voltage of the power grid is unbalanced, negative sequence current can be generated; to suppress the negative-sequence current, prevent the power electronics from over-current, the negative-sequence current reference value is determined as follows:
according to i + d_ref And i + q_ref And determining the voltage reference value output by the positive sequence inner loop current controller according to the following formula:
wherein e is d_ref + A positive sequence d-axis voltage reference, e, representing the output of the positive sequence inner loop current controller q_ref + Representing the positive sequence q-axis voltage reference, u, output by the positive sequence inner loop current controller sd + Representing the d-axis positive sequence AC network side voltage, u sq + Representing the positive sequence ac network side voltage of q-axis, i d + Representing positive sequence d-axis actual current, i q + Representing positive sequence q-axis actual current, k 5 、k 7 Denotes the proportionality coefficient, k 6 、k 8 Represents an integral coefficient;
according to i d_ref - And i q_ref - And determining the voltage reference value output by the negative-sequence current controller according to the following formula:
wherein e is d_ref - Reference value of negative sequence d-axis voltage, e, representing output of negative sequence current controller q_ref - Representing negative sequence q-axis voltage reference, u, of the negative sequence current controller output sd - Representing the negative sequence ac network side voltage of d-axis, u sq - Representing the q-axis negative sequence AC network side voltage, i d - Representing the negative sequence d-axis actual current, i q - Representing the negative-sequence q-axis actual current, k 9 、k 11 Denotes the proportionality coefficient, k 10 、k 12 Represents an integral coefficient;
e is to be d_ref + 、e q_ref + Carrying out dq/abc conversion to obtain three-phase positive sequence virtual electromotive force; e is to be d_ref - 、e q_ref - Carrying out dq/abc conversion to obtain three-phase negative sequence virtual electromotive force;
correction amount Deltau according to third harmonic voltage 3 And three-phase positive sequence and negative sequence virtual electromotive force, and determining the modulation wave voltage of the MMC according to the following formula:
wherein u is pj_ref Indicating modulated wave voltage, u, of upper bridge arm in MMC nj_ref Representing modulated wave voltage of lower arm in MMC j_ref + Representing a three-phase positive sequence virtual electromotive force, e j_ref - Representing a three-phase negative sequence virtual electromotive force.
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| CN111416376B (en) * | 2020-03-13 | 2021-09-07 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Voltage balancing method for extra-high voltage flexible direct-current constant active power MMC converter station |
| CN111786613B (en) * | 2020-06-11 | 2021-08-20 | 华中科技大学 | Three-phase series winding topology open circuit fault tolerance method for balanced modulation of wave amplitude |
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