CN110190767B - Modular multilevel converter bridge arm simplification method suitable for real-time simulation - Google Patents
Modular multilevel converter bridge arm simplification method suitable for real-time simulation Download PDFInfo
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- CN110190767B CN110190767B CN201910438550.4A CN201910438550A CN110190767B CN 110190767 B CN110190767 B CN 110190767B CN 201910438550 A CN201910438550 A CN 201910438550A CN 110190767 B CN110190767 B CN 110190767B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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Abstract
The invention relates to a Modular Multilevel Converter bridge Arm Simplification Method (An Arm Simulation Method of Modular Multilevel Converter for Real-Time Simulation) suitable for Real-Time Simulation, belonging to the technical field of power transmission and distribution. The method comprises six steps, and provides an MMC bridge arm simplification method suitable for real-time simulation according to expressions of a positive sequence, a negative sequence and a zero sequence of an electric quantity of a three-phase six-bridge arm of the MMC, instantaneous power fluctuation and a submodule capacitor voltage fluctuation expression. The bridge arm simplification method provided by the invention can greatly improve the simulation efficiency while ensuring the simulation precision, and is suitable for real-time simulation under the stable working condition of the MMC.
Description
Technical Field
The invention belongs to the technical field of power transmission and distribution, and particularly relates to a modular multilevel converter bridge arm simplification method suitable for real-time simulation.
Background
As one of voltage source converters (VSC-HVDC), a Modular Multilevel Converter (MMC) is convenient for capacity expansion and redundancy configuration because it is easy to implement modularization; the switching frequency is low, and the loss is small; the harmonic content is low; easy to construct DC power network, and is widely concerned by domestic and foreign scholars. It is anticipated that MMC-HVDC will find wider application in the future.
In practical engineering, a Modular multilevel converter based high voltage direct current (MMC-HVDC) system is generally constructed by cascading a large number of sub-modules in order to obtain a higher voltage level. At present, flexible direct-current transmission projects are rapidly developing towards the directions of high level, large capacity and multiple terminals. When the level number is high, when the MMC formed by a large number of power electronic devices performs electromagnetic transient simulation, the problem that the simulation speed is difficult to meet the research requirement is faced.
For various application scenarios: for example, a simulation model based on a cpu (central processing unit) is limited by communication capability due to the adoption of a serial data processing mode, and thus, the real-time simulation requirement of an MMC bridge arm is difficult to meet. The simulation model based on the Field Programmable Gate Array (FPGA) can realize highly parallel numerical calculation and high-speed data communication, and can meet the requirement of real-time simulation of the MMC bridge arm. Meanwhile, in order to improve the MMC electromagnetic transient simulation efficiency, the simulation complexity can be reduced by simplifying the MMC bridge arms to different degrees. Therefore, the modular multilevel converter bridge arm simplification method suitable for real-time simulation is provided while the efficiency and the precision are ensured, and the method has important significance for development of MMC real-time simulation.
Disclosure of Invention
The technical problem to be solved by the invention is a modular multilevel converter bridge arm simplification method suitable for real-time simulation. For convenience of describing the method, the present invention is described by taking an MMC consisting of an HBSM (half bridge sub-module).
The method specifically comprises the following steps:
step 1: in a three-phase six-bridge arm MMC, a fundamental frequency positive sequence, a double frequency negative sequence and a triple frequency zero sequence are obtained by utilizing circuit analysis, so that the frequency and the sequence components are connected.
Step 2: the relation between the upper bridge arm and the lower bridge arm of the MMC three phases is analyzed firstly, and expressions of positive sequence, negative sequence and zero sequence of electric quantities among the three phases are obtained.
And step 3: and then analyzing the relationship of the electric quantities between the upper bridge arm and the lower bridge arm of the a/b/c phase to obtain expressions of positive sequence, negative sequence and zero sequence of the electric quantities of the upper bridge arm and the lower bridge arm.
And 4, step 4: and deducing an expression of the voltage and current of the MMC three-phase six-bridge-arm bridge arm.
And 5: and deducing an expression of instantaneous power fluctuation of the three-phase six-bridge arm and capacitor voltage fluctuation of the sub-module.
Step 6: according to the relation between three-phase six-bridge arm electric quantities, a modular multilevel converter bridge arm simplification method suitable for real-time simulation is provided.
Through the 6 steps, the calculation complexity of the six bridge arms of the MMC can be simplified, and the method can be applied to the stable real-time simulation of the system level of the MMC.
Drawings
FIG. 1 is a diagram of the MMC topology provided by the present invention;
fig. 2 is a detailed topology diagram of an exemplary half-bridge sub-module of the present invention.
FIG. 3 is a MMC real-time simulation process in the present invention.
In fig. 1, SM indicates Sub-modules (SM), SM1, SM2, …, SMn, and indicates a first Sub-module, a second Sub-module, …, and an nth Sub-module in a bridge arm of MMC; l isarmIs a bridge arm reactor, UdcIs the dc side voltage.
In fig. 2, VT1 and VT2 represent Insulated Gate Bipolar Transistors (IGBTs), VD1 and VD2 represent diodes, C represents a capacitor, Rp represents a voltage equalizing resistor, K1 represents a mechanical switch, and K2 represents a high-speed thyristor.
In FIG. 3, step 1 is to apply the A phase upper and lower bridge arm and the B phase upper bridge arm current IarmNumber of breakover of AND submodule NONTransmitting to FPGA; step 2: the FPGA obtains thevenin equivalent voltage U of the bridge arm through a sequencing voltage-sharing triggering linkeqAnd submodule capacitor voltage UCTransmitting the signals to an A-phase upper bridge arm and a B-phase lower bridge arm of the MMC; and step 3: according to the deduced relation of the MMC three-phase six-bridge arm, the Thevenin equivalent voltage of the upper bridge arm and the lower bridge arm of the A phase and the Thevenin equivalent voltage of the upper bridge arm of the B phase and the capacitor voltage of the sub-module are delayed by delta t after time1-Δt3Mapping to the other 3 arms (Δ t)1-Δt3Delay times of different bridge arms, respectively); and 4, step 4: completing the calculation of a simulation step length, and connecting the currents I of the upper and lower bridge arms of the A phase and the upper bridge arm of the B phasearmNumber of breakover of AND submodule NONCalculating the result as the initial value of the next step lengthAnd the module is transmitted to an A-phase upper bridge arm and a B-phase upper bridge arm of the MMC.
Detailed Description
The MMC consisting of half-bridge sub-modules to which the present invention relates will be explained in detail below. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.
The technical problem to be solved by the invention is a modular multilevel converter bridge arm simplification method suitable for real-time simulation. The invention is realized by adopting the following technical scheme:
the invention is realized by the following six steps:
step 1: as shown in fig. 1, in a three-phase six-leg MMC, three-phase relationships a, b, and c of electric quantities such as voltage and current are analyzed according to phase angle lead-lag, and can be divided into a positive sequence, a negative sequence, and a zero sequence. By circuit analysis, the fundamental frequency positive sequence, the double frequency negative sequence and the triple frequency zero sequence are obtained, so that the frequency and sequence components are associated. The expression is shown as formula (1):
in the formula, subscript 1 represents a positive sequence fundamental frequency component, subscript 2 represents a negative sequence 2 frequency multiplication component, and subscript sequence represents a zero sequence 3 frequency multiplication component.
Step 2: as shown in fig. 1, the relationship between the three phases of the MMC is analyzed to obtain the expressions of positive sequence, negative sequence and zero sequence of the electrical quantities between the three phases.
Taking the abc three phases of the MMC marked by the blue dotted frame in fig. 1 as an example, the positive sequence, the negative sequence and the zero sequence of the electrical quantities between the three phases are shown in formulas (2) to (4):
the following relations among three abc phases of a fundamental frequency positive sequence, a double frequency negative sequence and a triple frequency zero sequence are obtained by analyzing in a time domain:
wherein a isj(t)、bj(t)、cjAnd (T) represents three phases abc, and T is a fundamental frequency period. The positive sequence, negative sequence and zero sequence components of the three-phase symmetrical electric quantity such as voltage, current and the like all satisfy the expression (4) in the time domain.
And step 3: as shown in fig. 1, the relationship of the electrical quantities between the upper and lower bridge arms of the a/b/c phase is analyzed to obtain the expressions of the positive sequence, the negative sequence and the zero sequence of the electrical quantities of the upper and lower bridge arms.
The red solid line boxes in fig. 1 mark the relationship between the electrical quantities in the circuit diagram. The MMC is determined by the inherent working property of the MMC, namely the complementary characteristic between the upper bridge arm and the lower bridge arm, and the complementary characteristic is expressed in the time domain that the electric quantity between the upper bridge arm and the lower bridge arm has a half period difference. The relationship among the fundamental frequency quantity, the frequency doubling quantity and the frequency tripling component among the upper bridge arm and the lower bridge arm is shown as the formula (6):
wherein a, b and c represent three phases, n represents a lower bridge arm, p represents an upper bridge arm, j represents frequency, and 1,2 and 3 … can be selected. Then, the relationship among the fundamental frequency components, the second harmonic component and the third harmonic component of the upper and lower bridge arms is expressed by the following expression, taking phase a as an example:
as can be seen from expressions (7) - (9), odd-numbered frequency components such as fundamental frequency components and triple-numbered frequency components of the upper/lower bridge arms are equal in magnitude and opposite in direction at any time, while even-numbered frequency components such as frequency doubling and frequency quadrupling are equal in magnitude and same in direction at any time.
And 4, step 4: and deducing an expression of the voltage and current of the MMC three-phase six-bridge-arm bridge arm.
In the MMC topology, the reference direction is based on the direction marked in fig. 1, and the bridge arm voltage of the upper bridge arm of the a-phase is:
in expression (10), UapIs the upper bridge arm voltage, UdcIs a DC voltage in a steady state condition, vaFor the amplitude of the a-phase modulation wave, and ω is the angular frequency of the fundamental wave, the relationship between the bridge arm voltages of the three-phase six-bridge arm can be expressed as:
the bridge arm current of the upper bridge arm of the phase a is as follows:
wherein iapIs instantaneous current of the upper bridge arm of phase a, IdcIs a direct side current, IsThe amplitude of the phase current at the fundamental frequency of the alternating current,
the current relationship of the three-phase six-leg also satisfies the relationship of equation (11) for the phase angle of the fundamental frequency current component.
And 5: and deducing an expression of instantaneous power fluctuation of the three-phase six-bridge arm and capacitor voltage fluctuation of the sub-module.
an expression formula of instantaneous power fluctuation of an upper bridge arm of the phase a and capacitor voltage fluctuation of the sub-modules is shown as a formula (13):
combining equations (11) and (13), the relationship between the upper and lower arms of the a-phase and the relationship between the a-phase and the b-phase can be obtained from equation (14):
by combining equations (11), (13) and (14), we can obtain that the relationship of the instantaneous power of the bridge arm between the three-phase six-bridge arms of the classical MMC topology will satisfy the following three points:
1) instantaneous power fluctuation among the six bridge arms of the three phases a, b and c and submodule capacitor voltage fluctuation have consistent waveforms in a time domain, and only time delay exists.
2) The waveform of the sub-module capacitor voltage fluctuation among the three phases a, b and c is consistent with that of the instantaneous power fluctuation of the bridge arm, only the time delay of T/3 period exists, and T is the fundamental frequency period.
3) The waveform of the sub-module capacitor voltage fluctuation between the upper bridge arm and the lower bridge arm is consistent with the waveform of the instantaneous power fluctuation of the bridge arm, only the time delay of T/2 period exists, and T is the fundamental frequency period.
The simplified expressions are shown in formulas (15) to (18):
step 6: according to the relation between three-phase six-bridge arm electric quantities, a modular multilevel converter bridge arm simplification method suitable for real-time simulation is provided. The electromagnetic transient characteristics of the MMC three-phase six-bridge arm are obtained by simulating the electromagnetic transient characteristics of 3 bridge arms, mapping the electromagnetic transient characteristics of the MMC three-phase six-bridge arm to the other 3 bridge arms through time delay according to the electric quantity, instantaneous power fluctuation and submodule capacitor voltage fluctuation difference between the three-phase six-bridge arms deduced in the step 1-5.
The process of performing the MMC real-time simulation according to fig. 3 includes 4 steps. Step 1, bridge arm currents I of an upper bridge arm and a lower bridge arm of the phase A and an upper bridge arm of the phase B are measuredarmNumber of breakover of AND submodule NONTransmitting to FPGA; step 2: the FPGA obtains thevenin equivalent voltage U of the bridge arm through a sequencing voltage-sharing triggering linkeqAnd submodule capacitor voltage UCTransmitting the signals to an A-phase upper bridge arm module, a B-phase upper bridge arm module and a MMC; and step 3: according to the deduced relation of the MMC three-phase six-bridge arm, the bridge arm Thevenin equivalent voltage of the A-phase upper bridge arm and the B-phase upper bridge arm and the sub-module capacitor voltage are delayed by delta t after time1-Δt3Mapping to the other 3 bridge arms, namely a B-phase lower bridge arm, a C-phase upper bridge arm and a C-phase lower bridge arm; and 4, step 4: completing the calculation of a simulation step length, and connecting the bridge arm currents I of the upper and lower bridge arms of the A phase and the upper bridge arm of the B phasearmNumber of breakover of AND submodule NONAnd the calculation result is used as a next-step length initial value and is transmitted to the A-phase upper bridge arm module, the B-phase upper bridge arm module and the MMC.
The bridge arm simplification method has the beneficial effects that the bridge arm simplification method is suitable for MMC simulation under a steady state condition, the complexity of the MMC bridge arm simulation can be greatly reduced, simulation resources are saved, and the simulation time is shortened.
The bridge arm simplification method suitable for real-time simulation can be popularized and applied to mixed MMC with different types and containing more than two types of sub-module topologies, and has engineering practical value.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (1)
1. The MMC bridge arm simplification method suitable for real-time simulation is characterized by providing an MMC bridge arm simplification method suitable for real-time simulation according to expressions of a positive sequence, a negative sequence and a zero sequence of an MMC three-phase six-bridge arm electric quantity, instantaneous power fluctuation and a submodule capacitor voltage fluctuation expression, and comprising the following steps of: step 1: in a three-phase six-bridge arm MMC, a fundamental frequency positive sequence, a double frequency negative sequence and a triple frequency zero sequence are deduced by utilizing circuit analysis, so that the frequency and the sequence components are connected; step 2: firstly, analyzing the relation between the upper/lower bridge arms of the MMC three phases to obtain the expressions of positive sequence, negative sequence and zero sequence of the electric quantities among the three phases; and step 3: analyzing the relationship of the electric quantities between the upper bridge arm and the lower bridge arm of the a/b/c phase to obtain expressions of positive sequence, negative sequence and zero sequence of the electric quantities of the upper bridge arm and the lower bridge arm; and 4, step 4: deducing an expression of the voltage and current of the MMC three-phase six-bridge-arm bridge arm; and 5: deducing an expression of instantaneous power fluctuation of a three-phase six-bridge arm and capacitance and voltage fluctuation of a submodule; step 6: according to the relation between three-phase six-bridge arm electric quantities, a modular multilevel converter bridge arm simplification method suitable for real-time simulation is provided.
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