CN111293894B - Capacitor voltage balance control method for modular multilevel matrix converter - Google Patents
Capacitor voltage balance control method for modular multilevel matrix converter Download PDFInfo
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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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M5/275—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/293—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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Abstract
The invention discloses a capacitor voltage balance control method of a modular multilevel matrix converter. Firstly, obtaining reference values of input and output current components in bridge arm current through output power control and total capacitance voltage balance control; secondly, obtaining reference values of two frequency circulating current components in the bridge arm current through inter-bridge arm capacitance-voltage balance control based on double-frequency circulating current injection, and further solving the reference values of the bridge arm current; finally, the bridge arm current actually measured by the current sensor is compared with a bridge arm current reference value, the bridge arm voltage reference value is obtained through proportional-integral control and feedforward control of input and output voltages, and the bridge arm voltage reference value is used for solving signals for controlling the sub-module switches. The invention does not need to carry out complex conversion on the circuit, and not only can realize the balance of the capacitor voltage, but also can ensure that the injected circulating current does not influence the input and output current when the transmission power of the bridge arm is unbalanced.
Description
Technical Field
The invention belongs to the technical field of application of a high-voltage high-power electronic technology in a power system, and particularly relates to a capacitance-voltage balance control method of a Modular Multilevel Matrix Converter (M3C).
Background
The modular multilevel matrix converter integrates the characteristics of the traditional matrix converter and the multilevel converter, is an AC/AC converter and can realize direct conversion of frequency. In addition, the power factor converter also has the capacity of energy bidirectional flow, can realize any power factor at the input side and any boosting and reducing ratio at the output side, and therefore has wide application prospect in the fields of variable frequency speed regulation and low-frequency high-voltage alternating-current transmission.
For M3C, power transfer between the input and the output needs to be performed through the bridge arm, which may cause fluctuation of the capacitor voltage on the M3C sub-module, and when the input power is not equal to the output power, dc bias of the capacitor voltage may be caused, which may cause instability of the capacitor voltage. The voltage value of the capacitor corresponds to the voltage stress of the power device, and the capacitor voltage is stabilized at a rated value, which is the premise that the whole system works normally and reliably. Therefore, the capacitor voltage of M3C must be controlled to stabilize at the rated voltage.
The power grid simulation device and the control method thereof disclosed in chinese patent with publication number CN106786535A propose a loop current control method for balancing M3C capacitance and voltage, where the loop current has the function of balancing the bridge arm capacitance and voltage and simultaneously suppressing the capacitance and voltage fluctuation, but in the method, no constraint condition is added to the loop current, and the loop current cannot be ensured not to affect the input and output currents; the chinese patent CN107240922A obtains 9 active currents of the balanced bridge arm power by comparing the given value of the dc voltage of the 9 bridge arms of M3C with the mean value, but the sum of the 9 active currents obtained by proportional-integral control is not necessarily 0, and may flow into the input and output currents; in the text "high efficiency Energy Balance Control Method for M3C based on injected Output Frequency Circulating Currents" (author Ma Jiankai, etc.), a single Frequency Circulating current injection Control Method is proposed, which realizes the capacitor voltage Balance Control under the condition of unbalanced Power grid by Injecting the Circulating current of Output Frequency, but the injected Circulating current of Output Frequency will flow into the input side Power grid under the condition of unbalanced bridge arm transmission Power.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems and the defects in the prior art, the invention aims to provide a capacitance-voltage balance control method of a modular multilevel matrix converter, which not only realizes the capacitance-voltage balance of M3C under the condition of unbalanced bridge arm transmission power, but also ensures that injected circulating currents with two frequencies only flow in a bridge arm and do not influence the input current and the output current of M3C.
The technical scheme is as follows: the invention relates to a capacitance-voltage balance control method of a modular multilevel matrix converter M3C. In the method, the three-phase input and the three-phase output of the M3C are connected through 9 bridge arms, two ends of each bridge arm are respectively connected with one phase of the three-phase input and one phase of the three-phase output, the bridge arms have the same structure and are connected in series with a bridge arm inductor L and N sub-modules, and each sub-module comprises an H-bridge circuit formed by 4 Insulated Gate Bipolar Transistors (IGBTs) and 1 capacitor. The method comprises the following steps:
(S1) based on the capacitance voltage values of all sub-modules of the M3C and a total voltage reference value urefObtaining a reference value of an input current component in bridge arm current;
(S2) obtaining the active power reference value P of the output side according to the power demand of the output side of M3C*And a reactive power reference value Q*Based on P*And Q*Calculating to obtain a reference value of an output current component in the bridge arm current;
(S3) obtaining a reference value of a circulating current component in the bridge arm current based on the capacitance voltage values of all the sub-modules of the M3C;
(S4) calculating a bridge arm current reference value based on the reference values of the output current component, the input current component and the circulating current component in the bridge arm current obtained in the steps (S1) to (S3), and calculating a bridge arm voltage reference value based on the comparison result of the bridge arm current reference value and the actual bridge arm current value measured by the sensor;
(S5) carrying out carrier phase shift modulation on the bridge arm voltage reference value to obtain actual action switch signals of each submodule.
Further, the step (S1) specifically includes the steps of:
(S11) acquiring the capacitance voltage values of all the submodules of the M3C through a voltage sensor, and calculating the overall capacitance voltage u of the M3Cc-tThen the alternating current fluctuation is removed by a filter to obtain the filtered capacitance voltage UC；
(S12) adding UCAnd the total voltage reference u of M3CrefComparing, and obtaining a direct-axis current reference value i of the input current in the synchronous rotating coordinate system through a proportional-integral controller* d-iIn order to ensure the unit power factor, the input current is subjected to a quadrature axis current reference value i under a synchronous rotating coordinate system* q-iSet to 0;
(S13) determining the synchronous rotating seat of the input current component in the bridge arm current according to the formula (1)Coordinate transformation matrix T from standard system to three-phase static coordinate systemdq/abc_iBased on T according to formula (2)dq/abc_iAnd i obtained in step (S12)* d-iAnd i* q-iCalculating to obtain a current reference value i of the input current under a three-phase static coordinate system* xX is A, B and C are the labels of all phases in the three-phase input; wherein:
wherein, thetaiPhase angle of three-phase input voltage of M3C, equal to angular frequency w of input currentiThe product with time t;
(S14) symmetry according to the M3C, based on i* xCalculating to obtain the reference value of the input current component in the bridge arm current, namely 1/3 multiplied by i* x。
Further, in step (S2), based on P*And Q*Calculating to obtain a reference value of an output current component in the bridge arm current, and specifically comprising the following steps:
(S21) based on P according to formula (3)*And Q*Obtaining a direct axis reference value i of the output current under a synchronous rotating coordinate system* d_oAnd quadrature axis current reference value i* q_oWherein u isdThe three-phase output voltage of the M3C is converted into a direct-axis output voltage component under a synchronous rotating coordinate system; (ii) a
(S22) determining coordinate transformation matrix T from synchronous rotating coordinate system to three-phase static coordinate system of output current component in bridge arm current according to equation (4)dq/abc_oBased on T according to formula (5)dq/abc_oAnd i obtained in step (S21)* d_oAnd i* q_oCalculating to obtain a current reference value i of the output current under a three-phase static coordinate system* yAnd y is a, b and c are the labels of all phases in the three-phase output, wherein:
wherein, thetaoPhase angle of three-phase output voltage of M3C equal to angular frequency w of output currentoThe product with time t;
(S23) symmetry according to the M3C, based on i* yCalculating to obtain the reference value of the output current component in the bridge arm current, namely 1/3 multiplied by i* y。
Further, the step (S3) specifically includes the steps of:
(S31) acquiring the capacitance voltage values of all the submodules of the M3C through a voltage sensor, and calculating the bridge arm voltage value U of the M3CC_xyAnd average value of bridge arm voltage
x is the label of each phase in the three-phase input, and x is A, B, C, y is the label of each phase in the three-phase output, and y is a, B, C;
(S32) calculating the bridge arm voltage value UC_xyAnd average value of bridge arm voltage
Performing difference comparison to obtain voltage deviation signals delta Uc _ xy of 9 bridge arms;
(S33) selecting 8 signals from the 9 voltage deviation signals delta Uc _ xy obtained in the step (S32), and carrying out proportional integral control on the 8 voltage deviation signals to obtain the circulating current amplitude of the corresponding 8 bridge arms;
(S34) selecting 4 circulating current amplitudes from the circulating current amplitudes of the 8 bridge arms obtained in the step (S33), and multiplying the selected circulating current amplitudes by a unit sine wave cos (omega) which is in phase with the input side grid voltageit+α)，ωiObtaining the circulating current of the input frequency injected in the 4 bridge arms, wherein the angular frequency of the input voltage is alpha and the phase angle of the input voltage is alpha; multiplying the remaining 4 currents by a unit sine wave cos (ω) in phase with the output side grid voltageot+θ)，ωoThe angular frequency of the output voltage is obtained, and theta is the phase angle of the output voltage, so that the circulating current of the output frequency injected into the rest 4 bridge arms is obtained;
(S35) calculating reference values of circulating current components in the 9 arms of the M3C based on the circulating current of the output frequency in each arm, the circulating current of the input frequency in each arm, and the following constraint conditions,
wherein ixy_cir_iA circulating current component, i, representing the input frequency in the bridge arm corresponding to the x-phase input and the y-phase outputxy_cir_oA circulating current component representing the output frequency in each bridge arm; the reference value of the circulating current component in the bridge arm is denoted ixy_cirIs axy_cir_iAnd ixy_cir_oAnd (4) summing.
Further, the step (S4) specifically includes the steps of:
(S41) summing the reference value of the input current component in each bridge arm current, the reference value of the output current component in the bridge arm current and the reference value of the circulating current component in the bridge arm current to obtain the corresponding reference value of the bridge arm current, and marking the reference value as i* xyX is the label of each phase in the three-phase input, and x is A, B, C, y is the label of each phase in the three-phase output, and y is a, B, C;
(S42)reference value i of each bridge arm current* xyCorresponding to actual value i of bridge arm currentxyPerforming difference comparison, and obtaining the inductance voltage u of each bridge arm of M3C through the control of a proportional-integral controller1And then the bridge arm voltage reference value u is obtained through the feedforward control of the input voltage and the output voltage by the formula (8)* xyAnd passing through the bridge arm voltage reference value u* xyGenerating a signal for controlling the M3C submodule to be switched on and off;
u* xy＝ux-uy-u1 (8)
wherein u isxRepresents the input voltage of x phase in M3C, wherein x is A, B, C, uyAnd (c) the output voltage of the y phase in the M3C, wherein y is a, b and c.
Has the advantages that: compared with the prior art, the invention has the following advantages:
1. the structural advantage of M3C is fully utilized, and only one proportional-integral controller is needed to realize the overall capacitance-voltage balance control of M3C. Meanwhile, the adopted cyclic current control of injecting two frequencies into the bridge arm current only uses 8 proportional-integral controllers in total, and the capacitance-voltage balance between the M3C bridge arms is realized. Therefore, the control method provided by the invention is simple and is convenient to realize.
2. Under the condition that the transmission power in the M3C bridge arm is unbalanced, the control method provided by the invention not only realizes the capacitor voltage balance of M3C, but also can avoid the condition that the circulating current injected in the bridge arm flows into the input and output currents of M3C, and ensures the harmonic characteristics of the input and output currents of the converter.
Drawings
FIG. 1 is a block diagram of a modular multilevel matrix converter topology;
FIG. 2 is a schematic diagram of two frequency cyclic current injection controls;
FIG. 3 is a schematic diagram of bridge arm circulating current;
FIG. 4 is an overall control block diagram of a modular multilevel matrix converter;
FIGS. 5(a) and 5(b) are respectively a waveform diagram of capacitance voltage of each arm and a harmonic analysis diagram of input current obtained by using a Control Method of "high Energy Balance Control Method for M3C based on input Frequency circuits" published in IEEE Transactions on Power Electronics;
FIG. 6(a) is the voltage waveform of each bridge arm capacitance; fig. 6(b) is a harmonic analysis diagram of the input current.
Detailed Description
The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.
The invention is mainly used for the capacitance-voltage balance control of M3C and has wide application in the fields of variable frequency speed regulation, offshore wind power high-voltage low-frequency grid connection, power electronic transformers and the like. FIG. 1 shows the topology of M3C, where the input side of M3C is connected to a 50/3Hz offshore low frequency wind power plant, with voltage and current respectively ux、ixAnd (x ═ a, B, and C are reference numerals of the respective phases on the input side). The output side of M3C is connected with the shore power grid, and the output voltage current is uy、iyAnd (y is a, b, and c are reference numerals of the respective phases on the output side). Inductors, respectively designated as L, are connected in series on the input side and the output side of M3CiAnd Lo. The three-phase input and the three-phase output of M3C are connected through 9 bridge arms (bridge arms Aa, Ba, Ca, Ab, Bb, Cb, Ac, Bc and Cc), the structure of each bridge arm is the same, and bridge arm inductors L and N sub-modules are connected in series. Each submodule comprises 4 Insulated Gate Bipolar Transistors (IGBTs) and 1 capacitor, each two IGBTs are connected end to form 1 bridge arm in the submodule, the 4 IGBTs correspond to the two bridge arms, and the capacitors are connected in parallel behind the two bridge arms to form an H-bridge circuit.
Fig. 4 shows a control block diagram of the method of the present invention. In the block diagram, the total capacitance voltage balance control, the output current control, the current closed loop control and the input voltage and output voltage feedforward control of M3C are respectively shown in four dashed boxes.
The reference value of the input current component in the bridge arm current can be solved through the total capacitance voltage balance control. In the control of the total capacitance-voltage balance, the following sub-steps are mainly included:
(S11) acquiring the capacitance voltage values of all the sub-modules of the M3C through a voltage sensor, and calculating the overall capacitance voltage u of the M3Cc-tRemoving AC fluctuation by filter to obtain capacitor voltage UC。
(S12) adding UCAnd the total voltage reference u of M3CrefComparing, and obtaining a direct-axis current reference value i of the input current under the synchronous rotating coordinate system through the control of a proportional-integral controller* d-iIn order to ensure the unit power factor, the input current is subjected to a quadrature axis current reference value i under a synchronous rotating coordinate system* q-iIs set to 0.
(S13) determining a coordinate transformation matrix T from a synchronous rotating coordinate system to a three-phase stationary coordinate system of the input current component in the bridge arm current according to equation (1)dq/abc_iBased on T according to formula (2)dq/abc_iAnd i obtained in step (S12)* d-iAnd i* q-iCalculating to obtain a current reference value i of the input current under a three-phase static coordinate system* xX is A, B and C are the labels of all phases in the three-phase input; wherein:
wherein, thetaiPhase angle of three-phase input voltage of M3C, equal to angular frequency w of input currentiThe product with time t.
(S14) symmetry according to the M3C, based on i* xCalculating to obtain the reference value of the input current component in the bridge arm current, namely 1/3 multiplied by i* x. The output electricity in the bridge arm current can be obtained through the control of the output currentReference values of the stream components. In the output current control, the following sub-steps are mainly included:
(S21) based on P according to formula (3)*And Q*Obtaining a direct axis reference value i of the output current under a synchronous rotating coordinate system* d_oAnd quadrature axis current reference value i* q_oWherein u isdThe three-phase output voltage of the M3C is converted into a direct-axis output voltage component under a synchronous rotating coordinate system;
(S22) determining a coordinate transformation matrix T from a synchronous rotating coordinate system to a three-phase stationary coordinate system of the output current according to equation (4)dq/abc_oBased on T according to formula (5)dq/abc_oAnd i obtained in step (S21)* d_oAnd i* q_oCalculating to obtain a current reference value i of the output current under a three-phase static coordinate system* yAnd y is a, b and c are the labels of all phases in the three-phase output, wherein:
wherein, thetaoPhase angle of three output voltages of M3C, equal to angular frequency w of output currentoThe product with time t;
(S23) symmetry according to the M3C, based on i* yCalculating to obtain the reference value of the output current component in the bridge arm current, namely 1/3 multiplied by i* y。
And the reference value of the circulating current component in the bridge arm current can be solved through current closed-loop control. The solving process is to inject circulating currents with two frequencies, namely an input current frequency and an output current frequency, into the bridge arm current of M3C, and it is required to ensure that the injected circulating currents only flow in the bridge arm under any condition, and the input current and the output current of M3C are not affected, that is, the following constraint conditions are required to be satisfied:
wherein ixy_cir_iComponent of circulating current representing input frequency in each arm, ixy_cir_oA circulating current component representing the output frequency in each bridge arm; the reference value of the circulating current component in the bridge arm is denoted ixy_cirIs axy_cir_iAnd ixy_cir_oAnd (4) summing.
According to this constraint, a control diagram of the injected cyclic current of two frequencies is given in fig. 2.
In fig. 2, the black stars indicate that the circulating current injected into the bridge arm is determined by the voltage feedback control of the bridge arm, and the white stars correspond to the bridge arm indicating that the circulating current injected into the bridge arm is calculated by the above constraint conditions. In order to fully utilize the degree of freedom of control, the circulating currents of two different frequencies of the same bridge arm are prevented from being calculated by voltage feedback control. Fig. 2 shows a possible cyclic current injection situation, in which the arms Aa and Ab select the cyclic current with the frequency of the injected output current, in order to ensure that the cyclic current component with the output frequency in the three arms Aa, Ab and Ac does not flow into the input current iAIn this case, the circulating current of the output frequency of the arm Ac cannot be obtained by the voltage feedback control, and can be calculated only by the equation (6). Similarly, the calculation method of the circulating currents of the other bridge arms in fig. 2 can be deduced. Further, in the method of injecting a circulating current shown in fig. 2, the circulating currents of two frequencies, i.e., the input current frequency and the output current frequency, injected in the arm Cb are calculated by the equations (6) and (7) due to the limitation of the degree of freedom of controlThis also indicates that the energy balance of bridge arm Cb needs to be achieved by the total capacitance-voltage balance control of M3C.
Fig. 3 gives a schematic diagram of the bridge arm circulating current. Comparing the difference between the capacitor voltages of the bridge arms Aa, Ab, Ba and Cc and the average value of the capacitor voltages of the bridge arms, multiplying the difference by the output frequency and phase angle of the phase a, the phase b, the phase a and the phase c on the output side after proportional-integral control, thereby obtaining the circulating current components of the output frequency in the four bridge arms, and respectively marking the circulating current components as iAa_cir_o，iAb_cir_o，iBa_cir_oAnd iCc_cir_oAnd the circulating current components of the output frequencies of the other five bridge arms are calculated by the formula (7). Similarly, the difference between the capacitance voltages of the bridge arms Ac, Bb, Bc and Ca and the average value of the capacitance voltages of the bridge arms is compared, and the difference is multiplied by the output frequencies and the phase angles of the phase A, the phase B and the phase C on the input side respectively after proportional-integral control, so that the circulating current components of the output frequencies of the four bridge arms are obtained and respectively marked as iAc_cir_i，iBb_cir_i，iBc_cir_iAnd iCa_cir_iThe circulating current components of the output frequencies of the remaining five bridge arms need to be calculated by equation (6). After the circulating current component of the output frequency and the circulating current component of the input frequency in the bridge arm current are obtained, the two circulating current components are superposed, and finally the circulating current component i injected into each bridge arm can be calculatedxy_cir。
According to the calculated input current component reference value, output current component reference value and circulating current component reference value, the reference value of bridge arm current can be calculated, then compared with bridge arm current actually measured by current sensor, and through proportional integral control and feedforward control of input and output voltage, the reference value u of bridge arm voltage can be calculated* xy. The method specifically comprises the following substeps:
(S41) summing the reference value of the input current component in each bridge arm current, the reference value of the output current component in the bridge arm current and the reference value of the circulating current component in the bridge arm current to obtain the corresponding reference value of the bridge arm current, and marking the reference value as i* xyX is the label of each phase in the three-phase input and x is equal to A,b, C, y are the labels of the phases in the three-phase output and y is a, B, C;
(S42) referring each bridge arm current to the value i* xyCorresponding to actual value i of bridge arm currentxyPerforming difference comparison, and obtaining the inductance voltage u of each bridge arm of M3C through the control of a proportional-integral controller1And then the bridge arm voltage reference value u is obtained through the feedforward control of the input voltage and the output voltage by the formula (8)* xyAnd passing through the bridge arm voltage reference value u* xyGenerating a signal for controlling the M3C submodule to be switched on and off;
u* xy＝ux-uy-u1 (8)
wherein u isxRepresents the input voltage of x phase in M3C, wherein x is A, B, C, uyAnd (c) the output voltage of the y phase in the M3C, wherein y is a, b and c. Obtaining a bridge arm voltage reference value u* xyThen, the voltage reference value is compared with the carrier wave, so that a signal for controlling the M3C sub-module to be switched on and off can be obtained.
FIG. 5 is a waveform diagram obtained by using the Control Method of "high Energy Balance Control Method for M3C base on Injecting Output Frequency Circulating Currents" published in IEEE Transactions on Power Electronics, wherein at 1s, the Power transmitted by the bridge arm Aa of the converter is reduced to 0, and as can be seen from FIG. 5(a), the capacitance and voltage of the bridge arm can tend to be balanced; as can be seen from fig. 5(b), the injection of the circulating current by this method has an effect on the input current.
Fig. 6 is a waveform diagram obtained by the control method of the present invention, and at 1s, the power transmitted by the bridge arm Aa of the converter is reduced to 0, and as can be seen from fig. 6(a), the capacitance and voltage of the bridge arm can tend to be balanced; as can be seen from fig. 6(b), the input current harmonic characteristics of M3C are good.
Claims (4)
1. A capacitor voltage balance control method of a modular multilevel matrix converter M3C is characterized in that a three-phase input and a three-phase output of M3C are connected through 9 bridge arms, two ends of each bridge arm are respectively connected with one phase of the three-phase input and one phase of the three-phase output, each bridge arm has the same structure and is connected with a bridge arm inductor L and N sub-modules in series, each sub-module comprises 4 Insulated Gate Bipolar Transistors (IGBTs) and 1 capacitor, each two IGBTs are connected end to form 1 bridge arm in a sub-module, each 4 IGBT corresponds to two bridge arms, and the capacitors are connected in parallel behind the two bridge arms to form an H-bridge circuit; characterized in that the method comprises the following steps:
(S1) based on the capacitance voltage values of all sub-modules of the M3C and a total voltage reference value urefObtaining a reference value of an input current component in bridge arm current;
(S2) obtaining the active power reference value P of the output side according to the power demand of the output side of M3C*And a reactive power reference value Q*Based on P*And Q*Calculating to obtain a reference value of an output current component in the bridge arm current;
(S3) obtaining a reference value of a circulating current component in the bridge arm current based on the capacitance voltage values of all the sub-modules of the M3C;
(S4) calculating a bridge arm current reference value based on the reference values of the output current component, the input current component and the circulating current component in the bridge arm current obtained in the steps (S1) to (S3), and calculating a bridge arm voltage reference value based on the comparison result of the bridge arm current reference value and the actual bridge arm current value measured by the sensor;
(S5) carrying out carrier phase shift modulation on the bridge arm voltage reference value to obtain actual action switch signals of each submodule;
the step (S3) specifically includes the steps of:
(S31) acquiring the capacitance voltage values of all the submodules of the M3C through a voltage sensor, and calculating the bridge arm voltage value U of the M3CC_xyAnd average value of bridge arm voltage
x is the label of each phase in the three-phase input, and x is A, B, C, y is the label of each phase in the three-phase output, and y is a, B, C;
(S32) calculating the bridge arm voltage value UC_xyAnd average value of bridge arm voltage
Performing difference comparison to obtain voltage deviation signals delta Uc _ xy of 9 bridge arms;
(S33) selecting 8 signals from the 9 voltage deviation signals delta Uc _ xy obtained in the step (S32), and carrying out proportional integral control on the 8 voltage deviation signals to obtain the circulating current amplitude of the corresponding 8 bridge arms;
(S34) selecting 4 circulating current amplitudes from the circulating current amplitudes of the 8 bridge arms obtained in the step (S33), and multiplying the selected circulating current amplitudes by a unit sine wave cos (omega) which is in phase with the input side grid voltageit+α)，ωiObtaining the circulating current of the input frequency injected in the 4 bridge arms, wherein the angular frequency of the input voltage is alpha and the phase angle of the input voltage is alpha; multiplying the remaining 4 currents by a unit sine wave cos (ω) in phase with the output side grid voltageot+θ)，ωoThe angular frequency of the output voltage is obtained, and theta is the phase angle of the output voltage, so that the circulating current of the output frequency injected into the rest 4 bridge arms is obtained;
(S35) calculating reference values of circulating current components in the 9 arms of the M3C based on the circulating current of the output frequency in each arm, the circulating current of the input frequency in each arm, and the following constraint conditions,
wherein ixy_cir_iComponent of circulating current representing input frequency in each arm, ixy_cir_oA circulating current component representing the output frequency in each bridge arm; the reference value of the circulating current component in the bridge arm is denoted ixy_cirIs axy_cir_iAnd ixy_cir_oAnd (4) summing.
2. The method for controlling the capacitive voltage balance of the modular multilevel matrix converter M3C of claim 1, wherein the step (S1) comprises the steps of:
(S11) acquiring the capacitance voltage values of all the submodules of the M3C through a voltage sensor, and calculating the overall capacitance voltage u of the M3Cc-tThen the alternating current fluctuation is removed by a filter to obtain the filtered capacitance voltage UC；
(S12) adding UCAnd the total voltage reference u of M3CrefComparing, and obtaining a direct-axis current reference value i of the input current under the synchronous rotating coordinate system through the control of a proportional-integral controller* d-iIn order to ensure the unit power factor, the input current is subjected to a quadrature axis current reference value i under a synchronous rotating coordinate system* q-iSet to 0;
(S13) determining a coordinate transformation matrix T from a synchronous rotating coordinate system to a three-phase stationary coordinate system of the input current component in the bridge arm current according to equation (1)dq/abc_iBased on T according to formula (2)dq/abc_iAnd i obtained in step (S12)* d-iAnd i* q-iCalculating to obtain a current reference value i of the input current under a three-phase static coordinate system* xX is A, B and C are the labels of all phases in the three-phase input; wherein:
wherein, thetaiPhase angle of three-phase input voltage of M3C, equal to angular frequency w of input currentiThe product with time t;
(S14) symmetry according to the M3C, based on i* xCalculating to obtain the reference value of the input current component in the bridge arm current, namely 1/3 multiplied by i* x。
3. The method for controlling the capacitive voltage balance of the modular multilevel matrix converter M3C of claim 1, wherein the step (S2) is based on P*And Q*Calculating to obtain a reference value of an output current component in the bridge arm current, and specifically comprising the following steps:
(S21) based on P according to formula (3)*And Q*Obtaining a direct axis reference value i of the output current under a synchronous rotating coordinate system* d_oAnd quadrature axis current reference value i* q_oWherein u isdThe three-phase output voltage of the M3C is converted into a direct-axis output voltage component under a synchronous rotating coordinate system;
(S22) determining coordinate transformation matrix T from synchronous rotating coordinate system to three-phase static coordinate system of output current component in bridge arm current according to equation (4)dq/abc_oBased on T according to formula (5)dq/abc_oAnd i obtained in step (S21)* d_oAnd i* q_oCalculating to obtain a current reference value i of the output current under a three-phase static coordinate system* yAnd y is a, b and c are the labels of all phases in the three-phase output, wherein:
wherein, thetaoPhase angle of three-phase output voltage of M3C equal to angular frequency w of output currentoThe product with time t;
(S23) symmetry according to the M3C, based on i* yCalculating to obtain the reference value of the output current component in the bridge arm current,i.e. 1/3 xi* y。
4. The method for controlling the capacitive voltage balance of the modular multilevel matrix converter M3C of claim 1, wherein the step (S4) comprises the steps of:
(S41) summing the reference value of the input current component in each bridge arm current, the reference value of the output current component in the bridge arm current and the reference value of the circulating current component in the bridge arm current to obtain the corresponding reference value of the bridge arm current, and marking the reference value as i* xyX is the label of each phase in the three-phase input, and x is A, B, C, y is the label of each phase in the three-phase output, and y is a, B, C;
(S42) referring each bridge arm current to the value i* xyCorresponding to actual value i of bridge arm currentxyPerforming difference comparison, and obtaining the inductance voltage u of each bridge arm of the M3C through the control of a proportional-integral controller1And then the bridge arm voltage reference value u is obtained according to the formula (8) through the feedforward control of the input voltage and the output voltage* xyAnd passing through the bridge arm voltage reference value u* xyGenerating a signal for controlling the M3C submodule to be switched on and off;
u* xy＝ux-uy-u1 (8)
wherein u isxRepresents the input voltage of x phase in M3C, wherein x is A, B, C, uyAnd (c) the output voltage of the y phase in the M3C, wherein y is a, b and c.
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