CN112332742A - Motor current transformation control system and control method thereof - Google Patents

Motor current transformation control system and control method thereof Download PDF

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Publication number
CN112332742A
CN112332742A CN202011079474.1A CN202011079474A CN112332742A CN 112332742 A CN112332742 A CN 112332742A CN 202011079474 A CN202011079474 A CN 202011079474A CN 112332742 A CN112332742 A CN 112332742A
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phase
modulation
voltage
value
circulating current
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Inventor
李贤隆
胡海琪
金德武
杨思城
王浩
杨波
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Gree Electric Appliances Inc of Zhuhai
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Gree Electric Appliances Inc of Zhuhai
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H02P27/085—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency
    • 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
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • 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
    • H02M7/487—Neutral point clamped inverters
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention relates to a motor variable flow control system and a control method thereof, wherein the control method comprises the following steps: in the low-frequency operation stage, based on the energy modulation principle and the zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation of voltage signals of upper and lower bridge arms of each phase of the MMC circuit. In addition, each bridge arm of the hardware topology of the system adopts a mode of adding an additional expansion module to a basic module, the mode can expand the modulation range, the control of the circulating current in the interval of the clamping phase arm is ensured, the signal overmodulation condition in the clamping period is prevented, and the system stability is good.

Description

Motor current transformation control system and control method thereof
Technical Field
The invention relates to the technical field of motor control, in particular to a motor variable flow control system and a control method thereof.
Background
With the development of power electronics and new energy technologies, Modular Multilevel Converter (MMC) technology has drawn more and more attention with its characteristics of flexible output, suitability for high-power loads, and the like. MMC technology has been applied to HVDC (high-voltage direct current) and power converters, but there has been little research and application related to motor control and permanent magnet synchronous motor driving.
The traditional multilevel modulation technology has great requirements on power devices and energy consumption, which is caused by adopting different modulation modes for the power devices and controlling the capacitance and voltage of the modules in order to meet the requirement of energy source transmission balance among module bridge arms.
The prior art discloses a four-quadrant frequency converter of a modular multilevel converter, which aims to solve the problems that the capacitance and voltage fluctuation exists when an MMC operates at a low frequency, and a high-frequency injection method can bring larger current impact and the like. However, the method is more suitable for high-voltage high-power electric energy conversion occasions, and the hardware topology adopts full-bridge rectification and is higher in cost. Meanwhile, the low frequency runs at 5Hz and 50Hz, and the transient change in the variable frequency regulation process cannot be reflected without establishing a control loop.
In addition, another random space vector pulse width modulation method based on carrier phase shift is adopted in the prior art to equivalently increase the switching frequency of the parallel inverter, average the switching subharmonic energy in a narrow frequency band and improve the output harmonic performance. However, the scheme does not improve the voltage ripple of the module capacitor, the energy consumption in the low frequency band is not compared with that in the high frequency band, the current transformation unit is of a multi-parallel inversion structure, and the energy consumption of the external multi-group balance reactor is large, so that the energy control effect cannot be judged.
In addition, the prior art also discloses a full speed range motor drive based on MMC, which is suitable for low-speed operation, has good starting performance and wide speed regulation range, but the driving mode only considers direct-current side voltage inversion and mainly acts as an induction motor. The modulation mode is VF, a continuous sinusoidal signal is basically adopted, and the energy consumption of the converter is large.
Disclosure of Invention
In view of the above, the present invention provides a motor converter control system and a control method thereof, so as to solve the problem of high energy consumption of a converter or a converter unit in the prior art.
According to a first aspect of the embodiments of the present invention, there is provided a motor variable flow control system, including:
the MMC circuit is connected with a controlled load motor and comprises three-phase cascade inversion modules, and each phase of upper and lower bridge arms respectively comprise a first number of basic modules and a second number of additional expansion modules which are sequentially cascaded;
a controller, connected to the MMC circuit, for:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit.
Preferably, the controller is further configured to:
and in the middle-high frequency operation stage, based on the MMC circuit, an SPWM modulation control mode is adopted to output PWM modulation signals for the controlled load motor.
Preferably, the basic module and the additional expansion module have the same structure, and each basic module and the additional expansion module comprise two series-connected IGBT modules and an electrolytic capacitor connected in parallel with the series-connected IGBT modules.
According to a first aspect of the embodiments of the present invention, there is provided a control method of a variable current control system of a motor, including:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit;
the MMC circuit comprises three-phase cascade inversion modules, wherein the upper bridge arm and the lower bridge arm of each phase respectively comprise a first number of basic modules and a second number of additional expansion modules which are cascaded in sequence.
Preferably, the method further comprises:
and in the middle-high frequency operation stage, based on the MMC circuit, an SPWM modulation control mode is adopted to output PWM modulation signals for the controlled load motor.
Preferably, the discontinuous modulation control method includes:
obtaining a per unit value of three-phase voltage of a controlled load motor based on a PMSM vector control technology;
obtaining a per unit value after the three-phase voltage differential transformation through energy modulation based on an energy modulation principle; obtaining voltage reference signals of upper and lower bridge arms of each phase of the MMC circuit according to the per-unit values of the three-phase voltage and the per-unit values after differential conversion of the three-phase voltage;
and injecting zero-sequence components into the voltage reference signals in a segmented manner according to the operating frequency and the operating period of the controlled load motor to obtain discontinuous modulation signals of upper and lower bridge arms of each phase of the MMC circuit.
Preferably, the method further comprises:
and taking the discontinuous modulation signal as a feedback quantity to participate in energy modulation.
Preferably, the obtaining a per unit value after the energy-modulated three-phase voltage differential transformation based on the energy modulation principle includes:
calculating a reference value of the interphase circulating current of the MMC circuit according to the per-unit value of the three-phase voltage and the three-phase sampling current of the controlled load motor;
calculating an adjustment value of the interphase circulating current based on an energy modulation principle;
calculating a circulating current error of the interphase circulating current according to the reference value, the adjustment value and the actual value of the interphase circulating current;
and inputting the circulating current error into a PI controller to obtain a per unit value after the three-phase voltage differential conversion through energy modulation.
Preferably, the calculating the adjustment value of the interphase circulating current based on the energy modulation principle includes:
calculating the capacitance voltage of upper and lower bridge arms of each phase of the MMC circuit according to the discontinuous modulation signal;
according to the capacitance voltage, calculating theoretical power values of upper and lower bridge arms of each phase of the MMC circuit;
calculating the difference value between the theoretical power value and each actual power value to obtain a power modulation signal to be modulated;
inputting the power modulation signal to a PI controller to obtain a reference current to be modulated;
and obtaining an adjustment value of the energy-modulated interphase circulating current according to the reference current and the per unit value of the three-phase voltage.
Preferably, the calculating a circulating current error of the interphase circulating current specifically includes:
and summing the reference value and the adjustment value of the interphase circulating current, and then subtracting the actual value to obtain the circulating current error of the interphase circulating current.
Preferably, the obtaining of the voltage reference signal of the upper and lower bridge arms of each phase of the MMC circuit according to the per unit value of the three-phase voltage and the per unit value after the differential conversion of the three-phase voltage specifically includes:
summing the per-unit value of each phase voltage with the per-unit value after the differential conversion of the three-phase voltage to obtain a voltage reference signal of an upper bridge arm of each phase of the MMC circuit;
and (4) making a difference between the per unit value of each phase voltage and the per unit value after the differential conversion of the three-phase voltage to obtain a voltage reference signal of the lower bridge arm of each phase of the MMC circuit.
The technical scheme provided by the embodiment of the invention can have the following beneficial effects:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation of voltage signals of upper and lower bridge arms of each phase of the MMC circuit, so that the conversion efficiency of the converter in the prior art is improved, the energy consumption of the converter is reduced, the capacitor voltage ripple of a module of the motor in the low-frequency operation is reduced, and the harmonic content of output current is reduced.
In addition, each bridge arm of the hardware topology of the system adopts a mode of adding an additional expansion module to a basic module, the mode can expand the modulation range, the control of the circulating current in the interval of the clamping phase arm is ensured, the signal overmodulation condition in the clamping period is prevented, and the system stability is good.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
Fig. 1 is a schematic diagram of a hardware architecture of a variable flow control system of an electric machine according to an exemplary embodiment;
FIG. 2 is an equivalent circuit schematic of FIG. 1;
FIG. 3 is a flow chart illustrating a method of controlling a variable flow control system of an electric machine in accordance with an exemplary embodiment;
FIG. 4 is a schematic diagram of an algorithm employing a discontinuous modulation control scheme in accordance with an exemplary embodiment;
FIG. 5 is a schematic diagram illustrating energy modulation according to an exemplary embodiment;
FIG. 6 is a graph illustrating a comparison of waveforms of a single-cycle zero-sequence component injection signal, a sinusoidal reference signal, and a discontinuous modulation signal in accordance with an exemplary embodiment;
fig. 7 is a schematic diagram illustrating upper and lower bridge arm clamp current flow paths of an MMC circuit according to an example embodiment.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.
Fig. 1 is a schematic diagram of a hardware structure of a variable flow control system of a motor according to an exemplary embodiment, where the system includes:
the MMC circuit is connected with a controlled load motor and comprises three-phase cascade inversion modules, and each phase of upper and lower bridge arms respectively comprise a first number of basic modules and a second number of additional expansion modules which are sequentially cascaded;
a controller (not shown in the figures) connected to the MMC circuit for:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit.
It should be noted that the first number and the second number may be equal or may not be equal.
Preferably, the first number > the second number.
It can be understood that, in the technical scheme provided in this embodiment, at the low-frequency operation stage, based on the energy modulation principle and the zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit, so that the conversion efficiency of the converter in the prior art is improved, the energy consumption of the converter is reduced, the capacitor voltage ripple of the module is reduced when the motor operates at low frequency, and the harmonic content of the output current is reduced.
In addition, each bridge arm of the hardware topology of the system adopts a mode of adding an additional expansion module to a basic module, the mode can expand the modulation range, the control of the circulating current in the interval of the clamping phase arm is ensured, the signal overmodulation condition in the clamping period is prevented, and the system stability is good.
Preferably, the controller is further configured to:
and in the middle-high frequency operation stage, based on the MMC circuit, an SPWM modulation control mode is adopted to output PWM modulation signals for the controlled load motor.
It should be noted that the PWM is called Pulse Width Modulation, which is to change the equivalent output voltage by changing the duty ratio of the output square wave.
The SPWM is named as Sinusoidal Pulse Width Modulation, and has changed Pulse Modulation mode based on PWM and Pulse Width time duty ratio arranged in sine mode, so that the output waveform may be sine wave output through proper filtering. The three-phase SPWM is used for simulating three-phase output of commercial power and is widely adopted in the field of frequency converters.
The low-frequency operation stage means that F is less than 30 Hz;
the medium-high frequency operation stage means that F is more than or equal to 30 Hz.
It can be understood that, in the technical scheme provided by this embodiment, in the low-frequency operation stage, based on the MMC circuit, a discontinuous modulation control mode is adopted to output a PWM modulation signal to the controlled load motor; in the middle-high frequency operation stage, based on the MMC circuit, the SPWM modulation control mode is adopted, PWM modulation signals are output for the controlled load motor, and the energy consumption requirements of the motor under different frequency operation conditions are met by adopting different modulation technologies in the low frequency band and the middle-high frequency band respectively.
Preferably, the basic module and the additional expansion module have the same structure, and each basic module and the additional expansion module comprise two series-connected IGBT modules and an electrolytic capacitor connected in parallel with the series-connected IGBT modules.
Referring to fig. 1, each phase of the upper and lower bridge arms of the MMC circuit is respectively composed of N (N is greater than or equal to 1) basic modules and M (M is greater than or equal to 1, N is greater than M) additional expansion modules, each inversion module adopts a half-bridge topology structure with 2 IGBTs cascaded, and the expansion modules can prevent signal overmodulation.
Firstly, a single-phase Alternating Current (AC) power supply outputs two equivalent voltage variables on a secondary side through the action of winding inductance, and then forms a direct current power supply V through the action of a boost rectification SM module (Signal module)dcAnd a direct current bus voltage is formed. Wherein each boost rectification SM module outputs equivalent voltage
Figure BDA0002718175680000071
Are connected in series to form a direct current power supply Vdc。
The equivalent circuit of fig. 1 is shown in fig. 2. The direct current bus voltage signal is output through a three-phase cascade inversion module, the upper and lower bridge arms of each phase are formed by cascading N + M sub-modules, wherein each sub-module has the same structure, and as shown by a dotted frame in fig. 2, a structure that 2 IGBTs are connected in series and then connected in parallel with a large electrolytic capacitor is adopted. And the three-phase voltage output by the MMC circuit acts on the stator side of the controlled load motor and is used for controlling the UVW three-phase voltage signal.
A method of controlling a variable flow control system of an electric machine is shown according to an exemplary embodiment, the method comprising:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit;
the MMC circuit comprises three-phase cascade inversion modules, wherein the upper bridge arm and the lower bridge arm of each phase respectively comprise a first number of basic modules and a second number of additional expansion modules which are cascaded in sequence.
It should be noted that the first number and the second number may be equal or may not be equal.
Preferably, the first number > the second number.
Preferably, the basic module and the additional expansion module have the same structure, and each basic module and the additional expansion module comprise two series-connected IGBT modules and an electrolytic capacitor connected in parallel with the series-connected IGBT modules.
It can be understood that, in the technical scheme provided in this embodiment, at the low-frequency operation stage, based on the energy modulation principle and the zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit, so that the conversion efficiency of the converter in the prior art is improved, the energy consumption of the converter is reduced, the capacitor voltage ripple of the module is reduced when the motor operates at low frequency, and the harmonic content of the output current is reduced.
In addition, each bridge arm of the hardware topology of the system adopts a mode of adding an additional expansion module to a basic module, the mode can expand the modulation range, the control of the circulating current in the interval of the clamping phase arm is ensured, the signal overmodulation condition in the clamping period is prevented, and the system stability is good.
Fig. 3 is a flow chart illustrating a method of controlling a variable flow control system of an electric machine, according to another exemplary embodiment, as shown in fig. 3, the method comprising:
step S1, in the low-frequency operation stage, based on the energy modulation principle and the zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation of the upper and lower bridge arm voltage signals of each phase of the MMC circuit;
step S2, in the middle-high frequency operation stage, based on the MMC circuit, adopting the SPWM modulation control mode to output PWM modulation signals for the controlled load motor;
the MMC circuit comprises three-phase cascade inversion modules, wherein the upper bridge arm and the lower bridge arm of each phase respectively comprise a first number of basic modules and a second number of additional expansion modules which are cascaded in sequence.
It should be noted that the first number and the second number may be equal or may not be equal.
Preferably, the first number > the second number.
Preferably, the basic module and the additional expansion module have the same structure, and each basic module and the additional expansion module comprise two series-connected IGBT modules and an electrolytic capacitor connected in parallel with the series-connected IGBT modules.
The hardware structure diagram of the motor variable flow control system is shown in fig. 1.
Referring to fig. 1, each phase of the upper and lower bridge arms of the MMC circuit is respectively composed of N (N is greater than or equal to 1) basic modules and M (M is greater than or equal to 1, N is greater than M) additional expansion modules, each inversion module adopts a half-bridge topology structure with 2 IGBTs cascaded, and the expansion modules can prevent signal overmodulation.
It can be understood that, in the technical scheme provided by this embodiment, in the low-frequency operation stage, based on the MMC circuit, a discontinuous modulation control mode is adopted to output a PWM modulation signal to the controlled load motor; in the middle-high frequency operation stage, based on the MMC circuit, the SPWM modulation control mode is adopted, PWM modulation signals are output for the controlled load motor, and the energy consumption requirements of the motor under different frequency operation conditions are met by adopting different modulation technologies in the low frequency band and the middle-high frequency band respectively.
In addition, each bridge arm of the hardware topology of the system adopts a mode of adding an additional expansion module to a basic module, the mode can expand the modulation range, the control of the circulating current in the interval of the clamping phase arm is ensured, the signal overmodulation condition in the clamping period is prevented, and the system stability is good.
Preferably, the step S1 includes:
step S11, obtaining per unit values of three-phase voltages of the controlled load motor based on a PMSM vector control technology;
step S12, obtaining per unit values after the three-phase voltage differential transformation through energy modulation based on the energy modulation principle;
step S13, obtaining voltage reference signals of upper and lower bridge arms of each phase of the MMC circuit according to the per-unit values of the three-phase voltage and the per-unit values after differential conversion of the three-phase voltage;
and step S14, according to the operation frequency and the operation period of the controlled load motor, injecting zero sequence components into the voltage reference signal in a segmented manner to obtain discontinuous modulation signals of upper and lower bridge arms of each phase of the MMC circuit.
Referring to fig. 1, firstly, a single-phase AC power supply outputs two equivalent voltage variables on the secondary side through the action of winding inductance, and then forms a dc power supply V through the action of a boost rectification SM module (Signal module)dcAnd a direct current bus voltage is formed. Wherein each boost rectification SM module outputs equivalent voltage
Figure BDA0002718175680000091
Are connected in series to form a direct current power supply Vdc。
The equivalent circuit of fig. 1 is shown in fig. 2. The direct current bus voltage signal is output through a three-phase cascade inversion module, the upper and lower bridge arms of each phase are formed by cascading N + M sub-modules, wherein each sub-module has the same structure, and as shown by a dotted frame in fig. 2, a structure that 2 IGBTs are connected in series and then connected in parallel with a large electrolytic capacitor is adopted. And the three-phase voltage output by the MMC circuit acts on the stator side of the controlled load motor and is used for controlling the UVW three-phase voltage signal.
The step S1, the schematic diagram of the algorithm using the discontinuous modulation control mode is shown in fig. 4, and includes:
step S11, obtaining per unit values of three-phase voltages of the controlled load motor based on a PMSM vector synchronous motor (permanent magnet synchronous motor) control technology, specifically:
acquiring working parameters of a controlled load motor through a detection module (not shown in the attached drawings), wherein the working parameters comprise: rotating speed, angle and three-phase current sampling values of the stator;
inputting the working parameters serving as input variables into a PMSM vector control module for processing to obtain per unit values v acting on three-phase voltagesUm，vVm，vWm(ii) a Wherein the content of the first and second substances,
Figure BDA0002718175680000101
i.e. by
Figure BDA0002718175680000102
Figure BDA0002718175680000103
vjm∈[-1,1]。
Due to per unit value v of three-phase voltageUm，vVm，vWmThe calculation belongs to the prior art, and the detailed description of the specific calculation steps is omitted here, which is briefly summarized as follows:
vector control of controlled load motor is based on magnetic field orientation control of stator and rotor, and three-phase sampling current i is measured and calculatedU iV iWAnd three-phase voltage vU vV vWObtaining the component of dq quadrant through Clark and park transformation, coupling the direct current component of torque and rotation speed control with the dq coordinate system to form the modulated current and voltage component of dq quadrant, forming the voltage and current modulation component of abc three-phase through park and Clark inverse transformation, and finally performing per unit treatment to obtain the per unit value v of the three-phase voltageUm，vVm，vWm。
Step S12, obtaining a per unit value after the energy-modulated three-phase voltage differential transformation based on the energy modulation principle, including:
step S121, calculating a reference value of the interphase circulating current of the MMC circuit according to the per unit value of the three-phase voltage and the three-phase sampling current of the controlled load motor;
step S122, calculating an adjustment value of the interphase circulating current based on an energy modulation principle;
step S123, calculating a circulation error of the interphase circulation according to the reference value, the adjustment value and the actual value of the interphase circulation;
and S124, inputting the circulating current error into a PI controller to obtain a per unit value after the energy-modulated three-phase voltage differential conversion.
Wherein, the step S121 specifically includes:
referring to fig. 2, in an ideal state, a reference value of the interphase circulating current of the MMC circuit
Figure BDA0002718175680000111
Wherein the upper bridge arm circulation and the lower bridge arm circulation are respectively as follows:
Figure BDA0002718175680000112
Figure BDA0002718175680000113
the step S122, based on the energy modulation principle, calculates the adjustment value of the interphase circulating current, including:
calculating the capacitance voltage of upper and lower bridge arms of each phase of the MMC circuit according to the discontinuous modulation signal;
according to the capacitance voltage, calculating theoretical power values of upper and lower bridge arms of each phase of the MMC circuit;
calculating the difference value between the theoretical power value and each actual power value to obtain a power modulation signal to be modulated;
inputting the power modulation signal to a PI controller to obtain a reference current to be modulated;
and obtaining an adjustment value of the energy-modulated interphase circulating current according to the reference current and the per unit value of the three-phase voltage.
Referring to fig. 5, first, the capacitance voltage of the upper and lower arms of each phase is calculated
Figure BDA0002718175680000114
And
Figure BDA0002718175680000115
secondly, according to the logical relation shown in fig. 5, the theoretical power value P of the upper and lower bridge arms of each phase of the MMC circuit is calculated* cjuAnd P* cjl；
Then, the theoretical power value P is calculated* cjuAnd the actual power value PcjuAnd inputting the difference value into a corresponding PI controller to obtain a reference current i to be modulated* pju；
Calculating theoretical power value P* cjlAnd the actual power value PcjlAnd inputting the difference value into a corresponding PI controller to obtain a reference current i to be modulated* pjl；
Finally, according to the logical relation shown in fig. 5, the per unit value v of the three-phase voltage is introducedjmAnd obtaining an adjustment value of the energy-modulated interphase circulating current:
Figure BDA0002718175680000116
the step S123 of calculating a circulating current error of the interphase circulating current specifically includes:
reference value for interphase circulating current
Figure BDA0002718175680000125
And the adjustment value
Figure BDA0002718175680000126
After summing, the sum is compared with the actual value ij_circMake a differenceAnd obtaining the circulation error of the interphase circulation.
Step S124, inputting the circulating current error to a PI controller, and obtaining a per unit value after the energy-modulated three-phase voltage differential conversion, specifically:
as the voltage reference signals of the upper and lower bridge arms of each phase of the MMC circuit are as follows:
Figure BDA0002718175680000121
Figure BDA0002718175680000122
according to the voltage difference conversion, the per unit value delta v of the three-phase voltage is obtainedjm。
In step S13, obtaining voltage reference signals of upper and lower bridge arms of each phase of the MMC circuit according to the per unit value of the three-phase voltage and the per unit value after differential conversion of the three-phase voltage, specifically:
summing the per-unit value of each phase voltage with the per-unit value after the differential conversion of the three-phase voltage to obtain a voltage reference signal of an upper bridge arm of each phase of the MMC circuit;
and (4) making a difference between the per unit value of each phase voltage and the per unit value after the differential conversion of the three-phase voltage to obtain a voltage reference signal of the lower bridge arm of each phase of the MMC circuit.
Referring to fig. 4, the step S13 specifically includes:
voltage reference signal v of upper bridge arm of each phasejum＝vjm+Δvjm；
Voltage reference signal v of each phase lower bridge armjlm＝vjm-Δvjm。
It will be understood that if Δ vjmA positive indication that the upper arm voltage is higher than the lower arm voltage, all modulation signals remain at the modulation limit [ -1,1 [ ]]. But if Δ vjmNegative, then in-phase over-modulation occurs with the reference value of the opposite leg to the clamped leg being greater than 1 or less than-1.
It should be noted that:
Figure BDA0002718175680000123
wherein
Figure BDA0002718175680000124
The upper arm is higher than the lower arm indicates Δ vjmIs positive and the modulation signal is [ -1,1 [)]Overmodulation does not occur because the typical modulation signal m value is the ratio of the fundamental signal amplitude to the carrier signal amplitude, which ranges between-1 and 1. But when Δ vjmWhen the voltage of the lower bridge arm is higher than that of the upper bridge arm when the voltage of the lower bridge arm is a negative value, overmodulation of a non-clamped bridge arm opposite to a clamped bridge arm, wherein the voltage reference value of the non-clamped bridge arm is larger than 1 or smaller than-1, occurs on the same phase in an inverter circuit, and M + N modules are needed to limit bridge arm circulation current. And considering overmodulation limitation, taking the upper bridge arm voltage terminal of the direct current bus as an example for analysis, and v is in each phasejm_max-1<vjm_min+1, i.e. indicates
Figure BDA0002718175680000131
So in the most severe cases
Figure BDA0002718175680000132
When the temperature of the water is higher than the set temperature,
Figure BDA0002718175680000133
in this case, M may exceed 1 or-1, so an additional M sub-modules are required to prevent overshoot.
As shown in fig. 1, each phase of the bridge arm of the motor control system adopts an N + M structure, where M is an additional sub-module. This approach can extend the modulation range beyond the interval-1, and thus can control the circulating current in the interval of the clamped phase arm.
And step S14, according to the operation frequency and the operation period of the controlled load motor, injecting zero sequence components into the voltage reference signal in a segmented manner to obtain discontinuous modulation signals of upper and lower bridge arms of each phase of the MMC circuit.
Preferably, the zero sequence component is defined in segments according to clamping intervals of six bridge arms of the MMC circuit and by combining modulation coefficients.
Assuming that the output current is in phase with the reference voltage, in this case a six leg clamp can be definedBit spacing and calculation of zero sequence component v0And the theta is the stator rotation angle of the permanent magnet synchronous motor, and the m is a modulation coefficient.
Figure BDA0002718175680000134
The final discontinuous modulation signal v of each phase of upper and lower bridge arms can be obtained by the zero sequence component and the voltage reference signals of the upper and lower bridge armsjudAnd vjldWherein v isjud＝vjum+v0，vjld＝vjlm+v0。
It can be understood that when the debugging coefficient m is low, the inter-phase clamping period is long, the switch of one bridge arm above and below the single-phase bridge arm is not changed, and the capacitor voltage is clamped. Therefore, the technical scheme provided by the embodiment has a good energy-saving effect in the field of low-frequency control (F is less than 30Hz), the voltage ripple of the sub-module capacitor is small, and the system efficiency is higher than that of the traditional SPWM modulation mode.
In the high-frequency control stage, the SPWM signal modulation and the discontinuous signal modulation are basically different, the algorithm modulation calculation of the discontinuous modulation is complex, and the high-frequency operation often has transient state regulation requirements of relevant dynamic variables such as power or voltage, so the technical scheme provided by the embodiment adopts the SPWM control mode (F is more than or equal to 30Hz) and does not inject zero-sequence components in consideration of the distribution requirement of system computational power.
It can be understood that, according to the technical scheme provided by the embodiment, the control is performed in different frequency bands in a segmented manner, the control mode is flexible, and the system redundancy is strong.
Fig. 6 shows a waveform diagram of zero sequence component, discontinuous modulation signal and output voltage current in one period. The discontinuous modulation comprises the step of injecting discontinuous zero sequence components into a reference signal of the three-phase current transformer. The zero sequence component causes one of the phase angles to be clamped at the upper or lower end of the dc bus at certain intervals, as shown in fig. 7.
Due to the injection of the zero sequence component, the linear working mode of the three-phase cascade inversion module is enhanced. In addition, since there are always phase legs that do not need to be switched for some time intervals, the average switching frequency of the power device is reduced, thereby reducing the switching power loss of the three-phase cascade inverter module. In this system model, all sub-modules of one arm of a particular phase leg are disabled for a period of time. Thus, the phase leg may be clipped to the upper or lower dc bus bar terminal. In the clamping time interval, because one arm of the three-phase cascade inversion module has no switch, the switching power loss is reduced. When applying discontinuous modulation to multi-level modulation, only one leg of a particular phase leg is clamped, while the other one of the same phase legs remains switched to control the circulating current.
In an interphase converter system, the larger the equivalent capacitance in a particular leg, the larger the output current through that leg. Thus, the leg (larger capacitance) that activates fewer sub-modules will carry more output current, and vice versa. Subsequently, during clamping, no current will flow through any sub-module capacitance of the entire phase leg. Thus, ideally, the capacitor voltage ripple can be minimized.
Referring to fig. 7, the submodules through which current flows are indicated by black lines, while voltage is applied to the capacitors, and the submodules through which no current flows are shown in dashed boxes. During clamping, the output current will flow through all the submodules on one leg, and the black line represents the current flow path of the upper or lower leg.
In the solution provided in this embodiment, when operating at a very low modulation index m and no zero sequence component is injected, a similar number of sub-modules are activated in the upper and lower arms. Under such operating conditions, the output current is equally divided between the two arms of the phase leg, flows through the N sub-modules, and produces a large deviation in the sub-module capacitance voltage. But under the same conditions, if discontinuous modulation is employed, the zero sequence component will cause the reference signal of all phases to change dynamically, which will significantly reduce the capacitor voltage ripple.
It can be understood that the technical scheme that this embodiment provided can improve the converter energy consumption problem when the motor low frequency operation, based on the MMC circuit, adopts the mode that zero sequence component injection and energy modulation combine, need not increase extra hardware cost, can also show and reduce submodule piece capacitor voltage ripple, prolongs the life of big capacitor components and parts, and user experience degree is good, the satisfaction is high.
Preferably, the method further comprises:
and taking the discontinuous modulation signal as a feedback quantity to participate in energy modulation.
It can be understood that after obtaining the discontinuous modulation signal, the signal will enter the energy modulation control as a feedback variable, and in combination with the MMC circuit structure, the capacitance voltage of the upper and lower arms of each phase is calculated as:
Figure BDA0002718175680000151
wherein v isc0The initial calculation is negligible for the initial capacitor voltage. Therefore, according to the voltage balance mode of the submodule of the MMC circuit, the capacitor voltage in each bridge arm is respectively
Figure BDA0002718175680000152
The voltage component of the energy modulation is generated by the feedback of the discontinuous modulation signal after the zero sequence component is injected, and a closed loop of energy control is formed.
It is understood that the same or similar parts in the above embodiments may be mutually referred to, and the same or similar parts in other embodiments may be referred to for the content which is not described in detail in some embodiments.
It should be noted that the terms "first," "second," and the like in the description of the present invention are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Further, in the description of the present invention, the meaning of "a plurality" means at least two unless otherwise specified.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.
In addition, functional units in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.
The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (11)

1. A variable flow control system for an electric motor, comprising:
the MMC circuit is connected with a controlled load motor and comprises three-phase cascade inversion modules, and each phase of upper and lower bridge arms respectively comprise a first number of basic modules and a second number of additional expansion modules which are sequentially cascaded;
a controller, connected to the MMC circuit, for:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit.
2. The system of claim 1, wherein the controller is further configured to:
and in the middle-high frequency operation stage, based on the MMC circuit, an SPWM modulation control mode is adopted to output PWM modulation signals for the controlled load motor.
3. The system of claim 1,
the basic module and the additional expansion module have the same structure and respectively comprise two series-connected IGBT modules and an electrolytic capacitor connected with the series-connected IGBT modules in parallel.
4. A control method of a motor variable flow control system is characterized by comprising the following steps:
in the low-frequency operation stage, based on an energy modulation principle and a zero-sequence component injection method, a discontinuous modulation control mode is adopted to realize discontinuous modulation on voltage signals of upper and lower bridge arms of each phase of the MMC circuit;
the MMC circuit comprises three-phase cascade inversion modules, wherein the upper bridge arm and the lower bridge arm of each phase respectively comprise a first number of basic modules and a second number of additional expansion modules which are cascaded in sequence.
5. The method of claim 4, further comprising:
and in the middle-high frequency operation stage, based on the MMC circuit, an SPWM modulation control mode is adopted to output PWM modulation signals for the controlled load motor.
6. The method according to claim 4, wherein the employing the discontinuous modulation control scheme comprises:
obtaining a per unit value of three-phase voltage of a controlled load motor based on a PMSM vector control technology;
obtaining a per unit value after the three-phase voltage differential transformation through energy modulation based on an energy modulation principle;
obtaining voltage reference signals of upper and lower bridge arms of each phase of the MMC circuit according to the per-unit values of the three-phase voltage and the per-unit values after differential conversion of the three-phase voltage;
and injecting zero-sequence components into the voltage reference signals in a segmented manner according to the operating frequency and the operating period of the controlled load motor to obtain discontinuous modulation signals of upper and lower bridge arms of each phase of the MMC circuit.
7. The method of claim 6, further comprising:
and taking the discontinuous modulation signal as a feedback quantity to participate in energy modulation.
8. The method according to claim 6, wherein the obtaining of the per unit value after the energy-modulated three-phase voltage differential transformation based on the energy modulation principle comprises:
calculating a reference value of the interphase circulating current of the MMC circuit according to the per-unit value of the three-phase voltage and the three-phase sampling current of the controlled load motor;
calculating an adjustment value of the interphase circulating current based on an energy modulation principle;
calculating a circulating current error of the interphase circulating current according to the reference value, the adjustment value and the actual value of the interphase circulating current;
and inputting the circulating current error into a PI controller to obtain a per unit value after the three-phase voltage differential conversion through energy modulation.
9. The method according to claim 8, wherein the calculating the adjustment value of the interphase circulating current based on the energy modulation principle includes:
calculating the capacitance voltage of upper and lower bridge arms of each phase of the MMC circuit according to the discontinuous modulation signal;
according to the capacitance voltage, calculating theoretical power values of upper and lower bridge arms of each phase of the MMC circuit;
calculating the difference value between the theoretical power value and each actual power value to obtain a power modulation signal to be modulated;
inputting the power modulation signal to a PI controller to obtain a reference current to be modulated;
and obtaining an adjustment value of the energy-modulated interphase circulating current according to the reference current and the per unit value of the three-phase voltage.
10. The method according to claim 8, wherein the calculating a circulating current error of the interphase circulating current is specifically:
and summing the reference value and the adjustment value of the interphase circulating current, and then subtracting the actual value to obtain the circulating current error of the interphase circulating current.
11. The method according to claim 6, wherein the obtaining of the voltage reference signal of the upper and lower bridge arms of each phase of the MMC circuit according to the per-unit values of the three-phase voltages and the per-unit values after differential conversion of the three-phase voltages specifically comprises:
summing the per-unit value of each phase voltage with the per-unit value after the differential conversion of the three-phase voltage to obtain a voltage reference signal of an upper bridge arm of each phase of the MMC circuit;
and (4) making a difference between the per unit value of each phase voltage and the per unit value after the differential conversion of the three-phase voltage to obtain a voltage reference signal of the lower bridge arm of each phase of the MMC circuit.
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