CN110808704B - Low control frequency control method of high switching frequency inverter - Google Patents

Low control frequency control method of high switching frequency inverter Download PDF

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CN110808704B
CN110808704B CN201911010299.8A CN201911010299A CN110808704B CN 110808704 B CN110808704 B CN 110808704B CN 201911010299 A CN201911010299 A CN 201911010299A CN 110808704 B CN110808704 B CN 110808704B
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switching
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coordinate system
kth
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CN110808704A (en
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黄允凯
张津栋
彭飞
姚宇
祝子冲
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Southeast University
Liyang Research Institute of Southeast University
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Liyang Research Institute of Southeast University
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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
    • H02P27/12—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 pulsing by guiding the flux vector, current vector or voltage vector on a circle or a closed curve, e.g. for direct torque control
    • 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
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/13—Observer control, e.g. using Luenberger observers or Kalman filters
    • 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
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/24—Vector control not involving the use of rotor position or rotor speed sensors
    • H02P21/26—Rotor flux based control

Abstract

The invention discloses a low control frequency control method of a high switching frequency inverter, wherein the angle of a voltage vector output by the high frequency inverter under a static coordinate system is rotated in each switching period of a control period, the rotation angle is the angle rotated by a dq rotating coordinate system in one switching period, the angle of the output voltage vector is compensated, and the compensation angle is the angle rotated by the dq rotating coordinate system in a half switching period; and calculating a voltage reference vector of the next switching period in the ABC static coordinate system in each switching period so as to compensate the one-beat delay characteristic of the PWM wave generator. The control method gives full play to the advantage of high switching frequency, can improve the proximity degree of the inverter output voltage vector and the reference voltage vector, improves the sine degree of the inverter output current, and obviously improves the control effect.

Description

Low control frequency control method of high switching frequency inverter
Technical Field
The invention belongs to the field of inverter control, and particularly relates to a low control frequency control method of a high switching frequency inverter.
Background
Thanks to the development of High-Frequency wide-bandgap devices, namely Silicon Carbide (SiC) devices and Gallium Nitride (GaN) devices, High-Switching Frequency inverters (HSFI) can be manufactured by using High-Frequency devices to deal with some occasions requiring High-Frequency driving so as to improve the control effect, for example, the High-Switching Frequency inverters can be used to control High-Frequency Permanent Magnet Synchronous motors (hfpmms) so as to significantly reduce current ripples. The high switching frequency inverter manufactured by using the wide bandgap device can improve the switching frequency to hundreds of kilohertz in the medium and small power occasions, which is far higher than the common inverter manufactured by using a Silicon (Si) device. When controlling a high switching frequency inverter, the used control frequency is usually difficult to reach as high as the switching frequency, and the reason for controlling a high frequency permanent magnet synchronous motor is mainly as follows: high frequency sampling is difficult; the computational resources of the controller are limited; the control program of the high-frequency permanent magnet synchronous motor is complex, the current link needs to be accurately discretized, and algorithms such as a position-sensor-free algorithm, a self-adaptive algorithm and a parameter identification algorithm are usually combined. Therefore, even if the switching frequency of the high switching frequency inverter can reach hundreds of kilohertz, the control frequency of the high switching frequency inverter can only reach dozens of kilohertz, which causes the high switching frequency and low control frequency inverter to be controlled, and the main characteristic is that one control period comprises a plurality of switching periods.
For the inverter control occasions with high switching frequency and low control frequency, the prior art does not perform special treatment on the high switching frequency, the control method is the same as the control method that the switching frequency is equal to the control frequency, and only the frequency of the PWM signal output by the controller is the switching frequency.
The inventor finds that the existing inverter control technology with high switching frequency and low control frequency has the following problems: although the load current ripple can be reduced by means of high switching frequency, the update frequency of the voltage reference value is only the control frequency, so that the output voltage vector is seriously deviated from the reference voltage vector, the current waveform is seriously malformed, and the high switching frequency is not fully utilized.
Based on the above shortcomings, the present application is made.
Disclosure of Invention
The invention aims to provide a low control frequency control method of a high switching frequency inverter, which fully exerts the advantage of high switching frequency, can improve the proximity degree of an inverter output voltage vector and a reference voltage vector, improves the sine degree of the inverter output current and obviously improves the control effect.
In order to achieve the above purpose, the solution of the invention is:
a low control frequency control method of a high switching frequency inverter compensates the angle of a voltage vector output by the high frequency inverter in a static coordinate system in each switching period of a control period, wherein the compensation angle is the angle rotated by a dq rotating coordinate system in a half switching period.
Calculating a voltage reference vector of the next switching period in an ABC static coordinate system in each switching period to compensate the one-beat delay characteristic of the PWM wave generator; completing the calculation of the controller control program before the last switching period of each control period, so that the voltage reference value of the 1 st switching period of the next control period can be calculated in the last switching period; the above feature can be expressed as that the voltage reference vector expression used by the PWM wave generator in the ith switching period of the kth control period is
Figure BDA0002244015920000021
Wherein it is assumed that there are q switching periods, T, in each control periodiPark(theta) is an inverse Park transformation matrix, theta k]For the electrical angle of the motor at the start of the kth control cycle, ω k]The electrical angular velocity of the motor at the start of the kth control cycle,
Figure BDA0002244015920000022
for the voltage reference vector in dq rotation coordinate system in the k control period, TswIs a switching cycle.
The expression of the voltage vector output by the high-frequency inverter in the kth control period in the ABC static coordinate system is shown as formulas (2) and (3);
Figure BDA0002244015920000023
Figure BDA0002244015920000031
the expressions of the voltage vector output by the high-frequency inverter in the kth control period in the dq rotation coordinate system are shown as (4) and (5);
Figure BDA0002244015920000032
Figure BDA0002244015920000033
wherein T isiPark(θ) is an inverse Park transformation matrix, Tr(theta) is a rotation matrix of the two-phase coordinate system, theta k]For the electrical angle of the motor at the start of the kth control cycle, ω k]The electrical angular velocity of the motor at the start of the kth control cycle,
Figure BDA0002244015920000034
a voltage reference vector under a dq rotation coordinate system in the kth control period; when a model of the control system is established, the expression of the inverter output voltage of the model in the kth control period in the ABC static coordinate system is shown in formulas (2) and (3), and the expression in the dq rotation coordinate system is shown in formulas (4) and (5).
An approximate expression of a voltage vector output by the high-frequency inverter in the kth control period in the ABC static coordinate system is shown as a formula (6);
Figure BDA0002244015920000035
an approximate expression of a voltage vector output by the high-frequency inverter in the kth control period in a dq rotation coordinate system is shown as a formula (7);
Figure BDA0002244015920000036
wherein T isiPark(theta) is an inverse Park transformation matrix, theta k]Is the kth controlElectric angle of motor at starting time of control cycle, omega k]The electrical angular velocity of the motor at the start of the kth control cycle,
Figure BDA0002244015920000037
a voltage reference vector under a dq rotation coordinate system in the kth control period; when a model of the control system is established, an expression of the inverter output voltage of the model in the kth control period in an ABC static coordinate system is shown as an equation (6), and an expression in a dq rotation coordinate system is shown as an equation (7).
Specifically, the present invention comprises the steps of:
(1) in the k-1 th control period TcIn the method, a voltage reference value under the dq coordinate system is calculated by the current controller ACR established under the dq rotation coordinate system
Figure BDA0002244015920000041
According to the characteristic that the digital control system delays one beat, the method can be seen
Figure BDA0002244015920000042
I.e. the voltage reference value of the kth control period in dq coordinate system, it is written as
Figure BDA0002244015920000043
In the k-1 control period, the starting time of the k control period, i.e. t ═ kT, is obtained by a program such as encoder decoding or no position observercDq coordinate system of time is electrical angle theta [ k ] under static coordinate system]And electrical angular velocity ω k]。
(2) At the time of the k-th control period, i.e. t ═ kTcMeanwhile, the 1 st switching period in the kth control period also arrives at the same time, and the control period interruption and the switching period interruption are triggered at the same time. Since the switching cycle interruption priority is higher than the control cycle interruption, the voltage switching program in the switching cycle interruption is preferentially operated, and the program updates the voltage reference value in the ABC coordinate system to be
θk,i＝θ[k]+(1.5)ω[k]Tsw (8)
Along with the update of the voltage reference value under the ABC coordinate system, the duty ratio of the PWM control signal output by the single chip microcomputer or the DSP is correspondingly changed, so that the control of the inverter is improved.
(3) When the 2 nd to q-1 th switching period of the kth control period comes, the switching period is interrupted and triggered, because the interruption priority is higher, the main control program stops running, the voltage switching program in the switching period interruption is preferentially run, and the program updates the voltage reference value under the ABC coordinate system to be
Figure BDA0002244015920000044
Wherein
θk,i＝θ[k]+(i+0.5)ω[k]Tsw,i＝2,3,…,q-1 (10)
(4) When the q-th switching period of the k-th control period comes, the interruption of the switching period is triggered, so that the main control program stops running, and the voltage switching program in the interruption of the switching period is preferentially run. Because the PWM signal generation link has the characteristic of delaying one beat, the voltage reference value set in the q switching period of the k control period should be the voltage reference value of the 1 switching period of the (k +1) control period, so that the voltage reference value under the ABC coordinate system is updated to be
Figure BDA0002244015920000051
This also means that the operation of the main control program must be completed in the first q-1 switching cycles of each control cycle when using the present control method, thereby obtaining
Figure BDA0002244015920000052
θ[k+1]And ω [ k +1 ]]The equivalent value is used for the calculation of equation (11).
(5) After the high switching frequency inverter is controlled by adopting the method, the expression of the output voltage vector of the inverter on the ABC static coordinate system in the kth control period is
Figure BDA0002244015920000053
Wherein
Figure BDA0002244015920000054
At omega [ k ]]TswWhen the value of (c) is small, it can be approximated that the voltage vector rotates at a constant speed, i.e., equation (12) can be written as
Figure BDA0002244015920000055
After the high switching frequency inverter is controlled by adopting the steps, the expression of the output voltage vector of the inverter on a dq rotation coordinate system in the kth control period is
Figure BDA0002244015920000056
Wherein
Figure BDA0002244015920000057
Wherein T isr(theta) two-phase rectangular coordinate system rotation matrix with the expression of
Figure BDA0002244015920000061
Similarly, it can be considered that the inverter output voltage vector is kept constant on the dq rotation coordinate system in the k-th control period approximately, that is, equation (15) can be written as
Figure BDA0002244015920000062
When the method is used for controlling the high-frequency inverter, the output voltage form of the inverter is different from that of a common control method, so when mathematical models such as a current link model, an observer model and the like of a load are established, the input voltage of the model is correspondingly changed according to the method. When a more accurate voltage description is adopted, the form of the input voltage in the stationary coordinate system in the kth control period is shown in formulas (12) and (13), and the form of the input voltage in the rotating coordinate system is shown in formulas (15) and (16); when the approximate voltage description is adopted, the form of the input voltage in the stationary coordinate system in the k-th control period is shown as formula (14), and the form in the rotating coordinate system is shown as formula (18).
By adopting the scheme, the invention aims at the high switching frequency inverter control occasion with the switching frequency higher than the control frequency, the angle of the inverter output voltage vector in the static coordinate system is changed according to the electric angular speed of the dq coordinate system in each switching period, and the angle of the inverter output voltage vector is compensated according to the rotation of the dq coordinate system and the delay one-beat characteristic of the PWM signal generator in the controller, so that the control effect that the control frequency is equal to the switching frequency can be achieved when the control system is in a steady state.
Compared with the prior art, the technical scheme provided by the invention has the beneficial effects that:
(1) the high switching frequency of the high-frequency inverter is fully exerted, and the steady-state control effect when the control frequency is equal to the switching frequency can be obtained by using a lower control frequency;
(2) the control frequency of the high-frequency inverter can be reduced, so that the requirement of the inverter on the calculation resources of the controller is reduced, the cost of the controller is reduced, or the calculation resources of the controller are released, and a control program can contain more functions and algorithms;
(3) the output voltage vector of the high-frequency inverter is closer to the reference voltage vector of the reference voltage vector, so that the harmonic content of the output voltage of the inverter is reduced, the sine degree of the output current is improved, and the control effect is obviously improved;
(4) reducing the harmonic content of the load current.
Drawings
FIG. 1 is a schematic diagram of a high switching frequency inverter control system;
fig. 2 is a program signal flow diagram of the proposed method of the invention;
FIG. 3 is a sequence diagram of the program operation of the proposed method;
FIG. 4 is a schematic diagram of a main control procedure of the proposed method;
FIG. 5 is a schematic diagram of a voltage switching procedure of the proposed method;
FIG. 6 is a steady state voltage vector diagram using the conventional method and the present method in an ABC coordinate system, wherein (a) is the steady state voltage vector diagram using the conventional method and (b) is the steady state voltage vector diagram using the present method;
FIG. 7 is a steady state voltage vector diagram using the conventional method and the present method in dq coordinate system, where (a) is the steady state voltage vector diagram using the conventional method and (b) is the steady state voltage vector diagram using the present method;
FIG. 8 is an A-phase voltage reference value simulation waveform using the normal method and the present method, wherein (a) is a simulation waveform using the normal method and (b) is a simulation waveform using the present method;
fig. 9 is a simulation waveform of a-phase current using a general method and a present method, in which (a) is a simulation waveform using a general method, and (b) is a simulation waveform using a present method.
Detailed Description
The invention provides a low control frequency control method of a high switching frequency inverter, which aims at the switching frequency fswAbove the control frequency fcOr a control period TcIn which there are a plurality of switching periods TswThe inverter control method of (1) changes the angle of the inverter output voltage vector according to the dq coordinate system electrical angular velocity in each switching period, and rotates the voltage vector output by the inverter in the stationary coordinate system by the angle rotated by the dq coordinate system in one switching period in each switching period in one control period. Compared with the prior art, the invention improves the rotation frequency of the voltage vector, and the motion track of the voltage vector is closer to an ideal circle.
The present invention will be further described with reference to the accompanying drawings.
Setting q switching cycles in each control cycle; the following analysis uses the voltage average assumption in each switching cycle that the output voltage of the inverter is considered to be the average of its actual output voltage in each switching cycle, which is the basis of mathematical modeling.
A schematic diagram of a control system of a high switching frequency inverter is shown in figure 1, a bridge arm of a wide bandgap device in the schematic diagram uses a GaN device or a SiC device as a switching device, and a controller samples to obtain an output current signal i of the inverterABCAnd the DC side voltage signal U of the inverterdcAnd outputting the PWM signal to a driving circuit, and sending a door machine driving signal to control a switching device by the driving circuit, so that the inverter outputs a voltage waveform in a PWM form, and the three-phase load is controlled.
The program operated in the controller of the method mainly comprises a main control program and a voltage switching program, wherein the main control program is a control program in the general sense, and has no special part, the operation priority is lower, and the operation frequency is control frequency; the voltage switching program is a core program of the method, is used for switching the voltage vector, has higher operation priority and the operation frequency is the switching frequency, so the voltage switching frequency of the high-switching-frequency inverter controlled by the method is the switching frequency. The program signal flow of the method is shown in FIG. 2, the input signal of the main control program is iABCThe output signal is the voltage reference value of dq coordinate system
Figure BDA0002244015920000081
The electric angle theta of the dq coordinate system and the electric angular speed omega of the dq coordinate system, and a voltage switching program receives the three signals and outputs the voltage reference value of the ABC coordinate system
Figure BDA0002244015920000082
Then the
Figure BDA0002244015920000083
And a PWM signal generation link is reached through a delay link, and the PWM signal is generated in the PWM generation link. Wherein
Figure BDA0002244015920000084
A delay element is passed because PWM generators in controllers such as DSPs or single-chip microcomputers all have a delay of one PWM period, i.e., a delay of one switching period.
It is to be noted that: the operation frequency of the main control program is the control frequency, the operation frequency of the voltage switching program is the switching frequency, the two programs have a front-back relationship in the signal flow diagram of fig. 2, but the operation of the two programs is mutually crossed, and the operation time sequence of the two programs is shown in fig. 3. The method comprises the steps that a main control program is written in control cycle interruption, a voltage switching program is written in switch cycle interruption, the priority of the switch cycle interruption is set to be higher than that of the control cycle interruption, and when the two interruptions arrive at the same time, the voltage switching program in the switch cycle interruption can be preferentially operated; when the switching period interrupts the main control program to arrive, the operation of the main control program is suspended, the voltage switching program is preferentially operated, and the main control program is continuously operated after the voltage switching program is operated. The voltage switching program runs for a short time compared to the main control program, as shown in fig. 3. It is to be noted that: the main control routine must be completed in the first q-1 switching cycles of each control cycle, subject to the one-beat delay of the PWM generation stage, as will be explained in more detail later.
The main control program is schematically shown in fig. 4, the speed angle observer obtains the electrical angle θ and the electrical angular velocity ω of the dq coordinate system through the current information and the voltage information (in some cases, the electrical angle θ and the electrical angular velocity ω are obtained through a rotation speed or phase sensor), and the speed controller obtains the reference angular velocity ω of the dq coordinate system through the reference angular velocity ω of the dq coordinate system*Calculating with the actual angular velocity omega to obtain a current reference value under the dq coordinate system
Figure BDA0002244015920000091
A current controller based on
Figure BDA0002244015920000092
And the actual current value idqObtaining a voltage reference value under the dq coordinate system
Figure BDA0002244015920000093
Due to the delayed one-beat characteristic of the digital control system,
Figure BDA0002244015920000094
will delay one beat, record the delayed
Figure BDA0002244015920000095
Is composed of
Figure BDA0002244015920000096
Main control program output
Figure BDA0002244015920000097
Theta, omega, etc., and transmits to the voltage switching program.
The schematic diagram of the voltage switching process is shown in fig. 5. In the k-1 control period, the current controller in the main control program calculates the k control period, i.e. t epsilon [ kT ]c,(k+1)Tc) Dq coordinate system voltage reference
Figure BDA0002244015920000098
The position and speed observer calculates the dq coordinate system at the initial time of the kth control period, namely t equals to kTcElectrical angular velocity of time omega k]And electrical angle theta k]So that it can be directly used in the k-th control period
Figure BDA0002244015920000099
ω[k]，θ[k]And (4) equivalence.
The approximation considers that the electric angular velocity of the dq coordinate system does not change in the kth control period, namely
ω(t)≈ω[k],t∈[kTc,(k+1)Tc) (19)
The starting point of the ith switching cycle of the kth control cycle, i.e. t ═ kTc+iTswIn time, the electrical angle of the dq coordinate system can be expressed as
θ[k,i]＝θ[k]+i·ω[k]Tsw (20)
The time range of the ith switching cycle in the kth control cycle is
t∈[kTc+(i-1)Tsw,kTc+iTsw),t＝1,2,…,q (21)
When the inverter system is controlled, mathematical modeling is established under the dq coordinate system, and the actual system is under the static coordinate system, so that the voltage vector output by the inverter is static on the static coordinate system and rotates reversely on the dq coordinate system. Ideally, the voltage reference vector in the dq coordinate system in the controller is at steady state for the control system
Figure BDA00022440159200000910
Both the amplitude and the angle of (c) are kept constant. When the product of the electrical angular velocity and the control period of the motor is omega.TcWhen the amplitude of the voltage vector output by the inverter in one control period is large, although the amplitude is unchanged in the dq coordinate system, the angle of the voltage vector is maximum thetad＝ω·TcSo that the inverter output voltage vector is offset from the reference voltage vector
Figure BDA00022440159200000911
Is a large angle, which is the most important reason for the difficulty of controlling the high-frequency three-phase load.
When the low control frequency control is performed on the high switching frequency inverter, the ordinary control algorithm does not perform any processing for the high switching frequency, and the offset of the voltage vector is the same as the above case. The proposed method aims at high switching frequencies, all in one switching cycle
Figure BDA0002244015920000101
The angle used for performing the inverse Park transformation is updated once. In order to ensure the accuracy of the generation of the PWM signal, a PWM wave generator in the singlechip or the DSP has a delay of one PWM period, namely a delay of one switching period. Considering that the PWM signal generation may be delayed by one beat, an angle of the starting time of the (i +1) th switching period should be used in the ith switching period; further, in order to minimize the angular deviation, the i +1 th switching cycle should be usedTime of day, i.e. t ═ kTc+(i-1+1+0.5)·TswThe motor rotor angle at the moment. Therefore, in the ith switching period of the kth control period, the angle used for carrying out the inverse Park conversion is
θu[k,i]＝θ[k]+(i+0.5)·ω[k]·Tsw (22)
When the angle shown in equation (22) is used, the maximum angular deviation between the inverter output voltage vector and the reference voltage vector is only 0.5 ω TswAt very high switching frequencies, i.e. TswUnder very small conditions, the angular deviation is very small. The voltage reference value of the ABC three-phase static coordinate system of the ith switching period in the kth control period obtained by the method is
Figure BDA0002244015920000102
Wherein T isiparkAnd (theta) is an inverse Park transformation matrix, and theta is an angle used by the inverse Park transformation.
In particular, since the PWM generator has a characteristic of delaying one switching period, a voltage value reference value of the 1 st switching period of the (k +1) th control period should be calculated in the last switching period of each control period, i.e., the q-th switching period, i.e., there is
Figure BDA0002244015920000103
Equation (24) illustrates that, when using the method, the control program must be calculated in the first q-1 switching cycles of the control cycle, so that θ [ k +1 ] can be used in the q-th switching cycle]，ω[k+1]，
Figure BDA0002244015920000104
The equivalence is subjected to correlation calculation.
The method will be described in detail below by taking the program operation in the kth control cycle as an example.
(1) When entering the kth control period, simultaneously entering the 1 st switching period of the kth control period, simultaneously triggering control period interruption and switching period interruption, and operating a voltage switching program firstly because the interruption priority of the latter is high, wherein the calculated voltage reference value under the ABC coordinate system is
Figure BDA0002244015920000111
Wherein
Figure BDA0002244015920000112
ω[k]，θ[k]The equivalence is the result of the main control program running in the (k-1) th control cycle.
The PWM wave generation link outputs PWM wave according to the reference value, and the PWM wave generator has the characteristic of delaying one beat so as to
Figure BDA0002244015920000113
The PWM waveform for reference will be output at the 2 nd switching period of the kth control period.
The voltage switching procedure is computationally very small and therefore runs very short, as shown in fig. 3. After the voltage switching program is run, the main control program with lower priority starts to run.
(2) When the 2 nd switching period of the kth control period is entered, the interruption of the switching period is triggered again, the running of the main control program is suspended at the moment due to the higher priority, the voltage switching program of the 2 nd switching period is run first, and the calculated voltage reference value under the ABC coordinate system is
Figure BDA0002244015920000114
Similarly, the PWM wave generator has the characteristic of delaying one beat, so that
Figure BDA0002244015920000115
The PWM waveform for reference will be output at the 3 rd switching period of the kth control period.
The case of the 3 rd, 4 th, … rd, q-1 th switching cycle in the subsequent kth control cycle is similar to the case of the 1 st, 2 nd switching cycle.
(3) When the last control period of the kth control period, namely the q-th switching period, is entered, the interruption of the switching period is triggered again, and because the priority of the interruption is higher, the operation of the main control program is suspended at this time, and the voltage switching program of the q-th switching period is operated first. Because the PWM wave generation ring has the characteristic of delaying one beat, the voltage reference value of the 1 st switching period of the (k +1) th control period should be calculated in the q-th switching period of the k-th control period, so that the voltage reference value in the ABC coordinate system calculated by the voltage switching program in the q-th switching period is
Figure BDA0002244015920000121
To be provided with
Figure BDA0002244015920000122
The PWM waveform for reference will be output at the 1 st switching period of the (k +1) th control period.
It can be seen that the delayed one-beat characteristic of the PWM wave generation link makes the main control program have to finish running in the first q-1 switching cycles when using the method, as shown in FIG. 3, so as to obtain θ [ k +1 ]]、ω[k+1]And
Figure BDA0002244015920000123
the equivalent value is used for the calculation in the q-th switching cycle.
The above is the program run in one complete control cycle when using the method.
When the method is used, in the kth control period, the expression of the voltage vector output by the high-frequency inverter in the ABC static coordinate system is shown as
Figure BDA0002244015920000124
Wherein
Figure BDA0002244015920000125
At omega [ k ]]TswWhen the value of (b) is small, it can be approximated that the voltage vector rotates at a constant speed, i.e., equation (30) can be written as
Figure BDA0002244015920000126
In the kth control period, the expression of the voltage vector output by the high-frequency inverter in the dq rotation coordinate system is
Figure BDA0002244015920000127
Wherein
Figure BDA0002244015920000128
Figure BDA0002244015920000131
Wherein T isr(theta) two-phase rectangular coordinate system rotation matrix with the expression of
Figure BDA0002244015920000132
Equations (28), (29), (31) and (32) show that the method enables the voltage vector output by the high-frequency inverter under the low control frequency to be closer to the ideal condition. This is reflected in the ABC stationary coordinate system that the rotation frequency of the voltage vector is the switching frequency, and the voltage vector trajectory is closer to a circle, as shown in formulas (28) and (29); the angle of the voltage vector offset reference vector is smaller under the dq rotation coordinate system, and is only 0.5 & omega [ k ] at the maximum]TswAs shown in formulas (31) and (32).
Since the switching frequency in the case of this method is high, even if the electric angular velocity ω of the dq coordinate system is high, 0.5 · ω k is usually the case]TswThe value of (2) is small, that is, the deviation angle of the inverter output voltage vector from the reference voltage vector is small, as shown in equations (31) and (32). The voltage vector output by the inverter can be approximately considered to be equal to the reference voltage vector.
Under the approximation, the expression of the voltage vector output by the inverter in the kth control period in the ABC static coordinate system is shown as
Figure BDA0002244015920000133
In the kth control period, the expression of the voltage vector output by the inverter in the dq rotation coordinate system is
Figure BDA0002244015920000134
The expressions (34) and (35) are defined as being 0.5. omega. k]TswUnder the condition that the value of the reference voltage vector is smaller, the voltage vector output by the high-frequency inverter under the low control frequency is approximately equal to the reference voltage vector. This is reflected in the ABC static coordinate system as the vector approximation of the inverter output voltage by ω k]Follows the reference voltage vector rotation, as shown in equation (34); the inverter output voltage vector is approximately static and coincides with the reference voltage vector in the dq rotation coordinate system, as shown in formula (35).
Because the output voltage of the inverter controlled by the method is different from that of the inverter controlled by the common method, the input voltage of the model is correspondingly changed when the current link of the control system is modeled. When in a more accurate form, the model input voltage is shown as (28) (29) (31) (32); when in approximate form, the input voltage to the model is shown as (34) (35).
To explain the advantages of the method more clearly, assume that the switching frequency of the high switching frequency inverter is fsw100kHz, the control frequency used is fc10kHz, three phasesThe AC load is a high-speed permanent magnet synchronous motor with the rated rotation speed of nN100kr/min, and the number of pole pairs of the motor is p 1. In steady state, the frequency f is controlledcAnd the electrical frequency f of the dq coordinate systemeHas a ratio of fc/fe＝fc·60/nNAt 6, the reference electric quantity of the motor rotates one turn every 6 control cycles in the steady state, or the reference electric quantity of the motor rotates 60 degrees every control cycle.
When the control system is in a steady state, the voltage vector output by the inverter in the normal method is shown in FIG. 6(a) (the voltage vector is shown more clearly, and the coordinate axis A, B, C is not shown in the figure) in the ABC stationary coordinate system, wherein u isiI in (t) represents the i-th control period, i.e., t ∈ [ iT ]c,(i+1)Tc) The voltage vector of the inverter output, see due to fc/feIs small, the trajectory of the output voltage vector is the vertex of a hexagon, and has a large difference from the ideal circular voltage vector trajectory. After the method is used, the situation of the voltage vector in the stationary coordinate system is shown in fig. 6(b) (A, B, C coordinate axes are not drawn in the figure for more clearly showing the voltage vector), wherein ui,jI, j in (t) represents the j-th switching period of the ith control period, i.e. t e [ iT ]c+(j-1)Tsw,iTc+jTsw) It can be seen that since the voltage vector is rotated once in each switching period by the method, the rotation frequency of the voltage vector after the method is used is higher than that of the voltage vector by fsw/fcThe trajectory of the voltage vector is a fixed point of the 60-sided polygon, which is closer to the ideal circular trajectory.
The inverter output voltage vector in dq rotation coordinate system is shown in fig. 7 (for more clearly showing the voltage vector, the d and q coordinate axes are not shown), each trace in the figure represents the rotation trace of the voltage vector, and the solid line represents the steady-state electrical angular velocity ωNThe constant rotation, the dotted line represents the instantaneous rotation caused by the switching of the voltage vector, and the shear at the end of the trajectory line represents the direction of rotation. Ideally, the control system is in a steady state, in dq coordinate systemBoth the angle and the amplitude of the lower voltage reference vector remain constant. The situation of the inverter output voltage vector in dq rotation coordinate system using the conventional method is shown in fig. 7(a), where the trace 1 represents the time in the kth control period, i.e., t e [ kT ]c,(k+1)Tc) The voltage vector is oriented at ω from the boundary 1 with the reference voltage vectorNThe angular speed of the rotating shaft rotates to the boundary 2 at a constant speed; trace 2 represents the transition time from the kth control period to the (k +1) th control period, i.e., (k +1) TcWhen the voltage vector is instantaneously switched from the boundary 2 to the boundary 1, the voltage vector motion forms of the track 3 and the track 4 are similar to those of the track 1 and the track 2. As can be seen from fig. 7(a), the inverter output voltage vector is gradually shifted from the reference voltage vector within one control period by 60 ° at the maximum shift angle. The situation of the inverter output voltage vector in the dq rotation coordinate system when the method is used is shown in fig. 7(b) (for more clear expression, the angle in the figure does not correspond to the actual angle), wherein the trajectory 1 represents the time in the ith switching period of the kth control period, i.e. t e [ kT ]c+(i-1)Tsw,kTc+iTsw) The voltage vector is then scaled by ω from the boundary 1NThe angular speed of the rotating shaft rotates to the boundary 2 at a constant speed; trace 2 represents the transition between the ith switching cycle and the (i +1) th switching cycle of the kth control cycle, i.e., t ═ kTc+iTswWhen the voltage vector is instantaneously switched from the boundary 2 to the boundary 1, the voltage vector motion forms of the track 3 and the track 4 are similar to those of the track 1 and the track 2. As can be seen from fig. 7(b), the maximum deviation angle of the voltage vector output by the inverter from the reference voltage vector is only 3 ° after using the present method, because the present method switches the angle of the voltage vector once in each switching period, and the rotation angle compensation has been made to the output voltage vector in consideration of the rotation of the voltage vector in the dq coordinate system.
The simulation waveform of the reference value of the a-phase voltage for driving the high-speed permanent magnet synchronous motor by controlling the high switching frequency inverter by using the common method and the method at the system steady state is shown in fig. 8. It can be seen that the variation frequency of the reference value of the a-phase voltage under the control of the ordinary method is only 10kHz, which causes the reference value of the output voltage to deviate seriously from the ideal sine, as shown in fig. 8 (a); the variation frequency of the reference value of the A-phase voltage under the control of the method is 100kHz, and the reference value of the output voltage is very close to an ideal sine, as shown in figure 8 (b). The simulation waveform of the a-phase current at the system steady state is shown in fig. 9, and the current reference value is set to 10A. It can be seen that the a-phase current under the control of the conventional method is severely shifted from the ideal sine, as shown in fig. 9(a), due to poor inverter output voltage; the waveform of the a-phase current controlled by this method is preferable, as shown in fig. 9 (b). Compared with the common method, the method can obviously improve the sine degree of the output voltage and current of the high switching frequency inverter, and can obtain the steady-state control effect when the control frequency is equal to the switching frequency by using lower control frequency, thereby better driving the load motor.
In summary, when the inverter with high switching frequency is controlled with low control frequency, the method provided by the invention can significantly improve the control effect.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.

Claims (4)

1. A low control frequency control method of a high switching frequency inverter is characterized in that: rotating the angle of a voltage vector output by the high switching frequency inverter under a static coordinate system in each switching period of a control period, wherein the rotating angle is the angle rotated by a dq rotating coordinate system in one switching period;
angle compensation is carried out on the voltage vector under the ABC static coordinate system output by the inverter in each switching period, and the compensation angle is the angle rotated by the dq rotation coordinate system in a half switching period, so that the angle deviation between the voltage vector output by the inverter and the reference voltage vector is minimum; calculating a voltage reference vector of the next switching period in an ABC static coordinate system in each switching period so as to compensate the one-beat delay characteristic of the PWM wave generator; completing the calculation of a main control program before the last switching period of each control period comes, and calculating a voltage reference value of the 1 st switching period of the next control period in the last switching period;
the specific content of the low control frequency control method of the high switching frequency inverter is that each control period has q switching periods:
1) in the (k-1) th control period, calculating a voltage reference value in a dq coordinate system through a current controller program
Figure FDA0002961521660000011
This is achieved by
Figure FDA0002961521660000012
That is, the voltage reference value of the kth control period in the dq coordinate system is written as
Figure FDA0002961521660000013
In the k-1 control period, the observer program calculates the starting time of the k control period, i.e. t ═ kTcDq coordinate system of time is electrical angle theta [ k ] under static coordinate system]And electrical angular velocity ω k]；
2) At the time of the k-th control period, i.e. t ═ kTcMeanwhile, the 1 st switching period in the kth control period comes at the same time, the control period interruption and the switching period interruption are triggered at the same time, the switching period interruption priority is higher than the control period interruption, the voltage vector switching in the switching period interruption is preferentially carried out, and the voltage reference value under the ABC coordinate system is updated to be
Figure FDA0002961521660000014
Wherein
θk,1＝θ[k]+(1.5)ω[k]Tsw (2)
TswIs a switching cycle;
3) when the 2 nd to q-1 th switching period of the kth control period comes, the switching period is interrupted and triggered, voltage vector switching in the switching period interruption is preferentially carried out due to the fact that interruption priority is high, and the voltage reference value under the ABC coordinate system is updated to be
Figure FDA0002961521660000021
Wherein
θk,i＝θ[k]+(i+0.5)ω[k]Tsw,i＝2,3,…,q-1 (4)
4) Before the q-1 switching period of the kth control period is finished, the current controller program in the kth control period is completely operated to obtain the voltage reference value of the (k +1) th control period
Figure FDA0002961521660000022
Before the q-1 switching period of the kth control period is finished, the observer program in the kth control period is completely operated, and the starting time of the kth +1 control period is obtained, namely T is (k +1) TcDq coordinate system of time is electrical angle theta [ k +1 ] under static coordinate system]And electrical angular velocity ω [ k +1 ]]；
5) When the q-th switching period of the kth control period comes, the interruption of the switching period is triggered, and the voltage vector switching in the interruption of the switching period is preferentially carried out; because the PWM signal generation link has the characteristic of delaying one beat, the voltage reference value set in the q switching period of the kth control period is the voltage reference value of the 1 switching period of the kth +1 control period, so that the voltage reference value under the ABC coordinate system is updated to be
Figure FDA0002961521660000023
2. The low control frequency control method of the high switching frequency inverter according to claim 1, characterized in that: the voltage reference vector expression used by the PWM wave generator in the ith switching period of the kth control period is
Figure FDA0002961521660000024
Wherein, it is assumed that there are q switching periods, T, in each control periodiPark(theta) is an inverse Park transformation matrix, theta k]For the electrical angle of the motor at the start of the kth control cycle, ω k]The electrical angular velocity of the motor at the start of the kth control cycle,
Figure FDA0002961521660000025
for the voltage reference vector in dq rotation coordinate system in the k control period, TswIs a switching cycle.
3. The low control frequency control method of the high switching frequency inverter according to claim 1, characterized in that: the expressions of the voltage vector output by the high switching frequency inverter in the kth control period in the ABC static coordinate system are shown as formulas (7) and (8);
Figure FDA0002961521660000031
Figure FDA0002961521660000032
expressions of voltage vectors output by the high switching frequency inverter in the kth control period in a dq rotation coordinate system are shown as formulas (9) and (10);
Figure FDA0002961521660000033
Figure FDA0002961521660000034
wherein T isiPark(θ) is an inverse Park transformation matrix, Tr(theta) is a rotation matrix of the two-phase coordinate system, theta k]For the electrical angle of the motor at the start of the kth control cycle, ω k]The electrical angular velocity of the motor at the start of the kth control cycle,
Figure FDA0002961521660000035
is the voltage reference vector in dq rotation coordinate system in the kth control period.
4. A low control frequency control method of a high switching frequency inverter according to claim 3, characterized in that: an approximate expression of a voltage vector output by the high switching frequency inverter in the kth control period in the ABC static coordinate system is shown as a formula (11);
Figure FDA0002961521660000036
an approximate expression of a voltage vector output by the high switching frequency inverter in the kth control period in a dq rotation coordinate system is shown as a formula (12);
Figure FDA0002961521660000037
wherein T isiPark(theta) is an inverse Park transformation matrix, theta k]For the electrical angle of the motor at the start of the kth control cycle, ω k]The electrical angular velocity of the motor at the start of the kth control cycle,
Figure FDA0002961521660000038
is the voltage reference vector in dq rotation coordinate system in the kth control period.
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