CN113381660B - Method for eliminating influence of low-order harmonic waves of PWM overmodulation region on closed-loop control - Google Patents
Method for eliminating influence of low-order harmonic waves of PWM overmodulation region on closed-loop control Download PDFInfo
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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
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/0003—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
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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
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- H02P21/14—Estimation or adaptation of machine parameters, e.g. flux, current or voltage
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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
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- H02P21/14—Estimation or adaptation of machine parameters, e.g. flux, current or voltage
- H02P21/18—Estimation of position or speed
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- 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
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
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- H—ELECTRICITY
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- 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
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- Y02E40/40—Arrangements for reducing harmonics
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Abstract
The invention relates to a method for eliminating the influence of low-order harmonic waves in a PWM overmodulation region on closed-loop control. The method adopts digital low-pass filtering technology to eliminate the influence of all low-order harmonics on control, overcomes the problem of slow dynamic response speed caused by the filtering technology by filtering control software, and has the basic logic function that when the load changes or the rotating speed instruction value changes, the filtering link is closed, the control system responds instantly, and the vector-controlled quadrature axis current is enabled to bei T Or electromagnetic torqueT em Generating jump; and when the transient process is finished, starting a filtering link. The method can solve the contradiction between filtering and dynamic response, effectively overcomes the influence of low-order harmonic waves of a PWM overmodulation region on closed-loop speed regulation vector control, expands the existing PWM control from a linear region to the overmodulation region, improves the maximum output fundamental wave voltage of PWM by 10 percent, and enlarges the corresponding numerical value of the constant-torque speed regulation range of the motor.
Description
Technical Field
The invention relates to a PWM overmodulation technology and vector control, in particular to a method for eliminating the influence of low-order harmonic waves of a PWM overmodulation region on closed-loop control.
Background
The PWM (pulse width modulation) overmodulation technology has obvious significance for improving the amplitude of the maximum output fundamental voltage and expanding the constant torque speed regulation range of the motor. Currently SVPWM (space vector p)Research on over-modulation algorithm of (SVPWM) is common [1-21] However, the algorithm is complex in structure and difficult to apply. PWM overmodulation technique using split variable modulation wave [22-23] Has the outstanding advantages that the PWM overmodulation algorithm is simple, and forms an extended relation of seamless connection with the prior SPWM (sinusoidal pulse width modulation) technology to form a covering M which belongs to the 0, 4/pi]The full-voltage range CBPWM (carrier-base PWM) algorithm has the advantages of low THD (total harmonic distortion) value and small harmonic influence in the full-voltage range. However, unlike PWM in the linear region, PWM waves in the overmodulation region have low harmonics of 5, 7, 11, 13, etc., and have large values, so that the output voltage is severely distorted, resulting in torque ripple of the motor. Although the amplitude of the rotational speed pulsation caused by the torque pulsation under the high-speed running condition is small, in a closed-loop speed regulation vector control system, the feedback quantity of a low-order harmonic component contained in the motor current influences the closed-loop PI (proportional integral) control, so that the closed-loop PI control cannot normally perform an operation function, and even the output voltage is oscillated. This problem prevents the use of PWM overmodulation techniques in closed loop control. Method for supplying power by adopting multi-level inverter at present [1][2] Inhibiting low-order harmonic wave, or eliminating 5 and 7-order harmonic wave by using a method of phase-shifting 30-degree double three-phase winding motor and supplying power by six-phase voltage source inverter [3] But not the 11, 13 th harmonics. All these methods require the use of a doubled number of power semiconductor switching devices and the PWM algorithms and controls are complex.
Fig. 1 shows a three-phase winding ac motor system powered by a three-level inverter, and compared with a general two-level inverter, the level number of output voltage is significantly increased, so that under the same switching frequency condition, the output voltage waveform quality is greatly improved, the harmonic content is significantly reduced, and the low-order harmonic influence in a PWM overmodulation region is favorably suppressed. However, the number of power semiconductor switches used is doubled compared to a two-level inverter. In addition, under the condition of load, the current flows through the midpoint O of the inverter, so that the potential of the midpoint O is easy to change, and deviates from the zero potential under the symmetrical condition, thereby influencing the sine degree of an output waveform, and additionally generating other harmonics. This is an inherent problem of three-level inverters.
Fig. 2 shows a method for eliminating 6n ± 1 (n =1,3,5, \ 8230;) harmonics by using a phase-shifted 30 ° dual three-phase winding motor and a six-phase voltage source inverter for power supply. The motor is provided with two sets of three-phase windings, namely A, B, C, D, E and F three-phase windings, which are spaced at an electrical angle of 30 degrees, and three-phase power supplies respectively applied to the two sets of windings are also different in time at an electrical angle of 30 degrees, so that 6n +/-1 (n =1,3,5, \ 8230;) subharmonics contained in the magnetic field of each winding are completely counteracted. But still 12n ± 1 (n =1,3,5, ...) harmonics exist without any attenuation. The harmonic of the 11 th and 13 th order voltages is relatively large, the current generated by the winding contains the same harmonic, and the feedback quantity of the harmonic will affect the closed loop PI (PI) control, and will still cause the output voltage to oscillate. Because the inverter power supply is six-phase, the number of required switch devices is doubled compared with the three-phase inverter power supply, thereby increasing the cost and increasing the control complexity.
In summary, the existing methods for eliminating or suppressing the low-order harmonic influence in the PWM overmodulation region have characteristics and disadvantages, and cannot completely eliminate the influence of the low-order harmonic current feedback generated during the PWM overmodulation region control on the closed-loop control. And the common disadvantage of the described methods is the use of a multiplied number of power semiconductor switching devices, which leads to increased costs. And the PWM algorithm and related control become complicated due to the large number of switching devices.
Reference:
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[6]Merlin Chai,Dan Xiao,Rukmi Dutta,et al.Space vector PWM techniques for three-to-five-phase indirect matrix converter in the overmodulation region[J].IEEE Transactions on Industrial Electronics，2016，63(1)：550.
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Yuan Yuan,Zhu Xiaoyong,Zuo Yuefei,et al.Decoupled SVPWM control strategy for open winding permanent magnet synchronous motor with common DC bus[J].Transactions of China Electrotechnical Society，2019，34(22)：4670.
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Huang Shoudao，Zhao Li，Zheng Jian，et al.Four-vector modulation method for six-phase motor SVPWM based on interior point algorithm ofweightedpath[J].Transactions ofChina Electrotechnical Society,2019，34(2)：264.
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Disclosure of Invention
The invention aims to provide a method for eliminating the influence of low-order harmonic waves of a PWM overmodulation region on closed-loop control, which adopts a digital low-pass filtering technology to eliminate the influence of all low-order harmonic waves on the control, overcomes the problem of slow dynamic response speed caused by the filtering technology through filtering control software, thereby solving the contradiction between filtering and dynamic response, effectively overcoming the influence of the low-order harmonic waves of the PWM overmodulation region on closed-loop speed regulation vector control, expanding the existing PWM control from a linear region to an overmodulation region, improving the maximum output fundamental voltage of PWM by 10 percent, and expanding the corresponding numerical value of the constant torque speed regulation range of a motor.
In order to achieve the purpose, the technical scheme of the invention is as follows: a method for eliminating the influence of low-order harmonic waves in a PWM overmodulation region on closed-loop control adopts a digital low-pass filtering discrete algorithm to eliminate the influence of all low-order harmonic waves on the control, and overcomes the problem of slow dynamic response speed caused by the digital low-pass filtering discrete algorithm through filtering control software; the basic logic function of the filtering control software is to close the filtering link when the load changes or the rotating speed instruction value changes, so that the control system responds instantly, and the vector-controlled feedback quadrature axis current i is enabled T Or electromagnetic torque T em Generating jump; and when the transient process is finished, starting a filtering link.
In an embodiment of the present invention, the implementation manner of eliminating the influence of all the low-order harmonics on the control by using the digital low-pass filtering discrete algorithm is as follows:
in order to eliminate the influence of low-order harmonic component contained in feedback current on feedback control, a filtering link is arranged on three PI calculation channels, and the method is specific: for feedback direct axis current i M I.e. with respect to Δ i M Is calculated by PIApplying low-pass filtering to the quadrature axis voltage V T I.e. with respect to Δ i T The output of PI operation is low-pass filtered, and feedback quadrature axis current i T I.e. with respect to Δ i T Applying low-pass filtering to the PI operation input quantity of (1); the digital low-pass filtering discrete algorithm adopted by the filtering link is as follows:
Y out (k)＝K 1 Y out (k-1)+K 2 Y in (k) (1)
in the formula, Y out (k) Filtering the output quantity for the k-th sampling period, Y out (k-1) is the filtered output of the k-1 sample period, Y in (k) The input quantity is filtered for the kth sampling period,
τ is the filter time constant, T C Is a PWM carrier period, namely a sampling period; at each cycle of the system, sampling period T C Real-time calculation of i by formula (1) M 、V T 、i T The calculation of the filtered output values of the quantities is a cyclic process, thereby realizing the input quantity Y to the formula (1) in (i M 、V T 、i T ) Filtering out the harmonic waves in the output signal to obtain an output Y out Only the fundamental wave conversion value is contained, and no harmonic wave is contained, so that the influence of the harmonic wave on the subsequent PI control is eliminated; before the loop operation is finished, the Y of the current operation should be saved out (k) The value is used as Y of the next cycle operation out (k-1) value.
In an embodiment of the present invention, in the digital low-pass filtering discrete algorithm, K is used 1 、K 2 Must satisfy K 1 ＞0，K 2 > 0 and K 1 +K 2 Relation of =1, K 2 The smaller the value, the better the filtering effect.
In an embodiment of the present invention, the filtering control software specifically implements the following functions:
controlling to close V aiming at transient process triggered by two conditions of motor load change or rotating speed instruction value change T 、i T Filtering until the transient process is finished; when the reference rotation speed n is measured ref I.e. the rotation speed command value is greater than the rated rotationFast opening V T 、i T Filtering, otherwise, closing the filtering; to keep the motor flux linkage constant, i is always aligned M Filtering; since the change of the load of the motor necessarily causes the change of the reference speed, when the change delta _ n of the reference speed is detected to exceed a given value, V is closed T 、i T Filtering to make the control system respond instantaneously, i.e. feedback of quadrature-axis current i T Or electromagnetic torque T em Jump is instantly generated to prompt the system to quickly reach a new state; closing V T 、i T The filtering time depends on the value of the variable delta _ t, the value is the transient response time of the system, the value depends on the system electric time constant, when the time counter t reaches the value of delta _ t, the transient process is finished, and V is opened T 、i T Filtering and resetting t; when the reference rotation speed n is measured ref Is changed and n ref New value greater than rated speed n N While closing V T 、i T Filtering, when the time counter t value reaches delta _ t value, the transient process is ended, and V is opened T 、i T Filter and reset t.
In an embodiment of the present invention, the filtering control software further has the following functions:
setting two variables of a rotating speed detection permission flag sp _ flight and a load detection permission flag load _ flight; when the transient process caused by load change is processed, the sp _ flight variable is reset, and the reference rotating speed n is forbidden ref Detecting the change until the transient process is finished; when processing the reference speed n ref And resetting the load _ floating variable during the transient process caused by the change, and forbidding the detection of the load change until the transient process is finished. Thereby avoiding the simultaneous confrontation with the load and the reference rotation speed n ref Transient processes caused by the change.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a new method for eliminating the influence of low-order harmonic waves of a PWM overmodulation region on closed-loop control, the method adopts a digital low-pass filtering technology to eliminate the influence of all the low-order harmonic waves on the closed-loop control, and the problem of slow dynamic response speed caused by the filtering technology is solved through filtering control software; the method has the following advantages:
1. the closed-loop speed regulation vector control system is suitable for the power supply of a general two-level inverter, the number of power semiconductor switching devices is not required to be increased, and the hardware cost is not increased;
2. the algorithm is simple, the filtering function can be realized only by embedding filtering control software into the conventional vector control system, the low-order harmonic influence in a PWM overmodulation region is eliminated, and the system software overhead is basically not increased;
3. after the influence of filtering on the dynamic response of the system is overcome, the dynamic performance of closed-loop speed regulation vector control in the PWM overmodulation region reaches the same level as that in the linear modulation region.
Drawings
Fig. 1 is a three-phase winding ac motor system powered by a three-level inverter.
Fig. 2 is a phase-shifted 30 ° dual three-phase winding ac motor system with a six-phase voltage source inverter supply.
Fig. 3 is a diagram of a vector control system.
Fig. 4 is a block diagram of a filtering process according to the present invention.
Detailed Description
The technical scheme of the invention is specifically explained below with reference to the accompanying drawings.
The invention relates to a method for eliminating the influence of low-order harmonic waves in a PWM overmodulation region on closed-loop control, which adopts a digital low-pass filtering discrete algorithm to eliminate the influence of all low-order harmonic waves on the control and solves the problem of slow dynamic response speed caused by the digital low-pass filtering discrete algorithm through filtering control software; the basic logic function of the filtering control software is to close the filtering link when the load changes or the rotating speed instruction value changes, so that the control system responds instantly, and the vector-controlled feedback quadrature axis current i is enabled T Or electromagnetic torque T em Generating jump; and when the transient process is finished, starting a filtering link.
The following is a specific implementation process of the present invention.
The invention provides a method for eliminating the low-order harmonic influence in a PWM overmodulation region. The basic idea of the method is that (1) a feedback current digital low-pass filtering algorithm is constructed. The algorithm adjusts the speed vector of the closed loopAnd filtering each subharmonic contained in the controlled PI input quantity (namely feedback quantity) and output quantity in real time. (2) Aiming at the problem of slow dynamic response speed caused by filtering, special control software is designed to overcome the problem. The basic logic function of the method is that when the load changes or the rotating speed command value changes, the filtering link is closed (not filtered), the control system responds instantly, and the quadrature axis current i is enabled to be T Or electromagnetic torque T em Generating jump; and when the transient process is finished, starting a filtering link. Therefore, the contradiction between filtering and dynamic response is solved, the influence of low-order harmonic waves of a PWM overmodulation region on closed-loop speed regulation vector control is effectively overcome, the existing PWM control is expanded from a linear region to the overmodulation region, the maximum output fundamental wave voltage of PWM is improved by 10%, and the constant-torque speed regulation range of the motor is also expanded to a corresponding value.
The novel method for eliminating the influence of the low-order harmonic of the PWM overmodulation region on the closed-loop control is composed of the following two parts:
1. constructing a digital low-pass filter discrete algorithm (i.e. feedback current digital low-pass filter algorithm)
Fig. 3 is a block diagram of a vector control system. For eliminating feedback current i A 、i B The influence of the low-order harmonic component on feedback control is selected to set filtering links on three PI calculation channels as shown in FIG. 3.
In FIG. 3, reference numeral 1 denotes a feedback direct axis current i M I.e. with respect to Δ i M Is low-pass filtered, and the symbol 2 represents the quadrature axis voltage V T I.e. with respect to Δ i T Applying low-pass filtering to the output of PI calculation T The filtering is to more effectively eliminate PWM output voltage oscillations. Reference 3 denotes the feedback quadrature axis current i T I.e. with respect to Δ i T The PI operation input amount of (1) is low-pass filtered.
The filtering adopts a digital low-pass discrete algorithm as follows:
Y out (k)＝K 1 Y out (k-1)+K 2 Y in (k) (1)
in the formula, Y out (k) Filtering the output quantity, Y, for the kth sampling period out (k-1) is the filtered output of the (k-1) th sampling period,Y in (k) The input quantity is filtered for the kth sampling period,
τ is the filter time constant, T C Is the PWM carrier period, i.e., the sampling period. When in use, it is used for K 1 、K 2 Must satisfy K 1 ＞0，K 2 > 0 and K 1 +K 2 Relation of = 1. K 2 The smaller the value is, the better the filtering effect is.
Fig. 3 typically employs digital control, with a sampling period T at each cycle of the system C Real-time calculation of i by formula (1) M 、V T 、i T The calculation of the filtered output values of the quantities is a cyclic process, thereby realizing the input quantity Y to the formula (1) in (i M 、V T 、i T ) Filtering out each harmonic in the output signal to make the output quantity Y out Only the fundamental wave conversion value, and no harmonic wave, thereby eliminating the influence of the harmonic wave on the subsequent PI control. Before the loop operation is finished, the Y of the current operation should be saved out (k) The value is used as Y of the next cycle operation out (k-1) value.
2. Filter control program
Filtering is associated with transient response mitigation problems, especially for K in equation (1) 2 When the value is very small, the transient response is more remarkably slowed down, and the dynamic performance of the system is influenced. For this purpose, it is contemplated that V is closed during transient events triggered by load changes or speed command value changes T 、i T Filtering element of each quantity (always keeping on i) M Filtering to make the motor flux linkage constant), so that the control system can respond instantly, i.e. quadrature axis current i T Or electromagnetic torque T em The jump is generated instantly to promote the system to reach a new state quickly. And when the transient process is finished, starting a filtering link. Thereby resolving the conflict between filtering and dynamic response. And because the filtering action only occurs in a PWM overmodulation region, the rotating speed of the motor corresponding to the region is above a rated value, and whether the i is controlled according to the rotating speed range M 、i T 、V T And (6) filtering. While for i in the linear region of PWM M 、i T 、V T No filtering is performed. Based on the above idea, a block diagram of a filtering control software program is prepared as shown in fig. 4.
The program of FIG. 4 controls the closing V for the transient process triggered by the change of the motor load or the reference rotating speed (rotating speed instruction) T 、i T And filtering until the transient process is finished. When the program detects the reference rotation speed n ref V is opened when the rotating speed is higher than the rated rotating speed T 、i T And otherwise, the filtering is closed. In order to keep the motor flux linkage constant, the pair i is always kept M And (6) filtering. Since the change in load necessarily causes a change in speed, when the program detects that the change in speed delta n exceeds a given value, V is closed T 、i T Filtering to enable instantaneous response of the control system, i.e. quadrature current i T Or electromagnetic torque T em The jump is generated instantly to promote the system to reach a new state quickly. Closing V T 、i T The filtering time depends on the value of variable delta _ t (the value is the transient response time of the system, the magnitude of which depends on the electrical time constant of the system, usually in milliseconds), when the time counter t reaches the value of delta _ t, the transient process is ended, and V is opened T 、i T Filtering and resetting t. When the program detects the reference rotation speed n ref Is changed and n ref New value greater than nominal speed n N While closing V T 、i T Filtering, when the time counter t value reaches delta _ t value, the transient process is ended, and V is opened T 、i T Filter and reset t. The program also sets two variables, namely a rotation speed detection permission flag sp _ flight and a load detection permission flag load _ flight. When the program processes the transient process caused by the load change, the sp _ flight variable is reset, and the reference rotating speed n is forbidden ref Detecting the change until the transient process is finished; when the program processes the reference speed n ref And resetting the load _ floating variable during the transient process caused by the change, and forbidding the detection of the load change until the transient process is finished. Thereby avoiding simultaneously facing the load and the reference speed n ref Transient processes caused by the change.
Based on the vector control DSP software (C language) shown in FIG. 3, the filtering control program of FIG. 4 is embedded in the corresponding position of each PI channelThen the coverage of M E [0, 4/pi ] can be realized]And (4) vector control PWM speed regulation in a full voltage range. The method is suitable for various PWM overmodulation technologies, such as SVPWM overmodulation technology [1-21] Or split type PWM overmodulation technique of variable modulation wave [22-23] And the like.
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.
Claims (3)
1. A method for eliminating the influence of low-order harmonic waves in a PWM overmodulation region on closed-loop control is characterized in that a digital low-pass filtering discrete algorithm is adopted to eliminate the influence of all low-order harmonic waves on the control, and the problem of slow dynamic response speed caused by the digital low-pass filtering discrete algorithm is solved through filtering control software; the basic logic function of the filtering control software is to close the filtering link when the load changes or the rotating speed instruction value changes, so that the control system responds instantly, and the vector-controlled feedback quadrature axis current i is enabled T Or electromagnetic torque T em Generating jump; when the transient process is finished, starting a filtering link;
the implementation method for eliminating the influence of all low-order harmonics on control by adopting the digital low-pass filtering discrete algorithm is as follows:
in order to eliminate the influence of low-order harmonic component contained in feedback current on feedback control, a filtering link is arranged on three PI calculation channels, specifically: for feedback direct axis current i M I.e. with respect to Δ i M Applying low-pass filtering to the PI operation input quantity of the voltage regulator to obtain quadrature axis voltage V T I.e. with respect to Δ i T The output of PI calculation is low-pass filtered, and the feedback alternating current i T I.e. with respect to Δ i T Applying low-pass filtering to the PI operation input quantity; the digital low-pass filtering discrete algorithm adopted in the filtering link is as follows:
Y out (k)＝K 1 Y out (k-1)+K 2 Y in (k) (1)
in the formula, Y out (k) Filtering the output quantity for the k-th sampling period, Y out (k-1) is the k-1 th sampleOutput of periodic filtering, Y in (k) The input quantity is filtered for the kth sampling period,
τ is the filter time constant, T C Is a PWM carrier period, namely a sampling period; at each cycle of the system, sampling period T C Real-time calculation of i by formula (1) M 、V T 、i T The calculation of the filtered output values of the quantities is a cyclic process, thereby realizing the input quantity Y to the formula (1) in (i M 、V T 、i T ) Filtering out each harmonic in the output signal to make the output quantity Y out Only the fundamental wave conversion value is contained, and no harmonic wave is contained, so that the influence of the harmonic wave on the subsequent PI control is eliminated; before the loop operation is finished, the current operation Y should be stored out (k) The value is used as Y of the next cycle operation out (k-1) value;
the filtering control software specifically realizes the following functions:
controlling to close V aiming at transient process triggered by two conditions of motor load change or rotating speed instruction value change T 、i T Filtering until the transient process is finished; when the reference rotation speed n is measured ref I.e. opening V when the rotation speed instruction value is greater than the rated rotation speed T 、i T Filtering, otherwise, closing the filtering; to keep the motor flux linkage constant, i is always aligned M Filtering; since the change of the load of the motor necessarily causes the change of the reference speed, when the change delta _ n of the reference speed is detected to exceed a given value, V is closed T 、i T Filtering to make the control system respond instantaneously, i.e. feedback of quadrature-axis current i T Or electromagnetic torque T em Jump is instantly generated to prompt the system to quickly reach a new state; closing V T 、i T The filtering time depends on the value of the variable delta _ t, the value is the transient response time of the system, the value depends on the system electric time constant, when the time counter t reaches the value of delta _ t, the transient process is finished, and V is opened T 、i T Filtering and resetting t; when the reference rotation speed n is measured ref Is changed and n ref New value greater than nominal speed n N While closing V T 、i T Filtering, when the t value of the time counter reaches delta _ t value, the transient process is ended, and V is opened T 、i T Filter and reset t.
2. The method for eliminating the effect of PWM overmodulation region low harmonic on closed loop control according to claim 1, wherein the discrete algorithm of digital low-pass filtering is applied to K 1 、K 2 Must satisfy K 1 ＞0，K 2 > 0 and K 1 +K 2 Relation of =1, K 2 The smaller the value, the better the filtering effect.
3. The method for eliminating the effect of PWM overmodulation region low order harmonics on closed loop control according to claim 1, wherein the filtering control software further comprises the following functions:
setting two variables of a rotating speed detection permission flag sp _ flight and a load detection permission flag load _ flight; when the transient process caused by load change is processed, the sp _ flight variable is reset, and the reference rotating speed n is forbidden ref Detecting the change until the transient process is finished; when processing the reference speed n ref Resetting a load _ floating variable during a transient process caused by change, and forbidding the detection of load change until the transient process is finished; thereby avoiding simultaneously facing the load and the reference speed n ref Transient processes caused by the change.
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