CN110868123A

CN110868123A - Motor asymmetric SVPWM reconstruction method based on zero vector insertion

Info

Publication number: CN110868123A
Application number: CN201810901984.9A
Authority: CN
Inventors: 严伟; 杨颢飞
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2018-08-09
Filing date: 2018-08-09
Publication date: 2020-03-06
Anticipated expiration: 2038-08-09
Also published as: CN110868123B

Abstract

The invention provides the motor phase current detection method which is easy to realize algorithm, relatively good in control effect and capable of effectively reconstructing three-phase current in a non-observation area only by using a direct current bus current acquisition mode when a space vector modulation mode is used for driving a motor. Aiming at the vector which cannot be subjected to accurate current sampling because the application time of the non-zero basic space vector in the PWM carrier period is too short, the SVPWM waveform is reconstructed by increasing the rear-end sampling time to enable the rear-end sampling time to meet the voltage sampling minimum window time under the condition that the magnitude and the direction of the vector sum in three continuous PWM carrier periods are not changed. According to the invention, the non-observation region is converted into the observation region by inserting the asymmetric PWM mode modulation of the zero vector in three continuous PWM carrier periods, and meanwhile, the algorithm period is constructed, so that the generation of voltage ripples is reduced, and the distortion of the voltage vector action is avoided.

Description

Motor asymmetric SVPWM reconstruction method based on zero vector insertion

Technical Field

The invention relates to the technical field of motor space vector modulation (SVPWM) phase current reconstruction, in particular to a motor phase current reconstruction method for generating a current acquisition time window by inserting vectors into an SVPWM waveform.

Background

In a permanent magnet synchronous motor control system, the detection of three-phase current of a motor is an important link for current feedback regulation. In the sensored phase current detection method, it is common to use current sensors such as current transformers to detect phase currents, that is, three or at least two current sensors are disposed at three-phase connections of the motor, and d-q axis currents of the motor are obtained according to an operation and are used as current feedback. A conventional current sensor is not easy to install and expensive, and a sensorless technology is urgently needed to perform current feedback in order to reduce cost. In applications where the requirement on the acquisition accuracy is not high and the cost is sensitive, current acquisition by directly connecting sampling resistors in series is a common way. The sampling resistor is connected in series, and one is that the sampling resistor is connected in series on a phase line of the motor, and the other is that the sampling resistor is connected in series on a direct current bus. Because the electric current that gathers on the motor phase line still needs other processings just can directly use in the chip, needs two at least sampling resistance can correct reduction three phase current simultaneously, is consequently being widely used carrying out the method that motor phase current gathered through direct current bus current sampling.

The motor phase current is detected by sampling the direct current bus current, namely a single resistance sampling (1-SHUNT sampling) technology. Fig. 1 is a structural schematic diagram of the technology, a sampling resistor is connected in series between an X point at the joint of three lower bridge arms and a negative end of a direct current power supply, and the purpose of reducing three-phase current can be achieved by using single resistor sampling according to bus current and analysis of the switching state of a switching tube. This method is therefore referred to as single resistance sampling.

For the single-resistor sampling technology, if the direct current bus current is correctly collected, the sampling time must be greater than a minimum window time T_MINThis time is approximately equal to the voltage stabilization time T_SAnd ADC sampling latch time T_HOf (a) and (b), i.e. T_MIN＝T_S+T_H. When the SVPWM mode is used for driving, the action time of a certain basic space vector in a PWM carrier period is less than T in the interval for generating the basic space vector and the low-speed interval_MINIn this case, the SVPWM waveform needs to be reconstructed to make the acting time of the basic space vector reach T_MIN。

When SVPWM modulation is carried out, the action time of any basic space vector is less than T_MINIs called a non-observation region, and all elementary space vector action times within a PWM carrier period are greater than or equal to T_MINIs referred to as an observable region. In general, in order to avoid the generation of the non-observation region, an insertion zero vector method, an asymmetric PWM reconstruction method, a symmetric PWM reconstruction method, or the like may be used. Inserting a zero vector method, namely inserting a zero vector carrier for observation between two PWM carrier waveforms in a non-observation region, and carrying out current collection when the zero vector exists; the asymmetric reconstruction method adopts asymmetric PWM modulation in a non-observation region to prolong the action time of the basic space vector to be more than T_MINThen compensating to correct size and direction through vector decomposition; and symmetric PWM reconstruction, namely, the SVPWM waveform is symmetrically reconstructed in a non-observation area according to the center of a PWM carrier triangular wave so as to achieve the aim of meeting the acquisition window time TMIN.

In the existing zero vector insertion method, because a zero vector is inserted into a normal waveform, a current vector generates large distortion, and current harmonics are increased more; and asymmetric and symmetric PWM wave modulation have similar problems.

In the motor phase current reconstruction method based on the symmetric PWM carrier of patent No. 201110331123.X, a method of decomposing a non-zero vector in a certain non-observation region into two adjacent non-zero basic vectors causes large harmonics due to the need to switch the states of two-phase switching tubes simultaneously when switching the vectors (for example, two non-zero basic vectors, V2(110) and V6(101), are needed when synthesizing V1). In the 201010039771.3 patent, "motor phase current detection method based on dc bus current", when the target current vector to be synthesized is close to zero, since the space vector in the non-observation region cannot be directly reconstructed in a small number of PWM cycles, a long algorithm cycle is required, which is not favorable for accurate sampling.

Disclosure of Invention

The invention aims to provide a space vector modulation method which is simple in algorithm, strong in universality and good in control effect and can continuously collect current in a traditional non-observation area, so that the defects of the conventional reconstruction method are overcome.

The technical problem solved by the invention can be realized by adopting the following technical scheme:

a phase current reconstruction method of a motor is characterized in that the motor is driven in a space vector pulse width modulation mode, and a sampling resistor is connected between an X point at the lower end connection position of a three-phase bridge arm and the negative end of a direct-current power supply in series. When the vector to be reconstructed is in a non-observation area, the rear end of the three-phase PWM wave is respectively prolonged by T in three PWM carrier periods by adding a zero vector at the rear end of the SVPWM wave_typTime (T)_typ≥2T_MIN) The vector sum of the reconstructed base space vector can be made equal to the space vector before reconstruction.

All modulation vectors in the invention adopt a PWM rear-end sampling mode to reconstruct the motor phase current.

The modulation method in the non-observed region is such that the minimum action time T will not be satisfied_MINThe effective level of three-phase PWM wave of the PWM carrier period in which the basic space vector is positioned respectively prolongs T in the three PWM carrier periods_typTime, equivalent to inserting a zero vector in three carrier periods, so that each PWM carrier period has different action time greater than T_MINThe three reconstructed PWM carrier periods are referred to as a basic control algorithm set.

In the invention, in order to reduce harmonic interference, PWM carrier cycles without reconstruction can be inserted between two basic control algorithm groups in a non-observation area, and the number of the inserted carrier cycles is N. And one basic control algorithm group and N non-reconstruction PWM carrier wave periods form an algorithm period. Algorithm reconstruction is not carried out in other PWM carrier periods in the same algorithm period, and the traditional SVPWM modulation algorithm is maintained so as to reduce harmonic interference. When N is 0, the duration of each basic control algorithm group is an algorithm period, that is, each PWM period is reconstructed.

The invention adopts an asymmetric PWM mode for modulation, and ensures that a basic control algorithm group in the traditional non-observation area is three PWM modulation cyclesDuring which at least two different non-zero basis space vectors have a continuous action time greater than or equal to a minimum action time T_MINTherefore, a non-observation area of the traditional SVPWM modulation method is eliminated, and stable collection of three-phase current of the motor in the non-observation area is realized.

Drawings

Fig. 1 is a schematic diagram of a conventional single-resistor sampling three-phase driving circuit.

FIG. 2 is a schematic diagram of six elementary space vectors

FIG. 3 is a schematic diagram of front-end and back-end sampling

FIG. 4 is a schematic view of a non-observation region

FIG. 5-a is a schematic view of a non-overlapping non-observed region (first non-observed region)

FIG. 5-b is a schematic view of an overlapping non-observed region (second non-observed region)

FIG. 6 is a schematic view of the non-processing (observable region)

FIG. 7 is a time region of current sampling in a first non-observation zone

FIG. 8 is a time region for current sampling in a second non-observation zone

FIG. 9-a shows a conventional SVPWM carrier modulation scheme when the space vector approaches the second non-observation region in the first sector during one algorithm cycle

FIG. 9-b is a diagram of a reconstructed SVPWM carrier modulation scheme of the present invention during an algorithm cycle when the space vector is close to the second non-observed region in the first sector

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained below by combining the specific drawings.

The reconstruction of motor phase current through dc bus current acquisition is a mature technique, also known as single resistor sampling. The main purpose is to reduce the high cost and the high installation difficulty caused by the current sensor phase current detection technology. In an application environment with low precision requirement and sensitive cost, the single-resistor sampling is widely accepted. Compared with a three-resistor sampling mode (3-SHUNT) which is widely adopted, the current flow direction problem is not considered, and two resistors can be used less, so that the cost is reduced.

First, the space vector modulation technique, SVPWM, will be explained. As shown in fig. 2, space vector modulation accomplishes mapping of space vectors and voltage vectors by projecting the voltage vectors into a space vector coordinate system. The space vector is divided into six sectors, and the boundary of each sector is respectively six non-zero basic space vectors (hereinafter referred to as basic space vectors). The space vector of any sector can be formed by combining any number of basic space vectors, and generally consists of two basic space vectors adjacent to the sector. In this way, any of the space vectors of the six sectors can be synthesized by modulating the magnitude and direction of the basic space vector.

As can be seen from fig. 1, the three-phase driving circuit is controlled by three sets of switching transistors (IGBTs), each basic space vector corresponds to a certain on-off state of the three sets of switches, and the basic space vectors are generated by respectively controlling the on-off states of the three sets of switches. By controlling the three groups of switching tubes, basic space vectors with any size and direction can be synthesized, and space vectors in any direction can be synthesized by combining the synthesized basic space vectors, so that the motor is driven.

The six basic space vectors shown in fig. 2 are synthesized by three sets of switching tubes in fig. 1, each set of switching tubes is represented by a number, "1" represents an open-circuit tube and a closed-circuit tube, and "0" represents an open-circuit tube and a closed-circuit tube. As can be seen from fig. 2, the elementary space vectors correspond to three sets of switch tube states as follows:

elementary space vector	Switching tube state
		V1
	100
		V2	110
V3	010
		V4	011
V5	001
		V6	101

If three-phase current is deduced through the voltage collected by the single resistor, the voltage collected at different moments needs to be used for calculation. Taking SVPWM modulation in the first sector as an example, two basic space vectors V1 and V2 are generated alternately, when a V1 vector is generated, the switching tube state is 100, i.e. the tube on and the tube off are closed in phase a in fig. 1, the tube on and the tube on in phase B, C are open, and the current flowing through the sampling resistor R is phase a current; when the vector V2 is generated, the switching tube state is 110, i.e. A, B in fig. 1, the tube is open and the lower tube is closed, and the tube is open and the C-phase, and the current flowing through the sampling resistor R is the C-phase current. Because the stator coil of the motor is inductive, the stator current cannot change suddenly in a short time, so that the phase B current can be deduced by using the kirchhoff current law, and the three-phase current is obtained by reconstruction.

The traditional SVPWM modulation method is a symmetrical waveform obtained by comparing a triangular wave with a comparison register, as shown in fig. 3, AD acquisition can be performed at the rising stage of the triangular wave or at the falling stage of the triangular wave, and the sampling at the two stages is called front-end sampling and back-end sampling, respectively. In order to be able to sample a stable voltage, sampling is carried outA voltage stabilization time T is needed before the sampling point_SAfter the sampling point, an ADC latch time T is needed_HTherefore, in back-end sampling, the duration of the action of the elementary space vectors must be kept above a minimum value T_MIN＝T_S+T_H. Otherwise the sampled data will have large errors.

In the traditional SVPWM modulation mode, when synthesizing vectors in a range close to a basic space vector and a range with smaller vector length, the application time of the basic space vector of the synthesized vector is shorter than T_MINThis range is the non-observation region, as shown in fig. 4. The synthesized vector in the non-observation area needs to be synthesized in a special way to ensure that the application time of the basic space vector is longer than T when the back-end sampling is carried out_MIN。

According to the difference of the current acquisition positions after the space vector reconstruction of the non-observation region, dividing the non-observation region into two parts, as shown in fig. 5-a, a first sector is divided into A, B, C, D four areas, and a B, C area of a shadow part is a first non-observation region; as shown in fig. 5-b, the first sector is divided into A, B, C, D four areas, and the hatched area a is the second non-observation area.

The invention aims to solve the problems that single-resistor sampling can be used for reducing three-phase current in a non-observation area, and the speed and the position of a motor are estimated according to the three-phase current. The method of the invention is to modulate by adopting an asymmetric vector synthesis mode when a modulation vector is in a non-observation area, and a sector I is taken as an example for explanation.

Referring to fig. 6, for the observable region, a conventional SVPWM waveform modulation algorithm is used, and no reconstruction is needed, and in order to synthesize the current vector V0, a vector in the V1 direction and a vector in the V2 direction are applied twice, and the magnitudes are applied as V1 'and V2', respectively. The four basic vectors synthesize the target current vector V0, and the effect of generating a V0 vector is achieved.

Referring to FIG. 7, for the first non-observation region, T_V1’＜T_MIN，T_V2’＞T_MIN. If the traditional SVPWM algorithm is used, althoughThen the application time of the basic space vector of the position of the first back-end sampling is more than T_MINBut since the time of application of the elementary space vector at the location of the other back-end sample is less than T_MINTherefore, the current cannot be accurately sampled, and the SVPWM waveform of this period needs to be reconstructed. By means of extension of the three-phase PWM waves within three PWM periods, respectively, the extension time is T_typIn the first carrier period, the application time of V1' is prolonged to a value not less than T_MINEven the application time T of V1 ″_V1”＝T_V1’+Ttyp，Ttyp≥2T_MINDue to T_V1”＞2T_MINAnd thus may be at T_V1”A relatively accurate sampling is performed during the application time. Current data can be directly collected before and after the transformation in the second carrier period, and the current data are not shown schematically. According to the results of two back-end sampling, the magnitude of the three-phase current can be deduced.

Referring to FIG. 8, for the second non-observation region, T_V1’＜T_MIN，T_V2’＜T_MIN. If the traditional SVPWM algorithm is used, the application time of the basic space vector in the time period of two back-end sampling is less than T_MINTherefore, the two back-end samples cannot obtain accurate results, and need to be reconstructed. By means of extension of the three-phase PWM waves within three PWM periods, respectively, the extension time is T_typThe first cycle extends the application time of V1' by not less than T_MINEven the application time T of V1 ″_V1”＝T_V1’+Ttyp，Ttyp≥2T_MINDue to T_V1”＞2T_MINTherefore, more accurate sampling can be performed within the application time of V2 ″; at the same time, the second cycle extends the application time of V3' to a value not less than T_MINEven the application time T of V3 ″_V3”＝Ttyp-TV1’，Ttyp≥2T_MINDue to T_V3”＞T_MINTherefore, a comparatively accurate sampling can be made within the application time of V3 ″. According to the results of two back-end sampling, the magnitude of the three-phase current can be deduced.

Referring to fig. 9-a and 9-b, the two figures are schematic diagrams of PWM carriers of the conventional algorithm and the reconstruction algorithm based on the present invention in the second non-observation region of the first sector. In order to avoid problems such as increase in current ripple and increase in calculation amount due to vector reconstruction performed every cycle, spatial vector reconstruction may not be performed every cycle. A PWM period without reconstruction can be inserted between two basic control algorithm sets to construct an algorithm period, which is a combination of one basic control algorithm set and N PWM periods without reconstruction, with N being 0-10 in size. In some cases, the magnitude of N is appropriately increased at low speed and decreased at high speed. As can be seen from fig. 9-a, in a conventional algorithm without reconstruction, the duration of the sampling regions at the front end and the back end of the voltage in the leftmost PWM period in the period is too short to perform accurate sampling, while in the modified reconstructed algorithm carrier pattern in fig. 9-b, the waveforms of the first three PWM carrier periods in one algorithm period have been reconstructed, and according to the above explanation, the size and the direction of the space vector in the three reconstructed PWM carrier periods are consistent with the vector before reconstruction, so that other PWM carrier periods in the same algorithm period do not need to be processed except for the basic vector in the three reconstructed PWM carrier periods. In this embodiment, the non-reconstructed PWM carrier period with N being 2 inserted in the algorithm period is merely exemplified and not limited to the present invention.

When space vector modulation is performed, only the non-observation regions of other sectors need to be reconstructed according to the situation, and the difference is that the sampling time of the rear end is different. Since the basic methods of processing are similar, they will not be described in detail.

While there have been shown and described what are at present considered to be the fundamental principles of the invention and its essential features and advantages, it will be understood by those skilled in the art that the invention is not limited by the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

1. Based on the motor phase current detection method of inserting the acquisition vector, the motor is driven by adopting a space vector modulation (SVPWM) mode. In the three-phase inverter switch circuit, a sampling resistor R is connected in series between a point X at the joint of three lower bridge arms and the negative end of a direct-current power supply. When space vector modulation enters a non-observation area, the action time of a non-zero basic space vector in a PWM period is too short to meet the minimum window time of voltage sampling, under the condition that the size and the direction of the total current vector in a period of time are not changed, the rear-end sampling time is increased to meet the minimum window time of voltage sampling to reconstruct an SVPWM waveform, and then the phase current of a motor in the PWM carrier period is reconstructed in a single-resistor sampling mode.

2. The asymmetric SVPWM reconstruction method of claim 1 based on inserted acquisition vectors, characterized by: the reconstruction method increases the acting time of the non-zero basic space vector to meet the minimum window time of voltage sampling by inserting a vector at the rear end of the three-phase SVPWM wave, and reconstructs the phase current of the motor by adopting a mode of sampling at the rear end of the PWM wave at any moment.

3. The asymmetric SVPWM reconstruction method of claim 2 for motors based on inserted acquisition vectors, characterized by: and constructing a basic control algorithm group, wherein each group of time is 3 times of the PWM carrier period, reconstructing the PWM wave of one phase respectively for the basic space vector of the non-observation area in each PWM carrier period in each algorithm group, and completing the reconstruction of the PWM wave of 3 phases by three PWM carrier periods, thereby forming a group of basic control algorithms.

4. The asymmetric SVPWM reconstruction method of claim 3 for motors based on inserted acquisition vectors, characterized by: inserting N non-reconstruction PWM carrier cycles between each basic control algorithm group to construct a control algorithm cycle, wherein each algorithm cycle consists of one basic control algorithm group and N non-reconstruction PWM carrier cycles, the cycle time of each control algorithm is the sum of the time of one basic control algorithm group and the time of N non-reconstruction PWM cycles, and the basic control algorithm group reconstruction is only carried out once in each algorithm cycle for basic space vectors in a non-observation area, and the algorithm group is positioned at the beginning of the whole algorithm cycle.

5. The asymmetric SVPWM reconstruction method of claim 4 for motors based on inserted acquisition vectors, characterized by: in the control algorithm period construction, N non-reconstruction PWM carrier periods are inserted, N can be 0-10, and the insertion of 0 non-reconstruction carrier periods is that each basic algorithm group is an algorithm period, namely, each PWM period is reconstructed.

6. The asymmetric SVPWM reconstruction method of claim 4 for motors based on inserted acquisition vectors, characterized by: except the PWM carrier wave period in the algorithm group which is reconstructed in the same control algorithm period, other PWM periods in the same control algorithm period are not reconstructed, and the algorithm is the same as the vector modulation mode of the observable area.