Method for single current sensor of permanent magnet synchronous motor

Abstract

The invention discloses a method for reconstructing bus current of a single current sensor of a permanent magnet synchronous motor, which comprises the following steps of: firstly, introducing a basic principle of bus phase current reconstruction on the basis of vector control adopting an SVPWM (Space Vector Pulse Width Modulation) technology, and dividing a current reconstruction blind area by considering the influence of non-ideal factors in an actual system; a phase current reconstruction strategy based on TCSVPWM is provided, the blind area problem is solved through the method, it is theoretically proved that the method does not affect the actually output voltage vector, the action range of TCSVPWM is analyzed, and the feasibility of TCSVPWM is proved. And the TCSVPWM is compared with a vector pulse insertion method, so that the TCSVPWM can effectively reduce the switching loss, and the creativity of the TCSVPWM is proved. And finally, the specific implementation process of TCSVPWM in different six sectors is elaborated in detail.

Description

Technical Field

[0001] A field for improving the blind area of bus current reconstruction based on a single current sensor of a permanent magnet synchronous motor.

[0002] The present invention belongs to the field of permanent magnet synchronous motor single current sensor control, and relates to a method for reconstructing bus current. Background Technique

[0003] With the development of microprocessor technology, power electronic devices, and motor manufacturing processes, coupled with the proposal of vector control algorithms as typical modern control theories, the vector control system of permanent magnet synchronous motors has surpassed traditional DC systems in terms of control performance. And compared with other types of motors, permanent magnet synchronous motors are superior in terms of reliability, power density, etc., and have been widely applied in the industrial field due to these advantages. However, due to the high cost of the vector control system of permanent magnet synchronous motors, to a certain extent, it restricts the expansion of its application fields. Therefore, how to reduce the cost while ensuring the high performance of the AC control system is of great significance.

[0004] The vector control block diagram of the permanent magnet synchronous motor is as Figure 1 shown. In addition to the microcontroller and power circuit, it is also necessary to detect the rotor speed and winding current in real time to complete the closed-loop control. Among them, the detection of the winding current is usually carried out using 2 to 3 current sensors. The application of these sensors undoubtedly increases the volume, raises the cost, complicates the signal conditioning circuit, and the product differences between multiple sensors also bring errors to the current detection. Therefore, the use of a single current sensor has important research value.

[0005] Among the current methods for implementing a single current sensor, the current sensor is placed on the bus side, and by measuring the bus current, the currents of the three-phase windings can be reconstructed, that is, the current reconstruction based on the bus. The method is relatively mature and the principle is simple, and the current reconstruction can be realized at low cost. However, it has a reconstruction blind area, resulting in a large error in the reconstructed current. Therefore, the research on bus current reconstruction technology has important engineering significance. Summary of the Invention

[0006] The present invention provides a method for reconstructing the bus current of a permanent magnet synchronous motor based on a single current sensor, and the implementation process is as follows:

[0007] First, analyze the reconstruction principle of the bus current. In the vector control system of the permanent magnet synchronous motor, a vector control strategy based on SVPWM technology is adopted. According to the on-off states of the six power switching devices in the inverter, the voltage vectors can be divided into six space vectors and two zero vectors, and each output voltage vector is composed of a combination of these eight basic voltage vectors.

[0008] The main circuit of the permanent magnet synchronous motor drive system is asFigure 2 For the shown topological structure, during the action of each basic voltage vector, there is a certain corresponding relationship between the bus current and the phase current of the motor winding. The state where the upper switch of each phase leg is turned on and the lower switch is turned off is defined as "1", and the state where the lower switch is turned on and the upper switch is turned off is defined as "0". When the switching state is (1 00), the current loop is the current of phase A winding; similarly, when the switching state is (1 10), the current loop is the current of phase C.

[0009] By analyzing the current loops under the switching states of eight basic voltage vectors, the corresponding relationship between the bus current and the phase current shown in Table 1 is obtained. The direction of current flowing into the winding is defined as positive, and the direction of current flowing out of the winding is defined as negative.

[0010] switch current switch current 100 +ia 010 +ib 101 -ib 110 -ic 001 +ic 000 0 011 -ia 111 0

[0011] Table 1

[0012] Based on the above analysis, taking the case where the given reference voltage vector is located in the third sector as an example, within each switching period, the reference voltage vector consists of four states: (0 0 0), (1 0 0), (1 1 0), and (1 1 1). When the switching state is (1 00), the bus current is detected to obtain the current of phase A winding, and when the switching state is (1 1 0), the bus current is detected to obtain the current of phase C winding. After obtaining the currents of phases A and C, the current of phase B can be calculated using the relationship ia + ib + ic = 0. Generally, the frequency of PWM is much higher than the operating frequency of the motor, so it can be approximately considered that the current remains unchanged within one switching period. Thus, the current values of each phase winding of the motor within this switching period are obtained.

[0013] Secondly, analyze the blind area problem in the reconstruction process. In the ideal case, the current sampling can be completed instantaneously, that is, the corresponding phase current information can be collected when the corresponding basic voltage vector acts for a very short time. However, in the actual circuit system, there are many non-ideal factors, such as the dead time Td, the turn-on delay Ton and turn-off delay Toff of power electronic devices, the time Th of the AD converter, and the current establishment time Tset. These factors will cause the phase current reconstruction to be unable to be completed in some cases. Therefore, it is necessary to ensure that the action time of a certain basic voltage vector state is not less than a minimum time value Tmin, and the minimum time should satisfy the inequality relationship of formula (1).

[0014] Tmin ≥ Td + Ton + Tset + Th (1)

[0015] It is introduced above that the basic voltage vector needs a minimum action time to ensure accurate current sampling. There are two special regions in the actual operation of the motor: the sector boundary region and the low modulation region, as Figure 3As shown, it is impossible to guarantee the minimum action time requirement of the voltage vector in such two regions.

[0016] In the sector boundary region, the output voltage vector in this region is close to the boundaries of the six sectors. At this time, there will be a situation where the amplitude of a certain basic voltage vector is too small. Taking the voltage vector in the fourth sector and close to the basic voltage vector U1 as an example, the synthesis of the basic vector voltage is as Figure 4 shown. The action time of the U3 voltage vector is too short, resulting in the inability to complete the sampling of the C-phase current and causing the reconstruction to fail.

[0017] In the low modulation region, when the motor is in no-load or light-load conditions and usually operates in this region, there will be a situation where the amplitudes of both basic voltage vectors are too small. Taking the fourth sector as an example again, the synthesis of the basic vector voltage is as Figure 5 shown. The action times of the voltage vectors U1 and U3 are both too short, resulting in the inability to collect the current values of the A-phase and C-phase and causing the reconstruction to fail.

[0018] Finally, if the current sampling is to be completed within the reconstruction blind area, the requirement of the minimum action time of the voltage vector must be met. At this time, it is necessary to optimize the voltage vector. While ensuring the completion of the current sampling of each phase, the phase and amplitude of the synthesized voltage vector are kept unchanged, so as to minimize the impact of the current reconstruction algorithm on the original vector control performance.

[0019] This paper proposes a phase current reconstruction strategy based on three-phase complementary space vector pulse width modulation (TCSVPWM).

[0020] When the voltage vector is in the sector boundary region, the action time of a basic voltage vector is insufficient, resulting in the inability to complete the sampling of the phase current and causing the reconstruction to fail. At this time, add 2Tmin time to the vector with insufficient action time. To prevent affecting the output voltage vector, insert two voltage vectors with a phase difference of 120° from this vector, and the action time of both is 2Tmin. The added vector and the two inserted vectors cancel out to the zero vector, without affecting the output voltage vector.

[0021] When the voltage vector is in the low modulation blind area, the action times of both basic voltage vectors are insufficient. At this time, add 2Tmin to the action times of both these vectors. To prevent affecting the output vector, insert two more vectors, whose phases differ by 180° from the added vectors respectively, and the action time of both is 2Tmin. The added vectors and the inserted vectors cancel out to the zero vector, without affecting the output voltage vector.

[0022] When the output vector is in the sector boundary region, two basic vectors with a phase angle difference of 120° are inserted instead of a basic vector with a phase angle difference of 180° to reduce more switching times, in order to maintain consistency with the low modulation blind area and reduce harmonics.

[0023] Due to the increase in the action time of the zero vector, it is necessary to analyze the working range, as shown in Equations (2) and (3). Taking the fourth sector as an example, when the synthesized voltage vector is close to U1:

[0024]

[0025] Where Tsm = Ts + 6tmin, Ts is the period time of a PWM wave, Vs is the output voltage vector, and Vsc is the output voltage vector after TCSVPWM reconstruction, and the two are equal.

[0026] To solve the problem of the voltage drop caused by TCSVPWM, it is necessary to increase the action time of the original basic voltage vector to Ts m / Ts times of the original after introducing the vector pulse to achieve the purpose of complete compensation. However, the sum of the times of T1 and T3 in the formula is at most Ts, so the limit amplitude and effective interval of the output voltage vector are reduced to Ts / Tsm of the original.

[0027] Compared with the traditional method of reconstructing the bus current blind area: the pulse insertion method, TCSVPWM can reduce the number of switching times.

[0028] Principle of the pulse insertion method: Insert a pulse sequence between adjacent switching cycles of the traditional space vector pulse width modulation technology, as Figure 6 shown. During the period when each pulse acts, sample the bus current, and the phase current of the winding can be accurately obtained. The currents of ia, ib, and ic are collected in the switching states (100), (010), and (001). Since the sum of the three inserted vectors is 0, it does not affect the finally synthesized voltage vector.

[0029] Since the pulse insertion method inserts a measurement cycle in each period and introduces three basic vectors, this will undoubtedly increase the number of switching times and increase the loss. It can be seen that each switch will have an additional state switching process from 0 to 1 and then to 0 in each cycle, resulting in 6 more switching times for the upper bridge arm, and a total of 12 more switching times.

[0030] Taking the fourth sector as an example for TCSVPWM, when the voltage vector is in the boundary blind area and close to the U1 boundary blind area, the PWM waveform is as Figure 7 shown. The red line is the waveform after TCSVPWM reconstruction. At this time, there is an additional process from 0 to 1 and then to 0 for the upper bridge arms of A, B, and C, a total of 6 times, and the loss is not reduced; when close to the U3 boundary blind area, asFigure 8 As shown, at this time, there is an additional process from 0 to 1 and then back to 0 on the upper bridge arms of A and B, a total of 4 times, reducing the switching loss by 2 times.

[0031] When the voltage vector is in the low modulation region, as Figure 9 shown, at this time, there is an additional process from 0 to 1 and then back to 0 on both the upper bridge arms of A and B, a total of 4 times, reducing the switching loss by 2 times.

[0032] And so on, calculate the number of switching times of the upper bridge arm of TCSVPWM in the 6 sectors respectively, and the results are shown in Table 2:

[0033]

[0034] Table 2

[0035] In the voltage vector hexagon, with the counterclockwise direction as the reference direction, the right boundary blind area is the first boundary blind area in each sector, and the left boundary blind area is the second boundary blind area. That is, in the first to sixth sectors, the right boundary blind area is the blind area close to the voltage vectors U4, U6, U2, U3, U1, U5; the left boundary blind area is the blind area close to the voltage vectors U6, U2, U3, U1, U5, U4.

[0036] Thus, it can be concluded that compared with the vector pulse insertion method, TCSVPWM reduces the switching loss by 16.7% in the boundary blind area, reduces the switching loss by 33.3% in the low modulation region, and reduces the overall switching loss by 22.2%. Description of the Drawings

[0037] Figure 1 is the control block diagram of the permanent magnet synchronous motor based on the single current vector system.

[0038] Figure 2 is the main circuit topology diagram of the permanent magnet synchronous motor based on the single current vector system.

[0039] Figure 3 is the schematic diagram of the current reconstruction blind area in the hexagon area formed by the voltage vectors.

[0040] Figure 4 is the vector synthesis diagram of the boundary blind area.

[0041] Figure 5 is the vector synthesis diagram of the low modulation blind area.

[0042] Figure 6 is the PWM waveform insertion of the vector pulse insertion method.

[0043] Figure 7 is the PWM correction of TCSVPWM in the fourth sector and close to the U1 boundary blind area.

[0044] Figure 8 It is the PWM correction of TCSVPWM in the fourth sector and close to the blind area of the U3 boundary.

[0045] Figure 9 It is the PWM correction of TCSVPWM in the fourth sector and located in the low modulation blind area. Specific implementation mode

[0046] The present invention will be further described below in conjunction with the accompanying drawings and implementation cases.

[0047] Taking the fourth sector as an example, the PWM waveform is as Figure 7 shown. When the voltage vector to be synthesized is close to U1, the action time of U3 is insufficient. Add 2Tmin to the action time of U3, and insert two basic voltage vectors U5 and U6 with a phase angle difference of 120° from U3, and act for 2Tmin; similarly, as Figure 8 shown. When the voltage vector to be synthesized is close to U3, the action time of U1 is insufficient. Add 2Tmin to the action time of U1, and then insert two basic voltage vectors U2 and U4 with a phase angle difference of 120° from U1, and act for 2Tmin.

[0048] When the voltage vector to be synthesized is in the low vector modulation area, as Figure 9 shown. The action times of U1 and U3 are insufficient. Add 2Tmin to the action times of both U1 and U3, and insert two basic voltage vectors U6 and U4 with a phase angle difference of 180° from U1 and U3 respectively, and act for 2Tmin.

[0049] According to the principle of TCSVPWM, the specific implementation schemes in each sector are as follows. The action times of the added vector and the inserted vector are both 2Tmin:

[0050] First sector: Close to the blind area of the U4 boundary, increase the action vector time of U6, and insert vectors U3 and U5; close to the blind area of the U6 boundary, increase the action vector time of U4, and insert vectors U1 and U2; close to the low modulation blind area, increase the action vector times of U4 and U6, and insert vectors U1 and U3;

[0051] Second sector: Close to the blind area of the U6 boundary, increase the action vector time of U2, and insert vectors U1 and U4; close to the blind area of the U2 boundary, increase the action vector time of U6, and insert vectors U3 and U5; close to the low modulation blind area, increase the action vector times of U2 and U6, and insert vectors U1 and U5;

[0052] Third sector: Close to the blind area of the U2 boundary, increase the action vector time of U3, and insert vectors U5 and U6; close to the blind area of the U3 boundary, increase the action vector time of U2, and insert vectors U1 and U4; close to the low modulation blind area, increase the action vector times of U2 and U3, and insert vectors U4 and U5;

[0053] Fourth sector: Near the blind area of the U3 boundary, increase the active vector time of U1 and insert the U2 and U4 vectors; near the blind area of the U1 boundary, increase the active vector time of U3 and insert the U5 and U6 vectors; near the low modulation blind area, increase the active vector times of U1 and U3 and insert the U4 and U6 vectors;

[0054] Fifth sector: Near the blind area of the U1 boundary, increase the active vector time of U5 and insert the U3 and U6 vectors; near the blind area of the U5 boundary, increase the active vector time of U1 and insert the U2 and U4 vectors; near the low modulation blind area, increase the active vector times of U1 and U5 and insert the U2 and U6 vectors;

[0055] Sixth sector: Near the blind area of the U5 boundary, increase the active vector time of U4 and insert the U1 and U2 vectors; near the blind area of the U4 boundary, increase the active vector time of U5 and insert the U3 and U6 vectors; near the low modulation blind area, increase the active vector times of U4 and U5 and insert the U2 and U3 vectors.

[0056] In summary, the basic voltage vectors inserted in different blind areas are shown in Table 3. The definitions of the right boundary, left boundary, and low modulation blind area are the same as those in Table 2.

[0057]

[0058] Table 3

[0059] The current research basis related to this project mainly includes:

[0060] Motor control theory and technology: Extensive literature research and theoretical analysis have been carried out on the modeling of permanent magnet synchronous motors, current reconstruction methods, and their implementation strategies. The principle and technical difficulties of bus current reconstruction under the condition of a single current sensor have been initially mastered.

[0061] Application research of the TCSVPWM algorithm: Existing literature and simulation studies have shown that the TCSVPWM algorithm has significant advantages in improving current sampling accuracy and system dynamic response. However, its stability under different working conditions still needs to be further verified and optimized to better meet the actual needs of the permanent magnet synchronous motor control system. Experimental data acquisition and analysis experience: Have basic experimental data acquisition capabilities and data analysis techniques, which can support the acquisition and processing of bus current waveforms during motor operation and provide data support for the performance evaluation of the TCSVPWM algorithm.

[0062] A patent for online parameter identification of permanent magnet synchronous motors is under substantive examination: Currently, an invention patent related to motor control is in the stage of substantive examination. The relevant technical achievements provide a good theoretical and technical extension basis for the implementation and optimization of the TCSVPWM algorithm in this project.

Claims

1. The present invention provides a method for reconstructing the voltage vector blind area of a single current sensor for a permanent magnet synchronous motor, which is introduced as follows: In the main circuit topology of the permanent magnet synchronous motor control system, there are six power switch devices. According to their on-off states, the voltage vectors can be divided into six space vectors and two zero vectors, and each output voltage vector is composed of a combination of these eight basic voltage vectors. By analyzing the current loops in the switching states of the eight basic voltage vectors, the corresponding relationship between the bus current and the phase current is obtained to achieve current reconstruction. However, in the actual circuit system, there are many non-ideal factors, such as the dead time Td, the on-off delay Ton (Toff) of the power electronic device, the minimum sampling and holding time Th of the AD converter, and the current establishment time Tset. To accurately sample the current, it is necessary to ensure that the action time of a certain basic voltage vector is not less than the minimum time value Tmin, and the minimum time should satisfy the inequality (1). Tmin≥Td+Ton+Tset+Th (1) Therefore, a phase current reconstruction strategy based on three-phase complementary space vector pulse width modulation (TCSVPWM) is proposed. When the voltage vector is in the sector boundary area, the action time of a basic voltage vector is insufficient, resulting in the inability to complete the sampling of the phase current and causing the reconstruction to fail. At this time, add 2Tmin time to the vector with insufficient action time. To prevent affecting the output voltage vector, insert two voltage vectors with a phase angle difference of 120° from this vector, and the action time of both is 2Tmin. The added vector and the two inserted vectors cancel each other out to form a zero vector, without affecting the output voltage vector. When the voltage vector is in the low modulation blind area, the action times of both basic voltage vectors are insufficient. At this time, add 2Tmin to the action times of both of these vectors. To prevent affecting the output vector, insert two more vectors, whose phase angles differ from the added vectors by 180° respectively, and the action time of both is 2Tmin. The added vectors and the inserted vectors cancel each other out to form a zero vector, without affecting the output voltage vector.

2. The phase current reconstruction strategy of three-phase complementary space vector modulation according to claim 1 is specifically implemented as follows: First, increase the action time of the voltage vector with insufficient action time by 2Tmin. Secondly, insert voltage vectors in the blind area. For the right boundary blind area from the first to the sixth sector, and the left boundary blind area from the second to the sixth and then to the first sector, insert six groups of vectors U3, U5; U1, U4; U5, U6; U2, U4; U3, U6; U1, U2 respectively; for the low modulation blind area from the first to the sixth sector, insert six groups of vectors U1, U3; U1, U5; U4, U5; U4, U6; U2, U6; U2, U3 respectively. The action time of the inserted vectors is also 2Tmin. In the voltage vector hexagon, with the counterclockwise direction as the reference direction, the right boundary blind area is the first boundary blind area in each sector, and the left boundary blind area is the second boundary blind area. That is, in the first to sixth sectors, the right boundary blind area is the blind area close to the voltage vectors U4, U6, U2, U3, U1, U5; the left boundary blind area is the blind area close to the voltage vectors U6, U2, U3, U1, U5, U4.

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