Permanent magnet synchronous motor and multi-resistor current sampling method thereof

Abstract

The invention discloses a permanent magnet synchronous motor and a multi-resistor current sampling method thereof. The permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy, and the method comprises the following steps: judging whether a current control period enters a two-phase non-sampling area or not; prolonging the lower bridge arm conduction time of two phases of which the sampling windows are less than the minimum sampling time in the three phases under the condition of judging to enter the region, so as to enable the direction of the voltage vector obtained after prolonging to be unchanged; and collecting the measurable current of the two phases after extension, and calculating the current of the third phase according to the collected current of the two phases. According to the invention, accurate control of the FOC is ensured by prolonging the conduction time of the lower bridge arms of the two phases while the direction of the voltage synthesis vector is kept unchanged. Under the condition of small external interference, a sampling window is not reserved, and current estimation in a non-sampling area is carried out through current in a symmetrical area, so that maximum torque output of the motor is ensured.

Description

Technical Field

[0001] The present disclosure relates to the field of motors, and in particular to a permanent magnet synchronous motor and a multi-resistance current sampling method thereof. Background Art

[0002] In the control process of permanent magnet synchronous motor (PMSM), in order to obtain the maximum torque output in the entire control cycle, FOC (Field-Oriented Control) is often used to control the motor.

[0003] In FOC control, it is necessary to sample the three-phase current i a 、i b and i c Participate in the control of the current loop. In multi-resistance sampling, three resistors (R a , R b and R c ) or two of the resistors are sampling resistors, and the third-phase current is calculated based on the currents collected on the two sampling resistors and Kirchhoff's law, thereby reconstructing the three-phase current.

[0004] When the motor torque is small, the maximum output voltage synthesis vector can be controlled within the sampleable vector circle interval (or sector). However, for some occasions that require maximum torque output and as high a speed as possible, the motor needs to enter the overmodulation area. At this time, the two-phase current cannot be sampled normally within a certain angle range, and the three-phase current cannot be reconstructed, affecting FOC control.

[0005] Therefore, an improved multi-resistance sampling method is needed. Summary of the invention

[0006] A technical problem to be solved by the present disclosure is to provide an improved multi-resistance sampling scheme for permanent magnet synchronous motors, which is particularly suitable for controlling motors under high load or high speed conditions. Since the motor cannot normally sample the two-phase current at this time, the present disclosure ensures the precise control of FOC by extending the conduction time of the lower bridge arm of the two phases while keeping the direction of the voltage synthesis vector unchanged. When external interference is small, the conduction time of each phase can be kept unchanged, and the current in the non-sampling area can be estimated by the current in the symmetrical area, thereby ensuring the maximum torque output of the motor.

[0007] According to a first aspect of the present disclosure, a method for sampling current of a permanent magnet synchronous motor with multiple resistors is provided, wherein the permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy, and the method comprises: judging whether a voltage synthesis vector synthesized by two three-phase conduction voltage vectors in a current control cycle enters a two-phase unsampling region, wherein the two-phase unsampling region refers to a region in which the sampling window times of two of the three phases are both less than the minimum sampling time T all Or the sampling window time of one phase among the three phases is less than the minimum sampling time T all At the same time, another phase cannot measure a continuous voltage synthesis vector angle area; when it is judged that the two-phase unsampling area has been entered, the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and make the voltage synthesis vector direction obtained after extension consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension; and collect the sampling window time in the three phases after extension greater than the minimum sampling time T all The current of two phases can be measured and the current of the third phase can be calculated based on the collected two-phase currents.

[0008] Optionally, the extended three-phase sampling window is less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and making the direction of the voltage synthesis vector obtained after the extension consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension also includes: extending the sampling window of the phase with the smallest sampleable window among the three phases to be equal to the minimum sampling time T all ; Extend the sampling window in the three phases to be less than the minimum sampling time T all The lower bridge arm conduction time of the other phase of the two phases is controlled so that the direction of the voltage synthesis vector obtained after extension is consistent with the direction of the predetermined voltage synthesis vector of the current control cycle without extension, wherein the voltage synthesis vector of the current control cycle is synthesized by two three-phase conduction voltage vectors.

[0009] Optionally, the extended three-phase sampling window is less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and the step of making the voltage synthesis vector direction obtained after extension consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension also includes: extending the sampling window in the three phases to be less than the minimum sampling time Tall The conduction time of the lower bridge arms of the two phases is extended so that the ratio of the conduction time of the two three-phase conduction voltage vectors used to synthesize the direction of the current voltage synthesis vector remains unchanged compared to before the extension.

[0010] Optionally, the extended three-phase sampling window is less than the minimum sampling time T all The step of increasing the conduction time of the lower bridge arm of the two phases so that the ratio of the conduction time of the two three-phase conduction voltage vectors used to synthesize the current voltage synthesis vector direction remains unchanged compared to before the extension also includes: in the case of judging that the two-phase non-sampling area is entered, assuming that the phase without the conduction time of the lower bridge arm is X, and there is a sampling window but the window time is less than the minimum sampling time T all The phase is Y, and the sampling window time is greater than the minimum sampling time T all The phase of the Y phase is Z, and the time t at which the upper bridge arm is turned on and the lower bridge arm is turned off and the lower bridge arm is turned on is obtained. Y ; Extend the sampling window of phase X to the minimum sampling time T all ; and change the sampling window of the Y phase from T-2t Y Extended to T-2t Y1 , t Y1 The value of satisfies Where T is equal to the time of one control cycle.

[0011] Optionally, the multi-resistance sampling is three-resistance sampling, and the current control cycle enters the two-phase unsampling area, which means that the voltage synthesis vector obtained by synthesizing the three-phase conduction voltage vector is located in the maximum regular hexagonal vector that can be output by FOC control, and the two-phase unsampling area includes: the switching area from sector I to sector II; the switching area from sector III to sector IV; and the switching area from sector V to sector VI.

[0012] Optionally, the multi-resistance sampling is three-resistance sampling, and when it is determined that the two-phase unsampling area has been entered, the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and making the direction of the voltage synthesis vector obtained after the extension consistent with the predetermined synthesis voltage vector direction of the current control cycle without extension also includes: extending the sampling window of the phase with the second smallest sampleable window among the three phases to be equal to the minimum sampling time T all ; Extend the sampleable window in the three phases to be less than the minimum sampling time T allThe lower bridge arm conduction time of the other phase in the two phases is set so that the direction of the voltage synthesis vector after extension is consistent with the predetermined synthesis voltage vector direction before extension, and the sampling window time in the three phases after the acquisition extension is greater than the minimum sampling time T all The steps of measuring the current of two phases and calculating the current of the third phase based on the collected two-phase currents include: collecting the current of the two phases corresponding to the extended maximum sampleable window and the second smallest sampleable window, and calculating the current of the third phase based on the collected two-phase currents.

[0013] Optionally, the multi-resistance sampling is two-resistance sampling, and the two measurable phases in the three phases correspond to the two phases configured with sampling resistors, and the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is set so that the sampling window of the two phases that can be measured in the three phases is not less than the minimum sampling time T all .

[0014] According to a second aspect of the present disclosure, a method for sampling current of a permanent magnet synchronous motor with multiple resistors is provided, wherein the permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy, and the method comprises: judging whether a voltage synthesis vector synthesized by two three-phase conduction voltage vectors of a current control cycle enters a two-phase unsampling region, wherein the two-phase unsampling region refers to a region in which the sampling window times of two of the three phases are both less than the minimum sampling time T all Or the sampling window time of one phase among the three phases is less than the minimum sampling time T all At the same time, another phase is not measurable in a continuous voltage synthesis vector angle area; in the case of judging that the two-phase unsampling area is entered, based on the current sampling value of the corresponding phase of the previous symmetrical area that currently enters the two-phase unsampling area, it is estimated that the sampling window time of the two phases that cannot be sampled in the current control cycle is less than the minimum sampling time T all The current sampling value of one phase; and the sampling window time of the three phases is greater than the minimum sampling time T all The measurable current of one phase can be obtained, and the current of the third phase can be calculated based on the collected current of one phase and the estimated current of one phase.

[0015] Optionally, when it is determined that the two-phase unsampling area has been entered, based on the current sampling value of the corresponding phase of the previous symmetrical area that currently enters the two-phase unsampling area, it is estimated that the sampling window time of the two unsampling phases in the current control cycle is less than the minimum sampling time T allThe step of calculating the current sampling value of one phase of the two-phase symmetrical region comprises: based on the current phase change rate of the corresponding phase in the previous symmetrical region, using the current and phase of the corresponding phase measured in the last control cycle of entering the two-phase unsampling region, estimating that the sampling window time of the two phases that cannot be sampled in the current control cycle is less than the minimum sampling time T all The current sampling value of one phase.

[0016] Optionally, the two-phase unsampling area is the area switching from sector A to sector B, and the previous symmetrical area is the area switching from sector C to sector D, wherein sector A is symmetrical with sector C, and sector B is symmetrical with sector D, and obtaining the current phase change rate of the corresponding phase in the previous symmetrical area includes: obtaining the last current and phase value of the corresponding phase located in sector C recorded before switching to sector D; obtaining the first current and phase value of the corresponding phase located in sector D recorded after switching to sector D; and based on the last and first current and phase values, obtaining the current phase change rate of the corresponding phase in the previous symmetrical area.

[0017] Optionally, when it is determined that the two-phase unsampling area has been entered, based on the current sampling values ​​of the corresponding phases in the corresponding two phases of the previous symmetrical area that currently enters the two-phase unsampling area, it is estimated that the sampling window time of the two unsampling phases in the current control cycle is less than the minimum sampling time T all The step of estimating the current sampling value of one phase includes: using the current sampling value of the corresponding phase of the previous symmetrical voltage vector angle of the current voltage synthesis vector angle to estimate the current sampling value of the corresponding phase in the current control cycle.

[0018] According to a third aspect of the present disclosure, a permanent magnet synchronous motor operation method is provided, comprising executing the multi-resistance current sampling method as described in the first or second aspect above when the motor is in an overmodulation state.

[0019] According to the fourth aspect of the present disclosure, a permanent magnet synchronous motor is provided, comprising: a motor; a magnetic oriented vector control module for controlling the motor, and comprising: a current sampling control module for executing the multi-resistance current sampling method as described in the first or second aspect above, to obtain a three-phase current for controlling the motor.

[0020] Therefore, the present disclosure proposes a method for accurately controlling the motor when the FOC enters the overmodulation area. One method is to ensure normal current sampling by reserving a minimum sampling window in the unsampling interval. This method is more accurate and suitable for various high-interference application scenarios. Another method is to not reserve a sampling window in the unsampling interval, directly output the maximum voltage vector, and predict the current value of the unsampling interval by the symmetrical interval current value, so that the maximum output vector is output along the regular hexagonal boundary of the vector. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components in the exemplary embodiments of the present disclosure.

[0022] Figure 1 The schematic diagram of FOC control for PMSM is shown.

[0023] Figure 2 The schematic diagram of the three-resistor sampling circuit is shown.

[0024] Figure 3 The space vector diagram of a three-phase inverter is shown.

[0025] Figure 4 A diagram showing the phase voltages of different sectors under the seven-segment SVPWM strategy.

[0026] Figure 5A -B shows an example of current flow in sector I.

[0027] Figure 6 A spatial vector diagram with unsamplifiable regions marked is shown.

[0028] Figure 7 A phase voltage diagram near U6 (110) during overmodulation is shown.

[0029] Fig. 8A -C shows Figure 7 The current flow direction at the phase voltage shown.

[0030] Fig. 9 A schematic flow chart of a method for sampling current using multiple resistors of a permanent magnet synchronous motor according to an embodiment of the present disclosure is shown.

[0031] Fig. 10A -F shows a comparison of the expected output in the unsampling area and the actual output after reserving the sampling window.

[0032] Fig.11 A schematic flow chart of a method for sampling current of a permanent magnet synchronous motor using multiple resistors according to an embodiment of the present invention is shown.

[0033] Fig.12 A synthetic vector map of the symmetric region with unsamplifiable regions marked is shown.

[0034] Fig.13 A current phase diagram with unsampling intervals and symmetric intervals marked is shown.

[0035] Fig.14A schematic diagram of the composition of a FOC module of a permanent magnet synchronous motor according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0037] In the control process of permanent magnet synchronous motor (PMSM), FOC is often used to control the motor in order to obtain the maximum torque output throughout the entire control cycle. Figure 1 The schematic diagram of FOC control for PMSM is shown.

[0038] As shown in the figure, a position sensor such as a magnetic encoder obtains the rotor speed n and the rotor position θ of the motor M. In practical applications, for example, a speed reference n obtained based on user input ref The subtraction is made from the acquired rotor speed n and is input to PID1 (i.e., speed loop PID). The output of the speed loop PID is the q-axis reference current i qref For simplicity, when weak magnetic control is not performed, the d-axis reference current i dref = 0. At this time, the reference current i of the q-axis and d-axis can be qref and i dref The q-axis and d-axis current i of the motor are actually fed back q and i d The q-axis and d-axis voltages V are output after being adjusted by PID2 (i.e., q-axis current loop) and PID3 (i.e., d-axis current loop) respectively. d and V q , and then converted into α-axis and β-axis voltage V through Park inverse transformation α and V β , and then through SVPWM (space voltage vector modulation) to obtain the three-phase voltage V a 、V b and V cc , and then drives the motor M to rotate through the three-phase inverter bridge. In FOC control, the three-phase current i is obtained through the sampling resistor a 、i b and i c After Clark transformation, the α-axis and β-axis currents i are obtained. α and i β , and then the feedback d-axis and q-axis currents i are obtained through Park transformation d and i q, respectively input PID2 and PID3 to participate in current loop control.

[0039] When the motor runs at low speed or the motor load is small, the output voltage vector V d 、V q Smaller, that is, a smaller voltage vector can control the motor to run in a double closed-loop stable state. When the motor load is large, or the given motor speed is high, the motor speed cannot reach the speed reference n ref , at this time, the motor will enter the overmodulation area. In the overmodulation state, the maximum output of the motor determines the maximum load capacity and maximum speed of the motor. That is, the greater the voltage vector output in the overmodulation state, the stronger the motor load capacity and the higher the maximum speed that can be achieved.

[0040] When the three-phase inverter is controlled based on the SVPWM strategy, the voltage vector in the FOC is synthesized by one or two voltage vectors among U4 (100), U6 (110), U2 (010), U3 (011), U1 (001), and U5 (101). When the torque is small, the maximum output vector can be controlled within the sampleable vector circle interval. At this time, the three-phase current can be sampled at all angles. When the motor enters the overmodulation area, the maximum output vector cannot be controlled within the sampleable vector circle interval because the maximum torque output and speed are required to be as high as possible. This results in that in some areas, especially near the output maximum voltage vector U6 (110), U3 (011), and U5 (101), the three resistors cannot normally sample the two-phase current, and thus cannot reconstruct the three-phase current, affecting the FOC double closed-loop control.

[0041] To this end, the present disclosure proposes a method for reserving a minimum sampling window in an unsampling interval by proportionally extending the conduction time of the lower bridge arms of the two phases to ensure normal sampling while maintaining the voltage vector method unchanged. As an alternative or supplement, the present disclosure also proposes a method for not leaving a sampling window in an unsampling interval, directly outputting the maximum voltage vector, and predicting the current value of the unsampling interval through the current value of the symmetrical interval.

[0042] In order to facilitate a thorough understanding of the present disclosure, the relevant principles of multi-resistance current sampling are first described here.

[0043] Figure 2 As shown in the schematic diagram of the three-resistance sampling circuit, in the three-phase drive circuit composed of six MOSFET tubes (VT1 to VT6), the three resistors (R a , R b and R c ) is a sampling resistor. The three-phase current can be reconstructed based on the current collected on the sampling resistor.

[0044] When the MOSFET of the lower bridge arm is turned off, no current flows through the sampling resistor (although there may be a short-term freewheeling condition). When the MOSFET of the lower bridge arm is turned on, current flows through the sampling resistor, and this current is equal to the phase current of the current phase.

[0045] Figure 2 The example of sampling the current of phase A is shown. The current of phase A can be sampled only when VT4 is turned on and VT1 is turned off. a Because, when VT4 is turned on and VT1 is turned off, no matter i a Regardless of the current direction, the current will always flow through the resistor Ra. Similarly, the currents of phases B and C can be sampled.

[0046] According to Kirchhoff's current law, the three-phase current i flowing through the three-phase system a ,i b and i c There are the following relationships:

[0047] i a +i b +i c =0 (1)

[0048] From formula (1), we can see that the instantaneous sum of the three-phase current values ​​is zero. Therefore, through the above relationship, two phases of the three-phase current can be collected to infer the third phase current. In this case, only two phases of current need to be collected in each PWM cycle. Since the on / off of the switch tube will affect the phase current, it takes some time to stabilize. In order to ensure that there is enough time to sample the two-phase current and the accuracy of the phase current, it is usually decided which two phases to collect based on the current sector of the SVPWM.

[0049] In the FOC control process, SVPWM (space vector pulse width modulation) strategy is often used to control the three-phase inverter. The basic principle of SVPWM is to represent the instantaneous value of the output voltage of the three-phase inverter with a space vector U rotating at an angular velocity ω = 2πf (f is the power frequency), and divide the 360° rotation space of the space vector U into six sectors (sectors I to VI). Figure 3The space vector diagram of the three-phase inverter is shown. As shown in the figure, the six sectors are respectively sector I (composed of voltage vectors U4 (100) and U6 (110)), sector II (composed of voltage vectors U6 (110) and U2 (010)), sector III (composed of voltage vectors U2 (010) and U3 (011)), sector IV (composed of voltage vectors U3 (011) and U1 (001)), sector V (composed of voltage vectors U1 (001) and U5 (101)) and sector VI (composed of voltage vectors U5 (101) and U4 (100)) in the two-phase αβ coordinate system. That is, the output voltage vector of FOC (i.e., the "voltage synthesis vector" described later) is synthesized by one voltage vector or two three-phase conduction voltage vectors. Among them, the three-phase conduction voltage vector includes U4 (100), U6 (110), U2 (010), U3 (011), U1 (001), and U5 (101) as shown in the space vector diagram.

[0050] The space vector U rotated to any sector can be synthesized by three position-specific space vectors located at the boundary of the sector. Common SVPWM is divided into seven-segment SVPWM and five-segment SVPWM. The seven-segment SVPWM has eight position-specific space vectors U0 to U7; the five-segment 000 injection SVPWM has seven position-specific space vectors U0 to U6; and the five-segment 111 injection SVPWM has seven vectors U1U7, of which U0 and U7 are zero vectors.

[0051] Figure 4 The diagram shows the phase voltage of different sectors under the seven-segment SVPWM strategy. In the same sector, the phase with the longest conduction time of the lower bridge arm remains unchanged, while in different sectors, the phase with the longest conduction time of the lower bridge arm is different. By controlling the action time of the three position-specific space vectors participating in the vector synthesis, the modulus and direction of the space vector U can be controlled. The same sector contains multiple control cycles. For example, in sector 1, the synthesized voltages at different angles have different U4 and U6 proportional relationships, and the modulus of the synthesized voltage depends on the length of the sampling window.

[0052] When three resistors are used for sampling, current is collected when the upper tube of the three phases is turned off, the lower tube is turned on, and the output voltage vector is U0(000), that is, Figure 4 The following will take sector I as an example to explain the specific current sampling process. Figure 5A -B shows an example of current flow in sector I.

[0053] In sector I, the conduction voltages are U4 (100) and U6 (110), respectively. The voltage vector that is conducted before the sampling window is U4 (100), that is, the upper MOS of phase A is turned on and the lower MOS is turned off; the upper MOS of phase B is turned off and the lower MOS is turned on; the upper MOS of phase C is turned off and the lower MOS is turned on. At this time, if Figure 5A As shown, the current flows as follows: the current flows from the positive end of the power supply through the upper tube MOS (VT1) of phase A, flows into the motor phase A, passes through the neutral point N, and is divided into two paths to flow to the negative end of the power supply. One path flows through the B phase winding, and then passes through the lower tube MOS (VT5) of phase B, and the sampling resistor R b One path flows into the negative terminal of the power supply; the other path flows through the C phase winding, and then passes through the C phase lower tube MOS (VT6), the sampling resistor R c The current flowing into the motor is positive, and the current flowing out of the motor is negative. b And the sampling resistor R c The currents on the b and -i c .

[0054] When entering the sampling window, the upper MOS is turned off and the lower MOS is turned on. Since the motor has a resistive-inductive characteristic, its current cannot change suddenly. Figure 5B As shown, the current flows as follows: the current flows from the negative end of the power supply through the A-phase lower tube MOS (VT4) into the motor A-phase through the neutral point N, and is divided into two paths to flow to the negative end of the power supply, one of which flows through the B-phase winding, and then through the B-phase lower tube MOS (VT5), the sampling resistor R b One path flows into the negative terminal of the power supply; the other path flows through the C phase winding, and then passes through the C phase lower tube MOS (VT6), the sampling resistor R c Flows into the negative terminal of the power supply.

[0055] In sector I, the two phases with longer lower tube conduction time are phase B and phase C. Therefore, the current of phase B can be sampled in the sampling window to obtain -i b , sample the C phase current to obtain -i c , and then reconstruct the third phase current i according to Kirchhoff's law a When sampling the current of phase B and phase C through ADC, the upper MOS of phase A needs to be turned off, and the lower MOS needs to be turned on for a delay of T1 (including the drive rise time and the current stabilization time) before sampling. At the same time, the fixed sampling time T of ADC needs to be ensured. sample That is, the minimum sampling window time is T all =T1+T sample That is, in the present disclosure, the minimum sampling time required for resistance sampling can be considered to be T all .

[0056] During the FOC control process, the voltage vectors that can be output are all within or on the boundary of the following regular hexagon. When the FOC operation enters the overmodulation area, between sectors Ⅰ to Ⅵ, the output voltage vector along the boundary line of the regular hexagon is the maximum effective output, and the motor speed can be further increased.

[0057] When outputting a regular hexagonal boundary voltage vector, it is usually necessary to ensure that there is enough sampling window to collect two-phase currents and then reconstruct the three-phase currents to provide the i required for FOC control. a 、i b and i c For three-resistance sampling, there are three areas that cannot be sampled. Figure 6 The spatial vector diagram with the unsampling area marked is shown. As shown in the figure, the three unsampling areas are: near U6 (110) (the area between vector ① and vector ③), near U3 (011) (the area between vector ④ and vector ⑥), and near U5 (101) (the area between vector ⑦ and vector ⑨). In these areas, there are two situations in the entire control cycle. One is that only one phase of the lower tube MOS is fully turned on, and the other two phases of the lower tube MOS are fully turned off (corresponding to the switching point, that is, vectors ②, ⑤ and ⑧); the other is that one phase of the lower tube MOS is fully turned on, one phase of the lower tube MOS is fully turned off, and the other phase of the lower tube MOS is briefly turned on, but the turn-on time is not enough to complete the current sampling (corresponding to other positions outside the switching point of the unsampling area). In both cases, the two-phase current cannot be normally collected and the three-phase current reconstruction cannot be completed. Here, for the convenience of understanding, the voltage vector near U6 (110) is analyzed, and its unsampling interval is the area between vector ① and vector ③.

[0058] When the motor rotates forward (CCW direction), the moving directions of the sector vector are sector I, sector II, sector III, sector IV, sector V, and sector VI. Figure 7 The phase voltage diagram near U6 (110) during overmodulation is shown. The dotted line in the figure shows the minimum sampling time T all Accordingly, Fig. 8A -B shows Figure 7 The current flow direction at the phase voltage shown.

[0059] Specifically, when the FOC control output vector is vector ①, the sampling window time is exactly the minimum sampling time T all At this time, the current flow in the sampling window is as follows Fig. 8A As shown. Sampling resistor R b And the sampling resistor R c The currents on the b and -i c , and then we can reconstruct i through Kirchhoff's law a .

[0060] At the next moment, the FOC control output vector changes, the voltage vector U4 (100) of the control output is further reduced, and the sampling window is also further reduced (the sampling window time is less than the minimum sampling time T all , the three-phase current cannot be sampled normally) until the output voltage vector ②. At this time, the output voltage vector is all U6 (110), and the output level is shown in ②. At this time, the current flow in the entire control cycle is as follows Figure 8B As shown. Since only the sampling resistor R c There is current flowing through it, so it is impossible to reconstruct the three-phase current.

[0061] At the next moment, the voltage vector of the FOC control output switches from sector I to sector II. Subsequently, the output voltage vector ② gradually changes to voltage vector ③, the U6 (110) voltage vector gradually decreases, the U2 (010) voltage vector gradually increases, and the sampling window gradually increases. When switching to voltage vector ③ (the sampling window is equal to the minimum sampling time T all , the voltage vector before this cannot complete the current sampling normally). At this time, the current flow direction in the sampling window interval is as follows Figure 8C As shown. Sampling resistor R a And the sampling resistor R c The currents on the a and -i c , and then we can reconstruct i through Kirchhoff's law b .

[0062] In order to achieve the three-phase current i in the non-sampleable voltage vector interval such as vector ①-③ a 、i b 、i c Participating in FOC control. This proposal proposes a method to reduce the voltage vector size but not change the output voltage vector direction by reserving a minimum sampling window in the non-sampling interval, thereby ensuring normal sampling.

[0063] Fig. 9 A schematic flow chart of a method for sampling current of a permanent magnet synchronous motor with multiple resistors according to an embodiment of the present disclosure is shown. The method is suitable for use in a process in which a permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy. In addition, the method is preferably applicable to a three-resistance configuration, and may also be applicable to a two-resistance configuration.

[0064] In step S910, it is determined whether the voltage synthesis vector synthesized by the two three-phase conduction voltage vectors of the current control cycle enters the two-phase unsampling area. The two-phase unsampling area refers to the area in which the sampling window time of two phases out of the three phases is less than the minimum sampling time T all Or the sampling window time of one phase among the three phases is less than the minimum sampling time Tall At the same time, a continuous voltage synthesis vector angle area in which the other phase cannot be measured. In the three-resistance sampling configuration, all three phases are measurable phases. At this time, the two-phase unsampling area refers to the area in which the sampling window time of two of the three phases is less than the minimum sampling time T all In the two-resistance configuration, the two phases that can be measured in the three phases are the two phases with sampling resistors set. At this time, the two-phase unsampling area refers to the sampling window time of two phases in the three phases is less than the minimum sampling time T all The situation can also be that the sampling window time of one phase among the three phases is less than the minimum sampling time T all At the same time, the other phase is unpredictable.

[0065] In step S920, when it is determined that the two-phase sampling area has been entered, the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and the voltage vector direction obtained after the extension is consistent with the predetermined voltage vector direction of the current control cycle without extension, that is, the voltage vector direction before and after the extension remains unchanged. Figure 7 For example, within the range of vectors ① to ②, only phase C can be sampled, and the sampling windows of phases A and B are both smaller than the minimum sampling time T all (Specifically, phase A has no sampling window, and the sampling window of phase B is too short.) To this end, the conduction time of the lower bridge arm of phase A and phase B can be extended so that at least the conduction time of the lower bridge arm of phase B is equal to the minimum sampling time T all (Thereby, current can be collected for phases C and B.) Extending the conduction time of the lower bridge arms of phases A and B requires that the direction of the voltage vector obtained after the extension is consistent with the predetermined voltage vector direction of the current control cycle without extension. In other words, using the method disclosed in the present invention will reduce the size of the output vector due to the reservation of the sampling window, but keep the direction of the output vector unchanged.

[0066] Then, in step S930, the sampling window time in the three phases after the extension is greater than the minimum sampling time T all The current of the two phases can be measured, and the current of the third phase is calculated based on the collected two-phase current. In the three-resistance configuration, since all three phases are measurable, as long as the sampling window time is greater than the minimum sampling time T all In the two-resistance configuration, since only the two phases configured with resistors can be measured, the sampling windows of these two phases need to be no less than the minimum sampling time T all .

[0067] Therefore, the method of reserving a sampling window disclosed in the present invention can ensure that the three-phase current required for FOC control is obtained while ensuring that the output voltage vector is in the same direction as when no window is reserved, thereby ensuring smooth control of the motor.

[0068] In addition, it should be understood that if it is determined that the two-phase unsampling area has not been entered, the two sampled phases can be sampled according to conventional methods, and the current of the third phase can be calculated based on the collected two-phase currents, thereby achieving the acquisition of the three-phase current required for FOC control.

[0069] In one embodiment, the sampleable window in the extended three-phase is smaller than the minimum sampling time T all When the lower bridge arm conduction time of the two phases is , the second smallest sampleable window in the three phases can be made equal to the minimum sampling time T all At the same time, the extended voltage vector direction is ensured to be consistent with the predetermined voltage vector direction before extension, and then the currents of the two phases corresponding to the maximum sampleable window and the second smallest sampleable window after extension are collected, and the current of the third phase is calculated based on the collected two-phase currents. For example, within the range of vectors ① to ②, only the sampling window of phase B is extended to T all (Although the sampling window time of phase A is not zero, it is shorter than T all At this time, the maximum voltage vector output can be achieved.

[0070] However, in some cases, it is possible to extend the sampling window of phase B only to T all And the sampling window time of phase A is extended, although it is not zero, it is longer than T all Shorter will cause current fluctuation problem when MOS tube is switched. Fig. 10A As shown in the upper part, at this time t B Just less than the minimum sampling time T all If only t B will be extended to be equal to the minimum sampling time T all , then in order to ensure that the adjusted vector direction does not change, at this time t A There will also be a short time of opening and closing (less than T all This leads to a minimum value of B When collecting current, there is t A The MOS tube is turned on and off at the time when t A When the value is extremely small and the MOS tube switches quickly, there will be current fluctuations caused by the MOS tube turning on and off during the sampling process, thus affecting the sampling accuracy.

[0071] To this end, in another embodiment, the two phases can be extended to a greater extent in consideration of the MOS tube switch fluctuation. Specifically, in the extended three-phase sampling window, the sampling window is less than the minimum sampling time Tall When the lower bridge arm conduction time of the two phases is set to , the voltage vector direction obtained after the extension can be kept consistent with the predetermined voltage vector direction of the current control cycle without extension, and the minimum sampleable window in the three phases is not less than the minimum sampling time T all , for example, making the minimum sampleable window equal to the minimum sampling time T all At this time, if all three phases are measurable (ie, corresponding to the case of a three-resistance configuration), current can be collected for any two of the three phases.

[0072] In the present disclosure, the extension of the two-phase sampling window needs to make the voltage vector direction obtained after the extension consistent with the predetermined voltage vector direction of the current control cycle without extension. In one embodiment, this can be achieved by extending the sampling window in the three phases to be less than the minimum sampling time T all When the lower bridge arm conduction time of the two phases is extended, the ratio of the conduction time of the voltage vectors on both sides of the sector used to synthesize the current voltage vector direction remains unchanged compared to before the extension. Specifically, it may include: when it is determined that the two-phase non-sampling area has been entered, the phase without the lower bridge arm conduction time is X, and there is a sampling window but the window time is less than the minimum sampling time T all The phase is Y, and the sampling window time is greater than the minimum sampling time T all The phase of the Y phase is Z, and the time t at which the upper bridge arm is turned on and the lower bridge arm is turned off and the lower bridge arm is turned on is obtained. Y ; Extend the sampling window of phase X to the minimum sampling time T all ; and change the sampling window of the Y phase from T-2t Y Extended to T-2t Y1 , t Y1 The value of satisfies Where T is equal to the time of one control cycle.

[0073] When the multi-resistance sampling is three-resistance sampling, the area where there is no sampling window in the current control cycle is located in: the switching area from sector I to sector II; the switching area from sector III to sector IV; and the switching area from sector V to sector VI. Figure 6 As shown, the area near U6 (110) (the area between vector ① and vector ③), the area near U3 (011) (the area between vector ④ and vector ⑥), and the area near U5 (101) (the area between vector ⑦ and vector ⑨).

[0074] The following will describe with reference to examples. Fig. 10A -F shows a comparison of the expected output in the unsampling area and the actual output after reserving the sampling window.

[0075] First, Fig. 10AAs shown, the desired output voltage vector is located in sector I, between vectors ① and ②. Here, T represents the time of a control cycle, and T / 2 represents the time of half a control cycle, which is the center position of the sampling window in the figure, that is, the position of the gray dotted line in the figure. The range of the thick black dotted line in the figure corresponds to the minimum sampling time T all . T A and t B They represent the moment when the corresponding phase (phase A, phase B) changes from upper bridge arm on to lower bridge arm off within half cycle T / 2, and its value is less than or equal to T / 2. When the corresponding minimum sampling time T is defined all After that, the corresponding critical sampling positions are vector ① and vector ② respectively. The B-phase sampling window time of vector ① is just equal to the minimum sampling time T all ,like Figure 7 As shown in the upper part. At this time, the sampling window time between vector ① and vector ② is less than the minimum sampling time T all , take a voltage vector between vector ① and vector ② as an example to describe. Fig. 10A As shown, during the entire control cycle T, the upper bridge arm of phase A is turned on and the lower bridge arm is turned off, so the current of phase A cannot be sampled; during most of the entire control cycle, the upper bridge arm of phase B is turned on and the lower bridge arm is turned off. Only during a short period of time around T / 2 is the upper bridge arm turned off and the lower bridge arm turned on, at which time the current of phase B can be collected; and during the entire control cycle, the upper bridge arm of phase C is turned off and the lower bridge arm is turned on, and the current of phase C can always be sampled. Therefore, only when the upper bridge arms of phases B and C are turned off and the lower bridge arms are turned on, can the current of phase A be reconstructed through Kirchhoff's law. At this time, the minimum sampling window is determined by phase B (phase C can be sampled throughout the cycle), and the sampling window time is Less than the minimum sampling time T all , it is impossible to collect two-phase current through sampling resistors and then reconstruct three-phase current. B The voltage vectors that are turned on before time t are all U6(110), and at t B The voltage vector that is turned on between T / 2 and T / 2 is U4(100), and the voltage vector output in the half cycle from T / 2 to T is completely symmetrical with it. At this time, the proportion of the expected output voltage vector U6(110) in the entire cycle is (The proportion of U4(100) voltage vector in the entire cycle is The ratio of the vectors is The ratio of this vector determines the direction of the output voltage vector.

[0076] In order to minimize the torque fluctuation during the control process, it is necessary to ensure that the minimum sampling window (minimum sampling time T all ) at the same time, ensure that the output torque direction does not change. Fig. 10A As shown in the lower part, this example shows that the minimum sampling window among the three phases (i.e., the sampling window of phase A) is equal to the minimum sampling time T all The effect of MOS switch on sampling is avoided by limiting the lower limit of the minimum sampling window length among the three items. That is, at this time, both phase A and phase B are theoretically sampleable. At this time, phase C remains in the same conduction state with the lower bridge arm, that is, t C1 =0, and the sampling window of phase A is equal to the minimum sampling time T all ,Right now, At this time, in order to ensure that the output torque direction does not change, it is necessary to control the extension of the B phase sampling window. The proportion of the voltage vector of U6 (110) after the reserved minimum sampling window to the entire cycle is 2t B1 / T, the proportion of U4(100) voltage vector in the whole cycle is (2t B1 -2t A1 ) / T. The ratio of the vectors is According to t A1 ,t B1 ,t C1 The value of can be obtained that the ratio of the vector before the reserved sampling window is the same as the ratio of the vector after the reserved sampling window Bring in, Then we can get t B1 The value of satisfies That is, the output composite voltage vector is simply scaled down proportionally, but its direction remains unchanged.

[0077] Subsequently, when the output voltage vector is between vectors ② and ③, the expected output voltage vector is located in sector Ⅱ. Since neither phase A nor phase B can be sampled in the expected output of vector ②, and the sampling window time of phase A of vector ③ is exactly equal to the minimum sampling time T all ,like Figure 7 As shown in the middle and lower parts. At this time, the sampling window time between vector ② and vector ③ is less than the minimum sampling time T all , which belongs to the unsampling interval. Take a voltage vector between ② and ③ as an example for description. Fig. 10BAs shown, in the entire control cycle T, the upper bridge arm of phase A is turned on and the lower bridge arm is turned off for most of the time in the entire control cycle. Only in a short period of time around T / 2 is the upper bridge arm turned off and the lower bridge arm turned on, at this time, the A phase current can be collected; the upper bridge arm of phase B is turned on and the lower bridge arm is turned off, and the B phase current cannot be sampled; and in the entire control cycle, the upper bridge arm of phase C is turned off and the lower bridge arm is turned on, and the C phase current can always be sampled. Therefore, only when the upper bridge arms of phases A and C are turned off and the lower bridge arms are turned on, the currents of phases B and C are sampled, can the A phase current be reconstructed through Kirchhoff's law. In order to minimize the torque fluctuation during the control process, it is necessary to ensure that the minimum sampling window (minimum sampling time T) is reserved. all ) while ensuring that the output torque direction does not change. Fig. 10B As shown in the lower part, this example shows that the minimum sampling window among the three phases (i.e., the sampling window of phase B) is equal to the minimum sampling time T all That is, at this time, both phase A and phase B are theoretically sampleable. At this time, phase C remains in the same conduction state with the lower bridge arm, that is, t C1 =0, and the sampling window of phase B is equal to the minimum sampling time T all ,Right now, At this time, in order to ensure that the output torque direction does not change, it is necessary to control the extension of the A phase sampling window. t A1 The value of satisfies That is, the output composite voltage vector is simply scaled down proportionally, but its direction remains unchanged.

[0078] Similar, such as Figures 10C to 10F As shown, there are also unsampling intervals with less than two sampleable phases between vectors ④-⑤, vectors ⑤-⑥, vectors ⑦-⑧, and vectors ⑧-⑨. Specifically:

[0079] When the output voltage vector is between vector ④ and vector ⑤, the minimum sampling window among the three phases (i.e., the sampling window of phase B is extended to T all ), at this time t A1 =0, In order to ensure that the output composite voltage vector is only proportionally reduced without changing its direction, t C1 The value of satisfies

[0080] When the output voltage vector is between vector ⑤ and vector ⑥, the minimum sampling window among the three phases (i.e., the sampling window of phase C is extended to T all ), at this time t A1 =0, In order to ensure that the output composite voltage vector is only proportionally reduced without changing its direction, t B1 The value of satisfies

[0081] When the output voltage vector is between vector ⑦ and vector ⑧, the minimum sampling window among the three phases (i.e., the sampling window of phase C is extended to T all ),at this time t B1 =0, In order to ensure that the output composite voltage vector is only proportionally reduced without changing its direction, t A1 The value of satisfies

[0082] When the output voltage vector is between vector ⑧ and vector ⑨, the minimum sampling window among the three phases (i.e., the sampling window of phase A is extended to T all ),at this time t B1 =0, In order to ensure that the output composite voltage vector is only proportionally reduced without changing its direction, t C1 The value of satisfies

[0083] As mentioned above, the multi-resistance sampling can be a two-resistance sampling, and the two measurable phases in the three phases correspond to the two phases configured with sampling resistors, and the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is set so that the minimum sampleable window in the three phases is not less than the minimum sampling time T all When using two-resistance sampling, in addition to the corresponding Figure 6 In addition to the three unsampling areas shown near U6 (110) (the area between vector ① and vector ③), near U3 (011) (the area between vector ④ and vector ⑥), and near U5 (101) (the area between vector ⑦ and vector ⑨), additional unsampling areas are also included. For example, when two resistors sample phases B and C, since the current of phase A cannot be sampled, the area near U2 (010) and near U1 (001) cannot be sampled. Similarly, when two resistors sample phases A and C, since the current of phase B cannot be sampled, the area near U1 (001) and near U4 (100) cannot be sampled. When two resistors sample phases A and B, since the current of phase C cannot be sampled, the area near U4 (100) and near U2 (010) cannot be sampled.

[0084] As an alternative, the present disclosure also proposes a method of directly outputting a maximum voltage vector without leaving a sampling window in the unsampling interval, and predicting the current value of the unsampling interval through the current value of the symmetrical interval.

[0085] According to the above analysis, when sampling three resistors, only one phase current can be sampled near U6 (110) (the area between vector ① and vector ③), near U3 (011) (the area between vector ④ and vector ⑥), and near U5 (101) (the area between vector ⑦ and vector ⑨). The area between vector ① and vector ③ can sample current i c ; The area between vector ④ and vector ⑥ can sample the current i a ; The area between vector ⑦ and vector ⑨ can sample the current i b In these areas, if another phase current can be obtained through the current observation algorithm, the three-phase current can be reconstructed through Kirchhoff's law to complete FOC control.

[0086] In the FOC control process, the current cycle is always synchronized with the voltage control cycle, and because the motor is a resistive inductive component, the current generally lags behind the voltage by a certain phase, although the lag phase varies for different motors and loads. However, when the output voltage phase changes by 180°, the current will also change by 180°.

[0087] Without considering the error, the B-phase current of vector ② can be expressed as i b =amp×sin(θ2), and the B-phase current in vector ②' can be expressed as i b =amp×sin(θ 2′ )=amp×sin(θ2+π)=-amp×sin(θ2). That is, the current in the unsampling interval can be predicted by the magnitude of a phase current when the phases are 180° apart.

[0088] For example, the current that can be collected near U6 (110) (the area between vector ① and vector ③) is the C phase current i c The current that cannot be collected is the A phase current i a and B phase current i b At this time, the B phase current i is collected through the symmetrical area b , predict the B-phase current in the area between vector ① and vector ③, and complete the reconstruction of the three-phase current according to Kirchhoff's law.

[0089] Fig.11 A schematic flow chart of a method for sampling current of a permanent magnet synchronous motor with multiple resistors according to an embodiment of the present invention is shown. The method is suitable for use in a process in which a permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy. In addition, the method is preferably applicable to a three-resistance configuration, and can also be used for a two-resistance configuration.

[0090] In step S1110, it is determined whether the voltage synthesis vector synthesized by the two three-phase conduction voltage vectors of the current control cycle enters the two-phase unsampling area. Here, the two-phase unsampling area refers to the sampling window time of two phases in the three phases being less than the minimum sampling time T all A continuous voltage synthesis vector angle area (three-resistance sampling and two-resistance sampling will encounter such a situation) or the sampling window time of one phase in the three phases is less than the minimum sampling time T all At the same time, a continuous voltage synthesis vector angle region of the other phase cannot be measured (only two-resistance sampling will encounter such a situation). Specifically, when three-resistance sampling is used, the sampling window time of two phases out of the three phases is less than the minimum sampling time T all A continuous voltage resultant vector angle region corresponds to Figure 6 The regions shown are near U6 (110) (the region between vector ① and vector ③), near U3 (011) (the region between vector ④ and vector ⑥), and near U5 (101) (the region between vector ⑦ and vector ⑨). In the case of two-resistance sampling, in addition to these three switching regions, there are also two additional sector switching regions as described above.

[0091] In step S1120, when it is determined that the two-phase unsampling area has been entered, based on the current sampling value of the corresponding phase of the previous symmetrical area that has entered the two-phase unsampling area, it is estimated that the sampling window time of the two-phase unsampling area in the current control cycle is less than the minimum sampling time T all The current sampling value of one phase of the two-phase unsampling area. Here, the "symmetrical area" of the two-phase unsampling area can be an area symmetrical to the two-phase unsampling area on the vector circle, that is, an area that differs by 180°. For example, the symmetrical area of ​​the area near U6 (110) is the area near U1 (001), the symmetrical area of ​​the area near U3 (011) is the area near U4 (100), and the symmetrical area of ​​the area near U5 (101) is the area near U2 (010). The "previous" symmetrical area that currently enters the two-phase unsampling area refers to the sampling value of the voltage vector when it last passed through the symmetrical area before reaching the current position. Here, the "corresponding phase" refers to the phase corresponding to the estimated one of the two unsampling phases. For example, when entering the area near U6 (110), since phases A and B cannot be sampled, the sampling value of any one of the corresponding two phases (i.e., phase A and phase B), such as phase B, when entering the area near U1 (001) for the last time before entering the area near U6 (110) can be used to estimate the sampling value of the corresponding phase (i.e., phase B) in the current control cycle.

[0092] Then, in step S1130, the sampling window time in the three phases is greater than the minimum sampling time T allThe measurable current of one phase can be obtained, and the current of the third phase can be calculated based on the collected current of one phase and the estimated current of one phase.

[0093] Therefore, the three-phase current can be obtained by prediction rather than reserving a sampling window, so that the motor can maintain maximum torque output to meet the requirements of heavy load or high speed.

[0094] In addition, it should be understood that if it is determined that the two-phase unsampling area has not been entered, the two sampled phases can be sampled according to conventional methods, and the current of the third phase can be calculated based on the collected two-phase currents, thereby achieving the acquisition of the three-phase current required for FOC control.

[0095] In one embodiment of the present disclosure, the current sampling value of the corresponding phase of the previous symmetrical voltage vector angle of the current voltage synthesis vector angle can be directly used to estimate the current sampling value of the corresponding phase in the current control cycle. For example, when the synthesis vector angle is 59°, the A-phase and B-phase currents can no longer be collected. At this time, the B-phase current collected when the previous synthesis vector angle of the motor was 239° (=59°+180°) can be used to estimate the B-phase current at 59°, for example, directly inverting the value of the B-phase current collected at 239° as the B-phase current at 59°. Of course, at this time, the A-phase current collected at 239° can also be used to estimate the A-phase current at 59°. Therefore, the B-phase or A-phase current can be reconstructed based on the estimated A-phase or B-phase current, together with the sampled C-phase current, thereby obtaining the three-phase current value.

[0096] In order to avoid fluctuations, the sampling value may be estimated based on the current phase change rate of the symmetrical area instead of a single value. At this time, in the case of judging that the two-phase unsampling area has been entered, the step of estimating the current sampling value of the corresponding one of the two phases that cannot be sampled in the current control cycle based on the current sampling value of one of the two phases in the previous symmetrical area that currently enters the two-phase unsampling area may include: based on the current phase change rate of the corresponding one phase in the previous symmetrical area, using the current and phase of the corresponding one phase measured in the last control cycle of entering the two-phase unsampling area, estimating the current sampling value of the corresponding one of the two phases that cannot be sampled in the current control cycle.

[0097] The current phase change rate can be obtained based on two or more pairs of current-phase values ​​obtained in the symmetrical region. Here, the two-phase non-sampling region can be set as the region where the sector A switches to the sector B, and the previous symmetrical region is the region where the sector C switches to the sector D. Here, the four sectors A, B, C, and D correspond to the four sectors in sectors I-VI, wherein sector A is adjacent to sector B, sector C is adjacent to sector D, sector A is symmetrical to sector C, and sector B is symmetrical to sector D V. For example, in one example, the four sectors A, B, C, and D are distributed corresponding to sectors I, II, V, and IV.

[0098] In one embodiment, obtaining the current phase change rate of a corresponding phase in the previous symmetrical area may include: obtaining the last current and phase value of a corresponding phase located in sector C recorded before switching to sector D; obtaining the first current and phase value of a corresponding phase located in sector D recorded after switching to sector D; and based on the last and first current and phase values, obtaining the current phase change rate of a corresponding phase in the previous symmetrical area.

[0099] For ease of understanding, the following will be combined with the attached Fig.12 and 13 Give a description. Fig.12 A synthetic vector map of the symmetric region with unsamplifiable regions marked is shown. Fig.13 A current phase diagram with unsampling intervals and symmetric intervals marked is shown.

[0100] Specifically, when the output voltage vector is in sector IV, the B phase current i is continuously recorded and saved. b As long as the voltage vector of the output is always in sector IV, the old saved value will be continuously overwritten with the new saved value until the output voltage vector enters sector V. At this time, the last B phase current i in sector IV is saved. b1′ and phase b1′ When the output voltage vector enters sector V, the first B-phase current i in sector V is saved. b3′ and phase b3′ The specific storage locations are as shown in the above figure at the positions of vector ①' and vector ③'.

[0101] When the FOC output voltage vector just enters sector I, its sampling window is sufficient to complete current sampling. As the output vector position changes, the sampling window gradually decreases. When the output vector is located between vectors ① and ③, it is an unsampling interval and the current needs to be predicted. During the calculation process, first record the B phase current i at the last normal sampling moment before entering the unsampling interval. b_base and phase b_base (For example, the B-phase current and phase of vector ①). The following formula is used to predict the current in the unsampling interval.

[0102]

[0103] Because I c The current can be obtained by sampling, so the predicted current i b After that, Kirchhoff's law can be used to calculate i a Reconstruction, that is, i a =-i b -ic . Then the reconstruction of the three-phase current is completed.

[0104] It should be noted here that since the vector ①' in this example corresponds to the last B-phase current i that can be measured in sector IV b1′ and phase b1′ Vector ③' corresponds to the first measurable B-phase current i in sector V. b3′ and phase b3′ However, there is no unsampling area near U1(001), so the angle between vector ①' and vector ③' is smaller than the angle between vector ① and vector ③. Fig.14 In the figure, the symmetrical region acquisition interval and the unsampling interval with different phase spans are shown. In other words, in the present disclosure, the actual angle span of the "symmetrical region" may be different from the span of the unsampling region. Of course, in other embodiments, the current and phase values ​​of vectors ①' and ③', which are exactly 180° different from vectors ① and ③, may also be used for estimation. In other words, in Fig.12 In the method shown, symmetrical regions of equal angular spans, symmetrical regions of different angular spans, or one or more pairs of current phase values ​​in symmetrical regions can be implemented to estimate the current value in the unsampleable interval. The present disclosure does not provide an exhaustive description of the estimation methods.

[0105] Similarly, the current that can be collected near U3(011) (the area between vector ④ and vector ⑥) is the A phase current i a The current that cannot be collected is the B phase current i b and C phase current i c At this time, the C phase current i is collected through the symmetrical area c The C-phase current in the area between vector ④ and vector ⑥ is predicted, and the three-phase current is reconstructed according to Kirchhoff's law.

[0106] Specifically, when the output voltage vector is in sector VI, the B phase current i is continuously recorded and saved. b As long as the voltage vector of the output is always in sector VI, the old saved value will be continuously overwritten with the new saved value until the output voltage vector enters sector I. At this time, the last C phase current i in sector VI is saved. c4′ and phase c4′ , when the output voltage vector enters sector I, the first C phase current i in sector I is saved c6′ and phase c6′ The specific storage locations are as shown in the above figure at the positions of vector ④' and vector ⑥'.

[0107] When the FOC output voltage vector is in sector III, its sampling window is sufficient to complete current sampling. As the output vector position changes, the sampling window gradually decreases. When the output vector is located between vectors ④ and ⑥, it is an unsampling interval and the current needs to be predicted. During the calculation process, first record the C phase current i at the last normal sampling moment before entering the unsampling interval. c_base and phase c_base The following formula is used to predict the current in the unsampling interval.

[0108]

[0109] Because I a The current can be obtained by sampling, so when the predicted current i is obtained c After that, Kirchhoff's law can be used to calculate i b Reconstruction, that is, i b =-i a -i c . Then the reconstruction of the three-phase current is completed.

[0110] The current that can be collected near U5 (101) (the area between vector ⑦ and vector ⑨) is the B phase current i b The current that cannot be collected is the A phase current i a and C phase current i c At this time, the A phase current i is collected through the symmetrical area a The A-phase current in the area between vector ⑦ and vector ⑨ is predicted, and the three-phase current is reconstructed according to Kirchhoff's law.

[0111] Specifically, when the output voltage vector is in sector II, the A phase current i is continuously recorded and saved. a As long as the voltage vector of the output is always in sector II, the old saved value will be continuously overwritten with the new saved value until the output voltage vector enters sector III. At this time, the last A phase current i in sector II is saved. a7′ and phase a7′ When the output voltage vector enters sector III, the first A-phase current i in sector III is saved. a9′ and phase a9， The specific storage location is as shown in the above figure at the positions of vector ⑦' and vector ⑨'.

[0112] When the FOC output voltage vector is in sector V, its sampling window is sufficient to complete current sampling. As the output vector position changes, the sampling window gradually decreases. When the output vector is located between vector ⑦ and vector ⑨, it is an unsampling interval and the current needs to be predicted. During the calculation process, first record the A phase current i at the last normal sampling moment before entering the unsampling interval. a_base and phase a_base The following formula is used to predict the current in the unsampling interval.

[0113]

[0114] i b The current can be obtained by sampling, and the predicted current i a After that, Kirchhoff's law can be used to calculate i c Reconstruction, i c =-i a -i b . Then the reconstruction of the three-phase current is completed.

[0115] When the motor is in an overmodulation state, the three resistors near the output maximum voltage vectors U6 (110), U3 (011), and U5 (101) cannot normally sample the two-phase current (in the case of two-resistance sampling, two additional sector switching areas are also included), and thus the three-phase current cannot be reconstructed, affecting the FOC dual closed-loop control. Therefore, this proposal proposes two solutions, one is to ensure normal sampling by reserving a minimum sampling window in the unsampling interval, and the other is to directly output the maximum voltage vector without leaving a sampling window in the unsampling interval, and predict the current value of the unsampling interval by the symmetrical interval current value. The universal motor was tested, and both methods can increase the maximum speed in the overmodulation interval. Among them, the method of reserving a minimum sampling window is more suitable for high-precision or high-interference scenarios, and the prediction method is suitable for application scenarios where the motor conditions are relatively stable.

[0116] In addition, the present invention can also be implemented as a permanent magnet synchronous motor. Fig.14 FIG. 1 shows a schematic diagram of the composition of a FOC module of a permanent magnet synchronous motor according to an embodiment of the present invention. Figure 1 , Fig.14 The FOC module shown additionally includes functions that can be executed Fig. 9 or Fig.11 The current sampling control module of the multi-resistance sampling method is shown.

[0117] Specifically, Fig.14The permanent magnet synchronous motor shown may include: a motor M; a magnetic oriented vector control (FOC) module 1500 for controlling the motor. All components except the motor M in the figure can be considered as part of the magnetic oriented vector control (FOC) module 1400. The FOC module 900 may include: a current sampling module 1410 for executing the multi-resistance current sampling method (reserved window method or prediction method) as described above to obtain three-phase current for controlling the motor.

[0118] The current sampling module 1410 can perform a continuous SVPWM control strategy on the three-phase inverter bridge. When the load increases and / or the speed increases, resulting in overmodulation, the voltage vector will enter the current unsampling area during the output process. At this time, the current sampling module 1410 can extend the conduction time of the lower bridge arm of the two phases that cannot be sampled (the extension needs to meet the requirements of the vector direction being unchanged and the minimum sampling time of the secondary small window), or use the sampled current value of the symmetrical area recorded previously for estimation. This ensures the precise operation of the motor during overmodulation and maximizes the torque output.

[0119] The above describes the permanent magnet synchronous motor and its multi-resistance current sampling method disclosed in the present invention in conjunction with the accompanying drawings. The present invention proposes a method for accurately controlling the motor when the FOC enters the overmodulation area. One method is to ensure normal current sampling by reserving a minimum sampling window in the unsampling interval. This method is more accurate and suitable for various high-interference application scenarios. Another method is to not reserve a sampling window in the unsampling interval, directly output the maximum voltage vector, and predict the current value of the unsampling interval by the symmetrical interval current value, so that the maximum output vector is output along the regular hexagonal boundary of the vector.

[0120] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terms used herein are selected to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for sampling current of a permanent magnet synchronous motor with multiple resistors, wherein the permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy, and the method comprises: Determine whether the voltage synthesis vector synthesized by the two three-phase conduction voltage vectors of the current control cycle enters the two-phase unsampling area, wherein the two-phase unsampling area refers to the sampling window time of two phases in the three phases is less than the minimum sampling time T all Or the sampling window time of one phase among the three phases is less than the minimum sampling time T all A continuous voltage synthesis vector angle region where the other phase cannot be measured at the same time; When it is determined that the two-phase non-sampling area has been entered, the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and make the direction of the voltage synthesis vector obtained after the extension consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension; and After the acquisition is extended, the sampling window time in the three phases is greater than the minimum sampling time T all The current of two phases can be measured and the current of the third phase can be calculated based on the collected two-phase currents.

2. The method of claim 1, wherein: The extended three-phase sampling window is less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and making the direction of the voltage synthesis vector obtained after the extension consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension also includes: Extend the sampling window of the phase with the smallest sampleable window among the three phases to be equal to the minimum sampling time T all ; Extend the sampling window in the three phases to be less than the minimum sampling time T all The lower bridge arm conduction time of the other phase of the two phases is set so that the direction of the voltage synthesis vector obtained after the extension is consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension. The voltage synthesis vector of the current control cycle is synthesized by two three-phase conduction voltage vectors.

3. The method of claim 1, wherein: The extended three-phase sampling window is less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and the step of making the direction of the voltage synthesis vector obtained after the extension consistent with the predetermined voltage synthesis vector direction of the current control cycle without extension also includes: Extend the sampling window in the three phases to be less than the minimum sampling time T all The conduction time of the lower bridge arms of the two phases is extended so that the ratio of the conduction time of the two three-phase conduction voltage vectors used to synthesize the direction of the current voltage synthesis vector remains unchanged compared to before the extension.

4. The method of claim 3, wherein: The extended three-phase sampling window is less than the minimum sampling time T all The step of increasing the conduction time of the lower bridge arms of the two phases so that the ratio of the conduction time of the two three-phase conduction voltage vectors used to synthesize the direction of the current voltage synthesis vector remains unchanged compared to before the extension also includes: In the case of entering the two-phase non-sampling area, let the phase without the lower bridge arm conduction time be X, and there is a sampling window but the window time is less than the minimum sampling time T all The phase is Y, and the sampling window time is greater than the minimum sampling time T all The phase of the Y phase is Z, and the time t at which the upper bridge arm is turned on and the lower bridge arm is turned off and the lower bridge arm is turned on is obtained. Y ; Extend the sampling window of phase X to the minimum sampling time T all ; and change the sampling window of the Y phase from T-2t Y Extended to T-2t Y1 , t Y1 The value of satisfies Where T is equal to the time of one control cycle.

5. The method of claim 1, wherein: The multi-resistance sampling is three-resistance sampling, and the current control cycle enters the two-phase non-sampling area, which means that the voltage synthesis vector obtained by synthesizing the three-phase conduction voltage vector is located in the maximum regular hexagonal vector that can be output by the FOC control, and the two-phase non-sampling area includes: The switching area from sector I to sector II; The handover region from sector III to sector IV; and Switching area from sector V to sector VI.

6. The method of claim 1, wherein: The multi-resistance sampling is a three-resistance sampling, and In the case of judging that the two-phase unsampling area is entered, extending the sampleable window in the three phases to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is extended so that the lower bridge arm conduction time of at least one phase of the two phases is not less than the minimum sampling time T all , and making the direction of the voltage synthesis vector obtained after the extension consistent with the direction of the predetermined synthesis voltage vector before the current control cycle is extended also includes: Extend the sampling window of the phase with the second smallest sampleable window among the three phases to be equal to the minimum sampling time T all ; Extend the sampleable window in the three phases to be less than the minimum sampling time T all The lower bridge arm conduction time of the other phase of the two phases is set so that the direction of the voltage synthesis vector after the extension is consistent with the predetermined synthesis voltage vector direction before the extension, and After the acquisition is extended, the sampleable window time in the three phases is greater than the minimum sampling time T all The steps of measuring the current of two phases and calculating the current of the third phase according to the collected two phase currents include: The currents of the two phases corresponding to the maximum sampleable window and the second smallest sampleable window after the extension are collected, and the current of the third phase is calculated based on the collected two-phase currents.

7. The method of claim 1, wherein: The multi-resistance sampling is two-resistance sampling, and the two measurable phases in the three phases correspond to the two phases configured with sampling resistors, and the sampling window in the three phases is extended to be less than the minimum sampling time T all The lower bridge arm conduction time of the two phases is set so that the sampling window of the two phases that can be measured in the three phases is not less than the minimum sampling time T all .

8. A method for sampling current of a permanent magnet synchronous motor with multiple resistors, wherein the permanent magnet synchronous motor controls a three-phase inverter based on an SVPWM strategy, and the method comprises: Determine whether the voltage synthesis vector synthesized by the two three-phase conduction voltage vectors of the current control cycle enters the two-phase unsampling area, wherein the two-phase unsampling area refers to the sampling window time of two phases in the three phases is less than the minimum sampling time T all Or the sampling window time of one phase among the three phases is less than the minimum sampling time T all A continuous voltage synthesis vector angle region where the other phase cannot be measured at the same time; In the case of entering the two-phase unsampling area, based on the current sampling value of the corresponding phase of the previous symmetrical area that currently enters the two-phase unsampling area, it is estimated that the sampling window time of the two unsampling phases in the current control cycle is less than the minimum sampling time T all A current sampling value of one phase of ; and The sampling window time in the three-phase acquisition is greater than the minimum sampling time T all The measurable current of one phase can be obtained, and the current of the third phase can be calculated based on the collected current of one phase and the estimated current of one phase.

9. The method of claim 8, wherein: In the case of judging that the two-phase unsampling area is entered, based on the current sampling value of the corresponding phase of the previous symmetrical area that currently enters the two-phase unsampling area, it is estimated that the sampling window time of the two unsampling phases in the current control cycle is less than the minimum sampling time T all The steps of sampling the current value of one phase include: Based on the current phase change rate of the corresponding phase in the previous symmetrical area, using the current and phase of the corresponding phase measured in the last control cycle entering the two-phase unsampling area, it is estimated that the sampling window time of the two unsampling phases in the current control cycle is less than the minimum sampling time T all The current sampling value of one phase.

10. The method of claim 9, wherein: The two-phase unsampling region is the region where the switch is made from sector A to sector B, and the previous symmetrical region is the region where the switch is made from sector C to sector D, wherein sector A is symmetrical to sector C, and sector B is symmetrical to sector D. And obtaining the current phase change rate of the corresponding phase in the previous symmetric region includes: Obtain the current and phase value of the corresponding phase in sector C recorded last time before switching to sector D; Obtaining the current and phase value of the first corresponding phase located in the D sector recorded after switching to the D sector; and Based on the last and first current and phase values, the current phase change rate of the corresponding phase in the previous symmetric region is obtained.

11. The method of claim 8, wherein: In the case of judging that the two-phase unsampling area is entered, based on the current sampling values ​​of the corresponding phases in the corresponding two phases of the previous symmetrical area that currently enters the two-phase unsampling area, it is estimated that the sampling window time of the two phases that cannot be sampled in the current control cycle is less than the minimum sampling time T all The steps of sampling the current value of one phase include: The current sampling value of the corresponding phase in the current control cycle is estimated by using the current sampling value of the corresponding phase of the previous symmetrical voltage vector angle of the current voltage synthesis vector angle.

12. A method for operating a permanent magnet synchronous motor, comprising executing the multi-resistance current sampling method as described in claims 1-11 above when the motor is in an overmodulation state.

13. A permanent magnet synchronous motor, comprising: Motor; A magnetic oriented vector control module is used to control the motor and comprises: A current sampling control module is used to execute the multi-resistance current sampling method according to any one of claims 1 to 11, and obtain three-phase current for controlling the motor.

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