Motor control system, current sampling method and motor control method

Abstract

The invention relates to a motor control system, a current sampling method and a motor control method. The system comprises a control unit, a driving unit, a single-resistor sampling unit and a holding unit. And the driving unit converts the direct-current bus current into three-phase current to drive the motor. The single-resistor sampling unit carries out sampling to obtain a sampling current signal. And the holding unit acquires and holds the sampling current signal, and keeps the signal unchanged in the AD conversion process, so that the sampling result is more stable and accurate, and the noise of motor control is reduced. The control unit controls different states of the driving unit to modulate the three-phase current, disconnects the holding unit and the single-resistor sampling unit after the holding unit completes holding of the sampling current signal, performs AD conversion on the held sampling current signal to obtain the three-phase current value of the motor, is not influenced by motor operation during the conversion period, and is safe and reliable. The duty ratio phase shift time can be reduced, the current distortion can be reduced, and the PWM control signal frequency can be improved.

Description

Technical Field

[0001] The present invention relates to the field of motor control, and in particular to a motor control system, a current sampling method and a motor control method. Background Art

[0002] The brushless permanent magnet motor is a driving support device. When controlling the motor, it is necessary to collect the phase current of the three-phase coil of the motor to realize the PWM modulation control of the motor. Single resistor current sampling is a commonly used low-cost acquisition method. In the prior art, the sampling resistor is directly sampled, and the sampling process is easily interfered by factors such as motor operation, resulting in errors in the sampling results and failure to achieve low-noise motor control.

[0003] In addition, single resistor sampling requires two samplings within one PWM cycle, and then the three-phase current is obtained through three-phase current reconstruction. Each sampling requires duty cycle phase shifting, and a certain window time is reserved to complete the AD conversion of the sampling signal, and then trigger the next phase PWM control signal. In addition, the two complementary signals of each phase PWM control signal need to set a dead time interval, which limits the frequency of the PWM control signal and cannot be increased, and there is a problem of excessive current distortion. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a motor control system, a current sampling method and a motor control method.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide a motor control system, including: a control unit, a driving unit, a single resistor sampling unit and a holding unit;

[0006] The driving unit is connected between the DC bus and the motor, and converts the DC bus current into a three-phase current to drive the motor;

[0007] The single resistor sampling unit is connected to the driving unit and is used to sample the DC bus current flowing through the driving unit to obtain a sampling current signal;

[0008] The holding unit is connected to the single resistor sampling unit to obtain and hold the sampling current signal;

[0009] The control unit is connected to the holding unit and the driving unit, and is used to control different states of the driving unit to modulate the three-phase current of the motor, and after the holding unit completes holding the sampled current signal, disconnect the holding unit from the single resistor sampling unit, and perform AD conversion on the held sampled current signal from the holding unit, thereby obtaining the three-phase current value of the motor.

[0010] Furthermore, it also includes: a switch unit connected between the single resistor sampling unit and the holding unit;

[0011] The control unit is connected to the switch unit, and switches on or off the connection between the holding unit and the single resistor sampling unit by controlling the switch of the switch unit.

[0012] Further, the holding unit includes a filter circuit, a voltage follower and an energy storage capacitor;

[0013] The in-phase input end of the voltage follower is connected to the single resistor sampling unit and is grounded through the energy storage capacitor; the output end of the voltage follower is connected to the control unit through the filter circuit;

[0014] The energy storage capacitor stores the sampling current signal, and outputs the retained sampling current signal after passing through the voltage follower and the filtering circuit.

[0015] Furthermore, the single resistor sampling unit includes a sampling resistor and a differential amplifier circuit;

[0016] The driving unit is grounded through the sampling resistor; the differential amplifier circuit is connected to the sampling resistor and the holding unit, obtains the voltage division at both ends of the sampling resistor and performs differential amplification processing to obtain the sampling current signal.

[0017] Further, the driving unit is a three-phase full-bridge inverter circuit, including a first-phase upper bridge arm, a first-phase lower bridge arm, a second-phase upper bridge arm, a second-phase lower bridge arm, a third-phase upper bridge arm and a third-phase lower bridge arm;

[0018] One end of the first-phase upper bridge arm connected to the first-phase lower bridge arm is also connected to the first end of the motor, one end of the second-phase upper bridge arm connected to the second-phase lower bridge arm is also connected to the second end of the motor, and one end of the third-phase upper bridge arm connected to the third-phase lower bridge arm is also connected to the third end of the motor;

[0019] The other end of each upper bridge arm is connected to the DC bus, and the other end of each lower bridge arm is grounded through the single resistor sampling unit;

[0020] The control end of each bridge arm is connected to the control unit, and receives a corresponding control signal from the control unit respectively, so that the driving unit switches to a corresponding state.

[0021] Further, the different states include an initial state, a first state, a second state and a third state;

[0022] The initial state is: all first bridge arms are disconnected, and all second bridge arms are turned on;

[0023] The first state is: the first bridge arm of the first phase, the second bridge arm of the second phase and the second bridge arm of the third phase are turned on, and the other bridge arms are turned off;

[0024] The second state is: the first bridge arm of the first phase, the first bridge arm of the second phase and the second bridge arm of the third phase are turned on, and the other bridge arms are turned off;

[0025] The third state is: all second bridge arms are disconnected, and all first bridge arms are turned on;

[0026] When the first bridge arm is the upper bridge arm, the second bridge arm is the lower bridge arm; when the first bridge arm is the lower bridge arm, the second bridge arm is the upper bridge arm.

[0027] Furthermore, it also includes: a signal amplifying unit connected between the control unit and the driving unit, for amplifying the control signal transmitted from the control unit to the driving unit.

[0028] A current sampling method based on single resistor current sampling and holding is also provided, which is applied to any of the motor control systems described above, wherein the control unit controls the drive unit to switch to an initial state, a first state, a second state and a third state in sequence; the method comprises the following steps:

[0029] After the driving unit switches to the first state and before switching to the second state, controlling the holding unit to turn on the single resistor sampling unit to perform a first holding of the sampling current signal obtained by the single resistor sampling unit;

[0030] After the first holding is completed, the holding unit and the single resistor sampling unit are disconnected, and the held sampling current signal is subjected to a first AD conversion from the holding unit to obtain a first sampling current;

[0031] After the driving unit switches to the second state and before switching to the third state, the holding unit is controlled to switch on the single resistor sampling unit to perform a second holding of the sampling current signal obtained by the single resistor sampling unit;

[0032] After the second holding is completed, the holding unit and the single resistor sampling unit are disconnected, and the held sampling current signal is subjected to a second AD conversion from the holding unit to obtain a second sampling current;

[0033] The three-phase current values ​​of the motor are obtained according to the first sampling current and the second sampling current.

[0034] Further, the difference between the time when the driving unit starts to switch to the third state and the time when it successfully switches to the first state is greater than or equal to the sum of the time required for the first holding, the time required for the first AD conversion, and the time required for the second holding.

[0035] A motor control method based on single resistor current sampling and holding is also provided, comprising the following steps:

[0036] The control unit sends a PWM control signal to the driving unit in the current PWM cycle, controls the driving unit to switch to the initial state, the first state, the second state and the third state in sequence, and then switches from the third state to the initial state in sequence;

[0037] In the process of controlling the drive unit, the control unit executes the current sampling method based on single resistor current sampling and holding as described in any one of the above items to obtain the three-phase current value provided by the drive unit for the motor;

[0038] The control unit adjusts the PWM control signal of the next PWM cycle according to the three-phase current value, thereby adjusting the operation of the motor.

[0039] The implementation of the present invention has the following beneficial effects: by holding the sampling current signal obtained by the single resistor sampling unit through the holding unit, the signal can be kept unchanged during the AD conversion process, so that the sampling result is more stable and accurate, and the noise of the motor control can be reduced. After the holding of the sampling current signal is completed, the connection between the holding unit and the single resistor sampling unit is disconnected, and the motor operation is not affected during the AD conversion, thereby reducing the duty cycle phase shift time, reducing current distortion, and increasing the PWM control signal frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0041] Figure 1 is a structural block diagram of an embodiment of a motor control system of the present invention;

[0042] Figure 2 is a circuit diagram of an embodiment of a motor control system of the present invention;

[0043] Figure 3 is a circuit schematic diagram of another embodiment of the motor control system of the present invention;

[0044] Figure 4 It is a waveform diagram of six-channel PWM control signals of the present invention;

[0045] Figure 5 This is a comparison diagram of the effects of the current sampling method based on single-resistance current sampling and holding of the present invention;

[0046] Figure 6 It is a schematic diagram of counting sampling within one PWM cycle of the present invention. DETAILED DESCRIPTION

[0047] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "upper" and "lower" are based on the directions or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific direction. They are only for the convenience of describing the technical solution, and do not indicate that the device or element referred to must have a specific direction, and therefore cannot be understood as a limitation to the present invention.

[0048] It should also be noted that the terms "first", "second", "third", etc. are only used to facilitate the description of the technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the features. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] like Figure 1 As shown, in an embodiment of the motor control system of the present invention, the motor control system includes: a control unit 10 , a driving unit 20 , a single resistor sampling unit 30 and a holding unit 40 .

[0050] In this embodiment, the drive unit 20 is connected between the DC bus and the motor M1, and converts the DC bus current into a three-phase current to drive the motor. The motor M1 is a three-phase motor. Under the control of the control unit 10, the drive unit 20 converts the DC power of the DC bus into a three-phase AC power with controllable frequency and phase, thereby driving the motor M1 to work. The drive unit 20 can sample a three-phase half-bridge inverter circuit, a three-phase full-bridge inverter circuit, or other circuits, as long as it can provide three-phase power for the motor M1.

[0051] The drive unit 20 of the present embodiment is a three-phase full-bridge inverter circuit. The drive unit 20 includes a first-phase upper bridge arm, a first-phase lower bridge arm, a second-phase upper bridge arm, a second-phase lower bridge arm, a third-phase upper bridge arm and a third-phase lower bridge arm. One end of the first-phase upper bridge arm connected to the first-phase lower bridge arm is also connected to the first end of the motor, one end of the second-phase upper bridge arm connected to the second-phase lower bridge arm is also connected to the second end of the motor, and one end of the third-phase upper bridge arm connected to the third-phase lower bridge arm is also connected to the third end of the motor. The other end of each upper bridge arm is connected to the DC bus, and the other end of each lower bridge arm is grounded through a single resistor sampling unit 30. The control end of each bridge arm is connected to the control unit 10, and receives corresponding control signals from the control unit 10 respectively, so that the drive unit 20 switches to the corresponding state.

[0052] Specifically, the three phases of the current are U phase, V phase and W phase. The first phase, the second phase and the third phase may be U phase, V phase and W phase in sequence, or may be W phase, V phase and U phase in sequence, or other combination sequences.

[0053] The present invention is described in the order of W phase, V phase and U phase, and other combination orders can be referred to accordingly. Figure 2 As shown, the upper bridge arm of the first phase includes an NMOS tube Q1, the lower bridge arm of the first phase includes an NMOS tube Q4, the upper bridge arm of the second phase includes an NMOS tube Q2, the lower bridge arm of the second phase includes an NMOS tube Q5, the upper bridge arm of the third phase includes an NMOS tube Q3, and the lower bridge arm of the third phase includes an NMOS tube Q6. The drains of the NMOS tubes Q1, Q2, and Q3 are connected to the same DC bus Vbus, the gates are all connected to the control unit 10, and the sources are respectively connected to the drains of the NMOS tubes of the corresponding lower bridge arms. The gates of the NMOS tubes Q4, Q5, and Q6 are all connected to the control unit 10, and the sources are all connected to the single resistor sampling unit 30 and then grounded.

[0054] The control unit 10 outputs 6 PWM control signals to the drive unit 20 to control the on and off of each bridge arm. Specifically, the W+ control signal is output to the W- phase upper bridge arm, the W- control signal is output to the W- phase upper bridge arm, the V+ control signal is output to the V- phase upper bridge arm, the U+ control signal is output to the U- phase upper bridge arm, and the U- control signal is output to the U- phase upper bridge arm. The W+ control signal and the W- control signal, the V+ control signal and the V- control signal, and the U+ control signal and the U- control signal are a pair of complementary signals with dead time, which can avoid the upper and lower bridge arms from being turned on at the same time.

[0055] Furthermore, the motor control system further includes: a signal amplifying unit 50 connected between the control unit 10 and the driving unit 20, for amplifying the control signal transmitted from the control unit 10 to the driving unit 20. The input end of the signal amplifying unit 50 is connected to the control unit 10, and the output end is respectively connected to the gate of each NMOS tube. The 6-way PWM control signal output by the control unit 10 is amplified and transmitted to the corresponding bridge arm. The signal amplifying unit 50 can adopt the signal amplifying circuit of the prior art.

[0056] In this embodiment, the single resistor sampling unit 30 is connected to the driving unit 20, and is used to sample the DC bus current flowing through the driving unit 20 to obtain a sampled current signal. Optionally, the single resistor sampling unit 30 includes a sampling resistor and a differential amplifier circuit. The driving unit 20 is grounded through the sampling resistor. The differential amplifier circuit connects the sampling resistor and the holding unit 40, obtains the voltage division at both ends of the sampling resistor, and then performs differential amplification processing to obtain a sampled current signal.

[0057] like Figure 3As shown, the driving unit 20 is grounded through the sampling resistor RS1, and the differential amplifier circuit collects the voltage division of the sampling resistor RS1, performs differential amplification processing, and obtains the sampling current signal. The differential amplifier circuit includes a resistor R1, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7 and an operational amplifier U1B. The inverting input terminal of the operational amplifier U1B is connected to one end of the sampling resistor RS1 through the resistor R3, and the non-inverting input terminal is connected to the other end of the sampling resistor RS1 through the resistor R5. One end of the resistor R6 is connected to the power supply +5V, and the other end is grounded through the resistor R7. The non-inverting input terminal of the operational amplifier U1B is also connected between the resistor R6 and the resistor R7. The output terminal of the operational amplifier U1B is connected to the resistor R4, and is connected to its own inverting input terminal through the resistor R1. The resistor R4 is connected to the holding unit 40 as the output terminal of the single resistor sampling unit 30.

[0058] In other embodiments, the differential amplifier circuit may also adopt other circuit structures, and the single resistor sampling unit 30 may also adopt other circuit structures, and specific details may be referred to the prior art.

[0059] In this embodiment, the input end of the holding unit 40 is connected to the output end of the single resistor sampling unit 30. When the holding unit 40 is connected to the single resistor sampling unit 30, the sampling current signal is obtained and maintained. Optionally, the holding unit 40 includes a filtering circuit, a voltage follower and an energy storage capacitor. The in-phase input end of the voltage follower is connected to the single resistor sampling unit 30 and grounded through the energy storage capacitor. The output end of the voltage follower is connected to the control unit 10 through the filtering circuit. The energy storage capacitor stores the sampling current signal and outputs the maintained sampling current signal after passing through the voltage follower and the filtering circuit.

[0060] like Figure 3 As shown, the filter circuit includes a resistor R2 and a capacitor C1. One end of the resistor R2 is connected to the output end of the voltage follower U2B, and the other end is used as the output end of the holding unit 40 and is grounded through the capacitor C1. The in-phase input end of the voltage follower U2B is connected to the single resistor sampling unit 30 and is grounded through the energy storage capacitor C2. In other embodiments, the holding unit 40 may also adopt other circuit structures, and specific reference may be made to the prior art.

[0061] In the prior art, the control unit 10 directly performs AD conversion from the output end of the single resistor sampling unit 30, which is easily affected by the fluctuation of the motor operation during the conversion process, and requires that the state of the drive unit 20 cannot be changed during the conversion process. The present invention adds a holding unit 40. When the holding unit 40 is connected to the single resistor sampling unit 30, the output of the single resistor sampling unit 30 is to charge the energy storage capacitor C2 to its peak value. After disconnecting the holding unit 40 from the single resistor sampling unit 30, the voltage of the energy storage capacitor can be maintained unchanged due to the action of the voltage follower U2B. Therefore, AD conversion after disconnection can obtain a stable sampling result and reduce the noise in the sampling process; the AD conversion of the control unit 10 is also not affected by the drive unit 20, which can reduce the time the drive unit 20 waits for the sampling to be completed.

[0062] Furthermore, a switch unit 60 is provided between the single resistance sampling unit 30 and the holding unit 40. The control unit 10 is connected to the switch unit 60, and the connection between the holding unit 40 and the single resistance sampling unit 30 is turned on or off by controlling the switch of the switch unit 60. The switch unit 60 can be a MOS tube, such as Figure 3 As shown, the control unit 10 is connected to the gate of the MOS tube Q7, and controls the on and off of the MOS tube Q7 through high and low levels.

[0063] In this embodiment, the control unit 10 is connected to the holding unit 40 and the driving unit 20, and is used to control different states of the driving unit 20 to modulate the three-phase current of the motor, and after the holding unit 40 completes the holding of the sampled current signal, disconnects the holding unit 40 from the single resistor sampling unit 30, and performs AD conversion on the held sampled current signal from the holding unit 40, thereby obtaining the three-phase current value of the motor.

[0064] Specifically, the control unit 10 can use an MCU, which controls the state of the driving unit 20 through a PWM control signal to control the waveform, size, direction, etc. of the three-phase current, performs sampling in different states, and obtains the three-phase current value after processing. For the specific sampling process, please refer to the current sampling method based on single resistor current sampling and holding below.

[0065] The different states include an initial state, a first state, a second state, and a third state. When the first bridge arm is an upper bridge arm, the second bridge arm is a lower bridge arm; when the first bridge arm is a lower bridge arm, the second bridge arm is an upper bridge arm. The following description assumes that the first bridge arm is an upper bridge arm and the second bridge arm is a lower bridge arm.

[0066] The initial state is: all first bridge arms are disconnected, and all second bridge arms are turned on. Figure 4The T0 range is the initial state, the W+, V+, and U+ control signals are low, all upper bridge arms are disconnected, the W-, V-, and U- control signals are high, and all lower bridge arms are turned on. The current vector sum is 0, no current passes through the motor, and the three-phase current cannot be collected.

[0067] The first state is: the first bridge arm of the first phase, the second bridge arm of the second phase and the second bridge arm of the third phase are turned on, and the other bridge arms are turned off. Figure 4 In the middle, T1 range is the first state, W-, V+, U+ control signals are low level, and W+, V-, U- control signals are high level. The upper bridge arm of W phase and the lower bridge arms of V phase and U phase are turned on, and the other bridge arms are turned off. The current flows into the motor from W phase and flows out from V phase and U phase. At this time, the W phase current can be collected.

[0068] The second state is: the first bridge arm of the first phase, the first bridge arm of the second phase and the second bridge arm of the third phase are turned on, and the other bridge arms are turned off. Figure 4 The T2 range is the second state, the W-, V-, and U+ control signals are low level, and the W+, V+, and U- control signals are high level. The current flows into the motor from the W phase and the V phase, and flows out from the U phase. At this time, the U phase current can be collected.

[0069] The third state is: all the second bridge arms are disconnected, and all the first bridge arms are turned on. Figure 4 The T3 range is the third state, the W+, V+, and U+ control signals are high, all upper bridge arms are turned on, the W-, V-, and U- control signals are low, and all lower bridge arms are disconnected. The current vector sum is 0, no current passes through the motor, and the three-phase current cannot be collected.

[0070] The current sampling method based on single resistor current sampling and holding of the present invention can be applied to the motor control system of any of the above embodiments. The control unit 10 controls the drive unit 20 to switch to the initial state, the first state, the second state and the third state in sequence.

[0071] In one embodiment, the method comprises the following steps:

[0072] A1. After the driving unit 20 switches to the first state and before switching to the second state, the control holding unit 40 switches on the single resistor sampling unit 30 to perform the first holding of the sampling current signal obtained by the single resistor sampling unit 30.

[0073] A2. After the first holding is completed, the holding unit 40 and the single resistor sampling unit 30 are disconnected, and the holding unit 40 performs a first AD conversion on the held sampling current signal to obtain a first sampling current.

[0074] A3. After the driving unit 20 switches to the second state and before switching to the third state, the holding unit 40 is controlled to switch on the single resistor sampling unit 30 to perform a second holding of the sampling current signal obtained by the single resistor sampling unit 30 .

[0075] A4. After the second holding is completed, the holding unit 40 and the single resistor sampling unit 30 are disconnected, and the holding unit 40 performs a second AD conversion on the held sampling current signal to obtain a second sampling current.

[0076] A5. Obtain the three-phase current value of the motor according to the first sampling current and the second sampling current.

[0077] Specifically, in the initial state, no data is collected. After the drive unit 20 is successfully switched to the first state, the energy storage capacitor C2 is fully charged after the holding unit 40 is connected to the single resistor sampling unit 30 for a certain time within the range of T1, and the first holding is completed. Then the holding unit 40 is disconnected from the single resistor sampling unit 30, and the control unit 10 performs the first AD conversion from the holding unit 40, and the first sampled current value obtained is the W phase current value Iw. After the drive unit 20 is successfully switched to the second state, after the holding unit 40 is connected to the single resistor sampling unit 30 for a certain time within the range of T2, the energy storage capacitor C2 is fully charged, and the second holding is completed. Then the holding unit 40 is disconnected from the single resistor sampling unit 30, and the control unit 10 performs the second AD conversion from the holding unit 40, and the second sampled current value obtained is the U phase current value Iu, and Iu is a negative sampling value. The V phase current value is obtained based on the sum of the three-phase currents being 0, that is, Iu+Iv+Iw=0, so the three-phase current values ​​of the motor can be obtained.

[0078] It should be noted that the present embodiment can start switching to the second state only after the first AD conversion is completed within the range of T1. Since the sampled current signal is maintained, the switching to the second state can also be started before the first AD conversion is completed. In other words, the first AD conversion can continue during the switching process of the second state, that is, it can continue within the dead time of the V+ and V- phase control signals (there is no current within the dead time); it can even continue within the range of T2 of the second state. The second AD conversion is the same. Under normal circumstances, as long as the first hold is completed before switching to the second state, the second hold is completed before switching to the third state, and the first AD conversion is completed before starting the second hold, the three-phase current value can be obtained later.

[0079] Further, the difference between the time when the driving unit 20 starts to switch to the third state and the time when it successfully switches to the first state is greater than or equal to the sum of the time required for the first holding, the time required for the first AD conversion, and the time required for the second holding.

[0080] That is: first state duration T1+dead time Td1+first state duration T2≥time required for first holding+time required for first AD conversion+time required for second holding.

[0081] The required holding time refers to the time it takes for the voltage-divided signal of the sampling resistor to reach the energy storage capacitor to charge it completely, which can be obtained based on specific circuit measurements. The required AD conversion time is related to the MCU performance of the control unit 10 .

[0082] When the SVPWM vector area is in the low modulation index area and the medium to high modulation index area when the interval changes from the interval, the T1 and T2 times are very small, so the duty cycle phase shift is required to ensure sampling. In the prior art, it is necessary to switch to the next state after each AD conversion is completed, and conversion cannot be performed during the dead time. In contrast, due to the addition of the holding unit 40, the minimum time for the present solution to complete two samplings can be shorter, the duty cycle phase shift time of the PWM signal can be reduced, and the current distortion and motor noise can be reduced; the PWM frequency can be made higher to reduce the ripple of the motor current; and the cost is lower.

[0083] Figure 5 (a) shows the time window before the absence of the holding unit 40, Figure 5 (b) shows the time window before the holding unit 40 is provided. It can be seen that after the holding unit 40 is added, T1 and T2 can be made very small, so the duty cycle phase shifting time is reduced and the current distortion is reduced.

[0084] In an embodiment of the motor control method based on single resistor current sampling and holding of the present invention, the following steps are included:

[0085] B1. The control unit 10 sends a PWM control signal to the driving unit 20 in the current PWM cycle, and controls the driving unit 20 to switch to the initial state, the first state, the second state and the third state in sequence, and then switches from the third state to the initial state in sequence.

[0086] B2. In the process of controlling the drive unit 20, the control unit 10 executes the current sampling method based on single-resistance current sampling and holding as in any of the above embodiments to obtain the three-phase current value provided by the drive unit 20 for the motor.

[0087] B3. The control unit 10 adjusts the PWM control signal of the next PWM cycle according to the three-phase current value, thereby adjusting the operation of the motor.

[0088] In this embodiment, a PWM cycle is formed when the register inside the MCU counts from 0 to the maximum value and then from the maximum value to 0. In other embodiments, the register may also count from the maximum value to 0 and then from 0 to the maximum value as a PWM cycle. Figure 6Among them, CH0CV is the count value of controlling the U-phase control signal, CH1CV is the count value of controlling the V-phase control signal, CH2CV is the count value of controlling the W-phase control signal, and CH3CV is the count value of controlling the CH3 signal (controlling the on and off of the switch unit 60). The control unit 10 can control the triggering order of each phase control signal by setting the order of the count values ​​of the three-phase control signals, and the current type of the two sampling results also changes. By setting the value of CH3CV, the execution time of AD conversion can be controlled.

[0089] The following description is based on “CH3CV secondary modification value (maximum value) > CH0CV > CH3CV primary modification value > CH1CV > CH3CV initial value > CH2CV”.

[0090] The register starts counting from 0, and the current PWM cycle starts. The W+, V+, and U+ control signals are low, the W-, V-, and U- control signals are high, and the CH3 signal is high. When the count value reaches CH2CV, the W- control signal jumps to a low level and starts to switch to the first state. After the dead time, the W+ control signal jumps to a high level and successfully switches to the first state. The first hold starts automatically. After the first hold is completed, the count value reaches the CH3CV initial value, the CH3 signal jumps to a low level, the switch unit 60 is disconnected, and the falling edge triggers the first AD conversion. After the conversion is completed, the control unit 10 changes CH3CV to a modified value, the CH3 signal jumps to a high level, and the switch unit 60 is turned on.

[0091] When the count value reaches CH1CV, the V- control signal jumps to a low level and starts switching to the second state. After the dead time, the V+ control signal jumps to a high level and successfully switches to the second state. The second hold starts automatically. After the second hold is completed, the count value reaches the CH3CV secondary modification value, the CH3 signal jumps to a low level, the switch unit 60 is disconnected, and the falling edge triggers the second AD conversion. After the conversion is completed, the control unit 10 changes CH3CV to the secondary modification value (maximum value), and the CH3 signal jumps to a high level and remains until the end of the current PWM cycle.

[0092] When the count value reaches CH0CV, the U- control signal jumps to a low level and starts to switch to the third state. After the dead time, the U+ control signal jumps to a high level and successfully switches to the third state. After the count value reaches the maximum value, the count is reduced and reaches CH0CV, CH1CV and CH0CV in sequence. The corresponding control signal jumps again. After passing through the second state, the first state and the initial state in sequence, the current PWM cycle ends.

[0093] By obtaining the current three-phase current value in the current cycle, the PWM control signal of the next PWM cycle can be adjusted to further adjust the three-phase current and control the operation of the motor. For example, the above count value is adjusted according to the measured three-phase current value, the duty cycle of the PWM signal in the next PWM cycle is adjusted, and the input voltage and frequency of the motor are adjusted to control the torque and speed of the motor.

[0094] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A motor control system, characterized in that: include: A control unit, a driving unit, a single resistor sampling unit and a holding unit; The driving unit is connected between the DC bus and the motor, and converts the DC bus current into a three-phase current to drive the motor; The single resistor sampling unit is connected to the driving unit and is used to sample the DC bus current flowing through the driving unit to obtain a sampling current signal; The holding unit is connected to the single resistor sampling unit to obtain and hold the sampling current signal; The control unit is connected to the holding unit and the driving unit, and is used to control different states of the driving unit to modulate the three-phase current of the motor, and after the holding unit completes holding the sampled current signal, disconnect the holding unit from the single resistor sampling unit, and perform AD conversion on the held sampled current signal from the holding unit, thereby obtaining the three-phase current value of the motor.

2. The motor control system according to claim 1, characterized in that: Also includes: A switch unit connected between the single resistor sampling unit and the holding unit; The control unit is connected to the switch unit, and switches on or off the connection between the holding unit and the single resistor sampling unit by controlling the switch of the switch unit.

3. The motor control system according to claim 1, characterized in that: The holding unit includes a filter circuit, a voltage follower and an energy storage capacitor; The in-phase input end of the voltage follower is connected to the single resistor sampling unit and is grounded through the energy storage capacitor; the output end of the voltage follower is connected to the control unit through the filter circuit; The energy storage capacitor stores the sampling current signal, and outputs the retained sampling current signal after passing through the voltage follower and the filtering circuit.

4. The motor control system according to claim 1, characterized in that: The single resistor sampling unit includes a sampling resistor and a differential amplifier circuit; The driving unit is grounded through the sampling resistor; the differential amplifier circuit is connected to the sampling resistor and the holding unit, obtains the voltage division at both ends of the sampling resistor and performs differential amplification processing to obtain the sampling current signal.

5. The motor control system according to claim 1, characterized in that: The driving unit is a three-phase full-bridge inverter circuit, including a first-phase upper bridge arm, a first-phase lower bridge arm, a second-phase upper bridge arm, a second-phase lower bridge arm, a third-phase upper bridge arm and a third-phase lower bridge arm; One end of the first-phase upper bridge arm connected to the first-phase lower bridge arm is also connected to the first end of the motor, one end of the second-phase upper bridge arm connected to the second-phase lower bridge arm is also connected to the second end of the motor, and one end of the third-phase upper bridge arm connected to the third-phase lower bridge arm is also connected to the third end of the motor; The other end of each upper bridge arm is connected to the DC bus, and the other end of each lower bridge arm is grounded through the single resistor sampling unit; The control end of each bridge arm is connected to the control unit, and receives a corresponding control signal from the control unit respectively, so that the driving unit switches to a corresponding state.

6. The motor control system according to claim 5, characterized in that: The different states include an initial state, a first state, a second state and a third state; The initial state is: all first bridge arms are disconnected, and all second bridge arms are turned on; The first state is: the first bridge arm of the first phase, the second bridge arm of the second phase and the second bridge arm of the third phase are turned on, and the other bridge arms are turned off; The second state is: the first bridge arm of the first phase, the first bridge arm of the second phase and the second bridge arm of the third phase are turned on, and the other bridge arms are turned off; The third state is: all second bridge arms are disconnected, and all first bridge arms are turned on; When the first bridge arm is the upper bridge arm, the second bridge arm is the lower bridge arm; when the first bridge arm is the lower bridge arm, the second bridge arm is the upper bridge arm.

7. The motor control system according to claim 1, characterized in that: Also includes: The signal amplifying unit connected between the control unit and the driving unit is used to amplify the control signal transmitted from the control unit to the driving unit.

8. A current sampling method based on single resistor current sampling and holding, characterized in that: The motor control system according to any one of claims 1 to 7, wherein the control unit controls the drive unit to switch to an initial state, a first state, a second state and a third state in sequence; the method comprises the following steps: After the driving unit switches to the first state and before switching to the second state, controlling the holding unit to switch on the single resistor sampling unit to perform a first holding of the sampling current signal obtained by the single resistor sampling unit; After the first holding is completed, the holding unit and the single resistor sampling unit are disconnected, and the held sampling current signal is subjected to a first AD conversion from the holding unit to obtain a first sampling current; After the driving unit switches to the second state and before switching to the third state, the holding unit is controlled to switch on the single resistor sampling unit to perform a second holding of the sampling current signal obtained by the single resistor sampling unit; After the second holding is completed, the holding unit and the single resistor sampling unit are disconnected, and the held sampling current signal is subjected to a second AD conversion from the holding unit to obtain a second sampling current; The three-phase current values ​​of the motor are obtained according to the first sampling current and the second sampling current.

9. The current sampling method based on single resistor current sampling and holding according to claim 8, characterized in that: The difference between the time when the driving unit starts to switch to the third state and the time when it successfully switches to the first state is greater than or equal to the sum of the time required for the first holding, the time required for the first AD conversion, and the time required for the second holding.

10. A motor control method based on single resistor current sampling and holding, characterized in that: The following steps are involved: The control unit sends a PWM control signal to the driving unit in the current PWM cycle, controls the driving unit to switch to the initial state, the first state, the second state and the third state in sequence, and then switches from the third state to the initial state in sequence; In the process of controlling the drive unit, the control unit executes the current sampling method based on single resistor current sampling and holding as claimed in claim 8 or 9 to obtain the three-phase current value provided by the drive unit for the motor; The control unit adjusts the PWM control signal of the next PWM cycle according to the three-phase current value, thereby adjusting the operation of the motor.

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