A current sampling method and constant torque control method for a switched reluctance motor

Abstract

A current sampling method for a switched reluctance motor is characterized by comprising the following steps: 1. Setting a conducting phase; 2. Loading a PWM pulse signal, wherein the output of the PWM pulse signal in each cycle T is configured as a complementary output; 3. Determining the channel mode in which the PWM pulse signal is running at the current moment, if it is running in the main channel mode, proceed to step four; if it is running in the complementary channel mode, proceed to step five; 4. Current sampling is performed on the conducting phase corresponding to the main channel mode, and the return is made to step three; 5. Current sampling is performed on the conducting phase corresponding to the complementary channel mode, and the return is made to step three. The present invention also discloses a constant torque control method for a switched magnetic motor implemented by the above-mentioned current sampling method. The advantage of the present invention is that by loading a pulse signal on the conducting phase in the form of a PWM complementary output, different phase currents can be sampled within the same PWM cycle, thereby preventing overcurrent and improving the current sampling accuracy.

Description

Technical Field

[0001] The invention relates to current detection of a switched reluctance motor, in particular to a current sampling method of a switched reluctance motor and a constant torque control method using the current sampling method. Background Art

[0002] As a new type of speed regulation motor, the switched reluctance motor is a type of speed regulation motor developed after the DC motor and the brushless DC motor (BLDC). It has the advantages of large starting torque, wide speed regulation range and simple structure. It is widely used in household appliances, aviation, aerospace, electronics, machinery and electric vehicles.

[0003] In practical applications, in order to realize current control of the switched reluctance motor system, it is usually necessary to obtain the current information of each phase winding of the motor. Generally, a current sensor is placed on each winding for current sampling to obtain accurate sampling current. However, this will inevitably lead to an increase in system volume and system cost, which is not conducive to the large-scale use of motors.

[0004] In the prior art, for example, the Chinese invention patent No. 201910963322.9, "A multi-phase switched reluctance motor system and its control method", proposes a low-cost multi-phase switched reluctance motor system and its control method, such as Figure 1 As shown in the figure, the patent separates the negative DC bus of the multi-phase power converter, installs a DC bus current sensor on the separated negative DC bus, and collects the bus current at a specific sampling time point of each phase through the DC bus current sensor. Only one DC bus current sensor is used to obtain the winding current of each phase of the multi-phase switched reluctance motor, which greatly reduces the volume and cost of the system. However, the current acquisition in the above patent adopts the auxiliary pulse method for sampling, such as Figure 2 As shown, the falling edge of the reference auxiliary pulse in a phase current sampling cycle is used to obtain the sampling time point of each phase. According to the sampling time point of each phase, the multi-frequency auxiliary pulse signal is delayed to obtain the multi-frequency auxiliary pulse signal of each phase, so that only one of the auxiliary pulse signals is at a high level at each sampling point. This method of inserting auxiliary pulses, if the phase currents of the five phases A, B, C, D, and E need to be obtained at T1, T2, T3, T4, and T5 respectively, requires 5Tpwm times (Tpwm is the period of the PWM carrier), for example, if the PWM carrier frequency is 10KHZ, then Tpwm = 0.1ms, for a single phase A, it is necessary to obtain a current sample every 0.1ms*5 = 0.5ms, and the actual sampling frequency is only 2KHZ.

[0005] Therefore, when the motor is running at a low speed, the above patent cannot accurately sample each cycle because the phase current has a large variation range, which can easily cause the motor current to be too large, thereby causing overcurrent, and also cannot ensure the stable operation of the motor at a constant speed. Therefore, in view of the above problems, further improvements need to be made to the current sampling and constant torque control methods of the existing switched reluctance motor. Summary of the invention

[0006] The first technical problem to be solved by the present invention is to provide a current sampling method for a switched reluctance motor that can effectively prevent overcurrent and has higher detection accuracy in response to the above-mentioned existing technical status.

[0007] The second technical problem to be solved by the present invention is to provide a constant torque control method of a switched reluctance motor implemented by sampling the above-mentioned current sampling method in response to the above-mentioned existing technical status.

[0008] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: a current sampling method for a switched reluctance motor, characterized in that: the current sampling method comprises the following steps:

[0009] Step 1: Start the motor and set the conduction phase according to the motor rotor position;

[0010] Step 2: Load a PWM pulse signal onto the current conducting phase, set the duty cycle of the PWM pulse signal to D, and configure the output of the PWM pulse signal in each cycle T as a complementary output;

[0011] Step 3: determine the channel mode in which the PWM pulse signal is currently running. If it is running in the main channel mode, proceed to step 4; if it is running in the complementary channel mode, proceed to step 5;

[0012] Step 4: perform current sampling on the conduction phase corresponding to the main channel mode, and return to step 3;

[0013] Step 5: perform current sampling on the conduction phase corresponding to the complementary channel mode, and return to step 3.

[0014] As a preference, in order to quickly obtain the channel mode in which the PWM pulse signal operates, in the step 3, after the PWM pulse signal starts to load, the timing time t is started, and the timing time t=0 is set, and the on time T of the PWM pulse signal in each cycle T is set to d =D×T; then the channel mode of the PWM pulse signal at the current moment is determined by the following method:

[0015] Step 3-1: Determine whether the current time t is less than T dIf yes, the PWM pulse signal is running in the main channel mode at the current moment; if no, the PWM pulse signal is running in the complementary channel mode at the current moment. The high level and low level conduction time of the PWM pulse (and the complementary output of the PWM pulse) can be calculated according to the duty cycle, and then the channel mode in which the PWM pulse signal (and the complementary output of the PWM pulse) is running can be directly known.

[0016] As a further preference, the duty cycle D of the PWM pulse signal has a value range of: 0<D<100%.

[0017] As a further preference, the value range of the period T of the PWM pulse signal is: 62.5 μs≤T≤200 μs.

[0018] Preferably, the motor is a four-phase 8 / 6-pole switched reluctance motor, which is started by energizing two-phase windings in sequence.

[0019] Preferably, the PWM pulse signal includes two complementary pulse signals with the same duty cycle and frequency within one period T, and the channel mode in which the PWM pulse signal loaded to flip from a high level to a low level in each period is operated is set as the main channel mode, and the channel mode in which the PWM pulse signal loaded to flip from a low level to a high level in each period is operated is set as the complementary channel mode.

[0020] The technical solution adopted by the present invention to solve the above second technical problem is: a constant torque control method of a switched magnetic motor, characterized in that: starting the switched reluctance motor, the switched reluctance motor adopts the current sampling method as described above to sample the current of each phase winding, and the constant torque control method includes the following steps:

[0021] Step 1: Obtain the phase current value i of the currently conducting phase winding according to the current sampling method;

[0022] Step 2: Determine whether the phase current value i is greater than or equal to the preset current upper limit value i set If yes, proceed to step 3; if no, return to step 1;

[0023] Step 3: When the current exceeds the upper limit i set A dead zone is embedded in the channel mode of the PWM pulse signal corresponding to the on phase;

[0024] Step 4, determine the current channel mode of the PWM pulse signal operation, if the current channel mode is the complementary channel mode, then execute the next step 5; if the current channel mode is the main channel mode, then return to step 3;

[0025] Step 5: Determine whether the current cycle of the PWM pulse signal is over. If so, return to step 2; if not, return to step 3.

[0026] Preferably, the current channel mode of the PWM pulse signal operation in step 4 is determined by the following method: within a cycle, after the PWM pulse signal starts loading, the timing time t is started; the method for determining the current channel mode includes the following steps: step 41, determining whether the current time t is less than T d If yes, the current channel mode is the main channel mode; if no, the current channel mode is the complementary channel mode.

[0027] Preferably, the determination of whether the current cycle of the PWM pulse signal has ended in step 5 is achieved by the following method: within one cycle, after the PWM pulse signal starts to be loaded, the timing time t is started; the method for determining whether the current cycle has ended includes the following steps: step 51, determining whether the current time t is less than T, if so, the current cycle of the PWM pulse signal continues; if not, the current cycle of the PWM pulse signal ends.

[0028] Compared with the prior art, the advantages of the present invention are: by loading a pulse signal on the conducting phase in the form of PWM complementary output, different phase currents can be sampled within the same PWM cycle, eliminating the overcurrent problem existing in the conventional scheme, and avoiding the problem of excessive phase current variation range caused by sampling for each individual cycle, thereby greatly improving the current sampling accuracy of the motor; in addition, by adopting the current sampling method of the present application and setting the phase current upper limit, the problem of component damage caused by excessive phase current can also be avoided, the current hysteresis effect is good, and the purpose of constant torque control can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The schematic diagram of a circuit for detecting the current of each phase winding using a single current sensor in the prior art.

[0030] Figure 2 The figure is a pulse-sampling time diagram of current sampling using an auxiliary pulse method in the prior art.

[0031] Figure 3 Schematic diagram of an asymmetric half-bridge power converter circuit of a switched reluctance motor according to an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of PWM pulse signal loading using a complementary configuration for a switched reluctance motor according to an embodiment of the present invention.

[0033] Figure 5 for Figure 4 The circuit schematic for T1 time-A phase sampling is shown in FIG.

[0034] Figure 6 for Figure 4The circuit schematic diagram of T2 time-B phase sampling is shown in FIG.

[0035] Figure 7 4 is a waveform diagram of the starting phase current according to an embodiment of the present invention.

[0036] Figure 8 4 is a hysteresis circuit diagram of an embodiment of the present invention.

[0037] Fig. 9 Schematic diagram of PWM pulse signal loading of the switched reluctance motor after inserting the dead zone according to an embodiment of the present invention.

[0038] Fig.10 4 is a hysteresis waveform diagram of the starting phase current according to an embodiment of the present invention.

[0039] Fig.11 4 is a flow chart of a current sampling method according to an embodiment of the present invention.

[0040] Fig.12 This is a flow chart of a motor constant torque control method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below with reference to the accompanying drawings.

[0042] The present embodiment relates to a current sampling method for a switched reluctance motor, and a method for implementing a constant torque control method for a motor using the current sampling method.

[0043] The switched reluctance motor of this embodiment includes a DC bus capacitor C and an asymmetric half-bridge power converter. The current sampling method is based on the single resistor method in the prior art to implement current sampling of each phase winding, such as Figure 3 As shown, a DC bus current sensor (i.e., current sampling resistor) for collecting currents of each phase is provided on the negative DC bus, and each phase half-bridge conversion circuit includes an upper switch tube and a lower switch tube, and each phase lower diode and lower switch tube are respectively connected to two circuits; the number of the above-mentioned DC bus current sensor is one, one end of the DC bus current sensor is connected to the negative electrode of the DC bus capacitor C and the negative electrode of the DC power supply, and the other end is respectively connected to the emitter of the lower switch tube in each half-bridge conversion circuit. Therefore, the motor of this embodiment adopts a two-phase starting method, the upper bridge arm of the asymmetric half-bridge power converter is always open, and the two-phase lower bridge arm adopts a PWM complementary output method.

[0044] A DC bus current sensor (i.e., a current sampling resistor) can also be connected in series to the positive DC bus. One end of the DC bus current sensor is connected to the positive electrode of the DC bus capacitor C and the positive electrode of the DC power supply, and the other end is connected to the collector of the upper switch tube in each half-bridge conversion circuit. At this time, the motor adopts a two-phase starting method, the lower bridge arm is always open, and the two-phase upper bridge arm adopts a PWM complementary output method.

[0045] This embodiment uses Figure 3 The asymmetric half-bridge power converter circuit diagram shown is based on the upper bridge arm, which is always open, and the two-phase lower bridge arm adopts PWM complementary output mode, thereby realizing the current sampling and constant torque control of the motor. The specific current sampling method is as follows Fig.11 As shown, the following steps are included:

[0046] Step 1: Start the motor by energizing the two-phase windings in sequence, and set the conduction phase according to the motor rotor position.

[0047] Step 2: Load the PWM pulse signal on the current conducting phase. In this embodiment, the output of the PWM pulse signal in each period T is configured as a complementary output; the complementary output of the PWM pulse signal means that two pulse signals are output at the same time, and when one outputs a high level, the other outputs a low level at the corresponding moment, and the two pulse signals are in a complementary relationship;

[0048] The PWM pulse signal of this embodiment includes two complementary pulse signals with the same duty cycle and frequency in one cycle T, and the channel mode operated by the PWM pulse signal loaded with a flip from a high level to a low level in each cycle is set as the main channel mode, and the channel mode operated by the PWM pulse signal loaded with a flip from a low level to a high level in each cycle is set as the complementary channel mode;

[0049] Among them, the duty cycle of the PWM pulse signal is set to D, and the value range of the duty cycle D of the PWM pulse signal is: 0<D<100%, preferably, D takes 50% as the best value; the value range of the period T of the PWM pulse signal is set to: 62.5μs≤T≤200μs, preferably, T=100μs is the best value.

[0050] Step 3: Determine the channel mode in which the PWM pulse signal is running at the current moment. If it is running in the main channel mode, execute the next step 4; if it is running in the complementary channel mode, go to step 5; Determine the channel mode in which the PWM pulse signal is running at the current moment, that is, determine the channel mode corresponding to the high level of the two PWM pulse signals of the complementary output;

[0051] In step 3, after the PWM pulse signal starts loading, the timing time t is started, and the timing time t=0 is set. The on time T of the PWM pulse signal in each cycle T is d =D×T; then the channel mode of the PWM pulse signal at the current moment is determined by the following method:

[0052] Step 3-1: Determine whether the current time t is less than T dIf yes, the PWM pulse signal is running in the main channel mode at the current moment; if no, the PWM pulse signal is running in the complementary channel mode at the current moment.

[0053] Step 4: perform current sampling on the conduction phase corresponding to the main channel mode, and return to step 3.

[0054] Step 5: perform current sampling on the conduction phase corresponding to the complementary channel mode, and return to step 3.

[0055] like Figure 4 to Figure 7 As shown, the motor of this embodiment is a four-phase 8 / 6-level switched reluctance motor, which adopts a two-phase starting mode, and the power-on sequence of each phase is AB→BC→CD→DA; the following takes the AB two-phase as an example to analyze the AB phase starting waveform, and the PWM waves loaded by the AB two-phase are complementary outputs. Preferably, the best starting effect can be achieved when the duty cycle of the PWM wave is 50%;

[0056] When the energized phase is AB phase, the lower bridge arm adopts PWM complementary mode control, where the upper bridge arm adopts normally open mode, and the sampling method is continuous sampling, that is, after the current sampling is converted once, the next conversion is carried out continuously. The current mainstream sampling rate is 1M, that is, a sample is taken once in 1 microsecond.

[0057] like Figure 4 , Figure 5 As shown, in the T1 time period, the V1 switch and V2 switch corresponding to the A phase winding are both turned on (this is a negative voltage loop, that is, the power generation mode), the V3 switch corresponding to the B phase winding is turned on, and the V4 switch is turned off; therefore, the A phase current can be sampled: i = i A ;

[0058] like Figure 4 , Figure 6 As shown, in the T2 time period, the V1 switch corresponding to the A phase winding is turned on, the V2 switch is turned off, and the V3 switch and the V4 switch corresponding to the B phase winding are both turned on (this is a negative voltage loop, that is, a power generation mode); thus, the B phase current can be sampled: i=i B .

[0059] like Figure 7 As shown in FIG. 1 , it is a waveform diagram of the starting phase current of an embodiment of the present invention. Different from the conventional two-phase starting method, this embodiment uses complementary PWM waves to drive the AB two-phase bridge arm, so that the current sampling can collect the waveforms of the two-phase current under the same PWM cycle T. Therefore, the above-mentioned current sampling method of this embodiment can effectively avoid the problem of excessive phase current variation range in the prior art, prevent overcurrent, and improve the accuracy of current sampling.

[0060] like Fig.12As shown in FIG. 1 , it is a flow chart of realizing constant torque control of the switched reluctance motor of the present embodiment. After the switched reluctance motor is started, the current sampling method is adopted to sample the current of each phase winding. The constant torque control method includes the following steps:

[0061] Step 1: Obtain the phase current value i of the currently conducting phase winding according to the current sampling method.

[0062] Step 2: Determine whether the phase current value i is greater than or equal to the preset current upper limit value i set If yes, proceed to step 3; if no, return to step 1.

[0063] Step 3: When the current exceeds the upper limit i set The PWM pulse signal corresponding to the on-phase operates in a channel mode in which a dead zone is embedded.

[0064] Step 4, determine the channel mode that the PWM pulse signal corresponds to at the current moment. If the channel mode is the complementary channel mode, execute the next step 5; if the channel mode is the main channel mode, return to step 3; determine the channel mode that the PWM pulse signal is running at the current moment, that is, determine the channel mode corresponding to the two PWM pulse signals of the complementary output when the pulse signal is at a high level;

[0065] The current channel mode of the PWM pulse signal in step 4 is determined by the following method: within a cycle, after the PWM pulse signal starts loading, the timing time t is started; the current channel mode determination method includes the following steps: step 41, determining whether the current time t is less than T d If yes, the current channel mode is the main channel mode; if no, the current channel mode is the complementary channel mode.

[0066] Step 5, judging whether the current cycle of the PWM pulse signal has ended, if so, returning to step 2; if not, returning to step 3. The judgment of whether the current cycle of the PWM pulse signal has ended in step 5 is realized by the following method: within a cycle, after the PWM pulse signal starts to load, the timing time t is started; the judgment method of whether the current cycle has ended includes the following steps: Step 51, judging whether the current time t is less than T, if so, the current cycle of the PWM pulse signal continues; if not, the current cycle of the PWM pulse signal ends.

[0067] Generally, the terminals of high-power motors and inverters are all H-bridges or three-phase bridges composed of high-power tubes, IGBTs and other components. The upper and lower half bridges of each bridge must not be turned on at the same time, but when the high-speed PWM drive signal reaches the control pole of the power component, it often produces a delay effect due to various reasons, causing a half-bridge component to not turn off when it should be turned off, thereby causing the power component to burn out.

[0068] Inserting / embedding dead zone means that after the upper half bridge is turned off, there is a delay before opening the lower half bridge, or after the lower half bridge is turned off, there is a delay before opening the upper half bridge, so as to avoid burning of power components. Usually, this delay time (that is, the components of the upper and lower half bridges are turned off) is the dead zone.

[0069] like Figure 8 to Figure 10 As shown, the torque T of the switched reluctance motor is known. e The formula is: That is, the motor current determines the size of the motor torque. When the motor output torque is determined, the motor phase current is also determined; if the phase current upper limit is set to i set By inserting / embedding the dead zone, phase current hysteresis can be achieved to prevent power components from being damaged due to excessive phase current.

[0070] The following still takes the AB two-phase as an example to analyze the AB phase hysteresis loop waveform. When the energized phase is the AB phase, the lower bridge arm adopts the PWM complementary mode control, and the duty cycle of the PWM wave is 50%. Among them, the upper bridge arm adopts the normally open mode, and the sampling method is continuous sampling, that is, after the current sampling is converted once, the next conversion is carried out continuously. The current mainstream sampling rate is 1M, that is, a sample is taken once in 1 microsecond.

[0071] like Figure 4 , Figure 5 As shown, in the T1 time period, the V1 switch and V2 switch corresponding to the A phase winding are both turned on (this is a negative voltage loop, that is, the power generation mode), the V3 switch corresponding to the B phase winding is turned on, and the V4 switch is turned off; therefore, the A phase current can be sampled: i = i A ;

[0072] like Figure 8 , Fig. 9 As shown, during the dead time, the V1 switch corresponding to the A-phase winding is turned on and the V2 switch is turned off, and the V3 switch corresponding to the B-phase winding is turned on and the V4 switch is turned off. At this time, the A-phase or B-phase current cannot be collected, and the phase current i=0. At this time, both AB phases are in the freewheeling state, and there is no risk of overcurrent.

[0073] like Figure 4 , Figure 6As shown, in the T2 time period, the V1 switch corresponding to the A phase winding is turned on, the V2 switch is turned off, and the V3 switch and the V4 switch corresponding to the B phase winding are both turned on (this is a negative voltage loop, that is, a power generation mode); thus, the B phase current can be sampled: i=i B .

[0074] The switched reluctance motor of this embodiment adopts a two-phase starting method. By setting a current sampling resistor (current sampling sensor) in the asymmetric half-bridge power conversion circuit, a single-resistance current acquisition solution with a simpler structure and lower cost is realized. At the same time, the upper bridge arm is normally open and the two-phase lower bridge arms adopt PWM complementary output, so that the current sampling can collect the waveform of the two-phase current in the same PWM period T, effectively preventing overcurrent and improving the current detection accuracy.

[0075] The motor of this embodiment can also use the above-mentioned current sampling circuit to set the current upper limit value i set Finally, the current hysteresis loop of the motor can be realized to achieve constant torque control of the switched reluctance motor and ensure the stability and safety of the motor operation.

Claims

1. A current sampling method for a switched reluctance motor, characterized in that: The current sampling method includes the following steps: Step 1: Start the motor and set the conduction phase according to the motor rotor position; Step 2: Load a PWM pulse signal onto the current conducting phase, set the duty cycle of the PWM pulse signal to D, and configure the output of the PWM pulse signal in each cycle T as a complementary output; Step 3: determine the channel mode in which the PWM pulse signal is running at the current moment. If it is running in the main channel mode, proceed to the next step 4; if it is running in the complementary channel mode, go to step 5; Step 4: perform current sampling on the conduction phase corresponding to the main channel mode, and return to step 3; Step 5: perform current sampling on the conduction phase corresponding to the complementary channel mode, and return to step 3; In the step 3, after the PWM pulse signal starts to load, the timing time t is started, and the timing time t=0 is set. The on time T of the PWM pulse signal in each cycle T is d =D×T; then the channel mode of the PWM pulse signal at the current moment is determined by the following method: Step 3-1: Determine whether the current time t is less than T d If yes, the PWM pulse signal at the current moment is running in the main channel mode; if no, the PWM pulse signal at the current moment is running in the complementary channel mode; The PWM pulse signal includes two complementary pulse signals with the same duty cycle and frequency within one cycle T. The channel mode in which the PWM pulse signal loaded with a flip from a high level to a low level operates in each cycle is set as the main channel mode, and the channel mode in which the PWM pulse signal loaded with a flip from a low level to a high level operates in each cycle is set as the complementary channel mode.

2. The current sampling method of the switched reluctance motor according to claim 1, characterized in that: The duty cycle D of the PWM pulse signal has a value range of 0<D<100%.

3. The current sampling method of the switched reluctance motor according to claim 1, characterized in that: The value range of the period T of the PWM pulse signal is: 62.5 μs≤T≤200 μs.

4. The current sampling method of the switched reluctance motor according to claim 1, characterized in that: The motor is started by energizing the two-phase windings in sequence.

5. A constant torque control method for a switched magnetic motor, characterized in that: The switched reluctance motor is started. The switched reluctance motor samples the current of each phase winding by using the current sampling method as claimed in any one of claims 1 to 4. The constant torque control method comprises the following steps: Step 1: Obtain the phase current value i of the currently conducting phase winding according to the current sampling method; Step 2: Determine whether the phase current value i is greater than or equal to the preset current upper limit value i set If yes, proceed to step 3; If not, return to step 1; Step 3: When the current exceeds the upper limit i set A dead zone is embedded in the channel mode of the PWM pulse signal corresponding to the on phase; Step 4, determine the current channel mode of the PWM pulse signal operation, if the current channel mode is the complementary channel mode, then execute the next step 5; if the current channel mode is the main channel mode, then return to step 3; Step 5: Determine whether the current cycle of the PWM pulse signal is over. If so, return to step 2; if not, return to step 3.

6. The constant torque control method of the switched magnetic motor according to claim 5, characterized in that: The current channel mode of the PWM pulse signal operation in step 4 is determined by the following method: within a cycle, after the PWM pulse signal starts loading, the timing time t is started; the method for determining the current channel mode includes the following steps: Step 41: Determine whether the current time t is less than T d If yes, the current channel mode is the main channel mode; if no, the current channel mode is the complementary channel mode.

7. The constant torque control method of the switched magnetic motor according to claim 5, characterized in that: In step 5, judging whether the current cycle of the PWM pulse signal has ended is achieved by the following method: within a cycle, after the PWM pulse signal starts loading, the timing time t is started; the method for judging whether the current cycle has ended includes the following steps: Step 51, determine whether the current time t is less than T, if so, the current cycle of the PWM pulse signal continues; if not, the current cycle of the PWM pulse signal ends.

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