FOUR-PHASE SWITCHED RELUCTANCE MOTOR TORQUE RIPPLE TWO-LEVEL SUPPRESSION METHOD

Abstract

A four-phase switched reluctance motor torque ripple two-level suppression method. A first set of torque thresholds is set in rotor position interval [0°, θr/4]. A second set of torque thresholds is set in rotor position interval [θr/4, θr/2]. Power is supplied to adjacent phase A and phase B for excitation. The power supplied for excitation to phase A leads the power supplied for excitation to phase B by θr/4. An entire commutation process from phase A to phase B is divided into two intervals. In rotor position interval [0°, θ1], phase A uses the second set of torque thresholds while phase B uses the first set of torque thresholds. Critical position θ1 automatically appears in the commutation process, thus obviating the need for additional calculations. Total torque is controlled between [Te+th2low and Te+th2up]. In rotor position interval [θ1, θr/4], phase A continues to use the second set of torque thresholds, phase B continues to use the first set of torque thresholds, and the total torque is controlled between [Te+th1low and Te+th1up]. This suppresses torque ripples of a four-phase switched reluctance motor and provides great engineering application values.

Claims

1. A method for torque pulsation two-level suppression of four-phase switch reluctance motor, characterized in that, it comprises the following steps: a. setting a first group of torque thresholds (th1.sub.low, th1.sub.up) in a rotor position interval [0°, θ.sub.r/4], and setting a second group of torque thresholds (th2.sub.low, th2.sub.up) in a rotor position interval [θ.sub.r/4, θ.sub.r/2], wherein, these four torque thresholds meet the following requirements:
th1.sub.up>th2.sub.up>0  (1)
th2.sub.low<th1.sub.low<0  (2)
|th1.sub.up|=|th2.sub.low|  (3)
|th2.sub.up|=|th1.sub.low|  (4) wherein, the rotor position 0° is the minimum phase inductance position, the rotor position θ.sub.r is the pitch angle, i.e., one rotor cycle, and half rotor cycle is θ.sub.r/2; b. setting the power supply excitation state of phase A as excitation state S.sub.A, wherein, excitation state S.sub.A=1 indicates the power supply excitation voltage of phase A is positive, and excitation state S.sub.A=−1 indicates the power supply excitation voltage of phase A is negative; setting the power supply excitation state of phase B as excitation state S.sub.B, wherein, excitation state S.sub.B=1 indicates the power supply excitation voltage of phase B is positive, and excitation state S.sub.B=−1 indicates the power supply excitation voltage of phase B is negative; setting the expected total smooth torque as T.sub.e; c. supplying power supply excitation to the adjacent phase A and phase B, wherein, the power supply excitation of phase A is ahead of the power supply excitation of phase B by θ.sub.r/4; at this moment, phase A is turned off, while phase B is turned on; thus, by commutation process of dividing into two intervals from phase A to phase B, torque pulsation two-level suppression of the four-phase switch reluctance motor is realized.

2. The method for torque pulsation two-level suppression for four-phase switch reluctance motor according to claim 1, wherein, the commutation process of dividing into two intervals from phase A to phase B is as follows: (1) in the rotor position interval [0°, θ.sub.1], the second group of torque thresholds (th2.sub.low, th2.sub.up) is used for phase A, the first group of torque thresholds (th1.sub.low, th1.sub.up) is used for phase B, and the critical position θ.sub.1 appears automatically in the commutation process without the need for any additional calculation; (1.1) entering into phase B breakover period at the position of rotor position 0°, the initial excitation state is set to S.sub.B=1, and the current and the torque of phase B begin to increase from 0; the excitation state S.sub.A remains in the original state S.sub.A=−1, and the current and the torque of phase A decrease. Since the inductance change rate and the current of phase B are lower at this position, the torque increasing rate of phase B is lower than the torque decreasing rate of phase A, and the total torque decreases along with phase A; (1.2) when the total torque reaches a torque value T.sub.e+th1.sub.low firstly, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues decreasing; (1.3) when the total torque decreases to a torque value T.sub.e+th2.sub.low, the state transition criteria for phase A are met; thus, the excitation state S.sub.A switches from −1 to 1, and the torque of phase A increases; phase B remains in the original state, and the torque of phase B continues increasing; consequently, the total torque increases; (1.4) when the total torque increases to a torque value T.sub.e+th1.sub.low, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues increasing; (1.5) when the total torque increases to a torque value T.sub.e+th2.sub.up, the state transition criteria for phase A are met; thus, the excitation state S.sub.A switches from 1 to −1, and the torque of phase A decreases; since the state transition criteria for phase B are not met, the excitation state S.sub.B remains in the original state, and the total torque begins to decrease; (1.6) the steps (1.2)˜(1.5) are repeated, and the excitation state S.sub.B always remains in the state of 1, i.e., phase B is excited by positive voltage, and the current and the torque of phase B increase at maximum rates; the excitation state S.sub.A switches between −1 and 1, and the total torque is controlled within a range of [T.sub.e+th2.sub.low, T.sub.e+th2.sub.up]; thus, the pulsation of the four-phase switch reluctance motor in the rotor position interval [0°, θ.sub.1] is inhibited; (2) in a rotor position interval [θ.sub.1, θ.sub.r/4], the second group of torque thresholds (th2.sub.low, th2.sub.up) is still used for phase A, and the first group of torque thresholds (th1.sub.low, th1.sub.up) is still used for phase B; (2.1) at rotor position θ.sub.1, the inductance change rate and the phase current of phase B have reached to a certain level; when the excitation state S.sub.B=1 and the excitation state S.sub.A=−1, the torque increase rate of phase B is not lower than the torque decrease rate of phase A anymore, the total torque change trend is determined by phase B, and the total torque increases; (2.2) when the total torque increases to a torque value T.sub.e+th1.sub.up, the state transition criteria for phase B are met; thus, the excitation state S.sub.B switches from 1 to −1, and the torque of phase B decreases; the excitation state S.sub.A remains in the state of −1, and the total torque decreases; (2.3) when the total torque decreases to a torque value T.sub.e+th2.sub.up firstly, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues decreasing; (2.4) when the total torque decreases to a torque value T.sub.e+th1.sub.low, the state transition criteria for phase B are met; thus, the excitation state S.sub.B switches from −1 to 1, and the torque of phase B increases; the excitation state S.sub.A remains in the state of −1; the total torque increases as the torque of phase B increases; (2.5) when the total torque increases to a torque value T.sub.e+th2.sub.up, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues increasing; (2.6) when the total torque increases to a torque value T.sub.e+th1.sub.up, the steps (2.2)˜(2.5) are repeated, the excitation state S.sub.A remains in the state of −1, the excitation state S.sub.B switches between −1 and 1, and the total torque is controlled within a range of [T.sub.e+th1.sub.low, T.sub.e+th1.sub.up]; thus, the pulsation of the four-phase switch reluctance motor in the rotor position interval [θ.sub.1, θ.sub.r/4] is inhibited.

Description

DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic diagram of the setting of two-level torque thresholds of a switch reluctance motor in the present invention;

[0026] FIG. 2(a) is a schematic diagram of power supply excitation state transition of phase B in the present invention;

[0027] FIG. 2(b) is a schematic diagram of power supply excitation state transition of phase A in the present invention;

[0028] FIG. 3 shows the torque waveform of a switch reluctance motor in the present invention.

EMBODIMENTS

[0029] Hereunder the present invention will be further described with the examples shown in the accompanying drawings:

[0030] As shown in FIG. 1, for a four-phase switch reluctance motor, the steps of the method are as follows: [0031] a. setting a first group of torque thresholds (th1.sub.low, th1.sub.up) in a rotor position interval [0°, θ.sub.r/4], and setting a second group of torque thresholds (th2.sub.low, th2.sub.up) in a rotor position interval [θ.sub.r/4, θ.sub.r/2], wherein, these four torque thresholds meet the following requirements:

th1.sub.up>th2.sub.up>0  (1)

th2.sub.low<th1.sub.low<0  (2)

|th1.sub.up|=|th2.sub.low|  (3)

|th2.sub.up|=|th1.sub.low|  (4) [0032] wherein, the rotor position 0° is the minimum phase inductance position, the rotor position θ.sub.r is the pitch angle, i.e., one rotor cycle, and half rotor cycle is θ.sub.r/2; [0033] b. as shown in FIG. 2, setting the power supply excitation state of phase A as excitation state S.sub.A, wherein, excitation state S.sub.A=1 indicates the power supply excitation voltage of phase A is positive, and excitation state S.sub.A=−1 indicates the power supply excitation voltage of phase A is negative; setting the power supply excitation state of phase B as excitation state S.sub.B, wherein, excitation state S.sub.B=1 indicates the power supply excitation voltage of phase B is positive, and excitation state S.sub.B=−1 indicates the power supply excitation voltage of phase B is negative; setting the expected total smooth torque as T.sub.e; [0034] c. supplying power supply excitation to the adjacent phase A and phase B, wherein, the power supply excitation of phase A is ahead of the power supply excitation of phase B by θ.sub.r/4; at this moment, phase A is turned off, while phase B is turned on; as shown in FIG. 1, the commutation process of dividing into two intervals from phase A to phase B is as follows: [0035] (1) in the rotor position interval [0°, θ.sub.1], the second group of torque thresholds (th2.sub.low, th2.sub.up) is used for phase A, the first group of torque thresholds (th1.sub.low, th1.sub.up) is used for phase B, and the critical position θ.sub.1 appears automatically in the commutation process without the need for any additional calculation; [0036] (1.1) entering into phase B breakover period at the position of rotor position 0°, the initial excitation state is set to S.sub.B=1, and the current and the torque of phase B begin to increase from 0; the excitation state S.sub.A remains in the original state S.sub.A=−1, and the current and the torque of phase A decrease. Since the inductance change rate and the current of phase B are lower at this position, the torque increasing rate of phase B is lower than the torque decreasing rate of phase A, and the total torque decreases along with phase A; [0037] (1.2) when the total torque reaches a torque value T.sub.e+th1.sub.low firstly, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues decreasing; [0038] (1.3) when the total torque decreases to a torque value T.sub.e+th2.sub.low, the state transition criteria for phase A are met; thus, the excitation state S.sub.A switches from −1 to 1, and the torque of phase A increases; phase B remains in the original state, and the torque of phase B continues increasing; consequently, the total torque increases; [0039] (1.4) when the total torque increases to a torque value T.sub.e+th1.sub.low, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues increasing; [0040] (1.5) when the total torque increases to a torque value T.sub.e+th2.sub.up, the state transition criteria for phase A are met; thus, the excitation state S.sub.A switches from 1 to −1, and the torque of phase A decreases; since the state transition criteria for phase B are not met, the excitation state S.sub.B remains in the original state, and the total torque begins to decrease; [0041] (1.6) the steps (1.2)˜(1.5) are repeated, and the excitation state S.sub.B always remains in the state of 1, i.e., phase B is excited by positive voltage, and the current and the torque of phase B increase at maximum rates; the excitation state S.sub.A switches between −1 and 1, and the total torque is controlled within a range of [T.sub.e+th2.sub.low, T.sub.e+th2.sub.up]; thus, the pulsation of the four-phase switch reluctance motor in the rotor position interval [0°, θ.sub.1] is inhibited; [0042] (2) in a rotor position interval [θ.sub.1, θ.sub.r/4], the second group of torque thresholds (th2.sub.low, th2.sub.up) is still used for phase A, and the first group of torque thresholds (th1.sub.low, th1.sub.up) is still used for phase B; [0043] (2.1) at rotor position θ.sub.1, the inductance change rate and the phase current of phase B have reached to a certain level; when the excitation state S.sub.B=1 and the excitation state S.sub.A=−1, the torque increase rate of phase B is not lower than the torque decrease rate of phase A anymore, the total torque change trend is determined by phase B, and the total torque increases; [0044] (2.2) when the total torque increases to a torque value T.sub.e+th1.sub.up, the state transition criteria for phase B are met; thus, the excitation state S.sub.B switches from 1 to −1, and the torque of phase B decreases; the excitation state S.sub.A remains in the state of −1, and the total torque decreases; [0045] (2.3) when the total torque decreases to a torque value T.sub.e+th2.sub.up firstly, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues decreasing; [0046] (2.4) when the total torque decreases to a torque value T.sub.e+th1.sub.low, the state transition criteria for phase B are met; thus, the excitation state S.sub.B switches from −1 to 1, and the torque of phase B increases; the excitation state S.sub.A remains in the state of −1; the total torque increases as the torque of phase B increases; [0047] (2.5) when the total torque increases to a torque value T.sub.e+th2.sub.up, the state transition criteria for phase A and phase B are not met, the excitation states S.sub.A and S.sub.B remain in the original states, and the total torque continues increasing; [0048] (2.6) when the total torque increases to a torque value T.sub.e+th1.sub.up, the steps (2.2)˜(2.5) are repeated, the excitation state S.sub.A remains in the state of −1, the excitation state S.sub.B switches between −1 and 1, and the total torque is controlled within a range of [T.sub.e+th1.sub.low, T.sub.e+th1.sub.up]; thus, the pulsation of the four-phase switch reluctance motor in the rotor position interval [θ.sub.1, θ.sub.r/4] is inhibited.

[0049] Power supply excitation is supplied to the adjacent phase B and phase C, when the power supply excitation of phase B is ahead of the power supply excitation of phase C by θ.sub.r/4, the torque threshold setting, commutation process and excitation state switch and transfer method of phase B and phase C are similar to those in the case described above.

[0050] Power supply excitation is supplied to the adjacent phase C and phase D, when the power supply excitation of phase C is ahead of the power supply excitation of phase D by θ.sub.r/4, the torque threshold setting, commutation process and excitation state switch and transfer method of phase C and phase D are similar to those in the case described above.

[0051] Power supply excitation is supplied to the adjacent phase D and phase A, when the power supply excitation of phase D is ahead of the power supply excitation of phase A by θ.sub.r/4, the torque threshold setting, commutation process and excitation state switch and transfer method of phase D and phase A are similar to those in the case described above.

[0052] The obtained torque waveform of the switch reluctance motor is shown in FIG. 3.