JP2010115052A - Phase current estimating device for motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the estimation accuracy of a phase current. <P>SOLUTION: This phase current estimating device 10 for a motor includes a phase current estimating section 23 estimating a phase current based on the DC-side current of an inverter 13 detected by a DC-side current sensor 31. The phase current estimating section 23 estimates a current value at each point in the phase current at timing symmetric relative to a carrier peak point in each voltage pattern symmetric relative to the carrier peak point at a maximum value or a minimum value in one cycle of a carrier signal, and includes a carrier peak point current value calculating section 23a calculating, as the current value of the phase current at the carrier peak point, an average value in terms of current values at the timing of two points each of which is one point estimated by the phase current estimating section 23, and a phase current calculating section 23c calculating the current value of the phase current at the carrier peak point and the current value of the phase current at optional timing in one cycle of the carrier signal based on a discretization formula obtained by discretizing the current equation of the motor 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a phase current estimation device for an electric motor.

Conventionally, for example, when converting a direct current output from a single direct current sensor into a three-phase alternating current, two different states of each carrier period are generated in the process of changing six different gate states by three pairs of transistors. A current detection method is known in which two current values of different phases are detected in each section, and the sum of three-phase currents is always equal to zero, and current values of other phases are calculated from these two current values. (For example, refer to Patent Document 1).
Japanese Patent No. 2563226

By the way, in the current detection method according to the above-described prior art, the detection timings of the phase current values for two phases detected by a single DC current sensor are not the same. When the assumption that the sum of the three-phase currents is equal to zero is applied to the value, an error in the current value of the estimated other one-phase phase current increases.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a phase current estimation device for an electric motor capable of improving the estimation accuracy of a phase current.

  In order to solve the above-described problems and achieve the object, a phase current estimation apparatus for an electric motor according to a first aspect of the present invention uses a three-phase AC electric motor (for example, the motor 11 in the embodiment) by a pulse width modulation signal. ), Which sequentially commutates energization to the current (), for example, the inverter 13 in the embodiment, and pulse width modulation signal generation means (for example, the PWM signal in the embodiment) that generates the pulse width modulation signal from a carrier wave signal. Generator 25), a DC-side current sensor (for example, DC-side current sensor 31 in the embodiment) that detects a DC-side current of the inverter, and the DC-side current detected by the DC-side current sensor. Phase current estimating means (for example, the phase current estimating unit 23 in the embodiment) for estimating the phase current, and the phase current estimating means has a maximum value in one cycle of the carrier wave signal. Is estimating the current value of each point of the phase current at a timing symmetric with respect to the carrier apex in each of the voltage patterns symmetric with respect to the minimum carrier apex. Carrier vertex current value calculating means (for example, in the embodiment) calculates an average value based on the current value at the timing of two points including the estimated one point as a current value of the phase current at the carrier vertex. A carrier peak current value calculation unit 23a), a current value of the phase current at the carrier peak calculated by the carrier peak current value calculation means, and a discretization formula obtained by discretizing a current equation of the motor, Based on the phase current calculation means for calculating the current value of the phase current at an arbitrary timing in one cycle of the carrier wave signal (for example, the phase current calculation unit 2 in the embodiment) Equipped with a c) and.

  Furthermore, in the phase current estimation device for the electric motor according to the second aspect of the present invention, the carrier peak current value calculating means is configured to calculate the carrier peak current value at the carrier peak for every two phase currents of the three phase currents. Calculating the current value of the phase current, and based on the current value at the carrier apex for each of the phase currents of the two phases calculated by the carrier apex current value calculating means, Among these, the current value calculation means (for example, the current value calculation unit 23b in the embodiment) for calculating the current value at the carrier apex of the other phase current is provided, and the phase current calculation means includes the three-phase A current value for each phase current of the three phases at the arbitrary timing is calculated from the current value at the carrier apex for each phase current and the discretization formula.

  Further, in the motor phase current estimation device according to the third aspect of the present invention, the phase current calculation means calculates the current value of the phase current at the completion of one cycle of the carrier wave signal as the arbitrary timing. To do.

According to the phase current estimation apparatus for an electric motor according to the first aspect of the present invention, estimation is performed at a timing symmetric with respect to the carrier vertex in each of the voltage patterns symmetric with respect to the carrier vertex in one cycle of the carrier wave signal. The average value of the phase currents is defined as the current value of the phase current at the carrier apex. Thereby, the error resulting from noise can be reduced, and the current value at the same timing can be accurately estimated for each phase current of the three phases.
Based on the current value of the phase current at the carrier apex and the discretization formula obtained by discretizing the current equation of the motor, the current value of the phase current at an arbitrary timing in one cycle of the carrier wave signal is accurate. It can be calculated well.

Furthermore, according to the phase current estimation device for an electric motor according to the second aspect of the present invention, the current value of the other one-phase phase current at the carrier apex based on the current value for each of the two-phase phase currents at the carrier apex. Can be calculated with high accuracy.
Furthermore, according to the phase current estimating apparatus for an electric motor according to the third aspect of the present invention, the estimated value is obtained by estimating the current value of the phase current at the completion of one cycle of the carrier wave signal as an arbitrary timing. It can be used for motor control in the next one cycle, and the latest phase current information can be applied to the motor control performed in synchronization with the top of a carrier wave signal such as a triangular wave without time delay.

DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of an electric motor phase current estimating apparatus according to the present invention will be described with reference to the accompanying drawings.
An electric motor phase current estimation device 10 (hereinafter simply referred to as a phase current estimation device 10) according to this embodiment estimates a phase current of, for example, a three-phase AC brushless DC motor 11 (hereinafter simply referred to as a motor 11). The motor 11 includes a rotor (not shown) having a permanent magnet used for a field and a stator (not shown) that generates a rotating magnetic field for rotating the rotor. Has been.
And the phase current estimation apparatus 10 is provided with the inverter 13 which uses the battery 12 as DC power supply, and the motor control apparatus 14, for example, as shown in FIG.

The three-phase (for example, U-phase, V-phase, and W-phase) AC motor 11 is driven by the inverter 13 in response to a control command output from the motor control device 14.
The inverter 13 includes a bridge circuit 13a formed by bridge connection using a plurality of switching elements (for example, MOSFETs: Metal Oxide Semi-conductor Field Effect Transistors) and a smoothing capacitor C, and the bridge circuit 13a performs pulse width modulation ( It is driven by the PWM signal.

  In this bridge circuit 13a, for example, a high-side and low-side U-phase transistor UH, UL paired for each phase, a high-side and low-side V-phase transistor VH, VL, a high-side and low-side W-phase transistor WH, WL is bridge-connected. Each transistor UH, VH, WH has a drain connected to the positive terminal of the battery 12 to form a high side arm, and each transistor UL, VL, WL has a source connected to the grounded negative terminal of the battery 12. It constitutes the low side arm. For each phase, the sources of the high-side arm transistors UH, VH, WH are connected to the drains of the low-side arm transistors UL, VL, WL, and the transistors UH, UL, VH, VL, WH, WL. Each of the diodes DUH, DUL, DVH, DVL, DWH, DWL is connected between the drain and the source so as to be in the forward direction from the source to the drain.

  The inverter 13 is, for example, a gate signal (that is, a PWM signal) that is a switching command that is output from the motor control device 14 when driving the motor 11 and is input to the gates of the transistors UH, VH, WH, UL, VL, WL. ), The DC power supplied from the battery 12 is converted into the three-phase AC power by switching the on / off (cut-off) state of each pair of transistors for each phase. By sequentially commutating energization to the windings, AC U-phase current Iu, V-phase current Iv and W-phase current Iw are passed through the stator windings of each phase.

  The motor control device 14 performs current feedback control (vector control) on the dq coordinates forming the rotation orthogonal coordinates, calculates the target d-axis current Idc and the target q-axis current Iqc, and calculates the target d-axis current Idc and Each phase voltage command Vu, Vv, Vw is calculated based on the target q-axis current Iqc, and a PWM signal that is a gate signal for the inverter 13 is output according to each phase voltage command Vu, Vv, Vw. The d-axis current Ids and q-axis current Iqs obtained by converting the phase currents Iu, Iv, and Iw supplied from the motor 13 to the motor 11 on the dq coordinate, and the target d-axis current Idc and the target q-axis current Iqc. Control is performed so that each deviation becomes zero.

The motor control device 14 includes, for example, a current sensor I / F (interface) 21, an overcurrent protection device 22, a phase current estimation unit 23, a control device 24, and a PWM signal generation unit 25. .
The current sensor I / F (interface) 21 is connected to a DC side current sensor 31 that detects a DC side current Idc of the bridge circuit 13a of the inverter 13 between the bridge circuit 13a of the inverter 13 and the negative terminal of the battery 12. Then, the detection signal output from the DC side current sensor 31 is output to the overcurrent protection device 22 and the phase current estimation unit 23.
The direct current sensor 31 may be disposed between the bridge circuit 13a of the inverter 13 and the positive terminal of the battery 12.
Further, it is output from the angle sensor 32 that detects the rotation angle of the rotor of the motor 11 (that is, the rotation angle of the rotor magnetic pole from the predetermined reference rotation position and the rotation position of the rotation shaft of the motor 11). The detection signal is input to the control device 24.
Note that the angle sensor 32 may be omitted, and a device for estimating the magnetic pole position of the rotor may be provided instead.

The overcurrent protection device 22 performs a predetermined overcurrent protection operation according to the DC side current Idc detected by the DC side current sensor 31.
The phase current estimation unit 23 actually uses the inverter 13 based on the DC side current Idc detected by the DC side current sensor 31 at the detection timing according to the gate signal (that is, PWM signal) output from the PWM signal generation unit 25. The phase currents Iu, Iv, and Iw supplied to the motor 11 are estimated. Details of the operation of the phase current estimation unit 23 will be described later.

  The control device 24 converts the phase currents Iu, Iv, Iw output from the phase current estimation unit 23 into dq coordinates according to the rotation angle of the motor 11 output from the angle sensor 32, and the d-axis obtained. Current feedback control (vector control) is performed so that each deviation between the current Ids and the q-axis current Iqs and the target d-axis current Idc and the target q-axis current Iqc becomes zero, and each phase voltage command Vu, Vv, Vw Is output.

  The PWM signal generation unit 25 compares each phase voltage command Vu, Vv, Vw with a carrier signal such as a triangular wave in order to pass a sinusoidal current to the three-phase stator winding, and A gate signal (that is, a PWM signal) for driving the transistors UH, VH, WH, UL, VL, WL on / off is generated. Then, the inverter 13 converts the DC power supplied from the battery 12 into three-phase AC power by switching the on (conductive) / off (cut-off) state of each transistor that forms a pair for each of the three phases. By sequentially commutating energization to each stator winding of the three-phase motor 11, AC U-phase current Iu, V-phase current Iv, and W-phase current Iw are energized to each stator winding.

The gate signal input from the PWM signal generation unit 25 to the inverter 13 is, for example, according to the combination of the on / off states of the transistors UH, UL and VH, VL and WH, WL that are paired for each phase. 1 and FIGS. 2A to 2H, the PWM (pulse width) corresponding to each of the eight switching states S1 to S8 (that is, the states of the basic voltage vectors V0 to V7 having different phases by 60 degrees). Modulation) signal. In Table 1 below, the transistors that are turned on among the high-side (High) and low-side (Low) transistors are shown, and the transistors that are turned on in FIGS. Is shaded.
Then, phase currents Iu, Iv, Iw are intermittently generated on the DC side of the bridge circuit 13a of the inverter 13 according to the switching states S1 to S8, and the DC side current Idc detected by the DC side current sensor 31. Is one of the phase currents Iu, Iv, Iw, or one of the phase currents Iu, Iv, Iw inverted, or zero.

The phase current estimation unit 23 includes, for example, a carrier apex current value calculation unit 23a, a current value calculation unit 23b, and a phase current calculation unit 23c.
The phase current estimation unit 23 is symmetric with respect to the carrier peak of the maximum value or the minimum value of the carrier signal (for example, the peak on the peak side or the peak on the valley side in the triangular wave) in one period of the carrier signal such as a triangular wave. In each of the voltage patterns, for each of the two phase currents out of the three phase currents, the current value at one point of the phase current at a timing symmetrical with respect to the carrier apex, and the DC side current at this timing. It is estimated from the DC side current Idc detected by the sensor 31.

  Then, the carrier apex current value calculation unit 23a calculates the average value of the phase currents at the timing of two points each consisting of one point for each phase current of the two phases, and the current of the phase current at the carrier apex. Calculate as a value.

For example, as shown in FIG. 3, in the case of three-phase modulation using a triangular carrier signal, the carrier signal with a voltage pattern symmetrical to the peak (carrier vertex) on the valley side of the triangular carrier signal is obtained. In the period of one cycle Ts, the detected value of each phase current for two phases can be acquired twice.
In other words, the phase current estimation unit 23 is symmetric with respect to the carrier vertex at times tu1 and tu2 (that is, at the time tp of the carrier vertex on the valley side) in the state of the two basic voltage vectors V1 symmetrical with respect to the carrier vertex. On the other hand, the first U-phase current Iu1 and the second U-phase current Iu2 are obtained from the DC-side current Idc detected by the DC-side current sensor 31 at the time having the same time interval T1, and further, with respect to the carrier vertex In the state of two symmetrical basic voltage vectors V3, direct current is generated at times tw1 and tw2 that are symmetrical with respect to the carrier apex (that is, the time having the same time interval T2 with respect to the time tp of the carrier apex on the valley side). The first W-phase current Iw1 and the second W-phase current Iw2 are acquired from the DC-side current Idc detected by the side current sensor 31.

  Then, the carrier peak current value calculation unit 23a of the phase current estimation unit 23 calculates an average value for each phase based on the phase currents Iu1, Iu2 and Iw1, Iw2, and calculates each average value at the carrier peak on the valley side. The current value at time tp is used.

  Then, the current value calculation unit 23b outputs a current value (for example, shown in FIG. 3) at the carrier peak for each of the two-phase phase currents (for example, the U-phase current and the W-phase current) output from the carrier peak current value calculation unit 23a. Current value of the carrier peak on the trough side at the time tp), the current value of the other one-phase current (for example, V-phase current) at the same timing as the corresponding timing (that is, the carrier peak) Calculation is performed using the fact that the sum of the current values of the three-phase phase currents at the timing becomes zero.

  The phase current calculation unit 23c of the phase current estimation unit 23 calculates the current value at the carrier apex (for example, the current value at the time tp of the carrier apex on the valley side shown in FIG. Based on the discretization formula obtained by discretizing the current equation, arbitrary timing in the period of one period Ts of the carrier signal, for example, at the completion of one period of the carrier signal (that is, for example, the peak of the carrier on the mountain side shown in FIG. Current value of each phase current at time ts).

  For example, in the case of an IPM (Interior Permanent Magnet) motor, the current equation of the motor 11 is the d-axis current id and q-axis current iq on the dq coordinate, the differential operator p, the winding resistance R, and the d-axis. An inductance Ld and a q-axis inductance Lq, one period Ts of a carrier signal, a d-axis electric voltage vd and a q-axis voltage vq, a rotational speed ω, and a magnetic flux component φ of a permanent magnet are shown in the following formula (1). Is described as follows.

The discretization formula obtained by discretizing the above equation (1) by Euler approximation is, for example, an arbitrary timing in the period of one cycle Ts of the carrier signal at the completion of one cycle of the carrier signal (that is, for example, FIG. 3), it is described as shown in the following formula (2).
In the following mathematical formula (2), an arbitrary natural number i represents the completion of one cycle of the carrier signal, and vd (i) and vq (i) represent the d-axis voltage at the completion of one cycle of the current carrier signal and It is a voltage value of the q-axis voltage, and id (i + 1) and iq (i + 1) are current values of the d-axis current and the q-axis current at the completion of one cycle of the next carrier signal.
An arbitrary natural number k indicates the time of the current value calculated by the carrier apex current value calculation unit 23a and the current value calculation unit 23b (ie, the time tp of the carrier apex on the valley side shown in FIG. 3), and id ( k), iq (k), and ω (k) are current values and rotational speeds of the d-axis current and q-axis current at the peak of the carrier on the valley side in one cycle of the current carrier signal.

The phase current calculation unit 23c performs dq conversion on the current value at the time tp of the carrier peak on the valley side for each of the three-phase phase currents output from the carrier peak current value calculation unit 23a and the current value calculation unit 23b. Values id (k) and iq (k) are calculated. Further, the phase current calculation unit 23c calculates the rotational speed ω (k) at the time tp of the carrier apex on the valley side based on the detection signal output from the angle sensor 32. The rotation speed ω (k) is, for example, the average of the rotation speed ω (i) at the completion of one cycle of the current carrier signal and the rotation speed ω (i + 1) at the completion of one cycle of the next carrier signal. It may be a value.
Then, the phase current calculation unit 23c calculates the current values id (i + 1) and iq (i + 1) of the d-axis current and the q-axis current at the completion of one cycle of the next carrier signal, for example, using the above formula (2). To do.
Note that the phase current calculation unit 23c, for example, when setting one cycle Ts of the carrier signal relatively long for the purpose of reducing the control processing load or the switching loss in the inverter 13 or the like, Instead, for example, the following mathematical formula (3) described by an exponential function whose base is the Napier number e may be used.

  The phase current calculator 23c calculates the current values of the d-axis current and the q-axis current at arbitrary timings during the period of one cycle Ts of the carrier signal. As the timing of the time interval T from the carrier vertex time tp, the time interval T is used instead of the coefficient (Ts / 2) in the above equation (2) or equation (3).

  Then, the phase current calculation unit 23c performs inverse dq conversion on the respective current values of the d-axis current and the q-axis current calculated by the above formula (2) or formula (3), and during the period of one cycle Ts of the carrier signal. The current value of each phase current is calculated at an arbitrary timing, for example, at the time of completion of one cycle of the carrier signal (that is, for example, the time ts at the peak of the carrier shown in FIG. 3).

As described above, according to the motor phase current estimation apparatus 10 according to the present embodiment, each of the voltage patterns symmetric with respect to the carrier vertex in one cycle of the carrier signal is symmetric with respect to the carrier vertex. Since the average value of the estimated phase current is the current value of the phase current at the top of the carrier, errors due to noise are reduced, and the current value at the same timing is accurately determined for each of the three-phase phase currents. Can be estimated.
Then, based on the current value of each phase current at the carrier apex and the discretization formula obtained by discretizing the current equation of the motor 11, any timing within one cycle of the carrier signal, in particular, 1 of the carrier signal. By estimating the current value of the phase current at the next completion of the cycle, this estimated value can be used for motor control in the next one cycle, and is performed in synchronization with the apex of the carrier signal such as a triangular wave. The latest phase current information can be applied to the motor control without time delay.
In addition, the DC current sensor 31 for overcurrent protection is effectively used without having to provide a phase current sensor that directly detects each phase current Iu, Iv, Iw actually supplied from the inverter 13 to the motor 11. Thus, each phase current can be accurately estimated.

  In the above-described embodiment, the carrier apex current value calculation unit 23a detects each phase current for two phases in the period of one cycle Ts of the carrier signal with respect to the three-phase modulation using a triangular wave carrier signal. The value is obtained twice and the average value is calculated. However, the present invention is not limited to this. For example, two-phase modulation as shown in FIG. 4 or a ½ period in one period Ts of an appropriate carrier signal When the on / off pattern of each transistor UH, UL and VH, VL and WH, WL is symmetric with respect to the carrier vertex at the timing, the detected value of each phase current for two phases is acquired twice. Thus, the average value may be calculated.

  In the above-described embodiment, the phase current calculation unit 23c obtains each phase obtained by performing inverse dq conversion on each current value of the d-axis current and the q-axis current calculated by the above formula (2) or formula (3). Although the current value of the current is calculated, the present invention is not limited to this. For example, when the control device 24 performs current feedback control (vector control) on the dq coordinates, the above formula (2) or formula (3) is simply used. The current values of the d-axis current and the q-axis current calculated by (1) may be output to the control device 24. In this case, the control device 24 uses the current values of the d-axis current and the q-axis current output from the phase current calculation unit 23c as the d-axis current Ids and the q-axis current Iqs in current feedback control (vector control). To do.

It is a block diagram of the phase current estimation apparatus of the electric motor which concerns on embodiment of this invention. It is a figure which shows each switching state S1-S8 of the inverter shown in FIG. It is a figure which shows the example of the detection timing of the on-off pattern and each phase current of the carrier wave and each transistor UH, UL and VH, VL and WH, WL which concern on embodiment of this invention. It is a figure which shows the example of the detection timing of the carrier wave which concerns on the modification of embodiment of this invention, the ON / OFF pattern of each transistor UH, UL, and VH, VL and WH, WL, and each phase current.

Explanation of symbols

10 Motor Phase Current Estimation Device 11 Motor (Electric Motor)
13 Inverter 23 Phase current estimation unit (phase current estimation means)
23a Carrier apex current value calculation unit (carrier apex current value calculation means)
23b Current value calculation unit (current value calculation means)
23c Phase current calculation unit (phase current calculation means)
25 PWM signal generator (pulse width modulation signal generator)
31 DC current sensor

Claims (3)

An inverter that sequentially commutates energization of a three-phase AC motor using a pulse width modulation signal; and a pulse width modulation signal generation unit that generates the pulse width modulation signal using a carrier wave signal;
A DC side current sensor that detects a DC side current of the inverter; and a phase current estimation unit that estimates a phase current based on the DC side current detected by the DC side current sensor,
The phase current estimation means is configured to detect the phase current at a timing symmetric with respect to the carrier vertex in each voltage pattern symmetric with respect to the maximum or minimum carrier vertex in one period of the carrier signal. Estimate the current value of each one point,
Carrier vertex current value calculating means for calculating an average value based on the current value at the timing of two points consisting of each one point estimated by the phase current estimating means as a current value of the phase current at the carrier vertex; ,
Based on the current value of the phase current at the carrier apex calculated by the carrier apex current value calculating means and the discretization formula obtained by discretizing the current equation of the electric motor, in one cycle of the carrier signal And a phase current calculating means for calculating a current value of the phase current at an arbitrary timing of the motor. The carrier peak current value calculating means calculates a current value of the phase current at the carrier peak for each of the two phase currents out of the three phase currents,
Based on the current value at the carrier apex for each of the phase currents of the two phases calculated by the carrier apex current value calculating means, the other phase currents at the carrier apexes of the phase currents of the three phases. A current value calculating means for calculating a current value;
The phase current calculation means calculates a current value for each phase current of the three phases at the arbitrary timing based on a current value at the carrier vertex for each phase current of the three phases and the discretization formula. The phase current estimating device for an electric motor according to claim 1, wherein the phase current estimating device is calculated. 3. The electric motor according to claim 1, wherein the phase current calculation unit calculates a current value of the phase current at the completion of one cycle of the carrier wave signal as the arbitrary timing. Phase current estimation device.

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