JP2010088260A - Apparatus for estimating phase current in motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an accuracy in estimation of phase current. <P>SOLUTION: The phase current estimating part 23 of an apparatus 10 for estimating the phase current of a motor estimates one point each of current value of a phase current with timing symmetrical about the apex of a carrier, in each within a voltage pattern symmetrical about the apex of the carrier of a maximum value or a minimum value in one cycle of a carrier signal, for every current of two phases. It includes: a current value computer 23a, which computes the average by the current values with two points of timing consisting of estimated one point each, as the current value of the phase current at the apex of the carrier, for every phase current of two phases; and a phase current computer 23b, which computes the current value of the phase current of another phase, based on the current value of every phase current of two phases computed by the current value computer 23a. <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. Current value calculating means for calculating 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 apex (for example, current in the embodiment) A value calculation unit 23a).

  Furthermore, in the phase current estimation device for an electric motor according to the second aspect of the present invention, the phase current estimation unit is configured to perform the timing at the two points with respect to each of the two phase currents out of the three phase currents. The current value is estimated, and the current value calculation means calculates the current value of the phase current at the carrier vertex for each of the two-phase phase currents, and the current calculation means Based on the calculated current value for each phase current of the two phases, phase current calculation means for calculating a current value at the carrier apex of the other phase current among the phase currents of the three phases (for example, implementation) A phase current calculation unit 23b).

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. Since the average value of the phase current is the current value of the phase current at the top of the carrier, the error due to noise is reduced and the current value at the same timing is accurately estimated for each of the three-phase phase currents. be able to.
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.

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, a PWM signal that is a gate signal for the inverter 13 is output according to each phase voltage command Vu, Vv, Vw, and the inverter is actually The d-axis current Ids and the 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 highlighted.
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 current value calculation unit 23a and a phase current calculation unit 23b.
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 current value calculation unit 23a uses, as the current value of the phase current at the peak of the carrier, the average value based on the current value of the phase current at the timing of two points each consisting of one point for each phase current of the two phases. calculate.
Then, the phase current calculation unit 23b calculates the current value of the other one-phase phase current at the same timing as the corresponding timing (that is, the carrier vertex) from the current value of the two-phase phase current at the carrier vertex. Calculation is performed using the fact that the sum of the current values of the three-phase phase currents at this timing is zero.

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 performs time tu1, tu2 symmetrical with respect to the carrier vertex (that is, time Ts / 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. 2, 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 a time having the same time interval T1), and further at the carrier apex. In the state of two basic voltage vectors V3 that are symmetrical to each other, times tw1 and tw2 that are symmetric with respect to the carrier vertex (that is, the same time interval T2 with respect to the time Ts / 2 of the carrier vertex 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 DC-side current sensor 31 at the time).

  Then, the 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 as the time Ts of the carrier peak on the valley side. The current value at / 2.

  Then, the phase current calculation unit 23b of the phase current estimation unit 23 uses the fact that the sum of the current values of the respective phase currents at the same timing is zero, so that the two-phase phase current (for example, the U-phase current and the W-phase) The current value of the other one-phase current (for example, V-phase current) is calculated from the current value of the current) (that is, the current value at the time Ts / 2 of the carrier peak on the valley side).

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.
Furthermore, based on the current value for each of the two-phase phase currents at the carrier apex, the current value of the other one-phase phase current at the carrier apex can be accurately calculated.
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, with respect to the three-phase modulation using a triangular carrier signal, the detected values of the phase currents for two phases are acquired twice in the period of one cycle Ts of the carrier signal, Although the average value is calculated, the present invention is not limited to this. For example, for the two-phase modulation as shown in FIG. 4 or for the carrier apex at the timing of ½ period in one period Ts of an appropriate carrier signal. When the on / off patterns of the transistors UH, UL and VH, VL and WH, WL are symmetric, the detection values of the respective phase currents for two phases are obtained twice, and the average value is calculated. Also good.

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 Current value calculation unit (current value calculation means)
23b Phase current calculation unit (phase current calculation means)
25 PWM signal generator (pulse width modulation signal generator)
31 DC current sensor

Claims (2)

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,
Current value calculating means for calculating an average value of the current values 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 apex. An apparatus for estimating a phase current of an electric motor. The phase current estimation means estimates the current value at the timing of the two points for each of the phase currents of two phases of the phase current of three phases,
The current value calculation means calculates the current value of the phase current at the peak of the carrier for each of the phase currents of the two phases,
Phase current calculation for calculating a current value at the top of the carrier of the other phase current among the phase currents of the three phases based on the current value for each phase current of the two phases calculated by the current calculation means The motor phase current estimating apparatus according to claim 1, further comprising: means.

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