JP2010088262A - Apparatus for estimating phase current in motor - Google Patents

Abstract

A phase current estimation accuracy is improved.
A phase current estimator 23 of a motor phase current estimator 10 is symmetric with respect to a maximum or minimum carrier vertex in one cycle of a carrier signal for each phase current of two phases. In each of the voltage patterns, the current value at the timing of each one point of the phase current is estimated, and a primary expression including the current value at the timing of two points composed of each estimated one point is expressed as the two-phase Current value for calculating the current value of the phase current at any timing in one cycle of the carrier wave signal for each phase current based on the arithmetic expression calculation unit 23a that calculates for each phase current and the primary expression A calculation unit 23b and a phase current calculation unit 23c that calculates a current value of another one-phase phase current based on the current value for each of the two-phase phase currents calculated by the current value calculation unit 23b.
[Selection] Figure 1

Description

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

Conventionally, for example, when a DC current is converted into a three-phase AC current, two current values having different phases in two different sections of each carrier cycle in the process of changing six different gate states by three pairs of transistors. Is detected by a single DC current sensor, and a current detection method is known in which the current value of the other phase is calculated from these two current values, assuming that the sum of the three-phase currents is always equal to zero ( For example, see 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 estimated phase current value of the other one phase increases.
In addition, in the current detection method according to the above-described prior art, the detection timing of each phase current value does not become the peak of a carrier wave such as a triangular wave, for example. Therefore, the detection timing of each phase current value is synchronized with the carrier wave as the peak of the carrier wave. In normal motor control in which the above control is performed, there is a possibility that a malfunction may occur in the control.
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. Estimates the current value at the timing of each point of the phase current in each voltage pattern symmetric with respect to the carrier peak of the minimum value, and each point estimated by the phase current estimating means An arithmetic expression calculating means (for example, an arithmetic expression calculating unit 23a in the embodiment) for calculating a linear expression including the current value at the timing of two points, and the carrier signal based on the primary expression Current value calculation means (for example, a current value calculation unit 23b in the embodiment) for calculating a current value of the phase current at an arbitrary timing in one cycle.

  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 arithmetic expression calculating means calculates the primary expression including the current value at the timing of the two points for each of the phase currents of the two phases, The current value calculation means calculates the current value of the phase current at an arbitrary timing in one cycle of the carrier signal for each of the phase currents of the two phases, and is calculated by the current value calculation means Based on the current value for each phase current of the two phases, phase current calculation means for calculating the current value of the other phase currents of the phase currents of the three phases (for example, the phase current in the embodiment) A calculation unit 23c).

According to the phase current estimation device for an electric motor according to the first aspect of the present invention, a linear expression is obtained from the current value of the phase current estimated in each of the voltage patterns symmetric with respect to the carrier vertex in one cycle of the carrier wave signal. Since the current value of the phase current at an arbitrary timing is estimated based on this linear equation, the error due to noise is reduced, and the current value at the same timing is obtained for each of the three-phase phase currents. It can be estimated with high accuracy. In particular, by estimating the current value of the phase current at the completion of one cycle of the carrier wave signal as an arbitrary timing, this estimated value can be used for motor control in the next cycle, such as a triangular wave The latest phase current information can be applied to motor control performed in synchronization with the peak of the carrier wave signal.
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 same timing based on the current value for each of the two-phase phase currents at the same timing. 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, an arithmetic expression 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 of the three phase currents, the current value at an appropriate timing of each point of the phase current is detected by the DC-side current sensor 31 at this timing. It is estimated from the DC side current Idc that is generated.

Then, the arithmetic expression calculation unit 23a calculates a primary expression including the current values of the phase currents at the timing of two points each consisting of one point for each phase current of two phases.
Then, the current value calculation unit 23b calculates the current value of each phase current at an arbitrary timing (for example, carrier apex, etc.) that is the same between the two-phase phase currents based on the linear expression.
Then, the phase current calculation unit 23c calculates the current value of the other one-phase phase current at the same timing as the corresponding timing from the current value of the two-phase phase current calculated based on the primary expression at this timing. It is calculated using the fact that the sum of the current values of the three-phase phase currents becomes 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.
That is, the phase current estimation unit 23 calculates the first current from the DC-side current Idc detected by the DC-side current sensor 31 at appropriate times tu1 and tu2 in the state of the two basic voltage vectors V1 symmetrical to the carrier vertex. The 1U-phase current Iu1 and the second U-phase current Iu2 are acquired, and further detected by the DC-side current sensor 31 at appropriate times tw1 and tw2 in the state of two basic voltage vectors V3 that are symmetrical with respect to the carrier vertex. The first W-phase current Iw1 and the second W-phase current Iw2 are obtained from the DC side current Idc.

Then, the calculation formula calculation unit 23a of the phase current estimation unit 23, for example, as shown in the following formula (1), for each phase, based on the phase currents Iu1, Iu2 and Iw1, Iw2, the current corresponding to the time t First, I ^{^} u and I ^{^} w are calculated.

Then, the current value calculation unit 23b of the phase current estimation unit 23 is based on the above formula (1), at any timing (for example, a peak on the valley side or a peak on the mountain side) at which the phase currents of the two phases are the same. The current value of each phase current is calculated.
For example, as shown in FIG. 3, the times tu1 and tu2 are symmetrical with respect to the carrier vertex (that is, the time having the same time interval Δtu with respect to the time Ts / 2 of the carrier vertex on the valley side), and If the times tw1 and tw2 are symmetrical with respect to the carrier vertex (that is, the time having the same time interval Δtw with respect to the time Ts / 2 at the valley-side carrier vertex), the valley-side carrier vertex (that is, the time The current values of the U-phase current and the W-phase current at Ts / 2) are described as shown in the following formula (2), for example, and these current values match the actual current values without error ( In other words, the error resulting from approximating the change in the current value according to time t by a linear expression is zero at the timing of time Ts / 2).
For example, as shown in FIG. 4, each current value of the U-phase current and the W-phase current at the completion of one cycle of the carrier signal (that is, the time Ts at the peak of the carrier peak) is, for example, These current values have a slight error with respect to each actual current value (that is, an error caused by approximating a change in current value according to time t by a linear expression). Have.

  Then, the phase current calculation unit 23c 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 currents ( For example, the current value of the other one-phase current (for example, V-phase current) is calculated from the current values of the U-phase current and the W-phase current.

As described above, according to the phase current estimating apparatus 10 for an electric motor according to the present embodiment, the current value of the phase current estimated in each of the voltage patterns symmetric with respect to the carrier vertex in one cycle of the carrier signal is 1 Since the following equation is calculated and the current value of the phase current at an arbitrary timing is estimated based on this linear equation, the error due to noise is reduced, and the current at the same timing for each of the three-phase phase currents. The value can be estimated accurately. In particular, by estimating the current value of the phase current at the completion of one cycle of the carrier signal as an arbitrary timing, this estimated value can be used for motor control in the next cycle, such as a triangular wave The latest phase current information can be applied to motor control performed in synchronization with the peak of the carrier signal.
Furthermore, based on the current value for each of the two-phase phase currents at the same timing, the current value of the other one-phase current at the same timing 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 change of the current value corresponding to time t for each phase is approximated by a linear expression, the present invention is not limited to this. For example, two-phase modulation as shown in FIG. 5 or one cycle of an appropriate carrier signal When the ON / OFF patterns of the transistors UH, UL and VH, VL, and WH, WL are symmetric with respect to the carrier apex at the timing of 1/2 cycle in Ts, The detection value may be acquired twice, and the change in the current value according to time t may be approximated by a linear expression for each phase.

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 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 Operational expression calculation unit (operational expression 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 (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 calculates the current value at the timing of each point of the phase current in each of the voltage patterns symmetric with respect to the carrier peak of the maximum value or the minimum value in one cycle of the carrier wave signal. Estimated
An arithmetic expression calculating means for calculating a linear expression including the current value at the timing of two points including the one point estimated by the phase current estimating means;
A phase current estimation device for an electric motor, comprising: current value calculation means for calculating a current value of the phase current at an arbitrary timing in one cycle of the carrier wave signal based on the linear expression. 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 arithmetic expression calculating means calculates the linear expression including the current value at the timing of the two points for each of the phase currents of the two phases,
The current value calculation means calculates a current value of the phase current at an arbitrary timing in one cycle of the carrier signal for each of the phase currents of the two phases,
Phase current calculation means for calculating a current value 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 value calculation means. The phase current estimation apparatus for an electric motor according to claim 1.

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