JP3499666B2 - AC motor control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC motor control device, and more particularly to an AC motor control device suitable for controlling an AC motor used for driving an electric vehicle.

[0002]

2. Description of the Related Art In recent years, a three-phase AC motor has become widespread as a driving motor for an electric vehicle typified by an electric vehicle and an electric motorcycle. In an electric vehicle using an AC motor of this type as a drive source, when a driver gives an instruction for a traveling speed as an accelerator opening, a torque command that enables traveling at the speed is issued as a target current value. The current value is AC
It is compared with the measured value of the exciting current flowing through each phase of the motor. Mode
The torque control unit performs torque control based on the comparison result so as to match the exciting current with the target current value, which enables vehicle speed control according to the accelerator opening.

FIG. 7 is a block diagram showing the configuration of a conventional AC motor control device. The battery voltage is applied to both ends of a pair of power switching elements, which are connected in series to form each inverter circuit 70U, 70V, 70W, and are converted into an AC voltage here, and each phase U of the motor 40 is converted. , V, W. Each phase U, V, W of the motor 40
The exciting currents IU, IV, and IW flowing through are detected by current sensors 50U, 50V, and 50W, respectively, and are input to the selection circuit 30 as exciting current symbols SU, SV, and SW, respectively.

The selection circuit 30 selectively outputs any one of the excitation current signals SU, SV, SW based on the output signal of the angle sensor 60 for detecting the rotation angle of the motor 40. The output exciting current signal is input to the non-inverting input terminal of the comparator 10, and its inverting input terminal is connected to the CPU.
A target current value (not shown) calculated according to the accelerator opening is input. The comparator 10 compares the two and outputs the comparison result to the PWM processing circuit 80. The PWM processing circuit 80 calculates the duty ratio according to the comparison result, and the PM with the duty ratio corrected based on the calculation result.
W signal is generated and output. When the excitation phase determiner 20 determines the excitation phase based on the detection signal of the angle sensor 60, the excitation phase determiner 20 supplies the PWM signal to the gate of the power switching element that constitutes the excitation phase inverter circuit.

[0005]

In the above-mentioned prior art, if any one of the current sensors 50U, 50V and 50W fails and the output signal thereof does not reflect the exciting current of each phase, accurate torque control is impossible. Will be. Therefore, for example, in Japanese Unexamined Patent Publication No. 7-177602, when a failure of the current sensor is detected, the feedback control based on the output signal is stopped to switch to the feedforward control, or the failed current sensor is detected. Is only one phase,
A technique is disclosed in which the output of the faulty current sensor is predicted based on the output signals of the remaining plural-phase current sensors and the feedback control is continued.

However, in the above-mentioned prior art, a plurality of control methods are provided, or the output of a failed current sensor is
There is a problem that the configuration is complicated because a configuration that is obtained based on the output signals of the remaining current sensors is required.

Further, the output signal of the current sensor 50 is CP
Depending on the U and the gate circuit, etc., as shown in FIG. 8, it fluctuates in the range of 0.5 to 4.5 V, and the forward direction current is centered around 2.5 V when the current is zero. The detection signal of 2.5 to 4.5 V is output according to the current value, and the detection signal of 2.5 to 0.5 V is output for the reverse current.

If the current sensor 50 fails and its output voltage is fixed at "L" level (0.5 V or less) or "H" level (4.5 V or more), the failure occurs. Although the detection is relatively easy, if the current is fixed at the zero current level (2.5 V), the current sensor 50 may show the zero current level even in a normal state, which makes the detection difficult. It was

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a fail-safe mechanism with a simple structure so that the current sensor can continue to run even if a part of the current sensor fails. Another object of the present invention is to provide an AC motor control device equipped with a fail-safe mechanism that allows the vehicle to continue running even in the event of a failure in which the output of the current sensor is fixed at the zero current level.

[0010]

In order to achieve the above-mentioned object, in the present invention, an inverter which converts a DC voltage into an AC voltage and supplies it to each excitation phase of an AC motor, and each of the above excitations. A plurality of current sensors for detecting currents flowing in the phases; a comparing means for comparing the output signals of the respective current sensors with a separately determined target value to output a comparison result; and a logical sum of the comparison results. And a current control means for controlling the current for the excitation phase selected based on the rotation angle of the AC motor based on the output signal of the logical sum circuit.

In such a structure, for example, U, V,
When an exciting current is flowing from the U phase to the V phase in a three-phase AC motor composed of the W phase, the current value of the U phase and the current value of the V phase are substantially the same, ignoring their directions. Should be. Similarly, when the exciting current is flowing from the U phase to the W phase, the current value of the U phase and the current value of the W phase are the same. Therefore, even if the current sensor for the U phase is out of order, the exciting current for the U phase can be represented by the detection value of the current sensor for the V phase during the period in which the exciting current is flowing from the U phase to the V phase. The period during which the current is flowing from the U phase to the W phase can be represented by the detection value of the current sensor regarding the W phase. Therefore, if the logical sum of the respective comparison results is taken, even if any of the current sensors has failed, the logical sum is no different from the output signal at all times, and an accurate AC motor with a simple structure. Control becomes possible.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of an AC motor control device according to an embodiment of the present invention, and the same symbols as those used above represent the same or equivalent portions. As is clear from comparison with the conventional technique described with reference to FIG. 7, the present embodiment is characterized in that a comparison / selection circuit 100a is provided in place of the comparator 10 and the selection circuit 30. Figure 2
3 is a block diagram specifically showing the configuration of the comparison / selection circuit 100a, and FIG. 3 is a diagram showing signal waveforms of the main parts of FIGS.

In FIG. 2, the exciting current signal SU relating to the U phase detected by the current sensor 50U is the non-inverting input terminal of the comparator 101 and the comparator 10.
2 is input to the inverting input terminal. Similarly, the current sensor 5
The exciting current signal SV output from 0V is the comparator 1
03, and the inverting input terminal of the comparator 104, the exciting current signal SW output from the current sensor 50W is input to the non-inverting input terminal of the comparator 105 and the inverting input terminal of the comparator 106. Is entered. The output voltage of each of the current sensors also fluctuates within the range of 0.5 to 4.5 V as described with reference to FIG. According to the above, the exciting current signal of 2.5 to 4.5 V is output, and the exciting current signal of 2.5 to 0.5 V is output for the reverse current.

The target value of the exciting current is the duty value.
The pulse signal PX converted into the magnitude of the ratio is output from the CPU 90. That is, if the target value is high, a pulse having a long "H" level period is output, and if the target value is low, a pulse having a short "H" level period is output. The pulse signal PX is input to the first integrating circuit 111 and also to the second integrating circuit 112 via the inverter 110.

First and second integrating circuits 111 and 112
Integrates the input pulse, converts it into a DC voltage of a level according to the duty ratio, and outputs it. Therefore, the pulse signal PX has an amplitude of 0-5V and a duty ratio of 80%.
If the “H” level period is 80%, the output signal IH of the first integrator circuit 111 is 4V, and the second integrator circuit 11 is
The output signal IL of 2 becomes 1V.

Output signal IH of the first integrating circuit 111
Are comparators 101, 103, 1 as positive target values.
05 input to the inverting input terminal of the second integration circuit 1
The output signal IL of 12 is input to the non-inverting input terminals of the comparators 102, 104 and 106 as the target value in the reverse direction. In this embodiment, the target value represented by the digital signal is converted into the DC voltage by using the integrating circuit, but a D / A converter may be used instead of the integrating circuit. Output signals S1 ... Of each comparator 101-106
S6 is input to the 6-input OR gate circuit 120, and the output signal of the OR gate circuit 120 is input to the PWM processing circuit 80.

In such a configuration, each current sensor 5
0U, 50V, 50W is functioning normally, P based on the exciting current signal output from each current sensor
When the WM control is executed, as shown in FIG. 3, for example, the exciting current signal SU relating to the U phase is compared while the current direction is the positive direction of the U phase to the V phase or the U phase to the W phase. Is compared with the forward target current IH by
If the exciting current signal SU exceeds the positive target value IH, the output signal S1 of the comparator 101 becomes "H" level. Further, while the direction of the current is in the reverse direction from the V phase to the U phase or from the W phase to the U phase, it is compared with the reverse direction target value IL by the comparator 102, and the exciting current SU shows the reverse direction target value IL.
If it is less than, the output signal S2 of the comparator 102 is "H".
It becomes a level. Further, the exciting current signal SU is set to the target value I
If it is between H and IL, both output signals S1 and S2 are at "L" level.

Similarly, regarding the V-phase exciting current signal SV and the W-phase exciting current signal SW, if the positive target value IH is exceeded, the output signals S3 and S5 of the comparators 103 and 105 become "H" level. , If the reverse direction target value IL is exceeded, the output signals S4, S6 of the comparators 104, 106 become "H" level, and the respective target values IH, IL
If it is between the two, the output signals S3 to S6 are all at the "L" level.

The output of the OR gate circuit 120 becomes "H" level if the output signal of either comparator is "H" level. Then, the PWM processing circuit 80
If the signal output from the OR gate circuit 120 is at the "L" level, the exciting current is increased, and if it is at the "H" level, a PWM signal for reducing the exciting current is generated and output. Torque control becomes possible.

Here, for example, if the current sensor 50U fails and the exciting current signal SU is fixed at the current zero level as shown in FIG.
The output signals of 1 and 102 also become "L" level. However, the remaining current sensors 50V and 50W function normally, and output pulses S3 to S of the comparators 103 to 106 are output.
If 6 is continuously output normally, the OR gate circuit 120 continuously outputs the pulse signal as in the case of FIG. 3, so that the PWM processing circuit 80 outputs the PW in the same manner as usual.
It becomes possible to generate and output the M signal.

As described above, according to the present embodiment, the PWM signal is generated based on the logical sum of the output signals of the respective current sensors. Therefore, the PWM signal is generated by the extremely simple structure when any one of the current sensors fails. -It becomes possible to make a relief, and the exciting current control according to the torque command can be continued. Further, in the present embodiment, since it is not necessary to select the current sensor output to be compared with the target current for each rotation angle of the motor in the comparison / selection circuit 100a, the configuration can be simplified.

Further, in this embodiment, when the current sensor fails and is fixed at the current zero level, the output signal of the comparator becomes "L" level, so that the output signal of the failed current sensor is OR. It will be ignored by the gate circuit 120. For this reason, the influence of the faulty current sensor is eliminated and the torque control can be continued.

In the above embodiment, when the current sensor 50U fails and the exciting current signal SU is fixed at "H" level or "L" level, the outputs of the comparators 101 and 102 are output. Is always at "H" level, the output waveform of the OR gate circuit 120 is always at "H" level. Therefore, the PWM processing circuit 80 generates a PWM signal for reducing the exciting current.

However, if torque control is performed by the PWM signal, the vehicle speed decreases, and eventually the vehicle stops, so there is no problem in terms of safety, but drivability decreases. Therefore, in the second embodiment of the present invention to be described next, even if the exciting current signal of the faulty current sensor is fixed to the “H” level or the “L” level, the vehicle can continue to run.

FIG. 5 is a block diagram showing the configuration of the comparison / selection circuit 100b according to the second embodiment of the present invention, and the same reference numerals as those used above represent the same or equivalent portions. The comparison / selection circuit 100b of the present embodiment can be used by replacing the comparison / selection circuit 100a of the first embodiment.

In this embodiment, each converter 101-101.
AND between the output stage 106 and the OR gate circuit 120
The gate circuits 201 to 206 are provided, and the exciting current signals SU, SV, and SW output from the current sensors 50U, 50V, and 50W are also input to the CPU 91, and the exciting current signals SU, SV, and SW are input in accordance with the exciting current signals of the current sensors. AND gate circuit 20
It is characterized in that it controls 1 to 206.

FIG. 6 is a flowchart showing the operation of the CPU 91. In step S1, the exciting current signal SU relating to the U phase is compared with the upper limit value Imax. If the exciting current signal SU exceeds the upper limit value Imax, the process proceeds to step S3, and if it falls below the upper limit value Imax, the process proceeds to step S2. The upper limit value Imax is set to a high voltage (for example, 4.6 V or higher) that cannot be output as long as the current sensor 50 functions normally.

In step S2, the exciting current signal S
U is compared with the lower limit value Imin, and when the exciting current signal SU is below the lower limit value Imin, the process proceeds to step S3, and when the exciting current signal SU is above the lower limit value Imin, the process proceeds to step S4.
This lower limit value Imin is also a low voltage (for example, 0.4 V or less) that cannot be output as long as the current sensor 50 functions normally.
Is set to.

In step S3, the U-phase current sensor 50
It is determined that U is out of order, and an appropriate warning such as a warning display or a warning sound is issued to the driver, and at the same time, the gate signal SUG is set to "L" level, and the AND gate circuit 201,
The output of 202 is fixed at "L" level.

Similarly, the exciting current signal S relating to the V phase
If V is out of the upper and lower limit values, the gate signal SVG is set to "L" level and the outputs of the AND gate circuits 203 and 204 are set to "L".
If the exciting current signal SW for the W phase deviates from the upper and lower limit values, the gate signal SWG is set to the “L” level and fixed to the level A
The outputs of the ND gate circuits 205 and 206 are fixed at "L" level. As a result, the output signal of the faulty current sensor will be ignored by the AND gate circuit.
Torque control can be continued without the influence of the faulty current sensor.

In the above embodiment, the PWM processing circuit 8
0 has been described as outputting the pulse signal of the duty ratio calculated based on the comparison result by the comparison and selection circuit 100a, but the present invention is not limited to this, and the comparison result (output of the OR gate circuit 120 Signal),
It can be similarly applied to a circuit that outputs a pulse signal whose level is inverted each time the comparison result is inverted.

In each of the above-described embodiments, when the output of the current sensor is higher than the target value (the output signal of the current sensor is higher than the positive direction target value IH or lower than the reverse direction target value IL), the comparator. When the output signal of the OR gate circuit 120 is at the "L" level, the exciting current is increased when the output signal of the OR gate circuit 120 is at the "L" level. If it is at "H" level, the control for reducing the exciting current is executed, and the purpose is as follows.

That is, if the reverse logic to the above is adopted, the output signal of the comparator becomes "L" level when the output of the current sensor is higher than the target value, and "H" level when it is lower than each target value. In addition, when the output signal of the OR gate circuit 120 is "H" level, the exciting current is increased, and when it is "L" level, the exciting current is reduced.

However, if such a logic is adopted, the output signal of the comparator becomes the "H" level when the output of the current sensor is fixed to the current zero level due to the failure of the current sensor, and the OR gate is used. The output of the output circuit 120 also becomes "H" level regardless of the outputs of the other current sensors. Then, this means that the control for increasing the exciting current to increase the vehicle speed is performed.

In order to prohibit such "control for increasing the vehicle speed", the AND gate described with reference to FIG. 5 is provided. At that time, the program processing described with reference to FIG. Determines whether the output of the current sensor is at the zero level, and when "zero level" is detected, the gate is closed. However, since the output of the current sensor can always be zero level, its detection program becomes very complicated.

On the other hand, according to the configuration of the above-described embodiment, "fixing the current sensor output to the zero level" which is difficult to detect can be ignored by the OR gate circuit 120, and it has been described with reference to FIG. Since the detection program only needs to detect the "H" level or "L" level, which is a signal level that cannot occur at all times, the processing becomes simple.

[0037]

According to the present invention, the following effects can be achieved. (1) Even if each current sensor fails and its output voltage is fixed at "L" level or "H" level, P is calculated based on the logical sum of the output signals of each current sensor.
Since the WM signal is generated, it is possible to perform fail-safe with an extremely simple configuration, and it becomes possible to continue the excitation current control according to the torque command.

Further, in the present invention, it is not necessary to select the current sensor output to be compared with the target current for each rotation angle of the motor in the comparison / selection circuit 100a, so that the structure can be simplified. (2) When each current sensor fails and its output is fixed at the current zero level, the output signal of the comparator is set to "L" level. Therefore, the output signal of the failed current sensor is OR gated. -Will be ignored by the circuit. For this reason, the influence of the faulty current sensor is eliminated and the torque control can be continued.

[Brief description of drawings]

FIG. 1 is a block diagram of an AC motor control device to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a first embodiment of a comparison / selection circuit 100a to which the present invention is applied.

FIG. 3 is a diagram showing signal waveforms of main parts of FIGS.

FIG. 4 is a diagram showing signal waveforms of main parts of FIGS.

FIG. 5 is a block diagram showing a configuration of a second embodiment of a comparison / selection circuit 100b to which the present invention is applied.

FIG. 6 is a flowchart showing the operation of the second embodiment.

FIG. 7 is a block diagram showing a configuration of a conventional technique.

FIG. 8 is a diagram showing output characteristics of a current sensor.

[Explanation of symbols]

50U, 50V, 50W ... Current sensor, 80 ... PWM processing circuit, 90, 91 ... CPU, 100a, 100b ... Comparison selection circuit, 101-106 ... Comparator, 111,
112 ... Integrator circuit, 120 ... OR gate circuit, 201 ...
206 ... AND gate circuit

Continuation of the front page (56) Reference JP-A-57-153571 (JP, A) JP-A-54-161026 (JP, A) JP-A-60-2075 (JP, A) JP-A-58-149095 (JP , A) JP-A-5-284777 (JP, A) JP-A-4-45078 (JP, A) JP-A-2-266884 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) B60L 3/00 B60L 15/00 H02M 7/48

Claims (3)

(57) [Claims] 1. A DC voltage is converted into an AC voltage to convert the AC voltage.
Inverter circuit for supplying to each excitation phase, a plurality of current sensors for detecting the current flowing in each excitation phase, and the output signal of each current sensor is compared with a separately determined target value. A comparison means for outputting a comparison result, a logical sum circuit for calculating a logical sum of the comparison results, and a current control for an excitation phase selected based on the rotation angle of the AC motor. An output signal of the logical sum circuit. The AC motor control device is characterized in that the comparison means outputs an "L" level signal if the output signal of the current sensor does not exceed the target value. 2. A means for detecting whether or not the output signal of the current sensor is out of a predetermined range, and a means for detecting the signal out of the predetermined range in the comparing means connected to the subsequent stage of the current sensor. The AC motor control device according to claim 1, further comprising gate means for prohibiting output. 3. The current control means, a PWM processing means for generating a PWM signal whose duty ratio is adjusted based on the output signal of the OR circuit, and an excitation amount based on the rotation angle of the AC motor. The AC motor control device according to claim 1 or 2, further comprising: an excitation phase determining unit that supplies the PWM signal to the excitation phase.