JPH0530602A - Motor control circuit for motor vehicle - Google Patents

Abstract

PURPOSE:To provide a motor drive circuit for motor vehicle in which overcurrent of motor is prevented under overload. CONSTITUTION:Power is fed to a motor M through motor circuits CP1, TR1-TR4 which compare an accelerator voltage with a triangular wave to produce a driving signal having pulse width variable with the accelerator voltage for PWM controlling power transistors TR1-TR4. The motor control circuit further comprises a current limiting circuit Rs for detecting a battery current being fed to the motor M and lowering the driving signal when thus detected battery current exceeds a reference level, a CP 2, and rotational speed control circuits 2-4 for detecting the rotational speed of motor M and varying the accelerator voltage based on thus detected rotational speed to perform constant speed control of the motor M. The rotational speed control circuit is provided with an overload prevenstion control circuit 10 for controlling the reference level of the current limit circuit when the rotational speed of motor is lower than a predetermined level and lowering the battery current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control circuit for an electric vehicle for controlling a drive motor of the electric vehicle, and particularly, the rotation of the motor is locked by an excessive load.
Alternatively, the present invention relates to a motor control circuit for an electric vehicle that prevents an unnecessary excessive current from flowing through the motor when the state is close to a lock.

[0002]

2. Description of the Related Art In an electric vehicle such as an electric wheelchair, a battery is used as a power source to supply an electric current to a DC motor to rotate the electric motor to drive the electric vehicle.

The motor control circuit for such an electric vehicle is one in which an unnecessary excessive current does not flow to the motor when the rotation of the motor is locked by an excessive load or becomes close to the locked state. is necessary.

FIG. 4 shows a motor circuit, in which a full bridge circuit supplies a current to the motor for driving, and M is a DC motor, TR1 to TR4.
Is a power transistor, R _s is a shunt resistor, S1 is a main switch, and V _B is a battery voltage.

The power transistor for driving the motor M is controlled so that TR1 and TR3 are turned on during forward rotation, and TR2 and TR4 are turned on during reverse rotation. As a result, the motor current I _{M in the} normal rotation direction or the reverse rotation direction is supplied to the motor M from the battery voltage V _B via the main switch S1, and the motor M rotates in the normal rotation or the reverse rotation.

In a current control circuit (not shown), shunt resistance R _s is obtained by performing pulse width control (PWM) at a frequency determined by the time constant of the detection circuit.
It operates so that the current I _B flowing through the circuit becomes a value close to the set level.

[0007] At this time, the shunt resistor R _s connected in series to the full bridge circuit, a current I _det detecting a battery current I _B generated when exceeding the current level current I _det is set, the driving power The transistor is controlled to stop energizing the motor M.

In the current detection method in the motor circuit shown in FIG. 4, the battery current (average value) is controlled, but the current I _M flowing through the power transistor or the motor M is not directly controlled.

FIG. 5 shows a conventional motor drive circuit, and shows the entire drive circuit including a current limiting circuit when the motor circuit of FIG. 4 is used. The same number is used. Codes TR5 and TR6
Is a driving transistor for the power transistor TR1, TR7 and TR8 are driving transistors for the power transistor TR2, and TR9 is a power transistor T.
A driving transistor for R3 and TR10 are driving transistors for the power transistor TR4, respectively.

Reference numeral VR1 is a variable resistor for generating an accelerator voltage, reference numeral 1 is a triangular wave generator for generating a triangular wave voltage having a constant period, CP1 is a comparator for comparing the accelerator voltage with the output of the triangular wave generator 1, and S2 Is a forward (F) / reverse (R) switch, INV is an inverter, and G1 and G2 are AND gates. The PWM control circuit is configured by these.

Further, reference numeral OA1 is an operational amplifier for amplifying the generated voltage of the shunt resistor R _s , VR2 is a variable resistor for determining a current limit value, CP2 is an output voltage of the operational amplifier OA1 and an output voltage of the variable resistor VR2. Comparing comparators, which form a current limiting circuit.
In FIG. 5, the motor M is applied to a load within a predetermined range.
The rotation speed control circuit that keeps the rotation speed of 1 constant is omitted.

In FIG. 5, the comparator CP1 compares the accelerator voltage from the variable resistor VR1 with the triangular wave voltage from the triangular wave generator 1, and the wider the accelerator operation, that is, the larger the accelerator voltage, the wider the width. Generates a pulse with a constant period. When the accelerator voltage is equal to or higher than a certain value, the output of the comparator CP1 is in a direct current (full conduction) state.

When the switch S2 is in the forward state, the gate G1 gives this pulse to the transistors TR5 and TR9, so that the power transistors TR1 and TR3 are turned on and the motor M is normally rotated. Further, when the switch S2 is in the reverse state, the gate G2 is opened to give a pulse to the transistors TR7 and TR10.
R2 and TR4 are turned on and the motor M is rotated in the reverse direction.

The operational amplifier OA1 amplifies the voltage of the shunt resistor R _s , and the comparator CP2 operates as an operational amplifier OA1.
The output voltage of the comparator CP1 is lowered when the battery current I _B exceeds a certain limit value by comparing the output voltage of the above-mentioned output voltage with the voltage determined by the variable resistor VR2. Since the PWM control is performed in this state, the pulse width at the output of the comparator CP1 becomes small, and the battery current I _B is maintained at a substantially constant value.

FIG. 6 shows a conventional motor drive characteristic, showing the relationship between the torque T and the motor current I _{M, the} battery current I _B and the rotation speed N in the motor drive circuit of FIG. There is.

Then, as shown in FIG. 6, in the rotational speed control range, the rotational speed N is constant even if the torque T increases,
When the torque further increases, the rotational speed gradually decreases.
Until the current limit circuit starts operating, the battery current I
_B and the motor current I _M have almost the same value, but when the current limit is reached and the PWM control is started when the limit current value I _LIM is reached, the battery current I _B is almost the set limit current value as described above. However, the motor current continues to increase.

[0017]

In the conventional motor drive circuit, when the motor rotation enters a locked state where it is not useful for the vehicle, the motor current increases even though the battery current is limited to a constant value. If a large amount of current flows through the motor and this current continues, the motor armature coil will burn out.

In order to avoid such a situation,
In the conventional motor drive circuit, the current limit value is lowered to reduce the vehicle performance, or the motor capacity is increased so as not to burn even if the current increases. Therefore, there is a problem that the vehicle performance is unduly reduced or an excessive motor capacity is required.

[0019]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art as described above, and in a motor drive circuit of an electric vehicle or the like, an excessive load causes the motor rotation to be in a locked state or a state close thereto. However, it is an object of the present invention to provide a motor drive circuit in which an excessive current does not flow and therefore vehicle performance is unduly reduced or an excessive motor capacity is not required.

[0020]

According to the present invention, an accelerator voltage is compared with a triangular wave to generate a drive signal having a pulse width that changes according to the accelerator voltage, and the power transistor is PWM-controlled by the drive signal to perform battery control. To the motor circuit (CP1, TR1 to TR4) for energizing the motor. Further, the current limiting circuit (R _s , CP2) that detects the battery current supplied to the motor (M) and reduces the drive signal when the reference value exceeds a predetermined reference value, and the rotation speed of the motor (M). And a rotation speed control circuit (2-4) for detecting and detecting the change of the accelerator voltage based on this to control the motor (M) at a constant speed. Then, the rotation speed control circuit is provided with an overload prevention control circuit 10 for controlling the reference value in the current limiting circuit to control the drop of the battery current value when the rotation speed of the motor is equal to or lower than a predetermined value. ing. This aims to achieve the above-mentioned object.

[0021]

The motor control circuit for an electric vehicle according to the present invention is as shown in FIG. The motor drive circuit compares the accelerator voltage with the triangular wave and generates a drive signal having a pulse width that changes according to the accelerator voltage, and the drive signal causes the power transistors (TR1 to TR4) to be generated.
The current limiting circuit (R _s , CP2) is provided for the motor circuit (CP1, TR1 to TR4) that energizes the motor (M) from the battery (V _B ) by PWM control of the power supply to the motor (M). The battery current is limited by lowering the drive signal in the motor circuit when the detected battery current exceeds a reference value. Further, a rotation speed control circuit (2-4) is provided to detect the rotation speed of the motor (M) and change the accelerator voltage according to a signal converted into a voltage signal. Constantly control within the range.

For such a motor drive circuit, control circuits (CP3, CP4) are provided to enable the comparator (C
An output is generated when the signal indicating the rotation speed is equal to or less than a predetermined value by P3), the output signal of the comparator (CP3) is delayed by the integration circuit (R1, C1), and the integration circuit (R1, C1) is delayed by the comparator (CP4). When the output of C1) exceeds the signal value obtained by delaying the output of the current limiting circuit, a control signal is generated. By controlling the reference value in the current limiting circuit according to this control signal, the battery current value is limited when the rotation speed of the motor (M) is equal to or lower than the predetermined rotation speed (N _L ).

Therefore, in the electric vehicle motor control circuit of the present invention, it is possible to prevent an excessive current from flowing even when the motor rotation is locked or is in a state close to this due to an excessive load, so that the vehicle performance is unduly lowered. Can be used
Alternatively, it becomes unnecessary to increase the motor capacity more than necessary.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 4 to 5 in the conventional example.
The same reference numerals are given to the same constituent members as in.

First, the embodiment shown in FIG. 1 compares an accelerator voltage with a triangular wave to generate a drive signal having a pulse width which changes according to the accelerator voltage, and PWM-controls a power transistor by the drive signal to perform battery control. To the motor circuit (CP1, TR1 to TR4) for energizing the motor. Also, a current limiting circuit (R _s , CP2) that detects the battery current supplied to the motor (M) and lowers the drive signal when it exceeds a predetermined reference value, and the motor (M)
And a rotation speed control circuit (2-4) for detecting the rotation speed of the motor and changing the accelerator voltage based on the rotation speed to control the motor (M) at a constant speed. An overload prevention control circuit 10 that controls the reference value in the current limiting circuit and controls the drop of the battery current value when the rotation speed of the motor is equal to or lower than a predetermined value is provided in the rotation speed control circuit.

The overload prevention circuit 10 includes a comparator (CP3) which produces an output when the signal indicating the number of revolutions is below a predetermined value, and an integrating circuit (R1, C1) which delays the output signal of the comparator (CP3). And the integration circuit (R
1, C1) and a comparator (CP4) that generates a control signal when the output of the current limiting circuit (R _s , CP2) exceeds a delayed signal value. The current limiting circuit (CP4) It is configured to control a predetermined value in R _s , CP2).

Here, reference numeral 2 indicates a rotation speed detector for generating an output voltage according to the rotation speed of the motor M, reference numeral 3 indicates an F / V converter for converting the rotation speed (frequency) into a voltage,
Reference numeral 4 indicates a rotation speed control unit. Also, D1, D2, D3
Is a diode forming a coupling circuit, and C2 is a capacitor. FIG. 2 shows a motor drive characteristic according to the present embodiment. The motor drive circuit of FIG. 1 has a motor current I _{M, a} battery current I _B and a rotation speed N, and a torque T.
Shows the relationship with.

In FIG. 1, a rotation speed detector 2 detects the rotation of the motor M, generates a pulse, and integrates the pulse to generate a signal having a frequency proportional to the rotation speed. The F / V converter 3 generates a voltage signal that changes according to this frequency.
The rotation speed control unit 4 outputs the output of the F / V converter 3 to the variable resistor V
By returning to the output of R1, in the rotation speed control range shown in FIG. 2, the rotation speed N is controlled to be constant even if the load changes.

The load rotation speed of the motor M is reduced by the increase in (torque T), the output of the rotational speed detector 2 is lowered, following the result torque T _a depicted in FIG. 2, F / V converter 3 When the output of is below N _L rotations, the output of the comparator CP3 becomes “H _a ”. This output is delayed by an integrating circuit consisting of a resistor R1 and a capacitor C1, and the comparator CP
4 inverting input.

At this time, when the output of the comparator CP2 of the current limiting circuit does not start the PWM control, in other words, in the light load state in which the current limiting circuit is not operating, the non-inverting input level of the comparator CP4 is " H ”. Since the respective parts are set so that “H _a <H”, the output of the comparator CP4 does not become “L” in this case even if the motor rotation speed is N _L or less.

When the load further increases and exceeds the torque T _a , the comparator CP2 of the current limiting circuit starts the PWM operation to generate an output, which causes the non-inverting input of the comparator CP4 via the smoothing capacitor C2. It becomes "L _a ".

Here, each part constant is set so that “H> H _a > L _a ”. As a result, the load (torque) is T
_{When it is a} or more, the output of the comparator CP4 becomes "L". This output lowers the reference voltage for setting the limiting current value for the comparator CP2 of the current limiting circuit via the diode D3 and its series resistance, so that the battery current I _B decreases as indicated by X in FIG. Then
As a result, the motor current I _M also decreases as indicated by Y.

As mentioned above, due to the delay due to the capacitor C2 at the non-inverting input of the comparator CP4,
Although there is a delay in the decrease of the motor current I _M , in such a state, when instantaneous torque is required, R
By appropriately selecting the time constant of the integrator circuit made up of C1 and C1, the characteristic of the motor current I _M can be adjusted as shown by Z in FIG. 2 so that the current flows through the motor.

FIG. 3 shows a current check routine, in the case where the microcomputer in the motor drive circuit shown in FIG. 1 is used for control.
The flowchart of an electric current check is shown.

That is, the battery current is first checked by the voltage of the shunt resistor R _s . And the battery current I
Is less than the limit value I _LIM shown in FIG. 6, the main routine or another check routine is executed as normal processing.

The battery current I is limited to the limit value I shown in FIG.
_When it exceeds _LIM , the motor speed N is checked by the output of the F / V converter 3, and when it is higher than the speed limit N _L , a normal current limiting subroutine is executed.

When the motor rotation speed N becomes lower than the limit rotation speed N _L , the counter is operated and the predetermined time t _see
Whether or not to continue, when it is not continued, the normal current limiting subroutine is executed, but when t _{see is} continued,
The process proceeds to the overcurrent reduction subroutine of the present invention.

Other configurations and operations are the same as those of the above-mentioned conventional example.

[0039]

Since the present invention is constructed and functions as described above, according to the present invention, in a motor drive circuit of an electric vehicle or the like, an excessive current is applied even if the motor rotation is in a locked state or a state close to this due to an excessive load. Can be prevented from flowing, which results in sufficient rotation below the required range without any control that would unduly reduce vehicle performance or without requiring excessive motor capacity. The number and torque can be obtained economically. At this time, the motor current is limited by giving a certain delay in the low rotation range of the overload that is not necessary under normal use conditions, and by adjusting this delay characteristic, even under such an overload condition, instantaneous It is possible to provide a motor control circuit for an electric vehicle, which has not been heretofore excellent, in which a current can be passed through the motor to generate the torque when a large torque is required.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a motor drive characteristic according to the present invention.

FIG. 3 is a diagram showing a current check routine.

FIG. 4 is a diagram showing a motor circuit.

FIG. 5 is a diagram showing a conventional motor drive circuit.

FIG. 6 is a diagram showing a conventional motor drive characteristic.

[Explanation of symbols]

M Motor TR1 to TR4 Power transistor V _B Battery R _s Shunt resistor CP1 to CP4 Comparator 1 Triangular wave generator 2 Rotation speed detector 3 F / V converter 4 Rotation speed control unit 10 Overload prevention control circuit

Claims (2)

[Claims] 1. A motor circuit that compares an accelerator voltage with a triangular wave to generate a drive signal having a pulse width that changes according to the accelerator voltage, and PWM-controls a power transistor by the drive signal to energize a motor from a battery. A current limiting circuit that detects the battery current supplied to the motor and reduces the drive signal when the current exceeds a predetermined reference value; and detects the rotation speed of the motor and based on this, the accelerator. A rotation speed control circuit for changing the voltage to control the motor at a constant speed is provided, and the rotation speed control circuit controls the reference value in the current limiting circuit when the rotation speed of the motor is equal to or less than a predetermined value to control the battery current. A motor control circuit for an electric vehicle, which is provided with an overload prevention control circuit for controlling the value to drop. 2. The overload prevention circuit includes a comparator (CP3) that generates an output when the signal indicating the rotational speed is less than or equal to a predetermined value, and an integrating circuit (R1, which delays the output signal of the comparator (CP3)). C1) and the integrating circuit (R
1, C1) outputs a control signal when the output of the current limiting circuit exceeds the delayed signal value of the current limiting circuit, and a comparator (CP4) for generating the control signal. The motor control circuit for an electric vehicle according to claim 1, wherein the motor control circuit is configured to control.