JPH10164887A - Drive control apparatus for motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a drive control apparatus by which a temperature rise is suppressed when the driving device of a motor in an overload operation. SOLUTION: On the basis of the opening of an accelerator and on the basis of the speed of rotation of a motor, a forced-operation discrimination circuit 17 discriminates whether the motor is at present in a forced operation (an overload operation) or not. A switch 16 is changed over to the side of a reference clock A14 in an ordinary operation, and a triangular-wave-carrier generation circuit 18 generates triangular waves on the basis of a high-frequency clock signal. Accordingly, a drive control signal which is outputted to a driving device (a power switching element) from a comparator 19 is normally at a high frequency. When it is discriminated by the forced-operation discrimination circuit 17 that the motor us in the forced operation, the switch 16 is changed over to a reference clock B15, and the drive control signal is at a low frequency. As a result the switching loss of the driving device (the power switching element) is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for driving and controlling an electric motor of an electric machine such as a battery forklift.

[0002]

2. Description of the Related Art A forklift generally carries a load on a fork, but may also perform a specific operation called a pushing operation.

[0003] The pushing operation is, for example, an operation of placing a load (a wooden box or the like) on a truck bed or the like by a forklift and pushing the load into the back of the bed. This means, for example, that the tip of the fork portion of the forklift is applied horizontally to the load, and the load is shifted in the horizontal direction by moving the forklift forward in this state.

[0004] At this time (depending on the shape, material, and weight of the load), the load is carried on a fork due to the frictional force between the lower surface of the load and a platform (other ground, etc.), etc. ,
Requires a large forward drive force.

[0005] Further, depending on the situation, a load which has been pushed into the middle of the loading platform in advance may be accompanied by pushing the next load.
There is also a loading method in which the plurality of loads are pushed together further. When such a plurality of loads are pushed together, a very large output is required for the driving device.

[0006] Here, there is a battery forklift using an electric motor as a driving device for running the forklift. This battery forklift is, for example, a PW
The motor output is controlled by changing the current (average current) supplied to the motor in accordance with a drive control signal from an M (Pulse Width Modulation) circuit.

When the pushing operation is performed by such a battery forklift, the number of revolutions is extremely small. On the other hand, since a large driving force is required,
The current supplied to the motor is large.

[0008]

As described above, in the conventional battery forklift, during the pushing operation, the current supplied from the drive unit to the motor in response to the drive control signal from the drive control unit (having a PWM circuit). Although the value is at the maximum rating (near the maximum rating), the rotation speed of the motor is very small (for example, several hundred rpm in some models).

On the other hand, a drive control signal for performing switching control of a switching element (power element) in the drive device is generated based on, for example, a 10 kHz clock signal.
There is a problem that the switching loss of the power element becomes large and the temperature rise of the driving device becomes very large.

An object of the present invention is to reduce the temperature rise of a driving device even when an electric machine driven by an electric motor such as a battery forklift performs an overload operation in which a large load is applied to the electric motor such as a pushing operation. It is to suppress.

[0011]

According to the present invention, there is provided a drive control device for an electric motor, comprising: an overload operation judging means for judging whether or not the electric machine is in an overload operation; And adjusting means for lowering a reference clock frequency which is a reference of a drive control signal for driving the electric motor when it is determined that the motor is in operation.

The drive control signal is for performing switching control of a power switching element for supplying electric power to the motor, and when the overload operation determining means determines that an overload operation is being performed, the adjustment is performed. The switching loss of the power switching element during the overload operation is reduced by reducing the reference clock frequency serving as the reference of the drive control signal by the means.

Thus, even when the electric machine is in an overload operation, a rise in temperature due to switching loss of the power switching element can be suppressed.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. In the following description of the embodiment, the pushing operation of the battery forklift will be described as an example of an overload state (mainly due to an external factor) of the electric machine operated by the electric motor, but the present invention is not limited to this. For example, the battery forklift may be climbing a steep slope. Alternatively, the present invention is not limited to a traveling motor, and may be, for example, a cargo handling motor that moves a fork up and down. Further, the present invention is not limited to the battery forklift, and may be another machine tool or the like operated by an electric motor, and may be any machine that abnormally overheats the driving device of the electric motor as in the pushing operation of the present embodiment. Applicable.

FIG. 1 is a block diagram showing the configuration of a drive system for running a battery forklift according to the present embodiment. In FIG. 1, a battery 1 is a DC power source serving as a power source of an electric motor for traveling, and is, for example, a large-capacity storage battery for an electric vehicle.

The power converter 2 (drive device) is composed of, for example, a plurality of power switching elements (for example, MOS FETs) and responds to switching control of a drive control signal (PWM wave) amplified and output from a driver 5 described later. ,
The electric power of the battery 1 is supplied to the electric motor 3.

That is, the power converter 2 is, for example, a current type PWM inverter (converting DC power to AC power). The electric motor 3 is an electric motor for traveling of a battery forklift driven by the power converter 2, and is, for example, a three-phase AC motor.

The rotation sensor 4 is a sensor for detecting the number of rotations of the motor of the electric motor 3, and outputs a signal indicating the number of rotations to the drive control circuit 6. The driver 5 converts a drive control signal output from the drive control circuit 6 to a level at which the power converter 2 can be driven and outputs the converted signal.

The drive control circuit 6 includes a rotation sensor 4, a current sensor 7, an accelerator potentiometer 8a, and a forward / reverse switching switch.
(Switch) The drive control signal is generated and output based on each output signal from the switch 9a.

For a detailed configuration of the drive control circuit 6,
This will be described later with reference to FIG. The current sensor 7 is a sensor unit that detects a motor current i that drives the electric motor 3 and outputs this motor current value to the drive control circuit 6.

The accelerator potentiometer 8a detects the operation state of the accelerator pedal 8 and outputs a signal (accelerator opening) indicating the operation state to the drive control circuit 6. The accelerator potentiometer 8a is, for example, a potentiometer using a variable resistor, and outputs a voltage value corresponding to a resistance value that changes according to the depression angle of the accelerator pedal 8 as the accelerator opening.

The forward / reverse switch SW (switch) 9a is a switch that is switched by operating the forward / reverse lever 9, and is turned on for forward operation and turned off for reverse operation, for example. Are input to the drive control circuit 6. Then, the forward / reverse control of the electric motor 3 is performed according to the ON / OFF signal.

FIG. 2 is a block diagram showing the configuration of the drive control circuit 6. As shown in FIG. In the figure, a current command value determination circuit 11 inputs a motor rotation speed from the rotation sensor 4, an accelerator opening from an accelerator potentiometer 8a, and an ON / OFF signal from a forward / reverse switching switch (switch) 9a. A current command value i ^* is obtained based on each of these input signal values, and this current command value i ^* is output to the difference circuit 12. The current command value i ^* is a target value of the motor current i according to a request by operating the accelerator pedal or the like.

The difference circuit 12 includes a current command value determination circuit 11
And outputs the difference current value Δi to the PI circuit 13 by taking the difference between the current command value i ^* output from the control circuit 7 and the actual motor current i detected by the current sensor 7.

The PI circuit 13 is a general current-voltage conversion circuit, and outputs a differential current value Δ
The command voltage v ^* corresponding to the value of i is output to the comparator 19.

The current command value determination circuit 11, the difference circuit 12,
And the PI circuit 13 is a configuration that has been used in the past, and thus will not be described in detail here. For example, the accelerator opening increases (the accelerator is
The current command value i ^* output from the current command value determination circuit 11 increases. As a result, the difference current value Δi increases, and the command voltage v ^* output from the PI circuit 13 increases. Therefore, the pulse width (ON) of the drive control signal output from the comparator 19 described later
Time), and the average motor current value increases. That is, the output of the electric motor 3 increases.

The reference clock A14 supplies a high-frequency clock signal and generates a clock of, for example, 10 KHz. The reference clock B15 supplies a low-frequency clock signal, and generates a clock of, for example, 2.5 KHz.

The switch 16 as an adjusting means is adapted to output one of the clock signals output from the reference clock A 14 and the reference clock B 15 to the triangular wave carrier generation circuit 18.
To be supplied. The switching of the switch 16 is performed according to the output from the pushing operation determination circuit 17. For example, when the output from the push-in operation determining circuit 17 is "H", it is switched to the reference clock B15, and when it is "L", it is switched to the reference clock A14.

The pushing operation determining circuit 17 determines the number of rotations of the motor from the rotation sensor 4 and the accelerator potentiometer 8a.
, The accelerator opening is input from the controller, and based on this, it is determined whether or not the current state of the forklift is “during pushing”. Then, for example, the above “H” or “L” is output to the switch 16 based on the result of this determination. During normal operation, the output from the push-in operation determination circuit 17 is "L". Therefore, the (high-frequency) clock signal from the reference clock 14A is supplied to the triangular wave carrier generation circuit 18.

The details of the push-in operation determining circuit 17 will be described later with reference to FIG. The triangular wave carrier generation circuit 18 is configured to output the reference clock A14, the reference clock B
A triangular wave is generated based on a clock signal from any one of Fifteen.

The comparator 19 inputs the command voltage v ^* from the PI circuit 13 to the inverting input terminal and inputs the triangular wave from the triangular wave carrier generating circuit 18 to the non-inverting input terminal, compares these signals, and controls the drive. Output a signal.

The drive control signal is a signal having a constant period according to the triangular wave, and its duty cycle (the ratio of H to L of the pulse width) changes according to the magnitude of the command voltage v ^*. is there. That is, while the voltage value of the triangular wave is lower than the value of the command voltage v ^* , the drive control signal becomes H. Therefore, as described above, when the command voltage v ^* increases, the pulse width of the “H” of the drive control signal increases, and the motor current value for the electric motor 3 increases.

In the drive system of the AC motor shown in FIGS. 1 and 2 described above, during normal operation (ie, when an operation other than an operation in which a very large load is applied to the motor such as a pushing operation is performed). , Triangular wave carrier generation circuit 18
Generates a triangular wave based on the clock signal of the reference clock A14 (high frequency).

Here, in the conventional AC motor drive system, since only the reference clock A14 is used, the frequency of the drive control signal does not change regardless of the normal operation or the pushing operation. Since the frequency of the reference clock A14 is set so as to be suitable for the control during the normal operation, the temperature rise of the power converter 2 due to the switching loss of the power switching element in the power converter 2 during the normal operation is a problem. Fits in no level. However, when the motor current is large (maximum rated value) as in the pushing operation, if the switching of the power switching element in the power converter 2 is performed at the frequency of the reference clock A14, the power converter 2 due to the switching loss is lost. The temperature rise will be very large.

In the drive system of the embodiment, the triangular wave is generated based on the clock signal of the reference clock B15 at the time of the pushing operation, for example, by the configuration of the reference clock B15, the switch 16, and the pushing operation determining circuit 17. That is, when the pressing operation determining circuit 17 determines that the pressing operation is being performed, the switch 1
6 is switched to the reference clock B15 side, and the triangular wave carrier generation circuit 18 generates a triangular wave based on the clock signal of the reference clock B15 (low frequency).

For example, in the above example, the clock signal is 10
Since the frequency is switched from KHz to 2.5 KHz, the number of times of switching of the power switching element in the power converter 2 per unit time is reduced to 1/4, and the switching loss is reduced. On the other hand, from the current command value determination circuit 11, the motor current value is determined based on, for example, a high accelerator opening (normally, the accelerator is depressed considerably during a pushing operation or the like) and a very low motor rotation speed. Since the current command value i ^* that gives the maximum (maximum rated value) is specified, the output of the electric motor 3 hardly changes.

The pressing operation determination of the pressing operation determining circuit 17 is performed by, for example, the configuration shown in FIG. FIG. 3 is a circuit block diagram illustrating an example of the configuration of the pressing operation determination circuit 17.

In the figure, the F / V converter 21
It converts the rotation speed (frequency) of the electric motor 3 detected by the rotation sensor 4 into a voltage value corresponding to the value, and is a general frequency-voltage conversion circuit. The converted voltage value is a high voltage value when the rotation speed of the electric motor 3 is high, and a low voltage value when the rotation speed is low.

The output of the F / V converter 21 is input to the inverting input terminal (-) of the comparator 22. The comparator 22 inputs a reference voltage determined in advance by the power source E and the resistors R ₁ and R ₂ to its non-inverting input terminal (+). "H" is output when the voltage is lower than the threshold. That is, when the rotation speed of the electric motor 3 becomes lower than the predetermined rotation speed, “H” is output. Here, for example, when the rotation speed is 500
The resistances R ₁ and R ₂ are set so as to output “H” when the speed becomes lower than rpm.
Is set.

The comparator 23 compares the accelerator opening from the accelerator potentiometer 8a with its non-inverting input terminal (+).
Is being entered. The accelerator potentiometer 8a is composed of a variable resistor as described above, and as the accelerator pedal angle increases, the accelerator opening (voltage value) increases. Comparator 2
The reference voltage (threshold) predetermined by the power supply E and the resistors R ₃ and R ₄ is input to the inverting input terminal (−) of No. ₃ .

The comparator 23 outputs "H" when the accelerator opening is larger than a threshold value (that is, when the accelerator pedal is depressed until the accelerator opening becomes a predetermined value or more). Here, for example, it is assumed that the accelerator opening is in a range of 0 to 5 (V), and for example, the accelerator opening is 4
It is assumed that the output is set to "H" when the output is equal to or higher than (V) (80% or higher).

The AND gate 24 outputs “H” to the switch 16 when both the comparator 22 and the comparator 23 output “H”. In response, the switch 16 switches the clock signal supplied to the triangular wave carrier generation circuit 18 to the reference clock B15 (low frequency) side.

In the pushing operation determining circuit 17 having the above structure, for example, the operator of the battery forklift has stepped on the accelerator greatly (in the above example, the accelerator opening is 4 (V)).
In the above state, when the motor rotation speed of the electric motor 3 is very small (500 rpm in the above example), it is determined that the pushing operation is being performed.

The above configuration can be applied to both forward and backward operations. This is not particularly limited to the pushing operation, but also to other overload operations such as when the battery forklift is climbing a steep slope as described above. That is, it is determined that the operation is performed such that an extremely large overload is applied to the electric motor as compared with the normal operation. From this, it can be said that the pushing operation determination circuit 17 is an overload determination circuit.

The pushing operation determining circuit 17 is not limited to the circuit configuration shown in FIG. 3, and is determined by signals output from a rotation sensor and an accelerator potentiometer (accelerator opening sensor).
Any other circuit configuration that can determine during the pressing operation may be used.

The accelerator is not limited to the pedal type.
Other structures such as a lever type may be used. Further, the types of the rotation sensor, the accelerator opening sensor, and the current sensor are not limited as long as they have the same detection function.

Further, in the above embodiment, the reference clock is set for two types of frequencies, high and low. However, the present invention is not limited to this, and another configuration for lowering the clock frequency may be used. For example, three or more types of reference clocks may be provided to perform more detailed switching control. Alternatively, the reference clock frequency may be changed steplessly.

Further, the motor is not limited to the AC type, but can be applied to other types of motors such as a DC type which can perform PWM control.

[0049]

As described in detail above, according to the motor drive control device of the present invention, an overload operation (for example, a pushing operation of a battery forklift, etc.) in which a large load is applied to the motor as compared with a normal operation. Is determined, the reference clock frequency serving as the reference of the drive control signal is reduced (for example, the frequency is switched from a high frequency (during normal operation) to a low frequency) to supply the motor current to the electric motor. The switching loss of the power switching element can be reduced.

As a result, even when a large motor current flows through the power switching element, for example, during a pushing operation, an abnormal rise in temperature due to switching loss can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a driving system for traveling of a battery forklift.

FIG. 2 is a configuration block diagram of a control circuit shown in FIG. 1;

FIG. 3 is a block diagram illustrating a configuration of a pressing operation determination circuit illustrated in FIG. 2;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 battery 2 power converter 3 motor 4 rotation sensor 5 driver 6 drive control circuit 7 current sensor 8 accelerator pedal 8a accelerator potentiometer 9 forward / reverse lever 9a forward / reverse switching SW 11 current command value determination circuit 12 difference circuit 13 PI circuit 14 reference clock A (high frequency) 15 Reference clock B (low frequency) 16 Switch 17 Push-in operation discriminating circuit 18 Triangular wave carrier generating circuit 19 Comparator (PWM circuit) 21 F / V converter 22 Comparator 23 Comparator 24 AND gate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02P 7/63 302 H02P 7/63 302M 302S

Claims (6)

[Claims] 1. An apparatus for controlling driving of an electric motor of an electric machine, comprising: an overload operation judging means for judging whether or not the electric machine is in an overload operation; An adjusting means for lowering a reference clock frequency serving as a reference of a drive control signal for driving and controlling the electric motor when it is determined that the electric motor is present, a driving control apparatus for the electric motor. 2. The drive control device for an electric motor according to claim 1, wherein the electric machine is a battery forklift. 3. The overload operation determining means determines that an overload operation is being performed when the rotation speed of the electric motor is equal to or less than a predetermined rotation speed and the accelerator opening is equal to or more than a predetermined value. The drive control device for an electric motor according to claim 1. 4. The power control element according to claim 1, wherein the drive control signal controls switching of a power switching element for supplying electric power to the electric motor. 4. The drive control device for an electric motor according to claim 1, wherein the switching loss of the motor is reduced. 5. The apparatus according to claim 1, wherein said adjusting means switches from a high-frequency reference clock to a low-frequency reference clock in order to reduce the reference clock frequency.
The drive control device for an electric motor according to any one of claims 1 to 4. 6. A method for controlling driving of an electric motor of an electric machine, comprising: determining whether or not the electric machine is in an overload operation based on a rotation speed of the electric motor and an accelerator opening; A drive control method for an electric motor, characterized in that when it is determined that there is, a reference clock frequency, which is a reference of a drive control signal for driving and controlling the electric motor, is reduced.