JPH10271609A - Method for controlling induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the motor efficiency of an induction motor which generates torque by the electric power supplied from a battery. SOLUTION: A controlling part 1 calculates and outputs a command value for making an induction motor 7 generate torque corresponding to the angle of a pushed accelerator 2 based on the state of a battery transmitted from a battery-state detecting part 10. This command value is used as a data for specifying the amplitude and frequency of an alternating current to be supplied to the induction motor 7. A power part 5 supplies the induction motor 7 with a motor current IM from a battery 6 based on the command value. Then, the induction motor 7 generates torque by the motor current IM.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for an induction motor supplied with electric power from a battery.

[0002]

2. Description of the Related Art An induction motor is known as one of electric motors that generate torque by supplying electric power. The induction motor includes a stator and a rotor, and generates an electromotive force by electromagnetic induction in a conductor (coil) of the rotor by a rotating magnetic field generated by the stator. This causes a coil current to flow through the rotor. Then, the rotor is rotated by an electromagnetic force between the coil current and the rotating magnetic field. Note that the rotating magnetic field is generally generated by connecting a three-phase AC power supply to a winding constituting the stator.

FIG. 7 is a diagram showing an example of a conventional system for controlling an induction motor. Here, an induction motor is used as a running motor of an electric vehicle, and a battery (DC power supply) is used.
An example is shown in which electric power supplied from an inverter is converted into alternating current by an inverter, and the traveling motor is driven by the alternating current.

In FIG. 7, when a CPU 101 detects a depression angle of an accelerator 102, an induction motor 1 generates torque corresponding to the depression angle.
06 is controlled. The current supplied to the induction motor 106 is obtained by converting the electric power supplied from the battery 105 into AC by the driver 104. Further, the memory 103 stores control parameters for generating a motor torque corresponding to the detected stepping angle according to the detected stepping angle of the accelerator. As the control parameters, a motor current to be supplied to the induction motor 106 and a slip s are stored. Then, the CPU 101 drives the induction motor 106 according to the control parameters retrieved from the memory 103 according to the accelerator pedal depression angle.

[0005]

In the above-described configuration, the battery 105 is used as the power supply of the induction motor 106. In general, as shown in FIG. 8, the output voltage of the battery increases as its discharge amount increases. descend. However,
On the other hand, the controller 100 is required to generate a predetermined torque with respect to the detected accelerator depression angle even when the battery voltage decreases. In order to satisfy this demand, it is assumed that the remaining amount of the battery 105 decreases, that is, the battery voltage decreases,
It must be possible to generate a torque corresponding to the maximum accelerator pedal depression angle even at the reduced battery voltage.

For this reason, in the conventional control method, a control parameter is set such that a torque corresponding to the maximum accelerator pedal depression angle can be generated even when the output voltage of the battery 105 is reduced, and the induction is performed according to the control parameter. The motor 106 was being driven. That is, for example, assuming the voltage V1 when the battery 105 is discharged by 80% as the battery voltage, the motor current and the slip s that can generate a torque corresponding to the maximum accelerator pedal depression angle in that state are stored in the memory. 103
Was set to.

However, when the battery 105 is almost fully charged, the battery voltage V0 is higher than the voltage (voltage V1) used as a reference for setting control parameters, as shown in FIG. Therefore, when the induction motor 105 is driven according to the control parameters stored in the memory 103,
The motor efficiency was poor, and the power consumption was unnecessarily large. As a result, the operating time of the battery is shortened.

As described above, in the conventional control method, a certain
The control parameters for driving the induction motor based on the two battery states are set, and even if the battery state changes, the induction motor is driven in accordance with the control parameters. was there.

An object of the present invention is to increase the efficiency of an induction motor that generates torque by electric power supplied from a battery.

[0010]

SUMMARY OF THE INVENTION The present invention is based on the premise that a system for controlling an induction motor that generates torque by electric power supplied from a battery is provided. And drives the induction motor based on the parameters. The parameters are, for example, the motor current supplied to the induction motor and the slip of the induction motor. The state of the battery is, for example, the remaining amount of the battery or the output voltage of the battery.

[0011] The motor efficiency depends on the setting of the above parameters. In the configuration of the present invention, the parameters are controlled according to the battery state so that the motor efficiency is increased. The present invention may be configured to include the following units. The torque instruction detecting means detects a torque instruction signal for instructing a torque generated by the induction motor. The battery state detecting means detects a state of the battery. The control means generates a control signal for causing the induction motor to generate the torque indicated by the torque instruction signal based on the torque instruction signal detected by the torque instruction detection means and the battery state detected by the battery state detection means. I do. The drive unit drives the induction motor according to a control signal generated by the control unit. The rotation speed detecting means detects the rotation speed of the induction motor.

The control means generates the control signal using the motor current supplied to the induction motor and the slip of the induction motor as parameters. The control means generates the control signal based on the rotation speed of the induction motor detected by the rotation speed detection means. The frequency of the alternating current supplied to the induction motor is determined from the slip as a parameter, and the amplitude of the alternating current is determined from the motor current as the parameter.

[0013]

Embodiments of the present invention will be described with reference to the drawings. In the following, an induction motor is used as a drive motor for an electric vehicle, and a battery (DC power supply) is used.
An example is shown in which electric power supplied from an inverter is converted into alternating current by an inverter, and the traveling motor is driven by the alternating current. Also, a configuration for controlling an induction motor by a vector control method will be described as an embodiment.

FIG. 1 is a configuration diagram of a system according to the present embodiment. In the system shown in the figure, the control unit 1 as a torque instruction detecting unit and a control unit transmits a torque corresponding to a stepping angle of the accelerator 2 as a torque instruction signal to the induction motor 7.
A command value to be generated in the power unit 5 is obtained and output, and the power unit 5
Supplies the current based on the command value from the battery 6 to the induction motor 7, thereby driving the induction motor 7.
In the motor drive control, the control unit 1 obtains the command value based on the battery state notified from the battery state detection unit 10. Hereinafter, each block will be described.

The control unit 1 detects the stepping angle of the accelerator 2 and detects the rotation speed of the induction motor 7 based on the output of the rotation sensor 9. Then, based on these detected values, a torque corresponding to the depression angle of the accelerator 2 is supplied to the induction motor 7.
A current command value as a torque command signal to be generated is calculated and output to the current control circuit 3. The current command value is a signal that indicates the frequency and amplitude of an alternating current (motor current IM) supplied to the induction motor 7. Note that the control unit 1
Battery 6 detected by battery state detection unit 10
Status (for example, battery voltage, battery level, etc.)
The current command value is obtained based on the above. The method of obtaining the current command value will be described later.

The accelerator 2 inputs a driver's instruction, that is, a torque required for the induction motor 7 to the control unit 1. The accelerator 2 includes, for example, a sensor including a variable resistor whose resistance value changes according to the step angle, and the control unit 1 receives an output of the sensor.

The current control circuit 3 receives the output of the current sensor 8 as a feedback signal, and adjusts the motor current IM supplied to the induction motor 7 to the current indicated by the current command value received from the control unit 1. Outputs pulse command signal. The PWM (pulse width modulation) signal generation circuit 4 outputs a pulse signal based on a pulse command signal.

The power section 5 supplies a motor current IM from the battery 6 to the induction motor 7 based on the pulse signal received from the PWM signal generation circuit 4. The motor current IM is
For example, three-phase alternating current. The battery 6 is a secondary battery that can be repeatedly charged, and is, for example, a lead-based, nickel-metal hydride-based, or lithium-based storage battery. The battery state detection unit 10 detects a battery state such as an output voltage of the battery 6 or a remaining battery level and notifies the control unit 1 of the detected state. The method of detecting the remaining battery level is a known technique, for example, a method of estimating from the battery voltage, a method of integrating the discharged current, and the like. Alternatively, an existing capacity meter may be used.

The induction motor 7 is used here as a running motor, and is driven by a motor current IM to generate a torque. The current sensor 8 directly or indirectly detects the motor current IM and outputs the detected value to the current control circuit 3. A rotation sensor 9 as a rotation speed detecting means detects the rotation speed of the induction motor 7 and outputs the rotation speed to the control unit 1.

FIG. 2A is an equivalent circuit of the induction motor. FIG. 2B is a vector diagram of the induction motor. When the induction motor is driven, a motor current IM (primary current) is supplied. When the motor current IM is supplied, the exciting current If flows to the stator side, and the torque current It flows to the rotor by electromagnetic induction. That is, the motor current IM is distributed to the exciting current If and the torque current It. The distribution ratio between the exciting current If and the torque current It is determined by the slip s of the induction motor. Slip s
Means that the rotation speed of the rotating magnetic field is N0 and the rotation speed of the rotor is N
Then, s = (N0 -N) / N0. In the system shown in FIG. 1, the rotation speed N0 of the rotating magnetic field is the reciprocal of the frequency specified by the current command value, and the rotation speed N of the rotor is the actual speed of the induction motor 7 detected by the rotation sensor 9. Is the number of rotations.

The torque of the induction motor is proportional to the product of the generated magnetic flux and the torque current It, and the magnetic flux is proportional to the exciting current If. Therefore, the torque of the induction motor is proportional to the product of the exciting current If and the torque current It. That is, the torque of the induction motor is proportional to the area of the rectangle shown in FIG.

The area of the rectangle is determined using the ratio of the length of the diagonal line (the magnitude of the motor current IM) to the length of the two sides constituting the rectangle (the distribution ratio of the excitation current If and the torque current It). Can be defined. Here, the ratio of the lengths of the two sides constituting the rectangle, that is, the distribution ratio between the exciting current If and the torque current It can be controlled by changing the slip s as described above. Therefore, if the motor current IM and the slip s are determined, the rectangular area shown in FIG. 2B is determined. That is, the torque of the induction motor can be controlled using the motor current IM and the slip s as parameters.

As described above, by controlling the motor current IM and the slip s (frequency and phase), the motor current IM is distributed inside the induction motor to the exciting current If and the torque current It according to the set values, and the desired value. To get the torque.

FIG. 3 is a block diagram of the control unit 1. The control unit 1 includes a CPU 11 and a memory 12. The memory 12 includes a RAM area and a ROM area, and stores control software 13 and a table 14. The control software 13 is a software program describing the control processing of the present embodiment, and is executed by the CPU 11. Table 14 stores control parameters for obtaining high motor efficiency when battery 6 is fully charged, and control parameters for obtaining high motor efficiency when battery 6 is 80% discharged. . The data stored for each battery state is the motor current selected so that the motor efficiency (the ratio of the mechanical output of the motor to the power input to the motor) is as high as possible when generating the torque corresponding to the accelerator pedal depression angle. I
M and slip s. These values are obtained, for example, by experiment or simulation. The motor current IM and the slip s are stored using the accelerator pedal depression angle as a key, and the CPU 11 accesses the table 14 using the accelerator pedal depression angle as a key to access the motor current IM.
And the slip s are taken out.

FIG. 4 is a diagram showing an operation example when the motor is driven according to the data stored in the table 14. This figure shows that the operation state for obtaining the optimum motor efficiency is different when the battery state is different.

FIG. 5 is a flowchart for explaining the processing of the control unit 1. Each function of this flowchart is described in a software program stored in the memory 12 as the control software 13, and the CPU 11 executes the program. The processing of this flowchart is
It is executed at predetermined intervals (for example, every 10 ms).

In step S1, the depression angle of the accelerator 2 is detected. In step S2, the battery state detection unit 10
To detect the battery state. Here, the remaining battery level is detected. In step S3, step S1
The table 14 is accessed by using the accelerator pedal depression angle detected in step 4 as a key to take out control parameters. That is, the motor current IM and the slip s corresponding to the detected accelerator depression angle are extracted. At this time, the data at full charge and 8
Both data at 0% discharge are taken out.

In step S4, the motor current IM and slip s corresponding to the battery state detected in step S2 are calculated. Here, the 2 extracted in step S3
The optimum motor current IM and slip s at the current remaining battery level are calculated based on each motor current IM and slip s in one battery state. For example, it is approximated that the optimum motor current IM and the slip s linearly change with respect to the change in the remaining battery level. In this case, for example, if the battery 6 is in the 40% discharged state, the average value of the motor current IM and the slip s in the fully charged state and the motor current IM and the slip s in the 80% discharged state are calculated.

In step S5, the rotation speed N of the induction motor 7 is detected from the output of the rotation sensor 9. Subsequently, in step S6, the rotation speed N0 of the rotating magnetic field is calculated from the slip s calculated in step S4 and the rotation speed N detected in step S5. That is, since the definition of the slip s is s = (N0 -N) / N0, the rotation speed N0 of the rotating magnetic field is obtained by calculating N0 = N / (1-s).

In step S7, a current command value for designating an alternating current to be supplied to the induction motor 7 is output. That is, a signal representing the amplitude corresponding to the motor current IM calculated in step S4 and a signal representing the frequency corresponding to the rotation speed N0 of the rotating magnetic field calculated in step S6 are output.

In steps S1 to S7, the current command value for generating the torque corresponding to the accelerator pedal depression angle is corrected and output so as to optimize the motor efficiency according to the battery state at that moment.

FIG. 6 is an example of a vector diagram of the induction motor control according to the method of the present embodiment. (a) to (c) are vector diagrams when the battery 6 is fully charged, and (d) to (f)
Is a vector diagram when the battery 6 is in the 80% discharged state. (A) and (d) are vector diagrams when the accelerator pedal depression angle is 30%, (b) and (d)
(e) is a vector diagram when the accelerator pedal angle is 60%, and (c) and (f) are vector diagrams when the accelerator pedal angle is the maximum.

By the way, considering the driving operability of the electric vehicle, it is not desirable that the relationship between the accelerator pedal depression angle and the motor torque changes with the change in the remaining amount of the battery 6.
That is, the electric vehicle should be designed to always output the same motor torque for a given accelerator pedal depression angle even when the remaining amount of the battery 6 changes. Therefore, in the present embodiment, in order to satisfy the above conditions, (a)
And (d), (b) and (e), and (c) and (f) determine the motor current IM and the slip s such that the areas of the respective rectangles are equal to each other.

When the accelerator pedal angle changes in a certain battery state, as shown in (a) to (c) or (d) to (f), the torque current It is fixed while the exciting current If is fixed.
Is changed, the torque of the induction motor 7 is changed.

Referring to FIG. 6, the present embodiment will be compared with the conventional method. In the present embodiment, the control parameters (motor current IM and slip s) are changed according to the battery state, whereas in the conventional method, the control parameters set in one battery state are changed over all battery states. I was using it.

In the conventional system, for example, as described above, a battery voltage at the time when the battery is discharged by 80% is assumed, and a control parameter that can generate a torque corresponding to the maximum accelerator pedal depression angle in that state is assumed. Was set. That is, in the conventional method, the induction motor is always driven in the state shown in FIGS. 6D to 6F regardless of the battery state. Therefore, when the battery is almost fully charged, the voltage (V0 in FIG. 8) higher than the voltage at the time of 80% discharge (V1 in FIG. 8) is output, but the high voltage is effectively used. It wasn't done and wasting power.

On the other hand, in the present embodiment, when the remaining battery power is high, the exciting current If is increased to improve the motor efficiency. Here, the motor efficiency is a ratio of the mechanical output (torque) of the induction motor 7 to the input power to the induction motor 7, and therefore, in the vector diagram shown in FIG. If the motor current IM corresponding to the length can be reduced, the motor efficiency increases. For example, comparing the case where the accelerator pedal depression angle is maximum in FIG. 6, the areas of the rectangles shown in (c) and (f) are the same, but the motor current IM in (c) is the same as the motor current in (f). It can be seen that the current is smaller than the current IM. For this reason, the power consumption of the induction motor decreases and the operating time of the battery increases.

In the above-described embodiment, a method has been described in which control parameters are set in two battery states and a parameter in an arbitrary battery state is calculated from those parameters. However, the present invention is limited to this configuration. It is not something to be done. That is, for example, an optimal control parameter is set for each of a large number of battery states, a battery state close to the current battery state is selected from the large number of battery states, and the selected state is determined. The induction motor may be driven using the set control parameters. Further, in the above embodiment, the rotation sensor is used as the rotation number detecting means. However, the rotation number detecting means is not limited to this. For example, the rotation number is estimated from other parameters such as voltage without using the sensor. Alternatively, the configuration may be such that detection is performed.

Further, the present invention is not limited to the case where the induction motor is used as a traveling motor of an electric vehicle, but may be applied to all configurations for driving the induction motor based on a torque instruction signal for instructing a torque generated by the induction motor. Applied.

[0040]

In the drive control of the induction motor to which the electric power is supplied from the battery, the control parameters of the induction motor are changed according to the state of the battery, so that the motor can be always driven efficiently and the power consumption is reduced. As a result, the operating time of the battery can be extended.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a system according to an embodiment.

2A is a diagram showing an equivalent circuit of an induction motor, and FIG. 2B is a vector diagram thereof.

FIG. 3 is a configuration diagram of a control unit.

FIG. 4 is a diagram illustrating an operation when a motor is driven according to data stored in a table.

FIG. 5 is a flowchart illustrating processing of a control unit.

FIG. 6 is an example of a vector diagram of induction motor control according to the method of the present embodiment.

FIG. 7 is a diagram showing an example of a conventional method for controlling an induction motor.

FIG. 8 is a diagram showing a relationship between a battery discharge amount and a battery voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control part 2 Accelerator 3 Current control circuit 4 PWM signal generation circuit 5 Power part 6 Battery 7 Induction motor (running motor) 8 Current sensor 9 Rotation sensor 10 Battery state detection part 11 CPU 12 Memory 13 Control software 14 Table

Claims (5)

[Claims] 1. A method for controlling an induction motor that generates torque by electric power supplied from a battery, wherein the parameter is changed while changing a parameter for generating a predetermined torque in the induction motor according to a state of the battery. The control method of the induction motor that drives the induction motor based on the control. 2. The control system for an induction motor according to claim 1, wherein the parameters are a motor current supplied to the induction motor and a slip of the induction motor. 3. The induction motor control method according to claim 1, wherein the state of the battery is a remaining amount of the battery or an output voltage of the battery. 4. A method for controlling an induction motor that generates torque by electric power supplied from a battery, comprising: a torque instruction detection unit that detects a torque instruction signal that indicates a torque to be generated by the induction motor; And a torque indicated by the torque instruction signal to the induction motor based on the torque instruction signal detected by the torque instruction detection means and the battery state detected by the battery state detection means. Control means for generating a control signal for generating the control signal; and driving means for driving the induction motor in accordance with the control signal generated by the control means. 5. The motor control apparatus according to claim 1, further comprising: a rotation speed detection unit configured to detect a rotation speed of the induction motor, wherein the control unit generates the control signal using a motor current supplied to the induction motor and a slip of the induction motor as parameters. The frequency of the AC current supplied to the induction motor is determined from the rotation speed of the induction motor detected by the rotation speed detection means and the slip as the parameter, and the AC current is determined from the motor current as the parameter. 5. The control method of an induction motor according to claim 4, wherein the amplitude of the current is determined.