JPH07106002B2 - Control method for induction motor for electric vehicle - Google Patents

Description

The present invention relates to a method for controlling an induction motor for an electric vehicle, and more particularly to an optimum control method for controlling a primary current applied to the induction motor to obtain a target output torque. It is a thing.

[Prior Art] Electric vehicles have been studied as pollution-free vehicles that do not generate harmful exhaust gas, and some have already reached the stage of practical application.

In the early days, a DC motor that was easy to control was used as a drive source for electric vehicles, but this DC motor is troublesome for maintenance of brushes and other parts. Induction motors have been used.

As is well known, unlike ordinary industrial motors, the motors used in electric vehicles are torque controlled, and induction motors are controlled by vector control or slip frequency control in order to perform the necessary torque control and stabilize the steering performance of the vehicle. Controlled.

[Problems to be Solved by the Invention] As is well known, the output torque of an induction motor is proportional to the product of the motor magnetic flux and the torque current, and in order to obtain the required torque, either of the motor magnetic flux and the torque current is used. It may be changed and the required primary current may be given to the induction motor.

However, in the conventional device, the control is performed in the constant magnetic flux region, and the output torque is changed only by changing the torque current.

According to such a conventional control method, the control process can be simplified, but on the other hand, there is a problem that the motor loss cannot always be reduced in response to the torque that fluctuates over a wide range.

That is, the motor loss of the induction motor has both a magnetic flux loss due to the motor magnetic flux and a torque current loss due to the torque current.These two losses depend on the set motor magnetic flux and torque current, respectively. When it is kept constant, there is a problem that the loss remarkably increases depending on the output torque of the induction motor.

In particular, in the case of control in which the motor magnetic flux is constant, normally, the constant magnetic flux is set as a region in which the motor magnetic flux is fixed to the maximum value, and it is impossible to always obtain optimum efficiency in a very wide range of output torque. Is.

Such an increase in motor loss increases the current consumption of the electric vehicle, reduces the distance that can be traveled with a limited battery capacity, and is a major impediment to the development of the electric vehicle.

The present invention has been made in view of the above-described conventional problems, and its object is to always secure a target torque that greatly fluctuates,
An object of the present invention is to provide an optimum control method for minimizing the total motor loss of both magnetic flux loss and torque current loss.

[Means for Solving the Problems] In order to achieve the above object, the present invention adjusts both the motor magnetic flux and the torque current to control the primary current, unlike the conventional motor magnetic flux constant control. First, the optimum motor magnetic flux that minimizes the total motor loss is calculated by the required target torque and the motor rotation speed, and then the transitional motor magnetic flux in which the change delay of the motor magnetic flux with respect to the motor magnetic flux command due to the primary current does not exceed a predetermined value. The command value is calculated stepwise, and the compensating torque current required to obtain the target torque is calculated from the motor magnetic flux / torque current characteristic data corresponding to each stepwise calculated transient motor magnetic flux. During the adjustment transient until the magnetic flux is obtained, the primary current command determined from the magnetizing current that obtains the transient motor magnetic flux that is calculated stepwise and the compensation torque current Is supplied to the induction motor, and after the transient motor magnetic flux reaches the optimum motor magnetic flux,
A primary current command that minimizes the motor loss determined from the magnetizing current that obtains the optimum motor magnetic flux and the optimum torque current calculated according to the target torque and the optimum motor magnetic flux based on the motor magnetic flux / torque current characteristics It is characterized by supplying to.

[Operation] Therefore, according to the present invention, the target torque is always obtained both during the transition of the adjustment of the motor magnetic flux until the optimum motor magnetic flux is obtained and after the adjustment, and the motor loss is minimized after the adjustment. The primary current can be supplied to the induction motor, which results in efficient current consumption in the entire torque range and frequency range, resulting in a significantly increased mileage of the electric vehicle.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows an ideal vector diagram in an induction motor, in which the motor magnetic flux Φ of the induction motor is generated by the magnetizing current I ₀ on the vertical axis, and the motor magnetic flux Φ is generated by the torque current I _{T on the} horizontal axis. A torque T can be generated in the motor together with Φ. Therefore, the magnetizing current I ₀ is applied to the induction motor.
The primary current I ₁ that is the vector sum of the torque current I _T is supplied.

Therefore, in the present invention, unlike the conventional case, the motor magnetic flux Φ
Even if the torque changes, the torque current I _T
By setting, it becomes possible to obtain the required target torque T ^* .

From this, it is understood that the primary current I ₁ can be arbitrarily selected such that the total loss of the individual losses determined by the motor magnetic flux Φ and the torque current I _T is minimized.

Further, in FIG. 3, the constant torque line shows an ideal constant torque characteristic ignoring the phase shift due to the resistance component and the inductance component of the motor coil. Causes a change delay with respect to the torque current.

Therefore, during the transition until the motor magnetic flux becomes the optimum motor magnetic flux, the motor output torque is the target torque T ^*.
Has not reached.

In the present invention, based on such a principle, first, the optimum motor magnetic flux Φ ^* which is the minimum motor loss for obtaining the required target torque T ^* is obtained, and then the magnetizing current for obtaining the optimum motor magnetic flux Φ ^*. In consideration of the change delay of the motor magnetic flux that occurs when adjusting the motor magnetic flux, the transient motor magnetic flux command value is calculated stepwise so that the change delay does not exceed a predetermined value, and the transient motor is calculated stepwise. The compensating torque current I _q ′, which is the torque current value required to obtain the target torque T ^* , is calculated according to the magnetic flux Φ ^* _t, and during the adjustment transition until the optimum motor magnetic flux is obtained, the motor magnetic flux Φ A primary current I ₁ determined from both the magnetizing current for obtaining the transient motor magnetic flux Φ ^* _t and the compensating torque current I _q ′, which is calculated stepwise according to the increase, is supplied to the induction motor, and the transient current after adjustment is adjusted. Motor magnetic flux Φ ^* _{After t} has reached the optimum motor flux [Phi ^* is determined from the optimum torque current I _T ^* both corresponding to [Phi ^* of the magnetizing current and the target torque T ^* and the optimum motor flux for optimum motor flux [Phi ^* The primary current I ₁ is supplied to the induction motor.

Fig. 4 shows the magnetic flux / loss characteristics for obtaining the total minimum motor loss of the induction motor. The horizontal axis shows the motor magnetic flux Φ and the vertical axis shows the total motor loss caused by both the motor magnetic flux and the torque current. η is shown.

In FIG. 4, the number of revolutions of the induction motor is kept constant, and the three characteristics have the output torque of the motor as a parameter, and the characteristics of large, medium, and small motor output torques are shown in the figure. .

Therefore, from FIG. 4, it is possible to know the motor loss minimum region shaded in the figure by connecting the regions that are the bottoms of the respective characteristics. From this figure, it is understood that as the motor output torque becomes smaller, the motor loss tends to become the minimum when the motor magnetic flux is small. Of course, FIG. 4 shows the characteristics at an arbitrarily determined constant rotation speed, and such characteristics can be obtained for all the motor rotation speeds required for the electric vehicle.

FIG. 5 is a diagram showing the magnetic flux / loss characteristics described in FIG. 4 on the map showing data that minimizes the total motor loss according to each change in the motor rotation speed N. In order to obtain the above, it becomes clear from the current motor speed N which value should be set for the motor magnetic flux Φ with the minimum loss.

Such magnetic flux / loss characteristic data is of course different for each induction motor or electric vehicle to be mounted, and these data can be determined in advance by either experiment or calculation for a specific type of electric vehicle. The data can be incorporated into a circuit for controlling the motor as ROM or other stored information so that it can be read out arbitrarily.

Then, if the optimum motor flux [Phi ^* is determined as described above, it is possible to obtain the optimum torque current I _T ^* based on the constant-torque characteristic of FIG. 3 described above, the torque current I _T ^* of The decision can also be easily derived from the predetermined data and such data can also be recorded on the ROM of the circuit.

FIG. 6 shows an example of a map for obtaining the predetermined torque current I _T, and the motor torque current I _T obtained according to the motor magnetic flux Φ and the motor output torque T is displayed on the map as shown. When the motor output torque is constant, the motor torque current I _T theoretically has a value that is inversely proportional to the motor magnetic flux Φ (see FIG. 3), but in reality it needs to be corrected because it is applied to the actual machine. FIG. 6 shows the values obtained as a map. Such motor torque current data can also be arbitrarily read and recorded on the ROM of the circuit as described above.

FIG. 1 shows a flow chart when the above-described control method according to the present invention is used for actual induction motor control for an electric vehicle, and a control circuit for executing the flow chart of FIG. 1 is shown in FIG. Has been done.

In FIG. 2, an induction motor which is a drive source of an electric vehicle
Reference numeral 10 is inverter-controlled, and vector control is used to perform the inverter control.

The torque calculation device 12 outputs a required target torque T ^* according to the traveling command and the traveling condition of the vehicle, and this target torque is sent to the efficiency optimizing circuit 14 so that the characteristic motor magnetic flux and torque current of the present invention can be obtained. Both operations are performed. Then, the compensation torque I _q ′ is calculated so that the target torque T ^* is always obtained according to the optimum motor magnetic flux Φ ^* thus obtained and each transient motor magnetic flux Φ ^* _t during the adjustment transient of the motor magnetic flux. Is supplied to the vector operation circuit 16 for vector control, and its output is supplied to the inverter main circuit 20 by the PWM control circuit 18, and the primary current of the induction motor 10 is controlled.

The current of the induction motor 10 is supplied from the battery 22 via the inverter main circuit 20.

Further, the voltage of the battery 22 is detected by the voltage detection circuit 24, the current supplied from the inverter main circuit 20 to the induction motor 10 is detected by the current detection circuit 26, and the rotation speed of the induction motor 10 is determined by the pulse generator 28. The detected signals are respectively supplied to desired arithmetic units and control circuits.

When the control circuit is initialized in FIG. 1, motor control according to the present invention is executed, and various data are read in step 101.

The read data is a forward / reverse switch, an accelerator sensor,
The torque calculation device 12 includes both traveling commands given from the accelerator switch, the brake sensor, and the brake switch and traveling conditions including the motor temperature, the inverter temperature, the motor rotation speed, the battery temperature, and the battery voltage. A required target torque T ^* is calculated based on the conditions (steps 102 and 103).

In the embodiment, step 103 shows a correcting action by the battery temperature or the inverter temperature, and when the temperature rises, the required torque normally obtained in step 102 is subtracted by a predetermined amount to determine the target torque T ^* .

The setting of the target torque in the motor running command and the running condition is calculated from the characteristic data set for each electric vehicle as in the conventional case, and FIG. 7 shows an example of such characteristic data.

In FIG. 7, the horizontal axis indicates the motor rotation speed N, the positive region indicates normal rotation, and the negative region indicates reverse rotation. The vertical axis indicates the motor output torque T.

When the electric vehicle is currently stopped, the vehicle is at the position indicated by the symbol a. When the vehicle moves forward in this state, the accelerator is opened, and the motor output torque sharply increases toward b until the characteristic of 100% accelerator is reached. . When the motor output torque is generated, the electric vehicle starts, and as indicated by a thick solid line, the motor rotation speed N sequentially increases, and the motor output torque also gradually decreases toward d at a constant motor rotation speed, that is, the position c. When the accelerator is returned from d, the motor output torque T also decreases to e while maintaining a constant motor rotation speed N, and the motor rotation speed N increases toward f at this accelerator opening degree.

When the vehicle is stopped from f, the accelerator is returned and the brake is depressed, the motor output torque T shifts to the negative region, and the motor output torque T is held at g determined by the brake depressed state. This state is the regenerative state. Is shown. As the brake pedal is stepped on, the motor speed N gradually decreases,
The vehicle stops at h and returns to the original position a again.

The characteristics shown in FIG. 7 are determined in advance according to the model of each electric vehicle, and the characteristic data is written in the ROM or the like of the torque calculation device 12 shown in FIG. Also, the target torque T ^* is appropriately read according to the traveling condition.

The target torque T ^* is the motor rotation speed output from the pulse generator 28, and in the embodiment, the motor frequency fm
At the same time, in the efficiency optimizing circuit 14, the transient motor magnetic flux command value Φ ^* _t for increasing the motor magnetic flux stepwise to the optimum motor magnetic flux Φ ^* and the target torque T ^* corresponding to this transient motor magnetic flux are always obtained. Compensation torque current
_Is converted to I _q ′. This calculation is performed by steps 104 to 1 in FIG.
It will take place at 06. First, the optimum motor flux Φ that minimizes the overall motor losses based on the flux / loss characteristics data shown in the fourth or fifth the previously described figures from step 104, the target torque T ^* and motor rotation speed N (fm) ^* Is required.

Then, in step 105, the actual change of the motor magnetic flux with respect to the motor magnetic flux command is taken into consideration in consideration of the change delay of the motor magnetic flux that occurs when the magnetizing current for supplying the obtained optimum motor magnetic flux Φ ^* is supplied. The transient motor magnetic flux command value is calculated stepwise so that the delay does not exceed the predetermined value.

The transient motor magnetic flux Φ ^* _t is a predetermined arithmetic expression according to the difference between the optimum motor magnetic flux Φ ^* and the current motor magnetic flux Φ ^* _t-1 ,
For example, Φ ^* _t = Φ ^* _t-1 + K (Φ ^* −Φ ^* _t-1 ) (1)

The transient term constant K for obtaining the transient motor magnetic flux Φ ^* _t
Is determined from the circuit time constant of the induction motor, and is mainly determined from the resistance component and the induct component of the coil.

Therefore, when the time constant of the induction motor is small, that is, when the transient delay in increasing the motor magnetic flux is small, the constant K
Is set to a large value, and for a motor having a large time constant of the induction motor, that is, a large magnetic flux rising delay, the constant diameter is set small to slowly control the transient increase in the magnetic flux of the motor. Further, in step 105, when the difference between the optimum motor magnetic flux Φ ^* and the current motor magnetic flux Φ ^* _t-1 is less than or equal to a predetermined value, the calculation by the equation (1) is stopped and the optimum motor magnetic flux Φ ^* is commanded. Is controlled.

Next, at step 106, the compensating torque current I _q ′ required to obtain the target torque T ^* is obtained from the obtained transient motor magnetic flux Φ ^* _{t at} each stage based on the data of FIG. 3 or FIG. To be

That is, the compensation torque current I _q ′ is larger than the optimum torque current I _T ^* , and the motor magnetic flux Φ is the optimum motor magnetic flux Φ.
At the time of a transient rising to ^*, it decreases as the transient motor magnetic flux Φ ^* _t increases, and becomes the optimum torque current I _T ^* when the transient motor magnetic flux Φ ^* _t reaches the optimum motor magnetic flux Φ ^* .

The calculation of the above steps 104 to 106 is constantly repeated in the efficiency optimization circuit 14, for example, every few msec. Therefore, even when the motor magnetic flux reaches the optimum motor magnetic flux Φ ^* , the motor magnetic flux command is issued. The actual motor magnetic flux without change delay following the value can be obtained and the efficiency optimization circuit
Optimal in 14 motor flux [Phi ^* target torque determined corresponding to the transient motor flux [Phi ^* _t that increases stepwise until T ^*
The compensating torque current I _q ′ required to obtain is always output.
Therefore, the torque current I _q ′ also decreases stepwise and finally changes to the optimum torque current I _t ^* .

When the transient motor magnetic flux Φ ^* _t and the compensation torque current I _q ′ are determined as described above, next, in the present embodiment, the calculation of the motor voltage V ₁ and the motor primary frequency f ₁ is performed by vector calculation. Performed by circuit 16 (step 10
8).

A motor frequency fm given from the pulse generator 28, a motor current I ₁ detected from the current detection circuit 26, and a battery voltage V ₀ detected from the voltage detection circuit 24 are input to the vector operation circuit 16, and these are A desired vector operation is performed by the detection signal of the above, the given transient motor magnetic flux Φ ^* _t and the compensation torque current I _q ′. The result of the vector operation is supplied to the PWM control circuit 18 as the motor voltage V ₁ , and the slip frequency Fs is added to the motor frequency fm to be supplied to the PWM control circuit 18 as the motor primary frequency f ₁ .

The PWM control circuit 18 supplies a pulse signal P, which is an inverter control signal, to the inverter main circuit 20 from the supplied motor voltage V ₁ and motor primary frequency f ₁ (step 109),
The inverter main circuit 20 converts the DC power of the battery 22 into the necessary AC power based on the given pulse signal P and supplies the desired primary current to the induction motor 16.

That is, a magnetizing current that obtains a transient motor magnetic flux Φ ^* _t that is increased stepwise to an optimum value, and a compensation torque current I _q ′ that is determined so as to always obtain a target torque T ^* corresponding to the motor magnetic flux at each step. The primary current determined from is commanded.

Therefore, by the above primary current control for obtaining the target torque T ^* , the motor magnetic flux can be increased to the optimum motor magnetic flux Φ ^* by following the motor magnetic flux command without change delay, and even during the motor magnetic flux adjustment transient. It is possible to secure the target torque.

[Effects of the Invention] As described above, according to the present invention, the induction motor can always output the target torque not only in the steady state but also in the transient transition of the motor magnetic flux. It is driven by an efficient controlled primary current. As a result, it becomes possible to remarkably extend the battery charging mileage and expand the range of action of the electric vehicle.

The extension of the mileage reduces the number of times the battery is charged,
It is extremely useful for practical application of electric vehicles because it reduces maintenance complexity.

Of course, the extension of the mileage can reduce the size of the battery itself and the weight of the vehicle by setting the required mileage shorter, and further, the miniaturization of the battery has the effect of increasing the degree of freedom in the design of the vehicle. Cause

[Brief description of drawings]

FIG. 1 is a flow chart showing a preferred embodiment of a control method according to the present invention, FIG. 2 is a control circuit diagram for executing the flow chart of FIG. 1, and FIG. 3 is a motor magnetic flux Φ and torque in an induction motor. Electric current
Fig. 4 is a characteristic diagram showing the relationship with I _T , Fig. 4 is a motor magnetic flux / loss characteristic diagram in which the motor output torque is a parameter when the rotation speed is constant, and Figs. 5 and 6 are used in the present invention. FIG. 7 is a data map diagram of a motor magnetic flux and a motor torque current, and FIG. 7 is a characteristic diagram showing a traveling state of an automobile using the present invention. 10 …… Induction motor 12 …… Torque calculator 14 …… Efficiency optimization circuit 16 …… Vector calculation circuit 18 …… PWM control circuit 20 …… Inverter main circuit 22 …… Battery.

Claims (1)

[Claims] 1. A method for controlling an induction motor for an electric vehicle, which obtains a target torque required for an induction motor based on a traveling command and a traveling condition, and supplies a desired primary current to the induction motor so that the target torque is output. In the above, the optimum motor magnetic flux that minimizes the motor loss is calculated from the predetermined magnetic flux / loss characteristic data according to the target torque and the motor rotation speed, and then the motor magnetic flux of the motor magnetic flux command based on the primary current is calculated. A transient motor magnetic flux command value whose change delay does not exceed a predetermined value is calculated stepwise, and the compensating torque current necessary to obtain the target torque corresponding to the transient motor magnetic flux calculated stepwise is calculated as follows: During the adjustment transient until the optimum motor magnetic flux is calculated from the torque current characteristic data, the magnetic flux that obtains the transient motor magnetic flux calculated stepwise is obtained. Current, and the compensation torque current, and supplies a primary current command determined from the induction motor, after the transient motor magnetic flux reaches the optimum motor magnetic flux,
A primary current command that minimizes the motor loss determined from the magnetizing current that obtains the optimum motor magnetic flux and the optimum torque current calculated according to the target torque and the optimum motor magnetic flux based on the motor magnetic flux / torque current characteristics The induction motor for an electric vehicle is characterized in that the target torque is obtained both during the transient transition of the motor magnetic flux and after the adjustment, and the primary current with the maximum efficiency after the adjustment is supplied to the induction motor. Motor control method.