JPH09121558A - Drive controller for motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the dead current controlling time of a drive controller and improve the responsiveness of the controller to the electric current by using the value of one control period before as the sampling value of the current used for the operation of dead time compensation and performing the operation after the feedback of the current is controlled. SOLUTION: An A/D converter 19 converts the current 18 of a motor into a digital value in accordance with an A/D conversion starting timing signal 22 and outputs the sampling value 21 of the current 18. A current controller 7 computes a voltage command value 8 from a current command value 6 and the sampling value 21 of the current 18. A dead time compensation computing element 20 computes a voltage compensating amount 23 in accordance with the polarity of the sampling value 21. An adder 25 computes an output voltage value 26 which is the sum of the command value 8 and compensating amount 23 and a PWM computing element 9 converts the voltage value 26 into a PWM pulse 10 containing dead time. A PWM voltage value command is updated before the dead time compensation computing element 20 completes operation and an output voltage computing means 25 uses the computed value of one control period before.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive control device provided with a current feedback control system, and more particularly to a digital control device which realizes good current response while compensating for dead time.

[0002]

2. Description of the Related Art AC servomotors include those using an induction motor and those using a permanent magnet synchronous motor, both of which are PWs having a current feedback control system.
Many are current controlled by M inverters. Conventionally, an analog method has been often used for the current control unit of these control systems. In recent years, semiconductor integrated circuits typified by digital signal processors and one-chip microcomputers have developed, and systems that digitize not only current control but also PWM pulse generation are appearing.

FIG. 13 shows a block diagram of a control system for an electric vehicle using an induction motor. This system includes a torque command calculator 3 that calculates a torque command value 4 based on an accelerator opening 2 that is an output of the accelerator opening sensor 1, and a rotation speed detector 15 that detects the torque command value 4 and the rotation speed of the induction motor 14. The current command calculator 5 that calculates the current command value 6 from the motor rotation speed 16 that is the output of the current command value 6, and the voltage command value 8 is calculated from the current command value 6 and the motor actual current 18 that is the output of the motor current detector 17. Current controller 7, voltage command value 8
Is composed of a PWM calculator 9 for calculating a PWM pulse 10 from a DC power supply 11, and a PWM inverter 12 for converting a DC voltage supplied from a DC power supply 11 into a three-phase AC voltage based on the PWM pulse 10. , Is driven at a predetermined frequency.

Now, let us consider the current sampling timing and the PWM pulse pattern update timing when the current controller 7 and the PWM calculator 9 are digitally processed by a microcomputer or the like. First, regarding the update timing of the PWM pulse pattern, since the normal PWM pulse generation is realized by comparing the counter that performs up-down counting operation in a triangular wave shape with the three-phase voltage command value, the voltage command value is updated. The timing is limited to the top of the triangular wave. At other timings, the pulse width, the number of times of switching, etc. will not be accurate.

Next, regarding the current sampling timing, as disclosed in, for example, Japanese Patent Laid-Open No. 3-215182, the zero vector section of the output voltage vector is set in order to accurately detect the actual current while avoiding the influence of the current ripple. A midpoint is desirable. The midpoint of the zero vector section is none other than the apex of the triangular wave. That is, both of them are performed at the same timing.

However, since dead time such as current sampling and current control calculation time is generated, the time from the current sampling to the output of the PWM pulse reflecting the dead time is the control dead time in the current control, and at least the PWM is used.
It becomes one half of the cycle. Further, when the processing time of the current controller 7 and the PWM calculator 9 is ½ or more of the PWM cycle, the processing time is not ½ of the PWM cycle but an integral multiple thereof.

By the way, when the dead time becomes long in the current control system, the phase margin of the control system decreases. Therefore, in order to perform current control with good response and controllability, it is desirable to reduce the dead time as much as possible.

FIGS. 18 and 19 show simulation results when the current control gain is the same when the dead time is short and when the dead time is long. If the dead time is long, oscillation has occurred and the gain must be lowered. Therefore, the responsiveness of the current is reduced.

In order to improve the influence of the control dead time in this current control, the current sampling value is compensated as shown in, for example, Japanese Patent Laid-Open No. 3-215182, and Japanese Patent Laid-Open No. 63-48196. Is known to do.

On the other hand, in the PWM inverter, the positive side and negative side switching elements forming the inverter are alternately turned on and off to control the output voltage. However, since the switching element has a delay in switching due to the turn-off time, a short-circuit prevention period (hereinafter referred to as dead time) is provided so that the positive side and the negative side do not conduct at the same time. Therefore, there is a problem that the output voltage of the inverter is distorted due to the influence of the dead time, and as a result the waveform of the output current is distorted.As a countermeasure against this, the output voltage of the inverter is changed by the compensation voltage according to the polarity of the output current. A method of reducing waveform distortion is generally known.

When the current control system in the current control type inverter is constructed by the analog system, the feedback gain can be set to be relatively high, so that the distortion of the current waveform due to the dead time is small. However, in the current control by the digital method, the feedback gain cannot be increased as much as that of the analog method, and the influence of the dead time becomes large. Therefore, the voltage compensation is essential. The effect of dead time will be described below.

First, digital current control and P
FIG. 14 shows a control flow when performing the WM calculation. There are two methods of current control: a three-phase AC coordinate system and a rotating magnetic field coordinate system. The latter will be considered. In step S140, the motor current is A / D converted and taken in as a digital amount. In step S142, the motor current in the three-phase AC coordinate system is coordinate-converted into the motor current in the rotating magnetic field coordinate system. In step S144, in the rotating magnetic field coordinate system,
The voltage command value of the rotating coordinate system is obtained by using the current command value and the motor current and performing a current control calculation including, for example, a proportional integral element. In step S146, the voltage command value of the rotating magnetic field coordinate system is coordinate-converted into the voltage command value of the three-phase AC coordinate system. In step S148, the voltage command value in the three-phase AC coordinate system is converted into a PWM pulse by, for example, the triangular wave comparison method. The triangular wave comparison method can be easily realized by hardware that compares the value of the up / down timer corresponding to the analog triangular wave with the time data corresponding to the voltage command value of the three-phase AC coordinate system and switches the polarity of the output pulse.
In this case, the processing of step S148 is only software processing such as writing the voltage command value to the output compare register.

FIG. 15 is a diagram showing a three-phase voltage command / current command / motor current when the above control is performed on an ideal inverter that does not need to set a dead time. The motor current follows the current command value, and there is no current distortion that occurs when dead time is set. on the other hand,
FIG. 16 shows the simulation result when the dead time is provided. Since the current feedback gain is small,
The effect of dead time appears as current distortion.
As shown by these results, in a motor drive control device that performs digital current control, especially a system in which the current control gain cannot be increased, that is, a system that drives a large output motor, or a system with a long PWM cycle,
Dead time compensation is mandatory.

Therefore, the dead time compensation will be added. That is, the voltage command value is compensated by the polarity of the motor current of the three-phase AC coordinate system obtained in step S140 of FIG. To describe the U-phase concretely, when the U-phase real current is positive, the conduction time of the switching element on the U-phase positive side is long (the conduction time of the negative-side switching element is short), and when the U-phase actual current is negative. The U-phase voltage command is compensated so that the conduction time of the switching element on the U-phase positive side is shortened (the conduction time of the switching element on the negative side is lengthened). The amount of compensation may be determined only by the dead time width or by considering the switching characteristics of the switching element in the dead time width, as disclosed in Japanese Patent Laid-Open No. 3-164071. The three-phase voltage command value and the motor actual current when controlled in this way are as shown in FIG. In the digital method, there is a control delay from the sampling of the output current to the output of the PWM pulse, and as in the case of the current control described above, the voltage compensation is not correctly performed due to the control dead time, so that the distortion of the output current remains. . Therefore, as a technique for improving this problem, Japanese Patent Laid-Open No. 6-62579 is known. This is to detect the output current of the inverter with a current detector, perform an operation to advance the phase of this detected current signal by the control dead time, and compensate the voltage command with the polarity of the compensation current signal obtained by this phase advance compensation. To do.

[0015]

As described above, in the digital motor drive control system, the dead time compensation including the compensation of the dead time is indispensable. However, the arithmetic processing increases the calculation amount. There is a problem that the dead time in the current control increases. As a method of compensating for the influence of the dead time in the current control, the above-mentioned JP-A-3-215182 and JP-A-63-4 are cited.
Although there is a publication such as Japanese Patent No. 8196, it is nothing but predicting the future from the present and controlling it, so that there is a problem that good compensation cannot be performed in a transient state and current followability is poor.

That is, if the dead time compensation for reducing the current distortion is performed, the amount of calculation increases, the current control dead time increases, and the current responsiveness deteriorates. On the other hand, if the dead time is compensated for, the compensation cannot be sufficiently performed in the transient state, and the current response is not good.

The present invention has been made by paying attention to such a conventional problem. In an AC motor drive control circuit having a current feedback control system, dead time compensation is performed and a good response is obtained. An object is to provide a digital control device that enables current control.

[0018]

According to the present invention, the calculation order in one control cycle is determined by the current sampling means,
The current control means, the output voltage calculation means, and the dead time compensation means are arranged in this order. The PWM voltage command is updated before the dead time compensation means finishes its calculation, and the dead time compensation value used in the calculation of the output voltage calculation means is one control cycle. Use the value calculated previously.

Further, according to the present invention, the execution order of the above-mentioned execution means is changed to a current sampling means, a current control means,
The output voltage calculating means, the dead time compensating means, and the output voltage calculating means are arranged in this order, and the PWM voltage command updating means performs the PWM voltage command updating before and after the dead time compensating means finishes the calculation.
The dead time compensation value used in the calculation of the output voltage calculation means is the value calculated one control cycle before, and the dead time compensation value used in the calculation of the output voltage calculation means is the value calculated in the current control cycle. By using it, it is possible to achieve current control with better response.

Time nTs to (n + 1) Ts (n is an integer,
The operation of Ts in one control cycle) will be described. First, the current i sampled at time nTs
The current control calculation is performed using (nTs). After that, the output voltage is calculated from the calculation result and the result of the dead time compensation calculation executed one control period before. After that, dead time compensation calculation is performed using the current i (nTs). Before the dead time calculation is completed, the PWM pulse is updated (the timing at the highest point of the carrier wave is before the dead time calculation is completed). With the above operation, the time from the current sampling to the reflection of the PWM calculation performed using this current value (update of the PWM output), that is, the dead time of the current control system is the same as that when dead time compensation is not performed. However, it is possible to perform dead time compensation, and current control with good current responsiveness and small current distortion is realized.

Further, in the second invention, PW is performed after the above calculation.
By updating the M output again, PW is performed twice in one control cycle.
The dead time of dead time compensation reflected in the pulse updated for the second time is made smaller than the dead time of dead time compensation of the first invention.

Of course, it is desirable to minimize the dead time for dead time compensation as well as the dead time for current control.
From the viewpoint of controlling the motor current, the effect of dead time in dead time compensation is often smaller than the effect of dead time in current control. Therefore, in such an application, the dead time compensation calculation uses the current sample value one control cycle before, and the response is improved by reducing the dead time of the current control. Furthermore, it is even better if the current at PWM pulse output is predicted from the current sample value used for dead time compensation and the dead time to perform the compensation calculation.
Further, in the current control calculation, it is more preferable to predict the current at the time of PWM pulse output from the current sample value and the dead time and perform the calculation.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a motor drive control device according to the present invention.

In this system, a torque command calculator 3 for calculating a torque command value 4 based on an accelerator opening 2 which is an output of the accelerator opening sensor 1, a rotation speed for detecting a torque command value 4 and a rotation speed of the induction motor 14. According to the A / D start timing signal 22, the current command calculator 5 that calculates the current command value 6 from the motor rotation speed 16 that is the output of the detector 15 and the motor current 18 that is the output of the motor current detector 17 are A / D according to the A / D start timing signal 22.
A that performs D conversion and outputs the motor current sampling value 21
A / D converter 19, a current controller 7 that calculates a voltage command value 8 from the current command value 6 and the motor current sampling value 21,
The dead time compensation calculator 20 that calculates the voltage compensation amount 23 according to the polarity of the motor current sampling value 21 and the adder 25 that inputs the voltage command value 8 and the voltage compensation amount 23 and calculates the output voltage value 26 which is the sum of them. , Converting this into a PWM pulse 10 with dead time, outputting the A / D start timing signal 22 and converting the current voltage supplied from the DC power supply 11 into a three-phase AC voltage based on the PWM pulse 10. The induction motor 14 is driven by the PWM inverter 12 at a predetermined voltage and a predetermined frequency.

First, the PWM calculator 9 will be described.
This is usually configured by hardware as shown in FIG. The two carrier wave generation up / down counters generate triangular waves while taking count values that are deviated by an amount corresponding to the dead time. The output voltage update timing signal 24 is output at the highest point of the triangular wave, and the A / D start timing signal 22 is output at the lowest point. The output voltage value 26 is written to the latch in synchronization with the output voltage update timing signal, and compared with the value of the carrier generation up / down counter by two digital comparators, respectively, and the positive side and negative side of the U phase to which dead time is added. It generates side PWM pulses Up and Un. This has been described for only one phase, but the other two phases can be realized with the same configuration. FIG. 3 shows the waveform diagram.

Other processing is usually realized by software. The flow of the processing is shown in FIGS. First, A /
By the D start timing signal 22, the A / D converter 19
Converts the current into A / D (Process 1). After that, the current controller 7 calculates the voltage command value 8 from the voltage command value 6 and the motor current sampling value 21 (process 2). After that, the voltage command value 8 and the voltage compensation amount 23 calculated one control cycle before
Then, the output voltage 26 is calculated by the adder 25 (process 3) and output to the PWM calculator 9. Then, the dead time compensation calculator 20 calculates the voltage compensation amount 23 according to the polarity of the motor current sampling value 21 (process 4).

The voltage command is updated 1/2 after the start of the control cycle.
It is performed when the cycle elapses. As shown in FIG. 5, the calculation up to this point is not completed before the output voltage update timing signal is generated (after current sampling and before 1/2 control cycle). During the dead time compensation calculation, the PWM calculator 9 generates the output voltage update timing signal 24, and the output voltage value 8
Is latched. Then, the PWM pulses Up and Un are created. As described above, the time delay from the sampling of the current to the output of the PWM pulse calculated based on this current, that is, the control dead time is 1/2 of one control cycle.

According to the conventional method, the dead time compensation calculation is performed using the first current sample value of the control cycle, and the output voltage is calculated using the calculated value. The calculation was not completed within / 2 control cycles, and the dead time was 1 control cycle. That is, the dead time can be reduced to half as compared with the conventional method.

On the other hand, the time until the voltage compensation amount by the dead time calculation is output from the current sample (hereinafter referred to as dead time compensation dead time) is 1 compared with the conventional method.
/ 2 control cycle becomes longer, but its effect is small for the following reasons, and in many cases, the effect of improving current followability by reducing current control dead time is greater.

The dead time compensation for dead time compensation is
This is easier than compensating for dead time in current control.

Since the dead time compensation value has the same magnitude and only needs to change the polarity in synchronism with the current polarity, if the dead time is compensated, no problem occurs in most cases even in a transient state.

Since the current control gain can be increased by reducing the dead time of the current control, the current distortion due to the dead time is reduced. Therefore, the need for dead time compensation itself is reduced.

FIG. 6 shows a case where control is performed by the conventional method.
FIG. 7 shows simulation results when control is performed in the present embodiment. It shows the output voltage value, current command value, and U-phase motor current of the U-phase. In the conventional method, the current control gain has to be reduced as compared with the case of the present embodiment due to the influence of dead time, and therefore the deviation from the command value becomes large.

Next, a second embodiment using the present invention will be described. The present embodiment is an embodiment in which the configuration of the PWM calculator 9 in the first embodiment (FIG. 2) is changed to reduce the dead time compensation dead time.
A waveform diagram for explaining the operation of the PWM calculator 9 is shown in FIG.
Further, FIG. 9 and FIG. 1 are diagrams showing the flow of calculation according to the present embodiment.
0 is shown. As shown in FIG. 8, the output voltage update timing signal is generated at the lowest point in addition to the highest point of the carrier wave. Therefore, as shown in FIG. 10, the dead time voltage compensation amount is updated twice in one control cycle. The dead time of the first compensation amount after the current sampling is the first
Although the control cycle is 2/3 as in the above embodiment, the dead time of the next compensation amount is one control cycle. Therefore, as compared with the first embodiment, the average dead time compensation dead time is shortened, and the influence of current distortion is small.

Next, a third embodiment using the present invention will be described. The present embodiment compensates for dead time in current control. FIG. 11 shows the current controller 7 in the present embodiment. The current controller 7 compensates the motor current sampling value 21 in consideration of the control dead time in the current control to obtain the motor current sampling compensation value 7
A current compensation calculator 702 that outputs 01 and a current controller 700 that calculates a voltage command value 8 from the current command value 6 and the motor current sampling compensation value 701. The configuration of the current controller 700 is the same as that of the current controller 7 in the first embodiment. As a compensation method of the current compensation calculator 702, for example, a method of predicting the current after the dead time from the current values of the previous time and this time can be considered.

Since the dead time of the current control is shorter than that of the conventional one, the accuracy of the current prediction is high. Therefore, it is possible to control the current with high accuracy even in a transient state.

Next, a fourth embodiment using the present invention will be described. The present embodiment compensates for dead time in dead time compensation. FIG. 12 shows the dead time compensation calculator 20 in the present embodiment. The motor current sampling compensation value 201 is compensated in consideration of the dead time in the dead time compensation, and is output, and the current compensation calculator 202 and the motor current sampling compensation value 20 are output.
Calculator 20 for calculating the voltage compensation amount of dead time from 1
0. The configuration of the dead time compensation calculator 200 that calculates the voltage compensation amount 23 is the same as that of the dead time compensation calculator 20 in the first embodiment.

In the present embodiment, the current value used for the dead time compensation calculation is shown only when it is an actual current, but a current command value may be used. Instead of the motor current sampling value 21 in the above embodiment, the current command value 4 may be input.

[0040]

According to the present invention, in the AC motor drive control circuit having the current feedback control system, the current sample value used for the dead time compensation calculation is the value one control cycle before, and the calculation processing is changed to the current feedback control. By adopting a configuration that is performed after the calculation concerned, the current control dead time is shortened and the current responsiveness is improved.

Further, by providing a means for compensating the sampling current value with respect to the control dead time shortened as compared with the conventional example, the responsiveness can be further improved.

Further, the current distortion can be improved by providing the dead time compensating means with means for compensating the sampling current value for the dead time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a motor control device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a PWM calculator according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram showing an operation of the PWM calculator according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a calculation according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a calculation order according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a simulation result when a motor is driven in a conventional system.

FIG. 7 is a diagram showing a simulation result when a motor is driven by the system of the present invention.

FIG. 8 is a waveform diagram showing an operation of the PWM calculator according to the second embodiment of the present invention.

FIG. 9 is a flowchart showing an operation according to the second embodiment of the present invention.

FIG. 10 is a diagram showing a calculation order according to a second embodiment of this invention.

FIG. 11 is a diagram showing a current controller according to a third embodiment of the present invention.

FIG. 12 is a diagram showing a dead time compensation calculator according to a fourth embodiment of the present invention.

FIG. 13 is a block diagram showing a motor drive control device in a conventional example.

FIG. 14 is a flowchart showing a control flow in a conventional example.

FIG. 15 is a diagram showing a simulation result of an ideal inverter in a conventional example.

FIG. 16 is a diagram showing a simulation result of an inverter provided with a dead time in a conventional example.

FIG. 17 is a diagram showing a simulation result of a conventional example in which dead time compensation is performed in the conventional example.

FIG. 18 is a diagram showing a simulation result when the dead time of the current control in the conventional example is long.

FIG. 19 is a diagram showing a simulation result when the dead time of current control in the conventional example is small.

[Explanation of symbols]

 1 Accelerator Position Sensor 2 Accelerator Position 3 Torque Command Calculator 4 Torque Command Value 5 Current Command Calculator 6 Current Command Value 7 Current Controller 8 Voltage Command Value 9 PWM Calculator 10 PWM Pulse 11 DC Power Supply 12 PWM Inverter 14 Induction Motor 15 Rotation speed detector 16 Motor rotation speed 17 Motor current detector 18 Motor current 19 A / D converter 20 Dead time compensation calculator 21 Motor current sampling value 22 A / D start timing signal 23 Voltage compensation amount 25 Adder 26 Output voltage value

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H02P 7/63 302 H02P 7/63 302K

Claims (4)

[Claims] 1. A current feedback control system for following a current command value, and a function for compensating for voltage distortion caused by dead time provided for preventing a short circuit of a switching element forming a three-phase bridge circuit. In an AC motor drive control device for controlling the drive of a motor by applying a PWM voltage, current control is performed using a current sampling means for sampling a motor current and a sampling current value obtained by the current sampling means. A current control unit that calculates a voltage command, a dead time compensation unit that calculates the compensation value of the voltage command obtained by the current control unit using the sampling current value, the current control unit, and the dead time compensation unit Output voltage calculation means for calculating an output voltage from the respective calculation results; An execution timing generation means for sequentially executing the stages in a predetermined cycle and a PWM command update means for inputting the output voltage and updating a PWM voltage command at a predetermined timing are provided. Within one control cycle, the execution order of each execution means is: the current sampling means, the current control means,
The output voltage calculating means and the dead time compensating means are in this order, and the PWM voltage command updating by the PWM command updating means is performed before the dead time compensating means finishes the calculation, and the dead time The motor drive control device, wherein the compensation value is a value calculated one control cycle before. 2. The execution sequence of the execution means is the current sampling means, the current control means,
The output voltage calculation means, the dead time compensation means,
The order of the output voltage calculating means is such that the PWM voltage command updating by the PWM command updating means is performed before the end of the calculation of the dead time compensating means and after the end of the calculation of the output voltage calculating means. The dead time compensation value used in the calculation of 1 is a value calculated one control cycle before, and the dead time compensation value used in the calculation of the output voltage calculation means is a value calculated in the current control cycle. The motor drive control device according to claim 1. 3. The motor drive control device according to claim 1, wherein the current control means includes means for compensating a sampling current value for a dead time of the current control. 4. The dead time compensating means comprises means for compensating the sampling current value only for the dead time of the dead time compensation control.
The motor drive control device according to claim 2.