JP2003116295A - Drive controller of motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive controller in which controllability is enhanced in the high-speed rotational region of a motor. SOLUTION: The drive controller for driving an AC motor by performing discrete digital current feedback control and driving an inverter with a PWM signal to convert DC power into AC power comprises a means for making a control operation period independent from a PWM period by generating interruption signals for a control operation period and a PWM period of digital current feedback control independently, wherein the PWM period is switched depending on the rotational speed of the motor to be short in the high-speed rotational region of the motor and to be long in the low-speed rotational region. The switching loss of the inverter is suppressed by shortening the PWM period in the high rotational region requiring to short the PWM period thereby enhancing control performance and elongating the PWM period in the low rotational region where the shortening of the PWM period is not required.

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 an electric motor, which outputs an alternating current having a variable frequency and a variable voltage from a direct current power source by using digital current feedback control.

[0002]

2. Description of the Related Art As an apparatus for controlling an AC electric motor (hereinafter referred to as a motor) using digital current feedback control, there is, for example, one described in Japanese Patent Application Laid-Open No. 7-255192. As described in this publicly known document, when the motor is controlled by using the normal PWM (pulse width modulation) control, an interrupt is generated in the computer at every cycle of the PWM signal, and the command PWM duty ratio Operation and P
The WM output register is set. In the above-mentioned publicly known document, the computer load is reduced by thinning out interruptions to the computer for each cycle of the PWM signal according to the computer load.

[0003]

In the conventional drive control device as described above, an interrupt is generated in the computer for each cycle of the PWM signal, the command PWM duty ratio is calculated, and the PWM output register is set. Since the upper limit of the PWM frequency is limited by the calculation time of the command PWM duty ratio and the calculation speed capability of the CPU, there is a problem that control in the high speed rotation range of the motor becomes difficult. It was

The present invention has been made in order to solve the problems of the prior art as described above, and an object of the present invention is to provide a drive control device for an electric motor with improved controllability in the high speed rotation range of the motor.

[0005]

In order to achieve the above object, the present invention is constructed as described in the claims. That is, in the invention described in claim 1, the control operation cycle interrupt signal for the digital current feedback control and the cycle interrupt signal for the PWM signal are separately generated, and the control operation cycle for the digital current feedback control and the PWM signal are generated. Signal cycle (hereinafter, PWM
It is configured so as to have a means for making the period independent). The control calculation of the digital current feedback control is to calculate the duty ratio of the PWM signal according to the current command value and the like, and the PWM cycle means the cycle of the PWM signal itself for driving the inverter.

According to the invention of claim 2,
The PWM cycle is switched according to the rotation speed of the electric motor, and the PWM cycle is short in the high speed rotation range of the electric motor and long in the low speed rotation range of the electric motor.

Further, in the invention described in claim 3,
The control calculation cycle is set to an integer multiple of the PWM cycle,
The interrupt signal for the PWM cycle is configured to be a trigger for sampling data used in the control calculation.

[0008]

According to the present invention, the control calculation cycle interrupt signal for calculating the duty ratio of the PWM signal is generated separately from the PWM cycle interrupt signal (interruption by the PWM timer), and the control calculation cycle By making the PWM cycle independent, it is possible to set the PWM cycle to a high frequency different from the control calculation cycle, thereby improving the control performance in the high speed rotation range of the electric motor.

According to the second aspect of the invention, the PW is changed by switching the PWM cycle according to the rotation speed of the electric motor.
Suppressing the switching loss of the inverter by speeding up the PWM cycle to improve the control performance in the high rotation range where M cycles need to be speeded up, and slowing down the PWM cycle in the low rotation range where high speed is not particularly required. You can do it.

According to the third aspect of the present invention, since the PWM cycle interrupt signal is used as the data sampling trigger for the control calculation, the data sampling time coincides with the PWM cycle interrupt, so that the electrical angle required for the calculation is estimated. The time and the delay time of the feedback calculation from the sampling of the current value to the output can be set to constant values, and the control stability can be improved. Also, the control calculation cycle is set to P
By setting the integral multiple of the WM period, the PWM output value for an integral number of times can be calculated by a simple correction calculation, so that the control calculation time can be shortened.

[0011]

1 is a block diagram showing the configuration of an embodiment of a drive control device to which the present invention is applied. Figure 1
In the current PI control unit 1, the current d-axis current Id and q-axis current Iq fed back from the three-phase / two-phase conversion unit 10 and the d-axis current command value Id ^* and the q-axis current command value Iq given from the outside are supplied. PI control on the ^* (PI control known proportional-integral control) performed, and outputs a d-axis voltage command value Vd ^* and the q-axis voltage command value Vq ^*. The d-axis current command value Id
^{The *} and the q-axis current command value Iq ^* are signals corresponding to the output torque command value (accelerator opening etc.) and the rotation speed, for example. The two-phase / three-phase conversion unit 2 calculates the voltage command values (Vu ^* , Vv) for three phases based on the input two-phase d-axis voltage command values Vd ^* , q-axis voltage command values Vq ^*, and the electrical angle θ. ^* , Vw ^* ) are calculated and output. The PWM conversion unit 3 inputs a three-phase voltage command value (Vu ^* , Vv ^* , Vw ^* ) and compares it with a triangular wave signal or the like to generate a three-phase PWM (Pulse Width).
Modulation) signal and thereby the inverter 4
Is driven to generate a three-phase alternating current and drive the three-phase motor 5.

The rotation angle sensor 6 detects the rotation angle (electrical angle θ) of the three-phase motor 5 and sends it to the two-phase / three-phase converter 2 and the three-phase / two-phase converter 10. The current sensors 7 and 8 detect the u-phase current iu and the v-phase current iv (both are analog values). The A / D converter 9 receives the input analog iu and i
v is converted into a digital value u-phase current Iu and v-phase current Iv. The three-phase / two-phase conversion unit 10 receives the input u-phase currents Iu and v
The d-axis current Id and the q-axis current Iq are calculated on the basis of the phase current Iv and the electrical angle θ and sent to the current PI control unit 1. Since the three-phase current value has a relationship of Iu + Iv + Iw = 0, Iw can be calculated. The current feedback control of the three-phase motor (synchronous motor) 5 is performed by repeating the above processing. Although the above description has been made on the ordinary current feedback control, the present invention relates to the relationship between the control calculation cycle and the PWM cycle when the above control is realized by the discrete control using the microcomputer.

First, a conventional control method will be described with reference to FIG. FIG. 2 is a diagram showing a timing chart in the case of realizing the above-mentioned current feedback control by discrete control using a microcomputer (conventional method). In normal motor control, if the PWM cycle is dt, PW
A control calculation is performed using the electrical angle sampled by the M interrupt 1 (in FIG. 2) and the A / D converted current value, and the result is written in the PWM output value write register (in FIG. 2). Then the next PWM interrupt 2 (shown in FIG. 2) is used for PWM
It is transferred to the output register (of FIG. 2) and is actually output (of FIG. 2). Subsequently, the current value and the electrical angle for the next output calculation are sampled, and the control is repeated thereafter. Therefore, the time T1 required from the PWM interrupt to the completion of data sampling, calculation, and writing of the PWM output value to the write register
The PWM cycle dt cannot be set to a cycle shorter than that (of FIG. 2), which makes it difficult to control the high-speed rotation of the motor. The control calculation of the current feedback control is to calculate the duty ratio of the PWM signal according to the current command value and the like, and the PWM cycle means the cycle of the PWM signal itself that drives the inverter.

According to the present invention, the PWM cycle interrupt and the control calculation cycle interrupt are separately generated, and the PWM is executed by one control calculation.
By shortening the PWM cycle dt by calculating the output value for two times, the above-mentioned PWM cycle dt can be set shorter than the time T1 required for calculation, and high-speed rotation control of the motor becomes possible. It was done.

FIG. 3 is a diagram showing an embodiment of a timing chart when the current feedback control according to the present invention is realized by discrete control using a microcomputer. In the present embodiment, it is assumed that "control calculation required time =
70 μs ”“ control calculation cycle Ts = 100 μs ”“ PWM
The case where the period dt = 50 μs ”is described. P
Current value I at interrupt 1 (shown in FIG. 3) by the WM timer
u / Iv A / D conversion start and electrical angle θ sampling (FIG. 3) are performed, and the value of the buffer A for temporary storage is transferred to the PWM output command buffer (FIG. 3: the meaning of this processing is (Described later), and the interrupt processing ends. In FIG. 1, the current values are iu, i before A / D conversion.
v, Iu and Iv after conversion, but they are commonly shown as Iu and Iv below. Next, the current value I sampled by the interrupt 1 (in FIG. 3) by the control calculation period timer
The output value is calculated using u, Iv, and the electrical angle θ (in FIG. 3). At this time, the interrupt by the PWM timer is set to be high by the priority of the interrupt so that the interrupt by the PWM timer always comes first. Set to.

In this control calculation, three-phase / two-phase conversion (three-phase / two-phase conversion unit 10 in FIG. 1) and PI control (current PI in FIG. 1) are performed.
Controller 1) Two-phase / three-phase conversion (two-phase / three-phase conversion unit 2 in FIG. 1)
The output value is calculated in this order, but at this time, the electrical angle value used in the two-phase to three-phase conversion is estimated and corrected at the time when the calculated output value is actually output. 125 μs after θ) and electrical angle θ ″
Using the binary value (estimated value 175 μs after the sampled electrical angle θ), two output values Dpwm ′ and Dpwm ″ are calculated, and Dpwm ′ is written in the PWM output command writing buffer (in FIG. 3), Dpwm "is written in the buffer A for primary storage (in FIG. 3). While this control calculation takes (70 + α) μs (where α is an increment of the output binary calculation) and the process is executed, an interrupt 2 (FIG.
Of) interrupts. In this interruption, the current values Iu, I
The A / D conversion of v is started and the electrical angle θ is sampled, but the setting is made so that once every two interrupt processes by the PWM timer, the electrical angle θ is not transferred to the data buffer and the process is terminated. As a result, the result is 2
Once at a time, soft processing is equivalent to doing nothing (Fig. 3). However, the output at this time is the value of Dpwm "because of the above-described processing (of FIG. 3). Therefore, the PWM cycle shorter than the control calculation cycle can be set, and the control during high-speed rotation of the motor can be performed. That is, in the example of Fig. 3, the PWM cycle is 1/2 of the control calculation cycle.
Therefore, the speed can be doubled.

Further, as in the example of FIG. 3, the control calculation cycle is set to an integral multiple of the PWM cycle, and the current values Iu and Iv are A.
By using the interrupt of the PWM cycle as the trigger of the / D conversion start and the sampling of the electrical angle θ, it is guaranteed that the sampling time of the data is always synchronized with the PWM timer. Therefore, the "electrical angle estimation time" and "feedback calculation delay time from current value sampling to output", which are important conditions for control performance, can be made constant. Further, by setting the control calculation cycle to be an integral multiple of the PWM cycle, the PWM output value for an integral number of times can be calculated by a simple correction calculation, so that the control calculation time can be shortened.

In the above description, the PWM cycle dt is set to a short value (for example, 50 μs) so that the high speed rotation range can be controlled. However, the low speed rotation range where the PWM cycle dt does not need to be shortened is set. When controlling, it may be performed as shown in FIG. 4 is different from FIG. 3 in processing. (1) The PWM cycle is set to 100 μs (in FIG. 4). (2) In both of the interrupts 1 and 2 by the PWM timer, the transfer from the primary storage buffer of the electrical angle θ to the data buffer is executed (in FIG. 4). (3) Only the estimated value θ ′ 150 μs after the sampled electrical angle θ is obtained as the electrical angle used in the two-phase / three-phase conversion during the control computation by the interrupt for the control computation period timer, and the output value computation is performed. Writes only Dpwm 'to the PWM output command writing buffer (in FIG. 4). That is, the value Dpwm ′ and θ ″ (175 μs) calculated using θ ′ (estimated value after 125 μs) as in the high speed region control.
2) and the value Dpwm ″ calculated using the latter estimated value), only Dpwm ′ calculated using the estimated value θ ′ after 150 μs is used.

By performing the above processing, it becomes possible to easily change the PWM cycle. Therefore, it is possible to control in such a manner that the PWM cycle is slowed down so as to suppress the switching loss of the switching module of the inverter in the low rotation speed range, and the PWM cycle is increased in the high rotation speed range to improve the controllability.

Next, the contents of the arithmetic processing in this embodiment will be described using a flow chart. FIG. 5 is a flowchart showing the contents of interrupt processing in the PWM cycle. In FIG. 5, first, in step 0, the current values Iu, Iv
A / D conversion is started, the electrical angle θ is taken into a buffer for temporary storage, and the process proceeds to step 1.

In step 1, it is determined whether the PWM cycle is the "Lo" mode (low speed mode). PWM here
If the cycle determination flag is "Lo" mode, the value of "Lo" mode is written to the PWM cycle setting register, and the process proceeds to step 2. If not, "Hi" mode (high speed mode) is written to the PWM cycle setting register. Value is written, and the process proceeds to step 3. In step 3, it is determined whether the PWM interrupt mode flag is "0" or "1". If the PWM interrupt mode flag is “0”, go to step 4.
If it is "1", the process proceeds to step 5. In step 4, the value of the buffer A (FIG. 3) for temporary storage is written in the PWM output value writing register, and the process proceeds to step 2. In step 2, the value of the buffer for temporary storage of the electrical angle θ written in step 0 is written in the buffer for electrical angle θ, and the process proceeds to step 5. In step 5, the PWM interrupt mode flag is inverted. PWM
If the value of the interrupt mode flag is "0", set it to "1".
If it is "1", "0" is written and the interrupt processing is ended.

Next, FIG. 6 is a flow chart showing the contents of interrupt processing in the control calculation cycle. In FIG. 6, first, in step 0, the PWM cycle mode is determined from the rotation speed of the motor. If the motor speed is in the low speed mode (operating in the low speed range), the PWM cycle determination flag is "Lo".
If the mode is set and the mode is the high speed mode (operating in the high rotation range), the PWM cycle determination flag is set to the “Hi” mode, and the process proceeds to step 1.

In step 1, the current values Iu and Iv are A /
Determine the end of D conversion. If the A / D conversion is not completed, the process proceeds to step 1 again, and if the conversion is completed, the process proceeds to step 2. In step 2, the current values Iu and Iv (Iw obtained by calculation) after A / D conversion are three-phase to two-phase converted to calculate two-phase current values Id and Iq, and the process proceeds to step 3. In step 3, the two-phase voltage command values Vd ^* , Vq ^{* are} PI-controlled (proportional-integral control) based on the two-phase current values Id, Iq calculated in step 2 and the externally applied current command values Id ^* , Iq ^{* .} Is calculated and the process proceeds to step 4.

In step 4, the PWM cycle determination flag is determined, and if it is the "Lo" mode, the process proceeds to step 5,
If it is the “Hi” mode, the process proceeds to step 6. In Step 5, the electrical angle θ ′ after 150 μs is estimated from the electrical angle θ sampled in Step 0 of FIG. 5, and 2 is calculated from this θ ′ and the voltage command values Vd ^* and Vq ^* calculated in Step 3.
Three-phase voltage command values Vu ^* , Vv ^* , Vw ^{* by} three-phase conversion
Is calculated and the process proceeds to step 7. In step 7, P
The values of Vu ^* , Vv ^* , and Vw ^* calculated in step 5 are written in the WM output value writing register, and the interrupt processing is ended.

In step 6, the electrical angle θ'after 125 μs is estimated from the electrical angle θ sampled in step 0 of FIG. 5, and this θ'and Vd ^* , Vq calculated in step 3 are calculated.
Vu ^* 1, Vv ^* 1, Vw ^* 1 is calculated from ^* by two-phase / three-phase conversion, and similarly, 1 is calculated from the sampled electrical angle θ.
The electrical angle θ ″ after 75 μs is estimated, and Vu ^* is calculated from this θ ″ and Vd ^* and Vq ^* calculated in step 3 by two-phase / three-phase conversion ^.
2, Vv ^* 2, Vw ^* 2 are calculated, and the process proceeds to step 8. However, Vu ^* 1, Vv ^* 1, and Vw ^* 1 are three-phase voltage command values when the electrical angle is θ ′ (value after 125 μs), and Vu ^* 2, Vv ^* 2, and Vw ^* 2 are electrical values. The angle is θ ”
This is a three-phase voltage command value when (value after 175 μs).

In step 8, the PWM interrupt mode flag is set.
The lag is determined, and if the value is “0”, step 8 is performed again.
If it is "1", the process proceeds to step 9. Ste
In step 9, Vu calculated in step 6^*1, Vv
^*1, Vw^*Write 1 to the register for writing the PWM output value
Vu calculated and calculated in step 6^*2, Vv ^*2, V
w^*Write 2 to buffer A (Fig. 3) for primary storage
End interrupt processing. Microcomputer
At startup, the electrical angle is the value at the end of the previous time, and the current value is
The sampling value at the time of (is normally 0) is used.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a drive control device to which the present invention is applied.

FIG. 2 is a diagram showing a timing chart when current feedback control is realized by discrete control using a microcomputer (conventional method).

FIG. 3 is a diagram showing an embodiment of a timing chart when the current feedback control according to the present invention is realized by discrete control using a microcomputer.

FIG. 4 is a diagram showing an embodiment of a timing chart when controlling in a low speed mode.

FIG. 5 is a flowchart showing the details of interrupt processing in a PWM cycle.

FIG. 6 is a flowchart showing the contents of interrupt processing in a control calculation cycle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current PI control part 2 ... 2 phase 3 phase conversion part 3 ... PWM conversion part 4 ... Inverter 5 ... 3 phase motor 6 ... Rotation angle sensor 7, 8 ... Current sensor 9 ... A / D conversion part 10 ... 3 phase 2 Phase converter

Continued front page    F-term (reference) 5H560 BB04 DA00 DC12 EB01 EC01                       RR05 RR06 TT15 TT20 XA02                       XA12 XA13                 5H576 BB09 DD05 EE01 EE14 GG04                       HB01 JJ03 JJ08 JJ16 JJ24                       JJ29 LL22 LL41

Claims (3)

[Claims] 1. A drive control apparatus for an electric motor, wherein digital current feedback control is performed in discrete control, and an inverter is driven by a PWM signal to convert DC power into AC power to drive an AC electric motor. And a means for independently generating the control calculation cycle of the digital current feedback control and the cycle of the PWM signal. Drive control device for electric motor. 2. The cycle of the PWM signal is switched according to the rotation speed of the electric motor, and the P signal is set in the high speed rotation range of the electric motor.
The drive control device for the electric motor according to claim 1, wherein a cycle of the WM signal is short and is long in a low speed rotation range. 3. The control operation cycle is set to an integral multiple of the cycle of the PWM signal, and an interrupt signal for the cycle of the PWM signal is used as a trigger for sampling data used in the control operation. The drive control device for an electric motor according to claim 1 or 2.