JP2003180095A - Controller of voltage driven pwm inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a voltage driven PWM inverter for controlling a motor in which the control performance and durability of an inverter element are enhanced. <P>SOLUTION: When the output frequency ωm of an inverter (proportional to a rotational speed) multiplied by a constant Kf is lower than a PWM carrier frequency Fpl at the time of low rotation, a PWM carrier frequency Fp is decreased gradually to Fpl (S1-S4→S8) and when it is not lower than the PWM carrier frequency Fpl at the time of low rotation, the PWM carrier frequency Fp is increased gradually to FpH (S1→S5-S7→S8). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mounted on an electric vehicle, a hybrid vehicle or the like which uses an electric motor as a prime mover,
The present invention relates to an inverter control device that converts a direct current into an alternating current to drive and control an alternating current motor.

[0002]

2. Description of the Related Art The inverter converts a carrier direct current into an alternating current by pulse width modulation and outputs the alternating current to a motor,
The rotation speed of the electric motor is controlled by changing the frequency of the alternating current by the frequency variable control by the pulse width modulation. Conventionally, the PWM carrier frequency is generally set constant regardless of the rotation speed control of the electric motor.

Japanese Patent Laid-Open Publication No. 9-46819 discloses that the PWM carrier frequency is variably controlled and the operating noise of the inverter is increased to suppress the feeling of strange sound when the hybrid vehicle is idle stopped. However, if the PWM carrier frequency is set higher in this way, the setting of the PWM carrier frequency becomes unnecessarily high in the low speed region such as during idle stop, and the switch of the element is The number of (ON / OFF switching) increases, the power loss (turn-on / turn-off loss) increases, and the amount of heat generation increases, which accelerates the deterioration of the element.

In the case of a voltage-driven PWM inverter, the pulse width of the PWM carrier wave is changed by duty control to continuously change the drive voltage to control the drive current (torque) of the electric motor. When the carrier frequency is increased, the pulse interval itself is shortened and the resolution is lowered. Particularly, since the electric motor has a characteristic that the current range becomes wider as the rotation speed becomes lower, the dynamic range of the current becomes wider in the low rotation region, and the control resolution of the current due to the pulse width becomes extremely poor.

If the PWM carrier frequency is set to a low value in accordance with the demand in the low speed control range of the electric motor, the higher the speed, the larger the distortion of the AC current waveform converted by the inverter, and the maximum rotation speed is limited. I will end up. The present invention has been made in view of such conventional problems, and an object thereof is to provide an inverter control device in which control performance of an electric motor and durability of an inverter element are improved.

[0006]

Therefore, in the invention according to claim 1, in a voltage-driven PWM inverter for controlling a motor, the PWM carrier frequency is lowered when the inverter output frequency is low, and the inverter output frequency is reduced. When it is high, it is characterized by making it high.

According to the invention of claim 1, the PWM is
By lowering the carrier frequency, it is possible to reduce power loss, improve the durability of the inverter element, and improve the resolution of current control. Further, during high rotation control of the electric motor, by increasing the PWM carrier frequency, the waveform of the alternating current converted by the inverter can be approximated to a sine wave, and thus the maximum rotation speed of the electric motor can be controlled to be high.

The invention according to claim 2 is characterized in that the lower limit value of the PWM carrier frequency is set near the lower limit frequency in the range where the influence of torque ripple is small. Claim 2
According to the present invention, it is possible to suppress the torque ripple phenomenon that occurs when the carrier wave frequency is made too low, and to perform stable torque control.

The invention according to claim 3 is characterized in that the element temperature of the inverter is detected, and when the element temperature is too high, the PWM carrier frequency is lowered even during high rotation control of the electric motor. According to the third aspect of the present invention, by performing fail-safe by detecting the element temperature, it is possible to avoid thermal destruction of the element and ensure durability.

The invention according to claim 4 is characterized in that the element temperature of the inverter is directly detected by a temperature sensor provided in the inverter body. The invention according to claim 5 is characterized in that the element temperature of the inverter is indirectly detected by a temperature sensor for detecting the temperature of cooling water for cooling the inverter body.

Further, the invention according to claim 6 detects the current flowing through the element of the inverter and the current flowing to the electric motor,
It is characterized in that the element temperature of the inverter is estimated and detected by the integrated value of the power loss calculated based on these detected values. According to the invention according to claim 4, claim 5 or claim 6, the element temperature of the inverter can be detected directly or indirectly.

Further, the invention according to claim 7 is characterized in that the electric motor is a traveling electric motor mounted on an automobile. According to the invention of claim 7, the invention can be particularly effectively exerted by being applied to the control of an electric motor having a wide range of rotation speed control such as an electric vehicle and a hybrid vehicle.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system schematic configuration of an electric vehicle equipped with an inverter control device according to an embodiment, in which a torque (current) and a rotation of a three-phase AC motor 3 are driven by an inverter 2 driven by electric power supplied from a battery 1. The speed is controlled.

2 and 3 show circuit configurations and operations of the inverter 2 and the electric motor 3, respectively. In FIG. 2, the inverter 2 has a pair of H, L switching elements of U, V, W phases connected to the battery 1 (power supply potential VB).
It has a configuration in which the outer terminals of the U-, V-, and W-phase coils of the electric motor 3 are connected to the connection points of the switching elements. Then, the U, V, and W phase switching elements are provided with a phase difference of 120 °, and the ON / OFF time ratio (duty) is periodically changed (pulse width modulation) to generate a direct current of three. Convert to phase alternating current. Here, the output current (torque) of the electric motor is controlled according to the average ON time ratio, and the frequency of the AC current is controlled by matching the frequency of the ON / OFF time with the electric motor rotation speed × pole number. ing.

FIG. 2A shows the state of point A in FIG. 3, in which the U-phase H-side switching element is turned ON, the V and W-phase H-side switching elements are turned OFF, and the U-phase L-side switching element is turned ON. The element is OFF and the V- and W-phase L-side switching elements are ON, and the current is U as shown by the arrow in FIG.
The phase branches into V and W phases. FIG. 2B shows the state of point B in FIG. 3, in which the U-phase H-side switching element is turned off and the V- and W-phase H-side switching elements are turned off.
ON the L side switching element of N and U phases, L of V and W phases
The side switching element is OFF, and current flows from the V and W phases to the U phase in a merged manner, as shown by the arrow in FIG.

In addition to such basic control, the present invention performs variable control of the PWM carrier frequency according to the rotation speed of the electric motor, that is, the output frequency of the inverter. A first embodiment of variable frequency control of a PWM carrier will be described with reference to the flowchart of FIG. In step 1, it is determined whether or not a preset arbitrary constant Kf times the electrical angular frequency ωm, which is the number of poles times the rotation speed of the electric motor, is greater than the PWM carrier frequency Fpl during low rotation.

When it is determined that Kf × ωm> Fpl, that is, during high speed rotation control, the routine proceeds to step 2, where the count value CNT of the frequency change counter is the PWM carrier frequency Fph for high rotation and the PWM carrier frequency for low rotation. Difference from Fpl (=
Fph-Fpl) or more is determined. And CNT
When it is determined that ≧ Fph−Fpl, the routine proceeds to step 3, where the count value CNT is limited as CNT = Fph−Fpl,
When it is determined that CNT <Fph-Fpl, the routine proceeds to step 4, where the count value CNT is increased by a predetermined value dltf (C
NT ← CNT + dltf).

Further, when it is determined in step 1 that Kf × ωm ≦ Fpl, that is, during low speed rotation control, the process proceeds to step 5 and it is determined whether the count value CNT is 0 or less, and CN
When T ≦ 0, CNT is limited to 0, and when CNT> 0, the process proceeds to step 6 to decrease the count value CNT by a predetermined value dltf (CNT ← CNT−dltf). Then, in step 5, the PWM carrier frequency Fp is set to a value obtained by adding the count value CNT to the low rotation PWM carrier frequency Fpl.

That is, the rotation speed of the electric motor is 100Ωm ≦
When the low rotation speed of Fpl is maintained, PWM
The carrier frequency Fp is the PWM carrier frequency Fpl for low rotation.
The rotation speed is increased to Kf × ωm> Fpl, and is gradually increased to the PWM carrier frequency Fph for high rotation. When the motor is decelerated from this state and Kf × ωm ≦ Fpl, the PWM carrier frequency Fp is gradually reduced to the low rotation carrier frequency Fpl.

As described above, by setting the PWM carrier frequency to the low frequency Fpl at the time of low rotation, the number of times of switching of the switching element of the inverter can be reduced to reduce the power loss and the heat generation amount of the switching element is also reduced. Breakage can be avoided and durability is also improved (see FIG. 5A). Further, since the pulse interval of the carrier can be increased by lowering the PWM carrier frequency, the current control resolution of the electric motor can be maintained at a high value (see FIG. 5 (B)).

However, if the PWM carrier frequency is too low, the energization / interruption period becomes large and the torque ripple is affected. Therefore, the lowest frequency (Fpl in this embodiment) is set so as not to exert the effect. On the other hand, during high speed rotation control, P
By setting the WM carrier frequency Fp to the high frequency Fph, the waveform of the alternating current can be made as close to a sine wave as possible (see FIG. 6). That is, as the rotation speed increases, the amount of change in the drive voltage per unit time increases. Therefore, if the PWM carrier frequency is low, the amount of change for each pulse becomes too large, and the distortion with respect to the sine wave shape becomes large.
In order to obtain a sine wave without distortion, at least PWM carrier frequency = inverter output frequency (= motor rotation speed / motor pole number) × about 100 times is required.

FIG. 7 shows the relationship between the motor characteristics and the PWM carrier frequency. Next, a second embodiment of frequency variable control of the PWM carrier wave will be described. The second embodiment has the same basic control as the first embodiment, but adds a fail-safe function. As the hardware, as shown in FIG. 8, an element temperature sensor 11 for directly detecting the temperature of the switching element of the inverter 2 is provided, or as shown by a dashed line in the figure, a water cooling system for cooling the inverter is provided. A water temperature sensor 12 that indirectly detects the temperature of the cooling water is provided. The element temperature sensor 11 or the water temperature sensor 12 can be configured by a thermocouple or the like. Further, instead of detecting the element temperature with a sensor, as shown in FIG. 9, a current sensor 21 for detecting a power supply current Ib and a current sensor 22 for detecting a conduction current Im of the electric motor 3 are provided, and these currents Ib, Im From the power loss ER of the element calculated from
The element temperature that correlates with?

ER = ∫ {Ib− (Im effective value) × Vb} dt Im effective value = √2 / 3 × (Im amplitude) / 2 FIG. 10 shows a control flow of the second embodiment. Steps 13 and subsequent steps are the same as those in FIG. 4 showing the flowchart of the first embodiment. In step 11, it is determined whether the element temperature of the inverter 2 detected by the element temperature sensor 11 or the water temperature sensor 12 or estimated from the power loss ER of the element is lower than the abnormality determination temperature, and is determined to be lower than the abnormality determination temperature. In this case, the process proceeds to step 13 and subsequent steps, and the PWM carrier frequency control according to the electric motor control state similar to that of the first embodiment is performed. Here, the abnormality determination temperature is set to a temperature of about 80 ° C to 100 ° C.

When it is determined in step 11 that the element temperature of the inverter 2 is equal to or higher than the abnormality determination temperature, the process proceeds to step 12 and the count value CNT of the counter described in the first embodiment is reset to zero. By doing this, step 2
PWM for low rotation when PWM carrier frequency set by 0
The carrier frequency Fpl is maintained. That is, when the element temperature becomes abnormally high, the PWM carrier frequency Fp is set low even during high-speed control of the electric motor,
The number of times of switching is reduced to suppress heat generation, suppress an increase in element temperature, avoid thermal destruction, and ensure durability.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of an electric vehicle equipped with an inverter control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a circuit configuration and an operation of an inverter and an electric motor of the same embodiment.

FIG. 3 is a time chart showing the operation of the inverter and the electric motor of the same.

FIG. 4 is a flowchart showing a first embodiment of PWM carrier frequency control.

FIG. 5 is a diagram showing a power loss reduction effect and a resolution improvement effect during low-speed control according to the same embodiment.

FIG. 6 is a diagram showing the effect of improving the waveform accuracy of an alternating current during high-speed control according to the same embodiment.

FIG. 7 shows the relationship between the motor characteristics and the carrier frequency of the above embodiment.

FIG. 8 is a diagram showing a hardware configuration in a second embodiment of frequency control of a PWM carrier wave.

FIG. 9 is a diagram showing another example of the hardware configuration in the second embodiment of the frequency control of the PWM carrier wave.

FIG. 10 is a flowchart showing a second embodiment of PWM carrier frequency control.

[Explanation of symbols]

1 battery 2 inverter 3 electric motor 11 element temperature sensor 13 Water temperature sensor 21, 22 Current sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tatsuo Matsumura             1370 Onna, Atsugi, Kanagawa             Nissia Jex F-term (reference) 5H007 AA04 AA06 AA08 BB06 CA02                       CB02 CB05 CC23 DA03 DB02                       DB03 DB13 DC02 DC03 DC08                       EA14 HA05                 5H115 PA15 PC06 PG04 PI16 PU08                       PV09 PV24 QN23 RB22 TO05                       TO12 TR02 TU11 TZ01                 5H575 AA17 BB04 BB06 BB09 DD03                       HA09 HB20 JJ03 JJ04 JJ12                       JJ22 LL01 LL22 LL33                 5H576 AA15 BB04 BB06 BB09 CC04                       DD02 EE15 EE19 HA04 HB02                       JJ03 JJ04 JJ12 JJ22 LL01                       LL22 LL43

Claims (7)

[Claims] 1. A voltage-driven PWM inverter for controlling a motor, wherein the PWM carrier frequency is low when the inverter output frequency is low, and is high when the inverter output frequency is high. Control device. 2. The control device for a voltage-driven PWM inverter according to claim 1, wherein the lower limit value of the PWM carrier frequency is set near the lower limit frequency within a range where torque ripple influence is small. 3. An inverter element temperature is detected, and when the element temperature is too high, PWM is performed even during high rotation control of an electric motor.
The control device for the voltage-driven PWM inverter according to claim 1 or 2, wherein the carrier frequency is lowered. 4. The control device for a voltage-driven PWM inverter according to claim 3, wherein the element temperature of the inverter is directly detected by a temperature sensor provided in the inverter body. 5. The control device for a voltage-driven PWM inverter according to claim 3, wherein the element temperature of the inverter is indirectly detected by a temperature sensor that detects a cooling water temperature for cooling the inverter body. 6. An inverter element temperature is estimated and detected by detecting a current flowing through an element of an inverter and a current flowing through an electric motor, and by integrating a power loss calculated based on these detected values. The control device for the voltage-driven PWM inverter according to claim 3. 7. The control device for an inverter according to claim 1, wherein the electric motor is a traveling electric motor mounted on an automobile.