JPH09121595A - Power converter protective structure from temperature rise - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a power converter fro temperature rise without decreasing torque, even if the temperature of a switching element of an inverter main circuit rises. SOLUTION: A limit torque command τL is obtained by limiting the upper limit of a torque command τ with a torque limit value, three-phase control voltage command (V) is obtained from the limit torque command τL, and a modulated command (P) is obtained from the three-phase control voltage command (V) pulse-width-modulated with a carrier signal CH or CL. This modulated command (P) turns on/off a switching element of the inverter main circuit to obtain an equivalent three-phase current (I), which is supplied to a motor 6. If the detected temperature (T) of the switching element rises, the high-frequency carrier signal CH is switched over to a low-frequency signal CL. If the temperature continue rising even after this process, the limit torque command τL is reduced by lowering the torque limit value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature protection mechanism for a power converter, and is devised so that when the temperature of a switching element of a main circuit rises, the temperature can be protected without causing a torque reduction immediately. Is.

[0002]

2. Description of the Related Art Motor drive control technology for driving a motor by an inverter is widely used.
In recent years, in order to improve the global environment, research and practical application of electric vehicles have been actively promoted. The motor drive control technology is applied to such an electric vehicle.

An example of the motor drive control system will be outlined with reference to FIG. In FIG. 2, a torque limit value τ _S is set in the torque limiter 1. When the torque command τ is input to the torque limiter 1, the torque limiter 1 outputs the limit torque command τ _L whose upper limit value is suppressed to τ _S. That is, when τ <τ _S , τ _L = τ, and when τ ≧ τ _S , τ _L = τ _S.

The power conversion control unit 2 outputs a three-phase control voltage command V according to the limit torque command τ _L.

The PWM circuit 3 has a PWM modulator 3a and a carrier signal generator 3b, and has a PWM (Pulse Wideth M)
odulation) Modulate. That is, the carrier signal generator 3
b outputs a carrier signal (for example, triangular wave) C, and PWM
The modulator 3a has a three-phase control voltage command V and a carrier signal C.
And the modulation command (base current) P is output. It should be noted that in order to realize reduction of noise and high response of current control, it is better to increase the frequency of the carrier signal C and increase the switching frequency.

The inverter main circuit 4 is formed of a switching element such as an IGBT, and the switching element is turned on / off according to the high / low of the modulation command P,
An equivalent three-phase current I is created from the current of the battery 5. This equivalent three-phase current I is supplied to the motor 6 and the motor 6 is rotationally driven.

The temperature sensor 7 is attached to the cooling fin of the inverter main circuit 4, detects the temperature of the switching element of the inverter main circuit 4, and outputs the detected temperature T.

The temperature protection device 8 decreases the value of the torque limit value τ _S set in the torque limiter 1 as the value of the detected temperature T increases. Because of this, when the temperature rises, the limit torque command τ _{L, and} consequently the three-phase control voltage command V and the equivalent three-phase current I, decrease, the loss in the inverter main circuit 4 is reduced, and temperature protection (temperature decrease) is performed. I am trying. Thus, thermal destruction of the switching elements of the inverter main circuit 4 is prevented.

[0009]

In the prior art shown in FIG. 2, when the temperature rises, the torque is reduced to prevent the temperature rise. However, depending on the application of the motor drive control technology, there are many applications where it is not desired to reduce the torque. For example, in the case of being applied to an electric vehicle, if the torque is reduced while climbing a slope, it will not be able to climb the slope and will stop.

In view of the above-mentioned conventional technique, the present invention provides a temperature protection mechanism for a power converter that can perform temperature protection without immediately reducing the torque when the temperature of the switching element rises.

[0011]

DISCLOSURE OF THE INVENTION The present invention for solving the above problems provides a torque limiter for outputting a limit torque command obtained by limiting an upper limit value of a torque command by a set torque limit value, and a limit torque command. A power conversion control unit that obtains and outputs a corresponding control voltage command, a PWM circuit that generates a carrier signal and PWM-modulates the carrier signal and the control voltage command to obtain a modulation command, and a switching element that responds to the modulation command. A temperature that detects the temperature of the switching element and outputs the detected temperature in a power converter consisting of an inverter main circuit that generates an equivalent AC current from a DC current by turning it on and off and supplies this equivalent AC current to a motor. When the sensor and the detected temperature exceed the preset overheat temperature, the frequency of the carrier signal is set to the set frequency. Lower than, characterized in that the detected temperature with a first temperature protection device for controlling to return to the set frequency to the frequency of the carrier signal and becomes less than the overheat temperature.

Further, according to the present invention, a torque limiter for outputting a limit torque command obtained by limiting the upper limit value of the torque command by the set torque limit value, and a control voltage command corresponding to the limit torque command are outputted. Equivalent to a DC current by a power conversion control unit, a PWM circuit that generates a carrier signal and PWM-modulates a carrier signal and a control voltage command to obtain a modulation command, and a switching element is turned on / off according to the modulation command. In a power converter including an inverter main circuit that generates an alternating current and supplies the equivalent alternating current to a motor, a temperature sensor that detects the temperature of the switching element and outputs the detected temperature, and a protection operation command are input. When the frequency of the carrier signal is lowered below the set frequency and the protection operation command is not input, the carrier signal A first temperature protection device for controlling the frequency of the signal to return to the set frequency, and when the protection operation command is input, the torque limit value is lowered below the set value, and when the protection operation command is not input, the torque limit value is reduced. A second temperature protection device for controlling the value to return to a set value, a first superheat temperature and a second superheat temperature higher than this are set, and the detected temperature is equal to or lower than the first superheat temperature. When the detected temperature exceeds the first overheat temperature, the protective operation command is sent to the first temperature protection device, and when the detected temperature exceeds the second overheat temperature, the first operation is performed. A temperature protection device and a protection method selection unit for sending a protection operation command to the second temperature protection device.

Further, according to the present invention, the first temperature protection device performs a switching operation by performing a hysteresis operation during a switching operation of lowering the frequency of the carrier signal below the set frequency or returning the lowered frequency to the set frequency. It is characterized by

In the present invention, when the temperature of the switching element of the inverter main circuit rises, the frequency of the carrier signal of the PWM circuit is first lowered, and when the temperature still rises, the torque is controlled to be lowered to prevent the temperature rise.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. It should be noted that parts having the same mechanism as those in the prior art are designated by the same reference numerals, and the description of the same functional parts will be simplified.

As shown in FIG. 1, in this embodiment, the torque command τ is a limit torque command τ _L whose upper limit is limited by the torque limit value τ _S set in the torque limiter 1. The power conversion control unit 2 uses the limit torque command τ
_The three-phase control voltage command V corresponding to _L is output, and the PWM circuit 3
Outputs a modulation command P according to the three-phase control voltage command V.
The switching element of the inverter main circuit 4 performs a switching operation according to the modulation command P, whereby the battery 5
An equivalent three-phase current I is obtained from the DC current of This equivalent three-phase current I is supplied to the motor 6 and the motor 6 is rotationally driven.

The PWM circuit 3 comprises a PWM modulator 3a and a carrier signal generator 3c. Of these, the carrier signal generator 3c is configured to generate a high frequency carrier signal C _H (having a set frequency) and a low frequency carrier signal C
_{One of L} is selectively output. Although details will be described later, when the temperature of the switching element of the inverter main circuit 4 is low, a high frequency carrier signal C _H is output, and when the temperature of the switching element is high, a low frequency carrier signal C _L is output. .

The PWM modulator 3a performs PWM modulation using the carrier signal C _H or the carrier signal C _L. At this time, noise is reduced when the high-frequency carrier signal C _H is used, but switching loss in the inverter main circuit 4 increases. On the other hand, when the low frequency carrier signal C _L is used, the noise (electromagnetic noise) increases, but the switching loss in the inverter main circuit 4 decreases.

Further, in this embodiment, in order to protect the temperature of the inverter main circuit 4, a temperature sensor 7, a protection method selection unit 10, a first temperature protection device 11 and a second temperature protection device 12 are provided. ing. The temperature protection device 11 comprises a hysteresis section 11a and a carrier signal switching section 11b.

Of these, the temperature sensor 7 is attached to the cooling fins of the inverter main circuit 4, and outputs the detected temperature T indicating the temperature of the switching element. In the following description, it is assumed that the temperature is t _LL <t _L <t _LH <t _H.

In the protection method selection section 10, a first superheat temperature t _L and a second superheat temperature t _H are set. Then, the protection method selection unit 10 determines that the detected temperature T is the first overheat temperature t _L.
When it is below, the protection operation command is not output, and when the detected temperature T exceeds the first overheat temperature T _L , temperature protection (described later) by the first temperature protection device 11 is started, and the detected temperature T is further increased to the second value. When the overheat temperature T _H is exceeded, temperature protection by the second temperature protection device 12 (described later) is started in addition to the temperature protection by the first temperature protection device 11.

That is, when the temperature of the switching element of the inverter main circuit 4 is low and the detected temperature T is lower than the first overheat temperature t _H , the carrier signal switching unit 11b of the first temperature protection device 11 switches the carrier signal. The command K _H is output and the carrier signal generator 3 c of the PWM circuit 3 outputs the high frequency carrier signal C _H. In addition, the second temperature protection device 12 sets the torque limit value τ _S set in the torque limiter 1 to a set value (large value).

When the detected temperature T exceeds the first overheat temperature t _L , the protection method selection section 10 sends a protection operation command to the first temperature protection device 11, and the temperature protection device 11 starts temperature protection. . That is, the hysteresis parts 11a are set with hysteresis temperatures t _LL and t _LH (where t _LL <t _L <t _LH ) which are slightly different from the first overheating temperature t _L. Then, when the detected temperature T becomes higher than t _{LH, the} carrier signal switching command K is issued from the carrier signal switching unit 11b.
_L is output, and the low-frequency carrier signal C _L is output from the carrier signal generator 3c. When the detected temperature T becomes lower than t _LL , the carrier signal switching unit 11b outputs the carrier signal switching command K _H , and the carrier signal generation unit 3
A high-frequency carry signal C _H is output from c.

Therefore, the detected temperature T is the first overheat temperature t.
_{When the} temperature exceeds _L and further exceeds the hysteresis temperature t _LH , the high frequency carry signal C _H is switched to the low frequency carrier signal C _L. When the low frequency carrier signal C _L is used, the switching loss in the inverter main circuit 4 is reduced. As a result, the temperature rise of the switching element is suppressed or the temperature is lowered. The value of the limit torque command τ _L does not change even when the carrier signal C _L is selected, so the output torque of the motor 6 does not decrease. Also, when the carrier signal C _L of low frequency is switched, the electromagnetic noise becomes high, so that the operator can know that the temperature is rising.

In this way, when the temperature of the switching element is lowered and the detected temperature T becomes smaller than the hysteresis temperature t _LL , the low frequency carrier frequency C _L is switched to the high frequency carrier C _H. In this example, the carrier signal C
_L, since a hysteresis characteristic to the switching of the C _H, never hunting occurs.

Temperature protection by the first temperature protection device 11
Low frequency carrier signal C operated _LEven when using
However, the detected temperature T continues to rise, and the detected temperature T
2 superheat temperature t_HIf it exceeds, the protection method selection unit 10
A protection operation command is also sent to the temperature protection device 12 of 2
The temperature protection by the degree protection device 12 is also started. That is, this
Like T> t_HTemperature protection device 12
Is the torque limit value τ set in the torque limiter 1.
_SDecrease the value of. Thus the torque limit value
τ_SIs reduced, the limit torque command τ_L， Three-phase system
The value of the control voltage command V and the equivalent three-phase current I decreases and the motor
Although the output torque of 6 decreases, it flows to the switching element.
Current is reduced and overheating of the switching elements is prevented.
You.

After all, when the detected temperature T exceeds the first overheating temperature t _L , in other words, when the switching element is overheated within a temperature range in which there is no risk of thermal destruction, the carrier is reduced without reducing the torque. Heat generation is suppressed by lowering the signal frequency. Also, the detected temperature T
Exceeds the second overheating temperature t _H , in other words, only when the temperature becomes so high that the switching element may be thermally destroyed, the torque is reduced to suppress heat generation. Therefore, in most cases, overheating can be prevented without lowering the torque, and the torque is reduced only in the rare cases where overheating occurs to the extent that thermal destruction may occur to ensure safety. Therefore, the circuit of FIG. 1 is optimal as a motor control circuit for an electric vehicle.

[0028]

As described above in detail with the embodiments, according to the present invention, the temperature rise is prevented by lowering the frequency of the carrier signal when the detected temperature exceeds the first overheat temperature. The temperature can be protected without reducing the output torque of the motor.

When the detected temperature exceeds the second overheat temperature, the temperature rise is prevented by lowering the frequency of the carrier signal and the torque so that the temperature rise can be surely prevented and the element is thermally destroyed. The serious accident will not occur and safety will be improved.

Furthermore, since the switching of the carrier signal frequency has a hysteresis characteristic, stable operation can be performed without causing hunting.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional technique.

[Explanation of symbols]

1 torque limiter 2 power conversion control unit 3 PWM circuit 3a PWM modulation unit 3b, 3c carrier signal generation unit 4 inverter main circuit 5 battery 6 motor 7 temperature sensor 8 temperature protection device 10 protection method selection unit 11 first temperature protection device 11a Hysteresis part 11b Carrier signal switching part 12 Second temperature protection device τ Torque command τ _L Limit torque command V Three-phase control voltage command P Modulation command I Equivalent three-phase current T Detection temperature C, C _H , C _L Carrier signal K _H , K _L Carrier signal switching command

Claims (3)

[Claims] 1. A torque limiter for outputting a limit torque command obtained by limiting an upper limit value of a torque command with a set torque limit value, and a power conversion control for obtaining and outputting a control voltage command according to the limit torque command. Department,
A PWM circuit that generates a carrier signal and PWM-modulates the carrier signal and a control voltage command to obtain a modulation command, and a switching element is turned on / off according to the modulation command to generate an equivalent AC current from a DC current. In a power converter including an inverter main circuit that supplies an equivalent AC current to a motor, a temperature sensor that detects the temperature of the switching element and outputs a detected temperature; and if the detected temperature exceeds a preset overheating temperature, A first temperature protection device for controlling the frequency of the carrier signal to be lower than a set frequency and controlling the frequency of the carrier signal to return to the set frequency when the detected temperature becomes equal to or lower than the overheat temperature. Power converter temperature protection mechanism. 2. A torque limiter for outputting a limit torque command obtained by limiting the upper limit value of the torque command by the set torque limit value, and a power conversion control for obtaining and outputting a control voltage command according to the limit torque command. Department,
A PWM circuit that generates a carrier signal and PWM-modulates the carrier signal and a control voltage command to obtain a modulation command, and a switching element is turned on / off according to the modulation command to generate an equivalent AC current from a DC current. In a power converter consisting of an inverter main circuit that supplies an equivalent AC current to a motor, a temperature sensor that detects the temperature of the switching element and outputs the detected temperature, and a frequency of the carrier signal when a protection operation command is input. Lower than the set frequency, and when the protection operation command is no longer input, the first temperature protection device that controls the frequency of the carrier signal to return to the set frequency; and when the protection operation command is input, the torque limit value is set. If the protection operation command is not input, the torque limit value will be returned to the set value. A second temperature protection device, a first overheat temperature and a second overheat temperature higher than the first overheat temperature are set. When the detected temperature is equal to or lower than the first overheat temperature, the protection operation command is not issued. When the detected temperature exceeds the first overheat temperature, a protection operation command is sent to the first temperature protection device, and when the detected temperature exceeds the second overheat temperature, the first temperature protection device and the second temperature protection device. A temperature protection mechanism for a power converter, comprising: a protection method selection unit that sends a protection operation command to the device. 3. The first temperature protection device performs a switching operation by performing a hysteresis operation during a switching operation of lowering the frequency of a carrier signal below a set frequency or returning the lowered frequency to the set frequency. The temperature protection mechanism of the power converter according to claim 1 or 2.