JPH0923664A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen a switching loss even when the voltage of a DC power supply fluctuates. SOLUTION: Transistors 13, 14 control a gate of a MOS-input type semiconductor switching element 2a. MOSFETs 29, 30 are serially connected to the transistors 13, 14 respectively through gate resistors 19, 20 and the voltage of a DC power supply of an inverter device is detected by a voltage detecting circuit 24. The MOSFETs 29, 30 are turned off when the detected voltage is higher than a specified level and they are turned on when the detected voltage is lower than the specified level. When the voltage of the DC power supply is high, the gate of the semiconductor switching element 2a is charged by charging resistances of resistors 44, 19, 21 and discharged by discharging resistances of resistors 21, 20, 45, and therefore charging and discharging speeds are slow. On the other hand, when the voltage of the DC power supply is low, the gate is charged by the charging resistances of the resistors 19, 21 and discharged by the discharging resistances of the resistors 21, 20, and therefore charging and discharging are done rapidly and there is only a small switching loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for driving an electric motor, which is suitable for electric vehicles and the like whose power supply voltage fluctuates.

[0002]

2. Description of the Related Art FIG. 1 shows a motor drive system for an electric vehicle as an inverter device for driving a motor. In FIG. 1, 1 is a DC power source, 2a, 2b, 2c, 2d,
2e and 2f are MOS input type semiconductor switching elements to which the DC power source 1 is connected, 3a, 3b, 3c, 3d and 3
e and 3f are MOS input type semiconductor switching elements 2a
~ 2f are diodes for freewheeling connected in anti-parallel respectively, 4 is a three-phase motor, 5a and 5b are current sensors for detecting U-phase and W-phase inverter output currents, and 6 is a signal from the current sensors 5a and 5b. Is a controller, 8 is an accelerator sensor provided in an accelerator of an automobile, and 9a, 9b, 9c, 9d, 9e and 9f are gate drive circuits having the same circuit configuration.

The controller 7 drives the gate drive circuits 9a to 9f so that the three-phase motor 4 outputs a predetermined torque in response to the accelerator signal from the accelerator sensor 8 so that the semiconductor switching elements 2a to 2f are energized. By switching control, the current path from the DC power supply 1 to the three-phase motor 4 is switched.

In the motor drive system having the above configuration, the circuit configuration of the conventional gate drive circuits 9a to 9f is shown in FIG. 5 with the gate drive circuit 9a as a representative. FIG.
, 10 is a DC power supply, 11 is a photo coupler, 1
2, 13, 14 are transistors, 15-18 are resistors, 1
Reference numeral 9 is a turn-on gate resistance, 20 is a turn-off gate resistance, and 21 is a gate resistance.

Next, the operation of the conventional gate drive circuit 9a will be described. First, a case where the MOS input type semiconductor switching element 2a is turned on will be described. When the controller 7 drives the primary side diode of the photocoupler 11, the secondary side phototransistor of the photocoupler 11 is turned on, and the transistor 12 is turned off to prevent the base current from flowing to the transistor 12. When the transistor 12 is turned off, a base current flows through the transistor 13 through the resistor 18, so that the transistor 13 is turned on. When the transistor 13 turns on,
The gate of the MOS input type semiconductor switching element 2a is charged through the resistors 19 and 21, and when the gate becomes equal to or higher than a predetermined potential (threshold voltage), the MOS input type semiconductor switching element 2a is turned on.

Next, when turning off the MOS input type semiconductor switching element 2a, when the controller 7 stops driving the primary side diode of the photocoupler 11, the secondary side phototransistor of the photocoupler 11 turns off, A base current flows in the transistor 12 through the resistors 15 and 16, and the transistor 12 is turned on. When the transistor 12 is turned on, the base current supplied to the transistor 13 through the resistor 18 stops flowing. Therefore, the transistor 13 is turned off, and at the same time, the base current flows through the transistor 12 to the transistor 14, so that the transistor 14 is turned on. When the transistor 14 is turned on, the MOS is passed through the resistors 20 and 21.
When the gate of the input type semiconductor switching element 2a is discharged and the gate becomes below a predetermined potential (threshold voltage), the MOS input type semiconductor switching element 2a is turned off.

Next, the switching characteristics of the MOS input type semiconductor switching element will be described. First, the turn-on switching characteristic will be described with reference to FIGS. 6 and 7. In FIG. 6, 22 is the stray inductance of the wiring, and 23 is the load inductance. In FIG. 6, consider the operation when the MOS input type semiconductor switching element 2d is turned on and the load current IL is flowing in the direction of the arrow (1) and the MOS input type semiconductor switching element 2d is turned off. .

MOS input type semiconductor switching element 2
When d is turned off, the load current IL flowing through the semiconductor switching element 2d is commutated to the diode 3a by the load inductance 23 and flows in the direction of arrow (2). Next, when the MOS input type semiconductor switching element 2d is turned on again, the direct current power source 1, the stray inductance 22, the diode 3a, and the diode 3a, as shown by an arrow (3), until the carrier of the diode 3a is released and the reverse recovery is performed. M
An instantaneous short circuit occurs through a circuit including the OS input type semiconductor switching element 2d. In fact, other wiring parts also have inductance, but they are omitted for simplicity of explanation.

A reverse recovery current flows in the reverse direction of the diode 3a to restore the reverse characteristic of the diode 3a. However, when the reverse recovery current is rapidly attenuated, the surge voltage due to the stray inductance 22 causes a MOS input type semiconductor switching element. 2a and diode 3a. This reverse recovery current can be identified by observing the forward current I of the diode 3a. When the MOS input type semiconductor switching element 2d is turned on at time t1, the current i becomes I.
It decreases from the magnitude of L to zero, and then suddenly becomes zero after a reverse recovery current flows. At this time, a large surge voltage VD is applied to the MOS input type semiconductor switching element 2a and the diode 3a by the stray inductance 22. To be done.

This surge voltage VD is the DC power supply voltage V
B, stray inductance 22 is L, VD = L
It becomes di / dt + VB. If the surge voltage VD is not suppressed below the rated voltage VS of the MOS input type semiconductor switching element, the element itself will break down withstand voltage, so it is necessary to reduce the surge voltage VD.

To reduce the surge voltage VD, the DC power supply voltage VB is reduced, the size of L of the stray inductance 22 is reduced, or di / dt is reduced to reduce the surge voltage VD. However, if the DC power supply voltage VB is reduced, the power supplied to the load is limited, and reducing L of the stray inductance 22 is limited in terms of wiring, so di / dt is generally used. Is effective.

One of the methods for reducing di / dt is to shorten the recovery time of the diode. Furthermore, a soft recovery diode that gently attenuates the recovery current has also been developed, but there is a limit, and the waveform A in FIG. 7 is a case where the MOS input type semiconductor switching element 2d is rapidly turned on. The current rises quickly and the surge voltage VD has a large value, which exceeds the rating VS of the MOS input type semiconductor switching element. On the other hand, the waveform B shows the case where the MOS input type semiconductor switching element 2a is gently turned on, and the value of the reverse current i and the value of di / dt are both small, and therefore the surge voltage VD is also low.

At this time, the turn-on time of the MOS input type semiconductor switching element 2d depends on the charging time of the gate, and in order to lengthen the turn-on of the MOS input type semiconductor switching element, the gate of the circuit shown in FIG. Resistance 1
The gate charging time may be lengthened by increasing the resistance values of 9 and 21. However, in order to suppress di / dt, increasing the resistance value of the turn-on gate resistors 19 and 21 as described above and slowing down the switching speed of the MOS input type semiconductor switching element increases the switching loss. Therefore, there is a problem that the loss of the inverter device increases.

Next, the turn-off switching characteristics of the MOS-input type semiconductor switching element will be described with reference to FIGS. 6 and 7. When the load current shown in FIG. 6 is switched from (1) to (2), the current flowing in the MOS input type semiconductor switching element 2d changes from IL to 0. Therefore, both ends of the MOS input type semiconductor switching element 2d are changed. The surge voltage VC is applied to. Surge voltage VC
Is represented by VC = L · di / dt + VB, and in order to suppress the surge voltage VC to be equal to or lower than the rating VS of the MOS input type semiconductor switching element like the turn-on switching characteristic, there is only di / dt suppression, and the MOS input type The turn-off time of the semiconductor switching element 2d depends on the discharge time of the gate. To increase the turn-off time of the MOS input type semiconductor switching element, the resistance values of the gate resistors 20 and 21 of the circuit shown in FIG. 5 are increased. Then, the gate discharge time may be lengthened. However, with respect to the loss aspect of the inverter device, similarly to the turn-on switching characteristic, slowing the turn-off switching speed of the MOS input type semiconductor switching element causes a problem of increasing switching loss.

[0015]

The surge voltage applied to the MOS-input type semiconductor switching element is L.di / d.
Since it is represented by t + VB, in a general-purpose inverter device supplied with electric power from a commercial power source, considering that the DC power supply voltage VB is almost constant, only the term of L · di / dt should be considered. However, in a vehicle equipped with a battery, such as an electric vehicle, the DC power supply voltage VB is charged when the battery is charged or when regenerating when going down a long steep downhill.
Rises, and conversely, during acceleration, the DC power supply voltage VB greatly changes such that the DC power supply voltage VB drops.

That is, as described above, the DC power supply voltage VB
If L rises, L-di / dt + VB is taken into consideration, the switching speed is slowed down to suppress the surge voltage, but if the DC power supply voltage is low, increase the switching speed to increase the surge voltage. However, since the absolute value of the surge voltage is small, the switching loss can be reduced without causing the breakdown voltage of the MOS input type semiconductor switching element.

According to the present invention, in a motor drive system such as an electric vehicle in which the DC power supply voltage of the inverter device fluctuates, the switching speed of the MOS input type semiconductor switching element forming the inverter device is appropriately adjusted according to the DC power supply voltage. The purpose of the control is to reduce the switch loss of the inverter device.

[0018]

According to the present invention, claim 1 is:
A DC power supply, a plurality of sets of voltage-driven semiconductor switching elements connected in series to the DC power supply, a feedback diode connected in antiparallel to each output terminal of the semiconductor switching element, and each semiconductor switching element turned on. In an inverter device that has a control circuit that performs off control and that controls the energization of a load connected to each series connection point of the semiconductor switching elements, the control circuit includes voltage detection means that detects the voltage of the DC power supply. The technical means is to provide a switching speed changing means for changing the switching speed of the semiconductor switching element according to the voltage of the DC power source detected by the voltage detecting means.

According to a second aspect of the present invention, in the first aspect, the semiconductor switching element is a MOS input type transistor, and the switching speed changing means parallels the switching means to at least one gate resistance of a plurality of gate resistances. Charge and discharge of the gate of the MOS input type semiconductor switching element by connecting and controlling the switch means according to the voltage of the DC power source to change the charge and discharge impedance of the gate of the MOS input type semiconductor switching element. The technical means is to control the switching time of the MOS input type semiconductor switching element by controlling the time.

According to a third aspect of the present invention, in the first and second aspects, the semiconductor switching element is a MOS input type transistor, and the voltage detecting means is configured to charge and discharge the gates of the plurality of MOS input type transistors. The technical means is to have each in the gate drive circuit.
A fourth aspect of the present invention is the gate drive circuit according to any of the first and second aspects, wherein the semiconductor switching element is a MOS input type transistor, and the voltage detecting means charges and discharges a gate of each of the plurality of sets of MOS input type transistors. The technical means is to be provided outside and to transmit to all of the gate drive circuits whether the voltage of the DC power supply is equal to or higher than a predetermined voltage.

[0021]

According to the present invention, the switching speed of the semiconductor switching element is controlled by detecting the voltage of the DC power supply by the voltage detecting means and controlling the charge / discharge time of the gate of the semiconductor switching element in accordance with the voltage. Change. As a result, when the voltage of the DC power supply is high, the switching speed of the semiconductor switching element is slowed down, and the L.di / dt component of the surge voltage applied to the semiconductor switching element due to the load inductance is reduced, so that a large surge voltage is applied to the semiconductor. It does not affect the switching element. On the other hand, when the voltage of the DC power supply is low, the switching speed of the semiconductor switching element increases and the L.di / dt component of the surge voltage applied to the semiconductor switching element increases due to the load inductance. Since the voltage itself is low, the absolute value of the surge voltage is low, and the semiconductor switching element is not applied with a surge voltage exceeding the withstand voltage. Further, at this time, since the switching time is shortened, the switching loss is reduced.

[0022]

As described above, according to the present invention, since the switching speed of the semiconductor switching element is changed according to the voltage of the DC power supply, the surge voltage can be reduced when the voltage of the DC power supply is high. Further, when the voltage of the DC power supply is low, the switching loss can be reduced.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an inverter device of the present invention will be described based on an embodiment of a motor drive system for an electric vehicle shown in FIG. The characteristic configuration of the present invention is applied to the gate drive circuits 9a to 9f of the motor drive system shown in FIG. 1, and the circuit configuration of the gate drive circuit 9 according to the embodiment of the present invention is shown in FIG. In FIG. 2, reference numeral 24 is a known voltage detection circuit composed of a differential amplifier circuit using an operational amplifier, and detects the voltage of the DC power supply 1 in the motor drive system. Reference numeral 25a is a comparator, 25b is an output transistor in the comparator 25a, 26 is a reference voltage source, 27 and 28 are transistors, and 29 is a P-type MOSFE.
T and 30 are N-type MOSFETs, 31 to 45 are resistors, and 46.
Is a diode and 47 is a photocoupler. Note that FIG.
In FIG. 5, the same components as those in FIG. 5 have the same configurations.

Next, the gate drive circuit 9 having the above configuration
Will be described. If the voltage of the DC power supply 1 in the motor drive system is equal to or higher than a predetermined voltage, the output transistor 25b in the comparator 25a is turned off, and the base current flows through the transistor 27 through the resistors 33 and 35. Turn on.
When the transistor 27 is turned on, the base current is supplied to the transistor 28, so that the transistor 28 is turned on. When the transistor 27 turns on, an N-type MOS
Since the gate of the FET 30 is discharged, N-type MOSFE
T30 turns off. Further, since the transistor 28 is turned on, the gate of the P-type MOSFET 29 is charged, so that the P-type MOSFET 29 is turned off. At this time,
The charging resistance of the gate of the MOS input type semiconductor switching element is the series resistance of the resistances 44, 19 and 21, and the discharging resistance of the gate is the series resistance of the resistances 21, 20 and 45.

On the contrary, if the DC power supply voltage of the inverter device is below a predetermined voltage, the output transistor 25b in the comparator 25a is turned on, so that the base current is not supplied to the transistor 27 and the transistor 27 is turned off. Become. When the transistor 27 is turned off, the base current is not supplied to the transistor 28, so that the transistor 28 is turned off. Here, in the diode 46, when the transistor 27 is off, the base current of the transistor 28 flows through the resistors 37, 42, and 43, and
It is reversely blocked so that 8 cannot be turned on accidentally. When the transistor 28 is turned off, the gate of the P-type MOSFET 29 is biased negatively with respect to the source, so that the P-type MOSFET 29 is turned on. Transistor 2
Since 7 is turned off, N
Since the gate of the type MOSFET 30 is biased positive with respect to the source, the N type MOSFET 30 is turned on.

Several A (ampere) class MOSFETs
When turned on, the on resistance becomes several tens of milliohms. At this time, therefore, the charging resistance of the gate of the MOS input type semiconductor switching element is almost the series resistance of the resistors 19 and 21, and the discharging resistance of the gate is the resistance 21, 20 series resistors. Therefore, when the voltage of the DC power supply 1 in the motor drive system becomes equal to or lower than a predetermined voltage, the charging and discharging of the gate of the MOS input type semiconductor switching element becomes faster and the charging and discharging time becomes shorter. As a result, the surge voltage L · di / dt generated when the MOS-input type semiconductor switching element is turned off and turned on increases,
Since the voltage of the DC power supply 1 is in a low state, the absolute value of the surge voltage is low, so that the switching loss can be reduced without causing the breakdown voltage of the MOS input type semiconductor switching element.

FIG. 3 shows the surge voltage waveform applied to the MOS input type semiconductor switching element and the current waveform flowing in the MOS input type semiconductor switching element when the gate drive circuit of this embodiment is used. In the figure, (A) is a case where the voltage VB of the DC power supply 1 of the motor drive system is high, and (B) and (C) are low. Also, (A),
(B) is the case where the control according to the present invention is performed, and (C) is the case according to the conventional technique in which the control is not performed. In addition, VMAX
Is the withstand voltage rating of the MOS input type semiconductor switching element.

In FIG. 3, VB1> VB2,
Comparing (A) and (B), when the voltage VB of the DC power supply 1 of the motor drive system is low (B), the switching speed becomes faster (di / dt becomes larger).
However, the surge voltage level is VMAX for both (A) and (B).
Comparing (B) and (C) below, in case of (B), since the switching time becomes short, the level of the surge voltage becomes large, but the level of surge breakdown voltage of the MOS input type semiconductor switching element is It has not reached VMAX.
Also, since the switching time becomes shorter, it can be seen that the switching loss becomes smaller than that in the case without control.

FIG. 4 shows a gate drive circuit according to the second embodiment of the present invention. In FIG. 4, 47 is a photocoupler.
In the second embodiment, voltage detecting means for detecting the voltage of the DC power supply 1 is provided in the controller 7, and the voltage of the DC power supply 1 is equal to or higher than a predetermined voltage from the controller 7 to the photocoupler 47 of each of the gate drive circuits 9a to 9f. The voltage detection circuit of each gate drive circuit can be omitted because a signal of less than or equal to is transmitted.

In each of the above embodiments, a gate drive circuit for a single power source is shown, but a gate drive circuit for both power sources may be used. Further, although bipolar transistors are used as 13, 14, 27 and 28, other switching means such as FET may be used. Although the photocoupler is used as the interface between the controller 7 and the gate drive circuit, other insulating means such as a pulse transformer may be used. Further, although the turn-on and turn-off are speeded up at the same time, they may be speeded up separately. Further, although the switching speed is divided into two stages of high speed and low speed, it may be divided into a plurality of stages more than that, and the number of stages may be set separately for turn-on and turn-off. Further, although the voltage detection circuit is used as the means for detecting the DC power supply voltage, other insulating means such as an isolation amplifier may be used.

As described above, according to the present invention, in the inverter device in which the power supply voltage fluctuates, the switching speed of the MOS input type semiconductor switching element forming the inverter device is appropriately controlled according to the power supply voltage. The switching loss of the inverter device can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a motor drive system of an electric vehicle showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a gate drive circuit of the motor drive system of the first embodiment.

FIG. 3 is a waveform diagram showing the operation of the first embodiment.

FIG. 4 is a circuit diagram showing a gate drive circuit of a motor drive system of a second embodiment.

FIG. 5 is a circuit diagram showing a gate drive circuit as a conventional technique.

FIG. 6 is a partial circuit diagram for explaining the operation of a conventional gate drive circuit.

FIG. 7 is a waveform diagram for explaining the operation of a gate drive circuit as a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC power supply 2a-2f MOS input type semiconductor switching element 3a-3f Diode (feedback diode) 4 Three-phase motor 7 Controller 9 Gate drive circuit (control circuit, switching speed changing means) 24 Voltage detection circuit (voltage detection means)

Claims (4)

[Claims] 1. A direct current power source, a plurality of sets of voltage-driven semiconductor switching elements connected in series to the direct current power source, feedback diodes antiparallelly connected to respective output terminals of the semiconductor switching element, An inverter device having a control circuit for controlling ON / OFF of a semiconductor switching element, wherein the load connected to each series connection point of the semiconductor switching element is energized and controlled, wherein the control circuit detects the voltage of the DC power supply. An inverter device comprising: a voltage detecting means for controlling the switching speed; and a switching speed changing means for changing the switching speed of the semiconductor switching element according to the voltage of the DC power source detected by the voltage detecting means. 2. The semiconductor switching element is a MOS
The switching speed changing means is an input type transistor, wherein the switching means is connected in parallel to at least one gate resistance of a plurality of gate resistances, and the switching means is controlled according to the voltage of the DC power supply, MO
By varying the charge / discharge impedance of the gate of the S input type semiconductor switching element to control the charge / discharge time of the gate of the MOS input type semiconductor switching element,
2. The inverter device according to claim 1, wherein the switching time of the MOS input type semiconductor switching element is controlled. 3. The semiconductor switching element is a MOS
3. The inverter according to claim 1, wherein the inverter is an input type transistor, and the voltage detection means is provided in each gate drive circuit that charges and discharges the gate of each of the plurality of sets of MOS input type transistors. apparatus. 4. The semiconductor switching element is a MOS
An input type transistor, wherein the voltage detecting means is provided outside a gate drive circuit for charging and discharging the gates of the plurality of MOS input type transistors, and whether the voltage of the DC power supply is equal to or higher than a predetermined voltage, The signal is transmitted to all of the gate drive circuits.
3. The inverter device according to claim 1.