JPH10127062A - Protective circuit for inverter for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the surge voltage produced when a switching element is turned off and prevent it from being damaged due to arm short-circuit irrespective of the voltage drop in the forward direction by connecting a capacitor to a power source of an inverter. SOLUTION: From a key switch 9, a resistor R4 and a Zener diode ZD1 re connected in series to a (-) power source line 3, and in parallel to the Zener diode ZD1, a capacitor C2 is connected. From a (+) line 8, a Zener diode ZD2 and resistors R5, R6 are connected in series to the (-) power source line 3. The connection point a of the resistor R5, R6 is connected through a resistor R10 to an inversion input terminal of an operational amplifier OPAMP. From a connection point b of the resistors R5, R6, a diode D3 and a capacitor C3 are connected in series to the (-) power source line 3. A resistor R7 is connected in parallel to the capacitor C3. The capacitor C3 is connected through a resistor R8 to a non-inversion input terminal of the operational amplifier OPAMP, and the non-inversion input terminal and an output terminal are connected by a resistor R9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an inverter for an electric vehicle.

[0002]

2. Description of the Related Art As overcurrent protection of a switching element,
There is JP-A-59-165961. Japanese Patent Application No. 7-99218 discloses an inverter used in an inverter.

[0003] These techniques utilize the fact that the value of the forward voltage drop of the switching element increases when an excessive current flows.

On the other hand, in order to reduce the loss due to the forward voltage drop of the switching element, improvements are made such as connecting the switching element in parallel or reducing the forward voltage drop of the element. Therefore, in the related art, the value of the voltage drop detected by the normal current and the value of the voltage drop detected by the excessive current has become difficult to distinguish. For this reason, there is a problem that it is not possible to distinguish between the fluctuation of the forward voltage drop due to the temperature change and the normal current value.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an overcurrent protection for a switching element which may be erroneously detected due to a temperature fluctuation of a forward voltage drop, or may be used to prevent the element from being damaged by an overcurrent without using a special current sensor. Is to prevent it.

[0006]

SUMMARY OF THE INVENTION In general, a capacitor is connected to a power supply of an inverter in order to reduce a surge voltage when a device used in the inverter is turned off.

According to the present invention, there is provided means for detecting the amount of change in the discharge voltage of the power supply capacitor, means for detecting whether the amount of change in the voltage exceeds a certain specified voltage within a certain specified time, and interrupting the drive signal of the inverter. Use a circuit that performs

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 2 is a main circuit diagram generally used.

A (+) voltage is supplied from the (+) power supply line 2 of the battery 1 to the inverter 11 via the (+) line 8 via the main contact 6 of the contactor 5. Key switch 9, contactor 5
And the transistor TR1 in series are connected to the (−) power supply line 3.

A power capacitor C1 is connected to the (+) line 8 and the (-) power line 3.

Switching elements Q1 and Q2 (Q3 and Q
4, and Q5 and Q6) constitute an arm 12, which is connected to an AC motor 13 from an intermediate point.

A current sensor 14 for detecting a current flowing in the battery 1 is connected to current sensors 15 and 16 for detecting a current flowing in the AC motor 13.

The wirings of the battery 1, the (+) power line 2 and the (-) power line 3 have an inductance component. Therefore, inverter 1
The current from the battery 1 is also intermittent, corresponding to the switching cycle of 1 on / off.

If the power supply capacitor 10 is not provided, the energy due to the conduction of the inductance 4 becomes a high voltage surge and is applied to the inverter 11. If the surge voltage is large, the switching element may be broken.

Thus, the power supply capacitor 10 absorbs the energy of the inductance 4 and reduces the surge voltage.

The larger the capacitance of the power supply capacitor 10, the smaller the voltage increase of the power supply capacitor 10. Then, the voltage applied to the switching element of the inverter 11 also decreases.

Inductance L in a battery fork truck
Assuming that the value of 1 is several microhenries, the value of the power supply capacitor C1 only needs to be about several hundred microfarads or more. FIG. 3 shows a commonly used inverter control circuit.

The control circuit 17 detects a power supply voltage from the key switch 9, a speed command signal from the accelerator 18, a rotation direction from the forward / reverse switch 9, a control current from the current sensors 14, 15, 16 and the like, and a gate signal. Is generated, and is formed into a gate pulse waveform by the gate drive circuit 21 via the signal cutoff circuit 20, and the switching elements Q1, Q2,
The gates of Q3, Q4, Q5 and Q6 are provided.

The key switch 9 is connected to the base of the transistor TR1 via the resistor R1.

From the arm short-circuit protection circuit 22 to the diode D
2 is connected to the resistor R2 through the
Through the resistor R3 to the base of the transistor TR2. The collector of the transistor TR2 is connected to the base of the transistor TR1, and the emitter of the transistor TR2 is connected to the (-) power supply line 3.

When the arm short-circuit protection circuit 22 operates and the output goes high, the output signal of the signal cutoff circuit 20 is cut off, and the base current of the transistor TR1 is cut off.
The current flowing through the coil 7 of the contactor 5 in FIG. 1 is interrupted, and the main contact 6 is opened.

Although not shown in the figure, the control circuit 17 has a protection circuit that opens the main contact 6 of the contactor 5 when a current value becomes excessive due to a signal from the current sensors 14, 15, 16.

FIG. 1 shows an arm short-circuit protection circuit according to the present invention.

A resistor R4 and a Zener diode ZD1 are connected in series from the key switch 9, connected to the (-) power supply line 3, and a capacitor C is connected in parallel with the Zener diode ZD1.
2 is connected. This constitutes a constant voltage circuit and is used as a power supply for the control circuit.

From the (+) line 8 to the Zener diode ZD
2. Connect the resistors R5 and R6 in series to the (-) power supply line 3.

From the connection point a of the resistors R5 and R6 to the resistor R10
To the inverting input terminal of the operational amplifier OPAMP, and connect the diode D3 and the capacitor C3 in series from the connection point of the resistors R5 and R6 to the (-) power supply line 3. A resistor R7 is connected in parallel with the capacitor C3.

The capacitor C3 is connected to the non-inverting input terminal of the operational amplifier OPAMP via the resistor R8, and the non-inverting input terminal and the output terminal are connected by the resistor R9.

The Zener diode ZD2 is for detecting a large change in the voltage of the power supply capacitor C1.
The resistors R5 and R6 are split resistors that determine a voltage level to be detected.

The diode D3 and the capacitor C3 are for maintaining a peak voltage. Operational amplifier OPAM
By using the FET input type for P, the discharge of the capacitor C3 is reduced.

The resistors R8 and R9 have a function of providing a hysteresis to the detection level and providing a difference in the operating point for stabilization.

An operational amplifier OPAMP, resistors R8, R9,
R10 constitutes the comparison circuit 23.

FIGS. 4A, 4B and 4C show voltage waveforms at point a shown in FIG.

FIG. 3A shows a general operation, and FIG. 3B shows a state in which over-modulation is performed, and the switching elements are fully conductive between times t1 and t2. (C) shows a case where the arm is short-circuited. This indicates that the voltage of the power supply capacitor C1 has dropped by VC3 within the time t4 after the short circuit at the time t3.

(T4−t3) is a switching cycle of the inverter 11, and VC3 is larger than VC2 and is a specified value for detecting a short circuit.

FIG. 5 shows the relationship between the voltage at point a and the voltage at point b in FIG.

The solid and dotted lines indicate the voltage at point a. The solid line shows the characteristics when the AC motor is not rotated, and the dotted line shows the case when the arm is short-circuited.

The voltage at the point b becomes d1 lower at the first time due to the voltage drop of the diode D3. The one-dot chain line slope of the voltage at the point b is set larger than the slope of the solid line. This is set by changing the value of the resistor R7 in FIG. The discharge circuit 24 determines a prescribed time constant by the capacitor C3 and the resistor R7 and lowers the voltage.

The values of the resistors R5, R6, R7 and R9 in FIG. 1 are set as follows in order to reduce the influence of the operation. The resistance R9 is several tens of times the resistance R7, and the combined resistance of the resistances R5 and R6 is several tenths of the resistance R7.

FIG. 6 shows another protection circuit according to the present invention.

The same symbols as in FIGS. 1, 2 and 3 used in this figure have the above functions.

As an output signal from the control circuit 17, FIG.
As shown in (d), when the current starts to flow in the inverter, a pulse is issued in synchronization. This signal is applied to the monostable multivibrator 26, and a constant pulse width is applied to the analog switch 27.

The capacitor C3 is charged with a voltage corresponding to the peak voltage of the power supply capacitor C1, and holds the voltage until the next pulse.

The voltage detected by the resistors R8 and R9 is
When the difference between the input voltage of the operational amplifier OPAMP and the input voltage exceeds a specified value, the output voltage of the operational amplifier OPAMP becomes high level, and the signal cutoff circuit shown in FIG. 3 is operated.

The specified time is a switching cycle of the inverter 11 (t4−t3).

Although the above-described protection is applied only to the short-circuit of the arm of the inverter, the same effect can be obtained for the ground fault or short-circuit of the motor 13. The same effect can be obtained in a device in which a power supply capacitor is connected to a chopper circuit.

[0047]

According to the present invention, element damage due to arm short circuit can be prevented regardless of the forward voltage drop of the switching element.

[Brief description of the drawings]

FIG. 1 is a protection circuit diagram according to an embodiment of the present invention.

FIG. 2 is a main circuit diagram of an inverter.

FIG. 3 is an inverter control circuit diagram.

FIG. 4 is an operation waveform diagram of FIG. 1;

FIG. 5 is an operation explanatory diagram of FIG. 1;

FIG. 6 is a protection circuit diagram according to a second embodiment of the present invention.

[Explanation of symbols]

3 ... (-) power line, 8 ... (+) line, 9 ... key switch,
10: power supply capacitor, 22: arm short-circuit protection circuit, 2
3 ... Comparison circuit, 24 ... Discharge circuit.

Claims (2)

[Claims] A means for detecting and holding a peak voltage of the power supply capacitor in a protection circuit for an electric vehicle inverter including a battery, a power supply capacitor, an inverter including a plurality of arms, an AC motor, a current sensor, and the like. Means for comparing the voltage of the power supply capacitor after continuous discharging, means for detecting whether this voltage has dropped below a certain voltage within a certain time, a protection circuit including the detection means, and an output signal of the protection circuit. A protection circuit for an inverter for an electric vehicle, comprising a circuit for shutting off a gate signal of the inverter. 2. The protection circuit according to claim 1, further comprising a circuit for comparing a voltage of a discharge circuit charged at a peak voltage of the power supply capacitor and discharged with a predetermined time constant with a voltage of the power supply capacitor continuously discharged. A protection circuit for an inverter for an electric vehicle, comprising a circuit for interrupting a gate signal of the inverter with an output signal of the protection circuit.