JPH09121553A - Inverter driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the useless current protecting operations of an inverter device by making the current detecting time constant of an overcurrent detecting circuit for an upper-arm transistor larger than that of an overcurrent detecting circuit for a lower-arm transistor. SOLUTION: A transistor 1 which drives a motor, etc., is provided with a sense current element to which a sense current which is proportional to a main current flows and makes an electric current to flow to a current sensing resistor 2. A drive circuit 3 drives the transistor 1. When the electric current flowing to the transistor 1 is not an overcurrent, signals from an input terminal drive the transistor 1 in a PWM state as they are through the drive circuit 3. When the current flowing to the transistor 1 becomes an overcurrent, however, the voltage detected by the sense resistor 2 rises and the transmission of the signals from the input terminal to the drive circuit 3 is stopped. When an overcurrent occurs, therefore, the output transistor 1 is disconnected so that the transistor 1 can be protected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device used for an inverter air conditioner, a general-purpose motor, etc., and more particularly to a protection system for the inverter device.

[0002]

2. Description of the Related Art A conventional inverter device of this type will be described with reference to the drawings.

The structure is as shown in FIGS. 1 and 2, and 1 is a transistor for driving a load device such as a motor, which is a BJT, FET, or IGBT.
Various elements are used, but the feature is that a sense current terminal in which a sense current proportional to the main current flows is provided, and a current can flow in the current sense resistor 2. Reference numeral 3 is a drive circuit (drive circuit) for driving the transistor 1. Various circuit schemes have been proposed according to the characteristics of the transistor 1, but they are not particularly described in the present invention. Reference numeral 4 is a voltage comparator for detecting that the value of the current flowing through the transistor 1 is in the overcurrent state. Reference numeral 5 is a timer circuit which receives the output of the voltage comparator 4 and produces a signal having a constant time width. The output signal of this timer circuit 5 turns on the original transistor 1.
It is connected so as to control the switch circuit 7 that controls the signal (PWM drive signal or the like) from the input terminal 6 of the signal to be turned off.

Therefore, when the overcurrent is not detected, the signal from the input terminal 6 is directly driven through the drive circuit 3 to PWM-drive the transistor 1. However, when an abnormal state such as motor load lock or overload occurs and the drive current of the transistor 1 increases and the overcurrent state occurs, the detection voltage of the sense resistor 2 increases and the voltage comparator 4 When the voltage exceeds the set voltage, the timer circuit 5 is operated, the switch circuit 7 is cut off for a certain time, and the transmission of the signal from the input terminal 6 to the drive circuit is stopped. This protects the output transistor from interruption for a certain period of time when an overcurrent occurs. In addition, since the transistor 1 cuts off the current and cancels the overcurrent state, the recovery from the protection operation is performed when the signal is input to the input terminal 6 after the set time of the timer circuit 5. is there. That is, the timer circuit 5 has a timer circuit configuration that creates a time delay both during operation and during recovery.

Further, in synchronization with the output of the timer circuit 5, a signal is output from the protection output terminal 8 during the transistor protection operation, and the inverter control computer (not shown).
It is informed that it is working against protection.

In FIG. 1, the circuit using one transistor 1 is explained, but in the three-phase inverter,
As shown in FIG. 2, it is general to use 6 in combination. Further, in a single-phase inverter, it is general to use four in combination. (Not shown).

These power modules (IPM
/ Power hybrid IC) trends and conventional technology trends, see, for example, 1992 National Conference of the Institute of Electrical Engineers of Japan.
Proceedings 4 ”(March 1992).

[0008]

However, in the above-mentioned structure, since each potential of the upper arm is a floating potential as compared with the potential of the lower arm, the stability of the circuit operation is The arm has far more instability factors. In particular, the current detection circuit of the upper arm always has an unstable factor as compared with the current detection circuit of the lower arm due to the influence of external noise or the switching (dv / dt) of the lower arm of the inverter arm.

As a result, in the three-phase inverter device as shown in FIG. 5, the upper arm erroneously detects an overcurrent due to external noise or the like and performs an irregular self-protection operation.
In order to turn off the transistor, the open phase operation is performed, resulting in a problem that the rotation of the motor is likely to be unbalanced.

The present invention solves the above-mentioned problems of the conventional example, and an object of the present invention is to improve the reliability of the protection operation of the inverter device, prevent unnecessary current protection operation, and realize smooth rotation of the motor. It is what

[0011]

In order to solve the above problems, the present invention provides an overcurrent detection function independently provided for each of a plurality of transistors forming an inverter, and shuts off each transistor independently when an overcurrent is detected. In an inverter system composed of a drive function for protection, the current detection time constant of the overcurrent detection circuit in the upper arm transistor is set larger than the current detection time constant of the overcurrent detection circuit in the lower arm transistor. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is an inverter having an overcurrent detection function independently provided for each of a plurality of transistors constituting an inverter and a drive function for independently cutting off and protecting each transistor when an overcurrent is detected. In the system, the inverter that is driven in the floating potential state is configured by setting the current detection time constant of the overcurrent detection circuit in the upper arm transistor larger than the current detection time constant of the overcurrent detection circuit in the lower arm transistor. The upper arm can prevent the overcurrent protection circuit from malfunctioning due to some short-time steep external noise or steep dv / dt due to switching of the lower arm.

In general, the overcurrent protection in a power transistor should be set by an appropriate time and current value in order to guarantee a driving condition within an ASO (safe operating area) peculiar to the transistor. In addition, from the point of view of its purpose, it is required to have agile circuit response as much as possible. However, when the inverter arm is configured as described above, the floating potential of the inverter arm makes the upper arm less stable to the current detection circuit when compared with the lower arm.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An inverter device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the inverter device of the present embodiment.
It is a block diagram which shows the structure of an upper arm. Further, FIG. 2 illustrates in detail only the structure for one arm. In the figure, reference numeral 1 is a transistor for driving a motor, etc., and various elements such as BJT, FET, and IGBT are used, but the feature is that it has a sense current element through which a sense current proportional to the main current flows. Therefore, the current can be passed through the current sense resistor 2. Reference numeral 3 is a drive circuit (drive circuit) for driving the transistor 1. Various circuit schemes have been proposed according to the characteristics of the transistor 1, but they are not particularly described in the present invention. Reference numeral 4 is a voltage comparator for detecting that the value of the current flowing through the transistor 1 is in the overcurrent state. The output signal of the timer circuit 5 controls the signal (PWM drive signal) of the ON / OFF signal of the transistor 1 from the input terminal 6 via the switch circuit 7.

Therefore, when the overcurrent is not detected, the signal from the input terminal 6 is PWM-driven by the drive circuit 3 as it is. However, when an abnormal state such as motor load lock or overcurrent occurs and the current of the transistor 1 increases, and the overcurrent state occurs, the detection voltage of the sense resistor 2 rises and the voltage comparator 4 is set. When the voltage exceeds the voltage, the switch circuit 7 is operated to stop transmitting the signal from the input terminal 6 to the drive circuit 3. As a result, the output transistor 1 is cut off and protected at the time of overcurrent. Further, the recovery from the protection operation is to be recovered after the timer circuit 5 has set the time constant.

As a method of providing a difference in the detection time of the overcurrent operation in the upper arm and the lower arm, C of the timer circuit is used.
By changing the R time constant, the operation time difference of the current detection circuit is realized between the upper arm and the lower arm. That is, the time constant for setting the operating time of the timer circuit 5 of the upper arm is set longer than that of the lower arm. In addition,
The return time constant in the return timer circuit 5 is set to the same time constant.

In the three-phase inverter, the configuration shown in FIG. 2 is obtained by combining three upper arms and three lower arms as shown in FIG.

The present structure can be realized not only in a three-phase inverter but also in a single-phase inverter device or a multi-phase inverter system having the same structure.

Although a transistor having a multi-emitter structure and a detection resistor are used as the overcurrent detecting function, other methods such as a shunt resistor may be used. Further, although the current overcurrent has been described as the function description of the protection, the same function can be realized also for a fault to be protected such as a short circuit current and a fault due to external noise.

[0021]

As is apparent from the above description, the present invention provides an overcurrent detection function independently provided for each of a plurality of transistors constituting an inverter and a drive for independently cutting off and protecting each transistor when an overcurrent is detected. In the inverter system consisting of functions, by setting the current detection time constant of the overcurrent detection circuit in the upper arm transistor at the floating potential larger than the current detection time constant of the overcurrent detection circuit in the lower arm transistor, It is possible to improve the withstand capability and increase the malfunction margin with respect to the switching dv / dt of the transistor, and it is possible to realize an inverter drive system with stable operation.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an inverter device according to an embodiment of the present invention.

FIG. 2 is a block diagram of an arm of an inverter device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Transistor 2 (For current detection) Resistance 3 Drive circuit 4 (For current) Voltage comparator 6 (PWM) signal input 7 (with control terminal) switch

Claims (1)

[Claims] 1. An upper arm in an inverter system comprising an overcurrent detection function independently provided for each of a plurality of transistors forming an inverter, and a drive function for independently cutting off and protecting only each transistor when an overcurrent is detected. An inverter drive device characterized in that a current detection time constant of an overcurrent detection circuit in a transistor is made larger than a current detection time constant of an overcurrent detection circuit in a lower arm transistor.