JPS5980115A - Circuit for protecting transistor inverter circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for a transistor inverter circuit.

As a conventional overcurrent protection method for a transistor inverter circuit, as shown in FIG. 1, a method of detecting a DC current that is the sum of currents of each phase has been widely used. In FIG. 1, 1 is a rectifier circuit, 2 is a smoothing capacitor, 3 is an inverter circuit, 4 is a load, 5 is a current detection resistor, and 6 is an overcurrent detection circuit. In the inverter circuit 3, R
The phase output is driven by transistors TR1 and TR2,
The S-phase output is driven by transistors TR+3 + TR4, and the T-phase output is driven by transistors TR5 and TR6. Each transistor TRI, TR2...T
Diode D is in R6! , D2...D6 are connected in parallel. The transistors of each phase are turned on and off according to a fixed sequence, respectively, and supply a three-phase AC voltage to the load.

By the way, in the circuit of FIG. 1, if two transistors of each phase are turned on at the same time, for example, the transistor T
A short circuit state when RI and TR2 are turned on is detected by an overcurrent detection circuit 6 using the voltage across the current detection resistor 5. Therefore, the overcurrent detection level is set to about 5, IpXl, where Ip is the maximum current value in a normal state, and when a current exceeding this is detected, all transistors TRt, TR2. ...The transistor/f inverter circuit 3 is protected by turning off the drive signal of TR6. However, in the above protection method, detection of overcurrent during abnormality is limited to 1.5
I.

Since this is done with a larger current than usual, it is necessary to increase the rating of each transistor accordingly.

In view of the above-mentioned problems, an object of the present invention is to detect the current flowing through a direct short circuit between the positive and negative sides of the power supply in each output phase of a transistor inverter circuit, regardless of the magnitude of the normal current level. An object of the present invention is to provide a protection circuit that can set a level for detecting a short circuit condition.

In the present invention, output circuits for each phase are provided in parallel at both the positive and negative ends of the output DC voltage of the rectifier circuit, and each phase output circuit has two switch transistors connected in series between the positive and negative ends of the DC voltage. In a transistor inverter circuit in which an output end of each phase is connected to a connection point between the two switch transistors, the first current flows toward the positive side of the DC voltage when viewed from the connection point in each phase output circuit. Means for detecting a second current flowing to the negative side of the voltage and a third current flowing to the load side, a sum of the first current and the third current, and a sum of the second current and the third current. The present invention is characterized in that the present invention is characterized by providing means for determining whether or not the absolute values of the two sums exceed a predetermined value. A protection circuit for a transistor inverter circuit is provided.

A protection circuit for a transistor inverter circuit as an embodiment of the present invention will be described below with reference to FIGS. 2, 3, and 4.

FIG. 2 shows a transistor inverter circuit provided with a protection circuit according to the invention. In Figure 2, 1
2 is a rectifier circuit, 2 is a smoothing content, and 3 is a transistor inverter circuit L4//i load circuit. In the transistor inverter circuit 3, RlS and T-phase output circuits are connected to both ends of the output DC voltage of the rectifier circuit 1.

In the R-phase output circuit, the emitter of the switch transistor TR1 whose collector is connected to the positive side of the DC voltage is connected to the connection point A via the current detection resistor R, and the emitter is connected to the negative side of the DC voltage. The collector of switch transistor TR2 is connected to connection point A via current detection resistor R2. Connection point A is also connected to load circuit 4 via current resistor Rsf.

Current detection resistors R1+R21R3 have the same resistance value. The S-phase and T-phase output circuits are similarly configured.

FIG. 3 shows the path through which current flows in the transistor inverter circuit of FIG. 2. In FIG. 5 shown in Figure 3
Of the two current paths II, I2...I5, 11+'
2+ 13+ 14 is a current edge 1 in a normal state, and I5 is a current path in an abnormal state.

Therefore, in the protection circuit according to the present invention, whether or not the abnormal current I6 is present is directly detected. For the current path It, 12 shown in FIG.
l+Va becomes O, and current path I3. For '14, V2+V3 becomes O. However, if an abnormal current Ig exists, the above two sums Vi +Vs and V2
Both +V3 take values other than 0.

Therefore, an abnormal condition, i.e. a short circuit condition in the output circuit of one phase, is the sum of the two above, V1+V3 and V
This is detected because none of 2+V3 is O.

FIG. 4 shows an example of the configuration of a circuit for detecting the above-mentioned abnormal state. The circuit of FIG. 4 is an adder 11.1.
2, window comparators 13 and 14, and an AND circuit 15.

The voltage across the current detection resistor ■l and V3 are the adder 11
V2 and v3 are input to the adder 12. The outputs of adders 11 and 12 are input to window comparators 13 and 14, respectively, and the outputs of window comparators 13 and 14 are input to AND circuit 15. The window comparators 13 and 14 output "0" when the absolute value of the input is below a predetermined level, and output "1" when it exceeds the predetermined level.

The predetermined level is used to determine whether the input is substantially O or not, and can be set extremely low within a range that is not affected by noise.

When the outputs of the window comparators 13 and 14 are both "1", the output of the AND circuit 15 is
When both 1+Va and Vz+Vs are not substantially zero, the value is % "1". The output of the AND circuit 15 is
It is used as an alarm output AL to turn off the switch transistors of each phase.

Therefore, in the protection circuit according to the present invention, since an abnormal state can be detected using an extremely low level current, the rating of the transistor can be set to a value close to the maximum current Ip in a normal state.

According to the present invention, in a transistor inverter circuit, an abnormal state can be detected at a level lower than the rating of the transistor, so that a transistor with a substantially lower rating can be used.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a transistor inverter circuit having a conventional protection circuit. FIG. 2 is a diagram showing a transistor inverter circuit having a protection circuit according to the present invention. FIG. 3 is a diagram illustrating the principle of abnormal state detection in the transistor inverter circuit of FIG. 2, and FIG. 4 is a diagram showing an example of the configuration of an abnormal state detection circuit in a protection circuit according to the present invention. (Explanation of symbols) 1... Rectifier circuit, 2... Smoothing capacitor, 3... Transistor inverter circuit, 4... Load circuit, 5... Current detection resistor, 6... Overcurrent detection Circuit, 11.12... Adder, 13.14...
Window comparator, 15...AND circuit.

Claims (1)

[Claims] Output circuits for each phase are provided in parallel on both positive and negative ends of the output DC voltage of the rectifier circuit, and each phase output circuit has two switch transistors connected in series between the positive and negative ends of the DC voltage, and In a transistor inverter circuit in which an output end of each phase is connected to a connection point of a switch transistor, a first current flowing toward the positive side of the DC voltage as viewed from the connection point in each phase output circuit to the negative side of the DC voltage. means for detecting the second current flowing and the third current flowing toward the load side; means for determining the sum of the first current and the third current; and the sum of the second current and the third current;
It is characterized by providing means for fully determining whether or not the absolute values of each of the two sums exceed a predetermined value.
Protection circuit for transistor inverter circuit.