JPS5837774B2 - Inverter no Kadenriyuhogosouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent protection device for an inverter.

FIG. 1 is a circuit diagram of a conventional device of this type, in which 1 is a DC power supply, 2 is a control element such as a transistor or thyristor, and 3 is a circuit diagram of a conventional device of this type.
4 is an overcurrent detection resistor, 4 is an overcurrent detection circuit, 5 is an overcurrent control circuit, 6 is an inverter consisting of transistors TR1 to TR6 and diodes D1 to D6, and 7 is a load.

Transistors TR1 to TR6 of the inverter 6 are provided with base signals shown as a to f in FIG. 2, and DC power is converted to AC power.

Next, we will explain the operation of the inverter overcurrent protection device shown in Figure 1 in the second diagram.
This will be explained with reference to the figures.

The period t1 to t2 in FIG. 2 will be described.

During this period, the base signal is sent to the transistors TRI, TR2, TR6, and the transistors TR1, TR2, TR
6 is conductive.

When the load 7 is a resistive load, the current passes through the DC power supply 1, the control element 2, the overcurrent detection resistor 3, the path of the transistor TRI, the load 7c, the transistor TR6, and the transistor TR.
2 - load 7b - transistor TR6 path.

At this time, the transistor TR6 is connected to the transistor TR1.
A current flows through the transistor TR2 and the transistor TR2, but this current is detected by the overcurrent detection resistor 3. Even if the current flowing through the transistor TR6 becomes an overcurrent, the current flowing through the transistor TR2 is connected between the terminals of the overcurrent detection resistor 3. Overcurrent detection circuit 4 detects this, and based on this detection signal, overcurrent control circuit 5 controls control element 2 to prevent overcurrent from flowing through transistor TR6.

However, in this circuit, when the load 7 is an inductive load, for example a motor load, a larger current may flow through the transistor TR1 than the transistor TR6, and the transistor TR1 may be destroyed.

This is period t in FIG. -t1, transistors TRI and TR5 are conductive, and transistor TR1-load 7
This is because a current flows through the load 7a through the path of the a-transistor TR5, and this current continues to flow through the load 7a during the next period t1 to t2.

That is, this is because a circulating current that circulates in the closed circuit of the diode D2 and the transistor TRI flows from the load 7a during the period t1 to t2.

FIG. 2g shows this state, where the solid line is the voltage waveform applied to the load 7a, and the broken line is the current waveform flowing through the load 7a.

Therefore, during the period from t1 to t2, the current flowing to the load 7c and the circulating current circulating from the load 7a flow through the transistor TR1, and although this circulating current is a large current, it is not detected by the overcurrent detection resistor 3. Therefore, the transistor TRI was destroyed due to overcurrent.

In other words, the inverter 6 could not be protected from overcurrent.

The present invention has been made to correct the above-mentioned defects, and provides an overcurrent protection device for an inverter that can protect an inverter from overcurrent with simple precautions.

That is, the present invention calculates the overcurrent flowing through the inverter based on the sum of the value of the DC current supplied to the inverter from the DC power source and the value of the circulating current circulating between the inverter and the load connected to the inverter. The present invention relates to an overcurrent protection device for an inverter, which protects the inverter from overcurrent by detecting the overcurrent and operating an overcurrent control circuit based on the detection signal.

Next, one embodiment of the present invention will be described based on the drawings.

FIG. 3 is a circuit diagram of the device of the present invention, and parts common to those in FIG. 1 are given the same reference numerals.

In this circuit, the inverter 6 of the overcurrent detection resistor 3
One end of the side is connected to the overcurrent detection circuit 4 via a resistor 9.

Also, a feedback line has the cathodes of the diodes D1 to D3 in common and is connected to the positive DC feed line, and a feedback line has the anodes of the feedback diodes D4 to D6 in common and is connected to the negative DC feed line. A current transformer 8 is provided to detect the circulating current flowing through the current transformer 8, and a rectifier RF is connected to the current transformer 8.

In addition, the rectifier RF is connected to both ends of the resistor 9, the positive output side is connected to the overcurrent detection resistor 3 side, and the negative output side is connected to the overcurrent detection circuit 4.
Connected to the side.

Next, the operation of this circuit will be explained in the period t1 to t2 in FIG.

If the load 7 is an inductive load such as a motor, first the load 7a
As explained above, a circulating current flows in the closed circuit between the diode D2-1 and the transistor TR1.

This circulating current is detected by current transformer 8 and rectifier RF
The current is rectified by and flows to the resistor 9.

A voltage corresponding to the current detected by the current transformer 8 is generated in the resistor 9 .

Next, the current supplied from the DC power supply 1 to the load 7 passes through the DC power supply 1 - control element 2 - overcurrent detection resistor 3, and then connects to the path of transistor TR1 - load 7c - transistor TR6 and transistor TR2 - load 7b = transistor TR6. flows to the path of

Therefore, the overcurrent detection resistor 3 includes transistors TR1,
The current of TR2, that is, the current of transistor TR6 flows, and a corresponding voltage is generated.

Incidentally, although the magnitude of the current detected by the overcurrent detection resistor 3 is different from the magnitude of the current flowing through the transistor TR1, all of the current from the DC power supply 1 flows through the transistor TR.
This is a size that can be considered as the size when flowing through the load 7 through the load 7.

Therefore, by detecting the sum of the voltage across the overcurrent detection resistor 3 and the voltage across the resistor 9, the overcurrent detection circuit 4 determines the maximum current that can flow through the transistor TR1.

Therefore, by operating the overcurrent control circuit 5 based on the value of this detected current and controlling the control element 2, overcurrent flowing through the transistor TFt1 is substantially prevented.

FIG. 4 shows a current waveform flowing through the transistor TR1 when a motor load is connected to the load 7 shown in FIG. 3, and as is clear from the figure, overcurrent is limited.

As described above, according to the present invention, the inverter is overloaded based on the sum of the value of the DC current supplied to the inverter from the DC power supply and the value of the circulating current circulating between the inverter and the load connected to the inverter. Since the current is detected and the overcurrent control circuit is operated based on this detection signal, the inverter can be protected from overcurrent.

The present invention is not limited to the embodiments, but can be further modified.

For example, the inverter operation signal may be stopped based on a signal from an overcurrent control circuit without providing a control element in the DC power supply line.

Further, the magnitudes of the resistors 3 and 9 may be changed depending on the magnitude of the current to be limited.

Moreover, it is applicable not only to Sanwa inverters but also to other polyphase inverters.

It can also be applied to silice inverters.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional inverter overcurrent protection device.
Figure 2 is a waveform diagram of each part of the inverter and load, Figure 3 is a circuit diagram showing one embodiment of the present invention, and Figure 4 is the current flowing through the transistors of the inverter when a motor load is connected to the load in Figure 3. It is a waveform. 2...Control element, 3...Overcurrent detection resistor, 4...Overcurrent detection circuit, 5...Overcurrent control circuit, 8... ···Current transformer.

Claims (1)

[Claims] 1 Detecting an overcurrent flowing through the inverter based on the sum of the value of the DC current supplied to the inverter from the DC power source and the value of the circulating current circulating between the inverter and the load connected to the inverter, An overcurrent protection device for an inverter, characterized in that the inverter is protected from overcurrent by operating an overcurrent control circuit in response to a detection signal.