JPH0626036Y2 - Inverter protector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an inverter protection device for preventing damage to a switching element for a full-bridge inverter due to an abnormality such as a short circuit of an arm of the inverter.

[Conventional technology]

Generally, a full-bridge inverter used as various power supply devices is constructed, for example, as shown in FIG. In the figure, (1) is a three-phase AC power supply, (2) is a thyristor and is a three-phase full-wave rectifier circuit that rectifies the AC of the AC power supply (1), and (3) and (4) are rectifier circuits (2). These are a smoothing reactor and a capacitor that are provided in series between the positive and negative output terminals, and the rectifier circuit (2), the reactor (3), and the capacitor (4) form a DC power supply unit (5).

In (6a) and (6b), the collector is a rectifier circuit via the reactor (3).
N is a switching element connected to the positive output terminal of (2).
The collectors of the PN type first and second transistors (6c) and (6d) are connected to the emitters of the first and second transistors (6a) and (6b), respectively, and the emitter is the negative output of the rectifier circuit (2). NPN type 3rd and 4th switching elements connected to terminals
Transistors (7a), (7b), (7c), (7d) are four flywheel diodes, and the first to fourth transistors (6a) to
The transistors (6a) to (6d) are connected in parallel in the opposite direction to (6d) to form a full-bridge inverter (8).

(9) is a load whose both ends are connected to the emitters of the first and second transistors (6a) and (6b), and (10) is an inverter controller.
The drive panel is output to the base that is the control terminal of each of the transistors (6a) to (6d), and the first and fourth transistors (6
a), (6d) and the second and third transistors (6b), (6c) are alternately turned on, the pulse width of the drive pulse is controlled, and the output control of the inverter (8) is performed. .

By the way, in this kind of inverter (8), the first and third transistors (6a) and (6c) are simultaneously turned on, the arm short circuit is caused by the second and fourth transistors (6b) and (6d) being simultaneously turned on, or Each transistor (6a) to (6
In order to prevent the transistors (6a) to (6d) from being damaged due to an overcurrent flowing in d), the third and fourth transistors (6
c), the current value detected by the current detector (11) provided in the energizing path between the emitter of the rectifier circuit (5) and the negative output terminal of the rectifier circuit (5) and the reference value to the inverter control unit (10). Comparing with a comparator (not shown) provided, if the detected current value exceeds the reference value, the output of the inverter control unit (10) is stopped and the operation of the inverter (8) is forcibly stopped because an overcurrent has flowed. Let the inverter
(8) is being protected.

In addition, as another method of protecting the inverter (8), for example, a fourth path may be provided in the energizing path between the DC power supply unit (5) and the inverter (8).
As shown by the broken line in the figure, a quick disconnect fuse (12) is provided.

[Problems to be solved by the device]

However, in the case of overcurrent protection using the former current detector (11), the inverter (8) may malfunction due to switching noise when high-frequency switching each of the transistors (6a) to (6d). In order to prevent such malfunctions, measures have conventionally been taken such as providing the comparator with a time constant and setting the reference value to a value considerably higher than the noise level. However, there is a problem that the response at the time of overcurrent becomes slow and the overcurrent protection of the inverter (8) cannot be performed promptly.

On the other hand, in the latter case of overcurrent protection using fast-acting fuse (12), the response of the fuse (12) is basically poor, so quick protection cannot be performed, and it is particularly unsuitable for high-frequency inverters. is there.

The present invention has been made in consideration of the above points, and detects the overcurrent abnormality directly and swiftly by using the detection result of the input voltage and the input current of the inverter and detects the overcurrent due to the arm short circuit or the like. The purpose of the present invention is to quickly and forcibly stop the inverter when a current is generated, thereby enabling high-speed and highly accurate inverter overcurrent protection.

[Means for Solving the Problems]

Next, means for achieving the above object will be described with reference to FIGS. 1 and 2 corresponding to the embodiment.

That is, the present invention is a switching element which is connected to the output terminal of the DC power supply unit (5) and supplies AC to the load (9).
~ Full bridge inverter (8) consisting of fourth transistors (6a) ~ (6d), and an inverter control unit (10) for outputting a drive pulse to the base which is the control terminal of each of the transistors (6a) ~ (6d) And comparing the detected value of the current flowing through the energization path between the DC power supply unit (5) and the inverter (8) with a reference value to detect an overcurrent of the input current of the inverter (8). An overcurrent detection unit (20) that outputs a detection signal, and a divided voltage of the input voltage of the inverter (8) are input to a low-pass filter (22) and a coefficient multiplier (23) for constant multiplication, and the low-pass filter (22 ) Output voltage exceeds the output voltage of the coefficient unit (23), a voltage drop detection unit (26) that detects a decrease in the input voltage of the inverter (8) and outputs a detection signal, and an AND gate (27). ) That stops the output of the inverter control unit (10) by the simultaneous input of the detection signal and the detection signal. Characterized in that a part.

[Action]

Therefore, according to the present invention, the overcurrent detector 20 compares the detection result of the input current of the inverter 8 with the reference value to detect the occurrence of the overcurrent of the input current of the inverter 8.

In addition, the voltage drop detection unit (26) divides the input voltage of the inverter (8) by removing unnecessary high frequency components from the stable output voltage of the low-pass filter (22) and dividing the input voltage of the inverter (8). Is compared with the output voltage that changes according to the partial pressure of the coefficient unit (23), which is a constant multiple of
Utilizing the fact that the output voltage of (28) drops first, the occurrence of voltage drop due to overcurrent is detected with good responsiveness from the input voltage of the inverter (8) only at the instant of occurrence.

When an arm short circuit or a load short circuit of the inverter (8) occurs, a detection signal is output from the overcurrent detection unit (20), and a detection signal is output from the voltage drop detection unit (26). And gate by simultaneous input with detection signal
(27) becomes active, the output of the drive pulse from the inverter control unit (10) stops, the inverter (8) is forcibly stopped,
Damage to the transistors (6a) to (6d) of the inverter (8) due to overcurrent is prevented.

At this time, the occurrence of the overcurrent is directly detected from the detection result of the input voltage and the input current of the inverter (8), and moreover,
Since the input voltage and input current detection results are used, the overcurrent detection unit (2
(0) The comparator has a time constant, and the reference value from the reference power supply is set higher than necessary to prevent the malfunction of the overcurrent detection unit (20) due to switching noise. , The response at overcurrent does not slow down,
The inverter (8) can be protected quickly.

Also, even if the overcurrent detection unit (20) malfunctions due to switching noise, the AND gate (27) does not become active unless the voltage drop detection unit (26) operates, so the influence of switching noise is prevented. , The inverter (8) can be protected accurately.

〔Example〕

Next, the present invention will be described in detail with reference to FIGS. 1 to 3 showing one embodiment thereof. Note that FIG. 1 is a connection diagram showing the entire configuration, FIG. 2 is a detailed block connection diagram of a part, and FIG. 3 is a signal waveform diagram.

In FIG. 1, the same symbols as those in FIG. 4 indicate the same or corresponding ones, and (13) and (14) are voltage detection provided in series between both ends of the capacitor (4) of the DC power supply unit (5). The two voltage dividing resistors, (15), are control devices and are constructed as shown in FIG.

In FIG. 2, (16) is a connection terminal connected to the output terminal of the current detector (11), (17) is a reference power supply, (18) is an adder, and (1)
9) is a comparator, which compares the current value detected by the current detector (11) with the reference value of the reference power supply (17), and when the former exceeds the latter, the high level (hereinafter H
The output signal of the current detector (11), the reference power source (17), the adder (18) and the comparator (19) are output.
This constitutes an overcurrent detection unit (20).

Further, in FIG. 2, (21) is both voltage dividing resistors (13), (14).
Connection terminal connected to the connection point (P) of (22) is the connection terminal (2
A low-pass filter that removes the high-frequency component of the voltage signal at the connection point (P) via 1), and (23) multiplies the voltage at the connection point (P) via the connection terminal (21) by a predetermined amount (about 1.5 times). A coefficient unit, (24) is an adder, and (25) is a comparator, which compares the output of the low-pass filter (22) with the output of the coefficient unit (23), and when the former exceeds the latter, the inverter input voltage Is detected, the H detection signal is output.
A voltage drop detection unit (26) is configured by (13), (14), the low-pass filter (22), the coefficient unit (23), the adder (24) and the comparator (25).

(27) is an AND gate that constitutes a stop unit, both input terminals are connected to the output terminals of both comparators (19), (25), and the AND gate ( 2
The output of 7) becomes H, and the H output of the AND gate (27) causes the output of the inverter control unit (10) to stop.

Now, if an arm short circuit occurs during operation of the inverter (8), the current value detected by the current detector (11) exceeds the reference value of the reference power supply (17). Is detected and an H detection signal is output to the AND gate (27).

On the other hand, due to the arm short circuit of the inverter (8),
The input voltage of (8) drops instantly, and as shown in Fig. 3,
The output voltage Vm of the coefficient unit (23) instantly drops at the same time when the arm short circuit occurs, and as shown in the figure, after the arm short circuit,
The output voltage Vr of the low pass filter (22), which gradually decreases,
Since the output voltage Vm of the coefficient unit (23) is exceeded, the voltage drop detection unit
By (26), the drop of the inverter input voltage is detected at the moment when it occurs, and the H detection signal is output to the AND gate (27).

Then, the output of the AND gate (27) becomes H by the input of the detection signal of H and the detection signal, and the inverter control unit
0) output stops and each transistor (6
The a) to (6d) are turned off, the inverter (8) is forcibly stopped, and the transistors (6a) to (6d) are prevented from being damaged by the overcurrent.

At this time, the overcurrent detection section (20) caused by switching noise
In order to prevent the malfunction of the comparator, as in the past, the comparator (19)
Since there is no need to take measures such as giving a time constant to the power supply or increasing the reference value by the reference power supply (17) more than necessary, the response at the time of overcurrent due to arm short circuit will not be delayed and the inverter (8) The protection of can be done promptly.

Also, even if the overcurrent detection unit (20) malfunctions due to switching noise, the output of the AND gate (27) does not become H unless the voltage drop detection unit (26) operates, so the influence of switching noise This will prevent the inverter (8) from being protected with high accuracy.

Even when the load is short-circuited, the inverter (8) is protected in the same manner as when the arm is short-circuited as described above.

Therefore, according to the above-described embodiment, when the arm short circuit or load short circuit of the inverter (8) occurs, the overcurrent detection unit (20) outputs the H detection signal and the voltage drop detection unit (26) outputs the H signal. Is output, and the output of the AND gate (27) becomes H by the input of the detection signal and the detection signal of H, and the output of the drive pulse from the inverter control unit (10) is stopped,
Since the inverter (8) is forcibly stopped, the comparator (19) of the overcurrent detection unit (20) has a time constant as in the past, and the reference value by the reference power supply (17) is set higher than necessary. It is not necessary to take measures against malfunctions, and the response at the time of overcurrent is not delayed, and the inverter (8) can be protected promptly.

Further, even if the overcurrent detection unit (20) malfunctions due to switching noise, the output of the inverter control unit (10) does not stop due to the AND condition unless the voltage drop detection unit (26) operates. The influence of switching noise can be prevented, and the inverter (8) can be protected accurately.

Then, with a simple configuration that self-detects the decrease of the input voltage of the inverter (8) due to the overcurrent only from the input voltage, the product of the input voltage of the inverter (8) and the detection result of the abnormality of the input current The inverter (8) is detected quickly and reliably and the inverter (8) is stopped, so the occurrence of overcurrent in the inverter (8) can be detected reliably and reliably, and the inverter (8) can be protected from overcurrent with high speed and accuracy. can do.

[Effect of device]

Since the present invention is configured as described above, it has the following effects.

The overcurrent detection unit compares the detection result of the input current of the inverter with the reference value to detect the occurrence of overcurrent of the input current of the inverter, and the voltage drop detection unit detects unnecessary high frequency components from the divided voltage of the input voltage of the inverter. The stable output voltage of the low-pass filter from which the voltage is removed is compared with the output voltage of the coefficient unit that is a constant multiple of the divided voltage of the input voltage of the inverter, and the output voltage of the coefficient unit that changes according to the divided voltage is compared. Utilizing the fact that the voltage drops first, the occurrence of voltage drop due to overcurrent is detected with good responsiveness from the input voltage of the inverter only at the instant of occurrence.

Then, the output of the inverter control unit is stopped only when the AND condition is satisfied between the detection of the overcurrent by the overcurrent detection unit and the detection of the instantaneous reduction of the inverter input voltage by the voltage reduction detection unit. It is possible to speed up the response of the inverter protection operation, prevent the influence of high frequency switching noise, and improve the accuracy of the inverter protection operation. With a simple configuration that self-detects a drop in the input voltage only from the input voltage, the inverter abnormality is directly detected from the product of the detection result of the input voltage of the inverter and the input current, and high-speed and highly accurate inverter overcurrent protection Will be possible.

[Brief description of drawings]

1 to 3 show an embodiment of an inverter protection device of the present invention, FIG. 1 is a wiring diagram, FIG. 2 is a detailed block wiring diagram of a part, and FIG. 3 is a diagram for explaining the operation. Signal waveform diagram,
FIG. 4 is a connection diagram of a conventional example. (5) ... DC power supply unit, (6a) to (6d) ... First to fourth transistors, (8) ... Inverter, (9) ... Load, (10) ... Inverter control unit, (20) ... Overcurrent detection Section, (26) ... Voltage drop detection section, (2
7)… And gate.

Claims (1)

[Scope of utility model registration request] 1. A full-bridge inverter, which is connected to an output terminal of a DC power supply unit and supplies alternating current to a load, an inverter control unit which outputs a drive pulse to a control terminal of the switching device, and the DC power supply. Section and the inverter, the detected value of the current flowing through the energization path and the reference value are compared, the overcurrent detection section that detects the overcurrent of the input current of the inverter and outputs a detection signal, and the overcurrent detection section of the inverter. The divided voltage of the input voltage is input to a low-pass filter and a coefficient unit for multiplying a constant, and when the output voltage of the low-pass filter exceeds the output voltage of the coefficient unit, a decrease in the input voltage of the inverter is detected to output a detection signal. Stop that stops output of the inverter control unit by simultaneous input of the detection signal and the detection signal, which consists of an output voltage drop detection unit and an AND gate And a protective device for the inverter.