JPS61132080A - Inverter control circuit - Google Patents

Abstract

PURPOSE:To protect against an overcurrent with preferable responsiveness by operating overcurrent detecting means when the state that the output of a current detector is the prescribed value or higher is continued for the prescribed time. CONSTITUTION:When the voltage between both terminals of a shunt resistor 30 of a current detector becomes the prescribed value or higher, the voltage of a capacitor 42 becomes the prescribed value or higher by the prescribed time delay, a light emitting diode 43a emits a light, and a phototransistor 43b is turned ON. Thus, the voltage of the connecting point A forcibly becomes a low level, a protection control signal S0 becomes logic '0' to stop operating of a switching circuit. When the voltage between the both terminals of the resistor 30 becomes the prescribed value higher than it, a capacitor 46 is charged in a short time, a light emitting diode 47a emits a light, and a phototransistor 47b is turned ON. Thus, the operation of the switching circuit is similarly stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an inverter control circuit having an overcurrent protection function for an inverter device.

[Technical background of the invention]

Generally, an air conditioner is equipped with a variable capacity compressor and an inverter device that supplies drive power to the variable capacity compressor, and controls the output frequency of the inverter device according to the air conditioning load. Some systems are designed to achieve optimal performance in response to the current situation, improve comfort, and improve energy-saving effects.

Incidentally, in such an air conditioner, the inverter device consists of a rectifier circuit that rectifies the AC power supply voltage and a switching circuit that converts the rectified output into AC power of a predetermined frequency and voltage. In this case, the current (pulse-like current synchronized with the switching cycle) flowing through the switching circuit of the inverter device becomes excessive, and the elements of the switching circuit may be destroyed.

Therefore, conventionally, an overcurrent control means is provided in the switching circuit of an inverter device, and the operation of the switching circuit is stopped when the current flowing through the switching circuit exceeds a certain value.

However, in this case, overcurrent protection is also activated due to the temporary occurrence of overcurrent during startup, resulting in unnecessary operation stoppage. To deal with this, there is a method that adds a time element to the overcurrent protection means, so that when a current exceeding a certain value flows through the switching circuit and this condition continues for a certain period of time, the operation of the switching circuit is stopped. . In other words, overcurrent protection does not work when a temporary overcurrent occurs, such as during startup, and only works when overcurrent occurs continuously, such as during normal overload operation. It turns out.

However, this too had its drawbacks. That is, the responsiveness to the occurrence of overcurrent deteriorates, and there is a risk that the element may be destroyed before overcurrent protection actually operates. Furthermore, during overload in a low frequency operating range, even if overcurrent continues to occur, the value of the overcurrent itself is not that large, and therefore overcurrent protection may not work at all.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose of this is to not provide overcurrent protection for temporary overcurrent occurrences such as during startup, but to provide overcurrent protection with good response to overcurrent occurrences other than startup. Furthermore, it is possible to provide reliable overcurrent protection even in situations where the overcurrent itself is not very large, such as when an overcurrent occurs in a low frequency operation range.
An object of the present invention is to provide a highly practical inverter control circuit that enables appropriate overcurrent protection for an inverter device.

[Summary of the invention]

This invention is provided with a current detector that detects the current flowing in the switching circuit of an inverter device, and is activated when the output of the current detector remains at a constant value 1 or more for a certain period of time T1 or more within a specified period of time. The output of the first overcurrent detection means and the current detector is a constant value V2 (>V
t) or more when constant 1172 (<'Tt)
A second overcurrent detection means is provided which is activated if the overcurrent continues, and the first overcurrent detection means has a different activation level and response time. When any one of the second overcurrent detection means is activated, the moving gate of the switching circuit is stopped.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

□ In FIG. 2, 1 is a commercial AC N source, and an inverter device 2 is connected to this power source 1. This inverter device 2 includes a rectifier circuit consisting of a diode bridge 21 and a smoothing capacitor 22, and a three-phase alternating current of arbitrary frequency and voltage by switching the output of this rectifier circuit.
It is composed of a switching circuit 23 that converts the current into electric power and outputs the converted electric power.

The output end of the switching circuit 23 is connected to the compressor motor 3 of the variable capacity compressor.

Therefore, an electric detector such as a shunt resistor 30 is inserted into the connection line between the negative output end of the rectifier circuit and the negative input end of the switching circuit 23 in the inverter device 2, and both ends of the shunt resistor 3o are protected. The second protection circuit 40 connected to the circuit 4o detects whether or not overcurrent is flowing through the switching circuit 23 based on the output of the shunt resistor 30, and sends the detection result to the inverter drive circuit 6.
It is designed to output for 0. The inverter drive circuit 60 drives the switching elements in the switching circuit 23 in response to a capacity setting command supplied from an air conditioner control unit, etc., and the protection circuit 4
o detects an overcurrent, it immediately stops operating.

Here, a specific example of the protection circuit 40 is shown in FIG.

That is, the voltage across the shunt resistor 30 is applied to the capacitor 42 via the resistor 41. A light emitting diode 43a of a photocoupler 43 is connected to both ends of the capacitor 42. Therefore, the collector of the phototransistor 43b of the photocoupler 43
A DC voltage V CC (5F) is applied to the capacitor 49'' between the emitters and through the charging resistor 48 in series.Furthermore, the capacitor 49 has a series circuit including a discharge resistor 50 and a diode 51. connected in parallel.

In addition, shunt resistance 30. The voltage across the resistor is 44°45
The voltage is divided and applied to the capacitor 46. A light emitting diode 47a of a photocoupler 47 is connected to both ends of the capacitor 46. Thus, the interconnection point A between the discharge resistor 50 and the diode 51 is grounded via the collector-emitter of the phototransistor 47b of the photocoupler 47.

In this way, resistor 41, capacitor 42, photocoupler 4
3. Charging resistor 48, capacitor 49, discharging resistor 50
, and the diode 51 constitute a first overcurrent detection means that is activated when the output voltage of the shunt resistor 30 remains at a constant value of 111 Vt or more for a predetermined time period T1 or more within a predetermined time period. In addition, a second fault is activated by the resistors 44, 45, the capacitor 46, and the photocoupler 47 when the output voltage of the shunt resistor 30 continues to be at or above a certain value V2 (>Vt) for a certain period of time (<<T2). A current detection means is configured. The voltage generated at the connection point A is output as an overcurrent protection signal SO.

Next, the operation of the above configuration will be explained with reference to FIG.

Now, it is assumed that AC power of a predetermined frequency and voltage is output from the inverter device 2 by driving the inverter drive circuit 60, and thereby the compressor motor 3 is operating at a predetermined rotation speed. In this state, a pulsed current synchronized with the switching cycle flows through the switching circuit 23 of the inverter device 2, and a voltage at a level corresponding to the magnitude of the current is generated across the shunt resistor 30.

When a voltage equal to or higher than a certain value V1 is generated across the shunt resistor 30, the voltage across the capacitor 42 becomes equal to or higher than a predetermined value, causing the light emitting diode 43a of the photocoupler 43 to emit light. When the light emitting diode 43a emits light, the phototransistor 43b is turned on, and the capacitor 49 is charged through the charging resistor 48. In this way, shunt resistance 3
Every time the voltage across 0 exceeds a certain value ■1, capacitor 4
9 is charged. Further, when the voltage across the shunt resistor 30 becomes equal to or lower than a certain value Vl, the phototransistor 43b is turned off, so that charging is not performed, and the voltage of the capacitor 49 is discharged through the discharge resistor 5o and the diode 51.

In this way, the voltage of the capacitor 49 is discharged every time the voltage across the shunt resistor 30 becomes equal to or less than the constant value ■l. However, in this case, the resistance value of the discharging resistor 50 is the same as that of the charging resistor 48.
Since the resistance value of the shunt resistor 30 is much larger than the resistance value, the discharging time constant is larger than the charging time constant. Each time a current is generated, the voltage of the capacitor 49 increases, and the charging resistor 48 and the capacitor 4
The voltage at the interconnection point B with 9 decreases. However,
If this state continues for a certain period of time T1 or more within a certain period of time,
The voltage at connection point B further decreases, and being pulled by this, the voltage at connection point A decreases to below 2. In other words, the protection control signal SO is set to logic "O" and the inverter drive circuit 60
supplied to The inverter drive circuit 6o stops driving the switching circuit 23 in response to the protection control signal SO of logic "On".

That is, in a situation where a not-so-large overcurrent continues for a certain period of time, such as when the compressor motor 3 is overloaded in a low frequency operating range, the first overcurrent detection means is activated and the switching circuit 23 is activated. Since the operation of the switching circuit 23 is stopped, destruction of the elements in the switching circuit 23 can be prevented.

On the other hand, when the voltage across the shunt resistor 30 exceeds the constant value ■2, the voltage across the capacitor 46 reaches a predetermined value or higher with an extremely small time delay T2 due to charging of the capacitor 46, and the light emitting diode 47a of the photocoupler 47
emits light. In this case, when the light emitting diode 47a emits light, the light becomes less than λ. In other words, the protection control signal SO
becomes logic "O", and the operation of the switching circuit 23 is stopped as in the case of overload in the low frequency operating range.

Therefore, when a large overcurrent flows through the switching circuit 23 and the voltage across the shunt resistor 30 becomes 2 or higher, as in the case of an overload in the normal frequency operation range, the second overcurrent detection means responds quickly. Switching circuit 23 immediately after activation (actually there is a very small time delay T2)
Since the operation of the switching circuit 23 is stopped, destruction of the elements in the switching circuit 23 can be prevented. That is, in response to a large overcurrent, the operation of the switching circuit 23 is immediately stopped without any time delay, which is extremely safe. Note that a large overcurrent is temporarily generated in the switching circuit 23 due to an overload at startup, but such secondary overcurrent is absorbed by the time delay T2 due to charging of the capacitor 46, and the second overcurrent is generated. The current detection means will not operate.

Note that in the above embodiment, the resistor 50 in the protection circuit 40
is the discharge resistance, but as shown in Fig. 4, the charging resistance 48
A resistor 52 is connected in parallel to the series circuit of the capacitor 49 and the resistor 52 is used as a discharge resistor, and the connecting direction of the diode 51 is reversed to use the resistor 50 as a pull-up resistor on the second overcurrent detection means side. Furthermore, the voltage at the connection point B may be output as a protection control signal. According to such a configuration, it becomes easy to set the charging time and the discharging time.

Furthermore, in the protection circuit 40 shown in FIG. 1, the charging resistor 48 may be replaced with a temperature-sensitive resistance element, such as a negative-characteristic thermistor 61, and the discharging resistor 50 may be replaced with a temperature-sensitive resistance element, such as a positive-characteristic thermistor 62. For example, the time element of overcurrent detection can be set to an appropriate state without being affected by ambient temperature, resulting in improved reliability. In this case, a resistor 41 connected to the shunt resistor 3o side
Alternatively, the same effect can be obtained by replacing the resistors 44 and 45 with temperature-sensitive resistance elements.

In general, it is also possible to extract the voltage at the connection point 8 in the protection circuit 40 not as a protection control signal but as an overload detection signal and use it as an operating frequency setting command or an air blowing amount setting command.

〔Effect of the invention〕

As described above, according to the present invention, electrician inspection for detecting the current flowing through the switching circuit of an inverter
f6゜, 'yu. □Inspection□.

The output of the first overcurrent detection means and the current detector is activated when the state in which the output is a constant value ■1 or more continues for a certain period of time T1 or more within a predetermined time. A second overcurrent detection means is provided which operates when the duration T2 (<<Tt) continues, and the first overcurrent detection means has a different operating level and response time. Since the operation of the ship's switching circuit is stopped when any of the second overcurrent detection means is activated, overcurrent protection is not performed in the case of a temporary overcurrent occurrence such as during startup. Overcurrent protection can be performed with good response to overcurrent occurrences other than during startup, and even in situations where the overcurrent itself is not very large, such as when overcurrent occurs in a low frequency operation range. It is possible to provide an excellent inverter control circuit that can perform reliable rich current protection and provide appropriate overcurrent protection for an inverter device.

[Brief explanation of drawings]

FIG. 1 is a specific configuration diagram of a protection circuit according to an embodiment of the present invention, the second cause is a schematic configuration diagram of the embodiment and an inverter device, and FIG. 3 is a diagram for explaining the operation of the embodiment. , the fourth factor, and FIG. 5 are configuration diagrams showing modified examples of the protection circuit in the same embodiment. □ 1... Commercial AC power supply, 2... Inverter device, 3...
...Compressor motor, 23...Switching circuit, 30
... Shunt resistor (current detector), 40... Protection circuit, 43.47... Photocoupler, 48... Charging resistor, 49... Capacitor, 50... Discharging resistor.

Claims (1)

[Scope of Claims] An inverter device that rectifies AC power supply voltage and converts the rectified output into AC power of an arbitrary frequency using a switching circuit and outputs the same, comprising: a current detector that detects a current flowing through the switching circuit; A first overcurrent detection means that operates when the output of the current detector is equal to or higher than a fixed value V_1 continues for a fixed period of time T_1 or more within a predetermined time;
a second overcurrent detection means that is activated when the condition above V_1) continues for a certain period of time T_2 (<<T_1); and means that stops the operation of the switching circuit when the first or second overcurrent detection means is activated. An inverter control circuit characterized by comprising: