JPS58175995A - Protecting circuit for inverter motor - Google Patents

Abstract

PURPOSE:To prevent an inverter motor from burning out by braking the motor in the reverse rotation when the motor is energized in the reverse rotation. CONSTITUTION:When an inverter motor 1 is rotated reversely to the normal rotating direction, the reverse rotation of the motor 1 is detected by the overcurrent detector (23-31) of the inverter. Simultaneously the drive frequency of the motor 1 is clamped to the prescribed value by a clamper, and the time for energizing the motor 1 is controlled in response to the speed of reverse rotation. Thus, the lower voltage is applied to the motor, thereby gradually increasing the control operation, and thereby preventing the motor from burning out.

Description

[Detailed Description of the Invention] The present invention relates to a protection circuit for an inverter motor, and in particular,
The present invention relates to a protection circuit for an inverter motor that detects and protects an excessive current that flows when the motor is rotated in a direction opposite to the normal rotation direction for some reason at the time of starting the motor.

First, the inverter motor will be explained with reference to FIG. 1 showing the basic configuration of switch elements of the inverter circuit and FIG. 2 showing a time chart of basic drive signals of the inverter motor.

That is, the inverter motor generates a DC power source from an AC power source through a rectifier and a smoothing capacitor, and as shown in FIG. It is operated by applying a square wave alternating voltage to the At this time, each of the semiconductor switch elements 2 to 7 receives drive signals Up and UN as shown in FIG.
.

Vp, VN, Wp, WN forces are transmitted, and rectangular wave three-phase alternating currents U, V, and W are created. The inverter motor 1 operated according to this principle is used as a variable speed motor by changing the frequency of the drive signal.

Note that in FIG. 1, DCI) and DCN are DC lines.

By the way, in general motors including variable speed motors, there is a phenomenon in which when the motor is turned on, the current flowing through the motor becomes larger than the motor's restraint current.

In particular, before operation, the fan motor for the outdoor unit of an air conditioner may be rotated in the opposite direction to the normal rotation direction due to the influence of wind, etc., and if the air conditioner starts operating in this state, Because excessive current flows through the fan motor,
There are problems that can lead to burnout.

When controlling the fan motor for an outdoor unit of an air conditioner using an inverter for variable speed control, conventional protection circuits have been used to detect the current flowing through the fan motor inside the inverter to overcome the above-mentioned problems. When an overcurrent is detected, the operation of the inverter is stopped, that is, the power supply to the fan motor is stopped, and the user of the air conditioner has to manually restart the inverter.

Before operation of an air conditioner system, it is necessary to ensure that the outdoor unit's fan motor is in normal operating condition as soon as possible, even if it is being rotated in the opposite direction to its normal rotation due to wind or other factors. Conventional protection circuits focused only on preventing burnout of the fan motor, making them undesirable for air conditioner systems.

In view of the above, when an inverter motor associated with a fan motor is rotated in a direction opposite to the normal rotation direction, the present invention applies a brake to the reverse rotation of the inverter motor, and immediately returns the inverter motor to the normal rotation direction. It is an object of the present invention to provide a protection circuit for an inverter motor, which can prevent the inverter from burning out and damaging the inverter motor.

The present invention is characterized by a converter circuit that generates DC power from an AC power source, a drive circuit that converts the DC power generated by this converter circuit into a semiconductor switch element and a switch circuit that generates a rectangular wave AC power, and a drive circuit that sequentially converts this switch circuit into a rectangular wave AC power source. 0N
- Equipped with a control signal circuit for OFF control, a V (voltage)-F (frequency) conversion circuit that generates a signal to this control signal circuit,
In the inverter motor operated by the rectangular wave AC power supply, an overcurrent detection circuit is provided to detect an overcurrent flowing from the DC power supply to the switch circuit, and this detects an overcurrent corresponding to the reverse rotation speed of the inverter motor. ,
Applied voltage depending on its magnitude.

The problem lies in a protection circuit for an input motor configured to adjust the application time.

In more detail, it is noted that, for example, when an inverter motor used in a fan motor is rotated in the opposite direction to the normal rotation direction, the current flowing through the inverter motor becomes larger than the locking current. The inverter's overcurrent detection circuit detects reverse rotation of the inverter motor, clamps the inverter motor's drive frequency to a certain constant value, and controls the time that the inverter motor is energized according to the speed of reverse rotation. This is a protection circuit that protects the

Next, embodiments according to the present invention will be explained in order with reference to FIGS. 3 to 9.

Here, FIG. 3 is a control signal circuit diagram according to an embodiment of the present invention, and FIG. 4 is a diagram of the control signal circuit according to an embodiment of the present invention. FIG. 3 is a basic time chart diagram of a control signal circuit.

First, the control signal circuit 3 of the in7C-event circuit shown in FIG.
Items related to 3.
)8 to 10 or FF11 to 13 constitute a ring collar, and drive signals Up and UN
, Vp , VN , Wp , WN
There are 4 to 19.

Note that DS is a data selector for switching the phase order of the reverse rotation of the inlet motor 1.

These operations, including those shown in FIG. 4, are as follows.

In other words, a V (voltage)-F (frequency) converter (hereinafter referred to as a V-F converter) as shown at 51 in FIG. The clock pulses CPI, CI) 2 are obtained, and the time charts 8Q, 8Q to IOQ, IOQ shown in FIG. It will be done.

By the clock pulse CP2, time charts 11Q, IIQ to 13Q, and 13Q shown in FIG. 4 are obtained by the FFs 11 to 13, which are also ring counters.

AND circuits 14 to 19 are used to generate drive signals Up, UN, and Vp for each of the outputs of the above-mentioned FFs.

VN, Wp, and WN are obtained as shown in the time chart shown in FIG. 4, and are transmitted to the bases of the semiconductor switching elements 2 to 7 shown in FIG. 1, and U, V.

A three-phase rectangular wave alternating voltage for each phase of W is obtained.

In the above, a protection circuit according to an embodiment of the present invention will be described with reference to FIGS. 5 to 9.

Here, FIG. 5 is a circuit diagram related to an overcurrent detection circuit and a rectangular wave oscillation circuit according to an embodiment of the present invention, FIG. 6 is a chopper circuit diagram, and FIG. A circuit diagram related to a clamp circuit and a V-F conversion circuit,
FIGS. 8 and 9 are time charts of a protection circuit according to an embodiment of the present invention.

Note that ■ and ■ in Figures 6 and 7 correspond to ■ in Figure 5.

This corresponds to ■.

First, in FIG. 5, an AC 100V power source is converted to DC via a rectifier stack 20, and a smoothing capacitor 21
The resistor 22 is a discharge resistor, and these are
This relates to a converter circuit that creates DC power from AC power.

Further, the current detection resistor 23, the resistors 24 to 29, the operational amplifier 30, the comparator 31, etc. are related to the overcurrent detection circuit.

This overcurrent detection circuit detects a detection voltage ER of the current detection resistor 23 in the DC line DCH, which is related to the detection signal.
is applied to the negative input terminal of the operational amplifier 30 via the resistor 24, and a constant voltage Tv is applied to the positive input terminal by resistors 26 and 27.

A resistor 25 is connected between the negative input terminal and the output terminal of the operational amplifier 30, forming an inverting amplifier circuit. is applied to.

The detection voltage ER of the current detection resistor 23 described above is also applied to the positive input terminal of the comparator 31.
A reference voltage Tf is applied to the negative input terminal through resistors 28 and 29.

This reference voltage Tf is set to be larger than the detection voltage ER of the overcurrent detection circuit when the motor 1 is locked.

Further, the output voltage Ec of the comparator 31 is applied to the base of the transistor 36 via the resistor 35, and controls the operation and stopping of the rectangular wave oscillation circuit 34 mentioned above. Note that 37 is a NOT circuit, which will be described later.

The comparator 31 and the rectangular wave oscillation circuit 34 are related to the gate circuit of the next chopper circuit 38, and the output signal Sl of the rectangular wave oscillation circuit 34 is used to chop the semiconductor switch elements 3, 5.7 shown in FIG. frequency.

The semiconductor switch elements 2 to 7 in FIG. 6 are switch circuits, and 32 is a drive circuit.

Thus, in FIG. 6, a switcher circuit 38 is constructed by resistors 39, 40.41 and transistors 42.43, and the output signal Sl of the rectangular wave oscillation circuit 34 is used to control the pace of the semiconductor switching elements 3, 5.7. By chopping the drive signals UN, VN, WN transmitted to the drive signals UN', VN'.

WN'. Note that these drive signals UN, VN, and WN are signals transmitted from the control signal circuit 33 shown in FIGS. 3 and 5 above.

As mentioned earlier, FIG. 7 shows the V-F conversion circuit 51.
and a clamp circuit 44.

That is, in the clamp circuit 44, the output voltage Ec of the comparator 31 shown in FIG. 5 is applied to the resistor 48 via the NOT circuit 37.

When the transistor 45 is turned off, the resistor 46
The voltage determined by This is related to the input command voltage to the F conversion circuit 51.

As described above, this V-F conversion circuit 51 transmits the clock pulses CPI and CP2 to the control signal circuit 33 shown in FIGS. 3 and 5.

Next, the operation of the protection circuit described above will be explained.

If motor 1 was rotated in the opposite direction to the normal rotation direction before operation, when operation is started in that state, an overcurrent will flow through motor 1 as described above, and as shown in Fig. 5, The output voltage Ec of the comparator 31 mentioned above is high (HI
GH), the operation of the rectangular wave oscillation circuit 34 is started, and an output signal Sl having a frequency corresponding to the output voltage EA of the operational amplifier 30 is transmitted to the chopper circuit 38 shown in FIG.

Further, the output voltage Ec of the comparator 31 mentioned above is NO
A low (LOW) signal is applied to the base of the transistor 45 via the T circuit 37 and the resistor 48 of the clamp circuit 44 shown in FIG.
5 is turned off, and as described above, the voltage determined by resistors 46 and 47 is applied to diode 50.5. Via resistor 52, V-
It is applied as the input voltage EB of the F conversion circuit 51.

Therefore, the clock pulses CPI and CP2, which are the outputs of the V-F conversion circuit 51, are transmitted to the control signal circuit 33 while being clamped to a constant frequency.

Furthermore, since the operational amplifier 30 shown in FIG. 5 constitutes an inverting amplifier circuit, as the detection voltage ER of the overcurrent detection circuit decreases, the input voltage Em of the rectangular wave oscillation circuit 34 increases. Therefore, the output signal S! of this rectangular wave oscillation circuit 34! , the chopping frequency of the chopper circuit 38 shown in FIG. 6 increases.

The above operations can be summarized as shown in FIGS. 8 and 9.

That is, when the motor 1 starts operating in a reverse rotation state, that is, when the reverse rotation speed is the highest, the chopping frequency is low, so a low voltage is applied to the motor 1, and braking is applied to the reverse rotation speed. As the voltage decreases, the applied voltage related to the above-mentioned low voltage increases, resulting in an increase in the braking effect.

In this way, when the motor 1 is braked and the detection voltage ER mentioned earlier becomes lower than the reference voltage Tt,
By inverting the output of the comparator 31 from high to low, the oscillation of the rectangular wave oscillation circuit 34 is stopped, and furthermore, the transistor 45 of the clamp circuit 44 is turned on, and normal operation according to the command from the sensor 49 is started. It is what it is.

According to the embodiment described above, even when the inverter motor is energized in the reverse rotation state, a low voltage is applied to the inverter motor to prevent the operation of the rectangular wave oscillation circuit, clamp circuit, and chopper circuit. Since the braking action is increased, it is possible to prevent burnout of the inverter motor, and furthermore, since the overcurrent energization time is shortened for the inverter circuit, it is possible to reliably improve the reduction in the life span of the inverter circuit.

In addition, it is possible to shift to normal operation without having to stop the inverter due to overcurrent detection as in the past, making it an optimal protection circuit for air conditioner systems and the like.

Therefore, the present invention is applicable not only to inverter motors used as fan motors in air conditioner systems, but also to general-purpose protection circuits for inverter motors that are rotated in a direction opposite to the normal rotation direction at the time of startup. .

In summary, according to the present invention, when the inverter motor is started, excessive current flowing through the inverter motor, which is rotated in the opposite direction to the normal rotation direction for some reason, is detected and protected. The present invention can provide a protection circuit for an inverter motor, and can be said to be an invention with excellent practical effects.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of switch elements of an inverter circuit, FIG. 2 is a time chart diagram of basic drive signals of an inverter motor, and FIG. 3 is a control signal circuit diagram according to an embodiment of the present invention. , FIG. 4 is a basic time chart thereof, FIG. 5 is a circuit diagram of an overcurrent detection circuit and a rectangular wave oscillation circuit according to an embodiment of the present invention, and FIG. 6 is a chopper circuit. , FIG. 7 is a circuit diagram of a clamp circuit and a (voltage)-F (frequency) conversion circuit, and FIGS. 8 and 9 are time charts of a protection circuit according to an embodiment of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1... Inverter motor, 2-7... Semiconductor switch element, 8-13... Flip-flop, 14-19
...AND circuit, 20... Rectifier stack, 21...
- Smoothing capacitor, 22... Resistor, 23... Current detection resistor, 24-29... Resistor, 30... Operational amplifier, 31... Comparator, 32... Drive circuit,
33... Control signal circuit, 34... Rectangular wave oscillation circuit,
35...Resistor, 36.42-44...Transistor, 37...NOT circuit, 38...Chopper circuit, 3
9~41.46~'48.52...Resistor, 44 River crank circuit, 49...Sensor, 50...Diode,
51...V (voltage)-F (frequency) conversion circuit, S]・
...output signal, ER...detection voltage, Tf...reference voltage, Tv...constant voltage, Up, UN, Vp, V
N, Wp, WN・” Drive signal. Agent Patent attorney Kosaku Fukuda 3 (and 1 other person) ゛1st (￥) ii! J2 diagram UN VN p N 1f, 30 4th - Figure N

Claims (1)

[Scope of Claims] 1. A drive circuit consisting of a converter circuit that generates DC power from AC power, a switch circuit that converts the DC power generated by this converter circuit into rectangular wave AC power using a semiconductor switch element, and this switch. In an inverter motor operated by the above-mentioned rectangular wave alternating current power supply, the inverter motor is equipped with a control signal circuit that sequentially controls the circuits on and off, and a (voltage) - FC frequency) conversion circuit that generates a signal to this control signal circuit.
An overcurrent detection circuit is provided to detect overcurrent flowing from the DC power supply to the switch circuit, and this detects overcurrent according to the reverse rotation speed of the inverter motor, and adjusts the applied voltage and application time depending on the magnitude. A protection circuit for an inverter motor, characterized in that it is configured to 2. In the device described in claim 1, V(It)-F is determined by the detection signal detected by the overcurrent detection circuit.
(Frequency) The inverter motor is equipped with a clamp circuit that clamps the output frequency of the conversion circuit to a certain constant frequency, and a chopper circuit that chops the rectangular wave alternating current power supply based on the detection signal of the overcurrent detection circuit. protection circuit. 3. The protection circuit for an inverter motor according to claim 2, wherein the chopping frequency of the chopper circuit is changed in accordance with the level of the detection signal of the overcurrent detection circuit. 4. An inverter motor according to claim 3, which includes a gate circuit that compares the detected voltage of the overcurrent detection circuit with a reference voltage and operates or stops the chopper circuit. protection circuit.