JPH089683A - Inverter control apparatus - Google Patents

Abstract

PURPOSE:To obtain an inverter control apparatus by which a motor can be driven surely at a low temperature by a method wherein, when a compressor is to be started, the motor is driven at a carrier frequency within a range of an inverter frequency which is permitted only in its start and, when the compressor is to be operated, the motor is driven by changing the carrier frequency into a carrier frequency within a range of an operation guarantee frequency. CONSTITUTION:In the case of an air conditioner, an inverter 2 supplies drive electric power to a compressor motor 3 at a frequency corresponding to an air conditioning load according to a PWM control signal from a microcomputer 8a for a controller. In this case, the current waveform of a DC current which flows to a DC line 10 on the DC side of the inverter 2 is a pulse waveform, and a DC pulse width is kept wide. Consequently, when the compressor motor 3 is driven by the inverter, it is driven while a carrier frequency is changed positively within a range of an inverter frequency which is permitted only in a start and within a range of an ordinary operation guarantee frequency. As a result, it is possible to eliminate a state that the compressor motor cannot be operated forever in its start even by using a high-speed switching element, and the motor can be driven surely at a low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control device, and more particularly to an insulated gate bipolar transistor (Insulated-Gate-Bi) having a short allowable short circuit time.
The present invention relates to an inverter control device in which a motor of a compressor is driven by an inverter with a high-speed switching element such as a polar-transistor (hereinafter referred to as an IGBT).

[0002]

2. Description of the Related Art In an air conditioner of a PWM (pulse width modulation) control system using an inverter power source, the pressure capability of a compressor motor is changed by changing the frequency in the range of 10 to 75 Hz according to the air conditioning load. Is adjusted.

Bipolar transistors, which are inexpensive and have a relatively large allowable current capacity, have been the mainstream of power semiconductor devices used for driving this kind of inverter. However, as a recent trend, a high-speed inverter driving element such as an IGBT is drawing attention. This IGBT
Uses a MOSFET on the input side and a bipolar transistor on the output side, and is a voltage-controlled type that has a fast on / off speed and allows a relatively large current to flow.

[0004]

However, this IGB
When the compressor motor is driven by an inverter with T, I
Although the GBT is capable of high-speed switching, when an abnormality such as a short circuit occurs, the GBT is destroyed in an extremely short time because the allowable short circuit time is short.

Therefore, a so-called overcurrent protection circuit is provided in order to protect the IGBT at the time of short circuit, and moreover, the sensitivity of the overcurrent protection is increased in order to ensure the protection against the overcurrent.

In such a state, when the compressor motor of the compressor is driven by the inverter with the current waveform of a certain carrier frequency, the lower the carrier frequency, the wider the current pulse width of the current waveform. When the compressor motor of the compressor is started at a low temperature while the temperature is low, the overcurrent protection is activated and it is difficult to start the compressor motor at a low temperature.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an inverter control device capable of reliably starting a motor at a low temperature.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an inverter control device for variably controlling an operating frequency of a compressor according to a refrigeration load by the inverter power supply. By controlling the motor of the compressor and this motor, the compressor is driven at the carrier frequency within the range of the inverter frequency that is allowed only when the compressor is started, and the compressor is operated when the compressor is operated. And a controller for driving the compressor in place of the carrier frequency within the guaranteed frequency range.

[0009]

In the present invention, the controller controls the motor of the compressor to drive the compressor at the carrier frequency within the range of the inverter frequency permitted only at the time of starting the compressor to start the compressor. During operation, the compressor is driven by changing it to a carrier frequency within the guaranteed operating frequency range of the compressor. As a result, even if a high speed switching element such as an IGBT is used, it is possible to prevent a state in which the protection operation is avoided and the operation cannot be performed forever at the time of startup.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a preferred embodiment of an air conditioner having an inverter control device of the present invention.

In FIG. 1, the converter 1 constituting the inverter power supply rectifies the three-phase AC power supplies R, S, T into DC power and supplies this DC power to the inverter 2 constituting the inverter power supply. ing.

The inverter 2 is a PWM (Pulse-Wav) from the microcomputer 8a of the controller 8.
In accordance with the e-Modulation) control signal, the drive power P (three phases) having a frequency corresponding to the air conditioning load is supplied to the compressor motor 3, and the amount of circulation of the refrigerant in the air conditioning unit 4 is changed by the change in the compression capacity of the compressor motor 3. Is controlled, and air conditioning operation is performed according to refrigeration (or air conditioning).

R on the AC side (input side) of the converter 1,
C for power wiring of either S or T, for example, T phase
A T (current transformer) 5 is provided. Since the detection signal of CT5 is AC, it is converted to a DC voltage via the rectifier circuit 6 and given to the input port of the controller 8 as a detection signal.

A shunt resistor 7 such as a non-inductive resistor is inserted in series in the current wiring on the AC side (output side) of the converter 1 and the DC side (input side) of the inverter 2, for example, on the load voltage side. The voltage corresponding to the voltage drop at the shunt resistor 7 is also applied to the input port of the controller 8 as an abnormality detection signal.

The controller 8 uses these detected currents as input data to make an abnormality determination by the built-in microcomputer 8a. This abnormality determination is executed by the operation control program stored in the ROM or the like in the microcomputer 8a.

FIG. 2 shows the circuit configuration of the inverter 2 and its surroundings. DC line 1 on the DC side of the inverter 2
The current waveform IW of the direct current flowing through 0 is shown in FIG. The current waveform IW is a pulse waveform having a current wave height of I (A) and a current pulse width of T (μsec).

FIG. 4 shows an overcurrent protection curve (indicated by a solid line) in an ordinary bipolar transistor BJT used in a conventional inverter drive, and an IGBT used as an inverter drive in the embodiment of the present invention (as an example). 75
An overcurrent protection curve (shown by a broken line) in the example of the A power element is shown.

FIG. 5 shows an example of the frequency at the time of starting the inverter, and FIG. 6 is an enlarged view showing an example of the protection range curve of the IGBT.

The bipolar transistor BJT is not broken even in the event of an abnormality such as a short circuit without protection against overcurrent in such a short time. Therefore, the bipolar transistor BJT allows the current pulse width T to be wide even if the current value I increases. On the other hand, IGB
In a high-speed switching element such as T, since the allowable short circuit time is short, the allowable value of the short circuit time is not so large for an abnormally large current value I.

In the state of the overcurrent protection curve in the IGBT shown in FIG. 4, the carrier frequency which is the same as the carrier frequency of 10 KHz during the normal operation of the compressor motor 3 remains 10 KHz (the current pulse width T of the current waveform IW in FIG. 3). When the inverter is started for the compressor motor 3 in a state where the temperature is still wide, a large current (overcurrent) flows through the IGBT when the compressor motor 3 is started at low temperature.

The carrier frequency indicates the number of current pulses of the current waveform IW shown in FIG. 3 per unit time.
By increasing the carrier frequency, a precise inverter drive can be performed and a beautiful sin curve can be reproduced.

As described above, the IGBT has a short allowable time with respect to a large current (allowable current), so that the current wave height I × current pulse width T shown in FIG.
It is necessary to prevent the protection circuit of the GBT from working.

However, as described above, the current waveform I of FIG.
Since the current pulse width T of W remains wide as shown in FIG. 5, the protection operation of the IGBT is started in the range of points A to B in FIG. 6, and the compressor motor 3 cannot be started by the inverter forever. .

Therefore, only when the compressor motor 3 is started by the inverter, if the carrier frequency is driven at 10 KHz to 15 KHz as shown in FIG. 5, for example, the protection range of the IGBT is B point or C in FIG. 6 even when the inverter is started. Since it shifts to the range of points, the protection operation of the IGBT is less likely to occur, and the problem that the compressor motor 3 cannot be started by the inverter forever can be solved.

That is, the current pulse width T is wide when the carrier frequency remains low at 10 KHz, but the current pulse width T can be narrowed by increasing the carrier frequency from 10 KHz to 15 KHz.
The protection operation of FIG. 6 from the protection range of points A and B of FIG.
Can be moved to the protection range of points B to C.

As described above, when the compressor motor 3 is driven by the inverter, the carrier frequency is positively changed within the range of the inverter frequency allowed only at the time of starting and the normal operation guaranteed frequency range, so that the starting at low temperature is started. Normal stable operation can be performed smoothly.

Incidentally, as shown in FIG. 7, as a preferable example at the time of starting, the inverter frequency is 10 to 29 Hz.
, The carrier frequency is 15 KHz, and as a preferred example during normal stable operation, the carrier frequency is 10 K in the range of the inverter frequency of 30 to 75 Hz.
Hz.

FIG. 7 shows a control flow by the microcomputer 8a. According to FIG. 7, when the compressor motor 3 is at the time of starting the inverter drive, the process proceeds from step S1 to S2, the inverter frequency is in the range of 10 to 29 Hz, the carrier frequency is slowly started at 15 MHz, and the operation is performed. Approximately 10 seconds later, shift to normal stable operation and the inverter frequency is 30 to 75 Hz.
When the range becomes, the carrier frequency is 10 KHz.
(Step S3).

On the other hand, if the normal stable operation is already performed (step S1), the operation is performed at the carrier frequency of 10 KHz in the inverter frequency range of 30 to 75 Hz (step S4).

As shown in FIG. 7, when the carrier frequency was operating at 15 MHz in the inverter frequency range of 10 to 29 Hz at startup, the normal operation was started and the carrier frequency was in the inverter frequency range of 30 to 75 Hz. Switching to 10 KHz is not a problem because the microcomputer 8a of FIG. 2 switches to the next pattern output after a certain pattern output under PWM control is completed.

By the way, the present invention can be variously modified without departing from the scope of the claims.

The inverter frequency range and carrier frequency value at start-up, and the inverter frequency range and carrier frequency value during normal operation are not limited to those in the above-mentioned embodiment, but vary depending on the size and type of the compressor motor. .

[0034]

As described above, according to the present invention, the controller controls the motor of the compressor so that when the compressor is started, the carrier frequency within the range of the inverter frequency that is allowed only when the compressor is started. The compressor is driven by, and at the time of operation of the compressor, the compressor is driven by changing the carrier frequency within the guaranteed operating frequency range of the compressor. This allows the IG
Even if a high-speed switching element such as BT is used, it is possible to avoid the protection operation and avoid a state in which the motor cannot be operated forever at startup, and the motor can be reliably started at low temperature.

[Brief description of drawings]

FIG. 1 is a block diagram showing a preferred embodiment of an air conditioner incorporating an inverter control device of the present invention.

FIG. 2 is a block diagram showing the inverter of FIG. 1 and its peripheral elements.

FIG. 3 is a diagram showing a current waveform on the input side of the inverter of FIG.

FIG. 4 is a diagram showing a comparison of relational examples of current pulse widths and conduction currents of a bipolar transistor and an IGBT.

FIG. 5 is a diagram showing an example of frequencies when the inverter is started.

FIG. 6 is a diagram showing an example of a protection range curve in an IGBT.

FIG. 7 is a diagram showing an example of a control flow by a microcomputer.

[Explanation of symbols]

 2 Inverter (inverter power supply) 3 Compressor 8 Controller

Claims (1)

[Claims] 1. An inverter control device for variably controlling an operating frequency of a compressor according to an air conditioning load by an inverter power supply, wherein a motor of the compressor driven by the inverter power supply and the motor are controlled to control the compressor. At startup, drive the compressor with a carrier frequency within the range of the inverter frequency that is allowed only when starting the compressor, and when operating the compressor, change the carrier frequency within the guaranteed operation frequency range of the compressor to drive the compressor. An inverter control device, comprising: