JPH09266694A - Control device for air conditioner - Google Patents

Abstract

(57) Abstract: In a control device for an air conditioner, an input AC current waveform is controlled to be a sine wave to reduce harmonics, while reducing power loss. An AC power supply 1 is converted into a DC voltage by a converter unit 10, the converted DC voltage is converted into an AC voltage by an inverter circuit 4 and applied to a motor 5 of a compressor to control the compressor by an inverter. At this time, the microcomputer 12 controls the switching element 10d of the converter unit 10 when the electric power is high and controls the switching element 10d when the electric power is low, according to the output frequency of the inverter control or the rotation speed of the motor 5. Is output to the converter control circuit 11. Converter control circuit 11
The switching element 10 according to the control signal Sc.
Control of d is started to make the input AC current waveform a sine wave to reduce harmonics, and control of the switching element 10d is stopped to reduce power loss due to the switching element 10d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique for an air conditioner, and more particularly to a control device for an air conditioner that reduces energy while reducing harmonics.

[0002]

2. Description of the Related Art An air conditioner of this type is of a type in which an input AC voltage is converted into a DC voltage, and this converted DC voltage is converted into a three-phase AC voltage by an inverter means and applied to a motor for driving a compressor. There is one.

The air conditioner is generally provided with a capacitor input type converter means and has a structure of a control device shown in FIG. 6, for example.

In FIG. 6, an AC power source (for example, AC20)
0 V, 50/60 Hz) 1 is input to the converter unit (converter means) 3 via the power factor correction circuit 2 in which a reactor and a capacitor are connected in parallel.

The converter section 3 is a diode bridge 3a.
And a smoothing capacitor 3b, which converts an AC voltage into a DC voltage and outputs the DC voltage to an inverter circuit (inverter means) 4. The inverter circuit 4 connects a plurality of transistors and diodes respectively in parallel, and also connects them to a three-phase bridge, converts an input DC voltage into a three-phase AC and applies it to a three-phase motor 5 that drives a compressor.

At this time, the microcomputer 6 controls the inverter circuit 4 according to the output frequency (compressor operating frequency) fo of the inverter circuit 4 which is determined according to the difference between the temperature detected by the room temperature sensor and the temperature set by the remote controller. And outputs a drive signal (PWM signal) for controlling the. The drive circuit 7 drives the transistor of the inverter circuit 4 according to the drive signal.

Since the desired three-phase alternating current is supplied to the motor 5 of the compressor as described above, the compressor can be controlled at a predetermined rotation speed, and the air conditioner can be properly operated. it can.

[0008]

In the air conditioner controller, the power factor improving circuit 2 can improve the power factor to about 90%.

However, in general, in a capacitor input type converter, as shown in FIG. 7, the input AC current waveform from the AC power supply 1 becomes a distorted wave containing many harmonic components (see FIG. 7B). Many of these harmonic components may adversely affect equipment or the like connected to the same system such as malfunction or heat generation, which is becoming a social problem.

The present invention has been made in view of the above problems, and an object thereof is to reduce harmonics in a large power region, while significantly reducing power loss in a small power region where harmonics are not a problem. An object of the present invention is to provide an air conditioner control device capable of preventing the adverse effects of higher harmonics and enabling energy saving.

[0011]

In order to achieve the above object, the present invention relates to a converter means for converting at least an AC voltage into a DC voltage and the converted DC voltage into a three-phase AC having a predetermined frequency and a predetermined voltage. A controller for an air conditioner that controls the compressor by an inverter, and a switching element included in at least the converter means for controlling the input AC current waveform; Means for controlling the input AC current waveform by controlling the switching element, and means for controlling and stopping the switching element according to the output frequency of the inverter control or the rotation speed of the motor of the compressor It is characterized by having and.

The present invention comprises at least converter means for converting an AC voltage into a DC voltage, and inverter means for converting the converted DC voltage into a three-phase AC having a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device which controls the compressor by an inverter, at least a switching element included in the converter means for controlling the input AC current waveform, and the input AC current waveform by controlling the switching element. Control means is provided, and means for stopping control of the switching element when the output frequency of the inverter means or the rotation speed of the motor of the compressor is equal to or lower than a predetermined value.

The present invention comprises at least converter means for converting an AC voltage into a DC voltage and inverter means for converting the converted DC voltage into a three-phase AC having a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device which controls the compressor by an inverter, at least a switching element included in the converter means for controlling the input AC current waveform, and the input AC current waveform by controlling the switching element. It is characterized in that it comprises controllable means and means for controlling the switching element when the output frequency of the inverter means or the rotation speed of the motor of the compressor is a predetermined value or more.

The present invention comprises at least converter means for converting an AC voltage into a DC voltage and inverter means for converting the converted DC voltage into a three-phase AC having a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device which controls the compressor by an inverter, at least a switching element included in the converter means for controlling the input AC current waveform, and the input AC current waveform by controlling the switching element. Controllable means, control of the switching element is started when the output frequency of the inverter means or the rotation speed of the motor of the compressor reaches a first predetermined value, and then the output frequency of the inverter means or the compression When the rotation speed of the motor of the machine reaches a second predetermined value, the control of the switching element is stopped. It is characterized in that it comprises and.

In this case, it is preferable that the second predetermined value is smaller than the first predetermined value.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. FIG.
6, those parts which are the same as those corresponding parts in FIG. 6 are designated by the same reference numerals, and a duplicate description will be omitted.

In FIG. 1, the control device for the air conditioner includes a converter section (converter means) 10 in place of the converter section 3 shown in FIG. 6, a converter control circuit 11 for controlling the converter section 10, and a converter control circuit 11 shown in FIG. In addition to the function of the microcomputer 6 shown, a microcomputer 12 for outputting the control signal Sc as H and L to the converter control circuit 11 according to the output frequency fo of the inverter circuit 4 or the rotation speed of the motor 5 of the compressor, and FIG. The inverter circuit 4 and the drive circuit 7 which are the same as those in FIG.

The converter unit 10 includes a rectifier circuit 10a composed of a diode bridge, a choke coil 10b and a diode (FRD) 10c connected in series to the positive terminal of the clear circuit 10a, and the choke coil 10b.
Circuit 10a between the diode and the diode (FRD) 10c
A switching element (IGBT; insulated gate transistor) 10d connected in parallel with the capacitor, a smoothing capacitor 10e for smoothing the output DC voltage, a resistor circuit 10f for detecting the output voltage waveform of the rectifier circuit 10a, and an output DC A resistance circuit 10g for detecting a voltage and a current detection resistance 10h are provided.

The converter control circuit 11 is composed of, for example, an oscillation circuit, an amplification circuit, a multiplier, a comparator and a drive circuit, and is composed of a control IC and its peripheral circuits. The converter control circuit 11 inputs the rectified voltage waveform divided by the resistance circuit 10f, the DC voltage divided by the resistance circuit 10d, and the current waveform detected by the current detection resistor 10h, and switches the converter unit 10 The drive signal (see FIG. 4B) of the element 10d is output to control the input AC current waveform so that the input AC current waveform becomes substantially a sine wave (see FIG. 6).

By the configuration and operation of the converter section 10 and the converter control circuit 11, the input AC current waveform is made to be a substantially sine wave to reduce distortion and harmonics and to improve the power factor. In this case, the output DC voltage of converter 10 is controlled to be constant at about 380V.

By the way, in the inverter type air conditioner (inverter control of the compressor), the input power range is wide and 0 kW in order to change the rotation speed of the motor 5 (output frequency of the inverter) according to the air conditioning load. From a few k
Go to W.

Within this input power range, harmonics, especially in a relatively high power region, pose a problem. That is, the harmonics contained in the input AC current are large at high power and small at low power.

Further, in order to reduce harmonics, the switching element 10d of the converter unit 10 is switched, but the power loss increases by that amount, that is, the efficiency deteriorates. Therefore, while reducing harmonics, it is a drawback in terms of energy saving.

Therefore, in the present invention, the inverter circuit 4
When the output frequency fo (or the rotation speed of the motor 5 of the compressor) is below a predetermined value, the switching element 10d is not controlled (control is stopped), and when the output frequency fo is above a predetermined value, switching is performed. The element 10d is controlled (control is started).

Specifically, when the output frequency fo of the inverter control reaches the first set value fON, the control of the switching element 10d is started, and the output frequency fo of the switching element 10d is controlled.
Is a second set value fOFF that is smaller than the first set value fON
When it reaches, the control of the switching element 10d is stopped.

That is, the first and second set values fO
By the N and fOFF, the control of the switching element 10d has a hysteresis to prevent hunting. Also, it is necessary to control the input AC voltage waveform to a sine wave,
It is less necessary to control the switching element 10d to control the input AC current waveform to be a sine wave when the power is relatively high with many harmonic influences, and the switching element 10d is stopped in the small power region where there is almost no influence of harmonics. The power loss due to the switching element 10d is reduced.

The second set value fOFF or less is a low power region where harmonics do not pose a problem. In this case, the converter unit 10 operates as a choke input type converter from the above-described configuration, and sets the output DC voltage to twice the square root of the input AC voltage (about 280V).

Therefore, the microcomputer 12 executes the routine of FIG. 2 in the operation processing of the air conditioner (including the inverter control of the compressor). FIG. 2 is a flowchart specifically explaining a part of the main routine of the air conditioner. First, in the initialization process at the start of operation of the air conditioner, in addition to the process required for operation, the converter control circuit 11 The control signal Sc given to the switch is set to L level (stop control of the switching element 10d) (step ST
1).

The converter control circuit 11 brings the switching element 10d into the stopped state by controlling the L level. Therefore, the power is the same as the conventional one, that is, the power loss does not increase.

Subsequently, when the process (program) required for the operation of the air conditioner is executed, the output frequency fo of the inverter control rises as shown in FIG. Note that FIG. 3 shows a general operation pattern of an inverter type air conditioner.

Here, the output frequency fo is the second set value f
It is determined whether or not 0FF or less (step ST2),
If the output frequency fo is less than or equal to the second set value f0FF, the process proceeds to step ST3, and the control signal (output control signal) Sc given to the converter control circuit 11 is kept at L level (A range shown in FIG. 3). .

Subsequently, the processing necessary for the operation of the air conditioner is executed, the processing returns to the initialization processing, and the above-mentioned processing is repeated. That is, the air conditioner is operated according to the setting of the remote controller, and the process of bringing the room close to the set temperature is executed.

By repeating the above process, the output frequency fo rises as shown in FIG. 3 and the second set value fOF is increased.
When F is exceeded, the process proceeds from step ST2 to ST4, and it is determined whether the output frequency fo is equal to or higher than the first set value fON.

If the output frequency fo is not equal to or higher than the second set value fON, the process proceeds to step ST5 and it is determined whether the output control signal Sc is at the H level. Since the output control signal Sc is at the L level, the process necessary for the air conditioner is executed, the process returns again, and the above-described process is repeated (B range in FIG. 3).

When the output frequency fo becomes equal to or higher than the second set value fON, the process proceeds from step ST4 to ST6, and the output control signal Sc is set to H level (C range in FIG. 3). In response to this, the converter control circuit 11 switches the switching element 10d.
Control is started, and the switching element 10d is controlled so that the input AC current waveform becomes a substantially sine wave as described above.

Therefore, since the switching element 10d is stopped until the output frequency fo reaches the second set value fON (in the so-called small power region), the power loss can be suppressed accordingly. on the other hand,
When the output frequency fo becomes equal to or higher than the second set value fON, the switching element 10d is drive-controlled, and the input AC current waveform can be made substantially a sine wave to suppress harmonics.

Since the above-described processing is repeated after the processing in step ST6, the output frequency fo further increases and reaches the maximum, but the operation processing is performed because the difference between the detected temperature in the room and the set temperature decreases. Instead, the output frequency decreases (C range in FIG. 3). At this time, it is monitored in step ST4 whether or not the output frequency fo is lower than the first set value fON, and when the output frequency fo is lower than the first set value fON, the process proceeds to step ST5 and the output control signal is output. It is determined whether Sc is at H level.

Since the output control signal Sc is at the H level, the process proceeds to step ST7 and the output control signal SC is set to the H level.
The above-mentioned processing is repeated with the level kept (D in FIG. 3).
range).

Then, when the output frequency fo further decreases and reaches the second set value fOFF, the process proceeds from step ST2 to ST3, and the output control signal Sc is set to L level. Receiving this, converter control circuit 11 stops controlling switching element 10d (E range in FIG. 3). Then, unless the output frequency fo rises and reaches the first set value fON, the output control signal Sc is never set to the H level.

By the way, in the operation of the inverter type air conditioner, a high power region (C range shown in FIG. 3)
It is also generally known that the operating time is about several percent throughout the year, and most of the operating time is in the low power region of the A, B and E ranges (particularly the E range) shown in FIG. That is, for example, when the room temperature reaches the set temperature when the room temperature reaches the set temperature, the output frequency fo of the inverter becomes low, and the state of the low output frequency fo continues for a long time although the electric power becomes large at the set temperature at startup.

By stopping the control of the switching element 10d in a small power region where such harmonics do not pose a problem, the power loss due to the switching element 10d can be greatly reduced, resulting in energy saving. become.

On the other hand, in the high power region where harmonics are a problem, the switching element 10d is driven and controlled as described above, so that the input AC current waveform becomes almost a sine wave and the harmonics can be reduced. It is possible to prevent adverse effects on other devices.

As a condition for drive control (control start) and stop control of the switching element 10d, a first value having a different value is used.
The hunting operation of the switching element 10d can be prevented because the setting value fOFF and the second setting value fON are set, that is, the control thereof has a hysteresis.

In this embodiment, the switching element 10d is controlled and driven based on the output frequency fo, but the switching element 10d may be controlled and driven based on the rotation speed of the motor 5. .

[0045]

As described above, according to the first aspect of the control device for an air conditioner of the present invention, the switching element for making the input AC current waveform substantially a sine wave is the output frequency of the inverter means or the compressor. Since the control is performed according to the number of rotations of the motor, it is possible to control the switching element at high power to reduce harmonics, and at low power, stop the control of the switching element to reduce power loss due to the switching element. There is an effect that the energy consumption can be significantly reduced, and as a result, it is possible to prevent adverse effects on other devices of the same system and to achieve energy saving.

According to the second aspect of the present invention, the control of the switching element is stopped in the low power region where the output frequency of the inverter means is low or the rotational speed of the compressor is small (so-called harmonic is not a problem). By doing so, it is possible to significantly reduce power loss and save energy. Especially, in the operation of the air conditioner, since the operation with a small amount of power is mostly performed throughout the year, the effect is great. .

According to the third aspect of the present invention, by controlling the switching element in the high power region (so-called harmonic region is a problem) where the output frequency of the inverter means is high or the rotation speed of the compressor is high. There is an effect that the input AC current waveform is made substantially a sine wave to reduce harmonics and prevent adverse effects on other devices in the same system.

According to claim 4 of the present invention, the switching element is used when the output frequency of the inverter means or the rotation speed of the compressor is equal to or higher than the first set value (in the case of a large power region where so-called harmonics are a problem). When the input AC current waveform is controlled to be a sine wave to reduce harmonics and the output frequency of the inverter control or the number of revolutions of the compressor is equal to or lower than the second set value (so-called harmonics are not a problem in a small power region. In this case), the control of the switching element is stopped, and the power loss due to the switching element is significantly reduced. Therefore, both the effects of claims 3 and 4 are achieved.

According to claim 5 of the present invention, since the second set value of claim 4 is made smaller than the first set value, in addition to the effect of claim 4, in controlling (starting, stopping) the switching element. The hunting of the switching element can be prevented, and the switching element can be appropriately controlled.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a control device for an air conditioner according to an embodiment of the present invention.

FIG. 2 is a schematic flowchart for explaining the operation of the control device shown in FIG. 1;

FIG. 3 is a schematic time chart diagram for explaining the operation of the control device shown in FIG.

FIG. 4 is a schematic time chart diagram for explaining the operation of the control device shown in FIG. 1.

5 is a schematic time chart diagram for explaining the operation of the control device shown in FIG. 1. FIG.

FIG. 6 is a schematic block diagram of a control device for a conventional air conditioner.

FIG. 7 is a schematic time chart diagram for explaining the operation of the control device shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 AC power supply 4 Inverter circuit (inverter means) 5 Motor (compressor) 10 Converter part (converter means) 10a Rectifier circuit 10b Choke coil 10c Reverse blocking diode (FRD) 10d IGBT (insulated gate type transistor; switching element) 10e Smoothing Capacitors 10f, 10g Resistance circuit 10h Current detection resistance 11 Converter control circuit 12 Microcomputer Sc Control signal

Claims (5)

[Claims] 1. At least converter means for converting an AC voltage into a DC voltage, and inverter means for converting the converted DC voltage into a three-phase AC of a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device for controlling the compressor by an inverter, at least a switching element included in the converter means for controlling the input AC current waveform, and controlling the switching element to control the input AC current waveform. Control of the air conditioner, which is provided with means for enabling and controlling the switching element according to the output frequency of the inverter means or the rotation speed of the motor of the compressor. apparatus. 2. A converter means for converting at least an alternating voltage into a direct current voltage, and an inverter means for converting the converted direct current voltage into a three-phase alternating current having a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device for controlling the compressor by an inverter, a switching element included in at least the converter means for controlling the input AC current waveform and an input AC current waveform by controlling the switching element. And a means for stopping the control of the switching element when the output frequency of the inverter means or the number of revolutions of the motor of the compressor is a predetermined value or less. . 3. A converter means for converting at least an alternating voltage into a direct current voltage, and an inverter means for converting the converted direct current voltage into a three-phase alternating current having a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device for controlling the compressor by an inverter, a switching element included in at least the converter means for controlling the input AC current waveform and an input AC current waveform by controlling the switching element. A control device for an air conditioner comprising: means for controlling the switching element when the output frequency of the inverter means or the rotation speed of the motor of the compressor is equal to or higher than a predetermined value. 4. A converter means for converting at least an alternating voltage into a direct current voltage, and an inverter means for converting the converted direct current voltage into a three-phase alternating current having a predetermined frequency and a predetermined voltage and applying it to a motor for driving a compressor. In an air conditioner control device for controlling the compressor by an inverter, a switching element included in at least the converter means for controlling the input AC current waveform and an input AC current waveform by controlling the switching element. Means and the output frequency of the inverter means or the rotation speed of the motor of the compressor reaches a first predetermined value, the control of the switching element is started, and thereafter the output frequency of the inverter means or the motor of the compressor is controlled. And a means for stopping control of the switching element when the rotation speed reaches a second predetermined value. A control device for an air conditioner. 5. The control device for an air conditioner according to claim 4, wherein the second predetermined value is a value smaller than the first predetermined value.