JP2003079050A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in a conventional air conditioner that, when an instantaneous power cut off occurs in an AC commercial power supply or when an instantaneous low voltage fluctuation occurs and then it is restored, the difference between an initial value and a target voltage of the output voltage of an active filter becomes larger; and a gain of feedback control in the control part becomes too large; so that a voltage increase of output voltage of a steep build up is applied to the active filter, and the control part controls to maintain the target voltage, with the result that an excessive current flows in the control element of the active filter, and it occasionally constitutes a factor causing breakdown or shortening of the life of the elements, the performance deterioration, or the like, and impairs the function of the air conditioner. SOLUTION: The air conditioner has a low voltage detection means to detect whether or not the output voltage of the active filter is at a certain voltage or higher; a means to control so as to stop switching operation of a switching element, when the output voltage is detected by the low voltage detection means that it is the certain voltage or lower; and a means to change a detected value of an output voltage detection means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner incorporating an active filter that improves the power factor of a power source and suppresses harmonic currents from the power source.

[0002]

2. Description of the Related Art In recent years, air conditioners are often equipped with so-called inverter control in which the number of revolutions of a compressor is changed according to the magnitude of load. Further, an active filter is often provided in the power supply unit in order to improve the power factor of the power supply and suppress the outflow of harmonic current from the power supply. However, while consideration is given to the method of controlling the active filter, no consideration is given to the method of protecting the switching elements that constitute the active filter against sudden fluctuations in the AC commercial power supply. There was a problem in configuring the harmony machine. As an example of a conventional air conditioner equipped with such an active filter, there is a technique described in Japanese Patent Application Laid-Open No. 9-19156.

An example of the configuration will be described with reference to FIG.

The output of the AC commercial power supply 201 is rectified by the bridge rectifier circuit 202, and the rectified voltage is smoothed by the smoothing capacitor 203 to become DC, which is input to the inverter circuit 204. In the inverter circuit 204, the direct current from the smoothing capacitor 203 is converted into an alternating current of an arbitrary frequency, and the alternating current is given to the electric compressor 205 as a load.

The active filter 206 is provided between the bridge rectifier circuit 202 and the smoothing capacitor 203, has a choke coil 207, a high speed diode 208 and a power transistor 209, and switches the power transistor to smooth the smoothing capacitor 203.
Controls the amount of input current to the. Power transistor 2
The switching of 09 is controlled by the switching control unit 211 as follows.

First, the DC voltage generated in the smoothing capacitor 203 is applied to the resistor 2 in the output voltage detector 211.
It is detected in a divided state by 31.232. The difference voltage between the detected voltage and the reference voltage generated by the reference voltage source 212 is output from the error amplifier 213. The reference voltage is set to a value according to the rated value of the DC voltage.

On the other hand, a signal voltage corresponding to the input voltage to the active filter 206 is generated by the input voltage detector 214 based on the output voltage of the bridge rectifier circuit 202.
The multiplier 215 multiplies the difference voltage from the error amplifier 213 and the signal voltage from the input voltage detector 214. As a result, in the multiplier 215, the input voltage waveform is corrected by the output of the error amplifier 213. Therefore, the multiplier 2
The output of 15 includes a component according to the DC voltage and a component according to the input voltage.
It corresponds to the increase in voltage due to.

The value of the input current is the current detection resistance 21.
When it becomes 0, it becomes a voltage signal, which is detected by the input current detector 216. The amplifier 218 amplifies the difference between the detected current value and the output of the multiplier 215 to detect a current waveform synchronized with the voltage waveform.

The output of the amplifier 218 is compared by the comparator 219 with the triangular wave having a constant period generated by the oscillator 220. At this time, when the output of the amplifier 218 is higher than the triangular wave, the pulsed PWM (Pulse Widt
h Modulation) signal is output. And this PWM
The signal is amplified by the drive circuit 221 and given to the control pole of the power transistor 209.

The above active filter 206 is called a step-up chopper type active filter and outputs the output voltage as
The energy stored in the choke coil 207 is operated to raise the voltage higher than the smoothing voltage obtained only by the bridge rectifying circuit 202 and the smoothing capacitor 203. The amount of increase is controlled by the switching controller 210 so as to reach a predetermined rated value.

Further, the active filter 2 as described above is used.
The output voltage of 06 is constantly fed back in the switching control unit 210 to maintain a constant voltage. Specifically, the switching control unit 210
The increase in the output voltage is obtained by calculating the voltage difference between the rated value (target value) and the detected output voltage with the error amplifier 213, and the pulse width of the PWM signal is changed so that the voltage difference becomes zero. ing.

Therefore, when the output voltage becomes lower than the rated value, the ON pulse width of the PWM signal becomes longer, and the control is performed so that the ON ratio of the power transistor is increased and the output voltage is increased.

[0013]

In the control method described above, an AC commercial power source is subjected to an instantaneous power failure (active filter 2
The smoothing voltage across the smoothing capacitor 203, that is, when an instantaneous power failure occurs for a certain period during the boosting operation of 06, or when an instantaneous low voltage fluctuation (a short-term low voltage during the boosting operation of the active filter 206) occurs, that is, When the DC output voltage starts to gradually decrease from the rated value, the difference between the output voltage of the active filter 206 and the target voltage becomes large, the gain of the feedback control in the control unit 210 increases, and the PWM signal turns on. The control is shifted so as to increase the pulse width, that is, increase the ON ratio to increase the output voltage.

At that time, when the momentary power failure or the momentary low voltage is restored, the power transistor 209 is controlled so that the ON state of the power transistor 209 becomes longer.
An excessive current flows through the transistor 209 which is a control element of the air conditioner, sometimes leading to factors such as breakage of the switching element, reduction of life, performance deterioration, and the like, which may impair the function of the air conditioner.

The present invention has been made in view of the above circumstances, and an active filter control element due to an excessive current generated when an AC commercial power source is restored from a momentary power failure or a momentary low voltage fluctuation when an air conditioner is operating. The purpose is to protect from damage.

[0016]

In order to solve the above-mentioned problems, the first air conditioner of the present invention has a means for rectifying an AC voltage output from an AC power source and a rectification means for rectifying the AC voltage. A smoothing means for smoothing the AC voltage into a DC voltage, and a DC-AC converting means for converting the DC voltage from the smoothing means into an AC voltage having a variable voltage and frequency and applying the voltage to the electric compressor. Is provided between the rectifying means and the smoothing means, and the amount of current flowing into the smoothing means via the choke coil is adjusted by switching of the switching element so that the input current has substantially the same phase as the input voltage and is substantially sinusoidal. An active filter that shapes the waveform into a wave, and an output voltage detection unit that detects the output voltage of the active filter,
It has a difference voltage detection means for outputting a difference between the detection output of the output voltage detection means and a predetermined reference value.

There is provided switching control means for controlling the duty ratio of switching of the switching element so as to maintain the output voltage of the active filter at a constant value based on the difference detected by the difference voltage detection means.

In the first air conditioner of the present invention, in the output voltage drop detecting means for detecting whether or not the output voltage of the active filter is above a certain voltage, the output voltage drop detecting means is below a certain voltage. When we detect that,
The means for controlling the switching operation of the switching element to stop can prevent the switching element from being damaged by an excessive current.

In the second air conditioner of the present invention, when the output voltage drop detecting means detects a certain voltage or less and stops the switching operation of the switching element and then the instantaneous power failure or the instantaneous voltage fluctuation value is restored, When the control to return to the original output voltage is performed, the control element in the active filter is excessively increased in current due to the sudden voltage increase operation by means of gradually increasing and changing the output voltage setting value within a predetermined period. It is possible to prevent the destruction of the element, the reduction of the life, the deterioration of the performance, etc. without flowing the current.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 1, the air conditioner according to this embodiment comprises a bridge rectifier circuit 2, a smoothing capacitor 3, an inverter circuit 4 and an active filter 5 as a power supply system, and a switching control unit as a control system. 7 and an inverter control unit 8.

In the power supply system, the output voltage of the commercial power supply 1 is rectified by the bridge rectifier circuit 2 and smoothed by the smoothing capacitor 3 to generate a DC voltage. Further, the power supply system is configured to generate a three-phase AC voltage in the inverter circuit 4 on the basis of the DC voltage and apply the AC voltage to the electric compressor 6.

The inverter circuit 4 includes six transistors 11 to 16 and six diodes 21 to 26. Transistors 11 and 12, Transistors 13 and 14
The transistors 15 and 16 are connected in series between two power supply lines. On the other hand, diode 2
1 to 26 are connected in parallel to each of the transistors 11 to 16. The inverter circuit 4 as the series-AC converting means outputs three-phase AC voltage by switching the transistors 11 to 16 under the control of the inverter control unit 8.

The electric compressor 6 has a transistor 11.1.
2, transistors 13 and 14 and transistor 15
It is connected to each of the 16 connection points. The electric compressor 6 is driven by the three-phase AC voltage from the inverter circuit.

Further, in the power supply system, the active filter 5 is connected between the bridge rectifying circuit 2 as the rectifying means and the smoothing capacitor 3 as the smoothing means.
The active filter 5 has a choke coil 31, a high speed diode 32, and a power transistor 33. In this embodiment, as the power transistor 33,
Although an insulated gate bipolar transistor is used, another high speed switching element may be used.

The choke coil 31 and the high speed diode 32 are provided in series with one of the power supply lines on the rectification side. Power transistor 3 as switching element
In 3, the collector is connected to the connection point between one end of the choke coil 31 and the anode of the high speed diode 32, and the emitter is connected to the other of the rectification side power supply lines.

The active filter 5 controls the current flowing in the choke coil 31 by switching the power transistor 33 with respect to the current flowing in the smoothing capacitor 3 via the choke coil 31 and the high speed diode 32. There is.

In the control system, the inverter control unit 8 as a control means includes transistors 11 to 11 depending on the air conditioning load.
The output frequency of the inverter circuit 4 is controlled by controlling the switching of 16. In addition, the inverter control unit 8 operates the switching control unit 7 in synchronization with the startup of the electric compressor 6. Further, the inverter control unit 8 also manages the operation of the active filter 5, and performs not only normal start and stop but also control such as emergency stop in the event of an abnormality.

On the other hand, the switching control section 7 as the switching control means controls the pulse width of the switching control signal given to the gate of the power transistor 33,
The output voltage of the active filter 5 is controlled. The switching control section 7 is adapted to perform feedback control in order to make the output voltage of the active filter 5 constant.

The switching controller 7 includes an input voltage detector 41, an output voltage detector 42, a reference voltage source 43, an error amplifier 44, an input current detector 45, a multiplier 46 and an amplifier 4.
7, an oscillator 48, a comparator 49 and a drive circuit 50.

The switching control unit 7 also includes resistors 51 to 53, a comparator 54, a low voltage reference voltage source 55 and a delay circuit 56 as output voltage drop detecting means.

The output voltage drop detecting means is a resistor 51.
˜53, comparator 54, low voltage reference voltage source 55 and delay circuit 56, resistors 57 and 58 are also included. Resistance 5
7 and 58 are provided between the active filter 5 and the smoothing capacitor 3 in the power supply, and divide and detect the output voltage of the active filter 5.

Input voltage detector 41, output voltage detector 4
2, reference voltage source 43, error amplifier 44, input current detection unit 45, multiplier 46, amplifier 47, oscillator 48, comparator 4
The main control unit composed of 9 and the drive circuit 50 has substantially the same function as the switching control unit in the conventional air conditioner (see FIG. 2) described above.

That is, in the above main controller, the DC voltage generated in the smoothing capacitor 3 is detected by the output voltage detector 42, and the difference between the detected value and the reference voltage generated by the reference voltage source 43. The voltage is output from the error amplifier 44.

The multiplier 46 multiplies the difference voltage from the error amplifier 44 and the voltage waveform from the input voltage detector 41. On the other hand, the input current to the active filter 5 is taken out as a voltage signal by the current detection resistor 34, and the voltage signal corresponding to the current is detected by the input current detection unit 45.

In the amplifier 47, the detected value and the multiplier 46
The output of the amplifier 47 is amplified by the PWM circuit composed of the comparator 49 and the oscillator 48.
Converted to a signal. This PWM signal is used by the drive circuit 5
It is amplified by 0 and given to the control electrode of the power transistor 33.

The main controller feedback-controls the output voltage of the active filter 5 to change the pulse width of the PWM signal so that the output voltage maintains a constant value.

Further, the main control unit is the active filter 5
The switching control is performed so that the input current of is in phase with the input voltage and has a sine wave.

Next, the operation of the output voltage drop detecting means will be described with reference to FIGS.

FIG. 3 is a waveform diagram for explaining the operation of the output voltage drop detecting means when the AC commercial power source experiences an instantaneous power failure or an instantaneous low voltage fluctuation.

FIG. 4 is a control for returning to the original output voltage when the output voltage drop detecting means detects a certain voltage or less and stops the switching operation of the switching element, and then restores the instantaneous power failure or the instantaneous voltage fluctuation. 3 is an embodiment for explaining a circuit for gradually increasing and changing the set value of the output voltage within a predetermined period.

In FIG. 3, when the AC voltage output from the AC power source suffers a power failure or voltage fluctuation (hereinafter, only the power failure will be described), the voltage of E1 drops to E2. If this is represented by an AC voltage input waveform (for example, 50 Hz), the AC voltage input waveform is cut off at the point at which the power failure starts, and the power is supplied at the point at which the power failure is restored.

Next, the value when the DC output voltage V0 of the active filter 5 is operating normally is shown. When the power failure starts, the DC output voltage starts gradually decreasing from V0 and goes to V1. Further, the DC output voltage shifts to V2 which is the low voltage detection value. Next, an output signal when a drop in the DC output voltage is detected by the comparator output OV1 which is the DC output voltage detecting means is shown.

Next, the operation of the reference voltage EE of the reference voltage source 43 of the error amplifier 44 which determines the DC output voltage of the active filter 5 is shown, and the reference voltage value EE of the reference voltage source EE is triggered by the comparator output OV1. The variation of the reference value is started according to the reference voltage value having the preset slope. This changing period is called a delay period.

In FIG. 4, the reference voltage source 43 is a resistor 43.
1 and 432 are connected in series, and power supplies VCC and G, respectively
It is connected to ND.

The middle point is connected to the input of the error amplifier 44 and the capacitor 565 of the delay circuit 56, and is connected in parallel to the resistor 432 of the so-called reference voltage source 43.

The capacitor 565 functions to stabilize the reference voltage EE which is the input of the error amplifier 44 and to delay the delay circuit.

Next, a transistor 561, a resistor 563, and a diode 564 are connected in series in parallel with the capacitor 565. Whether the series circuit is connected to the capacitor 565 in parallel or not is turned on / off of the transistor 561. It is decided by the operation, and the transistor 56
When 1 is turned on, the charge of the capacitor 565 is transferred to the resistor 563.
The diode 564 also has a role of causing rapid discharge.

Next, the resistor 562 changes the forward bias potential of the diode 564 by turning on and off the transistor 561, and the reference voltage EE input to the error amplifier 44.
It works to change the.

The operation of the delay circuit 56 will be described below.

When the AC voltage output from the AC power source causes a power failure (power failure period), the AC voltage source disappears and E1 to E
Drop to 2. Then, the DC output voltage V0 gradually decreases and starts decreasing from V0 to V1.

However, the main control unit largely changes the pulse width of the PWM signal in order to keep the output voltage constant, and continues the voltage increasing operation in order to increase the DC output voltage. However, because of the power outage, no current flows through the power transistor.

At this time, in the DC voltage drop detecting means,
Active filter 5 divided by resistors 57 and 58
The DC output voltage, that is, the power failure detection voltage, and the low voltage reference voltage value 55, that is, the DC voltage drop detection voltage (stop voltage determination value) are compared by the comparator 54.

As a result of the comparison, when it is determined that the voltage is the DC voltage drop detection voltage or less, the output OV1 of the comparator 54 causes the reference voltage source 43 to forcibly stop the output of the drive circuit 50. By changing the value of the generated reference voltage value and temporarily lowering the set value, the drive circuit 50
It is possible to reduce the factor that the switching control element of the active filter 5 for the DC output voltage is destroyed by temporarily stopping the output of.

Next, the AC voltage source is in the state before the power failure E
Even after returning from 2 to E1, the set value of the output voltage of the active filter 5 is temporarily lowered by the DC voltage drop detecting means, and the main control unit tries to keep the DC output voltage constant at V2. You will continue to control. This period is called a low voltage detection period in FIG. 3, and since the gain of feedback control in the control unit 7 is small, steep voltage amplification is not performed and an excessive current does not flow in the active filter 5.

Next, in the operation of the delay circuit in the normal state, the output of the comparator 54 is set to output the L level, and the transistor 561 of the delay circuit 56 is turned off. At this time, the collector of the transistor 561 is at the H level, and the series circuit of the resistors 562 and 563 and the diode 564 does not affect other circuits because the diode 564 is reverse biased in terms of bias potential.

Next, when the AC voltage output from the AC power source is detected by the output voltage drop detection means as a power failure, the comparator 54 outputs a H level as the comparator output OV1 due to the voltage drop, and the transistor 561 of the delay circuit 56 is turned on. Turn it on.

The set voltage value EE of the reference voltage source 43 is a combination circuit in which a series circuit of a resistor 563 of the delay circuit 56, a transistor 561, a diode 564 and a capacitor 565 and a resistor 432 of the reference voltage source 43 are connected in parallel. Further, it becomes a series circuit with the resistor 431, and the reference voltage value determined by the set voltage value EE at the connection point is set low and the error amplifier 4
4 is input.

At the same time, the electric charge charged in the capacitor 565 connected in parallel to the resistor 432 is discharged, and the main control unit performs control so as to keep the DC output voltage constant at the point of V2, that is, the value obtained by changing the setting. become.

Next, when the transistor 561 is turned off by the voltage drop detecting means, the transistor 5 of the delay circuit 56 is turned on.
In the circuit in which the series circuit including the resistor 61, the resistor 563, and the diode 564 is connected in parallel to the resistor 432 of the reference voltage source 43, the diode 564 becomes reverse biased in terms of bias and becomes invalid.

Therefore, the resistors 431 and 4 of the reference voltage source 43 are
The potential EE at the connection point of 32 is the resistance 431 and the capacitor 56.
The CR charging circuit of No. 5 is formed and starts to rise gradually. The rising curve is the capacitor 5 connected in parallel to the resistor 432.
A delay circuit is formed by 65.

Next, the main control unit gradually increases the DC output voltage from the point of V2 to perform the increase control to V1, V0 and the original DC output voltage value. This period is expressed as a delay period. There is.

Therefore, the switching control element can be eliminated from the cause of destruction by an excessive current or the like.

Although the above explanation has been made by using the CR delay circuit, the reference voltage value EE of the reference voltage source 43 is changed stepwise or the A / D input terminal of the microcomputer (MCU) is used to activate the active filter 5. The DC output voltage value is read and the result is programmed by the pseudo amplifier 4
Needless to say, the same operation can be obtained by D / A converting to 4 and inputting, and if a program is used, it is possible to perform a removing operation such as a malfunction due to a change amount of the rising curve or noise when reading the DC output voltage value. Advanced control actions can also be possible.

Further, in the DC voltage drop detecting means,
By adding hysteresis to the power failure detection voltage value of the active filter 5 with the resistors 51, 52, and 53, it is possible to perform overcurrent prevention control by restoring AC power without reacting excessively to changes in the output voltage. .

Therefore, even if the AC voltage output from the AC power source drops due to a momentary low voltage fluctuation, or the voltage fluctuates suddenly due to a momentary power failure due to switching of the transmission line of a power company, etc., the active filter 5 can be safely operated. Moreover, the air conditioner can be stably operated, and it is not necessary to temporarily stop the operation of the air conditioner.

[0067]

As described above, in the air conditioner according to the first aspect of the present invention, the means for rectifying the AC voltage output from the AC power source and the DC voltage for rectifying the AC voltage rectified by the rectifying means. Smoothing means for smoothing the DC voltage from the smoothing means, and a DC-AC converting means for chopping the DC voltage from the smoothing means to convert the voltage and frequency into an AC voltage and applying the AC voltage to the electric compressor; and the rectifying means. And an active filter which is provided between the smoothing means and the input current to rectify the input current into a waveform having substantially the same phase as the input voltage and a substantially sinusoidal waveform, and an output voltage of the active filter that is lower than a predetermined stop voltage determination. When the voltage is detected, the active filter is stopped.

On the other hand, the above-mentioned active filter gives hysteresis to the value of the stop voltage judgment value when the AC voltage output from the AC power source recovers from the AC power source after momentary power failure and momentary low voltage fluctuation, and the output voltage It does not react excessively to a change, and is provided with a DC voltage drop detection means due to power restoration.

As a result, it is possible to protect the control element from being destroyed due to an overcurrent flowing due to the operation of the active filter to keep the output voltage constant due to the abrupt change of the AC power supply.

Therefore, it is possible to prevent the air conditioner from stopping due to a malfunction of the active filter.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an air conditioner according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional air conditioner.

FIG. 3 is a waveform diagram showing the operation of the active filter and the operation of the voltage drop detection means in the air conditioner of FIG.

4 is a circuit diagram of an embodiment for explaining the operation of the voltage drop detecting means in the air conditioner of FIG.

[Explanation of symbols]

1 ... Commercial power supply, 2 ... Bridge rectifier circuit, 3 ... Smoothing capacitor, 4 ... Inverter circuit, 5 ... Active filter,
6 ... Compressor, 7 ... Switching control unit, 8 ... Inverter control unit, 31 ... Coil, 32 ... Rectifying diode, 33 ...
Power transistor, 34 ... Current detecting resistor, 41 ... Input voltage detecting section, 42 ... Output voltage detecting section, 43 ... Reference voltage source, 44 ... Error amplifier, 45 ... Input current detecting section, 46 ...
Multiplier, 47 ... Amplifier, 48 ... Oscillator, 49 ... Comparator,
50 ... Drive circuit, 54 ... Comparator, 55 ... Reference voltage source, 56 ... Delay circuit, 51.52.53.57.58 ...
Resistance, 431.432 ... resistance, 561, ... transistor,
562.563 ... Resistance, 564 ... Diode, 565 ...
Capacitors.

Continued front page    F term (reference) 3L060 AA01 AA02 CC19 EE21                 5G053 AA12 BA04 CA02 EA03 EB01                       EC03 FA04                 5H006 AA02 AA04 CA01 CA07 CA13                       CB01 CC02 DA02 DA04 DB02                       DB05 DC02 DC05 FA02 FA04                       GA04

Claims (2)

[Claims] 1. A means for rectifying an AC voltage output from an AC power source, a smoothing means for smoothing the AC voltage rectified by the rectifying means into a DC voltage, and a DC voltage from the smoothing means for chopping. Is provided between the rectifying means and the smoothing means, and a DC-AC converting means for converting the voltage and frequency into an alternating voltage having a variable voltage and applying the voltage to the electric compressor. By adjusting the amount of current flowing into the smoothing means by adjusting the input current into a waveform having an input current having substantially the same phase as that of the input voltage and an almost sinusoidal waveform, and an output voltage detection for detecting the output voltage of the active filter. And a difference voltage detecting means for outputting a difference between the detection output of the output voltage detecting means and a predetermined reference value. An air conditioner having switching control means for controlling the duty ratio of switching of the switching element so as to keep the output voltage of the active filter at a constant value based on the difference detected by the difference voltage detection means. , A voltage drop detecting means for detecting whether or not the output voltage of the active filter is a certain voltage or more, and a control for stopping switching of the switching element when the voltage drop detecting means detects that the output voltage is a certain voltage or less An air conditioner characterized by doing. 2. The air conditioner according to claim 1, wherein when the output voltage of the active filter is detected to be equal to or lower than a certain voltage, the detection value of the output voltage detecting means is changed.