Air conditioning device

Abstract: An air conditioning device is arranged such that an output voltage from a commercial power source is converted into a direct current by a rectifying circuit and a smoothing condenser, and thereafter, it is further converted into an AC voltage having a variable frequency by an inverter under the control of a microcomputer, thereby supplying it to a power compressor. Between the rectifying circuit and the smoothing condenser, provided is an active filter for shaping an input current to be an approximate sine wave almost in phase with an input voltage by switching a power transistor. The switching control section and the microcomputer for controlling the switching are activated independently by separately provided power sources. The switching control section supplies a high level signal when the active filter is a normal condition, while supplies a low level signal when the active filter is abnormal. A circuit which generates a low level signal when the power supply to the switching control section is shut off is provided. This enables the microcomputer to determine the occurrence of abnormality in the active filter or the switching control section even when the power supply is shut off.

Description: FIELD OF THE INVENTION The present invention relates to an air conditioning device including an inverter circuit that changes the frequency of a power compressor in an outdoor device to yield an optimal power for a load, and more particularly, to an air conditioning device furnished with an active filter that improves a power factor and suppresses a higher harmonic current from a power source. BACKGROUND OF THE INVENTION An air conditioner realizing a refrigerating cycle by sequentially operating a compressor, a condenser, a decompressor, and an evaporator has been known. A recent air conditioner additionally includes an inverter circuit for supplying an alternating current driving power to the compressor to control the output frequency thereof according to a load. This structure enables the air conditioner to operate at an optimal power for a load, thereby increasing the comfortableness of air conditioning while saving energy. As shown in Fig. 7, a conventional air conditioner rectifies an output from a commercial alternating current power source 501 using a bridge rectifier circuit 502 composed of four diodes, and smoothens the rectified voltage using a smootning condenser 503 to convert the same into a direct current, and thus operates as a condenser input type power supply circuit. The direct current from the smoothing condenser 503 is converted into an alternating current of an arbitrary frequency by an inverter circuit 504 and supplied to a power compressor 505 serving as a load. The inverter circuit 504 includes a three-phase transistor bridge circuit composed of six transistors 511- 516 connected to each other through three-phase bridge connection, and six diodes 521-526 provided in parallel with the transistors 511-516, respectively. Each of the transistors 511-516 supplies a three-phase alternating current power to the power compressor 505 when it is turned on at the timing at which a control signal from an inverter control section 506 is supplied to the control terminal thereof. The inverter circuit 504 operates most efficiently for a load by controlling the output frequency according to the load. In case of the above condenser input type power supply circuit, an input current flows when an input voltage is higher than a DC smoothed voltage V 0 and stops flowing when the input voltage is lower than V 0 as shown in Fig. 8. As a result, the above condenser input type power supply circuit presents problems that more power is lost due to a decrease in the power factor of the power supply circuit and an increase in a higher harmonic current, and that the higher harmonic current adversely affects an AC power line. Also, with the above-mentioned air conditioner, the power compressor 505 outputs a large power of 1-2 kW, and the smoothing condenser 503 correspondingly has a large capacity, thereby making the above problems more pronounced. To eliminate these problems, the IEC (International Electrotechnical Commission) will impose a regulation on the higher harmonics current of the power source in 1996, and some actions must be taken to comply with the regulation. Although a structure that employs a passive filter using a reactor (choke coil) is known as a higher harmonic current suppressing technique, this structure is not a perfect countermeasure because it can not maintain the higher harmonic current under the regulated value. Alternately, an air conditioner including an active filter 507 as shown in Fig. 7 is disclosed in Japanese Laid-open Patent Application Nos. 4-26374/1992 and 5-68376/1993. To be more precise, the active filter 507. includes a choke coil 531, a fast recovery diode 532, and a power transistor 533 between the bridge rectifier circuit 502 and the smoothing condenser 503. The switching action of the power transistor 533 is controlled by a switching control section 508. The switching control section 508 controls the switching action of the power transistor 533 in the following way. As shown in Fig. 9, a direct current voltage being generated by the smoothing condenser 503 is detected in resistors 561 and 562 (see Fig. 11) in an output voltage detecting section 541 in a decompressed (divided) state. The voltage difference between the voltage thus detected and a reference voltage generated by a reference voltage source 542 is outputted from an error amplifier 543. The reference voltage is set to a value corresponding to the rated value of the direct current voltage. On the other hand, a signal voltage corresponding to an input voltage to the active filter 507 is generated by an input voltage detecting section 544 based on an output voltage from the bridge rectifier circuit 502. Accordingly, a multiplier 545 multiplies the voltage difference from the error amplifier 543 by the signal voltage from the input voltage detecting section 544. As a result, in the multiplier 545, and the waveform of the input voltage is corrected by the output from the error amplifier 543. Thus, the output from the multiplier 545 includes the components corresponding to both the direct current voltage and input voltage, and matches with an increase of the voltage boosted by the active filter 507. An input current is detected by an input current detecting section 546. The input current thus detected is amplified in sync with the output of the multiplier 545 by an amplifier 547, thereby making a synchronous waveform with the input voltage. The output from the amplifier 547 is compared with a periodic chopping wave generated by an oscillator 548 by a comparator 549. As shown in Fig. 10 the comparator 549 outputs a pulsewise PWM (Pulse Width Modulation) signal only when the output from the amplifier 547 is higher than the chopping wave. The PWM signal is amplified by a driving circuit 550 and supplied to a control electrode of the power transistor 533. The driving circuit 550 switches the output of a switching control signal to on or off by an ON/OFF control signal outputted from an output ON/OFF circuit 551 based on a seizing signal. The active filter 507 is generally known as a voltage rise chopper type active filter, and it boosts the output voltage higher than a smoothed voltage yielded only by the bridge rectifier circuit 502 and smoothing condenser 503 by exploiting the energy stored in the choke coil 531. An increase in the boosted voltage is controlled to be a predetermined rated value by the switching control section 508. The active filter 507 supplies the energy stored in the choke coil 531 to the smoothing condenser 503 gradually by turning on or off the power transistor 533 at regular frequencies (tens of kilohertz) using the switching control signal outputted from the switching control section 508. As a result, the waveform of the input current is locked with that of the input voltage, and becomes an approximate sine wave. Thus, the input power factor is improved while the harmonic distortion is suppressed, and the utilization efficiency of the input power is upgraded as a consequence. In case of the air conditioner such as the one shown in Fig. 7, it is general to insulate the inverter control section 506 from the switching control section 508 and to drive each by their respective power sources. Thus, signals are sent between the inverter control section 506 and switching control section 508 through a photo-coupler. Also, the switching control section 508 has an additional function to detect an unusual event occurring in the active filter 507, and upon detecting such an unusual event, it turns on the photo-coupler by outputting a detection signal to notify the inverter control section 506 of the unusual event. However, with the above structure, once the switching control section 508 stops because of an unusual event, or namely, the power supply to the same is stopped for some reason, the switching control section 508 can not output the detection signal, thereby making it impossible to notify the inverter control section 506 of the unusual event. Thus, the inverter control section 506 can not stop the power compressor 505, and the power compressor 505 keeps on operating although the active filter 507 has already stopped. Moreover, the overcurrent may damage the devices composing the inverter circuit 504. It is general to use the above voltage rise chopper type active filter 507 for an air conditioner because of its advantages in terms of cost saving and noise reduction. However, the active filter 507 always outputs a voltage higher than the input voltage because of the boosting by the choke coil 531 and power transistor 533, and the output voltage easily increases or decreases according to the balance with respect to a load. To eliminate this drawback the feedback is provided by the switching control section 508, so that the output voltage from the active filter 507 maintains a constant value. To be more specific, should the output voltage from the active filter 507 change, the switching control section 508 controls the switching action of the power transistor 533 by changing the pulse width of the PWM signal based on the detected output voltage from the active filter 507, so that the output voltage from the active filter 507 will have a set value demanded by the inverter control section 506. The output voltage thus detected is also supplied to the inverter control section 506 as information. Accordingly, when the output voltage exceeds a certain range from the set value, the inverter control section 506 judges that either the power compressor 505 has stopped or something is wrong with the inverter circuit 504, and forcibly stops the active filter 507 to boost the voltage. Also, an overvoltage protection circuit which will be described in the next paragraph forcibly stops the active filter 507 to boost the voltage when the output voltage exceeds a predetermined protection voltage. The overvoltage protection circuit shown in Fig. 53 detects the output voltage from the active filter 507 using a voltage divided by resistors 561-562 provided as voltage dividing circuits of the output voltage detecting section 541, and the detected voltage is used to judge the overvoltage by a comparator 563. The comparator 563 compares the detected voltage with a protection voltage generated by resistors 564.565, and stops the output action of the driving circuit 550 when the detected voltage is higher than the protection voltage. On the other hand, another overvoltage protection circuit shown in Fig. 12 uses the output voltage from the active filter 507 divided by resistors 566.567, which are different from the resistors 561.562, as the detected voltage. However, when the active filter 507 boosts the output voltage to the set value in activating the driving action, the output voltage becomes unstable or exceeds the set value momentarily during a certain period, such as when the inverter circuit 504 starts or stops the operation, or the power compressor 505 is activated or deactivated. The inverter control section 506 judges such a condition as an unusual event even though the inverter circuit 504, active filter 507, etc. operate normally, and stops the active filter 507 to boost the voltage, thereby making the operation of the air conditioner unstable. In particular, when the active filter 507 activates the voltage boosting action, there is a considerable difference between an initial voltage and a target voltage of the output voltage, and thus the gain of the feedback control by the switching control section 508 becomes greater. Thus, the output voltage is boosted so rapidly from the start that it overshoots the target voltage. Once the active filter 507 has activated the voltage boosting action, the output voltage from the active filter 507 drops instantaneously because of the current flowing through the power compressor 505 at the time of its activation. Correspondingly, the active filter 507 boosts the output voltage using the feedback control by the switching control section 508 to compensate such a drop in voltage. However, once the power compressor 505 has started, the current flows constantly and hence the voltage is stabilized. Thus, the boosted output voltage overshoots the target voltage by an increase therein. Then, the output voltage drops more than necessary by the feedback to reduce the overshooted voltage, and undershoots the target value this time. The following output voltages remain in a stable condition because the ringing continues with the time constant of a feedback control system. Thus, the conventional air conditioner is disadvantageous in that it stops if the active filter 507 stops when the overvoltage protection circuit operates on an overshooted output voltage as has been explained. The increase value in the overshooted output voltage is large in an absolute value level, however, it is generated only in tens of milliseconds. Thus, the increase of this degree does not exceed the maximum rated values of the active filter 507, the switching element of the inverter circuit 504, and the smoothing condenser 503, and there occurs no problem such as damaging the elements, limiting the duration of life, and degrading the performance. Thus, the operating level of the overcurrent protection circuit may be raised to prevent the air conditioner from being stopped by the change in the input current as a result of the overshoot. However, by so doing, the overcurrent which should be detected is not detected, and it becomes impossible to protect the element from being damaged by the overcurrent. Since the protection voltage, which is compared with the detected voltage by the overvoltage protection circuit, is yielded by dividing the direct current voltage by the resistors 564-565, the affect of the output voltage to the same is negligible. Therefore, the output voltage and a reference voltage used in the overvoltage protection circuit are determined separately. However, variations in the resistor values of the resistors 561-562 or the resistors 564-565 provided to detect the voltage may reduce the detection margin (protection voltage minus output voltage) of the overvoltage protection circuit. To be more specific, when the resistor values of the resistor 561 vary in large numbers while those of the resistors 562 in small numbers, the voltage dividing circuit detects an output voltage lower than the normal voltage. Thus, if the output voltage is controlled based on the value thus detected, the output voltage is boosted higher than the normal voltage. On the other hand, when the resistor value of the resistor 564 varies in large numbers while that of the resistor 565 in small numbers, the protection voltage becomes lower than the normal voltage. Accordingly, the detection margin lessens, thereby making it easier for the overvoltage protection circuit to start the operation when the output voltage from the active filter 507 overshoots the normal voltage. As a result, the overvoltage protection circuit operates frequently, which presents a problem that the air conditioner can not operate continuously. Presently, the detection margin of each air conditioner is evaluated before the delivery to eliminate this problem. However, evaluating the detection margin individually causes problems during the manufacturing process, such as decreasing yield and making the inspection troublesome, and makes the resulting air conditioner expensive. The conventional air conditioner controls the air conditioning power by changing the operating frequency of the power compressor 505 from 15 Hz to 120 Hz. According to a typical specification, a compressor for the inverter operates at 60 Hz for the first one minute from the activation to stabilize the activation and refrigerating cycle. When the power compressor 505 is operated under such a specification, the load current of the same increases because the activation frequency of 15 Hz increases linearly to the operating frequency of 60 Hz as shown in Fig. 13. Accordingly, the output voltage from the active filter 507 decreases as the load current increases. Then, to compensate such a decrease in the output voltage, the switching control section 508 boosts the voltage value under the feedback control, so that the output voltage is maintained at the constant level. The above change in the output voltage does not occur instantaneously as has been explained but it occurs significantly and continuously over a long time period. Thus, the feedback control is delayed and causes a low frequency wave in the output voltage, and as shown in Fig.14, the waveform of the input current to the active filter 507, which is regular in general, correspondingly shifts to the one having an irregular fluctuation. As a result, the input current to the active filter 507 increases over the rated current, and the overcurrent protection circuit operates to stop the air conditioner. To prevent the air conditioner from being stopped by the change in the input current, the operating level of the overcurrent protection circuit may be raised. However, by so doing, the overcurrent caused by an unusual event which should be detected is not detected, thereby making it impossible to protect the element from being damaged by the overcurrent. The conventional air conditioner changes the operating frequency of the power compressor 505 from 10 Hz to 120 Hz (180 Hz in some case) depending on a load of air-conditioning. However, the ON/OFF action of the power transistor 533 of the active filter 507 is controlled independently of the load condition of the power compressor 505. Thus, the fluctuation of the output current becomes too large. As a result, the output voltage from the active filter 507 decreases under heavy-duty operation, and the terminal voltage of the smoothing condenser 503, or namely, the applied voltage to the inverter circuit 504, also decreases. In contrast, the output voltage from the active filter 507 increases under light-duty operation, and the applied voltage to the inverter circuit 504 also increases. Note that, under the light-duty operation, the voltage applied to the smoothing condenser 503 and inverter circuit 504 is above the maximum rated value, thereby possibly causing damages to the same. Under the no-load operation, the output voltage from the active filter 507 increases more than it does under the light-duty operation. Thus, the smoothing condenser 503 and inverter circuit 504 are more susceptible to the damages compared with the light-duty operation. In addition, the conventional air conditioner has the following disadvantage in terms of air conditioning power. An induction motor is generally used as the compressor for the inverter, and as shown in Fig. 15, the induction motor has the operating characteristics that the number of rotations is set to a value at which a load and a torque are balanced, because the torque is nil at the synchronous speed (number of rotations) N 0 . The difference between the synchronous number of rotations and the actual number of rotations is known as slip, which affects the rotation of the motor significantly. To be more specific, when the load increases, a load curve shifts from T 1 to T 2 , and the current in the motor increases to I 1 to I 2 . Accordingly, the slip also increases, and the air conditioning power degrades as the operating frequency, i.e., the number of rotations, of the power compressor 505 decreases from N 1 to N 2 . The air conditioning power degrades also when the current in the motor increases more than the rated value, because a command value of the operating frequency of the power compressor 505 is lowered to reduce the current in the motor. In the active filter 507, the switching frequency and switching loss of the power transistor 533, inductance and ripple current of the choke coil 531, input current, etc. have close correlation. More specifically, the ripple current ΔI in the coil current is expressed by Equation (1) below. ΔI = α/(f sw ·L) where α is a constant, f sw is the switching frequency of the power transistor 533, L is the inductance of the choke coil 531. Hence, given a certain value to the inductance of the choke coil 531, then multiplying f sw by ΔI yields a constant value (f sw x ΔI = a constant value). Thus, as shown in Fig. 16, increasing the switching frequency f sw reduces the ripple current; on the other hand, it increases the switching loss of the power transistor 533. Therefore, the switching frequency f sw is generally determined based on the current capacity and inductance of the choke coil 531. When the switching frequency f SW is fixed, the number of switching times per period of the power source output becomes inversely proportional to the power source frequency. Thus, there occurs a problem that the ripple current in the choke coil 531 increases as the power source frequency becomes lower. For example, when comparing the case of the power source frequency of 50 Hz and the power source frequency of 60 Hz, the number of switching per one cycle of the power source output is greater in the former case than the latter case. Thus, the former case of the power source frequency of 50 Hz has a greater ripple current and has a greater switching loss compared with the latter case of the power source frequency of 60 Hz. Further, there occurs a problem that the peak value of the current, which affects the maximum capacity of the power transistor 533, increases as the ripple current does so. When the direct current level in the coil using a core is changed, magnetic saturation occurs at a certain level and the inductance drops abruptly, which is known as coil's direct current super-imposing characteristics. In particular, in case of an air conditioner of a 230-V model, the choke coil 531 used to boost the voltage has a large maximum coil current up to 7 to 8 A rms, and it is almost impossible to make the direct current super-imposing characteristics flat. In fact, the inductance of the direct current super-imposing characteristics decreases as the coil current increases as shown in Fig. 17. It is understood from Equation (1) that the ripple current increases as the inductance decreases. Thus, as shown in Fig. 18, the larger the coil current, the larger the ripple current. To be more specific, a ripple current ΔI 1 is small when the coil current is small as shown in Fig. 19, and a ripple current ΔI 2 is fairly large when the coil current is large as shown in Fig. 20. The ripple current thus increased can not be removed by a noise filter and flows through the AC power supply line, thereby presenting a problem that the noise level of noise terminal voltage, noise power, unnecessary radiation, etc. is increased. The switching control section 508 demands a power source, such as a power source which outputs a voltage of +15 V or more, for the amplifier 547 or the like. Thus, the switching control section 508 is large in size and fairly expensive. Further, the switching control section 508 controls the switching action in such a manner that the phase of the input current becomes in sync with that of the input voltage to approximate to the sine wave. However, the actual waveform of the input voltage is distorted because a strain is likely to occur in the input current as it increases, which presents a problem that it is difficult to approximate the input current to the sine wave. The switching control section 508 mainly comprises a single integrated circuit. Thus, if the integrated circuit breaks, the output voltage detecting section 541 can not detect an excess increase in the output voltage when the output value increases more than necessary, thereby making it impossible to suppress an increase in the output voltage. The switching control section 508 finds the increase in the output voltage by calculating the voltage balance between the rated value and detected output voltage, and outputs the PWM signal such that makes the voltage balance nil. However, there is a considerable voltage balance at the time of activation of the active filter 507, and the output voltage changes after some time has passed since the switching control signal was outputted to the power transistor 533. Thus, if the switching control signal generated based on such a considerable voltage balance is supplied to the power transistor 533 after some time since the activation of the active filter 507, the output voltage is boosted higher than the rated value. Further, when less power is consumed due to the light-duty operation, the output voltage exceeds the rated value only by slightly widening the pulse width of the switching control signal from the switching control section 508 from a certain pulse width. Thus, it is required to output the switching control signal with a narrower range than the certain pulse width. To meet this requirement, the pulse width of the switching control signal can vary only in a limited range, thereby making it difficult to approximate the current waveform to the voltage waveform.. Accordingly, neither the higher harmonic components in the power supply current can be suppressed, nor can the power factor be improved. Since the voltage balance reaches its maximum at the activation of the active filter 507, the switching control signal is outputted with a widened pulse width, and if the active filter 507 starts up at the crest value of the input voltage, the current value to be determined by the switching control signal reaches its maximum pulse width. Since the maximum rated value of the power transistor 533 is determined by the maximum current value under such conditions, it is necessary to secure the maximum rated value for the power transistor 533 even when the maximum current value is far larger than the current value under the normally controlled conditions except for the activation. For this reason, the air conditioner demands a power transistor 533 with a fairly large maximum rated value, and makes the resulting air conditioner expensive. The air conditioner includes a 100V model driven by a power source voltage of 100V, and a 200V model driven by a power source voltage of 200V. As shown in Fig. 21, the former yields a direct current voltage of 280V by boosting a 100V voltage from the commercial power source 501 through a smoothing coil 561 using a voltage doubler rectifier circuit 571 comprising diodes 571a·571b and condensers 571c·571d. On the other hand, as shown in Fig. 22, the latter yields a direct current voltage by rectifying a 200V voltage from the commercial power source 501 using the bridge rectifier circuit 502. Thus, although it is not shown in the drawing, the air conditioner of the 200V model includes one active filter 507 like the air conditioner shown in Fig. 7. However, the air conditioner of the 100V model needs two active filters 507 for two capacitors 571c-571d. Thus, the latter is disadvantageous compared with the former because it is more expensive. DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic circuit diagram depicting the structure of an air conditioner in accordance with the first embodiment of the present invention. Fig. 2 is a schematic circuit diagram depicting the structure of a circuit for sending a signal between a microcomputer and a switching control section in the air conditioner of Fig. 1. Fig. 3 is a view showing a waveform representing the operation of an active filter and an inverter circuit in the air conditioner of Fig. 1. Fig. 4 is a circuit diagram depicting another structure of the air conditioner of Fig. I to compensate an applied voltage to a power compressor when the active filter breaks. Fig. 5(a) is a graph showing the relation between an operating frequency of the power compressor set invariably whether the active filter is broken or not and an effective value of the output from the inverter circuit. Fig. 5(b) is a graph showing the relation between the operating frequency and an applied voltage of the power compressor when the active filter operates normally and the same is broken. Fig. 6(a) is a graph showing the relation between the operating frequencies of the power compressor set separately when the active filter operates normally and the same is broken, and the effective value of the output from the inverter circuit. Fig. 6(b) is a graph showing the relation between the operating frequency and an applied voltage of the power compressor when the active filter operates normally and the same is broken. Fig. 7 is a schematic circuit diagram depicting the structure of a conventional air conditioner. Fig. 8 is a view showing a waveform representing an input voltage and an input current to a condenser input type power source circuit. Fig. 9 is a detailed schematic circuit diagram depicting the structure of a switching control section in the air conditioner of Fig. 7. Fig. 10 is a view showing a waveform representing the operation of a PWM circuit. Fig. 11 is a schematic circuit diagram depicting the structure of an overvoltage protection circuit employed in the conventional air conditioner. Fig. 12 is a schematic circuit diagram depicting the structure of another overvoltage protection circuit employed in the conventional air conditioner. Fig. 13 is a graph showing how the operating frequency of a power compressor is changed at a regular changing speed in the conventional air conditioner. Fig. 14 is a view showing a waveform representing an input current to the active filter, which correspondingly changes before and after the operating frequency is changed. Fig. 15 is a view showing the characteristics of a typical power compressor. Fig. 16 is a graph showing the relation among a switching frequency and switching loss of the power transistor, and a ripple current in the active filter. Fig. 17 is a graph showing the relation between a coil current and the inductance of a choke coil. Fig. 18 is a graph showing the relation between the coil current and ripple current. Fig. 19 is a view showing a waveform of the ripple current when the coil current is small. Fig. 20 is a view showing a waveform of the ripple current when the coil current is large. Fig. 21 is a schematic circuit diagram depicting the structure of a conventional air conditioner of 100V model. Fig. 22 is a schematic circuit diagram depicting the structure of a conventional air conditioner of 200V model. SUMMARY OF THE INVENTION It is desirable to provide an air conditioning device which permits a stable operation, for example, when starting up, and a protection of components against an abnormality. It is also desirable to provide an air conditioning device having a simplified structure by using some components in common. The present invention provides an air conditioning device as set out in claim 1. According to an air conditioning device according to an embodiment of the invention, when an abnormality or a shut off occurs at least in one of the active filter and the active filter control means, the occurrence of abnormality or the shut off is detected by the abnormality detection means. The abnormality detection means also detects a shut off of a power to be supplied to the active filter control means as an abnormality. Since this enables the control means to detect the shut off of the active filter control means caused by the stoppage of the power to be supplied thereto, a necessary operation can be taken such as stopping the power compressor. For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings. DESCRIPTION OF THE EMBODIMENTS [FIRST EMBODIMENT] The following descriptions will discuss one embodiment of the present invention with reference to Fig. 1 through Fig. 3. As shown in Fig. 1, an air conditioning device in accordance with the present embodiment includes a bridge rectifying circuit 2, a smoothing condenser 3, an inverter circuit 4 and an active filter 5 as a power source system. The air conditioning device also includes an input voltage detecting section 7, an output voltage detecting section 8, an inverter control section 11, a switching control section 12 and an interface section 13 (I/F in figures) as a control system. The inverter control section 11 is composed of a microcomputer 14 and a driving circuit 15. The power source system is provided for generating a DC voltage by rectifying an output from a commercial power source 1 in a bridge rectifying circuit 2 and smoothing it by the smoothing condenser 3. Further, based on the DC voltage , an AC voltage of three phases is generated by the inverter circuit 4 to be applied to a power compressor 6. The inverter circuit 4 includes six transistors 21 through 26 and six diodes 31 through 36. The transistors 21 and 22, the transistors 23 and 24 and the transistors 25 and 26 are respectively connected in series between two AC power source lines. On the other hand, the diodes 31 through 36 are respectively connected to the transistors 21 through 26 in parallel. The inverter circuit 4 outputs an AC voltage of three phases by switching the transistors 21 through 26 under the control of the microcomputer 14. The power compressor 6 is connected to respective junctions between the transistors 21 and 22, the transistors 23 and 24 and the transistors 25 and 26. The power compressor 6 is actuated by the AC voltage of three phases from the inverter circuit 4. In the power source system, the active filter 5 is connected between the bridge rectifying circuit 2 and the smoothing condenser 3. The active filter 5 includes a choke coil 41, a fast recovery diode 42 and a power transistor 43. In the present embodiment, an insulating gate bipolar transistor is adopted as the power transistor 43. However, other high speed switching elements may be used. The choke coil 41 and the fast recovery diode 42 are provided in series on the positive electrode side of the power source line. The power transistor 43 (switching element) is arranged such that a collector thereof is connected to a junction of one end of the choke coil 41 and an anode of a fast recovery diode 42, and an emitter thereof is connected to the power source line on the negative electrode side. The active filter 5 is provided for improving a harmonic suppression and a power factor. The active filter 5 controls a current flowing through the choke coil 41 with respect to the current flowing into the smoothing condenser 3 through the choke coil 41 and the fast recovery diode 42 by switching the power transistor 43. In the control system, the microcomputer 14 controls switching of the transistors 21 through 26 according to an air conditioning load so as to control an output frequency of the inverter circuit 4. The microcomputer 14 activates the switching circuit 12 in synchronous with a starting time of the power compressor 6. On the other hand, the switching control section 12 controls an output voltage from the active filter 5 by controlling the pulse width of the switching control signal to be applied to a control electrode of the power transistor 43. The switching control section 12 performs a feedback control so as to maintain the output voltage from the active filter 5 constant. The input voltage detecting section 7 includes a voltage dividing circuit composed of, for example, a resistor. The input voltage detecting section 7 divides and detects an input voltage to the active filter 5 generated between the rectifying power source lines. The output voltage detecting section 8 also includes the same voltage dividing circuit. The output voltage detecting section 8 divides and detects an output voltage from the active filter 5 generated between the DC power source lines. The switching control section 12 includes a normal driving section 12a, a voltage adjusting section 12b and a state detecting section 12c. Based on the control signal from the microcomputer 14 (to be described later), the normal driving section 12a generates a switching control signal based on the input voltage detected by the input voltage detecting section 7. More specifically, the normal driving section 12a controls the ON/OFF of the power transistor 43 so as to adjust the current flowing into the smoothing condenser 3 from the choke coil 41 through the fast recovery diode 42 in synchronous with the input voltage waveform from the bridge rectifying circuit 2. By the operation of the normal driving section 12a, the input current waveform is shaped to be an approximate sine wave. The voltage adjusting section 12b controls an output voltage by varying the time duration of the ON/OFF of the power transistor 43 according to a change in output voltage detected by the output voltage detecting section 8. The output voltage of the active filter 5 is adjusted to the voltage value set by the microcomputer 14. The state detecting section 12c detects if an abnormality has occurred in the active filter 5 based on the output voltage detected by the output voltage detecting section 8. More specifically, the state detecting section 12c outputs an abnormality detecting signal when the detection voltage from the output voltage detecting section 8 is set below a predetermined level so as to detect the active filter 5 in the abnormal state or the stop state. The microcomputer 14 controls each section of the air conditioner based on the content set by the operating section (not shown) provided in a main body of the air conditioner of the present embodiment. The microcomputer 14 outputs a drive control signal to the driving circuit 15 based on the output voltage detected by the output voltage detecting section 8. The driving circuit 15 generates a drive signal to be applied to a base of the transistors 21 through 26 at a timing based on the control signal. The microcomputer 14 stops the inverter circuit 4 upon detecting the occurrence of abnormality in the active filter 5 by the state detecting section 12c. Further, the microcomputer 14 determines that the power compressor 6 is in the stop state or an abnormality has occurred in the inverter circuit 4 when a detected voltage by the output voltage detecting section 8 exceeds a predetermined value, and is further raised above a predetermined voltage value and stops the active filter 5. A circuit for connecting the microcomputer 14 and the switching control section 12 will be explained. The microcomputer 14 and the switching control section 12 are electrically insulated, and are driven independently respectively by the power sources 16 and 17. A communication of the signal is performed optically through the interface section 13 between the microcomputer 14 and the switching control section 12. As shown in Fig. 2, the interface section 13 is composed of the photocouplers 13a and 13b. The photocoupler 13a is composed of a light emitting diode 18 and a photo transistor 19. The photocoupler 13b is composed of a light emitting diode 45 and a photo transistor 46. The photocoupler 13a and the state detecting section 21c constitute abnormality detection means. The light emitting diode 18 is arranged such that an anode thereof is connected to the power source 17, and a cathode thereof is connected to the state detecting section 12c. The photo transistor 19 is arranged such that the collector is connected to an abnormality detection port (hereinafter simply referred to as a port) S of the microcomputer 14 and the power source 16. The light emitting diode 45 is arranged such that an anode thereof is connected to the power source 16 and a cathode thereof is connected to the control signal output port (hereinafter simply referred to as a port) T of the microcomputer 14 through the transistor 47. The photo transistor 46 is arranged such that the collector is connected to the power source 17 and to the normal driving section 12a through the transistor 48. In the state where the switching control section 12 is normally operated by the power supplied from the power source 17, the photocoupler 13a is set in the ON position in the described circuit. As a result, a low level signal is always inputted to the port S in the microcomputer 14. In response to the low level signal inputted to the port S , the microcomputer 14 determines that the active filter 5 and the switching control section 12 are in the normal state, and transmits a high level ON signal from the port T . In response to the ON signal, the photocoupler 13b is set in its ON position, and the power is supplied to the normal driving section 12a from the power source 17. As a result, the normal driving section 12a is set in the operable state. On the other hand, if an abnormality has occurred which cause the power supply to the switching control section 12 to stop, the photocoupler 13a is set in its OFF position. As a result, the high level signal is inputted to the port S of the microcomputer 14. Even when the switching control section 12 is in the normal state, if an abnormality in the active filter 5 is detected by the state detecting section 12c, the photocoupler 13a is set in the OFF position, and a high level signal is inputted to the port S . In response to the signal of the high level inputted to the port S , the microcomputer 14 determines that an abnormality has occurred in at least one of the active filter 5 and the switching control section 12, and transmits a low level OFF signal from the port T . Then, the photocoupler 13b is turned OFF by an OFF signal, and a power is not supplied to the normal driving section 12a from the power source 17. As a result, the normal driving section 12a is set in an inoperable state. According to the air conditioner in accordance with the present embodiment, upon pressing a start button of the operational unit, a high level ON signal is transmitted from the port T of the microcomputer 14 so as to set the photocoupler 13b in the ON position. Then, the power is supplied to the switching control section 12. As a result, as shown in Fig. 3, the active filter 5 starts driving, and after an elapse of a predetermined time, the inverter circuit 4 also starts driving. In the power source system, the AC voltage from the commercial power source 1 is full wave rectified by the bridge rectifying circuit 2, and then inputted to the active filter 5. The switching control section 12 switches ON/OFF the power transistor 43 according to a control signal from the microcomputer 14 so that the output voltage from the active filter 5 becomes the set value. Since the power transistor 43 is set in the OFF position when the current flowing through the choke coil 41 is set to a predetermined value, the power is stored in the choke coil 41. On the other hand, since the power transistor 43 is turned ON when the current flowing through the collector and the emitter becomes higher than a predetermined value, the power stored in the choke coil 41 is released. As a result, the input current waveform becomes a sine wave in phase with the input voltage waveform, and the output voltage from the active filter 5 is raised to a predetermined value. The raised output voltage is smoothened by the smoothing condenser 3, and then supplied to the inverter circuit 4. As a result, the generation of the harmonic current can be suppressed, and the power factor can be improved, thereby achieving an effective use of the power source. On the other hand, when the inverter circuit 4 starts driving, a drive control signal is outputted from the microcomputer 14 to the driving circuit 15. Then, the driving circuit 15 switches the six transistors 21 through 26. As a result, the output voltage from the active filter 5 is chopped. The power compressor 6 is driven with an application of the chopped voltage (PWM waveform). By driving the power compressor 6 in the described manner, the air conditioner of the present embodiment starts driving. During the operation of the air conditioner in accordance with the present embodiment, the switching control section 12 always detects an output voltage from the active filter 5 by the output voltage detecting section 8. The switching control section 12 adjusts the output voltage by varying the time duration of the ON/OFF of the power transistor 43 according to the change in the output voltage. The photocoupler 13a is always set in the ON position by the state detecting section 12c, and thus a low level signal is inputted to the port S of the microcomputer 14. Then, from the low level signal, the microcomputer 14 determines that the active filter 5 or the switching control section 12 is in the normal state, and continues the normal operation of the air conditioner of the present embodiment. By stopping the supply of the power, for example, when an abnormality occurs in the active filter 5 or the switching control section 12, the photocouplers 13a and 13b are turned OFF in the interface section 13. Thus, the active filter 5 is stopped driving, and the application voltage to the power compressor 6 becomes short, thereby presenting the problem that the power compressor 6 is easily locked, or may even stop operating. In order to counteract the above-mentioned problem, the photocoupler 13a is set in the OFF position, so that the signal of the high level is inputted to the port S . In response to the input signal, the microcomputer 14 determines that an abnormality has occurred in the active filter 5 or the switching control section 12, and stops the operation of the inverter circuit 4 immediately. The shortage of the application voltage to the power compressor 6 due to the abnormality occurred in the active filter 5 can be prevented by other arrangements (to be described later). Furthermore, the microcomputer 14 always detects the output voltage from the active filter 5 by the output voltage detecting section 8. For example, when the operation of the power compressor 6 is stopped, or the abnormality has occurred in the inverter circuit 4, the output voltage would exceed the set value and is further raised above an overvoltage detection value (shown in Fig. 3). Then, a low level OFF signal is sent from the port T of the microcomputer 14. In response to the low level OFF signal, the photocoupler 13b is set in the OFF position. When the photocoupler 13b is set in the OFF position, as the power supply to the normal driving section 12a is stopped, the active filter 5 would be stopped operating. Additionally, when the active filter 5 or the inverter circuit 4 is stopped due to the abnormality occurred therein, the user would be informed by an LED, buzzer, etc., formed on the indoor unit of the air conditioner of the present embodiment. In the case where the air conditioner of the present embodiment is stopped by pressing the stop button in the operational unit, or by automatically stopping the air conditioner by the timer, the inverter circuit 4 also stops driving. After a predetermined time has elapsed after stopping the inverter circuit, the active filter 5 is also stopped driving, thereby terminating the operation of the air conditioner. As described, a signal is transmitted and received between the microcomputer 14 and the switching control section 12 through the interface section 13 composed of the photocouplers 13a and 13b. Therefore, when an abnormality has occurred in the active filter 5 or the switching control section 12, a signal of the high level is inputted to the port S so as to inform the microcomputer 14 of the occurrence of the abnormality. As a result, the active filter 5 can be prevented from being driven by the microcomputer 14 even when the abnormality has occurred. The microcomputer 14 stops the inverter circuit 4 upon detecting the abnormal state or the stop state of the active filter 5 or the switching control section 12. As a result, the power compressor 6 can be prevented from being locked due to the shortage of the application voltage. Furthermore, when the output voltage from the active filter 5 is raised above the overvoltage detection value, the microcomputer 14 determines that the inverter circuit 4 is in the abnormal state or the stop state and stops the operation of the active filter 5. As a result, the smoothing condenser 3 and the inverter circuit 4 can be prevented from breaking due to the overvoltage, and the occurrence of the secondary fault can be prevented. When the active filter 5 starts driving, the output voltage is raised with respect to the input voltage. Here, in response to the time lag of the feedback through the output voltage detecting section 8, as shown in Fig. 3, the output voltage may be raised above the overvoltage detection value for an instant. Furthermore, since a steady output voltage cannot be achieved also when the inverter circuit 4 starts and stops driving, the overvoltage may be generated as in the aforementioned case. In this case, although each section is being driven in a normal condition, the microcomputer 14 determines it to be in the abnormal condition by the overvoltage protecting function and stops the active filter 5. As shown in Fig. 3, in the microcomputer 14, an abnormality detection inhibiting period t, in which the detection of the abnormality is not performed, is set immediately after starting and stopping the driving of the inverter circuit 14 or immediately after starting the driving of the active filter 5. Therefore, even if the high level signal is inputted to the port S in the abnormality detection inhibiting period t, the active filter 5 nor the inverter circuit 4 would not be stopped. As a result, the problem that the active filter 5 and the inverter circuit 4 are stopped in the normal operation can be prevented, thereby driving the air conditioner of the present embodiment in a stable condition. In the present embodiment, the state detecting section 12c is formed in the switching control section 12. However, the present invention is not limited to this, and the state detecting section 12c may be actuated by a separately provided power source from the microcomputer 14 or the switching control section 12. Alternatively, it may be also arranged such that the microcomputer 14 also serves as the state detecting section 12c for directly detecting the state of the active filter 5 or the switching control section 12. Another arrangement for preventing the shortage of the power of the power compressor 6 will be explained. As shown in Fig. 4, the described arrangement includes a fault detecting section 51 for detecting the fault of the active filter 5 and the pattern change section 52. The fault detecting section 51 may be the circuit for detecting the fault of the active filter 5, for example, by detecting the load state of the power compressor 6. The fault detecting section 51 may be an output voltage detecting section 8 or the circuit for detecting the load current. When using the output voltage detecting section 8 as the fault detecting section 51, the stoppage of the power compressor 6 is detected by a drop in output voltage. The pattern change section 52 changes the table of the V/F pattern which represent the correlation between the driving signal voltage to be applied to the inverter circuit 4 from the inverter control section 11 and the operating frequency. Normally, the correlation between the effective value of the output voltage from the inverter circuit 4 and the operating frequency is on the assumption that the active filter 5 is being operated. Therefore, as shown in Fig. 5(a), the correlation is determined by the V/F pattern. However, when the active filter 5 is in failure, since the voltage rising operation by the active filter 5 cannot be performed, as shown in Fig. 5(b), the voltage to be actually applied to the power compressor 6 would drop. On the other hand, in the event of a failure in the active filter 5, the pattern change section 52 changes the V/F pattern (the linear line representing the off position of the active filter) as shown in Fig. 6(a). As a result, when a failure occurs in the active filter 5, the output voltage of the active filter 5 becomes higher than the normal operation state, and the effective value of the output voltage from the inverter circuit 4 with respect to the operating frequency of the power compressor 6 becomes higher than the normal operation state of the active filter 5. As a result, the correlation between the voltage to be actually applied to the power compressor 6 and the operating frequency is maintained constant irrespectively of the state of the active filter 5 (normal or abnormal) as shown in Fig. 6(b). Therefore, even if a failure occurs in the active filter 5, the operation of the air conditioner can be continued without stopping the power compressor 6. However, in the described state, since the operation is continued, it is required to inform the user of the failure of the active filter 5. As previously mentioned, the LED, the buzzer, etc., is used for informing the user that it is not in the normal operational mode. Since this enables the operation of the air conditioner to be continued as an emergency operation until the serviceman arrives, the user can manage the failure more efficiently.

Claims: An air conditioning device comprising: DC-AC conversion means (4) for outputting a controllable AC voltage for driving a compressor; AC-DC conversion means (2, 3) for generating a DC output from an AC source; active filter means comprising an active filter (5) associated with the AC-DC conversion means (2, 3) for conforming the input current to said DC-AC conversion means to an approximate sine wave; characterised in that : the device further comprises means (12c, 13) for detecting an abnormality in the operation of the active filter means including a failure of power supply to the active filter means and for outputting a signal indicating said power failure as an abnormality. An air conditioning device as claimed in claim 1 wherein said active filter means comprises active filter control means (12) and said abnormality detecting means (12c, 13) is for detecting an abnormality in the operation of at least one of the active filter (5) and the active filter control means (12) and for detecting a failure of power supply to said active filter control means (12) and outputting a signal indicating said power failure as an abnormality. An air conditioning device as claimed in claim 2 wherein the AC-DC conversion means comprises rectification means (2) for rectifying an AC voltage output from an AC power source and smoothing means (3) for smoothing an AC voltage rectified by said rectification means, the active filter (5) being provided between said rectification means (2) and said smoothing means (3); and wherein the DC-AC conversion means converts by chopping the DC voltage from said smoothing means; the device further comprising control means (11) for controlling the output of the DC-AC conversion means according to the load state of the compressor and for outputting instructions to the active filter control means (12), said control means (11) being powered by a power supply separate from the power supply for the active filter control means (12). An air conditioning device as claimed in claim 3 wherein said control means (11) shuts off said DC-AC conversion means (4) in response to a signal from said abnormality detection means (12c, 13). An air conditioning device as claimed in claim 3 wherein said control means (11) shuts off said active filter (5) by way of the active filter control means (12) upon detecting an abnormality or stoppage of said compressor (6). An air conditioning device as claimed in claim 3 wherein said control means (11) controls an output from said DC-AC conversion means (4) to raise the effective output voltage from said DC-AC voltage conversion means (4) based on a signal from said abnormality detection means (12c, 13).

Inventors: IKEBOU YASUHIRO, KAWASHIMA NOBUHIRO, TAKII HISAYOSHI, IKEBOU, YASUHIRO, KAWASHIMA, NOBUHIRO, TAKII, HISAYOSHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1995
Main classification: H02M5
IPC codes: H02M1, G05F1, H02M7, H02M5, H02P27, H02P23, H02H7