Control apparatus for controlling motor of air conditioner

Abstract: A control apparatus for controlling a motor of an air conditioner includes a converter (2), having switching means (2a) for improving an input power factor, for converting an AC power to a DC power and an inverter (4) for converting the DC power supplied from the converter to the AC power and supplying to a compressor (3). The output DC voltage of the converter is detected by a DC voltage detecting circuit. An input alternating current is detected by a current detecting circuit (11). A microcomputer (13) for controlling the inverter calculates a current command from data stored on the basis of the detected voltage. The detected current is compared with the current command, an ON percentage of a PWM signal to control the switching means is obtained, and the PWM signal is generated.

Description: FIELD OF THE INVENTION The present invention relates to a control apparatus for controlling a motor of an air conditioner and, more particularly, to a control apparatus for controlling a motor of an air conditioner via a converter and an inverter, the invention providing that the converter and the inverter are controlled by a single microcomputer, the converter being controlled to obtain a constant DC voltage which is necessary for the inverter circuit. DESCRIPTION OF THE RELATED ART Hitherto, an air conditioner has inverter control means for controlling a compressor, converts a commercial AC power into a DC power, and converts the converted DC voltage into the arbitrary AC voltage by the inverter control means, thereby supplying power to the compressor. As converting means for converting the AC power into the DC power, a converter of a capacitor input type is generally used. However, since an inputted alternating current waveform from the AC power source is a distorted wave, the input power factor is low and a harmonics current is generated. Therefore, a converter for converting the input current waveform to almost a sine wave has been proposed. An example of such an air conditioner will now be explained in detail with reference to Fig. 8. The air conditioner comprises: a converter circuit 2 to convert a commercial AC power from a power source 1 into a DC power; an inverter circuit 4 to convert the output DC voltage of the converter circuit 2 into a predetermined AC voltage and to supply it to a compressor 3; a microcomputer 6 for outputting inverter control signals (PWM signals) for ON/OFF controlling a plurality of transistors 4a which operates as switching means of the inverter 4, while inputting/outputting signals from/to some input/output circuits 5 necessary for controlling the air conditioner, the input/output circuits including a zero cross detecting circuit for detecting zero cross points of input AC current to be used for the discrimination of frequencies of the input AC and the transmitting/receiving signals of an indoor unit and an outdoor unit; a converter circuit 7 for outputting an IGBT control signal in accordance with the input current, input voltage (the rectified voltage) and output voltage of the converter 2; and an inverter driving circuit 8 for inputting an inverter control signal and for on/off driving the transistors 4a. In addition to the IGBT 2a, the converter circuit 2 comprises: a rectifying circuit 2b for rectifying the commercial AC power to a direct current; a reactor 2c; a diode 2d for blocking reverse current; and a smoothing capacitor 2e. Further, the converter control circuit 7 has a current detecting circuit, two voltage detecting circuits, an IGBT driving circuit, an oscillating circuit, an exclusive-use IC for controlling the converter, and the like. The converter control circuit 7 detects the current by using a current sensor 7a, detects the voltage waveform obtained by rectifying the AC voltage, and also detects the output DC voltage. The control signal (PWM signal) to control the IGBT 2a of the converter circuit 2 is generated so that the input AC current waveform from the AC power source becomes a sine wave by those detected current and voltage. As shown in Fig. 9, the converter control circuit 7 generates the IGBT control signal [shown in Fig. 9 (b)] to turn on/off the IGBT 2a so that the input AC current waveform of the converter circuit 2 is set to almost a sine wave. Consequently, as shown in Fig. 9 (a), since the input AC current from the AC power source doesn't become a distorted wave, the input power factor can be improved and a harmonics wave doesn't occur. However, such an air conditioner needs two control means such as microcomputer 6 and converter control circuit 7 in order to PWM control the switching means of the inverter circuit 4 and converter circuit 2. Therefore, there are problems such that not only the circuit configuration is complicated but also the number of parts is large, so that the costs are raised and the reliability is deteriorated. SUMMARY OF THE INVENTION It is an object of the invention to provide a control apparatus for controlling the motor of an air conditioner, in which an inverter control is executed by single control means and a converter to obtain a DC voltage which is necessary for the inverter circuit can be controlled. This object is solved by the features of Claim 1. A control apparatus for controlling a motor of an air conditioner according to the invention comprises: a converter having switching means for converting an input AC power into a DC power; an inverter for converting the DC power into an AC power and supplying this to the motor; voltage detecting means for detecting the output DC voltage of said converter; a microcomputer for controlling the inverter; and switching control means to control said switching means in the converter; wherein, while improving the input power factor, the control apparatus includes current detecting means adapted to measure the instantaneous input current from the AC power source, DC voltage comparing means for comparing the detected DC voltage and a set DC voltage, and - integrated into the microcomputer - current command calculation means and switching control means, as defined in claim 1. The microcomputer generates the current commands by calculating or selecting - dependent on the comparison result of the DC voltage comparing means - from data in the microcomputer or in external memory means, compares the current command with the measured input current, generates an ON percentage of a PWM signal to control the switching means, outputs the PWM signal, and thereby controls the switching means. With such a construction, when the output DC voltage of the converter means changes due to a fluctuation of a load or the like, the current command is varied in accordance with it. On the other hand, by comparing the current command and the input alternating current, the ON percentage of the PWM signal to control the switching means is calculated and varied and outputted. The switching means is driven by the PWM signal. Thus, the output DC voltage of the converter means is maintained at a predetermined necessary value (set DC voltage) and the input current is set to an almost sine wave. Since the switching means of the converter and the switching means of the inverter are PWM controlled by the single microcomputer, the circuit construction is simplified, the number of parts can be reduced, the costs can be decreased, and the reliability can be improved. According to the apparatus, the converter for converting the AC power to the DC power of the inverter is controlled by using the timer function, memory function, and arithmetic operating function of the microcomputer to inverter control the compressor, so that the air conditioner can be controlled by a single control means. The input current is set to a sine wave, the power factor is improved, the harmonics current is suppressed, and the output DC voltage (power source of the inverter) of the converter can be held constant. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic block diagram of a control apparatus for controlling a motor of an air conditioner showing an embodiment of the invention; Fig. 2 is a schematic timing chart for explaining the operation and control method of the control apparatus shown in Fig. 1; Fig. 3 is a schematic graph for explaining the operation of the control apparatus shown in Fig. 1; Fig. 4 is a schematic graph for explaining the operation of the control apparatus shown in Fig. 1; Figs. 5A and 5B are schematic flowcharts for explaining the operation and control method of the control apparatus shown in Fig. 1; Fig. 6 is a schematic timing chart for explaining the operation and control method of the control apparatus shown in Fig. 1; Fig. 7 is a schematic timing chart for explaining the operation and control method of the control apparatus shown in Fig. 1; Fig. 8 is a schematic block diagram of a control apparatus for controlling a motor of a conventional air conditioner; and Fig. 9 is a schematic timing chart for explaining the operation of the control apparatus shown in Fig. 8. DESCRIPTION OF THE PREFERRED EMBODIMENT A control apparatus for controlling a motor of an air conditioner according to the invention detects an input current from an AC power source, detects an output DC voltage of a converter, and compares the detected DC voltage and a set DC voltage. A microcomputer of the control apparatus obtains a current command by calculating or selecting from data in the microcomputer or data stored in external memory means on the basis of the comparison result, compares the current command with the detected input current, obtains an ON percentage of a PWM signal to control a switching device of a converter circuit, outputs the PWM signal, and controls the switching device. A construction of the control apparatus will now be described in detail with reference to Fig. 1. In the diagram, the same and corresponding portions as those in Fig. 8 are designated by the same reference numerals and their overlapped descriptions are omitted. In Fig. 1, the control apparatus comprises: a current sensor (CT) 10 and a current detecting circuit 11 for detecting the input alternating current of the converter circuit 2; a DC voltage detecting circuit 12 for detecting the output DC voltage of the converter circuit 2; a microcomputer 13 for outputting a control signal (PWM) to on/off control the IGBT (transistor) 2a included in the converter circuit 2 by varying as desired the ON percentage, in addition to the function [function to output an inverter control signal (PWM signal) or the like] of the microcomputer 6 shown in Fig. 8 ; and an IGBT driving circuit 14 for on/off driving the IGBT 2a by the PWM signal. The current detecting circuit 11 comprises a rectifying diode 11a and a resistor circuit 11b and converts the input AC waveform detected by the current sensor 10 to an input level (voltage value) suitable for the microcomputer 13. In the embodiment, although reference numeral lla denotes a fullwave rectifying circuit, a half-wave rectifying circuit can be also used. The DC voltage detecting circuit 12 comprises: a voltage dividing resistor circuit 12a for stepping down the output DC voltage of the converter circuit 2; and a photocoupler circuit 12b for isolating the stepped-down analog value, converting it to a digital value (H, L) and outputting this to the microcomputer 13. The voltage division ratio of the voltage dividing resistor circuit 12a is set in a manner such that the output of the photocoupler circuit 12b is set to the H level in the case where the output DC voltage of the converter circuit 2 is smaller than a voltage value (set DC voltage; for example, 300V) necessary for the inverter circuit 4 to drive the compressor 3, and that the output of the photocoupler circuit 12b is set to the L level in the case where the output DC voltage is larger than the set voltage value. Namely, the set DC voltage is compared with the detected output DC voltage of the converter circuit 2 and the comparison result is outputted as an H level or an L level. A zero-cross detecting circuit to detect a zerocross point of the input AC voltage is in the prior art included in the input/output circuit 5 to which according to Fig. 1 input/output circuit 15 corresponds. A zero-cross detection signal is outputted to the microcomputer 13. The zero-cross detection signal is used for judgment of the frequency of the input alternating current or for the transmission and reception of signals between an indoor apparatus and an outdoor apparatus. The operation of the control apparatus with the above construction and the functioning of its control method will now be described with reference to the timing charts of Figs. 2, 6, and 7, graphs of Figs. 3 and 4, and flowcharts of Figs. 5A and 5B. The microcomputer 13 executes input and output controls necessary for the control of the air conditioner, and inverter controls the compressor 3. In the case where the input AC waveform is as shown in Fig. 2 (a), the current detecting circuit 11 detects an AC waveform shown by a solid line in Fig. 2 (d). The detected AC waveform is converted to a voltage which is outputted to an analog input port of the microcomputer 13. In this instance, the microcomputer 13 detects the leading edge and the trailing edge of the zero-cross detection signal [shown in Fig. 2 (b)] from the input/output circuit 15 and detects the zero-cross point of the input AC voltage. The microcomputer 13 also detects outputs IR0 to IR9 (IRn) of the current detecting circuit 11 at every predetermined time T in the half period of the input AC voltage from the zero-cross detection [shown in Fig. 2 (d)] and stores them in an internal or external memory (for example, internal RAM) [shown in IRn in Table 1: IR0 to IR9]. On the other hand, the DC voltage detecting circuit 12 detects the output DC voltage of the converter circuit 2 for converting the commercial AC power 1 to the DC power, compares it with the set voltage and outputs the H-level or L-level signal as the comparison result to an input port of the microcomputer 13. For example, as shown in Fig. 3, when the output DC voltage of the converter circuit 2 is smaller than the set voltage 300V, the output level of the DC voltage detecting circuit 12 is set to the H level. When the output DC voltage of the converter circuit 2 is larger than 300V, the output of the DC voltage detecting circuit 12 is set to the L level. The microcomputer 13 stores data IM0 to IM9 (shown in Table 1: IMn) in an internal or external memory (for example, internal ROM), calculates current commands IS0 to IS9 (shown in Table 1: ISn) by the data IMn and the output level (comparison result) of the DC voltage detecting circuit 12, and stores them in an internal or external memory (for example, internal RAM). As shown in Fig. 4, the data of IMn (IM0 to IM9) are a sine wave data corresponding to the half period of the input alternating current of every predetermined time T from the zero-cross point. (n) denotes an integer. As IMn, data corresponding to 1/4 period of IM0 to IM5 can be also used. For example, the level of the output DC voltage of the DC voltage detecting circuit 12 is detected every zero-cross detection of the input AC voltage. When the detected level is at the L level, the output DC voltage of the converter circuit 2 exceeds 300V. Therefore, the current commands IS0 to IS9 are reduced by a but small predetermined percentage of the data IM0 to IM9. The same processes as mentioned above are repeated until the detected level is set to the H level. The current commands IS0 to IS9 are reduced every zerocross detection (shown in Fig. 4). When the detected level is at the H level, since the output DC voltage of the converter circuit 2 is equal to or lower than 300V, the current commands IS0 to IS9 are increased by a but small predetermined percentage of the data IM0 to IM9, and these processes as mentioned above are repeated until the detected level is set to the L level. The current commands IS0 to IS9 are increased every zero-cross detection (shown in Fig. 4). The current commands IS0 to IS9 obtained by the above processes are sequentially compared with the detection currents IR0 to IR9 of the current detecting circuit 11. On the basis of the comparison results, the ON percentage of the PWM signal to control the IGBT 2a is obtained [namely, D0 to D9 (Dn) shown in Table 1 are calculated]. For example, when ISn > IRn, data Dn in which the ON percentage was increased by (only) a predetermined value is obtained. When ISn < IRn, data Dn in which the ON percentage was decreased by (only) the predetermined value is obtained. The data D0 to D9 obtained as mentioned above are stored in the internal or external memory (for instance, internal RAM) of the microcomputer 13 and are patterned. The data D0 to D9 are sequentially set into a PWM timer of the microcomputer 13 at every predetermined time T synchronously with the zero-cross detection. Thus, the patterned PWM signal [shown in Fig. 2 (c)] to control the IGBT 2a is outputted from a PWM output port by the PWM timer synchronously with the zero-cross detection. In response to the PWM signal, the IGBT driving circuit 14 on/off drives the IGBT 2a. Explanation will be further made in detail with reference to Fig. 2. At the first half period of the input alternating current, the PWM signal [shown in Fig. 2(c)] to control the IGBT 2a is outputted from the PWM output port. In this instance, the input AC waveform is as shown in Fig. 2 (a). The output current of the current detecting circuit 11 is as shown in a solid line in Fig. 2 (d). When the microcomputer 13 detects the zero-cross point, it detects the output current IRn of the current detecting circuit 11 at every predetermined time T and stores the current value into the internal memory (RAM) and compares the stored current value and the current commands ISn in the internal memory. As shown by a solid line in Fig. 2 (d), for example, since the current waveform (input AC waveform) is distorted due to the influence of a power source impedance or the like, the current value is smaller than the current command for a period of time from a predetermined time T1 to T3. The current value is larger than the current command for a period of time from T5 to T9. The current value and current command are equal at times T0 and T4. The microcomputer 13 raises the data D0 to D2 of the ON percentage of the PWM signal to control the IGBT 2a by only a predetermined value (5%) and reduces the data D4 to D8 by (only) a predetermined value (5%) at the next half period (later half period) by the zero-cross detection [shown in Fig. 2 (c)]. Thus, as shown by a solid line in Fig. 2 (d), the output current of the current detecting circuit 11 has the same value as that of the current command, namely, the input current waveform can be set to the sine wave. The processes of the microcomputer 13 are realized by processing routines shown in Figs. 5A and 5B. The microcomputer 13 inputs the zero-cross detection signal and, when the zero-cross point of the input voltage waveform is detected, it executes the above routines. For example, as shown in Fig. 6 (a), when the output DC voltage of the converter circuit 2 is equal to or lower than a predetermined value (300V) because of a reason such that the load is heavy or the like, the output of the DC voltage detecting circuit 12 is set to the H level [shown in Fig. 6(b)]. Thus, the microcomputer 13 detects the H level (step ST1), sets the number (n) of detection times of the current detecting circuit 11 (step ST2), starts a timer of a predetermined time (T) (step ST3), and sets the data D0 of the internal memory into the internal PWM timer (step ST4). As already described above, the data D0 has been stored in the internal memory of the microcomputer 13 and is used to generate the PWM signal for controlling the IGBT 2a. By the setting of the PWM timer, the PWM timer is made operative. The PWM signal of the ON percentage according to the data D0 is outputted from the PWM output port of the microcomputer 13 to the IGBT driving circuit 14. Subsequently, the output IR0 of the current detecting circuit 11 inputted to the analog input port is detected and stored (step ST5). The current command IS0 in the internal memory is read out and the current command is calculated (step ST6). In the calculation of the current command, since the output of the DC voltage detecting circuit 12 is at the H level, the processing routine advances from step ST7 to step ST8. In order to raise the current command, a predetermined percentage of the data IM0 shown in Table 1 is added to the current command IS0 which was read out. In the case where the output of the DC voltage detecting circuit 12 is at the L level, namely, when the output voltage of the converter circuit 2 exceeds 300V, in the calculation of the current command, in order to reduce the current command, a predetermined percentage of the data IM0 shown in Table 1 is subtracted from the current command IS0 which was read out (step ST9). Subsequently, the calculated current command IS0 is compared with the current IR0 which has already been detected and stored (step ST10). When IR0 > IS0, the processing routine advances from step ST11 to step ST12. In order to reduce the ON percentage of the PWM signal, the data Dn-1 in Table 1 stored is reduced by (only) a predetermined value m. On the contrary, when IR0 < IS0, the processing routine advances from step ST11 to step ST13 and the data Dn-1 in Table 1 stored is raised by the predetermined value m in order to increase the ON percentage of the PWM signal. When n = 0, n - 1 = 9. Subsequently, a check is made to see if the processes in the above steps have been repeated ten times or not (step ST14). Unless n = 9, step ST15 follows and n is set to n+1. After the timer of the predetermined time T has been timed up, the processing routine is returned to step ST3 (step ST16). The same processes as mentioned above are repeated. The microcomputer 13 controls the inverter circuit 4 and input/output circuit 15 for the waiting time of the time-up. The current commands ISn calculated at the half period of the input current waveform and the data Dn of the ON percentage are stored in the internal memory of the microcomputer 13 (stored in a form of Table 1). The current command ISn and ON percentage Dn can be also stored each time they are calculated. Therefore, in the next half period, the ON percentage of the PWM signal which is outputted is updated on the basis of the data Dn (refer to Table 1) in the internal memory at every predetermined time T. As mentioned above, the output IR0 to IR9 of the current detecting circuit 11 are detected and stored. The current commands IS0 to IS9 are calculated on the basis of the data IS0 to IS9 (current commands in the former period) shown in Table 1, the output level of the DC voltage detecting circuit 12, and the data IM0 to IM9 shown in Table l. The calculated current commands IS0 to IS9 are compared with the detected currents IR0 to IR9, thereby varying the data D0 to D9 of the ON percentage in the next half period. In the case shown in Fig. 6, therefore, as the output DC voltage of the converter circuit 2 is smaller than 300V in the zero-cross detection and the output of the DC voltage detecting circuit 12 is at the H level, the current commands IS0 to IS9 are set to values shown by a broken line in Fig. 6(f). The microcomputer 13 sequentially compares the current commands IS0 to IS9 with the detected, output current IR0 to IR9 of the current detecting circuit 11. According to the comparIS0n results, since ISn > IRn at each of the predetermined times T1 to T9, the data D0 to D8 of the ON percentage at the next half period are increased by the predetermined value (5%) [shown in Fig.6(e)]. Thus, as shown in Fig. 6 (f), the current corresponding to the output of the current detecting circuit 11 is the same as the current command at the former half period. Namely, while the waveform of the input alternating current is set to an almost sine wave, the output DC voltage of the converter circuit 2 is raised [shown in Fig. 6 (a)]. Thus, the output DC voltage is controlled to a predetermined value. Fig. 7 shows an example in the case where the output DC voltage of the converter circuit 2 exceeds the predetermined value (300V) because of a reason such that there is only a light load or the like. In this case, processes similar to those in the example shown in Fig. 6 are executed in accordance with the processing routines shown in Figs. 5A and 5B. The detailed descriptions are omitted here. Figs. 7 (a) to 7 (f) correspond to Figs. 6 (a) to 6(f). In this case, since ISn < IRn for a period of time from the predetermined time T1 to T9, the data D0 to D8 of the ON percentage at the next half period are reduced by the predetermined value (5%) [shown in Fig. 7 (e)]. Thus, as shown in Fig. 7 (f), the currents IRn in which the output of the current detecting circuit 11 at the second half period coincide with the current commands ISn at the former half period, namely, the waveform of the input alternating current is almost set to the sine wave and the output DC voltage of the converter circuit 2 is reduced [shown in Fig. 7 (a)]. As mentioned above, while the output DC voltage of the converter circuit 2 is detected at every zero-cross point (at every half period) of the input AC voltage, the current commands ISn are respectively increased or decreased by the predetermined small value by the detected voltage level. The input alternating currents IRn are detected at every predetermined time T. The detected currents IRn are compared with the current commands ISn. In accordance with the comparIS0n results, the data Dn of the ON percentage of the PWM signal for controlling the IGBT (switching means) 2a of the converter circuit 2 is varied. The varied data Dn is set to the data at the next half period. Therefore, since the above processes can be realized by a software, by merely adding simple circuits such as current detecting circuit 11 and DC voltage detecting circuit 12, the converter circuit 2 can be controlled by the microcomputer 13 for inverter controlling the compressor 3. Namely, the voltage detecting circuit for detecting the voltage waveform obtained by rectifying the AC voltage, oscillating circuit, exclusive-use IC for controlling the converter, and the like as in the conventional example are unnecessary. Thus, there is no need to use the converter control circuit 7 including those circuits. The control is possible by the single microcomputer 13. Therefore, since the circuit construction is simplified, the number of parts can be reduced. The costs can be reduced and the reliability can be improved. The input current can be almost set to the sine wave. The power factor can be improved. The harmonics current can be suppressed. The output DC voltage of the converter circuit 2 can be maintained to the predetermined value (300V), so that there is no need to use the parts of larger rated values than they are needed in the conventional control apparatus. Therefore, the costs can be reduced also for this reason. The output DC voltage of the converter circuit 2 doesn't abnormally increase and doesn't excessively decrease. Consequently, a breakage of the parts of the control apparatus can be prevented, the parts can be protected, and an erroneous operation of the inverter control can be prevented. Although the number of data shown in the embodiment has been set to ten (IR0 to IR9 ; IS0 to IS9 ; IM0 to IM9 ; D0 to D9), the invention is not limited to such an example, but it is better to use a larger number of data. Although the ON percentage of the PWM signal has been updated at every half period in the embodiment, the invention is not limited to such a construction. For example, the ON percentage can be also updated at every period. Although ISn and Dn have been calculated each time the IRn are detected, the invention is not limited to such a case. For example, it is also possible to construct in a manner such that each time IRn are detected as shown in Table l, they are stored and, after the data of the former half period was stored, they can be also sequentially calculated for the later half period. Although the internal memory of the microcomputer has been used for the memory, the invention is not limited to such a memory but an external memory can be also used. Although the current command has been obtained by the calculation, the invention is not limited to such a case. It is also possible to previously store the current command into the memory and to selectively read out the current command and obtain it. Increasing or decreasing magnitudes by a pretermined percentage has been mentioned to be by 5 %; however, different values of increase or decrease, also different for different magnitudes to be altered, can be used. ROM RAM RAM RAM IM0 D0 IS0 IR0 IM1 D1 IS1 IR1 IM2 D2 IS2 IR2 IM3 D3 IS3 IR3 IM4 D4 IS4 IR4 IM5 D5 IS5 IR5 IM6 D6 IS6 IR6 IM7 D7 IS7 IR7 IM8 D8 IS8 IR8 IM9 D9 IS9 IR9 IMn Dn ISn IRn

Claims: A control apparatus for controlling a motor (3) of an air conditioner, constructed by: a converter (2) having switching means (2a) for converting an input AC power from an AC power source (1) to a DC power; an inverter (4) for converting said DC power to a working AC power and supplying it to the motor; voltage detecting means (12) for detecting the output DC voltage of said converter; a microcomputer (13) for controlling said inverter (4); and switching control means for obtaining an ON percentage of a PWM signal (Fig.s 2c, 6e, 7e) to control said switching means (2a), and for outputting said PWM signal, thereby controlling said switching means; wherein said microcomputer (13) also controls said switching means (2a), said apparatus being further constructed by: current detecting means (10, 11) adapted to measure the instantaneous input current and to supply consecutive measuring result signals (IRn) to the microcomputer (13); DC voltage comparing means (12) adapted to compare said detected DC voltage and a set DC voltage and to supply a comparison result signal to the microcomputer (13); current command calculation selecting means integrated into the microcomputer (13) and adapted to obtain consecutive current commands (ISn) calculated or selected by said microcomputer (13) from data (IMn) stored in an internal or external memory means of said microcomputer and the comparison result signal of said DC voltage comparing means (12) on the basis of the input current measuring result signals (IRn) ; and switching control means integrated into the microcomputer (13) and adapted to compare said consecutive current commands (ISn) and said consecutive input current measuring result signals (IRn) by said microcomputer (13), and to generate a signal (D) representative of the ON percentage of the PWM signal. The control apparatus according to claim 1, further characterized by zero-cross detecting means adapted to detect the zerocross points of the input AC voltage from said AC power source (1); and characterized in that said current command calculation selecting means (in 13) is adapted to obtain the consecutive current commands (ISn) at the time points of detection of said input current at predetermined instants in each interval of at least the input current half period after the detected zero-cross points, to store into the internal or external memory means of said microcomputer the input current measuring result signals (IRn), and to calculate the current commands (ISn) with reference to said comparison result signals, starting out from current command (ISn) data previously stored in said internal or external memory means of said microcomputer; and said switching control means (in 13) are adapted to sequentially compare said stored current commands (ISn) with said stored input current measuring result signals (IRn). The control apparatus according to claim 2, characterized in that said switching control means (in 13) is adapted to pattern the PWM signal and to output said patterned PWM signal synchronously with said detected zero-cross point, thereby controlling said switching means (2a). The control apparatus according to any of claims 1 to 3, characterized in that the current command calculation selecting means is adapted to calculate or select the consecutive current commands (ISn) on the basis of previous current commands (ISn) which are separately updated for the different instants from a series of initial values (IMn) positioned along a sine which series is stored in a ROM section of the internal or external memory. The control apparatus according to any of claims 1 to 4, characterized in that the voltage comparing means (12) is adapted to supply as the comparison result signal a binary signal. The control apparatus according to any of claims 1 to 5, characterized in that it includes the motor which is a compressor motor (3).

Inventors: OGAWA YOSHIO, OGAWA, YOSHIO, OGAWA, YOSHIO, C/O FUJITSU GENERAL LIMITED
Applicants: FUJITSU GENERAL LTD, FUJITSU GENERAL LIMITED
Application year: 1995
Main classification: F24F11
IPC codes: H02M1, F25B49, H02M7, H02P27, F24F11, F25B1, G05B11