1. Field of the Invention
The present invention relates to a controller that controls the rotational speed of a synchronous motor to the desired speed, an air conditioner that provides room air conditioning by controlling its internal compressor/blower driving synchronous motor by use of the above-mentioned controller, a refrigerator that provides refrigeration by controlling its internal compressor/blower driving synchronous motor by use of the controller, a washing machine that washes clothes by controlling its pulsator/spin-dry tub driving synchronous motor by use of the controller, and a vacuum cleaner that cleans rooms by controlling its blower driving synchronous motor by use of the controller.
2. Description of Prior Art
Because of their ease in maintenance, brushless direct-current (DC) motors each having a permanent magnet rotor and a stator coil assembly, are used in air conditioners, refrigerators, washing machines, and the like. Brushless DC motor driving control requires close linking between the magnetic pole position of the rotor and the positions of the stator coils which need to be energized. The motors for driving the compressors of air conditioners or of other electrical appliances use the sensorless position detection scheme, in which the magnetic pole position of the rotor is detected using the counter-electromotive force induced into the stator coils by their interactions with the magnetic pole of the rotor, not using a rotor position detection sensor such as a Hall element.
However, since the counter-electromotive force mentioned above is induced into the stator coils by the rotation of the rotor, when the motor is in a stopped status, the magnetic pole position of the rotor cannot be detected with the corresponding method. For this reason, used in prior art is the so-called low-frequency starting method, in which the position of the rotor is first made firm by energizing the stator coils of the two required phases during motor start, then after current conversion has been started and the current conversion time interval has been reduced in steps by synchronous operation to enable sensorless position detection with the counter-electromotive force, the driving mode is switched to driving based on sensorless position detection. The corresponding current conversion time interval and the voltage applied at this time are determined by the timing and value preset from the control unit.
The prior art for converting current, independently of the rotor position, by changing the voltage to be applied during motor start and then transmitting a current conversion signal to all phases of the stator coils in the timing that the current conversion time interval is to be forcibly given using the voltage at which the electrical quantities of non-energized phases change, is set forth in Japanese Application Patent Laid-Open Publication No. Hei 07-107777.
If the starting load torque is always kept constant, although the motor can be started in the preset voltage and timing, the starting load torque is usually unknown in the case of the motors for use in compressors and in washing machines. Therefore, when the starting current conversion time interval is too short and the starting voltage to be applied is too low, although the motor can be started if the load torque is small enough, it may not be possible for the motor to be started if the load torque is too large, since the motor may be insufficient in output torque.
Conversely, when the starting current conversion time interval is long enough and the starting voltage to be applied is high enough, although the motor can be started even if the load torque is too large, in the event that the load torque is too small, this will increase the motor current too significantly, thus easily generating an eddy current and, in the worst case, damaging the inverter module and the motor. In short, under the low-frequency starting method based on prior art, since current conversion independent of the rotor position occurs during synchronous operation, the motor is difficult to start properly, if the load torque is unknown.
In addition, in the case of the prior art, since current conversion independent of the rotor position occurs during synchronous operation, if the starting load changes significantly, the relationship between the position of the rotor and the cycle time of the load changes may not enable the motor to be started. Furthermore, during synchronous operation, since current conversion independent of the rotor position occurs, the possible significant changes in the output torque of the motor may cause significant vibration of the frame in which the motor is enclosed. Under the prior art, since current conversion independent of the rotor position occurs during synchronous operation, the motor characteristics cannot be utilized sufficiently and the motor is difficult to apply to products in which the motor speed needs to be increased rapidly.
An object of the present invention is to supply a synchronous-motor starting method and control apparatus that enable a synchronous motor to be started reliably and rapidly, even if its starting load torque is unknown.
Another object of the present invention is to supply a synchronous-motor starting method and control apparatus that enable a current to be converted rapidly according to the particular position of the rotor.
A yet another object of the present invention is to supply a synchronous-motor starting method and control apparatus that enable a synchronous motor to be started properly, even if its starting load torque changes.
A yet another object of the present invention is to supply a synchronous-motor starting method and control apparatus that minimizes any changes in the starting output torque of a synchronous motor and thus suppresses the vibration of the frame in which the motor is enclosed.
A yet another object of the present invention is to supply a synchronous-motor starting method and control apparatus that enable the rotational speed of a synchronous motor to be increased rapidly during its startup.
A yet another object of the present invention is to supply a synchronous-motor starting method and control apparatus that minimizes any decreases in motor current due to the counter-electromotive force generated during the rotation of the motor and thus prevents the insufficiency of its starting output torque.
A yet another object of the present invention is to supply a synchronous-motor starting method and control apparatus that enable a synchronous motor to be started with high efficiency by suppressing the motor current according to the starting load torque and reducing the load on the output circuit.
A yet another object of the present invention is to supply electrical appliances powered from the controlled synchronous motor mentioned above, especially, an air conditioner, a refrigerator, a washing machine, and a vacuum cleaner.
The start of a synchronous motor according to the present invention is accomplished by providing a first power supply pattern, a second power supply pattern, and a third power supply pattern as three successive startup power supply patterns, then after maintaining the respective power supply periods T1, T2, and T3 of the three power supply patterns in the relationship of T1 greater than T3xe2x89xa7T2xe2x89xa70, converting a current in the power supply pattern that enables the output torque of the synchronous motor to be increased when it is started.
The control apparatus for a synchronous motor, based on the present invention, has a position detection circuit for comparing the terminal voltage of the motor and a reference voltage and generating a rotor position detection signal, and detects rotor position information in the third power supply period T3 mentioned above.
The control apparatus for a synchronous motor, based on the present invention, has a timer for counting the time from the above-mentioned second current conversion or the above-mentioned third current conversion to the above-mentioned rotor position detection in the above-mentioned third power supply period T3, and a timer for counting the time from the above-mentioned position detection to the next current conversion.
The start of a synchronous motor according to the present invention is accomplished by measuring the time from the above-mentioned second current conversion or the above-mentioned third current conversion to the above-mentioned rotor position detection in the above-mentioned third power supply period T3, and determining the time to the next current conversion, based on the measured time.
The control apparatus for a synchronous motor, based on the present invention, has a function that increases the inverter output voltage in steps in the above-mentioned third power supply period T3.
The start of a synchronous motor according to the present invention is accomplished by increasing the inverter output voltage in the above-mentioned third power supply period T3 until the required motor speed has been reached or exceeded.
During the start of a synchronous motor according to the present invention, adjustment of the motor current according to the particular magnitude of the starting load torque is accomplished by setting the inverter output voltage beforehand.
During the start of a synchronous motor according to the present invention, the rotational speed of the motor and the position of its rotor are estimated from the angular acceleration of the motor and the inverter output voltage is controlled in each power supply period.