Driving system for single phase A-C induction motor

• US 5,252,905 A
• Filed: 12/10/1987
• Issued: 10/12/1993
• Est. Priority Date: 12/23/1985
• Status: Expired due to Term

• Current Assignee: York International Corporation (Johnson Controls International plc)
• Original Assignee: York International Corporation (Johnson Controls International plc)
• Inventors: Shaffer, Jacob E. Jr., Wills, Frank E.
• Primary Examiner(s): SALATA, ANTHONY J
• Application Number:
  US07/132,614
• Time in Patent Office: 2,133 Days
• Field of Search: 318/778, 318/799-812, 318/599, 318/85, 363/41
• US Class Current: 318/807
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor
• CPC Class Codes: H02P 25/04 Single phase motors, e.g. capacitor motors

Abstract

By employing a single phase pulse width modulated inverter system, a-c power line voltage may be effectively converted to single phase, variable amplitude and frequency sinusoidal voltage for driving a single phase a-c induction motor at an adjustable speed. The motor may be driven directly in response to the power line voltage (such as during start-up or when it is desired to run the motor at the power line frequency) by bypassing the inverter system and connecting the motor across the power line. Reduced energy consumption may be obtained by operating the motor in response to a reduced inverter output frequency. Switching the motor from the power line to the inverter, and vice versa, is accomplished without interruption. Immediately prior to each, switchover the inverter output voltage is synchronized to the power line voltage to minimize any electrical disturbance during the switching transition.

Claims

1. A driving system for driving a single phase A-C induction motor at selected, variable speeds comprising:

a positive D-C voltage of fixed magnitude;

a negative D-C voltage of the same fixed magnitude;

means for developing both a sinusoidally weighted pulse width modulated switching signal having a high frequency and a selectively adjustable single phase sine wave modulation signal representative of the desired A-C signal to be applied to the motor, the switching frequency of said switching signal being very high relative to that of the sine wave modulation signal;

means for selectively adjusting at least the frequency of said single phase sine wave modulation signal, as desired, to thereby adjust the speed of the motor;

a low pass filter having an inductance coil, connected in series with the motor, and a capacitor, connected in parallel with the motor, said low pass filter having the capability of filtering out the high frequency components associated with the switching signal and passing along to the motor only the components associated with the sine wave modulation component of the switching signal;

means, including a first power switch, for coupling the motor and low pass filter across the positive D-C voltage;

means, including a second power switch, for coupling the motor and low pass filter across the negative D-C voltage;

means, coupled with said means for developing a switching signal and responsive to said switching signal, for turning said power switch means on in alternation in order to couple the motor and low pass filter alternately to the positive and negative D-C voltages; and

said low pass filter filtering out all high frequency signal components and applying to the motor a selectively adjustable single phase sinusoidal voltage having a frequency equal at a given time to the then selected frequency of the sine wave modulation signal, whereby the speed of the motor is controlled by the adjusting means.

2. The driving system of claim 1 further comprising control means for selectively bypassing the output of the first and second power switch means and the low pass filter and applying an A-C power line voltage directly to the motor to drive the motor at a fixed speed determined by the power line frequency.

3. The driving system of claim 1 wherein said means for developing includes a sine wave generator means for producing a single phase sine wave control signal having an adjustable frequency representative of the desired speed of the A-C induction motor and wherein said means for selectively adjusting adjusts both the amplitude and frequency of the control signal.

4. The driving system of claim 3 wherein said means for developing includes a triangular wave generator means for producing a triangular shaped signal having a frequency which is very high relative to the frequency of the single phase sine wave control signal.

5. The driving system of claim 1 further comprising an A-C power line for providing a single phase A-C line voltage at a fixed frequency and means for developing, from said A-C power line voltage, said positive D-C voltage of fixed magnitude and said negative D-C voltage of fixed magnitude.

6. The driving system of claim 4 wherein said means for developing includes a differential comparator coupled with said sine wave generator and said triangular wave generator.

7. The driving system of claim 3 wherein said means for adjusting adjusts the amplitude of the single phase sine wave control signal as a function of the frequency of said single phase sine wave control signal.

8. The driving system of claim 3 wherein said means for adjusting achieves a constant ratio of the amplitude of said single phase sine wave control signal relative to the frequency of said single phase sine wave control signal.

9. The driving system of claim 8 wherein said adjusting means includes a high pass filter, coupled with said sinusoidal voltage generator, which attenuates the amplitude of said sine wave control signal from said sine wave generator in inverse proportion to the frequency of the sine wave control signal.

10. The driving system of claim 4 wherein said triangular wave generator means produces a triangular wave having a frequency of at least 10 kilohertz.

11. The driving system of claims 2 wherein said control means includes means for synchronizing the low pass filter output voltage to the power line voltage immediately prior to a switchover from one voltage source to the other to minimize any electrical disturbance during the switching transition.

12. The driving system of claim 11 including a phase detector for determining when the output voltage from the low pass filter and the power line voltage are in phase, thereby indicating when the frequencies of those voltages are equal, and means for effectively adjusting the amplitude of the output voltage of the low pass filter as a function of, and in direct proportion to, the frequency of the output of the low pass filter so that when the frequency of the low pass filter output voltage equals the fixed frequency of the power line voltage, those two voltages will have approximately the same amplitude.

13. The driving system of claim 2 wherein said bypassing means includes means for determining whether the power line voltage or the low pass filter voltage is supplied to the motor and means for adjusting the amplitude, frequency and phase of the low pass filter voltage as necessary to match the corresponding characteristic of the power line voltage just before a switchover is made from low pass filter voltage to power line voltage, or vice versa, in order to minimize any electrical disturbance during the switching transition.