Washing machine with improved braking method

1. A method of braking a washing machine from an operational speed to a zero speed, the washing machine driven by one of a synchronous or asynchronous three-phase motor, the method comprising:

upon receipt of a stop signal, collapsing the motor rotating magnetic fields for a predefined time period;

after the predefined time period, applying DC braking voltage to the motor stator windings at a controlled ramp-up rate to a fixed amplitude to generate a controlled ramped braking torque on the motor; and

applying the braking torque until the motor is stopped;

wherein for collapsing the stator rotating magnetic field, the frequency of the three-phase power signal is set to 0 Hz thereby freezing the phase angles of the power signal components, and the amplitude of the power signal components is set to 0 Volts, and wherein the DC braking voltage is subsequently generated by ramping up the amplitude of the power signal components at their respective frozen phase angles such that the amplitudes vary between the power signal components as a function of their frozen phase angles.

2. The method as in claim 1 , further comprising continuing to apply the DC braking voltage for a defined time period after the motor has stopped.

3. The method as in claim 1 , wherein the motor is an AC induction motor supplied with three-phase AC power from an inverter, further comprising disabling the inverter gate drivers for the predefined time period to collapse the rotating magnetic fields.

4. The method as in claim 1 , wherein the magnitude of the braking torque applied to the motor is a function of the amplitude of the applied DC braking voltage, and further comprising setting the amplitude of the DC braking voltage to a value to cause complete stopping of the motor within a defined time period.

5. The method as in claim 4 , wherein the ramp rate of the DC braking voltage is set to prevent excessive current spikes while achieving complete stopping of the motor within the defined time period.

6. The method as in claim 1 , wherein braking of the motor is controlled by a motor controller, and further comprising supplying the motor controller with a motor speed feedback signal for termination of the DC braking voltage after the motor as stopped.

7. The method as in claim 6 , wherein the motor is a three-phase AC motor supplied with three-phase AC power from an inverter, the inverter controlled by the motor controller for collapsing the rotating magnetic fields for the predefined time period and applying the DC braking voltage to the stator windings at the controlled ramp-up rate up to the fixed amplitude to generate the braking torque.

8. The method as in claim 7 , wherein the motor controller is programmable to change any combination of: time period between collapsing the rotating magnetic fields and application of the DC braking voltage, ramp rate of the DC braking voltage to the fixed amplitude, the value of the fixed amplitude, and a time period for continued application of the DC braking voltage at the fixed amplitude after the rotor has stopped.

9. A washing machine, comprising:

a synchronous or asynchronous motor configured for receipt of a multi-phase power signal for rotationally driving a spin basket;

a motor control circuit, said motor control circuit including an inverter and a motor controller, wherein up receipt of a motor stop signal, said motor controller is configured to:

control said inverter to collapse the rotating magnetic fields of said motor for a predefined time period;

after the predefined time period, control said inverter to apply DC braking voltage to stator windings of said motor at a controlled ramp-up rate to a fixed amplitude to generate a controlled increasing braking torque applied to said motor; and

control said inverter to apply the braking torque until said motor is stopped.

10. The washing machine as in claim 9 , wherein said inverter is controlled to apply the DC braking voltage for a defined time period after said motor has stopped.

11. The washing machine as in claim 9 , wherein said inverter is configured such that, upon receipt of the stop command by said motor controller, amplitude of the three-phase power signal components from said inverter is set to 0 volts and frequency is set to 0 Hz.

12. The washing machine as in claim 11 , wherein said inverter is configured to generate the DC braking voltage by ramping up amplitude of the power signal components at their respective frozen phase angles to the fixed amplitude such that the amplitudes vary between the power signal components as a function of their frozen phase angles.

13. The washing machine as in claim 9 , wherein the magnitude of the braking torque applied to said motor is a function of the amplitude of the DC braking voltage of the respective power signal components, said motor controller configured to set the ramp-up rate and fixed amplitude of the DC braking voltage to a value to cause complete stopping of said motor within a defined time period.

14. The washing machine as in claim 9 , wherein said motor controller is supplied with a motor speed feedback signal for termination of the DC braking voltage after said motor has stopped.

15. The washing machine as in claim 9 , wherein said motor controller is programmable for change any combination of: time period between collapsing the rotating magnetic fields and application of the DC braking voltage, ramp rate of the DC braking voltage to the fixed amplitude, the value of the DC voltage fixed amplitude, and a time period for continued application of the DC braking voltage at the fixed amplitude after said motor has stopped.