Circuit for using the sign transitions of a motor phase and a motor phase back EMF currents to control PWM

1. A circuit for optimizing power transferred from an inverter circuit to a motor, the circuit using an open loop method to start-up the motor and have it reach a minimum speed, each phase of the motor receiving voltage from the inverter circuit, the circuit comprising:

at least one phase detector circuit for sensing the sign of one or more currents, the sign of the current being used to detect a zero crossing of the current;

an interpolator for receiving a voltage reference and outputting a frequency reference and a phase shift reference, the phase shift reference being a difference between an imposed voltage modulation and the one or more currents; and

a regulator circuit for using an error between the phase shift reference and the sign of the one or more currents to calculate a phase shift compensation,

wherein the sign of the one or more currents is determined to be positive at first sign transition instances when a sinusoidal wave of the current crosses to a positive area and to be negative at second sign transition instances when a sinusoidal wave of the current crosses to a negative area, the first and second sign transition instances being used to detect a phase shift of the current versus the imposed voltage modulation.

2. The circuit of claim 1 , further comprising a circuit for determining a window of time for measuring the sign of the one or more currents and at least one multiplier circuit.

3. The circuit of claim 1 , wherein the one or more currents comprises a current of each phase of the motor and the phase shift is a difference between voltage modulation imposed on each phase of the motor and the current of each phase of the motor.

4. The circuit of claim 2 , wherein the one or more currents comprises a back EMF current of each phase of the motor and phase shift is a difference between the current of each phase of the motor and the back EMF current of said each phase of the motor.

5. The circuit of claim 4 , wherein the at least one phase detector circuit sensing the back EMF current further extracts a frequency of the back EMF current from the sign of the back EMF current, the frequency of the back EMF being the frequency of a motor rotor.

6. The circuit of claim 5 , wherein the frequency of the back EMF current is achieved by counting the first and second sign transition instances to create a first count and inverting the first count.

7. The circuit of claim 1 , wherein the frequency and phase shift references are being used for regime condition at every speed value of the motor.

8. The circuit of claim 1 , wherein the motor is a Brushless Permanent Magnet Motor.

9. The circuit of claim 1 , further comprising:

an external source for providing a voltage reference for starting the motor;

a linear relation circuit and a rate limiter for receiving the voltage reference and providing a normative frequency;

a circuit for providing a compensation signal by combining the normative frequency and the phase shift compensation; and

a PWM modulator circuit for receiving the compensation signal and changing frequency of voltage modulation to adjust said frequency for every working condition in a closed loop.

10. The circuit of claim 9 , further comprising a first switch connected between the linear relation circuit and the rate limiter.