Sensorless controller for electrostatic machine

Patent metadata

Field	Value
Publication number	US-11012003-B2
Application number	US-201916566250-A
Country	US
Kind code	B2
Filing date	Sep 10, 2019
Priority date	Sep 10, 2019
Publication date	May 18, 2021
Grant date	May 18, 2021

Abstract

A variable speed drive for an electrostatic motor provides feedback control according to rotor position and/or rotor rotational rate deduced from back currents (back-MMF). Extraction of the back currents is performed by a modeling of the stator and the development of isolated stator voltages from plate voltage measurements.

First claim

We claim:

1. An electrostatic motor drive for an electrostatic motor of a type having a stator with multiple stator electrodes adapted to generate a rotating stator electric field vector about an axis and a rotor having multiple rotor electrodes providing a rotor electric field interacting with the rotating electric field primarily by electrostatic forces rather than magnetic forces to rotate about the axis, the electrostatic motor drive comprising:
a set of current-stiff drives adapted to connect to the multiple stator electrodes;
a back-current monitor circuit detecting a back-current value from the electrostatic motor proportional to rotor speed;
a back-current conditioning circuit receiving the detected back-current value to provide an estimate of at least one of rotor position and rotor speed; and
a comparison circuit receiving the estimated one of rotor position and rotor speed and a motor control value and comparing the two to produce an error output to the set of current-source drives; wherein
the back-current monitoring circuit takes voltage measurements at connections between the current-source drives and corresponding stator electrodes.

2. The electrostatic motor drive of claim 1 wherein the speed drive of claim 1 and the current-source drives provide a set of electrical switches in series with a current-source implemented by an inductance serving to provide current stiffness and regulate the stator electrode voltage.

3. The electrostatic motor drive of claim 2 wherein the back-current monitoring circuit extracts stator voltages from measured signals and eliminates common mode voltages.

4. The electrostatic motor drive of claim 2 wherein the back-current monitoring circuit models an impedance of the stator circuit to deduce current through each stator electrode and compares that deduced current to a drive current from the current-source drive associated with the stator electrode to deduce back-current.

5. The electrostatic motor drive of claim 1 wherein the back-current conditioning circuit further measures a phase and magnitude of the back-current to A provide the rotor position and rotor speed signals.

6. The electrostatic motor drive of claim 1 further including:
a signal generator providing an injection signal to one of the rotor and stator;
an extraction circuit monitoring at least one of the rotor and stator to extract a resulting signal indicating at least one of capacitive coupling between the rotor and stator and changing effective capacitance of at least one of the rotor and stator; and
an injection processing circuit receiving the resulting signal to provide an estimated rotor position;
wherein the comparison circuit also receives the estimated rotor position signal from the injection processing circuit to develop the error output.

7. The electrostatic motor drive of claim 6 wherein the injection processing circuit further provides an estimated rotor speed.

8. The electrostatic motor drive of claim 7 further including a switch for selectively communicating one of the estimated rotor position signals from the injection processing circuit and the estimated rotor positioning signal from the back-current conditioning circuit for use by the comparison circuit.

9. The electrostatic motor drive of claim 8 wherein the switch is controlled by an estimated rotor speed derived from at least one of the back-current conditioning circuit and the injection processing circuit.

10. The electrostatic motor drive of claim 7 wherein the extraction circuit provides demodulation of the injection signal after modification by the electrostatic motor.

11. The electrostatic motor drive of claim 7 wherein the injection processing circuit further receives the detected injection signal after modification by the electrostatic motor to provide at an estimated rotor velocity signal; and wherein the comparison circuit further uses the velocity signal to provide the error output.

12. The variable speed drive of claim 1 further including an input circuit receiving a motor control value selected from the group of commands of torque and speed to control current applied to the stator electrodes.

13. The variable speed drive of claim 1 wherein the stator includes three electrically independent sets of electrodes in equal angles about the axis, the electrodes of each set joined electrically to a common terminal.

14. The variable speed drive of claim 1 further including an electrostatic motor of a type having a stator with multiple stator electrodes receiving output from the current-source drives and adapted to generate a rotating stator electric field vector about the axis and a rotor having multiple rotor electrodes providing a rotor electric field interacting with the rotating electric field primarily by electrostatic forces rather than magnetic forces.

15. The variable speed drive of claim 14 further wherein the electrostatic motor provides at least 60 poles.

16. An electrostatic motor drive for an electrostatic motor of a type having a stator with multiple stator electrodes adapted to generate a rotating stator electric field vector about an axis and a rotor having multiple rotor electrodes providing a rotor electric field interacting with the rotating electric field primarily by electrostatic forces rather than magnetic forces to rotate about the axis, the electrostatic motor drive comprising:
a set of current-stiff drives adapted to connect to the multiple stator electrodes;
a signal generator providing an injection signal to one of the rotor and stator;
an extraction circuit monitoring an other of the rotor and stator to extract a resulting signal indicating at least one of capacitive coupling between the rotor and stator and changing effective capacitance of at least one of the rotor and stator; and
a conditioning circuit receiving the resulting signal generator to provide an estimated rotor position;
a comparison circuit receiving the estimated rotor position and a motor control value and comparing the two to produce an error output to the set of current-source drives to control the electrostatic motor.

17. A method of providing variable speed control of an electrostatic motor of a type having a stator with multiple stator electrodes adapted to generate a rotating stator electric field vector about an axis and a rotor having multiple rotor electrodes providing a rotor electric field interacting with the rotating electric field primarily by electrostatic forces rather than magnetic forces to rotate about the axis, comprising the steps of:
providing a set of current-source drives for providing current to the stator electrodes;
detecting a back-current value from sensed voltages driving the electrostatic motor, the back current proportional to rotor speed;
processing the detected back-current value to provide an estimated rotor position;
receiving the estimated rotor position and measures of outputs of the current-source drives to develop a measured d-q vector;
receiving a desired d-q vector and comparing it to the measured d-q vector to produce an error output; and
transforming the error output to produce a set of outputs provided to the current-source drives for driving the stator electrodes.

Assignees

• Wisconsin Alumni Res Found

Inventors

• Ludois Daniel Colin
• Ghule Aditya N
• Killeen Peter

Classifications

• H02N1/004 Primary

  in which a body is moved along a path due to interaction with an electric field travelling along the path · CPC title

• H02N1/002

  Electrostatic motors · CPC title

• H02N1/00

  Electrostatic generators or motors using a solid moving electrostatic charge carrier · CPC title