Variable frequency electrostatic drive

Patent metadata

Field	Value
Publication number	US-9979323-B1
Application number	US-201715820829-A
Country	US
Kind code	B1
Filing date	Nov 22, 2017
Priority date	Mar 8, 2017
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

A variable speed drive for an electrostatic motor provides feedback control by conversion of measured current phases provided to the motor into a vector in a rotating rotor framework. This vector is used for evaluating corrective voltages and then reconverted to a non-rotating framework for application to the motor electrodes. Current-source drive circuits provide current stabilized outputs making such sophisticated control tractable.

First claim

We claim:

1. A variable speed 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, the variable speed drive comprising:
a set of current-source drives adapted to connect to the multiple stator electrodes wherein the current-source drives provide a set of electrical switches in series with a current source implemented by an inductance serving to regulate current to the stator electrodes;
a rotor position determination system;
an ABC-dq transformation circuit receiving a position signal from the rotor position detector and measures of outputs of the current-source drives to develop a measured d-q vector;
an input for receiving the desired d-q vector;
a comparison circuit providing an error vector based on the measured d-q vector and desired d-q vector; and
a dq-ABC transformation circuit receiving the position signal and providing an output based on the error vector to develop a set of electrode signals provided to the current-source drives for driving the stator electrodes of the electrostatic motor.

2. The variable speed drive of claim 1 wherein the inductance regulates current to the stator electrodes to within 25 percent of electrode signals provided to the electrical switches for a motor of at least 10 watts.

3. The variable speed drive of claim 2 wherein the current-source drives include a multi-phase H-bridge of electrical switches receiving current from an inductance operating to regulate current flow.

4. The variable speed drive of claim 2 wherein the current-source drive is a multiphase H-bridge of electrical switches and includes current to three inductances operating to regulate current flow to respective stator plates.

5. The variable speed drive of claim 2 wherein the current-source drive includes a multiphase H-bridge of electrical switches providing current to a multiphase transformer system providing a current regulating inductance.

6. The variable speed drive of claim 5 wherein the current-source drive provides for a controller controlling switching the electrical switches of the multiphase H-bridge according to a sensed current output and sensed voltage output of the multiphase transformer.

7. The variable speed drive of claim 1 further including an input circuit generating the desired d-q vector based on a received command selected from the group of commands of torque and speed to control current applied to the stator electrodes.

8. The variable speed drive of claim 7 wherein the input circuit selects an angle for the desired d-q vector between the d- and q-motor axes as a function of coupling capacitance between a rotor terminal and a stator terminal and a coupling capacitance between two stator terminals.

9. The variable speed drive of claim 1 wherein the input circuit selects an angle γ max for the desired d-q vector between the d- and q-motor axes from the group consisting of 0 and π (each ±5%).

10. The variable speed drive of claim 1 wherein the input circuit selects an angle γ max for the desired d-q vector between the d- and q-motor axes from the group consisting of π/4, −π/4, 3π/4, −3π/4 (each ±5%).

11. The variable speed drive of claim 1 wherein the position detection system is selected from the group consisting of a position encoder, an MMF sensor, and a saliency or MMF tracking sensor using injected high-frequency current.

12. 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.

13. 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.

14. The variable speed drive of claim 13 further including an insulating liquid contained to be present between the stator electrodes and rotor electrodes.

15. A variable speed 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, the variable speed drive comprising:
a set of current-source drives adapted to connect to the multiple stator electrodes;
a rotor position determination system;
an ABC-dq transformation circuit receiving a position signal from the rotor position detector and measures of outputs of the current-source drives to develop a measured d-q vector;
an input for receiving the desired d-q vector;
a comparison circuit providing an error vector based on the measured d-q vector and desired d-q vector; and
a dq-ABC transformation circuit receiving the position signal and providing an output based on the error vector to develop a set of electrode signals provided to the current-source drives for driving the stator electrodes;
wherein the input circuit selects an angle for the desired d-q vector between the d- and q-motor axes according to a formula:

γ
max

=

-

asin
⁡

(

C

1
⁢
mf

⁢

V
fd

±

C

1
⁢
mf

2

⁢

V
fd
2

+

8
⁢

C

2
⁢

Assignees

• Wisconsin Alumni Res Found

Inventors

• Ghule Aditya N
• Ge Baoyun
• Ludois Daniel Colin

Classifications

• H02N1/008 Primary

  Laterally driven motors, e.g. of the comb-drive type · CPC title

• 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