Sensorless controller for electrostatic machines

Abstract

A variable speed drive for an electrostatic motor provides feedback control based on rotor position and / or rotor rotation rate inferred from the reverse current (reverse MMF). The extraction of reverse current is performed by modeling the stator and generating isolated stator voltages from plate voltage measurements.

Description

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] --

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims the benefit of U.S. Patent Application No. 16 / 566,250, filed on September 10, 2019, which is incorporated herein by reference. Background Art

[0005] The present invention relates to electrostatic machines (motors and generators), and in particular to motor drive systems that sense rotor position and / or speed without the need for a separate resolver or the like mechanically attached to the rotor.

[0006] Electrostatic machines offer an alternative to electromagnetic machines, which use electrically induced electric fields and changes in capacitance to provide driving force. Electrostatic machines have many advantages over conventional electromagnetic rotating machines, including the elimination of magnets and expensive rare earth materials, the reduction of significant weight of ferrous materials, and the reduction of reliance on expensive high-current copper windings.

[0007] Another significant advantage of electrostatic machines is their ability to maintain torque or position without the significant current flow or resistive heat losses that occur in the electromagnetic coils of conventional electromagnetic machines. This characteristic makes electrostatic machines attractive for high torque, low speed operations and positioning.

[0008] Electrostatic machines for low speed or positioning applications may employ a large number of poles. For example, an electrostatic motor may include up to 96 poles or more, compared to an electromagnetic motor, which typically has a limited number of poles (e.g., 8). Accurate position control within the electrical cycle of an electrostatic motor having 96 poles requires a resolver with a mechanical resolution of an order of magnitude higher than that required for an electromagnetic motor, and exceeds the capabilities of a standard 12-bit encoder. Therefore, in such applications, an electrostatic machine may require an expensive 15-bit encoder or higher. Summary of the invention

[0009] It should be recognized that electrostatic motors provide a "reverse current" or reverse MMF (magnetic flux potential) that is roughly similar to the reverse EMF (electromotive force) of standard electromagnetic motors. The measurement of MMF, also known as reverse current, is usually a vector with phase and amplitude, one or both of which can provide information for inferring position and or speed. The present invention provides a method for extracting MMF measurements from an electrostatic motor when the electrostatic motor is advantageously powered by a current driver, such as in U.S. Pat. No. 9,979,323, named by co-inventor Ludois and incorporated herein by reference, describing this type of electrostatic motor. Importantly, the present invention allows easy-to-handle voltage sampling at the motor terminals without the need for bulky current transformers, etc. At moderate speeds, the MMF value can be used to infer position and / or motor speed without the need for a resolver with the necessary resolution. At low or zero speeds, when there is insufficient / insignificant MMF, position and / or speed can be sensed by injecting current in the rotor or stator instead of MMF measurement. On the other hand, at high speeds, injecting a current that can be distinguished from the drive current may be difficult to make MMF sensing more preferred.

[0010] Specifically, then, in one embodiment, the present invention provides an electrostatic motor driver for an electrostatic motor, the electrostatic motor driver comprising a set of current source drivers adapted to be connected to a plurality of stator electrodes. A reverse current monitoring circuit detects a reverse current value from the electrostatic motor that is proportional to the rotor speed, and a reverse current regulation circuit receives the detected reverse current value to provide at least one of an estimated rotor position and a rotor speed, the estimated rotor position and the rotor speed being provided to a comparison circuit that receives at least one of the estimated rotor position and the rotor speed and a motor control value, and compares at least one of the estimated rotor position and the rotor speed with the motor control value to generate an error output to the set of current source drivers. The reverse current monitoring circuit can obtain voltage measurements at the connections between the current source drivers and the corresponding stator electrodes.

[0011] It is thus a feature of at least one embodiment of the invention to provide motor shaft position and / or speed measurement of a high pole count electrostatic motor type for low speed and high torque applications using simple voltage monitoring, thereby eliminating the need for direct output reverse current sensing.

[0012] The current source driver may provide a set of electrical switches in series with a current source implemented by an inductor to modulate the current to the stator electrodes and regulate the voltage.

[0013] It is thus a feature of at least one embodiment of the invention to provide a resolver-less position / rotation rate sensor that is compatible with current source drives that are advantageous for electrostatic motors of the type described above.

[0014] The reverse current monitoring circuit can compare the voltage measurement with the common voltage to extract the stator voltage isolated from the common-mode voltage.

[0015] It is thus a feature of at least one embodiment of the invention to eliminate the effects of highly variable common-mode voltage on the calculation of reverse current.

[0016] The monitoring circuit may model the impedance of the stator circuit to infer the current through each stator electrode, and may compare the inferred current to the drive current from the current source driver associated with the stator electrode to infer the reverse current.

[0017] It is thus a feature of at least one embodiment of the invention to infer the forward current into the stator to calculate the reverse current as needed from voltage measurements.

[0018] The reverse current regulation circuit can also measure the peak value of the reverse current to provide a speed signal, and the comparison circuit can also use the speed signal to provide an error output.

[0019] It is thus a feature of at least one embodiment of the invention to provide an independent measurement of speed useful, for example, for speed control of an electric motor.

[0020] The reverse current regulation circuit can extract the estimated rotor position based on the change of reverse current.

[0021] It is therefore a feature of at least one embodiment of the invention that the position is inferred from the position-dependent change in the reverse current.

[0022] The electrostatic motor driver may further include: a signal generator that provides an injection signal to one of the rotor and the stator;

[0023] an extraction circuit that monitors at least one of the rotor and the stator to extract a resultant signal indicative of at least one of capacitive coupling between the rotor and the stator and a varying effective capacitance of at least one of the rotor and the stator based on saliency and spatial alignment; and

[0024] a regulation circuit that receives the resulting signal to provide an estimated rotor position;

[0025] Among them, the comparison circuit also receives the estimated rotor position signal from the saliency and spatial alignment adjustment circuit to generate an error output.

[0026] It is therefore a feature of at least one embodiment of the invention to adjust for a low signal-to-noise ratio of a reverse current signal at low speeds to perform low speed control.

[0027] The electrostatic motor drive may further include a switch for selectively transmitting one of the estimated rotor position signal from the saliency regulation circuit and the estimated rotor position signal from the reverse current regulation circuit for use by the comparison circuit.

[0028] It is thus a feature of at least one embodiment of the invention to provide an automatic basis for switching between reverse current and injected current position sensing.

[0029] The switches may be controlled by an estimated rotor speed derived from at least one of a reverse current regulation circuit and a saliency regulation circuit.

[0030] It is thus a feature of at least one embodiment of the invention to use the rotor speed derived from the sensing system of the invention to select between these sensing systems.

[0031] These particular features and advantages may apply to only some of the embodiments falling within the claims, and thus do not limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a simplified exploded view of the drive system of the present invention attached to an example axial flux electrostatic motor;

[0033] Figure 2 yes Figure 1 A detailed block diagram of a motor driver of the invention showing a current source driver and a reverse current sensing system and an injected current sensing system replacing a resolver for controlling the current source driver;

[0034] Figure 3 yes Figure 2 A more detailed block diagram of a current source driver that provides a separate current source for each of the three stator plates of a three-phase electrostatic motor;

[0035] Figure 4 is a more detailed block diagram of a reverse current regulation circuit as part of a reverse current sensing system for providing position information and speed information;

[0036] Figure 5 is a block diagram of an injection signal conditioning circuit that provides position information from which velocity information can be inferred;

[0037] Figure 6 is a graph of reverse currents of the d-conversion axis and the q-conversion axis;

[0038] Figure 7 is a graph of an injected signal before demodulation, showing position information in the injected signal envelope;

[0039] Figure 8is a graphical representation of the stator model used to infer the reverse current from the voltage measurements;

[0040] Fig. 9 is a simplified diagram of the stator electrodes, showing the voltage measurement of one electrode;

[0041] Fig.10 is a phasor diagram showing the extraction of isolated phase voltages; and

[0042] Fig.11 yes Figure 2 A partial view of a block diagram of , showing an alternative method of injecting current into the rotor. DETAILED DESCRIPTION

[0043] Electrostatic Motor Design

[0044] Now refer to Figure 1 , the electrostatic drive system 10 may include an electrostatic motor 12, which in one example has one or more disc-shaped plates with radially extending, circumferentially displaced stator electrodes 16. The stator electrodes 16 interact with corresponding radially extending, circumferentially displaced rotor electrodes 20 on a corresponding disc-shaped rotor 18 positioned adjacent to the disc-shaped stator 14. For simplicity, the stator electrodes 16 and the rotor electrodes 20 are shown on visible surfaces of the stator 14 and the rotor 18; however, the stator electrodes 16 and the rotor electrodes 20 are typically in close proximity on opposing faces of the stator 14 and the rotor 18. This type of motor will be referred to as an "axial field" motor, generally referring to the alignment of the electrostatic field along the rotational axis 25 of the rotor 18.

[0045] The present invention also contemplates operation with a "radial field" motor having an electric field extending perpendicular to the axis 25, such as a circumferentially nested cylindrical plate or an axially extending bolt ring. Typically, the number of rotor poles 20 in each of these types of motors will match the number of poles of the motor. The number of poles will typically exceed 16, more typically exceed 60, and preferably be 96 or more.

[0046] Axial field motors and radial field motors are described in U.S. Patents 9,184,676, 2016 / 0211775, and 2016 / 0344306, all of which are assigned to the assignee of the present invention and are incorporated herein by reference. The present invention is applicable to both types of motors.

[0047] In both radial flux motor and axial flux motor designs, the rotor 18 may be supported to rotate on a drive shaft 24 extending along an axis 25 to extract mechanical work. A slip ring or brushless power transmission system 22 (e.g., capacitor or inductor) is attached to the drive shaft 24 so that power from a stationary rotor power supply 26 can be conducted to the rotating rotor electrodes 20, as is generally understood in the art, to provide static polarization of the rotor 18.

[0048] Overview of Variable Speed ​​Drives

[0049] The variable speed drive 32 can provide controlled application of electrical power to the stator electrodes 16 of the stator 14 based on the position signal generated by the position detection system 30. In this regard, the variable speed drive 32 can receive a command signal 34 such as position, speed, torque or other relevant quantity and determine an appropriate variable current to be applied to the stator electrodes 16 to provide operation of the electrostatic motor 12 consistent with the command signal 34. Thus, the output of the variable speed drive 32 will provide a plurality of phases 36 (also designated as A, B, C for a three-phase embodiment) associated with different stator electrodes 16, thereby providing those stator electrodes 16 with the sinusoidal or other continuously varying signals required to control the operation of the motor.

[0050] Now refer to Figure 2 , the instantaneous value of the output phase 36 required for a given command signal 34 may be a function not only of the command signal 34 but also of the rotor position and characteristics of the motor 12. This processing required to generate the output phase 36 may be simplified by a coordinate transformation known in conventional electromagnetic motors, in which the constantly changing multiple phases 36 are mapped to a reference frame that rotates with the motor rotor 18. This reference frame is referred to as the dq reference frame, in which the d-axis (direct axis) is aligned with the positive electrode on the electrode 20, and the q-axis (orthogonal axis) is positioned at 90 degrees relative to the d-axis. Viewed in this reference frame, the complexity of the waveform at the multiple phases 36 (e.g., referred to as A, B, C in a three-phase system) is transformed into a single vector that is largely invariant for steady-state operation of the motor 12. For example, the details of this transformation in the context of electromagnetic machines are described in DW Novotny and T Alipo, "Vector Control and Dynamics of AC Drives," Oxford University Press, 1996, 1st edition (including pages 88 to 102), where the underlying mathematics also applies to the present invention.

[0051] Using this transformation, the present invention provides feedback control of the current source driver 40, with the phase 36 connected to each stator pole 16. In this aspect, the voltage from each of these phases 36 is measured and these measurements are received by the ABC-dq transformation circuit 42. The ABC-dq transformation circuit 42 also receives the position signal 44 and the speed signal 45 from the position detection system 30 to convert the received phase signal (A, B, C) into a vector in dq space, which is referred to as the "measured" dq vector 48.

[0052] The input command signal 34 will be converted to a similar "desired" dq vector 50 by the input conversion circuit 52. When the electrostatic motor 12 is not operating in a steady state, this desired dq vector 50 will generally have a different angle and a different magnitude than the measured dq vector 48. When the input command signal 34 is a torque value, the magnitude of the desired dq vector 50 will be proportional to the desired torque, and the ideal angle relative to the q-axis will depend on the type of motor 12. For non-salient machines, the angle will simply be zero degrees (the desired dq vector 50 is aligned with the q-axis); however, for salient machines, the calculation will be more complex, as discussed in U.S. Patent 9,979,323, assigned to the assignee of the present invention and incorporated herein by reference. The ideal angle is the angle that provides maximum torque per voltage, thereby reducing motor losses. Alternatively, the command signal 34 can be a speed value, in which case the speed signal 45 is used. More generally, any control strategy can use both the position signal 44 and the speed signal 45.

[0053] Once the desired dq vector 50 is determined, the desired dq vector 50 is compared to the measured dq vector 48 to generate an error value 53 at a comparison circuit 54 that controls the current source 40. In the simplest case, the error value 53 is simply the difference between the desired dq vector 50 and the measured dq vector 48; however, alternatively, the difference may be further processed, such as under a proportional / integral / derivative type control strategy, where the error value 53 is a weighted combination of the difference, the time-running integral of the difference, and the derivative of the difference. It should also be understood that the comparison circuit 54 may use other control strategies, including feedback and / or feedforward of other measured variables obtained from the motor 12.

[0054] Still refer to Figure 2 The error value 53 is then provided to a dq-to-ABC transformation circuit 56 (as an inverse transformation) that operates in the opposite direction to the ABC-to-dq transformation circuit 42 to change the error value 53, which is a vector in the dq space, into a phase 36 in the non-rotating frame.

[0055] This feedback control process traversing the loop of the ABC-to-dq transformation circuit 42 and the dq-to-ABC transformation circuit 56 continues during operation of the motor 12 .

[0056] When the command signal 34 is a different value, such as a desired rotational speed (e.g., RPM), an additional optional feedback loop may be incorporated, for example, at an optional comparison block 58, using the position signal 44 for inferring the speed and using the difference between the desired RPM and the inferred RPM of the command signal 34 to create a torque value that can then be processed as discussed above with respect to the torque signal. Other input signals may also be processed in this manner, and in this regard, the present invention contemplates that the programmable command signal 34 may be used for, for example, soft starting and soft stopping of the motor 12 and different states at different motor RPMs or operating conditions.

[0057] The ABC-to-dq conversion circuit 42, input conversion circuit 52, comparison circuit 54, and dq-to-ABC conversion circuit 56 may be implemented by discrete circuit systems, or preferably by a high-speed computer processor executing a program stored, for example, as firmware in a non-volatile computer memory and operating in the digital domain using an analog-to-digital converter.

[0058] Now refer to Figure 3 The practical implications of complex field control of the electrostatic motor are achieved through the ability to generate a "rigid" current output signal at the power level required to drive the electrostatic motor 12, i.e., an open loop current controlled output can be provided in the face of rapidly fluctuating voltages at the multiple phases 36 caused by capacitive coupling as the motor 12 rotates. The present invention contemplates that the electrostatic motor 12 will be operated at powers in excess of 10 Watts, typically in excess of 100 Watts, and desirably in excess of 1000 Watts.

[0059] The inductive property of resisting changes in current through the inductor, the accumulation of self-induced energy within the inductor's magnetic field, can be exploited to produce the necessary "current source" output by using one or more series inductive elements 78. The present invention recognizes that this property can be exploited to provide sufficient output current stiffness to enable regulation of the output voltage without hindering the dynamic control of the current necessary for "charge steering" control or variable speed capability of the motor. In this regard, the inductance must be sized to provide current regulation (and therefore energy storage) at the expected motor power level to provide, for example, control of the current output to the motor to within 25%, typically within 10%, and desirably within 5% of the command value controlling the semiconductor switches. The construction of such a current source driver is described in U.S. Patent 9,960,719, assigned to the assignee of the present invention and incorporated herein by reference.

[0060] In one implementation, a DC power source is provided to a set of solid-state switches 72, such as transistors such as MOSFET transistors, thereby receiving the ABC current value from the switching logic circuit 73. The solid-state switches 72 are configured, for example, in an H-bridge in which each of the phases 36 is connected to a node between a pair of series-connected switches 72, which in turn bridge the positive power rail 74 and the negative power rail 76, thereby providing a direct current stabilized by the inductor 70. Initial use of this circuit can produce a square wave output; however, the present invention contemplates that the generated phase 36 is a continuous waveform of any shape and frequency determined by the control algorithm. Therefore, the switch 72 will receive a control signal that determines its switching state, which is pulse width modulated (or modulated by a similar modulation technique including pulse density modulation, etc.). In pulse width modulation, the on time of the switch 72 is changed to determine the average current value output through the phase 36. In such modulation, the switch 72 is operated in a switching mode (on or off) for energy efficiency, but switches at a high rate to produce a continuous waveform (e.g., a sine wave of varying frequency) that is smoothed by the capacitance of the electrostatic motor 12. In pulse width modulation, the switching speed of the semiconductors is many times the fundamental frequency of the waveform of the phase 36, and typically exceeds 10 to 20 times that frequency.

[0061] Inductor 70 may be placed in series with switch 72 of the H-bridge to stabilize the DC bus feeding switch 72. Other placements of inductors (eg, one on each of phases 36) or using transformers with leakage inductance may provide similar effects.

[0062] Position Sensing

[0063] Refer again Figure 2 , the position signal 44 and the speed signal 45 can be obtained from the resolver; however, in the present invention, these signals can be provided by the position detection system 30 that receives the voltage signal 90 from each of the phases 36 of the current source driver 40. The position detection system 30 can include two different components: a reverse current or "reverse MMF" (magnetic flux potential) detector system 93, which includes an MMF detector 92 and a conditioning circuit 120; and an injection current system 131, which includes a current injection circuit 130 and a conditioning circuit 144. Both systems receive voltage measurements provided to the phases 36 of the electrodes 16 of the stator 14 to generate position and speed signals.

[0064] The reverse MMF detector 93 detects the reverse MMF which is a function of the rotor speed and can also be used to provide a position signal based on the variation of the MMF with rotation.

[0065] Now refer to Figure 8 and Fig. 9, the MMF detector 92 can measure the voltage at each phase 36 relative to a common voltage reference 94 (e.g., ground) to provide a raw phase voltage 96 associated with each phase (e.g., V in the example 3-phase motor). AG is the voltage between phase A and ground, V BG is the voltage between phase B and ground, and V CG is the voltage between phase C and ground.) These raw phase voltages 96 will include common mode voltages that are highly variable and can obscure the desired reverse current measurement.

[0066] Therefore, and with reference to Fig.10 , each raw phase voltage 96 can be combined to extract the isolated phase voltage for each electrode 16. The extraction process can be graphically understood by envisioning the isolated phase voltages as phasors 98 extending at equal angles from and rotating about a common voltage center 100 that varies with the common mode voltage. It should be understood that under the constraint that the phasors 98 must be at equal angles to each other, the length of each phasor 98 (isolated phase voltage) can be uniquely calculated using geometric analysis from knowledge of the lengths and relative angles of the phasors 96, thereby eliminating the effects of the common mode voltage.

[0067] Now refer to Figure 8 , each of the stator electrodes 16 can be modeled by a fixed capacitance 102, a fixed resistance 104, and a current source 106 representing the inverse MMF as a function of rotor speed. The capacitance 102 will typically vary as a function of rotor position, but can be modeled as an empirically determined average value, with position variations attributed to the current source 106. The capacitance 102 and fixed resistance 104 can be determined empirically or can be inferred during operation of the electrostatic drive system 10.

[0068] The model can be used to determine the reverse MMF of the current source 106 by applying an isolated phase voltage (e.g., V A ) to determine the voltage to be measured on the model (e.g., V A ) will appear in the case of a received current 108 (the combined current through capacitor 102 and resistor 104). This received current 108 can then be compared to a commanded current 110 from the current source driver 40. The difference between current 110 and current 108 will be the effective current from current source 106 as a reverse MMF.

[0069] Now refer to Figure 6, the calculated reverse MMF current will vary over time due to the actual change in capacitance 102 as the rotor 18 rotates to generate the reverse MMF signal 115. However, the amplitude 112 of the calculated reverse MMF signal 115 will be proportional to the rotational speed of the rotor 18 and can therefore be used to determine the rotor speed. The change in the MMF signal 115 over a cycle 114 provides an indication of the position of the rotor 18, and the rotational distance per cycle 114 will be equal to the rotational travel of 360° divided by the number of poles of the motor 12 (three in this simplified case). It will be apparent that angular positions less than one cycle 114 can also be determined based on regular voltage changes during the cycle 114.

[0070] In general, the position signal from each phase can be transformed into a d component and a q component, where Figure 6 In , the d component is shown as a solid line and the q component is shown as a dashed line, and is simply represented as the length of the corresponding orthogonal phasor.

[0071] Now refer to Figure 4 , the inverse MMF signal 115 may be typically processed by a conditioning circuit 120, such as providing a bandpass filter 122 to extract a noise-reduced MMF signal 115 that may be provided to a mapper 124, which maps, for example, voltage values ​​within a period 114 to specific angle values ​​as the position signal 44, and a peak follower 126 to extract the amplitude 112 for use as the velocity signal 45. Other well-known signal conditioning techniques may be used, including, for example, constructing an observer that fits the data to a model, etc.

[0072] Reference Figure 2 and Figure 5 An alternative source of position information may be obtained through current injection provided by a current injection circuit 130. Typically, the current injection circuit 130 may create a high frequency injection signal through an injection signal generator 132, for example, the frequency of the high frequency injection signal is at least 10 times the period 114. The injection signal generator 132 may provide an injection output 134, which may be added to the output of the transformation circuit 56 to superimpose an additional current signal onto one electrode 16 of the stator 14 through the current source driver 40.

[0073] This injection signal can be used in two ways. The first method uses the injection signal to measure the capacitive coupling between the stator 16 and the rotor 20, such as changes as the rotor 20 rotates. In this case, the voltage signal 136 induced by the injection output 134 on the stator can be received by the rotor 118 but modified by the mutual capacitance between the rotor 18 and the stator 14 changing as the rotor 18 rotates. The signal 136 can be received by a high pass filter 139 for reducing noise content, and then demodulated using an extraction circuit such as a demodulator 138 (schematically depicted as a rectifier 141 and a low pass filter 143) to extract the envelope of the signal 136 having the modulated frequency. The modulated frequency will have a period representing a frequency corresponding to the rotational speed of the rotor 20, and can therefore be used to determine the rotor speed 45, such as determined using a frequency detector 145, such as by measuring the period and inverting it. The envelope of the phase can be used to determine the rotor speed 45 in a manner similar to that described above with respect to Figure 6 The described approach provides a position signal 44 measurement. These output signals 44 and 45 may again be processed by conditioning circuitry 144, for example to provide filtering or more complex signal conditioning using observer techniques or the like.

[0074] Temporary reference Fig.11 , it will be appreciated that the injection process may be reversed, wherein the injection circuit 130 injects directly into the rotor 20 and then monitors the resulting changes in the signal 90. In this case, no Figure 2 Signal 134 is shown.

[0075] As an alternative to measuring the above-mentioned capacitive coupling changes, the injection signal can be used to detect the saliency changes of the electrostatic motor 12. Figure 7 , in which case the voltage signal 90 may be monitored by a saliency detection circuit 131 to detect load changes in the injection signal from the current source driver 40 caused by changes in the saliency of the stator 16. The voltage signal 90 may be received by a saliency circuit 131 which provides the same functional components as the current injection circuit 130, including a high pass filter for reducing noise content and a demodulator and low pass filter 143 for extracting the envelope 150 of the signal 136 having the modulation frequency. The modulation frequency will have a period 152 which represents a frequency which is typically twice as fast as the period 114, and may therefore be used to determine the rotor speed 45, for example using a frequency detector 145, for example by measuring the period 152 and inverting it. The envelope 150 of the phase may be used to determine the rotor speed 45 in a manner similar to that described above with respect to Figure 6 The described approach provides a position signal 44 measurement. The output signal from either the saliency circuit 131 or the current injection circuit 130 can be selected by the switch 161 for use as the output signals 44 and 45.

[0076] Refer again Figure 2 , each of the MMF detector 92 and the current injection circuit 130 or the saliency circuit 131 can provide both a position signal and a velocity signal; however, the MMF detector 92 has a poor signal-to-noise ratio at low rotor speeds, and therefore, at low rotor speeds, the current injection circuit 130 or the saliency detection circuit 131 can be used to provide both a position measurement and a velocity measurement. On the other hand, when the motor 12 is moving at a high speed, the superior measurement provided by the MMF detector 92 can be used.

[0077] In this aspect, the switch circuit 160 can automatically select between the output from the regulation circuit 120 and the output from the regulator 140 based on the speed signal obtained from the comparison circuit 54. In this aspect, the comparison circuit 54 switches the position detection system between these different detection systems based on the speed of the rotor 18.

[0078] It will be appreciated that the present invention provides the ability to appropriately control the voltage vector applied to the electrostatic motor through closed loop voltage regulation, thereby also providing the ability to control torque, and in this manner provides torque control.

[0079] Certain terms are used herein for reference purposes only and are therefore not intended to be limiting. For example, terms such as "upper," "lower," "above," and "below" refer to directions in the drawings to which reference is made. Terms such as "front," "rear," "back," "bottom," and "side" describe the orientation of portions of a component within a consistent but arbitrary reference frame, which becomes clear by reference to the text and associated drawings describing the component in question. Such terms may include the words specifically mentioned above, their derivatives, and words of similar meaning. Similarly, the terms "first," "second," and other such numerical terms referring to structures do not imply a sequence or order unless the context clearly indicates otherwise. Although the stator and rotor are shown as discs in the disclosed embodiments, it is not required that the stator or rotor be in disc form.

[0080] When introducing elements or features of the present disclosure and exemplary embodiments, the articles "a", "an", "the" and "said" are intended to mean that there are one or more such elements or features. The terms "comprise", "include" and "have" are intended to be inclusive and mean that there may be additional elements or features in addition to the elements or features specifically pointed out. It should also be understood that unless specifically identified as an execution order, the method steps, processes and operations described herein should not be interpreted as necessarily requiring them to be performed in the specific order discussed or shown. It should also be understood that additional or alternative steps may be adopted.

[0081] Specifically, the present invention is not intended to be limited to the embodiments and descriptions contained herein, and the claims should be understood to include modifications of these embodiments within the scope of the appended claims, including combinations of parts of the embodiments and elements of different embodiments. All disclosures described herein, including patent disclosures and non-patent disclosures, are hereby incorporated by reference in their entirety.

Claims

1. An electrostatic motor drive for an electrostatic motor of the type described below, the electrostatic motor having a stator and a rotor, the stator having a plurality of stator electrodes adapted to generate a rotating stator electric field vector about an axis, the rotor having a plurality of rotor electrodes providing a rotor electric field that interacts with the rotating electric field primarily by electrostatic force rather than magnetic force to rotate about the axis, the electrostatic motor drive comprising: a set of current source drivers adapted to be connected to the plurality of stator electrodes; a reverse current monitoring circuit that detects a reverse current value from the electrostatic motor that is proportional to a rotor speed; a reverse current regulation circuit that receives the sensed reverse current value to provide an estimate of at least one of rotor position and rotor speed; and a comparison circuit that receives one of the estimated rotor position and rotor speed and a motor control value and compares the one of the estimated rotor position and rotor speed to the motor control value to generate an error output to the set of current source drivers; in The reverse current monitoring circuit takes voltage measurements at connections between the current source drivers and corresponding stator electrodes.

2. The electrostatic motor driver according to claim 1, wherein: The current source driver provides a set of electrical switches in series with a current source implemented by an inductor for providing current stiffness and regulating the stator electrode voltage.

3. The electrostatic motor driver according to claim 2, wherein: The reverse current monitoring circuit extracts the stator voltage from the measurement signal and eliminates the common mode voltage.

4. The electrostatic motor driver according to claim 2, wherein: The reverse current monitoring circuit models the impedance of the stator circuit to infer the current through each stator electrode and compares the inferred current with the drive current from the current source driver associated with the stator electrode to infer reverse current.

5. The electrostatic motor driver according to claim 1, wherein: The reverse current regulation circuit also measures the phase and amplitude of the reverse current to provide a rotor position signal and a rotor speed signal.

6. The electrostatic motor driver of claim 1, further comprising: a signal generator providing an injection signal to one of the rotor and the stator; an extraction circuit that monitors at least one of the rotor and the stator to extract a resultant signal indicative of at least one of a capacitive coupling between the rotor and the stator and a varying effective capacitance of at least one of the rotor and the stator; as well as injection processing circuitry receiving the resultant signal to provide an estimated rotor position; Wherein, the comparison circuit also receives the estimated rotor position signal from the injection processing circuit to generate the error output.

7. The electrostatic motor driver according to claim 6, wherein: The injection processing circuit also provides an estimated rotor speed.

8. The electrostatic motor drive of claim 7 further comprising a switch for selectively transmitting one of the estimated rotor position signal from the injection processing circuit and the estimated rotor position signal from the reverse current regulation circuit for use by the comparison circuit.

9. The electrostatic motor driver according to claim 8, wherein: The switch is controlled by an estimated rotor speed obtained from at least one of the reverse current regulation circuit and the injection processing circuit.

10. The electrostatic motor driver according to claim 7, wherein: The extraction circuit provides demodulation of the injection signal after modification by the electrostatic motor.

11. The electrostatic motor driver according to claim 7, wherein: The injection processing circuit also receives the detected injection signal after modification by the electrostatic motor to provide an estimated rotor speed signal; and wherein the comparison circuit also uses the speed signal to provide the error output.

12. The electrostatic motor drive of claim 1 further comprising an input circuit that receives a motor control value selected from a command group of torque and speed to control current applied to the stator electrodes.

13. The electrostatic motor driver according to claim 1, wherein: The stator includes three sets of electrically independent poles equiangularly around the axis, with each set of poles electrically joined to a common terminal.

14. The electrostatic motor drive according to claim 1 further includes an electrostatic motor of the type described above, wherein the electrostatic motor has a stator and a rotor, wherein the stator has a plurality of stator electrodes that receive the output from the current source drive and are suitable for generating a rotating stator electric field vector around the axis, and the rotor has a plurality of rotor electrodes that provide a rotor electric field that interacts with the rotating electric field mainly through electrostatic force rather than magnetic force.

15. The electrostatic motor driver according to claim 14, wherein: The electrostatic motor provides at least 60 poles.

16. An electrostatic motor drive for an electrostatic motor of the type having a stator and a rotor, the stator having a plurality of stator electrodes adapted to generate a rotating stator electric field vector about an axis, the rotor having a plurality of rotor electrodes providing a rotor electric field that interacts 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 source drivers adapted to be connected to the plurality of stator electrodes; a signal generator providing an injection signal to one of the rotor and the stator; an extraction circuit that monitors the other of the rotor and the stator to extract a resultant signal indicative of at least one of a capacitive coupling between the rotor and the stator and a varying effective capacitance of at least one of the rotor and the stator; as well as a conditioning circuit that receives the resulting signal to provide an estimated rotor position; A comparison circuit receives the estimated rotor position and the motor control value and compares the estimated rotor position with the motor control value to generate an error output to the set of current source drivers to control the electrostatic motor.

17. A method of providing variable speed control to an electrostatic motor of the type having a stator and a rotor, the stator having a plurality of stator electrodes adapted to generate a rotating stator electric field vector about an axis, the rotor having a plurality of rotor electrodes for providing a rotor electric field that interacts with the rotating electric field primarily by electrostatic forces rather than magnetic forces to rotate about the axis, the method comprising the steps of: providing a set of current source drivers for providing current to the stator electrodes; detecting a reverse current value according to a sense voltage driving the electrostatic motor, the reverse current being proportional to a rotor speed; processing the detected reverse current value to provide an estimated rotor position; receiving an estimated rotor position and a measurement of an output of the current source driver to produce a measured dq vector; receiving a desired dq vector and comparing the desired dq vector to the measured dq vector to generate an error output; as well as The error output is transformed to generate a set of outputs provided to the current source driver to drive the stator electrodes.

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