US-20260128685-A1 - High-Voltage DC Transmission System

US20260128685A1US 20260128685 A1US20260128685 A1US 20260128685A1US-20260128685-A1

Abstract

An electrostatic generator adapted for high-voltage DC transmission provides a set of individual electrostatic generators connected in tandem to a mechanical input and employing floating voltage sources to allow series connection of the individual electrostatic generators without diode ladders or the like. Brushless operation can be provided through generator building blocks having electrically separated stators communicating with electrically joined rotors.

Inventors

Daniel Ludois
David Skrovanek
Dominic Groß

Assignees

WISCONSIN ALUMNI RESEARCH FOUNDATION

Dates

Publication Date: 20260507
Application Date: 20241106

Claims (20)

1 . A high-voltage electrostatic generator system comprising: an input shaft adapted to move under an applied mechanical force; and a set of electrostatic generators communicating with the input shaft and each providing: (a) a set of rotor plates communicating with the input shaft to move with motion of the input shaft; (b) a set of corresponding stator plates capacitively coupled to the rotor plates to provide at least one varying capacitor between corresponding stator plates and rotor plates with movement of the rotor plates with respect to the stator plates; (c) a floating voltage source connected to electrically charge the at least one varying capacitor with each floating voltage source providing a voltage prior to movement of the rotor plates with respect to the stator plates; and (d) a rectifier assembly operating to steer current along a single charging direction, where that current results from the movement of the rotor plates with respect to the stator plates; wherein the rectifier assemblies of the set of electrostatic generators are connected in series.
2 . The high-voltage electrostatic generator system of claim 1 wherein the electrical power of the floating voltage sources is inductively or capacitively isolated from the varying capacitors.
3 . The high-voltage electrostatic generator system of claim 1 wherein each rectifier assembly includes a shunting capacitor.
4 . The high-voltage electrostatic generator system of claim 1 wherein each rectifier assembly conducts the same average current.
5 . The high-voltage electrostatic generator system of claim 1 wherein each rotor plate and stator plate provides multiple variable capacitors having different phases of capacitance with respect to motion of the input shaft and wherein the rectifier assembly provides a separate rectifier circuit for each of the multiple variable capacitors operating to steer current from a change in the multiple variable capacitors along a common charging direction.
6 . The high-voltage electrostatic generator system of claim 1 wherein the rectifier assembly steers current in either of two directions from the varying capacitor to the single charging direction.
7 . The high-voltage electrostatic generator system of claim 1 wherein the floating voltage sources have a voltage in excess of 1000 V.
8 . The high-voltage electrostatic generator system of claim 1 further including an output voltage monitor monitoring a voltage across the series connected electrostatic generators and controlling voltages of the floating voltage sources according to that monitoring.
9 . The high-voltage electrostatic generator system of claim 8 wherein the output voltage monitor increases the excitation voltage as the monitored voltage rises within a protection region and decreases the excitation voltage as the monitored voltage increases in an operating region.
10 . The high-voltage electrostatic generator system of claim 1 wherein a subset of first and second sets of rotor plates of a given electrostatic generator electrically communicate through a conduction path moving with the input shaft and wherein the floating voltage sources for each electrostatic generator are connected across stator plates associated with different of the first and second sets of rotor plates.
11 . The high-voltage electrostatic generator system of claim 1 wherein the rotor plates of different pairs of subsets of first and second sets of rotor plates are at different voltages.
12 . The high-voltage electrostatic generator system of claim 1 where in the rectifier assembly includes a DC to DC converter.
13 . The high-voltage electrostatic generator system of claim 12 wherein the DCDC to DC converter is selected from the group consisting of a buck converter, a boost converter, and a boost-buck converter.
14 . A method of transmitting electrical power employing a high-voltage electrostatic generator system having: an input shaft adapted to move under an applied mechanical force; and a set of electrostatic generators communicating with the input shaft and each providing: (a) a set of rotor plates communicating with the input shaft to move with motion of the input shaft; (b) a set of corresponding stator plates capacitively coupled to the rotor plates to provide at least one varying capacitor between corresponding stator plates and rotor plates with movement of the rotor plates with respect to the stator plates; (c) a floating voltage source connected to electrically charge the at least one varying capacitor with each floating voltage source providing a voltage prior to movement of the rotor plates with respect to the stator plates; and (d) a rectifier assembly operating to steer current along a single charging direction, where that current results from the movement of the rotor plates with respect to the stator plates; wherein the rectifier assemblies of the set of electrostatic generators are connected in series; the method comprising: (a) applying a source of mechanical power to the input shaft; (b) extracting electrical current from a series connection of the rectifier assemblies of multiple electrostatic generators; (c) applying the electrical current to high-voltage transmission lines for remote transmission of at least 20 km; and (d) reducing the voltage of the electrical current and converting the electrical current to alternating current for use by consumers.
15 . The method of claim 14 wherein outputs of the floating voltage sources provide a source of voltage when disconnected from the varying capacitors of high-voltage electrostatic generator system.
16 . The method of claim 14 wherein outputs of the floating voltage sources excluding connection to the rotor plates and stator plates are free from ohmic interconnections with other floating voltage sources.
17 . The method of claim 14 wherein the floating voltage sources have a voltage in excess of 1000 V.
18 . The method of claim 14 wherein each rotor plate and stator plate provides multiple variable capacitor having different phases of capacitance with respect to motion of the input shaft and wherein the rectifier assembly provides a separate rectifier circuit for each of the multiple variable capacitors operating to steer current from a change in the multiple variable capacitors along a common charging direction.
19 . The method of claim 14 further including monitoring a voltage across the series connected electrostatic generators and controlling voltages of the floating voltage sources according to that monitoring.
20 . The method of claim 14 wherein the source of mechanical power is selected from the group consisting of a wind turbine, a water turbine, and a steam turbine.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION The present invention relates generally to high-voltage electrical transmission using direct current and in particular to a high-voltage electrical transmission system using electrostatic generators. Electrical power must frequently be transmitted a substantial distance from a generation source to its point of use using high-voltage transmission lines. Long-distance transportation can be particularly important for many clean energy sources such as hydroelectric, solar, and wind where the generating sources cannot be readily located close to the ultimate consumer. Commonly, methods of high-voltage electrical transmission make use of alternating current electricity at kilovoltage levels. Alternating current permits the use of transformers to step the voltage up for efficient long-distance transmission (reducing resistive losses) and then to step the voltage down again for use by the consumer. There are a number of drawbacks to the transmission of high voltage alternating current including: induced or eddy current losses in surrounding material (for example, seawater surrounding undersea lines), reactive power losses, that is, resistive losses in reactive phases of current flow which do not contribute to power transmission, and skin effects which cause current to be concentrated unevenly through the conductors reducing conductor efficiency. The use of alternating current also introduces the complexity of synchronizing multiple generators to a common phase when their outputs are confined. The above drawbacks can be largely eliminated through the use of high-voltage DC transmission (HVDC). A conventional approach to HVDC uses common magnetic synchronous generators to produce alternating current power stepped up to high voltages in excess of 100 kV using electrical transformers. This high-voltage alternating current is then converted to DC power for transmission using, for example, a voltage source converter or other rectifying system. At the receiving end of the transmission line, the high-voltage direct current is converted to AC power using a solid-state commutator. Electrostatic generators present an attractive alternative to magnetic synchronous generators for high-voltage DC transmission because they can inherently operate at higher voltages eliminating the need for a step-up transformer and commutative rectifier such as centralized voltage source converters operating at the transmission voltage level. Such electrostatic generators may employ a high-voltage excitation source operating to charge a variable capacitor produced by movable plates on a stator and rotor and operating as a charge pump to output current proportional to the excitation voltage. A current challenge in the use of electrostatic generators is a practical limit to the excitation voltage, dictated in part by breakdown voltages across the capacitive gaps between the generator plates, resulting in an output that is less than the desired transmission voltages for high transmission. One method of addressing this limitation is to combine the output of multiple electrostatic generators together using a diode ladder such as is described, for example, in S. F. Philip, “The vacuum-insulated, varying capacitive machine,” IEEE Transactions on Electrical Insulation, volume 12, number 2, pages 130-136, 1977, hereby incorporated by reference. SUMMARY OF THE INVENTION The present invention provides an improved system for combining the outputs of electrostatic generators to produce a desired, greater high voltage through the use of floating excitation sources. In some embodiments, brushless combinations of these different sources can be obtained by electrically interlinking two different sets of rotor plates to present excitation terminals exclusively at locations on the two stators associated with the two different sets of rotor plates. Elimination of a diode ladder required to connect a single excitation source to multiple generators reduces delays in the control of the output voltage caused by the need to charge a diode ladder over successive cycles, and thus produces a system practical for integration into high-voltage DC transmission networks that must promptly respond to the variable demand. In one embodiment, the invention provides a high-voltage electrostatic generator system having an input shaft adapted to move under an applied mechanical force and a set of electrostatic generators communicating with the input shaft. Each electrostatic generator includes a set of rotor plates communicating with the input shaft to move with motion of the input shaft and a set of corresponding and stationary stator plates capacitively coupled to the rotor plates to provide at least one varying capacitor between corresponding stator plates and rotor plates with movement of the rotor plates. In each electrostatic generator, a floating vol