The torque of a motor operated by an inverter circuit is controlled to allow maximum torque in the motor when the motor is stalled or at low rotation speeds. Control is accomplished by providing a switching frequency to the motor at a first switching frequency, detecting a rotation speed of the motor, and switching the current to the motor to a second switching frequency when the rotation speed of the motor drops to a predetermined slow rotation speed. The second switching frequency is less than the first switching frequency.

Torque controller in an electric motor

A high efficiency power converter is achieved utilizing a resonant DC link between a DC source, such as a converter rectifying power from an AC power system, to a variable frequency voltage source inverter. A resonant circuit composed of an inductor and capacitor is connected to the DC power supply and to a DC bus supplying the inverter and is caused to oscillate stably at a high frequency to provide a uni-directional voltage across the DC bus which reaches zero volts during each cycle of oscillation of the resonant circuit. The switching devices of the inverter are controlled to switch on and off only at times when the DC bus voltage is zero, thereby eliminating switching losses in the inverter. The resonant circuit can be caused to oscillate utilizing pairs of switching devices in the inverter or a separate switching device across the capacitor, which again are caused to switch on and off only at times of zero voltage on the DC bus. For AC to AC conversion, enabling bi-directional power flow, the switching devices of the power source which converts AC power to DC power may have switching devices which are also switched only at the times of zero voltage so that switching losses in these devices is also minimized. A clamp limits the maximum voltage applied to the switching devices, thereby reducing voltage stresses on the devices, and preferably returns energy to the resonant circuit during each cycle of oscillation.

Static power conversion method and apparatus having essentially zero switching losses and clamped voltage levels

An apparatus and method therefor transfers electric charge between a charge storage device (25) and a first power terminal (11) having a plurality of first-nodes. The method interchanges charge between the charge storage device and a first first-node of the plurality of first-nodes through an inductive section (22), and, when a predetermined charge has been interchanged between the charge storage device and the first first-node, replacing the first first-node by a second first-node of the plurality of first-nodes. Charge is interchanged between the charge storage device and the second first-node through the inductive section. Preferably, the ratio of the charge interchanged between the charge storage device and the first first-node and the charge interchanged between the charge storage device and the second first-node is equal to a ratio of the currents drawn from the first first-node and the second first-node. Charge can also be interchanged between the charge storage device and a second power terminal (12) using a similar method.

Charge transfer apparatus and method therefore

The power conversion system (PCS) developed by the author is a new technology that efficiently transforms power between AC and DC. The conversion process permits the input voltage level to be stepped up or down without the use of magnetic core transformers. The transformation is accomplished using solid state switching devices, capacitors, air-core inductors and an intelligent control system. The technology is based on the property of resonance charging, thereby permitting the use of self commutating switches. The current through the switches, being sinusoidal in nature, has a low dI/dt. This permits the use of slower, less expensive thyristors, similar to those used in high voltage phase control applications. Using these components, a highly efficient inverter can be constructed for a variety of large utility applications.

Compact and efficient transformerless power conversion system

The present invention relates to a method for operating a wind turbine with the steps: detection of the values of predetermined operating parameters by means of suitable sensors, detection of at least one predetermined initial condition, comparison of the detected values to stored values of the operating parameters. The invention further relates to a wind turbine for implementing the method. Therefore, the object of the present invention is, to be able to adapt the operation of a wind turbine to changes using a method of the type named above, such that when the detected parameter values deviate from the stored parameter values, as a function of the initial condition, either the stored parameter values are adapted to the detected parameter values or the operation of the wind turbine is influenced as a function of the detected parameter values. In this way, the invention is based on the knowledge that, from a pragmatic view, the formation of ice on a rotor blade is also a (temporary, meteorologically-related) change to the rotor blade shape. From this it follows that the formation of ice on the rotor blades always leads to a change of the aerodynamic profile and thus to a negative effect of the output of the wind turbine. However, deviations from this shape and thus deviations in the magnitude of the generated output also result just from manufacturing-dependent deviations of the rotor blades from the predetermined optimum shape and from gradual soiling of the rotor blades during operation.

Method for operating a wind turbine

A DC to N phase AC converter, where N is an integer greater than 2, includes a DC source having first and second terminals for deriving equal amplitude opposite polarity DC voltages, a series resonant circuit, and N output terminals, one for each phase of the converter. The series resonant circuit is selectively connected in series with the first and second terminals and the N output terminals for an interval equal to one half cycle of the resonant circuit resonant frequency, so that current flows between a selected one of the first and second terminals and the resonant circuit and a selected one of the N output terminals during the interval. The resonant circuit current is zero at the beginning and end of the interval. A capacitor shunting each of the output terminals has a value relative to the capacitance of the series resonant circuit such that the voltage across each output terminal remains approximately constant between adjacent exchanges of energy between the resonant circuit and the output terminal. The selective connection is in response to a comparison of the actual voltage across each of the N output terminals and a reference voltage for each of the N output terminals. The comparison controls when the flow of current between the selected first and second terminals and the selected output terminal via the resonant circuit begins. The frequency of the AC voltage developed across the N output terminals is much less than the resonant frequency of the circuit.

Series resonance charge transfer regulation method and apparatus

A variable output induction motor drive system for use with a polyphase variable output alternating current motor including a rotor and stator to drive an operating load such as an automotive vehicle, the variable output induction motor drive system comprises a sine wave current generator operatively coupled to a direct current power source to receive direct current therefrom and to generate a variable sine wave current and operatively coupled to the polyphase variable output alternating current motor to selectively feed the variable sine wave current thereto and a sine wave current control coupled between the sine wave power current generator and the polyphase variable output alternating current motor to monitor the operating parameters of the polyphase variable output alternating current motor and to control the amplitude and frequency of the variable sine wave current fed from the sine wave current generator to the polyphase variable output alternating current motor to control the output torque and speed thereof.

Variable output induction motor drive system

An electro-mechanical energy conversion system coupled between an energy source and an energy load comprising an energy converter device including a permanent magnet induction machine coupled between the energy source and the energy load to convert the energy from the energy source and to transfer the converted energy to the energy load and an energy transfer multiplexer to control the flow of power or energy through the permanent magnetic induction machine.

Electro-mechanical energy conversion system having a permanent magnet machine with stator, resonant transfer link and energy converter controls

An energy transfer multiplexer to control the flow of power or energy between an energy source and an energy load comprising a bi-directional inverter including a first bank or plurality of switches or first plurality of energy transfer control points and a second bank or plurality of switches or second plurality of energy transfer control points operatively coupled by a series resonant transfer link to selectively control the direction of power or energy flow between the first and second bank or plurality of switches or the first and second plurality of energy transfer control points.

Richard H. Baker

Papers

Series resonance charge transfer regulation method and apparatus

Variable output induction motor drive system

Electro-mechanical energy conversion system having a permanent magnet machine with stator, resonant transfer link and energy converter controls

Energy transfer multiplexer

Permanent magnet induction machine