An off-grid power generating apparatus is provided. The apparatus includes an engine, an alternator and an excitation control device. The alternator includes a rotor, a switch and a stator. The switch is movable between a first position and a second position. An output portion of the stator has first and second segments each of which has at least one coil. The first and second segments are operatively and separately connected with the switch. The first and second segments are connected in series at the first position and in parallel at the second position to provide a high voltage and a low voltage respectively. The excitation control device controls the output voltage to make it have a predetermined frequency, and to regulate the engine speed in response to the load power of the engine.

The present invention provides an acceleration method for V/f controlled induction motor in flux-weakening region, which comprises: acquiring no-load magnetizing current I.sub.m of the induction motor at current stator frequency; selecting a smaller one of 0.5.Math.I.sub.m(1/+1) and (I.sub.m.sup.2+)/(I.sub.m+I.sub.m) as magnetizing current set point, in which is an estimated total leakage inductance coefficient; getting an error signal by subtracting the magnetizing current of the induction motor from the magnetizing current set point; determining the stator frequency for the next control period according to the error signal which is provided as a controlling variable of negative feedback. The acceleration method of the present invention can provide the maximum output torque in flux-weakening region and has a larger tolerance for the error of the estimated leakage inductance.

The present subject matter is directed to an electrical power circuit connected to a power grid and method of operating same. The electrical power circuit has a power converter electrically coupled to a generator, such as a doubly-fed induction generator, having a rotor and a stator. Thus, the method includes operating rotor connections of the rotor of the generator in a wye configuration during a first rotor speed operating range. Further, the method includes monitoring a rotor speed of the rotor of the generator. Thus, the method also includes transitioning the rotor connections of the rotor from the wye configuration to a delta configuration if the rotor speed changes to a second rotor speed operating range.

The invention relates to a system for supporting the stability of an electrical grid by storing/releasing electrical energy from/to said electrical grid, comprising: an asynchronous electric machine including a rotor provided with an accessible rotor circuit and a stator provided with a stator circuit; a flywheel coupled to the rotor; a static converter, and electronic control means. The stator circuit is connected to the electrical grid to be fed by the latter. The static converter is connected between the electrical grid and the rotor circuit and is controllable to supply said rotor circuit with an electrical power supply with adjustable frequency and voltage. The asynchronous electric machine is configured to: absorb electrical energy from the electrical grid by converting the absorbed electrical energy into kinetic energy and storing said kinetic energy by means of the flywheel; and deliver electrical energy to the electrical grid by converting the stored kinetic energy by means of the flywheel into electrical energy and providing the latter to the electrical grid. The electronic control means are configured to: receive measurement data indicative of a measured electrical grid frequency; determine, based on the received measurement data, ROCOF values indicative of a derivative of the measured frequency of the electrical grid; and control the operation of the static converter based on the determined ROCOF values. Furthermore, in case of a change in the frequency of the electrical grid, the asynchronous electric machine is configured to immediately provide an uncontrolled natural inertial response to said change in frequency by absorbing active power from the electrical grid in case of an increase in frequency or by supplying active power to the electrical grid in case of a reduction in frequency; and the electronic control means are configured to determine a given ROCOF value relative to said change in frequency and, once said given ROCOF value has been determined, begin to control the operation of the static converter such that the asynchronous electric machine begins to supply a controlled synthetic inertial response wherein the active power absorbed/supplied is modulated according to the given ROCOF value determined and the uncontrolled natural inertial response already provided.

A system and method of operating a pumped storage power plant using a double fed induction machine with a frequency converter in a rotor circuit is disclosed. A current target value for the rotor current frequency is determined based on a target power to be transmitted between an electrical grid and the double fed induction machine depending on measured actual operating variables. A current inadmissible synchronous deadband is determined depending on variables characterizing a current state of the pumped storage power plant. The synchronous deadband is determined by a permissible minimum required rotor current frequency or speed difference of the rotor speed from the synchronous speed for the stationary operation. The converter is controlled to generate voltages and currents with the current target value of the rotor current frequency if the current target value of the rotor current frequency or speed does not fall in the current inadmissible synchronous deadband.

Exhaust gases from an engine, input to turbo-compounder, drive a bladed turbine rotor therein, which drives a multi-phase AC generator, the output of which is used to electrically drive a multi-phase induction motor, the rotor of which is mechanically coupled to the engine, so as to provide for recovering power to the engine. The multi-phase AC generator may be coupled to the engine either by closure of a contactor, engagement of an electrically-controlled clutch, or by control of either a solid-state switching or control system or an AC excitation signal, when the frequency (f.sub.GENERATOR) of the multi-phase AC generator meets or exceeds that (f.sub.MOTOR) of the multi-phase induction motor.

Exhaust gases from an engine, input to turbo-compounder, drive a bladed turbine rotor therein, which drives a multi-phase AC generator, the output of which is used to electrically drive a multi-phase induction motor, the rotor of which is mechanically coupled to the engine, so as to provide for recovering power to the engine. The multi-phase AC generator may be coupled to the engine either by closure of a contactor, engagement of an electrically-controlled clutch, or by control of either a solid-state switching or control system or an AC excitation signal, when the frequency (f.sub.GENERATOR) of the multi-phase AC generator meets or exceeds that (f.sub.MOTOR) of the multi-phase induction motor.

A method of controlling the operation of a doubly fed induction machine is provided. The DFIM includes a stator electrically coupled to a power grid and a rotor rotating with a rotational speed. The DFIM has a synchronous rotational speed of the rotor and a rated rotational speed of the rotor. Rotation of the rotor at the synchronous rotational speed generates one or more slot harmonic distortions having a harmonic order. The method comprises operating the DFIM at the rated rotational speed of the rotor, wherein the rated rotational speed of the rotor is set to a value selected such that a shift of the harmonic order of one or more of the slot harmonic distortions at the rated rotational speed of the rotor is an integer number or is within a predefined limit of an integer number.

A method of controlling an induction generator is provided connected to a utility grid, the method including: receiving an actual grid frequency; and controlling rotor windings of the generator by a rotor control signal having a rotor winding reference frequency being set in dependence of the actual grid frequency.

An object of the present invention is to provide an electric power generation system that can stably control, with one electric power converter, output electric power of a main winding and an auxiliary winding of a dual-winding induction electric power generator. For this purpose, in an electric power generation system including an electric power generator having a stator including a main winding and an auxiliary winding, a rectifier connected to the main winding, an electric power converter that is connected to the auxiliary winding and controls voltages of the main winding and the auxiliary winding, and a controller that outputs a control signal according to a voltage command value of the auxiliary winding to the electric power converter, the controller calculates a voltage change amount of the auxiliary winding generated by interference of a magnetic flux of the main winding with the auxiliary winding, on the basis of a current and the voltage of the main winding, and adds the voltage change amount to the voltage command value of the auxiliary winding.