70 results about "Doubly fed induction machine" patented technology

An electro-mechanical energy conversion system coupled between an energy source and an energy load comprising an energy converter device including a doubly fed 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 doubly fed induction machine.

Ceramic adhesive is applied inside the slots of an electric machine squirrel cage rotor prior to casting or insertion of rotor conductors. This heat-resistant insulation provides superior electrical insulation that is also mechanically rugged, thus enabling casting of squirrel cage rotors by die or cost-effective consumable pattern casting. The consumable pattern cast copper rotors are electrically well insulated, thus minimizing rotor losses. The ceramic insulation in cast rotors enables longer conductors to be cast by thermally insulating the molten metal from the cooler laminations. The ceramic insulation in fabricated rotors withstands the high temperatures of end ring attachment. This method is applicable to both conventional induction machine rotors and brushless doubly-fed induction machine rotors and provides the degree of electrical isolation of the bars from the laminations needed to avoid excessive parasitic torques in doubly-fed machines, while ensuring adequate thermal conductivity to dissipate conductive bar heat to the laminations.

Several embodiments of an uninterruptible power supply (UPS) system, which system provides highly reliable output power to a load using a slip-ring induction machine and a flywheel combination, are disclosed as well as methods relating thereto. In a preferred embodiment, the UPS system comprises a back-up power source, e.g., an engine and generator, and a slip-ring, or wound-rotor, induction motor and flywheel combination, which are in parallel to a primary power source, e.g., a utility grid. During normal operation of the UPS, the primary power source supplies alternating current and voltage to the load and the UPS compensates for voltage drop across the isolating inductor. Moreover, the primary power source keeps the slip-ring induction machine and flywheel in an excited state, i.e., the rotor of the slip-ring induction machine, the shaft of which is shared by the flywheel, is excited above normal synchronous speed. When the primary power source fails, the flywheel, which is rotating at super-synchronous speed and storing kinetic energy, drives the rotor of the slip-ring induction machine and generates, i.e., induces current in the stator. Accordingly, the flywheel and slip-ring induction machine combination provides instantaneous, short term power to the load until the back-up power source has powered up and been brought on line.

The invention relates to a protection system of a doubly-fed induction machine, the system comprises a doubly-fed induction machine with a stator and a rotor, the stator of said doubly-fed induction machine is connected to a grid and the rotor of said doubly-fed induction machine is connected to the grid via a converter, said converter comprises a machine side converter, a DC-link and a line side converter. The system comprises additionally at least one crowbar, said crowbar is connected to the rotor, at least one DC-chopper provided in the DC-link, a converter controller and a separate protection device. The object of the present invention to provide a protection system and a protection method of a doubly-fed induction machine which can be easily used with high sampling rates and which provides a good protection for the doubly fed induction machine is resolved in that the DC-chopper and the crowbar are controlled with the separate protection device.

A method and arrangement for controlling a doubly-fed induction machine by a frequency converter including a rotor side converter (INU) connected to a rotor circuit of a doubly-fed induction machine (DFIG) and having a control system with rotor flux as a feedback variable, a grid side converter (ISU) connected to an AC power network, and a direct voltage intermediate circuit (DC) connected between the rotor side converter (INU) and the grid side converter (ISU). The method includes forming a rotor flux reference (ψ_r,ref), forming a damping signal (ψ_ref,D), summing the damping signal and the rotor flux reference for obtaining a modified rotor flux reference (ψ_ref), and feeding the modified rotor flux reference to a controller of the rotor side converter (INU) for damping sub-synchronous resonances.

A protection system for an electrical variable speed doubly fed induction machine having a stator and a rotor, comprising:

• • instrument transformers capable of measuring low frequency signals from the rotor and stator, in particular low frequency signals in the range of 0.1 Hz to 6 Hz;
  • a protection relay which is configured to receive measurement values from the instrument transformers and to sample said measurements values at a constant sampling rate.

The invention discloses a motor speed regulation control method and system. According to the method, based on power side stator flux orientation, a dual-closed-loop cascading structure of a rotary speed, a reactive power outer ring and a control side stator current inner loop is established by simplifying a mathematical model; influence from a current cross coupling item is counteracted through feedforward control; and decoupling control on the speed and reactive power of a brushless doubly-fed induction motor is realized; meanwhile, by adopting a phase-locked loop design thought, a power side stator flux observer is configured to obtain information of amplitude value, frequency, phase angle and the like of the stator flux so as to complete coordinate transformation of related electric quantity; by adoption of the method, dependency on parameter is low; the decoupling control on electromagnetic torque and reactive power can be realized; the static performance of a speed regulation system of the brushless doubly-fed induction motor can be ensured while high dynamic response performance also can be ensured under sudden change conditions of load and speed; and in addition, the technical scheme is simple to realize, low in calculated quantity and low in parameter dependency.

In order to carry out fault detection on the doubly-fed induction generator, the invention provides a doubly-fed induction generator fault detection method based on a sliding mode observer. Because asliding mode observer is simple in structure, is not liable to be affected by parameters, is high in anti-interference capability, and the like, the sliding mode observer is used for the fault detection of the doubly-fed induction generator. Firstly, a sliding mode observer is built according to a mathematical model of the doubly-fed induction generator, the rotor current and the rotating speed ofthe doubly-fed induction generator are observed, and self-detection of faults is achieved by comparing the residual error between the actual rotor current value and the observed value, then three faults of a power grid end voltage drop fault, a doubly-fed induction generator stator turn-to-turn fault and a rotor current sensor fault are given so as to prove that the sliding-mode observer can wellperform fault detection on faults occurring at different positions, and the sliding-mode observer has the characteristics of the high response speed, the good stability and the like.

The present invention discloses a fuzzy control method for double-fed electric field subsynchronous oscillation inhibition. The method concretely comprises the following steps: 1, establishing an aerodynamic model, a shafting model, a double-fed induction motor model, a rotor side and net-side convertor control module, a direct current capacitor dynamic process model and a serial compensation line model; 2, allowing the magnetic torque Te control outer shroud of a double-fed fan rotor side convertor to employ fuzzy control taking replacing of a traditional PI control method, taking an electromagnetic torque error E and an error variation EC as an input variation, and taking the variation DU of the control amount as an output amount to design a fuzzy controller; 3, adding a self-adjusting module, and constructing the fuzzy controller capable of parameter online self adjusting; and 4, employing the fuzzy controller to control the double-fed electric field subsynchronous oscillation, and completing the inhibition of the double-fed electric field subsynchronous oscillation. The method is reasonable and reliable, and the applied fuzzy controller has better inhibition effect on the subsynchronous oscillation and has better engineering application prospect.

The invention provides a direct characteristic control based novel double-fed induction motor control technology, comprising the following steps: 1, giving a voltage equation with regards to the alpha axis and beta axis of a stator of a double-fed induction motor under a stationary frame; 2, based on the voltage equation given in the step 1 and with the currents of the alpha axis and beta axis of the stator and flux linkages of the alpha axis and beta axis of a rotor as state variables, putting forward a corresponding state equation observer; 3, designing a sliding mode variable structure observer based on the step 2 so as to observe the currents of the alpha axis and beta axis of the stator and the flux linkages of the alpha axis and beta axis of the rotor at the current state; 4, carrying out discretization based on the state equation put forward in the step 2, thus obtaining a prediction control equation, namely predicting the currents of the alpha axis and beta axis of the stator and the flux linkages of the alpha axis and beta axis of the rotor at next time; and 5, using the predicted currents of the alpha axis and beta axis of the stator and currents of the d axis and q axis of the stator, calculated according to a given torque and a given rotor flux linkage together to solve a characteristic equation to obtain the voltages of the alpha axis and beta axis of the stator and sending the voltages to SVPWM. The direct characteristic control based novel double-fed induction motor control technology can be applied to the field of wind power generation and the like.

The invention provides a doubly-fed wind turbine generator hybrid fault ride-through method. According to the method, fault ride-through capability of a doubly-fed wind turbine generator can be improved through connecting in series with a protection circuit of a doubly-fed induction motor stator winding, connecting in parallel with a DC unloading circuit of a converter DC bus and coordination control of a doubly-fed induction motor rotor in a current fault control mode. Through the method, blocking a rotor side converter is not necessary, the doubly-fed induction motor is not out of control, too-fast increase of a rotating speed in a fault period of a system can be inhibited, the electric network voltage is supported, after the proper rotor current fault control strategy is employed, start frequency of a hardware protection circuit is reduced, and thereby low voltage ride-through transient performance of the doubly-fed wind turbine generator is improved.

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.

The invention relates to a method to control power output of a doubly-fed induction machine to a grid including the steps of measuring grid voltage and grid current in a three phase coordinate system, transforming grid voltage and grid current into a stator frame coordinate system, decomposing the grid voltage and grid current in the stator frame coordinate system in a positive sequence system and in a negative sequence system, calculating active and reactive power in the positive and negative sequence system, and controlling active and reactive power in the positive and negative sequence system.; The object to provide a method to control power output of a doubly-fed induction machine which provides good dynamics and is able to allow fault-ride-through operations when unbalanced grid voltages occurs is solved in that active and reactive power in the positive and negative sequence system are used as independent state variables in a state controller, whereas the state controller generates manipulated values in the positive and negative sequence system separately which are subjected as manipulated state vectors to a state feedback in a stator frame coordinate system without further control loops before the manipulated vector resulting from state feedback is used to set the rotor voltage.

The invention discloses a low voltage crossing scheme of a double-fed fan based on superconducting magnetic energy storage and improved control, comprising a superconducting magnetic energy storage device and a control strategy matching with the superconducting magnetic energy storage device. A super-conduction magnetic energy storage device comprises a super-conduction coil, a DC-DC Converter, aCapacitor and a Voltage Source Inverter. The superconducting coil is connected in parallel to the rotor side of the doubly-fed induction motor through a DC-DC converter, a superconducting magnetic energy storage side inverter and a filter inductor. and the control strategies include transient voltage control and current backtracking control. In that event of power grid voltage failure, After failure, At that same time, the rotor-side invert and the inverter of the superconduction magnetic energy storage device are switched to the current reverse tracking control and the transient voltage control, Each inverter shares 50% of the rotor overcurrent to ensure that the reactive current is injected into the rotor side by transient voltage control while each inverter does not exceed the current,so that the stator side emits reactive current to support the grid voltage, thereby improving the low voltage ride-through capability of the fan.

The invention discloses a reactive power optimization method for wind power system on the basis of improved particle swarm optimization, and belongs to the technical field of power information. A double-fed induction machine mathematical model is established, a reactive input range of the wind power system is determined, the node admittance matrixes of a power grid are listed, the power initial value of each node is set, the reactive optimization model of the power grid is established, original data in load flow calculation is input, a plurality of variables which control reactive power optimization in the power grid are determined, a particle population is initialized, the load flow calculation is carried out, a related fitness function value is calculated, the particle swarm optimizationof an effective group utilization strategy is adopted to update a particle position, the particle position in a current group is used as the initial position of the particle for iteration, and optimal node voltage and active power loss are output. By use of the method, calculation time can be effectively reduced, meanwhile, the global search ability of particles can be enhanced, local optimum canprevent from being caught, so that the voltage level of the system is improved, and the power loss is reduced.

The invention discloses a double-fed induction fan system based on coordinated control and a low-voltage crossing method thereof. The double-fed induction fan system is characterized by including a double-fed induction fan stator winding, a double-fed induction fan rotor, a rotor-side converter and an inductance type superconducting fault current limiter connected in series between the rotor and the rotor-side converter, wherein the fault current limiter comprises a superconducting coil and a power electronic switch which are connected in parallel. Through adoption of the inductance type superconducting fault current limiter and improvement of the control technology of the rotor-side convert of a double-fed induction fan, the superconducting fault current limiter is utilized to directly limit rotor overcurrent and reduce torque oscillation, and reactive power output of the double-fed induction motor is utilized during a fault period, thereby improving the low-voltage crossover capacityof the double-fed induction fan. At the same time, key parameter setting principles of the fault current limiter are determined by accurately controlling the current of the rotor-side converter during the fault period, so the impedance value of the superconducting fault current limiter is effectively reduced and the cost is saved.

The invention provides a doubly-fed induction generator low-voltage ride-through control system which comprises a three-phase power gird, a doubly-fed motor, an inverter, a PLL (phase locked loop), a stator voltage and current Clarke conversion unit, a stator active power and reactive power calculation unit, a rotor current Clarke/Park conversion unit, a power outer ring, a rotor current inner ring, a SVPWM modulation and computing unit, and a Crowbar circuit. The low-voltage ride-through control system also comprises a stator damping resistor switching device, and the stator winding of the doubly-fed motor is connected to the three-phase power gird through the stator damping resistor switching device. The stator damping resistor switching device is realized by the parallel connection of a bidirectional thyristor and a damping resistor. The invention provides the doubly-fed induction generator low-voltage ride-through control system with the acceleration of stator magnetic linkage demagnetization process and the improvement of the control characteristic of a unit in a low voltage-ride through process.

The invention discloses a method for controlling dynamic bifurcation of a wind driven generator based on nonlinear feedback control. The method comprises the following steps of: 1, establishing a simplified dynamic model of a doubly-fed inductor motor; 2, designing a Hopf bifurcation controller by adopting a nonlinear feedback control rule; 3, inhibiting sub-critical bifurcation; 4, calculating a frequency value; 5, calculating a period value of a voltage signal; 6, measuring an angular speed; and 7, controlling the dynamic bifurcation. The method has the advantages that: 1, the transfer of a Hopf bifurcation point of a system can be realized, the stability region of the system is enlarged, the sub-critical bifurcation is inhibited, simultaneously the stability and the amplitude value of a limit cycle can be controlled, and the voltage oscillation of the system can be inhibited; 2, a very good control effect for the wind driven generator is achieved by designing the Hopf bifurcation controller by adopting the nonlinear feedback control rule; and 3, a circuit design method is simple and easy to implement.