226 results about "Doubly fed electric machine" patented technology

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.

The excitation overcurrent detection unit for the doubly-fed electric machine is provided with a function to determine an excitation current magnitude relationship among three phases. The firing pulse is held to on-state or off-state to cause the largest-current phase and the second-largest-current phase to charge the DC capacitor by the operation of diodes. The conduction ratio of the third-largest-current phase or minimum current phase is controlled according to the detected current value to protect against a possible short-circuit across the DC capacitor. When the voltage of the DC capacitor exceeds a preset value, the voltage is suppressed by operating active or passive power devices.

The invention relates to a fault identification method for inter-turn short circuit of stator windings in doubly-fed motor at sea. The method comprises the following steps of: obtaining three-phase voltage and three-phase current of the stator of the doubly-fed motor whose fault has yet to be recognized; calculating the three-phase voltage and three-phase current of the stator through a modified Park's vector method to obtain the 2 times fundamental frequency component amplitude I2p caused by the inter-turn short circuit fault of the stator windings; and determining whether the 2 times fundamental frequency component amplitude I2p caused by the inter-turn short circuit fault of the stator windings reaches the fault pre-warning value or not. If so, the doubly-fed motor whose fault has yet to be recognized at sea is confirmed to have an inter-turn short circuit fault. Compared with the prior art, the identification method of the invention has robustness to the motor stator voltage imbalance and load variation, and the discrimination is both accurate and strong.

The invention relates to a voltage unbalanced mathematical model-based control strategy for a brushless double-feed motor grid-side converter. Unbalanced voltage vectors are decomposed into balanced positive sequence components, negative sequence components and zero sequence components by utilizing a symmetrical component method; a mathematical model of the grid-side converter is created when the voltage is unbalanced; and the problems of coupling terms and external disturbance existing in the grid-side converter are observed and compensated by utilizing an expansion state observer and a self anti-interference control theory. A nonlinear control method designed in the invention can inhibit the harmonic wave problem of the grid-side converter under the voltage unbalanced condition very well, and has the advantages of strong anti-interference capability, favorable robustness, and the like.

The invention provides a method and device for controlling uninterruptible operation of a wind generator system in case of faulted power grid voltage. An existing doubly-fed motor rotor-side frequency converter and a CROWBAR circuit are utilized to realize the uninterruptible operation of a DFIG (doubly-fed induction generator) wind generator system when the power grid generates the serious voltage faults. The method at least comprises the following steps: 1) detecting the voltage of the power grid; 2) triggering CROWBAR protection; 3) waiting a voltage of the power grid to recover; 4) cutting off the CROWBAR protection; 5) starting a grid-side current transformer; and 6) starting a motor-side current transformer. In the invention, motor time sequences of corresponding states of the current transformer are given when the power grid voltage is seriously asymmetrical and when the motor is in a non-voltage state; the CROWBAR protection circuit of the current transformer is used to finishthe protection for the wind generator system and the current transformer; and the method and device provided by the invention are suitable for various faults of the power grid such as a symmetric voltage fault of the power grid, an asymmetric fault of a small voltage value of the power grid, a seriously asymmetric voltage fault of the power grid and a non-voltage fault of the power grid, and meets grid-connected requirements of the wind generator system formulated by a power grid corporation. Mechanical installation of equipment is simple and the installation is convenient and quick.

The invention discloses a control system for low voltage ride through of a doubly-fed wind generator. A doubly-fed wind generator-side converter is formed by assembling a core circuit, a sampling circuit and a main circuit, wherein the core circuit takes a digital signal processor (DSP) as a controller; the sampling circuit is formed by analog acquisition conversion; and the main circuit is formed by an intelligent power module (IPM) intelligent switch modular circuit. According to the control system for the low voltage ride through of the doubly-fed wind generator, disclosed by the invention, by aiming at the problem that the doubly-fed wind generator-side converter is excessive in current due to the depth of network voltage drop and the running status of the doubly-fed wind generator when the voltage drops, rotor-side overcurrent is restrained by adopting the virtual impedance technology so as to prevent a bar protection circuit from being triggered, so that the doubly-fed wind generator still is in a controllable state under the condition of network faults, and therefore, the doubly-fed wind generator meets the fan-class grid-connection national standard.

The invention relates to a variable-speed constant frequency electricity generation control device and electricity generation method based on a brushless doubly-fed motor. The device comprises a double-PWM frequency conversion system and an electricity generation control system for controlling the double-PWM frequency conversion system. The electricity generation control system comprises a setting unit, a power winding voltage detection unit, a control winding current detection unit, a voltage outer loop controller, a current inner loop controller and a phase-locked loop controller, and the voltage outer loop controller, the current inner loop controller and the phase-locked loop controller drive a PWM rectifier and a PWM inverter to achieve system variable-speed constant frequency electricity generation in a space vector control mode. By the adoption of the vector control mode, the double-closed-loop feedback control method and the phased-locked loop control method, even though loads or prime power changes and causes fluctuation of rotation speed, current and frequencies of windings can be controlled by accurately adjusting the brushless doubly-fed motor, so that the electricity generation voltage amplitude and the frequencies on the power winding side keep stable, the control process is simple, and the device and the method are applicable to wide use.

The invention provides a method and device for starting a megawatt-level double-fed motor. A frequency converter at a rotor side of an existing double-fed motor is utilized to control a rotor current (voltage) to generate rotating magnetic fields, so that stator windings which are subjected to short circuit by a stator short-circuit contactor generate an induced current and stator fields, thus the motor generates electromagnetic torques to drive rotors to rotate, thereby realizing zero-speed start of the double-fed motor. In the invention, the frequency converter at the rotor side of the existing double-fed motor is utilized to realize flexible start of the motor, and the stator short-circuit contactor is added. Compared with a rotor series resistance method or stand-by motor dragging method and the like, the method provided by the invention is low in cost, and has no impact on a power grid. Because only one stator short-circuit contactor is added, the system structure is simple, the processes of motor startup, synchronization and speed adjustment are simple without the impact cohesion, and are automatically and completely controlled by a converter, thus the complete automation is realized and the reliability is high.

The invention provides a reluctance rotor field modulation double-stator brushless doubly-fed motor. The motor comprises two stators and one reluctance rotor which are concentrically arranged from inside to outside, wherein the external stator (1), the rotor (3) and the internal stator (8) are arranged in turn from outside to inside, an external air gap (2) is arranged between the external stator and the rotor, and an internal air gap (7) is arranged between the internal stator and the rotor. The external stator (1) comprises an external stator yoke (11), external stator teeth (12) which are arranged at the internal side of the external stator yoke (11) and power windings (10). The internal stator (8) comprises an internal stator yoke (13), internal stator teeth (14) and control windings (9). The rotor (3) comprises magnetic-conductive iron core blocks (4) and nonmagnetic-conductive material blocks (6) which are evenly distributed along a circumference. The magnetic-conductive iron core blocks (4) internally include magnetic separation slots (5). The gaps between the external stator teeth (12) form external stator slots, and the power windings (10) are embedded in the slots. The gaps between the internal stator teeth (14) form internal stator slots, and the control windings (9) are embedded in the slots.

The invention discloses a three-phase short circuit current calculating method for a double-fed motor. The method comprises calculating the stator side equivalent reactance after short circuit; calculating and obtaining the stator side linkage initial value and the rotor side linkage initial value before short circuit according to the stator side equivalent impedance after short circuit and the double-fed aerogenerator electromagnetic transient equation under the space rotating coordinates; calculating and obtaining the transient stator side linkage and the transient rotor side linkage according to the stator side linkage initial value and the rotor side linkage initial value before the short circuit; calculating and obtaining the stator side current according to the transient stator side linkage and the transient rotor side linkage; and obtaining the short circuit for A-phase, B-phase and C-phase, the short circuit current instantaneous maximum value and the short circuit current periodic component effective value by performing transformation of coordinates for the stator side current. The three-phase short circuit current calculating method for a double-fed motor is higher in calculating accuracy.

The invention discloses a dual-stator brushless double-fed motor. The motor comprises an outer stator, a rotor, an inner stator and a bidirectional rectification inverter, wherein a 2p-pole stator winding on the outer stator is a power winding directly connected with a power grid; a 2q-pole stator winding on the inner stator is a control winding connected with the power grid through the bidirectional rectification inverter; the rotor is provided with two layers of squirrel cages; guide strips of the two layers of squirrel cages are correspondingly connected at one end of the rotor; and the guide strips of the two layers of squirrel cages are respectively short-circuited through two end rings at the other end of the rotor. The dual-stator brushless double-fed motor has excellent adaptability, can be designed into not only a variable-speed constant-frequency generator but also a constant-frequency adjustable-speed motor, has a simple and compact structure, is high in power density, and has high reliability and low operation and maintenance costs due to omission of a brush slip ring.

The invention discloses a high-power brushless double-fed motor three-level bidirectional frequency conversion speed regulation system, which is characterized in that the system is composed of a brushless double-fed motor and a three-level dual PWM AC speed regulation system. The dual-PWM AC speed regulation system includes a brushless doubly-fed motor three-level PWM rectifier unit and a brushless doubly-fed motor three-level inverter unit. In the main circuit structure of the three-level dual-PWM AC speed regulation system of the present invention, four power devices are connected in series for each phase bridge arm. The three-level PWM rectifier can realize two-way flow of energy, improve energy recovery rate, and reduce energy loss of motor AC speed control system. It is suitable for high-voltage and high-power motor drive occasions.

The invention provides a programmable logic controller (PLC)-and-frequency-converter-based energy saving control system for a doubly-fed motor. The system is characterized by comprising a starting switch, a state transition switch, a protection switch, the doubly-fed motor, a PLC, a frequency converter, a human-computer interface ((HMI), a stepdown transformer, a frequency converter input reactor, a rotating speed detection unit and a starting control unit. On the stator side of the doubly-fed motor, a stator is connected to a power grid by the starting switch and the protection switch. On the rotor side of the doubly-fed motor, a rotor is connected to the power grid by the state transition switch, the protection switch, the stepdown transformer, the frequency converter and the frequency converter input reactor. The system not only has a simple structure and high reliability, but also can utilize the peculiar control advantages and energy-saving characteristic of the doubly-fed motor.

The embodiment of the invention discloses an asynchronous oscillation suppression method of an separately controlled doubly fed electric machine and a doubly fed electric machine system of the asynchronous oscillation suppression method. The method comprises the steps that active power of a rotor of the electric machine is calculated; an oscillating component of the active power is extracted from the active power; a slip frequency compensation quantity is calculated according to the oscillating component; slip frequency of the electric machine is compensated through the slip frequency compensation quantity. According to the asynchronous oscillation suppression method of the separately controlled doubly fed electric machine and the doubly fed electric machine system of the asynchronous oscillation suppression method, the slip frequency compensation quantity of the electric machine is calculated according to the oscillating component of the active power of the rotor and used for conducting compensation on the slip frequency, system damping is increased, stability of the system and rapidity of a response are improved, and the inherent unstable problems such as out-of-step which is prone to occurrence and overcurrent of a separately controlled doubly fed speed regulating system are solved.

The invention discloses an axial dual-stator brushless double-fed motor. The motor comprises a bidirectional rectification inverter, an end cover, a rotating shaft and a rotor arranged on the rotating shaft, as well as a left stator and a right stator symmetrically arranged on two axial sides of the rotor, wherein the rotating shaft and the end cover are connected through a bearing; and air gaps are reserved between the two stators and the rotor. The axial dual-stator brushless double-fed motor has excellent adaptability, can be designed into not only a variable-speed constant-frequency generator but also a constant-frequency adjustable-speed motor, has a simple and compact structure, is high in power density, and has high reliability and low operation and maintenance costs due to omission of a brush slip ring.

The invention discloses a gearbox torque testing system comprising a motor unit, a generator unit, a prime mover unit and a tested gearbox unit. The gearbox torque testing system is characterized in that the motor unit comprises a motor G1 and an inverter C1; the generator unit comprises a motor G2 and an inverter C2, and the motors in the motor unit and the generator unit are doubly-fed motors; the tested gearbox unit comprises a tested gearbox R1 and a tested gearbox R2 which have the same speed ratio, wherein the low-speed ends of the tested gearbox R1 and the tested gearbox R2 are rigidly connected through flanges, and high-speed ends are respectively connected with the motors in the motor unit and the generator unit; a prime mover G3 in the prime mover unit is connected with the motor G1 or the motor G2; and connecting wires of stator power supplies of the motor G1 and the motor G2 are connected with each other. The system has the advantages of simple structure, convenient production and low cost and is suitable for extensive popularization in the field of gearbox torque testing.

The invention discloses a low-voltage ride through control method and a low-voltage ride through control device for a doubly-fed wind power generating system. The device comprises a reversible power converter, a motor controller, a signal detection circuit and a crowbar protection circuit. The crowbar protection circuit consists of a three-phase uncontrolled bridge rectifier, a primary release circuit and a secondary release circuit. When a power grid has a low-voltage failure, the reversible power converter stops working, the primary and secondary release circuits in the crowbar protection circuit are switched on at the same time and work in parallel to rapidly release transient impact current in a rotor winding of a doubly-fed motor; when the current of a rotor attenuated to a rated value, the secondary release circuit stops working, and the primary release circuit is still switched on to release the transient current in the rotor wining; and after the low-voltage failure of the power grid is eliminated to recover the voltage of the power grid, the reversible power converter restarts working, and the crowbar protection circuit completely stops working. By the method and the device, high ride through capability and good effects are ensured, the time of a transient process for low-voltage ride through can be shortened, the voltage recovery of the power grid can be accelerated and secondary over-current can be effectively prevented.

The invention discloses a method for calculating a short circuit current of a double-fed motor by considering Chopper protection. When the short circuit current of the double-fed motor is calculated, the influences of Chopper resistance and direct current bus capacitance on the calculation for the short circuit current are considered, so that the magnitude of the short circuit current under the short-circuit state of the double-fed motor can be more accurately expressed. Compared with a present formula, the method has the advantages that the calculation precision is improved, and the method has significance in accurately selecting materials for electric equipment and guaranteeing the safety of a wind power plant.

The invention discloses a control method of a wind power generation double-feed converter space vector pulse width modulation (SVPWM) based on a variable switching frequency. The control method comprises the steps of: sampling three-phase current at the side of a motor rotor when a double-feed motor is normally combined to a grid to generate power; converting a voltage value of a three-phase static coordinate system into a two-phase synchronous rotation coordinate system; sampling the rotating speed of the motor rotor by a photoelectric encoder; obtaining torque at corresponding rotating speed according to a wind power curve; calculating out a q-axis current component of the side; taking the obtained current value under the two-phase synchronous rotation coordinate system as a feedback value, and the q-axis current component of the converter as a given value, and obtaining the current given value by calculation, inputting the values into a proportion integration differentiation (PID) link given by the current at the side of the converter; calculating out a given current value, and obtaining Ualpha and Ubeta under a two-phase static coordinate system; simultaneously, calculating out the frequency of SVPWM according to the given and feedback values of the q-axis current of the converter; and obtaining on/off of an upper pipe and a lower pipe of a three-phase bridge circuit according to different values of a switch function of a three-phase bridge arm of the side converter.

Brushless doubly-fed machine (BDFM) is expected to be widely used in wind power generation due to its characteristics of doubly-fed machine without brush and slip ring. Doubly-fed wind turbine has a great influence on the system stability when it is connected to the grid through the power electronic interface, especially in the grid with high wind power permeability. If the wind turbine generatorsystem can have the friendly characteristics of traditional energy, it will greatly improve the stability of the system. Therefore, the invention provides a virtual synchronous control method for a brushless doubly-fed machine based on the control principle of the virtual synchronous generator, which simulates the operation characteristics of the synchronous generator. The phase angle and currentof the winding are controlled by active and reactive power respectively, and the operation characteristics of the synchronous motor are simulated. The inertia characteristics, frequency response characteristics and voltage regulation characteristics of synchronous generator set are simulated effectively by the control system.