197results about How to "Reduce harmonic current" patented technology

The invention relates to a control system of a flexible wind power DC convertor on the sea, which pertains to the technical field of power transmission in wind power generation and comprises the doubly closed loop control structure of a sending end rectifier on the sea and the doubly closed loop control structure of a receiving end inverter on the coast; the doubly closed loop control structure of the sending end rectifier on the sea is used for controlling the active power of a flexible DC transmission system and the voltage stability of a wind power AC system; the doubly closed loop control structure of the receiving end inverter on the coast is used for controlling the constant voltage of the DC side of a receiving end convertor and the dynamic regulation of the reactive power of the main network accessing end of the receiving end convertor; two control structures are mutually independent and no data communication exists between the two control structures. The control system can fast and correctly control the active power of wind power transmission on the sea as well as promote the stability of the wind power AC system on the sea and the transmission efficiency and the power quality of the whole DC transmission system.

A detached island effect test method and a device based on active frequency deviation relate to a test method and a device to test distributive new energy grid integration power supply, in particular to a detached island effect test method and a device based on active frequency deviation. Regarding the utility model, 25 cyclic waves form a major cycle. Chopped wave rate cf of the first 15 cyclic waves is 0, and variance trend of the frequency is tested. Under the circumstance that frequency tends to rise, frequency disturbance with the chopped wave rate of cf is added in the grid frequency in the last ten cyclic waves, and initial value cfmax of the chopped wave rate cf is positive. Under the circumstance that the frequency tends to reduce, frequency disturbance with the chopped wave rate of cf is added in the grid frequency in the last ten cyclic waves, and initial value cfmin of the chopped wave rate cf is negative. By adopting the invention, not only the operation probability of the detached island tested is improved; but also testing time is reduced, and current harmonics injected into the grid is reduced.

The invention discloses a double three-phase permanent magnet motor vector control method based on a proportional resonance regulator. The double three-phase permanent magnet motor vector control method aims at weakening and eliminating (6m+/-1)th power of motor harmonic components under double three-phase permanent magnet motor vector control, wherein m=1,3,5.... The double three-phase permanent magnet motor vector control method is characterized in that on the basis of vector space decoupling vector control, a proportional-resonant regulator is adopted to carry out tracking control on the components (isz1 and isz2) on z1-z2 harmonic sub planes after static coordinate transformation is carried out on six-phase electric currents. By the adoption of the double three-phase permanent magnet motor vector control method, optimal control of a double three-phase permanent magnet synchronous motor can be achieved. Compared with traditional double three-phase motor vector control, the double three-phase permanent magnet motor vector control method has the advantages that current wave forms are more sinusoidal, the harmonic content is greatly reduced, especially the (6m+/-1)th power of the current harmonic components is reduced, system loss is low, and good steady-state performance is achieved.

The invention relates to a control method for a bidirectional quasi-Z-source inversion type motor driving system. The control method comprises the following steps of collecting the voltage of a capacitor C2 and the current of a permanent magnet synchronous motor; obtaining voltage components of a d axis and a q axis; obtaining a direct-connection duty ratio; carrying out an SVPWM (space vector pulse width modulation) algorithm by inserting the direct-connection duty ratio according to the voltage components of the d axis and the q axis and the direct-through duty ratio to obtain six paths of PWM control signals for controlling the on and off of three-phase bridge arms of a three-phase bridge type inverter; and carrying out logic calculation on the six paths of PWM control signals to output a PWM control signal for controlling the on and off of an IGBT switch tube S7. Compared with the prior art, the average direct-connection duty ratio and the capacitor voltage closed loop control closed loop policy are added to the conventional SVPWM control method, so that the direct current side voltage has the voltage boosting capability; and on the basis, the power switch S7 which is complementary with the direct-connection state is further designed, so that the bidirectional flow of energy can be realized.

The invention discloses a control device and a control method for an AC-DC (Alternating Current-Direct Current) series resonant matrix converter for capacitor charging and mainly aims at solving the problem in the prior art that the control property of a capacitor charging power supply is not high enough to meet the power supply requirement of a high-power microwave system. The control device for the AC-DC (Alternating Current-Direct Current) series resonant matrix converter for capacitor charging comprises a zero-crossing comparator, an On-Off state control unit, a timing sequence generating unit, a control parameter calculation unit, a load voltage acquisition circuit and a trigger driving circuit. The invention further discloses a control method of the control device. With the technical scheme, the control device and the control method, disclosed by the invention, have the advantages that the price/performance ratio is relatively high property, the power supply requirement of the high-power microwave system can be sufficiently met, and the practical value and the popularization value are high.

The invention discloses a charging and discharging control system and a charging and discharging control method of a flywheel battery. The system comprises a three-phase uncontrollable rectifying circuit, an energy storage filter capacitor, an insulated gate bipolar translator (IGBT) power conversion circuit, a zero passage detection circuit, a voltage detection circuit, a current detection circuit, a direct current voltage detection and overvoltage protection circuit, a sampling and filtering overcurrent protection circuit, a displacement sampling circuit, a temperature sampling circuit, a digital signal processor controller, an energy storage inductor, a three-phase linked switch and a rotary transformer signal processing circuit, wherein the energy storage inductor is connected between the output end of each phase on the alternating current side of the IGBT power conversion circuit and the input end of a flywheel motor; the three-phase linked switch is connected in parallel with the energy storage inductor respectively; and the rotary transformer signal processing circuit is connected between the signal output end of a rotary transformer of the flywheel motor and the quadrature encoder pulse (QEP) port of the DSP controller. In the method, charging and discharging control of a flywheel battery is realized based on the system. The system has stable output direct current voltage, small high-frequency ripple, quick dynamic response, and is particularly suitable for quick charging and quick discharging working conditions; and the power factor and efficiency of the system are improved greatly.

The present invention discloses a large-capacity cascades multiphase multi- electrical level power converter without transformer, which belongs to high pressure large-capacity multiphase multi- electrical level frequency conversion technology field, and characterized in that a single-phase main circuit is composed by identical prime power convert unit through cascades; three single-phase main circuits are connected to the three phase electric network through star or triangle shape; the prime power convert unit constitutes 'back to back' AC-DC-AC inverter circuit topology through DC bus capacitance with multiphase inverter by H-type rectifying bridge; different electrical level, types, number of phases and connecting relation of the prime power convert unit can extends various different polyphase converter practical topology circuit, which saves phase-shifting transformer that original absolutely necessarily but volume weight covers more than one third of that of system, which reduces greatly volume and cost of complete appliance. The present invention is capable of realize high performance operation of speed governing system in four quadrant scope, can feedback energy from the electric motor to the electric network when the electric motor brakes, enhances working condition operation efficiency of speed governing system; and communicate electric network side current harmonics small and power factor close to 1.

The invention relates to a method for compensating three-phase unbalanced currents on the basis of an SVG (static var generator). The method includes determining whether load currents needs to be compensated or not via three-phase unbalanced judging links by the aid of load current signals which are used as control input; acquiring frequencies and phases of power grid voltages via adaptive frequency locking and phase locking links when the load currents need to be compensated; filtering harmonic current components in the load currents by the aid of discrete second-order generalized integrators; computing negative-sequence current values required to be converted for various phases if the three-phase unbalanced currents are in balanced states; transmitting the negative-sequence current values to control instruction computation modules in SVB devices; driving IGBT (insulated gate bipolar transistors) to act; generating currents equal to fundamental negative-sequence components in the load currents so that the three-phase unbalanced currents can be in the balanced states. The negative-sequence current values are used as reference current signals. The directions of the currents are opposite to the directions of the fundamental negative-sequence components in the load currents. The method has the advantages that the three-phase unbalanced currents can be dynamically compensated, and accordingly the stability and the reliability of power grids can be improved; low-pass filters can be omitted when negative-sequence currents are extracted, and accordingly the method is low in computational burden and high in response speed and tracking precision.

Disclosed are a method and a system for controlling current of a grid-side converter of a doubly-fed wind driven generator under an unbalanced power grid condition. The method includes combining voltage of a power grid, alternating-current-side voltage of the grid-side converter and delay signals of the power grid and the grid-side converter with given active power and given reactive power, and analyzing and computing to obtain an instruction value of alternating-current-side current of the converter; and further computing to obtain alternating-current-side instruction voltage of the grid-side converter according to a mathematic module of the grid-side converter and a principle that an actual current value of a next time interval is equal to the instruction value, and then generating a pulse signal for controlling on and off of a switching tube via SVPWM (space vector pulse width modulation). In the method, rotational coordinate transformation and positive and negative sequence decomposition are not required, grid-side current and inductance parameters are either not required, fluctuation of direct-current-side voltage of the grid-side converter can be suppressed under an unbalanced voltage condition of the power grid, grid-side harmonic current is reduced, and unity power factor is maintained.

A DC power supply unit is provided that allows for improving efficiency and reducing harmonic currents. A DC power supply unit includes: a bridge rectification circuit having diodes and MOSFETs; a reactor that is arranged between the AC power supply and the bridge rectifier circuit; a smoothing capacitor that is connected to an output side of the bridge rectifier circuit and smoothes a voltage; and a converter control unit that executes, based on predetermined threshold values, a diode rectification control that uses diodes and parasitic diodes of the MOSFETs, a synchronous rectification control that switches the MOSFETs in synchronization with a polarity of the voltage of the AC power supply, a partial switching control that repeats partially short-circuiting the reactor multiple times in a half cycle of the AC power supply, or a fast switching control that short-circuits the reactor at a predetermined frequency over a full AC cycle.

The invention concerns an installation constituting a railway propulsion chain, characterized in that it comprises, sequentially arranged, in the power electrical circuit, between a power transformer powered by a catenary and an electric motor of said vehicle, said catenary being capable of supplying a plurality of voltages, alternating or direct, said electrical circuit comprising a plurality of contact switches for selecting a given catenary voltage, at least one of the following elements: a controlled rectifier bridge (A1, A2), preferably a single-phase bridge with forced switching; a substantially reactive input filter (A3), preferably comprising at least a capacitance and/or at least an induction coil; a braking chopper capable of including also a clipping function (B); a multiphase and multilevel static converter (C1, C2, C3), preferably three-phase; electronic components, preferably IGBT power semiconductors for each element, each element belonging to at least an elementary power arm of the modular circuit diagram.

The invention discloses a method for controlling a network side rectifier of a tandem type brushless double-feed wind-driven generator under an unbalanced electric network, and aims to calculate given compensation values of active and reactive powers on a static coordinate system according to electric network voltage, delayed signals and active and reactive initial given values. The summation of the active and reactive initial given values and the given compensation values is a final power instruction value which is taken an unbalanced condition of the electric network voltage into account, then alternating-current side instruction voltage is calculated according to a mathematical model of the network side rectifier, and a driving signal of a switching device is obtained by using space vector pulse width modulation (SVPWM) decomposition. According to the method, transformation of rotational coordinates and decomposition of positive and negative sequence components are not required, second harmonic fluctuations of direct-current side voltage of the network side rectifier when the electric network voltage is unbalanced can be inhibited, and the network side harmonic current is reduced.

A DC power supply apparatus comprising: a rectifying circuit including, a first rectifying portion, a second rectifying portion, a third rectifying portion and a fourth rectifying portion; a current detection portion; a first switching portion; and a second switching portion; wherein each of the first rectifying portion cooperatively operating with the first switching portion and the second rectifying portion cooperatively operating with the second switching portion is a semiconductor element which is formed by using a Schottky junction formed between silicon carbide or gallium nitride and metal and has a withstanding voltage property with respect to a voltage of an AC power supply.

The invention provides a novel rotating rectifier with a fault monitoring function, and relates to rotating rectifying systems. The invention aims at solving the problems that an existing rectifier is low in output power of an alternating-current exciter and high in harmonic component, a rotating rectifying controller cannot be timely started and a system fault exists. The novel rotating rectifier with the fault monitoring function comprises a three-phase triple voltage rectifying circuit, an alternating-current exciter, a rotating bridge rectifier module based on VIENNA, a start power module, a start resistor, a rotating rectifying controller, a synchronous electric exciter set, a fault detection module, a wireless communication device, a first wireless transceiving device, a second wireless transceiving device and an external monitoring module. According to the novel rotating rectifier with the fault monitoring function, a neutral-point potential balance method of injecting zero-sequence voltages is adopted, zero-sequence voltages VZ(+) and VZ(-) are injected into a three-phase reference voltage at different moments, and the problem is solved that two capacitor voltages of a direct current busbar are not balanced.

Disclosed is a virtual flux-based dual-PWM frequency converter model prediction direct power control method. The method comprises the steps of collecting three-phase alternating current power grid voltages e<sa>, e<sb> and e<sc>, rectifier grid side three-phase line currents i<sa>, i<sb> and i<sc>, a direct current bus voltage u<dc>, and three-phase stator currents i, i and i<c>; enabling adifference value between the direct current bus voltage u<dc> and a given direct current bus voltage u<dcref> to pass through a PI regulator to obtain a given load current I<dcref>; enabling the givenload current to be multiplied with the direct current bus voltage to obtain given active power p<ref>, wherein the given reactive power q<ref> is equal to 0; obtaining instantaneous active power andinstantaneous reactive power according to the components of the rectifying side three-phase alternating current voltages and three-phase line currents in an alpha-beta coordinate system and by virtueof the virtual flux <Psi><s>, and solving power differential, and obtaining active and reactive prediction values before the next period is started according to a one-order linear equation; and enabling the inversion side to perform conversion of coordinates according to a rotor flux orientation vector control strategy so as to realize full decoupling of the motor torque and flux control. By virtue of the method, the dynamic response speed of the system is improved, the anti-disturbance performance of the system is improved, and the frequency conversion system has higher advantages.