1148 results about "Active power filter" patented technology

A method is provided for determining a control scheme for a neutral point clamped (NPC) voltage source converter (VSC) with at least 3 levels and a topology of three bridge legs between each of three phases of a grid and a neutral point. Each leg includes at least four active switches, and a clamping carrier modulator synchronized with the grid is provided for the control of no-switching intervals. The method includes: analyzing the waveform of the grid and/or a load voltage and determining windows defining an allowed period for no-switching of the corresponding bridge leg; operating or simulating the operation of the voltage source converter with different clamping carrier modulator frequencies, and then analyzing the balance in the operating junction temperatures and/or power losses across the active switches and also analyzing the total losses of the voltage source converter; comparing the balance and the total losses of different clamping carrier modulator frequencies and selecting either the clamping carrier modulator frequency according to showing, as primary criterion, the better balance and, as secondary criterion, the lower total losses; operating or simulating the operation of the voltage source converter with the selected clamping carrier modulator frequency, while iteratively changing at least one of the following operating parameters of the voltage source converter: switching frequency, DC-link voltage reference, duty cycle of clamping carrier modulator, phase shift of the clamping carrier modulator relative to the grid, and optimizing the balance in the operating junction temperatures and/or power losses across the active switches and the total losses of the voltage source converter as a function of the adjustment of these operating parameters until reaching optimum operation parameters for the control scheme.

The invention discloses an alternating current and direct current mixed micro power grid system and a control method thereof. The system comprises a photovoltaic module, an inverter, a direct-current converter, a storage battery, a super capacitor, an alternating current load, a direct current load, a direct current bus, an alternating current bus, an SVG (scalable vector graphics) and an APF (active power filter) and the like. The control method comprises the following steps: firstly detecting the voltage and frequency of a main network, if the voltage and the frequency are normal, grid-connected operation is adopted in the system, otherwise, isolated island operation is adopted; if the grid-connected operation is adopted in the system, PQ (performance qualification) control is adopted in the inverter, and constant voltage control is adopted in the direct current converter; if the isolated island operation is adopted in the system, V/F control is adopted in the storage inverter with maximum capacity and a super capacitor, the PQ control is adopted in other inverters, and the constant voltage control is adopted in the direct current converter; and finally, the energy storage capacity is enabled to be within an optimum range under the condition that the system is in normal operation. With the adoption of the alternating current and direct current mixed micro power grid system and the control method thereof, the problem of operation control of the alternating current and direct current mixed micro power grid system is solved, the reliability, safety and economy of the system are improved, and the utilization efficiency of renewable energy sources is improved.

An active power filter comprises an energy storage capacitor, an inverter, a filtering circuit and a controller. The inverter is controlled to act as a virtual resister at a fundamental frequency for compensating for the power loss of the active power filter, act as a virtual capacitor at a fundamental frequency for compensating for a fundamental reactive power of the load, and/or generate a harmonic current for suppressing the harmonic currents of specific orders of the load.

Current transformer DC side voltage closed-loop control method of active power filter characterizes in a selective harmonic detect method, which will get two-phase coordinate system current after detecting the N time of harmonic active or reactive DC component and through delay compensated angle variable matrix, and to deduct DC side voltage adjust signal to make the compensate current signal contain a certain basic wave active current component, in which, adjust signal is the difference between the given value of the current transformer DC side capacitance voltage and feed back value of the side capacitance voltage adjusted by an adjuster.

The invention belongs to the technical field of DC (Direct Current) power transmission, particularly a DC power transmission system with a function of unidirectionally transmitting a power. The DC power transmission system is characterized in that both ends of a diode rectifier are connected in parallel with low-power modularized multilevel converters; an AC (Alternate Current) end of the diode rectifier is connected with a sender system; a DC end of the diode rectifier is connected with a sender of a DC power transmission circuit; AC ends of the low-power modularized multilevel converters are connected with the sender system; DC ends of the low-power modularized multilevel converters are connected with the sender of the DC power transmission circuit; a DC end of a full-power modularized multilevel converter is connected with a receiver of the DC power transmission circuit; and an AC end of the full-power modularized multilevel converter is connected with a receiver system. The low-power modularized multilevel converters are used as active power filters to filter out a harmonic current generated by the diode rectifier, provide start power (such as service power) for the sender system when the sender system loses power, provide an AC voltage resource for the sender system.

Disclosed is an active power filter with a reduced VA rating for reducing harmonic currents in a neutral line in a three-phase four-line power system. An inverter is connected to the neutral line for PWM-controlling current flow of the neutral line based on a voltage control signal from a controller so that a fundamental component of a load-side neutral current flows to the three-phase AC power source and its harmonic component is circulated to the load. A transformer is connected between the neutral line and each phase line of the three-phase AC power source for forming a current path whereby the harmonic component flows to the load through the phase line. A rectifier is connected between the transformer and the inverter for rectifying drive voltage into DC voltage and applying it to the inverter.

The invention discloses a modularized multi-machine parallel-connection large-power APF (active power filter) control system and a realization method. By coordinating an upper layer controller and a lower layer controller, an effect for reasonably allocating the compensative capacity and improving the compensation precision can be realized; the upper layer controller is used for carrying out the coordination and switching control on each power module, for example, the upper layer controller is used for operating and monitoring the quantity of the power modules to be put into use according to a load requirement, numbering the power modules according to a rule and eliminating the switching subharmonic by utilizing the carrier phase shifting; the lower layer controller is used for receiving a compensation order of the upper layer controller and a synchronous signal of a previous sequence number controller and feeding back state information of the power module to the upper layer controller. By adopting the modularized multi-machine parallel-connection large-power APF control system, the compensation capacity of the power module and the computation of an upper layer and a lower layer of the control system are reasonably allocated, the entire system can be enabled to run stably and orderly, the stopping of the entire system caused by the malfunction of one power module can be avoided, and the feasibility and practical value are good.

A power regulator including a coil connected to an output of a DC power source for rectifying an AC voltage, a charge-and-discharge capacitor for charging a current supplied from the DC power source through the coil and a backflow preventing diode, a switching device connected to a connection point of the coil and backflow preventing diode in parallel with the DC power source, and a microcomputer for detecting a zero-cross point of the magnetic field energy generated in the coil or the current flowing through the coil, and for bringing the switching device into conduction in response to the detection of the zero-cross point. This makes it possible to solve a problem of a conventional device in that the switching period of the switching device cannot be changed in accordance with variables such as temperature change, errors in circuit constants and the like because switching periods of the switching device are predetermined values.

The invention relates to a system for harmonic detection and control of an APF (active power filter) based on windowed all-phase FFT (fast Fourier transform), which comprises an alternating-current power grid with a nonlinear load and an active current filter, and is characterized by also comprising a control module and a detection module. A working method comprises: signal detection, command triggering, pulse uttering and generation of compensating current. The system and the method have the advantages that (1), the system is simple and the cost is medium; (2) the frequency, the amplitude and the phase of the harmonic current can be detected in an accurate and real-time way, and the compensating performance of the APF can be guaranteed; (3) the accuracy and the real-time performance of calculation can be improved; and (4) the current tracking control effects of the APF can be improved.

The embodiment of the invention discloses a resonance wave detecting and phase-locking method and a resonance wave detecting and phase-locking method for an active power filter. The method comprises the following steps of: carrying out phase shift filtering to a sampled three-phase voltage signal to obtain a first-grade processing signal; substituting the first-grade processing signal into an sequence-dividing formula to obtain a three-phase voltage fundamental positive sequence component; and adopting a dq synchronous coordinate system to lock phase of the three-phase voltage fundamental positive sequence component. The embodiment of the invention extracts the three-phase voltage fundamental positive sequence component in an unbalanced grid by using a way of dividing sequence first and locking phase consequently, locks phase of the positive sequence component by using a dq synchronous coordinate system phase-locking algorithm to obtain a positive sequence fundamental phase angle and eliminate the influence of grid imbalance on the phase locking link, so that the phase locking precision is wholly improved and the technical effect that the real-time and precise phase locking can also be carried out in the situation of unbalanced voltage in the grid is achieved.

The invention discloses a disposal method used for the digital delay of an active power filter and the corresponding devices. The invention comprises the following steps that a load current is sampled by selecting a time point which is prior to the time Vt when duty cycle loading is implemented, and the current value of the load at current time is detected; the harmonic component in the load current is calculated based on a change detection algorithm; the output current of active power filter is sampled by selecting the middle-point times of all switch periods of PWM signals; close ring control is carried out for the harmonic component of the load current and the output current of the active power filter, the PWM signal is modulated and a power device is driven. By adopting the method, the effect of digital delay to the compensation precision of the active power filter is reduced; the sampling delay of the load current with periodic harmonic is eliminated; the operation time is little, and full digitization is easy to be implemented. The invention is more applicable to the microprocessor chips with medium prices and processing speed, and reduces the cost of active power filter.

The invention discloses an output current wave shape control method for a triphase Active Power Filter (APF). A T-shaped filter and a current wave shape controller are adopted to control the output current wave shape of the triphase AFT. The output filter for each phrase bridge arm of an inverter is a capacity connected to the middle point of two inductances connected with each other in series, and form a T-shaped structure, namely T-shaped filter; the calculation method for wave shape controlling is conducting Alfa, Beta, Omicron transformations to instruction current of the triphase APF, actual output current and the voltage of the power network, so as to realize decoupling of the wave shape controlling of the abc triphase output current; and respectively conducting pole assignment to the single-phrase system under decoupled Alfa, Beta, Omicron axis system, and correcting the error between the APF actual output current an the instruction current, so as to get instruction voltage of each phrase under the alfa, beta, Omicron axis system; and at last sending the instruction voltage to a space vector modulating module, so as to confirm the on-off signal of each bridge arm switch tube, thereby causing the actual output current of the PFA to accurately track the instruction current.

The invention provides an electric vehicle charging station system based on an AC/DC double bus. The electric vehicle charging station system based on the AC/DC double bus adopts a system framework of the AC/DC double bus, connection of the bus with multiple subsystems, modularization in each subsystem and dual data interaction channels, and has the complete function of the electric vehicle charging station system. The electric vehicle charging station system based on the AC/DC double bus takes a bidirectional converter as the core, the AC side of the bidirectional converter is connected with the AC bus, the DC side of the bidirectional converter is connected with the DC bus, and energy flows bi-directionally between the DC and AC buses through the bidirectional converter. The DC bus is connected with an energy storing subsystem, a photovoltaic subsystem, a wind power subsystem and a plurality of DC charger subsystems. The AC bus is connected with an electric supply access subsystem, an active power filter APF access subsystem, a diesel engine generator access subsystem and a plurality of AC charger subsystems. The quantities and the capacities of the AC charger subsystems and the DC charger subsystems can be flexibly selected according to actual needs. The electric vehicle charging station system based on the AC/DC double bus is flexible in configuration and high in power supply reliability, enables the electric vehicle charging station load to combine with new energy power generation, and realizes the sustainable and stable operation of the system.

The invention discloses an active power filter device based on a coupled inductance, which is composed of a signal acquisition module, a main control module, a drive module, a power conversion module and an LCL filter module based on a coupled inductance. The steps of extracting command current are as follows: first, extract sinωt and cosωt which are synchronized with grid A-phase voltage ua through digital phase-locked loop; secondly, transform the three-phase grid current into dqo coordinates to obtain current id, iq in dqo coordinate system , io; the third is to perform digital low-pass filtering on id and iq to extract their DC components; the fourth is to inversely transform io, sinωt and cosωt to dqo coordinates; the fifth is to perform subtraction to obtain the three-phase grid current The fundamental reactive and harmonic currents in . After hysteresis comparison control, PWM gating signals and trigger pulses are generated to control the orderly on-off of each IGBT in the power conversion module to generate PWM voltage, which is filtered by the filter module and then injected into the grid for compensation.

An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load, said drive circuit comprising an a-c source, a rectifier connected to said a-c source and producing a rectified output voltage connected to a positive d-c bus and a negative d-c bus, a PWM inverter having input terminals coupled to said positive d-c bus and negative d-c bus and having a controlled a-c output, a load driven by said a-c output of said PWM inverter, a ground wire extending from said load, and a current sensor for measuring the common mode current in said drive circuit in said ground wire, said current sensor producing an output current related to said common mode current, said active filter comprising a first and second MOSFET transistor, each having first and second main electrodes and a control electrode, and an amplifier driving a respective one of the transistors; said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being coupled to said positive d-c bus and said negative d-c respectively; each of said amplifiers having an input coupled to said output of said current sensor and each having an output connected to a respective one of said control electrodes; and a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire.

The invention discloses a low pass filter, an active power filtering device and a harmonic detection method based on the active power filtering device.. The low pass filter is formed by an IIR (infinite impulse response) filter and an MA (moving average) filter in a cascade manner. The active power filtering device comprises a main circuit, a mutual inductance regulating circuit, an AD (analog-to-digital) sampling circuit, a detection circuit and a control circuit, wherein the main circuit is used for injecting compensation current to a three-phase power grid, the detection circuit utilizes the low pass filter, and the control circuit is used for forming a driving signal of the main circuit. Through utilizing the active power filtering device, the harmonic detection method disclosed by the invention comprises the following steps of: sequentially detecting, regulating and carrying out AD sampling on load current of the three-phase power grid; extracting harmonic current; and forming a driving signal according to the harmonic current. The invention prevents a problem that the separation of direct current amount and alternating current amount of active current and reactive current is poor in the traditional harmonic detection technique, improves the filtering precision, has quick dynamic response and can quickly and exactly detect the content of the harmonic current in the power grid.

A fully-integrated continuous-time active complex bandpass IF filter that may contain transmission zeros yielding much sharper roll-off than that of an all-pole filter is implemented using transconductors and capacitors only. Each of the filter second-Order sections realizes a pair of complex poles and a may realize a double imaginary axis zero. Since the transconductors are electronically tunable the positions of filter zeros and poles are adjustable using an automatic tuning system. In each filter section the value of different transconductors are modified to separately change the pole frequency, its Q-factor and the zero frequency. Each pole and zero are separately tuned, which achieves a higher level of tuning accuracy than in case where all poles and zeros were adjusted simultaneously.

The invention discloses an active power flow optimizing distribution method for an alternating-direct current parallel system containing soft direct current power transmission, and solves the reasonable distribution problem of the active power flow of the alternating-direct current system under the alternating-direct current parallel operation mode of the soft direct current power transmission. The method comprises the steps of obtaining basic parameters of a power grid to be analyzed; establishing corresponding target functions by taking factors such as alternating-direct current equipment loss, avoiding parallel loop current, the safety and stabilization of the power grid, the utilization rate of the alternating-direct current equipment and fault rate as target conditions according to the obtained basic parameters of the power grid; establishing multiple target optimization functions according to all established target functions; designing a subjection function for each target function according to the fuzzy theory; and resolving the optimal solution of the multiple target functions by adopting a fuzzy algorithm. The method considers the constrain of multiple target conditions, obtains the optimal active power control reference value under the alternating-direct current parallel operation of the soft direct current power transmission system by resolving the multi-target optimal function, and is more reasonable in comparison with the method relying on experience to set the active power reference value.

The invention discloses a self-adaptive fuzzy control method for an active power filter based on feedback linearization, relates to the technical field of an active power filter, and respectively designs independent self-adaptive controllers aiming at a current loop and a voltage loop. As the current loop adopts the self-adaptive fuzzy controller for the active power filter based on the feedback linearization, the feedback linearization theory, fuzzy control, sliding mode control, self-adaptive control and Lyapunov stability theory are comprehensively utilized, and on the basis of ensuring the global stability, the purpose of harmonic compensation is realized. As the voltage loop adopts the self-adaptive fuzzy PI (process integration) control, according to the fuzzy rule, the control strategy can automatically adjust the PI parameter, strengthen the robustness of the system, improve the dynamic performance of the system, and ensure the tracing to the command voltage.