72results about How to "Improve current quality" patented technology

The invention provides a compensation method of direct current (DC) voltage fluctuation of a photovoltaic grid-connected inverter, and the method can be used for improving the quality of the grid-connected current through compensating an input DC side secondary pulse voltage by adding a DC voltage pulse compensation module in a DC / AC (direction current / alternating current) high-frequency link, and eliminating a grid-connected current harmonic wave caused by the DC voltage pulse. The control performance of the system can be improved without adding a filter device and adding any extra appliance.

The invention provides a second-order generalized integrator-based control method for a single-phase gird-connected inverter. Two-phase orthogonal fundamental current signals are reconstructed by a second-order generalized integrator; decomposition of a fundamental active component and a fundamental reactive component of a current in a synchronous rotating reference frame, so that decoupling control on the active component and the reactive component of the fundamental current is achieved; observation and control on output current harmonics of the inverter are achieved by the reconstructed fundamental current signals; and power quality of a single-phase grid-connected system is improved. The control method is simple, feasible, and insensive to an input signal, and meets the dynamic and static properties of the system. Compared with a traditional control strategy, the system can still be kept stable and has relatively good engineering practice value under the conditions of an amplitude drop and a frequency change of an input signal.

The invention discloses a method for controlling an active power filter through model reference self-adaption fuzzy control. An alternating-current side current compensation controller designed according to the T-S fuzzy control theory and the Lyapunov method has all aspects of advantages of fuzzy control and self-adaption control, integrates the advantage of strong disturbance rejection performance of T-S fuzzy approximation and T-S fuzzy control on the premise that the overall system stability is guaranteed and utilizes the advantages that model reference and self-adaption control can overcome uncertainty of controlled objects and can achieve fast and accurate tracking, and therefore voltage is set through precise tracking of the voltage of a direct-current side capacitor, current is compensated for at the same time to quickly and accurately track a directive current signal, the compensation performance and system robustness of the active power filter can be greatly improved, harmonics can be eliminated, and the quick popularization of the active power filter is facilitated.

The invention relates to an LCL type three-phase grid-connected inverter control method. The method includes first obtaining a preliminary PWM modulation signal by a traditional active damping controlmethod, then estimating the current after the resonance peak is suppressed according to the feature that an L-type filter and an LCL filter are consistent in characteristic at the low and medium frequency, obtaining the difference between the current and the actual current to be corrected by a current observer at the low and medium frequency, meanwhile feeding the higher harmonic part of the error current back to a control loop and introducing a network voltage feed forward item to obtain a final modulation signal and further control the access current of a grid-connected inverter. The accesscurrent is controlled in a two-phase rotating coordinate system, and the shortcoming that PI control cannot track an AC signal without static difference is overcome. On the basis of taking into account the advantages of active damping, the access harmonic components are further attenuated, and the grid-connected current quality and the system rapid response capability are improved. The method hasthe advantages of high control precision, high reaction speed and high reliability and is suitable for new energy integration grid-connected power generation systems.

The invention discloses a modulation method for suppressing leakage current of a two-H-bridge cascaded inverter. The method comprises the following steps of calculating total parasitic capacitor voltage v<Nto> value of the two-H-bridge cascaded inverter at each switch-on state; selecting all switch-on states when the total parasitic capacitor voltage v<Nto) is -v<dc>; forming a combination of two switch-on states according to requirements of maximum level output, switch stress reduction and output power balance of a module; and comparing a modulation wave with a triangle carrier wave which is laminated by two same or opposite phases, and generating pulse width modulation (PWM) signals conforming to the above switch-on state combination, and allocating the PWM signals to corresponding pins. By the scheme, extra hardware cost is not needed, leakage current flowing into a power grid can be eliminated, and meanwhile, the leakage current of a single module is suppressed; and the method only requires two carrier waves to compare, the computation of a processor is reduced, and the implementation mode is simple.

The invention relates to a DC voltage conversion device and a bridge arm control method thereof. The device comprises a basic conversion unit, and a monopolar structure or a bipolar structure is formed by the basic conversion unit, thereby realizing DC energy conversion. The basic conversion unit is formed by two phases or multiple phases of basic function modules in parallel. Through a bridge arm control method, DC energy conversion is realized. Through adopting a method of combining a full-control device serial connection structure and sub module cascading, the topology realizes voltage conversion in a condition of no transformer, soft switching of serially-connected devices can also be realized, and the investment and the land occupation are reduced.

The invention discloses a motor fault-tolerant control method and device. The method includes the following steps: collecting non-fault five phases of currents of a six-phase motor in a current sampling period, and converting the five phases of currents into five current components under a decoupled coordinate system; using a mathematical model of the motor and the five current components to predict the phase current value of each phase of the motor in the next sampling period, and predicting the optimal voltage vector output by a motor controller in the next sampling period according to the instruction value of each phase of current; converting the optimal voltage vector into five voltage components under the decoupled coordinate system, and limiting the amplitude of a voltage vector synthesized from a-axis and d-axis voltage components; and transmitting the a-axis and d-axis voltage components after amplitude limiting back to a phase coordinate system, converting the final optimal voltage vector into the duty ratio per phase, and adjusting the drive signal of each phase of voltage according to the duty ratio per phase to drive the motor. The phase current harmonic of the six-phase motor under the open-circuit fault tolerance condition of one phase of winding is significantly reduced while the dynamic performance of the motor is not affected.

The invention discloses an MMC apparatus sub-module capacitor voltage balance method by adopting model predictive control. The balance method specifically comprises the following steps: step 1, a system-level main control CPU obtains each phase of control signals of an MMC main circuit; step 2, a phase-control circuit divides sub modules into a discharging group, a charging group and an undifferentiated treatment group according to voltage levels; and step 3, the finally input sub modules are determined in a pulse allocation link, and corresponding trigger pulse is generated; and after the trigger pulse passes through a driving circuit, a PWM signal is generated for controlling on-off of a corresponding switching device IGBT, so as to complete sub-module capacitor voltage grouping type model predictive control of the MMC apparatus. By adoption of the balance method, the nonlinear characteristic of the MMC system is maintained while the sub-module capacitor voltage control of the MMC system is effectively ensured as well, the control precious of the system is remarkably improved, burden of a processor is reduced, and the calculated amount of the existing model predictive technology can be reduced to the maximum extent.

According to a single-phase unipolar grid-connected inverter, a control strategy of a unipolar critical current continuous mode is adopted to realize zero voltage turn-on of a switch tube in order to reduce switch loss. Since the voltage value at a voltage zero crossing part of a power grid is extremely small, the expected critical current continuous control strategy cannot be realized, and the problem of current oscillation on the voltage zero crossing part of the power grid is caused. The invention provides the unipolar critical current control strategy in which gradual change is adopted at the zero crossing part of the power grid, so the problem of zero crossing point oscillation of grid-connected current is solved. The improved unipolar critical current continuous control strategy is suitable for the grid-connected inverter application occasions with smaller power and higher switch frequency.

The invention discloses a modulation method for inhibiting leakage current of H-bridge cascade inverters. The modulation method can maintain the sum of parasitic capacitance voltages of all modules to be constant, and thus the leakage current is eliminated. The method comprises the following steps: dividing all modules into module groups in pairs according to rules, and dividing into a power frequency module group and a high frequency module group; obtaining the on-off state of the power frequency module group through comparison of modulating waves and fixed values; obtaining the on-off state of the high frequency module group through comparison of corrected modulating waves and two stacked triangle carriers; and generating corresponding PWM signals through the combination of the on-off states, and distributing to corresponding pins. The scheme can be used for multiple H-bridge cascade inverters, and extra hardware cost does not need to be added, so that the leakage current flowing into a power grid can be eliminated, meanwhile the switching loss is relatively low, and the implementation manner is simple.

The invention relates to a carrier frequency conversion control method, belonging to the field of power supply technologies. According to the method, the carrier frequency conversion control is realized through the following cycle steps of: storing a mutual restraint relationship table of predetermined current deviation values and carrier frequencies; finding a nearest predetermined current deviation value from the relationship table according to an actually-measured current deviation value, and selecting a carrier frequency corresponding to the predetermined current deviation value; and generating a PWM (Pulse Width Modulation) signal according to the selected carrier frequency, and outputting the PWM signal to a switching device which controls a DC-AC (Direct Current to Alternating Current) inverter so as to enable the actual value of the output current to be close to a target value of the output current. The carrier frequency conversion control method has the remarkable advantages of high response speed, low switching loss, easiness in filter design, and the like.

The invention provides a grid-connected current low-frequency harmonic suppression method of a cascaded H-bridge medium-voltage converter. The method is applied to a grid-connected converter. The grid-connected converter comprises a plurality of three-phase voltage source-type pulse width modulation (PWM) sub-converters. The method comprises the step of introducing a second-order frequency conversion trapper into a voltage ring control loop of the three-phase voltage source-type PWM sub-converters to suppress low-frequency harmonics introduced by voltage fluctuation of a DC bus. The influence of the voltage fluctuation of the DC bus of a power module on the grid-connected current is prevented by changing the voltage ring control loop on the condition that a cascaded H-bridge medium-voltage converter system topological structure is not changed, and the quality of the grid-connected current is improved.

In a method for current measurement in a multiphase current network, a conductive connection is produced between a plurality of the phases of the multiphase current network such that the plurality of the phases is short-circuited with one another. At a detection time, a current value flowing between the conductive connection and a first voltage potential is detected.

The invention discloses a low common-mode voltage control method and system for a three-level converter. The method comprises the following steps: drawing a space vector diagram, dividing the space vector diagram into a plurality of sectors, and judging the number of the sectors according to the size relation between three-phase reference voltages; selecting a plurality of basic voltage vectors from a sector where the reference voltage vector is located, and constructing a plurality of switch sequences; calculating the action time and the output current ripple slope of each basic voltage vector in each switch sequence; synchronously modifying the action time of each basic voltage vector in each switch sequence to obtain the action time of each modified basic voltage vector in each switch sequence; combining the output current ripple slope of each basic voltage vector in each switch sequence with the modified action time to determine the switch sequence enabling the output current ripple to be minimum and the optimal adjustment time; and controlling the three-level converter by using the determined switch sequence and the optimal adjustment time.

The invention discloses a resonance suppression method and system for an electrolytic-capacitor-free variable-frequency drive system, and belongs to the field of drive control of permanent magnet synchronous motors. The method comprises the steps: multiplying a bus voltage resonance component by the feedback proportional gain to obtain a damping current of the system; multiplying a damping currentby a current bus voltage to obtain equivalent damping power of the input side of an inverter, and converting LC oscillation of the input side of a driving system to the output side of the inverter; dividing the equivalent damping power of the input side of the inverter by the current output current of the inverter to obtain the equivalent damping output voltage of the inverter, and superposing the equivalent damping output voltage to the damping voltage of the alpha axis and the damping voltage of the beta axis according to the current of the alpha axis and the beta axis of the motor, so thatresonance components are absorbed by the current of the motor, and LC resonance suppression is realized. According to the invention, the LC resonance in the driving system can be effectively suppressed, the power factor of the driving system without the electrolytic capacitor can be improved, the calculation is simple, and the digital realization is easy.

The invention discloses a three-phase non-isolated grid connection converter and an air-conditioning system. The three-phase non-isolated grid connection converter comprises a direct current terminal, a first alternating current terminal, a second alternating current terminal, a third alternating current terminal, a first capacitor, a second capacitor, a first inductor, a second inductor, a third inductor, a first switch and a second switch, wherein the first capacitor and the second capacitor are connected between the direct current terminal and the ground in series; the first ends of the first inductor, the second inductor and the third inductor are respectively connected to the first alternating current terminal, the second alternating current terminal and the third alternating current terminal; the second ends of the three inductors are respectively connected to a first intermediate node, a second intermediate node and a third intermediate node; the third intermediate node is the intermediate node between the first capacitor and the second capacitor; the first ends of the first switch and the first switch are respectively connected to a first node and a second node; the second ends of the switches are connected to the direct current terminal; the third ends of the switches are connected to the ground; the fourth ends of the switches are connected to a third node; and the first ends of the first switch and the second switch are selectively connected to one of the second ends, the third ends and the fourth ends. Electric energy from a power grid, solar energy and a storage battery is selectively adopted by the air-conditioning system for providing electricity to a compressor of an air conditioner.

The invention discloses an adaptive control method of a single-phase shunt active power filter and belongs to the technology of active power filter control. An adaptive law for controlling an SAPF (shunt active power filter) following reference model is established based on an SAPF approximately-linear dynamic model and by means of control of the model reference adaptive theory, and an adaptive controller is designed to enable the SAPF to output current capable of compensating circuit harmonic, reactive power and the like. By the aid of the adaptive control method, the single-phase SAPF can be effectively controlled, harmonic current and reactive power current of nonlinear circuits are accurately and rapidly compensated, current distortion and reactive power are reduced and eliminated, and current quality of the circuits is improved. The adaptive controller enables nonlinear current distortion to be improved to be within the national standards, and the adaptive control method is of economic significance and has good market prospect.

The invention relates to single-phase and three-phase electric energy quality controllers with novel structures. In the single-phase electric energy quality controller with the novel structure, a load side inverter comprises an inverter bridge switching tubes and is sequentially connected in series by two of the inverter bridge switching tubes; a power grid side inverter comprises inverter bridgeswitching tubes and is sequentially connected in series by two of the inverter bridge switching tubes; a two-way semiconductor power switch and a first low-pass filter are connected in series betweena power grid and a load; the connection point of the two inverter bridge switching tubes of the load side inverter is connected with the connection point of the two-way semiconductor power switch andthe first low-pass filter; and the connection point of the two inverter bridge switching tubes of the power grid side inverter is connected to the power grid after being connected in series with a second low-pass filter. The electric energy quality controllers provided by the invention replace a series transformer with the two-way semiconductor power switch, thereby not only having the function of simultaneously improving the voltage quality and the current quality, but also having a simple structure and a light weight.

The invention discloses an adaptive control method and control system for a grid-connected converter under a weak power grid. The steps are as follows: an adaptive control module is added to the control structure of a grid-connected converter, wherein the input signal of the adaptive control module is the voltage of the point of common coupling (PCC) and the grid current; a grid voltage estimationsignal is obtained through an adaptive algorithm; the grid voltage estimation signal instead of a PPC voltage sampling signal is sent to a feed-forward compensation module and a phase-locked loop module respectively; and finally, the duty cycle of the grid-connected converter is generated through current control, carrier interception and other modules. The adaptive control method is simple and easy to implement. A grid-connected converter based on the method has excellent grid current quality and system stability under wide change range of grid impedance. The method and the system are suitable for grid voltage synchronous control and grid current control in grid-connected inverters, rectifiers, reactive power compensators and other grid-connected AC equipment.

The invention discloses a robust phase-locked system for a grid-connected converter. The robust phase-locked system comprises a current feed-forward module, a first subtractor, a second subtractor, aphase compensation module and a phase-locked ring module. The invention also discloses a robust phase-locked method for a grid-connected converter. The robust phase-locked method comprises the steps of 1, subtracting a grid voltage sample signal by an output signal of grid current subjected to first-order differentiation element so as to obtain a voltage corrected signal; 2, subjecting a fundamental frequency grid current amplitude reference signal to phase compensation element to generate a phase compensation angle signal, and acquiring a difference between an expected power factor angle signal and the phase compensation angle signal to generate a power factor angle corrected signal; feeding the voltage corrected signal, the power factor angle corrected signal and the fundamental frequency grid current amplitude reference signal to the phase-locked ring module so as to generate an output signal synchronous to grid voltage. The robust phase-locked system and method have the advantagesof great applicability to large-range grid impedance changes, good grid current quality, simple structure and good design convenience.

The invention discloses a ring main unit electrical contact temperature measurement sensor which comprises a metal shell of which both ends are open. A PCB board of which the middle part is hollowed-out is embedded in the metal shell; a first conductive layer and a second conductive layer are respectively arranged on the inner surface and the outer surface of the PCB board; a temperature measurement chip, a microprocessor, a communication module and a power supply module are arranged on the PCB board; the signal output end of the temperature measurement chip is connected with the signal processing input end of the microprocessor by an electrical signal; the input end of the communication module is in communication connection with the signal processing output end of the microprocessor; thepower supply module comprises a voltage division circuit and a rectification and voltage stabilization circuit; the voltage division circuit comprises a voltage division device; an anode of the voltage division device is electrically connected with the first conductive layer; a cathode of the voltage division device is electrically connected with the second conductive layer; the input end of the rectification and voltage stabilization circuit is connected in parallel with the voltage division device; and the output end of the rectification and voltage stabilization circuit, the microprocessor,the temperature measurement chip and the communication module form a closed electric loop. According to the invention, electric energy at an electrical joint can be collected so as to implement powerself-taking of the temperature measurement sensor.

The present invention provides a circuit for driving a flat panel display, including a storage capacitor, a transmission gate and a current-limiting transistor. A first terminal of the storage capacitor is coupled to a system voltage, and a second terminal of the storage capacitor is at storage voltage. A first input / output terminal of the transmission gate is coupled to the storage voltage, and the second input / output terminal of the transmission gate is coupled to the data current source. A first gate terminal of the transmission gate is coupled to the first signal; a second gate terminal of the transmission gate is coupled to the second signal. A gate terminal of the current-limiting transistor is coupled to the storage voltage, wherein a first source / drain terminal is coupled to the system voltage, and a second source / drain terminal provides current for driving the flat panel display.

The invention provides an input / output linearization-based quasi-Z-source inverter photovoltaic grid-connected control method. According to the method of the invention, the input / output linearizationmodeling method of a QZSI (quasi-Z-source inverter) and a QZSI grid-connected control strategy are provided, and therefore, when the QZSI changes greatly at an operating point, a reference input voltage can be better tracked, the influence of a direct-current side on an alternating-current side can be decreased, and grid-connected current quality can be improved.

The invention discloses a method for controlling a self-adpative sliding mode of a single-phase SAPF (Shunt Active Power Filter), which belongs to the technical field for controlling an active filter. A similar linear dynamic model based on an SAPF is controlled by utilizing a self-adaptive sliding mode theory, a self-adaptive rule which overcomes the phenomena of uncertain parameters and unknown upper limit of external disturbance is built, and a self-adaptive sliding mode controller is designed so that the SAPF can output current for compensating circuit harmonic wave, reactive power and the like. The error between the harmonic wave and the inductive current can be selected to be an input value of the self-adaptive sliding mode controller when in actual work, an optional value from 0 to 1 can be output by the controller at the moment and is transformed into a PWM (Pulse-Width Modulation) pulse in a certain way, the control for an APF (Active Power Filter) can be realized, and thus the current such as the harmonic wave can be compensated. Through a simulation experiment, the self-adaptive sliding mode controller can improve the non-linear current distortion within the national standard and has good economic significance and market prospect.

The invention relates to the technical field of grid-connected inverter control, and relates to a fractional phase compensation control method and device for an LCL grid-connected inverter under a weak power grid. The method comprises the steps: 1, respectively obtaining a voltage signal and a grid-connected current signal; 2, extracting voltage phase angle information; and generating a grid-connected current reference signal in the control system; 3, dividing the obtained grid-connected current signal into two paths, feeding back an inherent harmonic peak of an active damping suppression LCL grid-connected inverter through the grid-connected current, obtaining an error signal by subtracting the other path from the grid-connected current reference signal, and transmitting the error signal to a current controller for modulation; 4, after the error signal is modulated by a current controller, subtracting the error signal from a grid-connected current feedback active damping signal to obtain a modulated wave signal; and 5, comparing to obtain a control signal. The current controller structure is a proportional resonance parallel repetitive control structure with a fractional phase compensation function, the design is simple, and flexible fractional phase compensation can be provided under a weak power grid.

The invention discloses a dead zone compensation method for H-bridge topology. With the method adopted, the influence of odd-order harmonics brought by dead zone control can be decreased when the deadzone control is carried out, and output quality is improved. The method includes the following steps that: A, all working modes of an H-bridge topology circuit in corresponding modulation modes are analyzed; B, the average error voltage of the H-bridge topology circuit in each working mode is calculated; C, the current working mode of the H-bridge topology circuit is judged; D, an average error voltage corresponding to the current working mode of the H-bridge topology circuit which is judged in the step C is selected from the average error voltages calculated in the step B; and E, the averageerror voltage selected in the step D is converted to a PWM duty cycle compensation amount, and the PWM duty cycle compensation amount is superimposed on the original PWM duty cycle reference of the current H-bridge topology circuit.

According to a three-phase two-level inverter current ripple minimum effective value PWM method and system provided by the invention, a relation between a current ripple RMS and PWM is established by constructing a current ripple RMS prediction model, zero vector distribution is optimized in real time through a calculation result, and finally, a three-phase reference modulation signal is calculated by using an optimized zero vector distribution factor, and an output control pulse is generated. When the current ripple RMS of an inverter is reduced, the current THD and the switching frequency are reduced, the current quality is effectively improved, and the loss is reduced.

A charging station for charging electric vehicles is provided. The charging station includes a plurality of AC charging terminals, each for charging an electric vehicle by means of alternating current. Each of the AC charging terminals is connected to a three-phase power supply via a respective phase-change device in order to be supplied thereby with three-phase electric current. The power supply has three supply lines for providing three voltage phases, and each AC charging terminal has three connection lines for connection to the three supply lines, for applying the three voltage phases to the connection lines. Each phase-change device is set up to change a connection assignment between the three supply lines and the three connection lines.