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 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 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 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 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.

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.