58results about How to "Improve harmonic characteristics" patented technology

The invention discloses an electromagnetic transient mathematical model of a distributed power-flow controller based on an MMC, control system and a modeling method. The distributed power-flow controller comprises a parallel connection side converter composed of a three-phase converter based on the MMC at the parallel connection side and a parallel connection side single-phase converter and a series connection side converter composed of multiple sets of series connection side single-phase converter; the electromagnetic transient mathematical model mainly comprises a parallel connection side converter model and a series connection side converter model; the control system comprises a parallel connection side control model and a series connection side control model, the parallel connection side control model comprises a three-phase converter control module based on the MMC at the parallel connection side and a parallel connection side single-phase converter module, and the series connection side control model comprises a series connection side third harmonic control module and a series connection converter active power reactive power control module. The electromagnetic transient mathematical model is designed by adopting modularization, the sub module switch-on and switch-off frequency is lowered, and the loss is lowered; the control system adapts to different voltage grades, and is applicable to flexible alternating current transmission occasions.

The invention relates to the technical filed of the multi-power-level high-voltage transducer, in particular to a five power-level transducer and the control method thereof. The five power-level of the invention is formed by connecting a high-voltage rectifier circuit, a high-voltage capacitor filter circuit, a voltage balancing circuit, and an inverting circuit in turn. The invention is characterized in that the inverting circuit adopts one or two apparatus/apparatuses in the IGBT and the IGCT to form an inverter, adopts a diode clamping five-power-level structure and three inverters with uniform bridge arms. The invention can provide higher resolution and can obtain better harmonic characteristic for the low-voltage area of a signal, better output characteristic and high-voltage high-power output for the high-voltage area of the signal; in addition, the invention has the advantages of easy control, and being safe and reliable.

The invention discloses a method for MMC type VSC-HVDC system precharge control. The method is based on a CPSM (carrier phase shifted modulation) strategy and controls by adoting a voltage outer ring and a current inner ring, wherein the voltage ring controls capacitor voltage of a sub-module, and the current ring controls three-phase AC current. The method disclosed by the invention gives consideration to the precharge speed and the precharge efficiency while limiting impact current and preventing overvoltage. The control method is clear in thinking, easy in engineering realization, and has good dynamic performance and steady-state performance.

The invention discloses a double-stator doubly salient hybrid excitation motor drive system, and the system comprises fault reconstruction five-phase T-type three-level inverters and a double-stator doubly salient hybrid excitation motor; two sets of windings of the double-stator doubly salient hybrid excitation motor are separately powered by two sets of fault reconstruction five-phase T-type three-level inverters, and the two sets of fault reconstruction five-phase T-type three-level inverters are independent with each other. The double-stator doubly salient hybrid excitation motor adopts a double-stator structure which comprises an outer stator, an inner stator, doubly salient rotor, a permanent Nd-Fe-B magnet, a permanent Al-Ni-Co magnet, a magnet regulating coil and an armature winding; and the two stators share one doubly salient rotor. According to the invention, the double-stator doubly salient hybrid excitation motor drive system is provided, a control method of the system is also provided, and the system has advantages of high power density, high efficiency, high reliability, high magnet regulating ability and the like.

The invention discloses a mixed carrier-based multi-level PWM method. The method first takes the absolute value of a reference sinusoidal signal v<ref> to obtain a modulation signal v<m(abs)> of a high voltage unit, and then obtains a modulation signal v<m(LVC)> of a low voltage unit through comparison and operation. The modulation signal of the high voltage unit is compared with a triangular carrier signal v<trb> whose frequency is f2 to obtain a logic pulse signal B, and is compared with a voltage reference signal v<rh> to obtain a logic pulse signal P. The modulation signal of the low voltage unit is compared with triangular signals v<tra> and v<trc> whose frequency is f1 to obtain logic pulse signals A and C. The reference sinusoidal signal is compared with zero voltage to obtain a polarity pulse signal D. Then the four logic pulse signals and the polarity pulse signal pass through a driving logic distribution unit to generate an optimized PWM drive signal. The method provided by the invention does not have the problem of power backflow, and optimizes equivalent switching frequency of high- and low-voltage units of an inverter.

The invention relates to an inverter which comprises a circuit system and a control system. The circuit system comprises a solar cell panel and a power grid output. A direct current switch, a BOOST boosted circuit, a single phase full bridge circuit and a grid-tied filter are sequentially arranged between the solar cell panel and the power grid output. The control system comprises a digital signal processor (DSP) control platform, the DSP control platform is connected with a protection module, a sampling and conditioning module, a passage zero comparison module and a level switch module, and the level switch module is connected with an input/output (I/O) information module, a driving module and a power amplifier module. The inverter has the advantages of being based on the DSP control platform, using modes of topology, modulation and the like, and having high efficiency, light weight, small size and the like in actual use. The highest efficiency reaches to 97.51%. Simultaneously, the inverter can control and track grid-tied voltage phase without dead beat, and achieves unity power factor grid-tied. Grid-tied current has good harmonic characteristics, and full load total harmonic distortion (THD) is 1.57%.

The invention relates to the technical field of a multiple level high voltage transducer, in particular to a seven level high voltage transducer which is formed by mixing couplet components and a controlling method. The seven level high voltage transducer of the invention comprises a high voltage rectification circuit, a high voltage capacitance filtering circuit, an equalizer circuit and an inversing circuit which are connected in turn, which is characterized in that the inversing circuit is formed into an inverter through adopting one or two components of IGB and IGCT, adopting the inverter with the structure of diode clamping seven level structure, and three bridge arms of the inverter are same. The transducer of the invention can provide a higher differentiate ratio to a low voltage area of signals, obtain a better harmonious wave characteristic, and the transducer can obtain a better output characteristic to the high voltage area, also obtain a high voltage large power output, and simultaneously the transducer has simple control, safety and reliability.

The invention discloses a double-carrier-wave modulation method of a modular multilevel converter. The method comprises two parts, i.e., double-carrier-wave modulation and a voltage balance control method. First of all, according to reference voltages of upper legs and lower legs, quantities of submodules needing to be invested for the upper legs and the lower legs are respectively obtained through the double-carrier-wave modulation, a submodule change quantity needing to be invested at a current control period is further obtained, and then capacitance voltage balance is realized through the capacitance voltage balance control method. An operation condition is determined according to an absolute value of the invested submodule change quantity, only submodules needing switching operation or removal are calculated, the computation complexity is further reduced on the basis that a switch frequency is reduced, and the performance of a control system is improved. The method provided by the invention has the advantages of easy realization, good harmonic wave characteristics, low switch loss and the like.

The invention relates to a DC transformer for the access of new energy to a DC power grid, and an implementation method for the DC transformer. The DC transformer employs an isolation-type DC/DC converter mode, and is characterized in that the DC transformer comprises a low-voltage side full-bridge converter and a high-voltage side modular multi-level converter; the low-voltage side single-phase full-bridge converter and the high-voltage side single-phase modular multi-level converter are connected through a high-frequency transformer. The DC transformer provided by the invention can achieve the interconnection of a new energy DC power generation station with the low voltage level and a DC power grid with the high voltage level. The low-voltage side single-phase full-bridge converter is used for connecting the new energy DC power generation station with the low voltage level. The high-voltage side single-phase modular multi-level converter is used for connecting the DC power grid with the high voltage level.

The invention provides a dual unipolar voltage module chain and a hybrid multilevel converter, and belongs to the fields of a power electronic technology and power transmission and distribution. The dual unipolar voltage module chain consists of N unipolar voltage modules which are connected in series in sequence, wherein the N unipolar voltage modules comprise N1 positive electrode unipolar voltage modules and N2 negative electrode unipolar voltage modules; when a bidirectional current passes through, bipolar voltage output capability is formed; the hybrid multilevel converter based on the module chain at least comprises two same phases, wherein each phase comprises a dual unipolar voltage module chain, a three-level bridge arm and an electric reactor, wherein one port of the dual unipolar voltage module chain is connected with the midpoint of the three-level bridge arm while the other port of the dual unipolar voltage module chain is connected with one end of the electric reactor; and the other end of the electric reactor is connected with an alternating current voltage. By adoption of the dual unipolar voltage module chain and the hybrid multilevel converter, wide-range alternating current-direct current conversion can be realized at a relatively low engineering cost and in a compact occupied space; and meanwhile, high conversion efficiency, good harmonic characteristic and direct current fault ride-through capability are achieved.

The invention relates to a PWM modulation method for improving harmonic characteristic of an output current of a three-phase photovoltaic inverter. According to the method, a sine SPWM modulation wave is injected with third harmonics with smooth waveform to obtain SVPWM modulation wave; the SVPWM modulation wave is adopted for PWM modulation; and the waveform peak value slope in the third harmonics is close to be zero. By adoption of the PWM modulation method, the problem caused by sudden change of the common-mode voltage slope can be solved, the harmonic characteristic of the output current can be improved, and a better modulation effect can be obtained.

A power grid voltage supporting type modularized active power filter and a control algorithm are provided and belong to an active power filter and a control algorithm. The topology of the active power filter is a serial combination structure of a power grid voltage supporting portion and an active filtering portion. Each phase of the power grid and voltage support portion consists of n power grid voltage supporting module units connected in series, and each unit consists of an H-bridge circuit and a shunt capacitor; and the active filtering portion consists of m active filtering module units connected in parallel, and each unit consists of a three-phase full-bridge circuit, an AC filtering inductor and a shunt capacitor. The power grid voltage supporting portion adopts a carrier phase-shifting modulation technique to track a grid-side voltage of a common coupling point, so as to reduce voltage demands at the DC side of the active portion; and the active filtering portion adopts an improved current prediction technique to track a harmonic current, so as to be adapted to the power grid voltage supporting structure. The algorithm has the advantages of low costs, high reliability, strong universality, and easy extension, and can be widely used in harmonic treatments in high voltage and high power occasions such as petroleum mining and precision manufacturing and tiny weak power grids.

One or more embodiments of the invention provide a method and device for controlling a stator flux linkage track of an alternating-current motor. The method comprises the steps of dividing a fundamental cycle of an output voltage of an inverter of the alternating-current motor into a plurality of control cycles, the plurality of control cycles corresponding to a plurality of time steps and respectively denoted as T1, T2,... TN, where N is a positive natural number; determining a stator flux linkage track reference value and a stator flux linkage estimated value corresponding to the current time step; and controlling the track of the stator flux linkage based on an error between the stator flux linkage estimated value and the stator flux linkage track reference value. According to the invention, the technical problems of high sampling rate requirement, large calculation amount and the like in control of the stator flux linkage track in the prior art are solved.

The invention belongs to the field of control, in particular to a current harmonic suppression control algorithm of a four-quadrant converter, and particularly relates to a current low-order harmonicsuppression method for a four-quadrant converter of an electric locomotive. The method is a harmonic suppression method fused in a four-quadrant control algorithm, solves the problems of influence ofcurrent low-order harmonics of the four-quadrant converter on the control of the converter and pollution to the electric energy quality of a power grid, and solves the problem of influence caused by filtering the low-order harmonics by adopting a software filter method. According to the method, a harmonic extraction and suppression function is added to the four-quadrant converter control algorithm, no extra hardware control circuit or device is added, so the method has high adaptability and flexibility, the purpose of harmonic suppression can be achieved, and meanwhile the design cost is reduced.

The invention provides a three-phase CLC immittance converter-based photovoltaic grid-connected topology and belongs to the technical field of photovoltaic power generation. The three-phase CLC immittance converter-based photovoltaic grid-connected topology comprises a parallel photovoltaic array, an LC low-pass filter circuit, a current-type three-phase bridge inverter circuit, a three-phase CLC immittance conversion circuit and a grid-connected circuit, wherein a modulation wave frequency of the current-type three-phase bridge inverter circuit is consistent with a resonant frequency of the three-phase CLC immittance conversion circuit and is equal to a 50Hz grid frequency; and generated power of the parallel photovoltaic array is controlled through regulating a phase of a modulation wave of the current-type three-phase bridge inverter circuit. The three-phase CLC immittance converter-based photovoltaic grid-connected topology has the advantages that the photovoltaic array is connected in parallel, so that additional power loss caused by local shadow shielding can be eliminated; voltage required for grid connection can be obtained without a booster circuit; a relatively high harmonic characteristic can be obtained without a filter circuit; the output power of the photovoltaic array can be controlled through controlling the phase of the modulation wave; and MPPT control is simplified.

The invention provides a cascaded multilevel converter with interconnected single-phase direct-current ports. The cascaded multilevel converter comprises a first single-phase double-winding transformer, two cascaded multilevel voltage source type converter sets and a reactor set located on the alternating-current side of any one or two converter sets. Each cascaded multilevel voltage source type converter set comprises a plurality of single-phase voltage source converters, the alternating current side of the first cascaded multilevel voltage source type converter set is connected to a single-phase power grid power supply through a first single-phase double-winding transformer, and the alternating current side of the second cascaded multilevel voltage source type converter set is connectedto another single-phase power grid power supply. And a direct-current filter bank is also arranged between the direct-current sides of the two cascaded multilevel voltage source type converter banks.And a second single-phase double-winding transformer or an alternating-current filter is arranged on the alternating-current side of the second cascaded multilevel voltage source type converter groupand is used for supplying power to the single-phase passive power grid. The cascaded multilevel converter has the advantages of good harmonic characteristics of alternating current ports on two sides,high operating efficiency in a full-load range, low loss, high reliability in fault locking and redundant operation and the like.

The invention discloses a modular submarine power supply capacitor voltage ripple suppression method and system and a controller, and the method comprises the steps: taking each phase of bridge arm of a modular submarine power supply as a target object, and combining the equivalent capacitance values of an upper bridge arm and a lower bridge arm according to the principle that the upper bridge arm and the lower bridge arm are in parallel connection with the AC side current for shunting; and extracting a circulating current instruction value used for suppressing a capacitor voltage ripple component, obtaining modulation signals of the upper bridge arm and the lower bridge arm, and finally determining that the upper bridge arm and the lower bridge arm are put into sub-modules so as to realize ripple suppression of the capacitor voltage on the premise of meeting the requirements of direct-current side voltage input and alternating-current side voltage output. The problems that capacitor voltage ripples reduce the internal energy stability of the modular submarine power supply and increase the harmonic distortion rate of the output voltage on the alternating current side of the power supply are solved.

The invention discloses a cross-coupled filter, which comprises a minimum resonance structure, the minimum resonance structure is composed of four resonators, in the minimum resonance structure, two resonators in the same row form a group, and the two resonators in the same row are mainly electrically coupled or magnetically coupled; the two resonators in the same column are electromagnetically mixed and coupled; and the coupling polarities of the two groups of resonators of the two rows of resonance units are opposite, and at least one cross coupling is formed. According to the invention, miniaturization and light weight are realized in terms of structural characteristics, and low loss and good harmonic characteristics are realized in terms of electrical performance.