76results about How to "Reduce output harmonics" patented technology

The invention discloses a large-capacity battery converter and control method thereof. The converter of the invention comprises several branch single stage type DC/AC converter modules parallel to one another. Each battery cluster (Battery Cluster BC) converges energy to an AC bus via each branch single stage type DC/AC converter module to be transformed in voltage in order to connect to an AC grid or to operate independently with load. The invention solves the circular current and uniform current problems brought by serial and parallel connection of the battery cluster, and adopts the technology of module combination and alternate balance to effectively improve the system efficiency under low power and power quality at the AC and DC sides and to realize balanced use of the battery cluster. Each battery branch can conduct intelligent charge and discharge management and the control function and the protection function are configured independently to ensure the largest availability of the system. The invention has simple structure, small volume, small energy loss, easy modularization, high reliability, small output harmonic wave, good system expansibility and low requirement to insulating ability of the converter and can operate with reduced capacity when the unit is in failure. The control method of the large-capacity battery converter of the invention is convenient and simple in operation and easy in realization.

The invention discloses a method for detecting an island of a photovoltaic grid-connected inverter. The method comprises the following steps of: 1), detecting a voltage frequency at a common coupling point of the inverter and a power grid, wherein when the voltage frequency is between f11 and f12, a phase position of output current of the inverter is the same to that of voltage at the coupling point; and, by modifying the phase position between the output current of the inverter and the voltage at the coupling point, compared with the voltage at the coupling point, the output current is ahead of time in theta degrees (when fgrid is more than f12 and less than f22) or lags in theta degrees (when fgrid is more than f21 and less than f11); and 2), to compensate a dead zone appeared in frequency detection, judging whether an island effect exists by modifying an amplitude value of the output current of the inverter within one power frequency period after every four power frequency periods and recovering the amplitude value of the output current into an original value after the period. According to the method, harmonic waves output by the inverter to the power grid can be effectively reduced; the detection time is short; the calculation method is simple; and the computing resource of a control chip can be saved.

The invention relates to a unified power flow controller based on a modular multilevel converter structure. The unified power flow controller comprises a static synchronous compensator and a static synchronous series compensator, wherein positive and negative buses of the static synchronous compensator are connected with positive and negative buses of the static synchronous series compensator; and an output end of the static synchronous compensator and an output end of the static synchronous series compensator are respectively connected with a power grid. According to the invention, as a modular-mode cascaded form is adopted, the requirements on components are reduced; a modular design is realized, the integrated level is high, and the design is convenient; through a design on a bridge arm, an effect of individual-phase control is achieved; through using a redundancy technique, a fault unit can be bypassed, thereby improving the operation reliability of a device; in an original technique, for reducing the outputting of harmonic waves, a scheme of connecting IGBT (insulated gate bipolar translator) devices in series is usually high in switching frequency, therefore, the loss of the device is large; in the invention, a modular multilevel technique is adopted, so that the switching frequency of each component is low, but an effect of extremely high external equivalent switching frequency can be achieved, and the outputting of harmonic waves is reduced, therefore, the device is low in running loss.

The invention discloses a reactive power control circuit of a single-phase photovoltaic inverter. The reactive power control circuit comprises a bus voltage supporting capacitor, a single-phase full-bridge inversion circuit, a filtering inductor, an EMC (Electro Magnetic Compatibility) filtering circuit, a sampling circuit, a power switch pipe driving circuit and a DSP (Digital Signal Processor), wherein the DSP consists of a PLL (Phase Locked Loop) control module, a voltage outer ring PI control module, a current inner ring PI feedforward control module and a sinusoidal PWM (Pulse-Width Modulation) wave sending control module, and an input signal of the sinusoidal PWM wave sending control module of the DSP further includes a current inner ring current given amount Ig. The invention further provides a reactive power control method of the single-phase photovoltaic inverter. The method not only can be used for judging whether the voltage Uac of a power grid is larger than zero, and comparing the absolute value of a PWM wave sending control input modulation wave Upwm with a given triangular carrier wave Uc, but also can be used for judging whether the given current inner ring current amount Ig is larger than zero. Not only can the conduction loss of a power switching tube be reduced, and the conversion efficiency of the inverter is improved, but also the current waveform can be continuous, an output harmonic wave is reduced, and the pollution on a harmonic wave of a power grid is reduced.

The invention discloses a photovoltaic grid-connected inverter. The photovoltaic grid-connected inverter comprises a photovoltaic array, a plurality of unit bodies, three unit body series branches, an alternating current reactor, a grid-connected switch, unit body controllers and a master controller, wherein the preceding stage of each unit body is respectively connected with the photovoltaic array; the unit body series branches are connected into a power grid after being connected with the alternating current reactor and the grid-connected switch in series; and each unit body comprises one of the unit body controllers. The invention also discloses a photovoltaic grid-connected inverter control method. In the inverter and the control method disclosed by the invention, the unit bodies are connected in series instead of directly connecting power devices in series, so that the problem of voltage-sharing of devices are solved; the power level is high; the limitation of load capacity of power electronic devices is overcome; a unit phase shift wave overlapping technology is adopted, so that an output harmonic wave is small; because of the action of an energy storage battery, when illumination disappears suddenly, a system cannot be off-grid and standby suddenly; and because of adopting a unit body automatic bypass technology, the security of the system is improved.

The invention provides an HVDC (high voltage direct current controller) and UPFC (unified power flow controller) system based on a modularized multi-level converter. The HVDC and UPFC system comprises converting devices (1, 2 and 11), grounding circuits (3 and 12) and a direct current transmission line (13). The UPFC is formed by the converting device (1) and the converting device (2). The HVDC is formed by the converting device (1) and converting device (11). The HVDC and the UPFC shares one converting device, so that cost and investment for engineering construction are saved, equipment utilization rate is improved, concentrated management and control are facilitated. The converting devices use the topological structure of the modularized multi-level converter, so that technical difficulty in component serial connection is avoided, split-phase control and modularization are facilitated, fault units can be bypassed through redundancy, operation stability of the devices is improved, on and off frequency of components is low, and device operation loss is low.

The invention relates to a unified power flow controller used for an unbalanced system. The unified power flow controller comprises a static synchronization compensator and a static synchronization series compensator. An upper part split capacitance and a lower part capacitance are arranged between the static synchronization compensator and the static synchronization series compensator. The upper part split capacitance and the lower part split capacitance are connected in series and then respectively connected with the static synchronization compensator and the static synchronization series compensator in parallel. The upper part split capacitance and the lower part split capacitance are connected in series and then a split capacitance branch circuit is formed. A midpoint of the split capacitance branch circuit is connected with a neutral point of the static synchronization series compensator. Output ends of the static synchronization compensator and the static synchronization series compensator are respectively connected with a power grid. The unified power flow controller is convenient to split-phase control and modularization design, small in running loss, good in voltage control capacity, good in zero-sequence current controlling, few in element quantity, low in cost and high in cost performance.

The invention relates to a control system and a control method of a permanent magnet synchronous motor of a series-connected cascade-type multi-level converter and belongs to the field of power electronic control technology, and solves the problem that traction motors are huge in harmonic wave output and low in output power quality in the existing new energy electric cars, so that safety and comfortableness of new energy electric cars are affected. In the invention, traditional traction motor driver structure is abandoned, topology of the series-connected reaction type multi-level converter is provided, high-performance drive control of the motor can be realized and the problem of single direct-current power supply is solved, the control method is optimized, and more reasonable multi-level current wave form output design is provided according to different requirements of current harmonics to built-in permanent magnet synchronous motors in low speed, middle speed and high speed. The control system and the control method of the permanent magnet synchronous motor of the series-connected cascade-type multi-level converter are applicable to new energy automobiles which need high-efficiency and high-performance output, and single power to supply energy source.

A sequence mapping circuit and method for digital audio circuits generates a pulsed output. Over time, the mapping circuit generates pulses with a substantially identical average centroid for each of the possible output waveforms. For at least some of the output waveforms, two or more sets of pulses are provided representing the same waveform but having different centroids. The output is alternated among the available sets of pulses to maintain the desired average centroid over time. Shuffling of the output among the available pulses representing a given waveform may be randomly determined, or the pulses used may be tracked and the output pulses sequentially alternated among the available output pulses. The shuffled mapping method reduces output harmonics compared to conventional static mappers.

The invention relates to a frequency converter, in particular to a high-voltage matrix converter. At present, frequency converters are high in cost, large in size, short in service life, high in output voltage harmonics and low in power factor. The high-voltage matrix converter comprises a phase shift isolation transformer, a matrix transformation unit array and a general controller, wherein the phase shift isolation transformer is provided with 3n three-phase secondary windings, and the matrix transformation array is of array structure formed by arranging 3n matrix transformation units in a mode that 3 rows time n lines. In the matrix transformation unit array, power output ends of the matrix transformation units of each row are serially connected, each matrix transformation unit is composed of an input filter, a power switch array and sub-controllers. Power wires of the sub-controllers are connected with any two or three phases in input ends of preceding-stage three-phase bridge rectifying circuits in the power switch arrays, and signal wires of the sub-controllers are connected with the power switch arrays. The high-voltage matrix converter is low in cost, small in size, long in service life and easy to realize energy feedback, and the frequency converters are safe and stable in operation and low in cost.

The invention discloses a grid connected inverter, which comprises an alternating current output filtering unit, a data acquisition unit and a controller, wherein the data acquisition unit is used for acquiring the output current of a three-phase inverter bridge and outputting the acquired current data to the controller; the alternating current output filtering unit comprises at least one LC filter or LCL filter; the inductive branch of each LC filter or each LCL filter is connected in series with at least one second inductor; the capacitive branch of the LC filter is connected in parallel with at least one second capacitor. In the grid connected inverter disclosed by the invention, combined filtering is realized only by adopting two switching devices, thereby reducing the using number of the switching devices and reducing the cost. By adopting the output filtering method provided by the invention, output harmonic in case of low output current is reduced, and the conversion efficiency in case of low output current is increased.

A method for converting medium and high voltage is as follows: 1. turn the input medium and high AC voltage to N channels of AC circuit 2. turn NAC channels to high frequency AC circuit 3. process every channel of high-frequency AC circuit for step transform by high frequency transformer then to be overlapped after rectification-inversion transformation to output the AC circuit with required frequency and amplitude. The device includes symmetrical same input and output transformation step (formed by N step same power serial transforming modules) and middle isolated transforming step made up of N high-frequency transformers and the outputs of which are coupled to output transforming step by high-frequency transformer.

The frequency converter (FC) includes rectification unit (RU), DC unit, two pieces of inversion unit with three electrical levels (IUTEL), and two pieces of LC filtering unit with three phases (FUTP). Positive and negative bus bars of RU are connected to positive and negative ends of DC unit respectively. Two pieces of inversion unit are connected to each other in parallel. Positive bus, negative bus, and neutral point of IUTEL are connected to a group of positive bus, a group of negative bus, and a neutral point of DC unit respectively. The output ends of IUTEL are connected to the input ends of two pieces of LC FUTP respectively. The output ends of two pieces of LC FUTP are connected to two groups of three phase winding taps in electromotor respectively. Based on phase shift of carrier wave, the invention makes frequency of equivalent switch of FC rise one time so as to reduce harmonic content of input voltage of electromotor, and raises efficiency of FC effectively.

The invention discloses a clamping cascading frequency-multiplication multi-level power converter and a control method thereof. The converter comprises multiple cascaded inversion modules. Each cascading module comprises a clamping five-level H bridge inversion unit. A high voltage direct current source is connected to the input end of an inverter. A voltage average resistor is used for balancingthe direct current input voltage of each module and carrying out switching control of each module IGBT, so it is achieved that a single module outputs five-level stair waves. Through superposition ofthe waveforms output by the modules, multi-level voltage output is formed. In the control method, by setting different module carrier wave phase position initial values, PWM control signals of the IGBTs are output asynchronously and voltage stair waves output by the modules are serially connected and superposed, so multi-level output voltage is formed. According to the invention, by use of the modularization design, through the modularization cascading, increasing of the number of stairs of the output stair waves is achieved; switching frequency of the IGBTs is reduced; switching loss is reduced; and output harmonic waves are greatly reduced.

The invention relates to an SVG device-based method for improving the low voltage ride through capability of a wind farm. A static dynamic reactive power compensation device SVG is connected to an outgoing line side of a new energy power station in parallel; and the static dynamic reactive power compensation device SVG dynamically adjusts reactive power output of the tail end in real time according to the control mode issued by a system dispatcher and the monitored operating condition in the power station and compensates reactive power of line transmission and reactive power loss of a main transformer in the power station. By the SVG device-based method, the operating performance of a power grid system can be improved; and the plant factor of the wind farm is improved.

The invention relates to the technical field of new energy generation and particularly relates to a DC bus voltage control-based tidal current generation control system and a DC bus voltage control method thereof. The system comprises a water turbine, a permanent magnet direct-drive generator, an uncontrollable rectifier device, a filter device, a battery cabinet, a three-phase inverter, an ashore switch cabinet, a main control system, an energy release unit and the like. The main control system is the core part of the tidal current generation control system. The main control system is composed of a DSP 2406 chip. The DSP 2406 chip comprises an A/D conversion module, an I/O module, an encoder interface and an RS 232 serial port. The main control system controls the on/off time of an IGBT in real time, the power supply of the battery cabinet and the extra power consumption of the energy release unit, so that the voltage pressure of the three-phase inverter in a power electronic system is effectively reduced. The system is strong in flexibility. The power generation efficiency of the entire power generation system is improved.

The invention relates to a five-level topological structure used for a power conversion system. The five-level topological structure comprises twelve switch tubes, four bus capacitors and two clampingcapacitors, wherein the first to the fourth switch tubes, the seventh to the eighth switch tubes and the eleventh to the twelfth switch tubes are connected to form two T-shaped units which are connected onto a direct-current bus in parallel; a clamping resistor, a first switch tube group and a second switch tube group are arranged between the two T-shaped units; the four bus capacitors are connected onto the direct-current bus in parallel after being connected in series; the first switch tube group is serially connected among the second bus capacitor and the third bus capacitor on the direct-current bus and the clamping capacitors on the upper side and the lower side, the second switch tube group is serially connected among the second switch tube, the third switch tube and the two clamping capacitors, and an output terminal is led out between the second switch tube and the third switch tube. According to the five-level topological structure, the control process is simplified, the quantity of the switch tubes in changing on-off state in the level conversion process is reduced, the five-level topological structure has preferable fault-tolerant operation capacity and reliability, thecontrol mode can be adjusted flexibly, the dead zone effect is eliminated effectively, and the five-level topological structure can be widely applied to power conversion devices such as inverters andfrequency converters.

The invention provides a method, a device and a system for eliminating a narrow pulse in two-level SVPWM modulation and an inverter. A narrow pulse determination amount Dmin is preset to judge whetherthe narrow pulse exists in three-phase voltage duty ratios Ta, Tb and Tc obtained by a SVPWM modulation algorithm. If the narrow pulse exists, a average value Tav of the three-phase voltage duty ratios Ta, Tb and Tc is calculated, and a compensation amount T0 is determined according to the Tav. The three-phase voltage duty ratios Ta, Tb and Tc are compensated, and whether the compensated three-phase voltage duty ratios Ta, Tb and Tc still have the narrow pulse is determined. If so, an over-modulation region of SVPWM is entered into, the narrow pulse is directly eliminated, and a hexagonal wave is modulated and output by using DPWM. In the method, the narrow pulse is eliminated when SVPWM modulation cannot satisfy a control requirement due to a fact that the narrow pulse is identified andjudged, and a special hardware circuit does not need to be added so that a failure rate of a power device is reduced, a bus voltage utilization rate is increased, and an output harmonic wave is reduced.

The invention discloses a three-level power unit main circuit which comprises the components of two wire inlet end circuits; two rectifying circuits, wherein each rectifying circuit is parallelly connected with one wire inlet end circuit; two filtering capacitors, wherein each filtering capacitor is connected with one rectifying circuit and the two filtering capacitors are serially connected; an inverter circuit which is a three-level H bridge, wherein the two filtering capacitors are parallelly connected with the DC input side of the three-level H bridge; and a wire outlet end circuit which is parallelly connected with the AC output side of the three-level H bridge. The three-level power unit main circuit is advantageous in that the two rectifying circuits are used for rectifying, thereby effectively settling midpoint voltage fluctuation and eliminating harmonic pollution of a variable-frequency speed regulating device to a power grid; smaller number of power units, more compact power unit structure, easier power unit realization, effective output level number increase and low output harmonic wave of the power unit are realized, thereby obtaining better user-friendly performance to motor insulation.