31results about How to "Reduce output harmonic content" patented technology

The invention provides an electromagnetic mixed compensation system for quality of electric energy in electrified railways. The electromagnetic mixed compensation system comprises an RPC, two MSVCs and a V/V traction transformer. The V/V traction transformer is in a V/V type formed by connecting two single-phase transformers. The primary side of the V/V traction transformer is connected to a three-phase public power grid, and traction power supply arms serve as two output ends of the secondary side of the V/V traction transformer. Each MSVC comprises a magnetic controlled reactor, a third single harmonic filter branch circuit and a fifth single harmonic filter branch circuit, and the magnetic controlled reactor, the third single harmonic filter branch circuit and the fifth single harmonic filter branch circuit are connected in parallel. The RPC comprises two H-bridge converters with a shared direct-current side. The MSVCs and the RPC are used in cooperation with each other, and therefore the problem of unbalanced harmonic and negative sequences of the electrified railways is solved. Due to the adoption of MSVC and RPC mixed compensation, compensation capacity of the RPC is effectively reduced, and the construction cost of the system is accordingly reduced.

The invention discloses an all-digital naturally sampling SPWM control method and system based on FPGA, the concrete control method comprises the steps as follows: generating the synchronizing signal; accumulating the address for the sine modulation wave to obtain the sine function value of the sine modulation wave of current region; determining the region of the current switch state according to the sine function value of the sine modulation wave and triangular carrier slope state, the sine modulation wave and triangular carrier slope are different in different regions; taking the clock signal of FPGA as the standard, fast sampling sine wave and triangular wave and comparing the value, using the counter for counting the clock signal; stopping comparing while the relationship of the sine modulation wave and triangular wave changes and recording the number of clock signal, determining the start and stop ideal value for the part according to the number of clock signal; adjusting the start and stop ideal value to obtain the actual start and stop time for realizing the symmetry dead zone.

The invention relates to a three-level ANPC convertor neutral-point voltage balance control method. The method comprises the following steps of (1) acting on a three-level ANPC convertor through an SVPWM (space vector pulse width modulation) pulse sequence; (2) detecting the voltage of the direct current side capacitor of the convertor in real time to obtain a neutral-point voltage, and comparing the neutral-point voltage with a reference neutral-point voltage to determine whether the direct current side capacitor requires charging or discharging; (3) in real time detecting the positive and negative direction of the three-phase load current of the convertor; (4) integrating detecting values of the steps (2) and (3), within every switching period, dynamically adjust the duty ratio of the zero state of the switch sequence of a three-phase bridge arm until neutral-point voltage balance, and repeating the step to maintain fluctuation of the neutral-point voltage within a relatively small range. The three-level ANPC convertor neutral-point voltage balance control method can dynamically adjust the charging and discharging time of the capacitor according to the direction of the three-phase load current and the size of the neutral-point voltage to rapidly balance of the neutral-point voltage and to maintain fluctuation of the neutral-point voltage within a relatively small range.

The invention provides a low frequency model predictive control method based on a hybrid modular multilevel converter. A low frequency model predictive control policy based on upper, middle and lowerlayer control is realized. The upper-layer control establishes an index function and selects a bridge arm output level which meets current, circulating current and bridge arm capacitor voltage controlrequirements of the alternating current side. The optimization calculation amount is effectively reduced. The middle-layer control uses an H-bridge module control algorithm to stabilize the H-bridgemodule capacitor voltage. The equivalent output level is calculated. The number of switching of a bridge arm half-bridge sub-module is determined. The lower-layer control determines the switching signal of each sub-module according to the optimization control policy of the sub-module capacitance voltage. Balance control of the sub-module capacitance voltage is realized. The average switch frequency of sub-modules is reduced.

The invention provides a grid-connected inverter circuit and a control method thereof. The grid-connected inverter circuit comprises an inverter, an (N+1)-port transformer, a 2N-phase rectifier, 2N voltage dividing capacitors and a (2N+1)-end inverter; direct-current voltage is subjected to high-frequency inversion via the inverter to generate high-frequency square wave, the high-frequency square wave passes through the (N+1)-port transformer to boost the voltage into voltage of N voltage levels, the square wave of the N voltage levels is respectively rectified to form voltage of 2N different levels, the voltage of 2N different levels and a zero potential grounding point form (2N+1) level branches, the levels are isolated by the capacitors connected in series longitudinally and charge the capacitors, and the (2N+1) level branches are respectively connected with the (2N+1)-end inverter. The whole circuit adopts multi-level inversion, so that the content of output harmonic is greatly reduced, additional high-capacity filters are not needed, and the structure is simple.

The invention discloses a high-performance test system for a pump. The system comprises an incoming power supply cabinet, a frequency conversion system, an outgoing power distribution system and a test console. The outgoing line power distribution system is connected with a motor; the motor is connected with a pump; the inlet wire power supply cabinet is connected with the frequency conversion system through a cable. The frequency conversion system is connected with the outgoing line power distribution system through a cable, the incoming line power supply cabinet, the frequency conversion system, the outgoing line power distribution system, the motor and the pump are connected with the test console through cables and communication lines, and the test console is used for detecting signalsof the incoming line power supply cabinet, the frequency conversion system, the outgoing line power distribution system, the motor and the pump and feeding back the signals. The invention provides a high-performance test system for a pump, which not only can complete a conventional function test and a performance test of the pump according to the requirements of a pump test working condition, butalso can meet the test requirements of a pump with a wide capacity range and multiple voltage classes, and is low in cost and small in space occupation ratio.

The invention discloses an orthogonal iron core type controllable electric reactor with a wedge-shaped groove and an equivalent magnetic path length calculating method of the orthogonal iron core type controllable electric reactor with the wedge-shaped groove under direct-current magnetic bias. The controllable electric reactor comprises a working iron core and a control iron core with the wedge-shaped groove. According to the controllable electric reactor and the equivalent magnetic path length calculating method, as the wedge-shaped groove is formed in the control iron core, the harmonic content output by the controllable electric reactor can be effectively reduced, the defect that a traditional electric reactor is high in harmonic content is overcome, and the working performance of the electric reactor is improved. Meanwhile, simulation software ANSOFT special for an electromagnetic field is adopted to calculating the alternating current equivalent magnetic path length, data of the magnetic induction intensity on a specific cross section in the orthogonal iron core type controllable electric reactor are derived and processed according to a studied algorithm, and the equivalent magnetic path length is accordingly calculated. By means of the method, errors, caused by unclear magnetization conditions of the internal iron cores, of calculation of the equivalent magnetic path length in a traditional method are reduced, the alternating current magnetization curve of the electric reactor has the higher scientificity accordingly, and guarantees are provided for studying the iron consumption and other characteristics of the orthogonal iron core type controllable electric reactor.

The invention discloses a common direct-current bus bidirectional converter and a control method thereof. The bidirectional converter mainly comprises an active and reactive controller, a CPS-SPWM controller and a plurality of converter modules. The control method mainly comprises the following steps: judging whether a load is accessed to a direct-current bus or not; if yes, detecting the number of converter modules connected to the system; judging whether an alternating-current power grid needs active feedback or not; if the alternating-current power grid does not need active feedback, controlling all the modules connected to the system in a voltage and current double-closed-loop mode, controlling all the modules through the same reference voltage, or else, averagely distributing active power needing to be fed back to all the working converter modules, changing the feedback current direction of the working converter modules, and then adopting power outer-loop current and inner-loop double-closed-loop control; when no load exists, judging whether the alternating-current power grid needs electric energy quality management or not, and if yes, adopting a voltage and current double-closed-loop control method under a d-q coordinate system, and adding reactive power and harmonic waves needing to be output into current loop control; and if not, only keeping the direct-current voltage.

The invention discloses an output harmonic suppression method for an H-bridge cascaded static synchronous compensator, and the method sequentially comprises the following steps: adding a voltage feedforward control link on the basis of CPS-SPWM modulation; dividing the average voltage control of each section of direct-current capacitor into average control and balance control; optimizing the modulation performance of the output harmonic suppression of the H-bridge cascaded STATCOM; adding a current decoupling control link; taking a dq-axis component output by the low-pass filter as a referenceinstruction current for PI feedforward decoupling control; controlling the compensation signals to achieve current static-error-free tracking and harmonic treatment. Independent control and trackingof parameters are achieved, the quality of voltage and current output by the compensator is improved, then the output harmonic content of the static synchronous compensator is reduced, and the controlperformance of the static synchronous compensator is optimized.

The invention discloses a T-shaped multi-level inversion circuit, and the circuit comprises two T-shaped three-level circuits, two switching tubes, two pairs of reverse parallel switching tubes, and an LC filter circuit. The input power heteropolarity ends of the two T-shaped three-level circuits are connected through the two switching tubes, and the two pairs of reverse parallel switching tubes enables the homopolarity input power ends of the two T-shaped three-level circuits to be connected. The LC filter circuit is connected to central nodes of inversion bridge arms of the two T-shaped three-level circuits, and the ratio of the input power voltages of the two T-shaped three-level circuits is 5. The circuit generates more levels through fewer switching tubes, greatly reduces the number of power switching tubes, further reduces the cost of a multi-level inverter, improves the efficiency of the inverter, and reduces the switching frequency.

The invention discloses a method for series triple-phase hopping AC-AC frequency conversion. A main frequency conversion circuit is formed on the basis of the same circuit as the traditional series triple thyristor AC-AC frequency conversion method, the frequency conversion control is carried out by an innovative method called phase hopping frequency conversion, the idea of frequency conversion control is to control each circuit separately, a pair of thyristors in a positive group and a negative group are simultaneously triggered for each repetition, communicating an output of the heavy circuit with a phase input of the heavy circuit, and the second trigger is carried out after a time interval related to the desired output frequency, so that the re-output terminal is connected with the next phase input, and the phase of the output voltage is continuously hopped by constantly switching the connection relationship, thereby obtaining the effect of changing the output frequency as a whole.At the same time, the phase of the output voltage of each multiple circuit is arranged according to the requirement, and the magnitude of the total output voltage is regulated by the vector superposition of the output voltages of each multiple circuit. The method has the advantages of low cost and high reliability.

The invention discloses a transformer-free three-phase DC-AC convertor for a direct-current micro grid. The transformer-free three-phase DC-AC convertor for the direct-current micro grid comprises at least two DC-AC conversion units which are connected in parallel in a fault-phase mode. In addition, the DC-AC convertor can be automatically controlled by adopting a CPU through a PWM control technology. According to the transformer-free three-phase DC-AC convertor for the direct-current micro grid, a transformer does not need to be inserted between a direct-current bus and a low-voltage grid, the DC-AC convertor can work within the best modulation rate range, the convertor efficiency is improved, and harmonic wave output is reduced.