43results about How to "Improve DC voltage utilization" patented technology

The invention discloses a topological structure of a photovoltaic power station system based on bipolar direct-current transmission. The topological structure of the photovoltaic power station system based on bipolar direct-current transmission comprises a positive direct-current transmission line, a negative direct-current transmission line, two groups of photovoltaic inverters which are connected in parallel, and a boosting transformer, wherein each group of photovoltaic inverters comprises a Boost circuit, a direct-current bus, a three-phase bridge inverter and an alternating-current filter which are sequentially arranged along a direct-current transmission direction, and the output ends of the two groups of photovoltaic inverters are connected to the a boost transformer. The topological structure of the photovoltaic power station system based on bipolar direct-current transmission designed by the invention is capable of running simultaneously, and running singly and independently, thus the running reliability is enhanced, a high-power photovoltaic inverter is applicable, the power generation efficiency of a photovoltaic array is further increased, the input range of the direct-current voltage of the inverter is expanded, and the utilization rate of the direct-current voltage of the photovoltaic array is increased; two paths of output are connected with two three-phase windings of a grid-connected transformer, thus the switching frequency can be equivalently increased, and the harmonic waves of a grid-connected current can be reduced.

The invention belongs to a multi-level power converter technique, particularly relating to a topological structure of a cascade multi-level converter. In the invention, the amount of using direct current power supply is reduced under the condition of outputting the level amount which is the same as that output by the traditional cascade type converter. The implementation method is as follows: a capacitance is used to replace the direct voltage source in the traditional topology, and the capacitance voltage is maintained through disconnected charging for the capacitance. The topological structure is mainly used for a high-voltage and high-power situation, and a multi secondary transformer in the original cascade circuit is omitted. Under the condition that small harmonic wave of the traditional multi-level converter is retained and each power transistor only bears the haploid power supply voltage, sine wave output which is triple as big as power supply voltage amplitude can be obtained, and high-capacity and energy bidirectional circulation are easy to realize.

The invention discloses a control strategy for restraining circulating currents of three-phase four-leg inverters on the basis of third-harmonic injection, and provides a method for restraining circulating currents of three-phase four-leg inverters on the basis of third-harmonic injection. The method includes that three-phase current reference signals outputted by voltage loops are synthesized into a zero-sequence current reference signal (4) on the basis (1) of parallel-connection voltage and current double-loop control of the three-phase four-leg inverters for a parallel-connection topology of two three-phase four-leg inverter modules (2) and (3), and error amplifiers track the zero-sequence current reference signal for a mid-line inductive current in a fourth leg of each module, so that mid-line currents of the two three-phase four-leg inverters are shared, and purposes of restraining the circulating currents of the mid-line currents, protecting power tubes and improving the efficiency of each inverter are achieved; and output signals of current loops of the two modules are synthesized to form two third-harmonic signals (5), the two third-harmonic signals (5) are added to obtain a sum (6), an average value (7) of the sum is used as a common third-harmonic signal (8) for being injected into three-phase and mid-line modulation signals of the two inverter modules, zero-sequence modulation components in the third-harmonic signals are eliminated, and the instantaneous zero-sequence circulating currents caused by factors such as inconsistency of parameters of a main circuit filter and inconsistency of switching time of switching tubes are restrained. The method has the outstanding advantages that the circulating currents of the mid-line currents are effectively restrained; control loops are simple; and third-harmonic injection of the parallel-connection inverters is unaffected, and the direct-current voltage utilization rate is increased.

The invention discloses an inverter parallel-connection loop current restraining system based on PR control and dual-carrier modulation. By means of the inverter parallel-connection mode, the power capacity of an inverter system is increased. Meanwhile, a proportion resonance control device is adopted in an inverter, and therefore low-frequency zero-sequence loop currents can be effectively restrained; the dual-carrier modulation method is used, a zero vector is replaced by a non-zero vector so that the high-frequency zero-sequence loop currents can be restrained. The restraining system has the advantages of being high in direct-current voltage utilization rate and small in zero-sequence loop current.

The invention discloses a maximum power point tracking controller for a three-phase photovoltaic power generation system. The controller mainly comprises a BOOST type DC / DC converting circuit, a three-phase inversion circuit, a control circuit and a power circuit. The technical scheme includes that a variable-structure fuzzy control method is applied to MPPT (maximum power point tracking) of photovoltaic power generation so that tracking precision can be improved, and the method can effectively realize maximum power point tracking when illumination and temperature vary. By means of variable-structure fuzzy control, different fuzzy sub-controllers are designed according to different working conditions, the discourse domain range, control rules, parameters and the like of the fuzzy sub-controllers are different, the fuzzy sub-controllers form a variable-structure fuzzy controller, and accordingly one fuzzy sub-controller constantly enables the system to achieve the optimal control quality in system running.

The invention discloses a secondary ripple eliminating circuit of a single-phase PWM rectifier. The secondary ripple eliminating circuit comprises an alternating current side, a converter and a direct current side, the alternating current side is connected with the converter through an inductor, the other side of the converter is connected with the direct current side, a capacitor C2 is connected to the input end of the alternating current side and the negative electrode end of the direct current side, and a capacitor C1 is connected to the input end of the alternating current side and the positive electrode end of the direct current side. According to the secondary ripple eliminating circuit, compared with an original H bridge converter, a filter inductor on the alternating current side is divided into two parts, a capacitor bridge arm is additionally arranged, secondary ripple power is absorbed, the direct-current bus voltage supporting effect is achieved, and therefore the aims of reducing secondary ripples on the direct current side and replacing an original large capacitor on the direct current side are achieved.

The invention discloses a method and system for improving the DC voltage utilization ratio of a three-phase and four-switch fault-tolerant inverter. The method comprises the steps of (S1) calculating and judging whether an unbalanced coefficient epsilon of capacitor voltage at a DC side is zero or not, if so, executing the step (S3), or else, executing the step (S2); (S2) correcting four effective voltage vectors of the four-switch fault-tolerant inverter and calculating corrected voltage vector amplitudes respectively; (S3) calculating a reference voltage vector amplitude; (S4) calculating a modulation ratio parameter M on the basis of the reference voltage vector amplitude; (S5) carrying out modulation area division on a complex plane formed by the four voltage vectors; (S6) setting overmodulation algorithms corresponding to various areas respectively and selecting corresponding vectors to synthesize corresponding compensation voltage vectors; and (S7) calculating action time of two effective voltage vectors corresponding to the compensation voltage vectors and an equivalent zero vector to finish PWM modulation. By the method and the system, the DC voltage utilization rate of the inverter is improved; meanwhile, electromagnetic torque is improved; output harmonics are reduced; and the method is simple and easy to implement in engineering.

The invention discloses a method for suppressing a transient drop of DC voltage of a photovoltaic inverter. The method comprises the steps of (1) calculating differential Udc-d of DC voltage Udc of aninverter in each control period; (2) summing the differential Udc-d of the DC voltage and the DC voltage Udc, producing a difference between the sum and a reference value Udc<*> of the DC voltage toobtain an error of the DC voltage, and obtaining output Udc-out of an outer DC voltage loop through a DC voltage PI controller according to the error of the DC voltage; (3) adding DC all-feedforward iffd to the output Udc-out of the outer DC voltage loop to obtain a reference value i1<*> of an inner current loop; (4) subtracting a current sampling value i1 from the reference value i1<*> of the inner current loop to obtain a current error value, and obtaining controlled quantity of the control period through an inner current loop PI controller according to the current error value; and (5) modulating the controlled quantity to obtain PWM pulses of various switch tubes. According to the method, the transient drop of the DC voltage can be greatly suppressed and the response is fast.

An MMC half-bridge sub-module capacitor voltage ripple multi-scale suppression method comprises the following steps that: a three-phase voltage signal and current signal usj and isj on an alternating-current side, three-phase upper and lower bridge arm current signals ipj and inj and a direct-current bus voltage signal udc are collected, expressions of instantaneous power Ppj and Pnj of an upper bridge arm and a lower bridge arm are obtained through calculation, the sum of the instantaneous power of the upper bridge arm and the instantaneous power of the lower bridge arm is controlled to be zero to obtain circular injection value, modulation functions spj and snj of the upper bridge arm and the lower bridge arm are derived to enable the values to be equal to 0, so as to obtain a function relationship between a moment tmax corresponding to a peak value of a modulation wave and m3 and phi3, and a maximum modulation ratio value and the sum of the number of submodules input by the upper bridge arm and the lower bridge arm at the moment are taken as constraint conditions, so as to obtain an optimal injected third harmonic. Through cooperation of the two injection modes, the DC voltage utilization rate of the MMC can be effectively improved, and it is ensured that the modulation crest value of the system is not increased due to circular current injection, so that a better capacitor voltage fluctuation suppression effect is achieved.

The invention discloses a space vector pulse width modulation (SVPWM) interleaving system and an interleaving control method thereof. The interleaving system comprises a first power module and a second power module, wherein the first power module and the second power module both employ two-level three-phase fully-controlled bridge topological structures. The interleaving control method comprises a starting procedure and an interrupt procedure, wherein the starting procedure comprises energizing the interleaving system, initializing a register, setting a continuous increase and decrease mode of a timer, judging a power module of executing the procedure, inquiring whether the power modules are standard and synchronous or not and enabling the timer to be interrupted, and the interrupt procedure comprises calculating and inputting a modulation wave, performing three seconds coordinate conversion, judging a sector, calculating action time of adjacent vectors and comparing corresponding loading of the register. The interleaving system and the interleaving control method have the advantages that an interleaving idea is transplanted to an SVPWM algorithm, the DC voltage utilization ratio of the interleaving system is improved, and the output waveform quality of the interleaving system is improved.

The invention discloses a power balanced modulation method suitable for a mixed cascaded H-bridge nine-level inverter. The method comprises that an absolute value is taken from a sinusoidal modulatedwave vref to obtain a modulated wave vref2 of a unit 2, and a modulated wave vref1 of a unit 1 and a modulated wave vref0 of an auxiliary unit are obtained via comparison and operation. The modulatedwave vref2 intersects with a comparison level psi2 to obtain a logic pulse signal C, the modulated wave vref1 intersects with the comparison level psi1 to obtain a logic pulse signal B, the modulatedwave vref0 is compared with triangular carrier waves vtra1 and vtra2 to obtain logic pulse signals A1 and A2, and the sinusoidal modulated wave vref is compared with a zero voltage to obtain a polar pulse signal D. A driving logical distribution unit generates an optimized PWM driving signal according to the logic pulse signals and the polar pulse signal. Via the method, it is ensured that the mixed cascaded H-bridge nine-level inverter has a good output characteristic within a full modulation ratio range, power of the two main power units is controlled in a balanced way, and the multi-level inverter is more practical.

The invention relates to a normalized nonlinear PWM carrier modulating method of a current transformer, which belongs to a PWM carrier modulating method of the current transformer, in particular to a nonlinear PWM carrier modulating method of the current transformer. In the method, a feed-forward signal is introduced into direct current bus voltage and is used for processing an original carrier signal, thereby realizing the normalized nonlinear PWM carrier modulation and effectively eliminating the influence brought by ripples on a direct current bus to output control in real time; the method reduces the capacity of a flat wave filter capacitor and the hardware cost; and the method effectively improves the direct current voltage utilization rate of the current transformer, thereby improving the efficiency, power density and integration degree of the current transformer.

The invention is applicable to the technical field of wind power generation, and provides a direct-drive permanent magnet synchronous wind power system and a control method thereof. The system comprises a wind turbine, a direct-drive permanent magnet synchronous wind generator set, a machine-side converter and a nine-switch converter. The nine-switch converter comprises an equivalent grid-side converter and an equivalent dynamic voltage restorer, and is used for converting a direct current output by the machine-side converter into an alternating current for grid connection. The equivalent grid-side converter is used for maintaining the stability of the direct-current side voltage. The equivalent dynamic voltage restorer is used for injecting a compensation voltage when the power grid fails. According to the system, the nine-switch converter is adopted to replace a grid-side converter in a direct-drive wind power system, the grid-connected operation and voltage compensation functions ofthe direct-drive permanent magnet synchronous wind generator set can be achieved, the direct-current voltage utilization rate of the converter is increased by adopting space vector pulse width modulation, and the design value of the direct-current side voltage is reduced.

The invention discloses a three-phase sine wave inverter control method having a high DC voltage utilization ratio, and aims to solve the technical problem of difficulty in online voltage regulation in the prior art. The technical scheme is that through the mixing of switching node preset PWM and unipolar SPWM, the purpose of regulating output voltage by adjusting the modulation ratio of a unipolar SPWM wave is achieved; and meanwhile, when the modulation ratio M of the unipolar SPWM wave is equal to 0, the control method provided by the invention is degraded to the switching node preset PWM, thereby retaining the characteristic of high DC voltage utilization ratio. With the combination of the switching node preset PWM and the unipolar SPWM, the technical problem of difficulty in online voltage regulation for the switching node preset PWM is solved. According to the invention, the output voltage fundamental voltage amplitude and the modulation ratio M are in linear relationship that U1=-1.7299*M+1.0134, and thus the inverter applying the method is allowed to work at low voltage.

The invention discloses a six-phase seven-bridge-arm series winding circuit topology with a reverse winding and a modulation method of the six-phase seven-bridge-arm series winding circuit topology, and belongs to the field of alternating current motors and driving control. The voltage utilization rate is improved by changing the series connection sequence of the phase windings of the six-phase motor and reversely connecting part of the windings. Compared with a wiring mode of a six-phase seven-bridge-arm series winding circuit in which phase windings are sequentially connected in series and [delta]n is equal to 1, the six-phase seven-bridge-arm series winding circuit with the reversely-connected windings is high in direct-current voltage utilization rate and can be applied to application scenes where direct-current bus voltage is limited and the high direct-current voltage utilization rate is needed, such as electric automobiles, ship pushing systems and the like; and compared with a wiring mode of a six-phase eight-bridge-arm series winding circuit with phase windings sequentially connected in series and [delta]n=2, the six-phase seven-bridge-arm series winding circuit with the reversely-connected windings has the advantages that the direct-current voltage utilization rate is the same, the number of required bridge arms is small, the power density is higher, and the cost is lower.

The present invention discloses an AFD (Active Frequency Drift) islanding detection method of a three-phase grid-connected inverter. The AFD islanding detection method comprises three parts consistingof an AFD algorithm based on a phase-locking angle disturbance, blind spot detection analysis and semi-decoupling disturbance control. A three-phase grid-connected inverter play an important part infields of a new energy generation system, an electric car and the like, and islanding detection is very necessary for ensuing safe and stable operation of a system. The AFD islanding detection methodfor controlling a three-phase grid-connected inverter based on space vector pulse width modulation (SVPWM) is provided to apply disturbance to a phase-locking angle calculated by a phase-locked loop (PLL). Causes of formation of an islanding detection blind area are analyzed and possibility of the blind area is eliminated, three-phase currents is subjected to harmonic wave analysis after the disturbance is applied, and an improved semi-decoupling control algorithm for harmonic wave inhibition is provided.

The invention discloses a state observation based IGBT turn-off voltage peak inhibition system and control method. The method comprises the following steps that a controller reads a bus voltage valueVdc and an output current value Ic of an IGBT module within a switching period; the read bus voltage value Vdc and the output current value Ic of an IGBT module within the switching period are analyzed, and a turn-off control instruction is output to a drive board; a multi-level turn-off circuit adds one level of voltage to a gate electrode signal of the IGBT module in the turn-off process, and the drive board adjusts the duration of a voltage Vm of the multi-level turn-off circuit according to the received turn-off control instruction; and the turn-off voltage peak of the IGBT module inhibited via the process in which the multi-level turn-off circuit changes the gate electrode of the IGBT module. According to the IGBT state after observation, the multi-level turn-off circuit is adjusted,the inhibition effect of the IGBT turn-off voltage peak is improved, and the total turn-off delay time and total turn-off loss of the IGBT are reduced effectively.

The invention discloses a 66kV collection access-based flexible direct-current offshore converter station, a system and a control method, and the flexible direct-current offshore converter station is characterized in that the offshore converter station comprises a connection transformer, a flexible direct-current converter valve and a bridge arm reactor, wherein the primary side of the connection transformer is connected with a bus bar of an offshore wind plant; the primary side is connected with the input end of the flexible direct current converter valve, the output end of the flexible direct current converter valve is connected with the first end of the bridge arm reactor, and the second end of the reactor is connected with the direct current submarine cable. And the investment and maintenance cost of an offshore booster station is saved. By increasing control strategies, increasing module voltage, reducing the total number of converter valve modules, reducing capacitance value, improving transmission capacity of equipment and reducing size and weight of an offshore wind power plant, the problems of land occupation, large load, high cost and the like of an offshore converter station can be effectively solved, technical cost of engineering implementation is remarkably reduced, and the method is suitable for large-scale popularization and application. The method has better economical efficiency and is of great significance to large-scale development and utilization of offshore wind power.

The invention belongs to the technical field of AC-DC-AC electric drive, and discloses a bi-directional power conversion AC based on IGBT. DC control system and method, The control system is providedwith an access terminal, a first high-voltage start-up switch tube, a circuit control terminal, a current source, a second high-voltage start-up switch tube, a monitoring device, a terminal, an upperswitch group, an isolator, a control system, a controllable switch, a power supply module, a comparator, a lower switch group, a three-phase inverter, a diode group, a display screen, a voltage sensor, a temperature sensor and a current sensor. The control system of the invention adopts a voltage outer loop and a current inner loop double closed loop system, wherein the voltage outer loop controlsthe output voltage and the current inner loop controls the input current, so as to realize the correction of the unity power factor. The DC system can be reassembled in multiple sets and the controlterminals are reserved, which can be distributed intelligently according to the BMS system and the current load level for the convenience of users.

The invention discloses a control strategy for restraining circulating currents of three-phase four-leg inverters on the basis of third-harmonic injection, and provides a method for restraining circulating currents of three-phase four-leg inverters on the basis of third-harmonic injection. The method includes that three-phase current reference signals outputted by voltage loops are synthesized into a zero-sequence current reference signal (4) on the basis (1) of parallel-connection voltage and current double-loop control of the three-phase four-leg inverters for a parallel-connection topology of two three-phase four-leg inverter modules (2) and (3), and error amplifiers track the zero-sequence current reference signal for a mid-line inductive current in a fourth leg of each module, so that mid-line currents of the two three-phase four-leg inverters are shared, and purposes of restraining the circulating currents of the mid-line currents, protecting power tubes and improving the efficiency of each inverter are achieved; and output signals of current loops of the two modules are synthesized to form two third-harmonic signals (5), the two third-harmonic signals (5) are added to obtain a sum (6), an average value (7) of the sum is used as a common third-harmonic signal (8) for being injected into three-phase and mid-line modulation signals of the two inverter modules, zero-sequence modulation components in the third-harmonic signals are eliminated, and the instantaneous zero-sequence circulating currents caused by factors such as inconsistency of parameters of a main circuit filter and inconsistency of switching time of switching tubes are restrained. The method has the outstanding advantages that the circulating currents of the mid-line currents are effectively restrained; control loops are simple; and third-harmonic injection of the parallel-connection inverters is unaffected, and the direct-current voltage utilization rate is increased.

The invention discloses a converter circuit based on nine-switch structure. The converter circuit includes an input power supply, an output end and 9 same module circuits which are arranged between the input power supply and the output end and serve as power elements. Each module circuit includes a module circuit input power supply, a power circuit and an output port which are successively connected. Along with the changes of the power circuit, each module circuit has at least circuit modals that the voltage of the output port are positive input power supply voltage, inverted input power supply voltage and zero potential. The replacement of the original power switch tube in the converter with the module circuits which have a plurality of circuit modals enables the module circuits to adopt specific control and control the module circuits to enter different circuit modals, and the output of multiple port voltages effectively increases utilization of DC voltage of a busbar and increases output electrical levels.

The invention discloses a control system for a three-phase cascaded multilevel photovoltaic grid-connected inverter. The control system comprises a master controller, an optical fiber communication unit, multiple sub controllers, first drivers, second drivers, a zero-crossing comparator and a voltage transformer. The master controller is connected with all the sub controllers through the optical fiber communication unit. The sub controllers are used for driving signals of DC-DC modules to be directly connected with the second drivers, the sub controllers are used for driving signals of DC-AC modules to be multiplied by output signals of the zero-crossing comparator and then to be connected with the first drivers. The control system for the three-phase cascaded multilevel photovoltaic grid-connected inverter is simple in structure and convenient to operate, independent control over all the DC-DC modules and all the DC-AC modules of the three-phase cascaded multilevel photovoltaic grid-connected inverter can be achieved, work of different modules in the same phase does not affect each other, the three-phase inverter is totally independently controlled, the reliability and the stability of a circuit are improved, the DC voltage utilization rate of the controlled three-phase cascaded multilevel photovoltaic grid-connected inverter is high, the switching frequency of a switching pipe is low, and the system energy utilization rate is high.

A unidirectional hybrid three-phase three-level rectifier is composed of a three-phase rectifier bridge, a filter, a boost circuit, a voltage sensor, a current sensor, a DSP controller, and a signal conditioning circuit for closed-loop control. The rectifier consists of five modules. A module 1 is composed of a filter inductor. A module 2 and a module 3 are respectively a three-phase diode rectifier bridge and a three-phase IGBT rectifier bridge. A module 4 is an IGBT boost circuit. A module 5 is a filter capacitor. The rectifier is mainly characterized in that a diode bridge rectifier circuitand a PWM rectifier circuit are combined, control and voltage output are stable, the rectifier has excellent power tracking ability and strong robustness, and harmonic components are reduced.

The invention discloses a tap inductor-type Z source inverter, which comprises a DC power supply Udc, a three-phase inverter and an inductor tap Z source network, wherein the output end of the DC power supply Udc is connected with the input end of the inductor tap Z source network; the output end of the inductor tap Z source network is connected with the input end of the three-phase inverter; the output end of the three-phase inverter is connected with a power grid or a load; the inductor tap Z source network comprises a tap inductor Lt, a diode Din, a diode D1, a diode D2, a capacitor C1, a capacitor C2 and an inductor L3; and the tap inductor Lt comprises a winding N1 and a winding N2. The tap inductor-type Z source inverter can be used in situations of power generation and grid connection of new energy sources and motor drive and has the advantages of high step-up ratio, small capacitance voltage stress, high DC voltage utilization rate, small start impact and the like.