33results about How to "Capacitor voltage equalization" patented technology

The invention discloses an optimal pressure equalizing control method of a modular multilevel converter type direct current transmission system. By setting an upper limit and a lower limit on voltage, the pressure equalizing control is mainly carried out on submodules with out-of-limit capacitor voltage, and capacitor voltage sequencing for submodules with no out-of-limit capacitor voltage is processed by combing the charging/discharging conditions of bridge arm current so as to increase the probability of maintaining an original switching state for the submodules with no out-of-limit capacitor voltage when the next action is in triggering control and lower the switching frequency of devices. The introduction of the pressure equalizing control can not lower the working frequency of triggering control and the tracking speed of a converter by using submodule capacitor voltage sequencing and triggering control to work at different frequencies. The optimal pressure equalizing control method of the invention can greatly lower the switching frequency of the devices on the premise of having no obvious increment on submodule capacitor voltage fluctuation.

The invention discloses a parallel active filter based on a modularization multi-level converter and a control method of the parallel active filter and belongs to the technical field of power harmonic suppression in a medium-high voltage high-power occasion. The problem that an existing parallel active filter cannot carry out harmonic combination compensation effectively, so that power distribution network electric energy quality is poor is solved. The filter comprises the modularization multi-level converter, a current transformation unit, a harmonic current detecting unit, a current controller, a capacitor C and a power grid electric reactor LS. The modularization multi-level converter is of a half-bridge-type topological structure, and an upper bridge arm and a lower bridge arm of the modularization multi-level converter respectively comprise n submodules SMn. According to the control method, a carrier phase-shifting modulation method is used, so that under the same switch frequency, equivalent switch frequency is high, switching loss is reduced, meanwhile, a capacitive coupling voltage sharing and ring current suppression strategy is used, and capacitor voltages and direct current bus voltages of the submodules are kept stable. The parallel active filter is used for harmonic suppression of a power grid.

The invention discloses a multi-power-supply gridconnected system control method based on a modularized multilevel convertor. The multi-power-supply gridconnected system control method comprises the following steps: the power control part of the modularized multilevel convertor generates a sinusoidal modulation wave; the sinusoidal modulated wave is sequentially subject to direct current supply control, an interphase circumfluence control and a gridconnected current direct current component inhibit control to superpose corresponding regulation value, and is finally subject to carrier wave dephasing SPWM modulation to generate a switch driving signal. The multi-power-supply gridconnected system control method can flexibly control the interphase circumfluence according to the operation state of the multi-power-supply gridconnected system.

The invention discloses a photovoltaic inverter bus capacitance pressure equalization and bus overvoltage protection control circuit, which comprises a boosting module, an inversion module, an anode bus, a cathode bus, a bus capacitance group, a capacitance and voltage equalization module and an overvoltage protection module, wherein the boosting module is electrically connected with a photovoltaic array; the inversion module is electrically connected with a municipal electric network; the anode bus and the cathode bus are connected with the boosting module and the inversion module; the bus capacitance group comprises at least one group of serial capacitors, and each group of serial capacitors is connected between the anode bus and the cathode bus in parallel; the capacitance and voltage equalization module is connected between the anode bus and the cathode bus in parallel for equalizing the voltage of each capacitor of the bus capacitance group; and the overvoltage protection module is used for detecting voltage between the cathode bus and the anode bus, and when the voltage exceeds a set value, the voltage is fed back to the boosting module to lower the output voltage of the boosting module. The protection circuit is simple, and can realize capacitance and voltage equalization without complex control circuits, the capacitance and voltage equalization is a self-balancing process, and a hardware protection circuit can carry out high and low voltage isolation, quickly responds to bus voltage and has a reliable protection measure.

The invention provides a mixed double sub-module MMC voltage balancing control method and device. For any bridge arm, comprehensive voltage indexes of each sub-module are ranked according to the current direction of the bridge arm, plus or minus of the sum of voltage differences in modules of the whole bridge arm and plus or minus of the number of input sub-modules, and the output states corresponding to the sub-modules are determined; the comprehensive voltage indexes are relevant to the plus or minus of capacitor voltage sum in the modules and the capacitor voltage difference in the modules. Based on voltage balancing control of inter-module ranking of the comprehensive voltage indexes, the effects of capacitor voltage balance in the modules and capacitor voltage balance between the modules are achieved, and a good voltage balancing effect can be achieved under multiple working conditions of start, normal operation, fault ride-through and the like of a mixed double sub-module MMC system.

The invention relates to a valve level control method for a flexible DC power transmission system and belongs to the technical field of power electronics and custom power. The method comprises the steps that correlation operation is performed on a three-phase modulation signal received by valve level equipment to obtain the number of sub-modules which should be input by upper and lower bridge arms; afterwards, capacitor voltage values of the collected sub-modules are sequenced from small to large; finally, the direction of bridge arm current is judged, the sub-modules with lower capacitor voltages are input if the direction of the bridge arm current is the same as that of charging current, and the sub-modules with higher capacitor voltages are input if the direction of the bridge arm current is the same as that of discharging current. According to the valve level control method, the balance of the capacitor voltages can be maintained while the time consumed by a sorting algorithm is shortened remarkably, and the capacitor voltages of all the bridge arm sub-modules can be effectively maintained to be on the same level on the basis of guaranteeing that the valve level control cycle reaches the microsecond level below; in addition, the harmonic content of AC output voltage is low, reduction of system loss is facilitated, and the construction cost is also lowered.

The invention provides an MMC sub-module with fault current blocking and self-voltage-sharing capabilities. The MMC sub-module comprises a half-bridge sub-module consisting of switching tubes T1 and T2, diodes D1 and D2 and a capacitor C1, and a sub-module consisting of switching tubes T3, T4 and T5, diodes D3 to D8 and a capacitor C2, wherein the capacitor C1 and the capacitor C2 are connected inparallel through a diode; a connection part between the switching tubes T1 and T2 is connected with one wire outlet end of the MMC sub-module; and the lower end of a two-way switch formed by the diodes D5 to D8 and the switching tube T5 is connected with the other wire outlet end of the MMC sub-module. According to the MMC sub-module, only 2.5 IGBTs are needed for outputting unit level; and compared with an existing sub-module topology with a fault current blocking capacity, the MMC sub-module has the advantage of being more cost-effective. According to the invention, the difficulty of capacitor voltage balance control is simplified by the sub-module; after a fault is locked, when a forward fault current flows through, the capacitors are connected into a fault loop in series; and when a reverse fault current flows through, the sub-module connects the capacitors to the fault loop in parallel, thereby facilitating rapid recovery of a system after a fault.

The invention discloses a hybrid ride-through method for a DC short-circuit fault of an MMC-MTDC system, and relates to the technical field of power supply power systems, and the method comprises the steps: providing a non-locking fault ride-through strategy based on negative DC voltage control, and improving the clearing speed of a fault current through controlling a converter station to output a negative DC voltage; a hybrid ride-through method is provided on the basis, the converter station is not locked under the condition that overcurrent does not occur, the converter station is actively locked when overcurrent occurs on the bridge arm, and the locked converter station is cut off, so that the unlocked converter station continues to operate, direct current fault ride-through is achieved more safely and quickly, and the fault ride-through efficiency is improved. The influence of direct current fault disturbance on the system is reduced to the maximum extent, and the direct current fault disturbance resistance of the multi-terminal direct current power grid can be improved.

The invention discloses a multi-mode smooth control method and system for a cascade type three-level BUCK-BOOST converter. The method and the system are applied to the cascade type three-level BUCK-BOOST converter. Aiming at the inherent dead zone, capacitor voltage imbalance and mode oscillation problems of the cascaded three-level BUCK-BOOST converter, the multi-mode smooth control method provided by the invention is used for controlling the converter, so that the problems can be solved, and smooth change of step-up and step-down is realized.

The invention discloses a rapid voltage-sharing method for a cascaded multilevel converter, and the method comprises the steps: obtaining all switching tube drive signals of each submodule after a bridge arm reference voltage modulation wave signal of the cascaded multilevel converter is compared with a phase-shifting triangular carrier; and performing logic AND operation on the driving signals outputting the positive level in all the sub-modules, adding the driving signals outputting the positive level to obtain a positive level number output by the bridge arm, performing logic AND operationon the driving signals outputting the negative level in all the sub-modules, adding the driving signals outputting the negative level to obtain a negative level number output by the bridge arm, and outputting zero level by the remaining sub-modules; according to the number of the bridge arm positive and negative level output modules, carrying out sorting and voltage-sharing control, thereby finally achieving the effect of bridge arm capacitor voltage rapid equalization, and solving the problems that the carrier phase shift control voltage-sharing speed is low and the harmonic content of outputcurrent of a traditional sorting and voltage-sharing method is high when the number of sub-modules is small. According to the method, the capacitor voltage of the sub-module is rapidly balanced, thebridge arm is ensured to have high equivalent switching frequency, and the current harmonic content of the alternating current side is ensured to be low.

The present disclosure relates to a phase-splitting control method and system of a star chain STATCOM. Among them, the method includes: calculating the neutral point voltage of the star chain static synchronous compensator based on the preset three-phase voltage modulation signal and the three-phase grid voltage; The positive and negative sequence components of the current are compensated and the load reactive power and negative sequence current are calculated; the single-phase AC current is controlled separately based on the preset resonant controller; the phase-locked loop based on the second-order generalized integrator obtains the single-phase AC voltage phase respectively; The direction of the single-phase AC output current adjusts the output voltage to realize the balance control in the phase and complete the phase-splitting control of the star chain STATCOM. The present disclosure does not need complex coordinate transformation and current decoupling control, and does not need complex calculation of zero-sequence voltage or negative-sequence voltage, and can automatically adapt to the unbalanced voltage and load conditions of the power grid, and better realize the control of each chain through phase-separated control. The equalization of the capacitor voltage of the cell.

The invention relates to a voltage-sharing and current-sharing control method for a chopper of a superconducting magnetic energy storage system. An adopted chopper comprises n + m chopper sub-moduleswith the same structure, the middle terminal of the chopper sub-module SM1 is connected with the positive electrode of the direct current bus, the middle terminal of the chopper sub-module SMk is connected with the lower terminal of the chopper sub-module SMk-1, and the lower terminal of the chopper sub-module SMn + m is connected with the negative electrode of the direct current bus; the n + m chopper sub-modules are sorted according to the magnitude of the current of the superconducting magnet after each control period; when the superconducting magnetic energy storage system is charged, n chopper sub-modules are sequentially selected according to the current of the superconducting magnet from small to large, and for each selected chopper sub-module, the charging power of the superconducting magnet Lsc is kept equal to the charging power of the capacitor C, so that the voltage of the capacitor C is kept constant; and the remaining m chopper sub-modules are controlled, and the superconducting magnet Lsc are kept in a follow current state all the time in a control period.

The invention discloses a voltage-sharing control method in a pole-to-ground fault ride-through period of a modular multilevel converter. The method comprises the following steps: firstly, detecting electrical quantity of an MMC AC-DC side in real time, and judging whether a DC pole-to-ground fault occurs or not; when it is detected that a direct-current pole-to-ground fault occurs, the MMC is immediately switched to a pole-to-ground fault ride-through control strategy, and meanwhile, a fundamental frequency feed-forward compensation item FD is superposed on a circulating current suppressor control instruction; and completing the balance of the capacitor voltage according to the loop current suppressor control instruction after the superposition of the fundamental frequency feed-forward compensation item. Complex additional control does not need to be added, and the capacitor voltage balance of the upper and lower bridge arm sub-modules can be realized only by superposing a fundamental frequency ring current feed-forward item on an existing ring current suppressor control instruction; according to the method, the capacitor voltage balance of the upper and lower bridge arm sub-modules of the MMC in the pole-to-ground fault ride-through period can be effectively maintained, and the circulation can be minimized, so that the amplitude of the bridge arm current is reduced, and the operation loss of the MMC is reduced.

The invention relates to an MMC five-level half-bridge anti-series submodule FLHASM topological structure, and belongs to the technical field of flexible direct current power transmission. The structure comprises an MMC sub-module topology, the MMC sub-module topology comprises sub-module output ends, the sub-module output ends are a voltage positive electrode output end and a voltage negative electrode output end, the sub-module topology further comprises a left half part and a right half part, the left half part is formed by reversely connecting two half-bridge sub-modules in series, and the right half part is a complete sub-module topological structure formed by connecting two reverse half-bridge sub-modules through a power device group T7 and a power device group D7 and then connecting the two parts through a high-power diode D10. Compared with a full-bridge sub-module outputting the same level number, the five-level half-bridge anti-series MMC sub-module has the advantages that the number of switching tubes used by the five-level half-bridge anti-series MMC sub-module is greatly reduced, and the five-level half-bridge anti-series MMC sub-module has better direct-current fault clearing capability.