The invention relates to a self coupled modular multilevel high-voltage DC-DC transformer and a control method thereof. An upper portion converter of the transformer adopts a full bridge sub module and half bridge sub module mixed modular multilevel one, a lower portion converter is a half bridge sub module type modular multilevel one, and energy interaction of the upper and lower portion converters is implemented in a self coupling manner. According to the determined alternate current transformer optimal rated transformation ratio and sub module selection principle, on the premise of maintaining the direct current failure isolating capability, the component requirements are lowered to the utmost extent, and the cost is reduced accordingly; on the basis of the precision feedback linear control strategy, the characteristics that the alternate current portion of a direct current transformer is free of power grid interference and system parameters can be measured accurately can be utilized completely, and the fine control performance is provided; by means of the fast direct current failure isolation, the direct current failure transmission and expansion of two direct current power grids can be prevented effectively; the transformer has the advantages that the transmission capacity is large, the direct current voltage level is high, and the transformer is adaptive to a high-voltage large capacity direct current power grid power conduction occasions.

Self coupled modular multilevel high-voltage DC-DC transformer and control method thereof

Unique systems, methods, techniques and apparatuses of power transmission systems are disclosed herein. One exemplary embodiment is an AC power transmission system converted for transmission of high voltage direct current (HVDC) power, the converted system comprising an AC cable system, a first converter system, a second converter system, and a control system. The first converter system is structured to receive and convert AC power to DC power and output the DC power. The second power converter system is structured to receive the DC power, convert the DC power to a second AC power, and output the second AC power. The control system is structured to receive power demand information, determine a reduced DC voltage less than a rated HVDC voltage, control the first converter system such that the DC power is controlled to the reduced voltage, and control the second power converter system to operate in an active power control mode.

Direct current transmission system and method

The invention relates to a second harmonic filter of a high-voltage direct-current transmission system and a parameter design method thereof. The second harmonic filter comprises a power capacitor, an electric reactor and a damping resistor, wherein one output end of a converter of the direct-current transmission system is connected with one end of the power capacitor, the other end of the power capacitor is in serial connection with one end of the electric reactor, and accordingly a second harmonic series-connection resonance circuit is formed; the other end of the electric reactor is connected with the other output end of the converter of the direct-current transmission system and is grounded; the two ends of the electric reactor are further in parallel connection with the damping resistor with an adjustable resistance parameter; one end of the power capacitor and other end of the electric reactor are respectively connected with an alternating power grid, and non-linear high-frequency characteristic harmonic generated by the converter of the direct-current transmission system is input into the alternating power grid after being filtered. The second harmonic filter can effectively filter second harmonic in the high-voltage direct-current transmission system and is suitable for being used in the field of second harmonic filtering of a high-voltage direct-current transmission line.

Second harmonic filter of high-voltage direct-current transmission system and parameter design method thereof

A method of designing a multiple-tuned filter (MTF) of a high voltage direct current (HVDC) system is provided. The method includes selecting an input parameter for the MTF, setting a resonance frequency of the MTF, calculating values of inductance (L) and capacitance (C) which are filter parameters of the MTF on the basis of the input parameter and the resonance frequency, combining a value of resistance (R) with the filter parameters and calculating a price according to the combination, and storing the combined values of R, L, and C when the calculated price falls within a predetermined price range.

Multiple-tuned filter design method for hvdc system

The invention provides a novel photovoltaic modular multi-level converter and a control method thereof. The photovoltaic modular multi-level converter comprises n sub-unit modules, wherein n is equal to or more than 2. The input end of each sub-unit module is connected with a photovoltaic component, and the output end accesses a direct current power grid. The method uses a capacitor voltage sorting method to control voltage balance of both ends of n voltage-stabilized capacitors in the modular multi-level converter. Compared with the prior art, the novel photovoltaic modular multi-level converter and the control method, which are provided by the invention, have the advantages that the control of the converter is easier; the efficiency of the converter is improved; switching devices are reduced; and total drive power and switching loss are reduced.

Novel photovoltaic modular multi-level converter and control method thereof

The utility model relates to an auto-coupling modular multi-level high-voltage DC-DC transformer. An upper current converter of the transformer adopts a modular multi-level current converter of a mixed type by a full-bridge sub module and a half-bridge sub module, a lower current converter adopts a modular multi-level current converter of a half-bridge sub module type, and the upper and lower current converters achieve energy interaction by means of auto-coupling. According to an optimum rated transformation ratio of a given AC transformer and a sub module selection principle, device needs are minimized so as to reduce cost under the premise of reserving the DC fault isolation capacity. On the basis of an accurate feedback linear control strategy, the characteristics of no power grid disturbance at an AC side part of a DC transformer, capability of accurate measurement of system parameters and the like can be made full use of to obtain excellent control performance. According to the utility model, DC fault quick isolation can effectively prevent DC fault transfer and expansion among two DC power grids, and the auto-coupling modular multi-level high-voltage DC-DC transformer has the advantages of large transmission capacity, high DC voltage level and the like and is suitable for high-voltage large-capacity DC power grid transmission occasions.

Auto-coupling modular multi-level high-voltage DC-DC transformer

The invention relates to a control protective method for an ultra-high-voltage direct-current engineering direct-current change-over switch with a parallel structure. The control protective method comprises the steps of determining a loop state according to information of two fractures of the direct-current change-over switch; when a switching-off operation of the direct-current change-over switch is executed, controlling a protective system to initially send out an auxiliary fracture switching-off instruction, and then to send out a main fracture switching-off instruction after a separating position state of the auxiliary fracture is received and subjected to preset time delay; if the separating position state of the auxiliary fracture is not received or the separating position state duration cannot satisfy the preset time delay, automatically stopping sequential control; when a switching-on operation of the direct-current change-over switch is executed, controlling the protective system to initially send out a main fracture switching-on instruction, and then to send out an auxiliary fracture switching-on instruction after a closing position state of the main fracture is received and subjected to preset time delay; and if the closing position state of the main fracture is not received or the closing position state duration cannot satisfy the preset time delay, automatically stopping sequential control. The control protective method can be widely applied to control and protection of the ultra-high-voltage direct-current engineering direct-current change-over switch.

Control protective method for ultra-high-voltage direct-current engineering direct-current change-over switch with parallel structure

The utility model relates to a secondary harmonic filter for a high-voltage DC (direct current) power transmission system. The secondary harmonic filter includes an electric power capacitor, an electric power reactor and a damping resistor. One output end of a direct-current power transmission system converter is connected with one end of the electric power capacitor, and the other end of the electric power capacitor is connected with one end of the electric power reactor in series, and thus a secondary harmonic series resonance circuit is formed. The other end of the electric power reactor is connected with the other end of the direct-current power transmission system converter and is connected to ground. The damping resistor in which a resistance parameter is adjustable is connected in parallel with the two ends of the electric power reactor. One end of the electric power capacitor and the other end of the electric reactor are connected to an alternating-current network, and remove non-linear high-frequency characteristic harmonic waves generated by the direct-current power transmission system converter by filtration and then input the electric power into the alternating-current network. The secondary harmonic filter can effectively remove the secondary harmonic waves in the high-voltage DC power transmission system, and is suitable for the field of secondary harmonic wave filtering of high-voltage DC power transmission lines.

Secondary harmonic filter for high-voltage DC (direct current) power transmission system

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