WO2024040876A1 - 一种无变压器型广义统一潮流控制器、方法及系统 - Google Patents

一种无变压器型广义统一潮流控制器、方法及系统 Download PDF

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Publication number
WO2024040876A1
WO2024040876A1 PCT/CN2023/074778 CN2023074778W WO2024040876A1 WO 2024040876 A1 WO2024040876 A1 WO 2024040876A1 CN 2023074778 W CN2023074778 W CN 2023074778W WO 2024040876 A1 WO2024040876 A1 WO 2024040876A1
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Prior art keywords
power flow
voltage
phase
transmission line
control
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PCT/CN2023/074778
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English (en)
French (fr)
Inventor
张建文
周剑桥
施刚
蔡旭
刘勇
梁克靖
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Shanghai Jiao Tong University
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Shanghai Jiao Tong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/04—Arrangements for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling the transfer of power between connected networks; Controlling load sharing between connected networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/20—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/28—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for meshed systems
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/46—Controlling the sharing of generated power between the generators, sources or networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2103/00—Details of circuit arrangements for mains or AC distribution networks
    • H02J2103/30—Simulating, planning, modelling, reliability check or computer assisted design [CAD] of electric power networks

Definitions

  • the invention relates to the technical fields of AC power grid power flow control and power electronics, and in particular to a transformerless generalized unified power flow controller with multi-port active power flow control capability suitable for AC power grids and its control method and system.
  • the first option is to upgrade existing transmission lines or add transmission lines to enhance the grid structure. This option is limited by factors such as the lack of transmission corridors, the difficulty of land acquisition for new substations, and economic issues. It is difficult to realize due to restrictions; the second solution is to realize active power flow control of transmission lines through flexible AC transmission devices.
  • This solution can control all electrical parameters that affect power transmission through power electronic devices, making the power grid flexible and controllable. Not only does it not need to change the structure of the existing power grid, it also has the advantages of flexible power flow adjustment, dynamic compensation, and oscillation suppression. At the same time, we make full use of the real-time and rapidity of power electronic device control to achieve rapid and dynamic adjustment of power flow on transmission lines, thereby optimizing power flow distribution.
  • the existing power flow controller with the most comprehensive power flow regulation function is mainly the generalized unified power flow controller.
  • the typical topology of the existing generalized unified power flow controller consists of a parallel voltage source converter and multiple series voltage source converters. The converters are connected back-to-back, and the converters are connected to the transmission lines through power frequency isolation transformers. By adjusting the amplitude and phase angle of the series-side converter voltage, the active power and reactive power of multiple transmission lines can be adjusted independently.
  • this topology requires the use of expensive and bulky power frequency isolation transformers, which results in a large overall volume of the device and high installation, operation and maintenance costs.
  • a series power frequency isolation transformer and three-phase voltages need to be added. Source-type converters have high port expansion costs.
  • the technical problem solved by the present invention is: in view of the existing power flow controller equipment at the current stage, the overall volume is large, the operation and maintenance costs are high, and the equipment volume and operation and maintenance costs are reduced and it is difficult to achieve the functions of the power flow controller.
  • a new structure of a transformer-less power flow controller was designed by fully considering the portability, economy and practicality of the power flow controller.
  • the present invention provides the following technical solutions:
  • Transformerless generalized unified power flow controller includes,
  • a reactive power compensation module includes a cascade bridge inverter
  • a power flow adjustment module includes a multi-port single-phase MMC
  • the multi-port single-phase MMC is connected in series with the cascade bridge inverter
  • the reactive power compensation module is a voltage source converter with a reactive power two-way compensation function, which can absorb reactive power from the system and provide reactive power compensation for the system;
  • the power flow regulation module realizes decoupling control of the active power and reactive power of the transmission line.
  • the cascade bridge inverter is composed of multiple sub-modules cascaded.
  • the multi-port single-phase MMC includes a power flow regulating multi-port single-phase MMC and an energy balancing multi-port single-phase MMC;
  • the energy balancing multi-port single-phase MMC and the power flow regulating multi-port single-phase MMC are connected in parallel;
  • the cascade bridge inverter is connected to the AC output port of the energy-balanced multi-port single-phase MMC to realize the series connection of the cascade bridge inverter and the multi-port single-phase MMC;
  • the AC output port of the power flow regulating multi-port single-phase MMC is connected in series with the transmission line.
  • the active power and reactive power of the transmission line are realized. Decoupled control.
  • the control target of the line power flow control loop is:
  • Reference value for the AC component of the output voltage of the AC output port of a power flow regulated multi-port single-phase MMC connected to a power flow regulated balanced transmission line is the reference value of the AC component of the output voltage of the power flow regulating multi-port single-phase MMC AC output port connected to the power flow control transmission line.
  • the subscript i indicates that the i-th transmission line is a power flow regulating balanced transmission line, and the subscript j indicates the j-th transmission line.
  • the cascaded bridge inverter control loop includes:
  • the control goal of the cascade bridge inverter control loop is to regulate the power flow and balance the reactive power of the transmission line to reach a reference value.
  • the sum of the three-phase capacitor voltages of the cascade bridge inverter is stable as the reference value.
  • the output of the cascade bridge inverter control loop is the reference value of the AC component of the voltage at the AC output port of the cascade bridge inverter.
  • the reactive power control outer loop adjusts the reactive power reference value of the balanced transmission line according to the power flow. Calculate the reference value of the q-axis component of the current in the balanced transmission line for power flow regulation
  • the current control inner loop is controlled in the dq coordinate system, and uses a proportional integral controller to control the d-axis component and q-axis component of the power flow adjustment balance transmission line current respectively.
  • the mathematical equation is:
  • V Cid and V Ciq are the d-axis component and q-axis component of the AC component of the AC output port voltage of the power flow regulating multi-port single-phase MMC connected to the power flow regulating balanced transmission line
  • V SMd and V SMq are related to the cascade bridge type
  • k p2 is the proportional link gain coefficient of the proportional integral controller
  • k i2 is the integral link gain of the proportional integral controller
  • Coefficients V id , V iq , V Cid , V Ciq , V SMd , and V SMq are feedforward terms.
  • Their function is to enhance the anti-interference ability of the control loop and speed up the response speed of the control loop. It is a decoupling term, and its function is to realize the decoupling control of d-axis
  • the control target of the common DC bus voltage balance control loop is to stabilize the common DC bus voltage to a reference value.
  • the output of the common DC bus voltage balance control loop is the common DC bus balance reference voltage
  • the control of the common DC bus voltage balance control loop is carried out in the abc coordinate system.
  • the proportional integral controller is used to control the abc three-phase public DC bus voltage.
  • the mathematical equation is:
  • V linka , V linkb , and V linkc are the three-phase public DC bus voltages
  • I pa , I pb , and I pc are the three-phase currents of the cascade bridge inverter branch.
  • k p3 is the gain coefficient of the proportional link of the proportional-integral controller
  • k i3 is the gain coefficient of the integral link of the proportional-integral controller.
  • the control target of the circulation suppression control is to suppress the circulation between the multi-port single-phase MMCs of each phase, and the output of the circulation suppression control is to generate The double frequency voltage of the circulating current can be suppressed by compensating the sub-module modulation signal;
  • the circulation suppression control is carried out in the abc coordinate system, and a quasi-proportional resonance controller is used to suppress the intra-phase circulation of the abc three-phase.
  • the mathematical equation is:
  • G QPR (s) is the transfer function of the quasi-PR controller
  • ⁇ is the resonant frequency
  • ⁇ c is the cut-off frequency that mainly affects the system bandwidth
  • k p4 is the gain coefficient of the proportional link of the quasi-proportional resonant controller
  • k r is the quasi-proportional resonance Controller resonance link gain coefficient
  • s is the model variable under Laplace change
  • i lkp and i lkn are the power flow regulation multi-port single-phase MMC upper bridge arm current and lower bridge arm current connected to the kth transmission line
  • the subscript l is l phase parameters.
  • the bridge arm voltage balance control includes two implementation methods: bridge arm voltage DC component adjustment and injection fundamental frequency circulating current adjustment.
  • the adjustment method of the DC component of the bridge arm voltage includes adjusting the DC components of the upper and lower bridge arms to control the balance of the upper and lower bridge arm capacitor voltages, and outputting the multi-port single-phase MMC upper bridge arm and lower bridge arm sub-module voltage DC component reference values;
  • the bridge arm voltage equalization control uses a PI controller to control the DC component of the bridge arm voltage of the abc three-phase multi-port single-phase MMC.
  • the mathematical equation is:
  • the adjustment method of injecting fundamental frequency circulation adjustment includes:
  • the bridge arm voltage balance control of the fundamental frequency circulation injection adjustment achieves the balance of the upper and lower bridge arm voltages by injecting the fundamental frequency circulation with the same phase as the voltage.
  • the output of the injection fundamental frequency circulation adjustment is the reference value of the injected fundamental frequency circulation.
  • V average,lkp and V average,lkn are the upper and lower bridge arm voltage averages of the power flow regulating multi-port single-phase MMC
  • ⁇ k Adjust the phase of the fundamental frequency component of the multi-port single-phase MMC output voltage for the power flow connected to the k-th transmission line
  • k p6 is the gain coefficient of the proportional link of the proportional-integral controller
  • k i6 is the gain coefficient of the integral link of the proportional-integral controller.
  • the series compensation voltage vector expression required in series between the first transmission line and the k-th transmission line is, is the vector expression of the AC component of the energy-balanced multi-port single-phase MMC AC output port voltage in the multi-port single-phase MMC power flow regulation module connected to the cascade bridge inverter, is the conjugate vector expression of the alternating current on the k-th transmission line, is the conjugate vector expression of the AC current of the cascade bridge inverter branch, and n is the number of transmission lines interconnected by the transformerless generalized unified power flow controller.
  • the core equipment of the control system is the transformerless generalized unified power flow controller, AC transmission lines and substations;
  • the transformerless generalized unified power flow controller is installed at the convergence of multiple AC transmission lines;
  • the AC transmission line is connected to a transformerless generalized unified power flow controller.
  • the AC transmission line can be connected to a high-voltage system via a step-up transformer, and can be connected to a low-voltage AC system via a step-down transformer.
  • the low-voltage AC system can be connected to a low-voltage AC load, Energy storage equipment and electric vehicle fast charging stations.
  • the overvoltage protection of the voltage connected in series on the transmission line includes a protection device
  • the protection device is connected in parallel with the AC output port of the power flow adjustment multi-port single-phase MMC in the multi-port single-phase MMC power flow adjustment module to protect the overvoltage of the voltage connected in series on the transmission line;
  • the protection device is composed of a metal oxide voltage limiter and a thyristor bypass switch connected in parallel;
  • the thyristor bypass switch is an anti-parallel thyristor, a resistor-capacitor loop, a static resistor in parallel and then in series with a saturated reactor;
  • the metal oxide voltage limiter limits the voltage to a safe voltage while the thyristor bypass switch achieves overvoltage protection by bypassing the AC output port of the power flow regulating multi-port single phase MMC.
  • the AC output port of the multi-port single-phase MMC sub-module is connected in parallel with the thyristor bypass switch, so that when the multi-port single-phase MMC sub-module fails, the faulty sub-module can be quickly bypassed through the thyristor bypass switch, and redundant sub-modules can be put in at the same time. module, so that the failure of the sub-module does not affect the overall operation of the equipment;
  • the DC side of the multi-port single-phase MMC sub-module is equipped with a DC unloading circuit for capacitive energy release to prevent overvoltage from damaging power devices.
  • the AC port of the cascade bridge inverter sub-module is connected in parallel with a fast mechanical switch, so that when the cascade bridge inverter sub-module fails, the faulty module can be quickly removed;
  • the DC side of the cascaded bridge inverter sub-module is equipped with a DC unloading circuit that releases capacitive energy to prevent overvoltage from damaging the power devices.
  • the existing cascade bridge inverter only has the reactive power compensation function and does not have the multi-AC transmission line interconnection and transmission line active power flow decoupling control functions.
  • the present invention introduces multi-port single-phase
  • the MMC power flow regulation module provides multiple AC interconnection ports to realize the interconnection of multiple AC transmission lines. By adjusting the amplitude and phase of the series compensation voltage connected in series on the transmission lines, it can realize active power decoupling of the active power and reactive power of the transmission lines. Control, compared with the existing unified power flow controller, the expensive and bulky power frequency isolation transformer is eliminated, which not only reduces the area of the device and the cost of installation and operation of the device, but also speeds up the response speed of the device and reduces the loss. lower.
  • the traditional generalized unified power flow controller needs to add a three-phase inverter and a power frequency isolation transformer, and the port expansion cost is very high.
  • the transformerless generalized unified power flow controller in the present invention only need to increase the number of single-phase small-capacity MMC modules, and the expansion of the power flow control port can be realized quickly and economically.
  • control method based on the controller of the present invention can realize the basic functions of the controller and ensure normal operation of the control.
  • the AC transmission line of the control system of the present invention can not only be connected to the high-voltage system via the step-up transformer, but also can be connected to the low-voltage AC system via the step-down transformer.
  • the low-voltage AC system can be connected to the low-voltage AC load, Energy storage equipment and electric vehicle fast charging stations.
  • the equipment protection method based on the controller of the present invention can avoid serious damage to the internal components of the converter under fault conditions.
  • Figure 1 is a schematic diagram of the topological structure of the transformerless generalized unified power flow controller and the system of interconnecting multiple transmission lines according to the present invention.
  • Figure 2 is a schematic diagram of the system of the transformerless generalized unified power flow controller without the energy-balanced multi-port single-phase MMC connected to the cascaded bridge inverter and its system of interconnecting multiple transmission lines according to the present invention. picture.
  • Figure 3 is a schematic diagram showing a typical topology example of the cascaded bridge inverter and the multi-port single-phase MMC described in the transformerless generalized unified power flow controller of the present invention.
  • Figure 4 is a schematic diagram of the topology of the multi-port single-phase MMC power flow adjustment module described in the transformerless generalized unified power flow controller of the present invention.
  • Figure 5 shows the control method of the transformerless generalized unified power flow controller of the present invention.
  • the multi-port single-phase MMC power flow adjustment module adopts an MMC with two-level single-phase half-bridge type sub-modules in parallel, and the cascade bridge type inverter adopts Block diagram of the control method of the dual-port power flow control device in the cascaded full-bridge topology.
  • Figure 6 is a control system diagram of the transformerless generalized unified power flow controller of the present invention.
  • Figure 7 shows the control system of the transformerless generalized unified power flow controller of the present invention.
  • the multi-port single-phase MMC power flow adjustment module adopts a two-level half-bridge type sub-module, and the cascade bridge-type inverter adopts a double-level cascade full-bridge topology.
  • Figure 8 is a wiring diagram of the voltage overvoltage protection method and a schematic diagram of the protection device of the equipment protection method of the transformerless generalized unified power flow controller of the present invention.
  • Figure 9 shows the control system of the transformerless generalized unified power flow controller of the present invention.
  • the multi-port single-phase MMC power flow adjustment module adopts a two-level half-bridge type sub-module, and the cascaded bridge-type inverter adopts a cascaded full-bridge topology.
  • Figure 10 shows the control method of the transformerless generalized unified power flow controller of the present invention.
  • the multi-port single-phase MMC power flow adjustment module adopts an MMC with parallel two-level single-phase half-bridge type sub-modules, and the cascade bridge-type inverter adopts a stage Block diagram of the control method of the three-port power flow control device with full-bridge topology.
  • Figure 11 is a simulated power flow of each transmission line and voltage waveforms of each capacitor in the device under three working conditions of the transformerless generalized unified power flow controller, method and system of the present invention.
  • references herein to "one embodiment” or “an embodiment” refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. "In one embodiment” appearing in different places in this specification does not all refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.
  • connection should be understood in a broad sense.
  • it can be a fixed connection, a detachable connection, or an integrated connection; it can also be a mechanical connection, an electrical connection, or a direct connection.
  • a connection can also be indirectly connected through an intermediary, or it can be an internal connection between two components.
  • the specific meanings of the above terms in the present invention can be understood on a case-by-case basis.
  • an embodiment of the present invention which provides a transformerless generalized unified power flow controller, including a reactive power compensation module, with a reactive power two-way compensation function, which can absorb reactive power from the system, or Provide reactive power compensation for the system; the power flow adjustment module realizes decoupling control of the active power and reactive power of the transmission line.
  • the reactive power compensation module is a voltage source converter with a reactive power bidirectional compensation function. It can absorb reactive power from the system and provide reactive power compensation for the system.
  • the reactive power compensation module includes a cascade bridge type inverter. Inverter, cascade bridge inverter is composed of multiple sub-modules cascaded, as shown in Figure 3. Schematic diagram of typical topology examples of the cascade bridge inverter and multi-port single-phase MMC in the invented controller.
  • the sub-modules of the cascade bridge inverter can be three-level or five-level. Yes, it can also be other multi-level sub-modules.
  • the power flow adjustment module realizes decoupling control of the active power and reactive power of the transmission line.
  • the power flow adjustment module includes a multi-port single-phase MMC, and the multi-port single-phase MMC is connected in series with a cascade bridge inverter.
  • Figure 1 is a schematic diagram of the topology of the controller of the present invention and its system of interconnecting multiple transmission lines.
  • the multi-port single-phase MMC includes a power flow regulating multi-port single-phase MMC and an energy balancing multi-port single-phase MMC. Energy balance The multi-port single-phase MMC is connected in parallel with the power flow regulating multi-port single-phase MMC.
  • the cascade bridge inverter is connected to the AC output port of the energy-balanced multi-port single-phase MMC to realize the cascade bridge inverter and the multi-port single-phase MMC.
  • the AC output port of the multi-port single-phase MMC for power flow regulation is connected in series with the transmission line.
  • multi-port single-phase MMC power flow regulation is achieved.
  • Figure 2 is a schematic diagram of the system in which the controller of the present invention omits the energy-balanced multi-port single-phase MMC connected to the cascade bridge inverter and its interconnected multi-transmission lines.
  • the multi-port single-phase MMC The power flow regulation module includes multiple power flow regulation multi-port single-phase MMCs that share the same common DC bus and are connected in parallel with each other.
  • the AC output port of the power flow regulation multi-port single-phase MMC is connected in series with the transmission line. By adjusting the power flow in series on the transmission line
  • the amplitude and phase of the multi-port single-phase MMC AC output port voltage realizes active control of the active power and reactive power of the transmission line.
  • Figure 4 is a schematic diagram of the topology of the multi-port single-phase MMC power flow adjustment module of the controller of the present invention.
  • the multi-port single-phase MMC power flow adjustment module only includes a power flow adjustment multi-port single-phase MMC
  • the cascade bridge type The inverter is directly connected to the positive or negative pole of the public DC bus, which can realize the series connection of the cascade bridge inverter and the multi-port single-phase MMC power flow regulation module.
  • the multi-port single-phase MMC power flow regulation module also includes a power flow regulation multi-port For single-phase MMC and energy-balanced multi-port single-phase MMC
  • the AC output port of the cascade bridge inverter can be connected to the AC output port of the energy-balanced multi-port single-phase MMC
  • the cascade bridge inverter can also be connected to Series connection of multi-port single-phase MMC power flow regulation modules.
  • the control system uses a transformerless generalized unified power flow controller to realize the device topology and system connection of the power flow control of the transmission lines at both ends.
  • the transformerless generalized unified power flow controller includes a cascaded bridge type with a three-phase cascaded full-bridge topology. Inverter and multi-port single phase in series with it MMC power flow regulation module.
  • the multi-port single-phase MMC power flow regulation module includes three MMCs of single-phase half-bridge sub-modules that share the same common DC bus.
  • the MMCs of the three single-phase half-bridge sub-modules are connected to two AC transmission lines and stages respectively.
  • the bridge-type inverters are connected one by one, and by adjusting the series compensation voltage connected in series on the transmission line, the AC component of the MMC AC output port voltage of the single-phase half-bridge type sub-module connected in series with the cascaded bridge-type inverter, The amplitude and phase of the AC component of the AC output port voltage of the cascade bridge type inverter, where the series compensation voltage is the AC component of the AC output port voltage of the power flow regulating multi-port single-phase MMC connected in series on the transmission line.
  • the internal energy balance of the transformerless generalized unified power flow controller realizes the active control of the active power and reactive power on the AC transmission line, that is, the decoupling control of the line power flow.
  • an embodiment of the present invention provides a control method based on a transformerless generalized unified power flow controller, including:
  • Line power flow control loop cascade bridge inverter control loop, common DC bus voltage balance control loop, circulating current suppression control and bridge arm voltage balance control.
  • the line power flow control loop is the main control including:
  • the control goal of the line power flow control loop is for the active power of the power flow control transmission line to reach the reference value and the reactive power to reach the reference value.
  • Reference value for the AC component of the output voltage of the AC output port of a power flow regulated multi-port single-phase MMC connected to a power flow regulated balanced transmission line is the reference value of the AC component of the output voltage of the power flow regulating multi-port single-phase MMC AC output port connected to the power flow control transmission line.
  • the subscript i indicates that the i-th transmission line is a power flow regulating balanced transmission line, and the subscript j indicates the j-th transmission line.
  • the line power flow control loop first calculates the d-axis component reference value of the power flow control transmission line current based on the active power reference value and reactive power reference value of the power flow control transmission line. and q-axis component reference value
  • the calculation method is to solve the following system of equations:
  • V represents the node voltage of the transmission line
  • I represents the current of the transmission line
  • ⁇ represents the AC frequency of the transmission line
  • L represents the equivalent inductance value of the transmission line
  • L PFCM represents the equivalent inductance value of the multi-port single-phase MMC bridge arm
  • R represents the equivalent resistance value of the transmission line
  • the subscript i of V, I, L and R represents the parameters of the power flow adjustment and balancing transmission line
  • the subscript j represents the parameter of the jth power flow control transmission line
  • the subscript d represents the d-axis component
  • the subscript q represents the q-axis component
  • the superscript * represents the reference value
  • k p is the gain coefficient of the proportional link of the proportional integral controller
  • k i is the gain coefficient of the integral link of the proportional integral controller
  • V id V iq , V jd
  • cascade bridge inverter control loop is the main control including:
  • the control goal of the cascade bridge inverter control loop is to regulate the power flow and balance the reactive power of the transmission line to reach the reference value.
  • the sum of the three-phase capacitor voltages of the cascade bridge inverter is stable as the reference value
  • output is the reference value of the AC component of the voltage at the AC output port of the cascade bridge inverter.
  • the reactive power control outer loop adjusts the reactive power reference value of the balanced transmission line according to the power flow.
  • Calculate the reference value of the q-axis component of the current in the balanced transmission line for power flow regulation The calculation formula is:
  • the current control inner loop is controlled in the dq coordinate system, and the proportional integral controller is used to control the d-axis component and q-axis component of the power flow adjustment balance transmission line current respectively.
  • the mathematical equation is:
  • V pa , V pb , V pc , V Cid , V Ciq are the d-axis component and q-axis component of the AC component of the power flow regulating multi-port single-phase MMC AC output port voltage connected to the power flow regulating balanced transmission line
  • V SMd and V SMq is the d-axis component and q-axis component of the AC component of the energy-balanced multi-port single-phase MMC AC output port voltage connected to the cascade bridge inverter
  • k p2 is the proportional link gain coefficient of the proportional integral controller
  • k i2 is the gain coefficient of the integral link of the proportional integral controller
  • V id , V iq , V Cid , V Ciq , V SMd , and V SMq are feedforward
  • the common DC bus voltage balance control loop is the main control including:
  • the control goal of the common DC bus voltage balance control loop is to stabilize the common DC bus voltage to a reference value. And the output is the common DC bus balanced reference voltage
  • control of the common DC bus voltage balance control loop is carried out in the abc coordinate system, and the proportional integral controller is used to control the abc three-phase public DC bus voltage.
  • the mathematical equation is:
  • V linka , V linkb , and V linkc are the three-phase public DC bus voltages
  • I pa , I pb , and I pc are the three-phase currents of the cascade bridge inverter branch.
  • k p3 is the gain coefficient of the proportional link of the proportional-integral controller
  • k i3 is the gain coefficient of the integral link of the proportional-integral controller.
  • the transformerless generalized unified power flow controller topology includes an energy-balanced multi-port single-phase MMC connected to the cascade bridge inverter, the output reference voltage of the line power flow control loop can be obtained Finally, the reference voltage of the AC output port of the power flow regulating multi-port single-phase MMC is:
  • the reference voltage of the output port is the output voltage of the power flow control loop, It is the power flow adjustment multi-port single-phase MMC AC output port connected to the power flow adjustment balanced transmission line calculated according to any one of the series compensation voltage distribution methods in the distribution method based on the transformerless generalized power flow controller provided by the present invention.
  • the AC component of the reference voltage, the feedforward three-phase reference voltage in the common DC bus voltage balance control loop, Equal to zero, the reference voltage of the energy-balanced multi-port single-phase MMC AC output port is:
  • the reference voltage of the AC output port of the cascade bridge inverter is:
  • the transformerless generalized unified power flow controller topology does not include an energy-balanced multi-port single-phase MMC connected to the cascade bridge inverter, the output reference voltage of the line power flow control loop is obtained Finally, the reference voltage of the AC output port of the power flow regulating multi-port single-phase MMC is:
  • Reference voltage for the AC output port of the power flow regulated multi-port single phase MMC connected to the power flow regulated balanced transmission line The reference voltage for the power flow regulating multiport single-phase MMC AC output port connected to the jth power flow controlled transmission line, the feedforward three-phase reference voltage in the common DC bus voltage balance control loop, The power flow adjustment multi-port single-phase MMC AC output port connected to the power flow adjustment balanced transmission line calculated by any one of the series compensation voltage allocation methods in the distribution method based on the transformerless generalized power flow controller provided by the present invention.
  • the AC component of the reference voltage, the feedforward terms V SMd and V SMq in the current control inner loop of the cascade bridge inverter control loop are equal to zero, and the reference voltage of the AC output port of the cascade bridge inverter is:
  • a plus sign is taken when the AC output port of the cascade bridge inverter is connected to the negative pole of the common DC bus
  • a minus sign is taken when the AC output port of the cascade bridge inverter is connected to the positive pole of the public DC bus.
  • circulation suppression control includes:
  • the control goal of the circulating current suppression control is to suppress the circulating current between the multi-port single-phase MMCs of each phase.
  • the output of the circulating current suppressing control is the double frequency voltage that generates the circulating current. By compensating the sub-module modulation signal, the circulating current is suppressed.
  • the circulation suppression control is carried out in the abc coordinate system, and a quasi-proportional resonance controller is used to suppress the intra-phase circulation of the abc three-phase.
  • the mathematical equation is:
  • G QPR (s) is the transfer function of the quasi-PR controller
  • ⁇ is the resonant frequency
  • ⁇ c is the cut-off frequency that mainly affects the system bandwidth
  • k p4 is the gain coefficient of the proportional link of the quasi-proportional resonant controller
  • k r is the quasi-proportional resonance Controller resonance link gain coefficient
  • s is the model variable under Laplace change
  • i lkp and i lkn are the power flow regulation multi-port single-phase MMC upper bridge arm current and lower bridge arm current connected to the kth transmission line
  • the subscript l is l Phase parameters
  • the phase-locked loop locks the power flow and adjusts the node three-phase voltage of the balanced transmission line to obtain the phase of the locked line.
  • bridge arm voltage equalization control includes:
  • the bridge arm voltage balance control is realized in two ways: the DC component adjustment of the bridge arm voltage and the injection fundamental frequency circulating current adjustment.
  • the method of adjusting the DC component of the bridge arm voltage includes adjusting the DC components of the upper and lower bridge arms to control the balance of the capacitor voltages of the upper and lower bridge arms, and outputting it as a multi-port single-phase MMC upper bridge arm and lower bridge arm sub-module voltage DC component reference value , the bridge arm voltage balance control uses the PI controller to control the DC component of the bridge arm voltage of the abc three-phase multi-port single-phase MMC.
  • the mathematical equation is:
  • V link,l is the DC bus voltage
  • the subscript k is connected to the kth transmission line
  • the adjustment method of injecting fundamental frequency circulating current includes adjusting the bridge arm voltage by injecting fundamental frequency circulating current.
  • Balance control achieves the balance of upper and lower bridge arm voltages by injecting fundamental frequency circulating current with the same phase as the voltage. Its output is the reference value of the injected fundamental frequency circulating current.
  • the mathematical equation is:
  • V average,lkp and V average,lkn are the upper and lower bridge arm voltage averages of the power flow regulating multi-port single-phase MMC
  • ⁇ k Adjust the phase of the fundamental frequency component of the multi-port single-phase MMC output voltage for the power flow connected to the k-th transmission line
  • k p6 is the gain coefficient of the proportional link of the proportional-integral controller
  • k i6 is the gain coefficient of the integral link of the proportional-integral controller.
  • This embodiment is the third embodiment of the present invention, which provides a distribution method based on a transformerless generalized unified power flow controller, including:
  • the allocation method of the controller is any group that satisfies the basic condition equations solution.
  • the first transmission line is a power flow regulation balanced transmission line
  • Real is the real part
  • the series compensation voltage vector expression required in series between the first transmission line and the k-th transmission line is, is the vector expression of the AC component of the energy balance multi-port single-phase MMC AC output port voltage in the multi-port single-phase MMC power flow regulation module connected to the cascade bridge inverter
  • n is the number of transmission lines interconnected through the transformerless generalized unified power flow controller.
  • a transformerless generalized unified power flow controller with active power flow control capability suitable for AC power grids is used to distribute the compensation voltage in series on the distribution network transmission lines. It is characterized by simplicity.
  • Another method of allocating the series compensation voltage is The choice satisfies To obtain the minimum value, the AC component amplitude of the required output voltage of the single-phase converter can be minimized.
  • the distribution method of the series compensation voltage can also be any selection method that satisfies the basic condition equation.
  • the voltage component of the AC output port of the single-phase converter in the multi-port single-phase MMC power flow regulation module contains different AC components required for control.
  • an embodiment of the present invention which provides a control system based on a transformerless generalized unified power flow controller, including:
  • the core equipment of the AC power grid multi-transmission line power flow control system is a transformerless generalized unified power flow controller, and the other components are AC transmission lines and substations. It should be noted:
  • the transformerless generalized unified power flow controller is installed at the gathering point of multiple AC transmission lines.
  • the AC transmission lines are connected to the transformerless generalized unified power flow controller.
  • the AC transmission lines can be connected to the high-voltage system through a step-up transformer, and can also be connected to the high-voltage system through a step-down transformer.
  • the transformer is connected to the low-voltage AC system, and the low-voltage AC system can be connected to low-voltage AC loads or energy storage equipment or electric vehicle fast charging stations.
  • the multi-port single-phase MMC power flow adjustment module of the control system of the present invention adopts a two-level half-bridge type sub-module, and the cascade bridge-type inverter adopts a dual-port power flow control device with a cascade full-bridge topology.
  • the power flow control system of both ends of the transmission line implemented by the transformerless generalized unified power flow controller.
  • the internal energy balance of the transformerless generalized unified power flow controller is expressed as the common DC bus. If the capacitor voltage remains stable and the capacitor voltage in the cascade bridge inverter remains stable, the active power flowing into the above capacitor is required to remain zero, that is:
  • the equation in the first row expresses that the active power flowing into the common DC bus capacitor is zero
  • the equation in the second row expresses that the active power flowing into the cascade bridge inverter capacitor is zero
  • Represents the AC component vector expression of the voltage at the MMC AC output port of the single-phase half-bridge submodule connected to the cascaded bridge inverter Represents the AC component vector expression of the voltage at the AC output port of the cascade bridge inverter
  • a transformerless generalized unified power flow controller is used to realize power flow control of three transmission lines.
  • the transformerless generalized unified power flow controller includes a three-phase cascaded full-bridge topology inverter and a multi-port single-phase MMC power flow regulation module connected in series.
  • the multi-port single-phase MMC power flow regulation module The module contains four MMCs of single-phase half-bridge sub-modules that share the same common DC bus.
  • the MMCs of the four single-phase half-bridge sub-modules are respectively connected to three AC transmission lines and cascaded H-bridge inverters.
  • the AC component of the AC output port voltage of the MMC of the single-phase half-bridge submodule connected in series with the cascade bridge inverter, the AC output port of the cascade bridge inverter By adjusting the series compensation voltage connected in series on the feeder, the AC component of the AC output port voltage of the MMC of the single-phase half-bridge submodule connected in series with the cascade bridge inverter, the AC output port of the cascade bridge inverter.
  • the amplitude and phase of the AC component of the voltage realizes the internal energy balance of the transformerless generalized unified power flow controller, and on the other hand, realizes the active control of the active power and reactive power on the AC feeder, that is, the decoupling of the line power flow. control.
  • an embodiment of the present invention provides an equipment protection method for a controller, including overvoltage protection of voltages connected in series on transmission lines, multi-port single-phase MMC sub-module fault bypass protection and cascade bridge type Inverter sub-module protection.
  • the overvoltage protection of the voltage connected in series on the transmission line is to protect the overvoltage of the voltage connected in series on the transmission line through a protection device.
  • Figure 8 is a wiring diagram and a schematic diagram of the protection device of the voltage overvoltage protection method of the equipment protection method of the present invention.
  • the protection device is composed of a metal oxide voltage limiter and a thyristor bypass switch connected in parallel.
  • the metal oxide voltage limiter To limit the voltage to a safe voltage, the protection device is connected in parallel with the AC output port of the power flow regulating multi-port single-phase MMC in the multi-port single-phase MMC power flow regulating module. Protect against overvoltage of the voltage connected to the transmission lines.
  • multi-port single-phase MMC sub-module fault bypass protection includes:
  • the multi-port single-phase MMC sub-module is connected in parallel with the thyristor bypass switch through the AC output port of the multi-port single-phase MMC sub-module, so that when the multi-port single-phase MMC sub-module fails, the failed sub-module can be quickly bypassed through the thyristor bypass switch.
  • redundant sub-modules are invested so that the failure of the sub-module does not affect the overall operation of the equipment.
  • the DC side of the multi-port single-phase MMC sub-module is equipped with a DC unloading circuit for capacitive energy release to prevent overvoltage damage to power devices. , to protect multi-port single-phase MMC sub-module fault bypass.
  • the thyristor bypass switch is an anti-parallel thyristor, a resistor-capacitor loop, and a static resistor connected in parallel and then in series with a saturated reactor.
  • the thyristor bypass switch bypasses the AC output port of the power flow regulating multi-port single-phase MMC to achieve overflow. pressure protection.
  • cascade bridge inverter sub-module protection includes:
  • the cascade bridge inverter sub-module is connected in parallel with the fast mechanical switch through the AC port of the cascade bridge inverter sub-module, and the DC side of the cascade bridge inverter is equipped with a DC unloading circuit that releases capacitive energy.
  • the bridge type inverter sub-module is used for protection.
  • Cascade bridge inverter sub-module protection includes the AC port of the cascade bridge inverter sub-module being connected in parallel with a fast mechanical switch, so that when the cascade bridge inverter sub-module fails, the faulty module can be quickly removed.
  • the transformerless generalized unified power flow controller blocks all sub-modules and triggers the protection device and the thyristor bypass switch at the same time.
  • the protection device is triggered, the voltage in series on the transmission line is clamped. to about 0V, after the parallel cascade bridge inverter blocks all sub-modules, due to Then regardless of the direction of the current, the capacitor can be charged, where M is the number of sub-modules per phase of the cascade bridge inverter, V C is the DC voltage of the sub-module, U phase is the effective value of the grid phase voltage, and U ab is the grid line Voltage rms value.
  • the interconnection system of three transmission lines with flexible interconnection is implemented by a transformerless generalized unified power flow controller.
  • a transformerless generalized unified power flow controller Refer to Figure 9 for the connection schematic diagram.
  • the multi-port single-phase MMC power flow adjustment module of the control system of the present invention adopts a two-level half-bridge.
  • the topological structure of the three-port power flow control device using the cascaded full-bridge topology of the sub-module and cascade bridge inverter and its system diagram for interconnecting three transmission lines.
  • the multi-port single-phase MMC power flow adjustment module of the control method of the present invention adopts MMC and cascade bridge-type inverter with two-level single-phase half-bridge sub-modules in parallel.
  • the transformerless generalized unified power flow controller contains four MMCs of single-phase half-bridge sub-modules, among which three single-phase half-bridges are connected to the AC transmission line.
  • the MMC of the bridge sub-module controls the active power and reactive power on transmission line 2 and transmission line 3, and the corresponding control loop is the line power flow control loop.
  • the MMC of the single-phase half-bridge submodule connected to the cascade bridge inverter controls the common DC bus voltage balance, and the corresponding control loop is the common DC bus voltage balance control loop.
  • the cascade bridge inverter compensates the reactive power on the transmission line 1, and the corresponding control loop is the cascade bridge inverter control loop.
  • the simulation example of the distribution method of the series compensation voltage of the transformerless generalized unified power flow controller on the distribution network transmission line considers the optimization target as the output required by the MMC of the single-phase half-bridge submodule.
  • the AC component of the output voltage has the smallest amplitude, that is The choice satisfies Get the minimum value.
  • Figure 11 shows the simulation results of the three working conditions of the present invention, including a total of 11 waveform diagrams. From left to right and from top to bottom, they are: transmission line 1 active power P 1 waveform diagram, transmission line 1 reactive power Power Q 1 waveform diagram, transmission line 2 active power P 2 waveform diagram, transmission line 2 reactive power Q 2 waveform diagram, transmission line 3 active power P 3 waveform diagram, transmission line 3 reactive power Q 3 waveform diagram, transmission line Voltage waveform diagram of multi-port single-phase MMC capacitor connected to 1, voltage waveform diagram of multi-port single-phase MMC capacitor connected to transmission line 2, voltage waveform diagram of multi-port single-phase MMC capacitor connected to transmission line 3, and cascade bridge type inverter The multi-port single-phase MMC capacitor voltage waveform connected to the inverter and the cascade bridge inverter capacitor voltage waveform.
  • the simulation waveform results show that when three transmission lines are interconnected, the transformerless generalized unified power flow controller not only realizes active power flow control with active power and reactive power decoupling on the transmission lines, but also maintains the stability of the device.
  • Internal internal energy balance that is, stable capacitor voltage, and port expansion capabilities.
  • the topology of the present invention also has independent power flow adjustment capabilities.
  • the specific details are compared as shown in the table below:
  • the traditional unified power flow controller contains a bulky power frequency transformer, the overall volume of the equipment is large, and the cost of operation and maintenance is high.
  • the T-type transformerless power flow controller eliminates the bulky power frequency transformer and has advantages in size and cost, it needs to sacrifice a degree of control freedom to maintain the balance of the controller power, so it cannot control the reactive power at the source end, and
  • the ports of the T-type transformerless power flow controller cannot be expanded.
  • Both back-to-back voltage source converters and Hexverter-based power flow controllers are full-power topologies, which make the equipment larger and the cost of port expansion higher.
  • the power flow controller proposed by the present invention has independent power flow control capability, small equipment size, low operation and installation costs, easy port expansion, and low expansion costs.

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Abstract

本发明公开了一种无变压器型广义统一潮流控制器、方法及系统包括：无功补偿模块和潮流调节模块，无功补偿模块包括级联桥型逆变器，潮流调节模块包括多端口单相MMC，其中，多端口单相MMC与级联桥型逆变器进行串联，无功补偿模块为电压源型变流器，具备无功功率双向补偿功能，可以从系统吸收无功，也可以为系统提供无功补偿，潮流调节模块实现输电线有功功率和无功功率的解耦控制。和现有统一潮流控制器相比，本发明省去了昂贵且笨重的工频隔离变压器，不仅减小了装置的占地面积，更降低了装置安装运行的成本，且无变压器型的设计使得装置响应速度更快，损耗更低。

Description

一种无变压器型广义统一潮流控制器、方法及系统 技术领域
本发明涉及交流电网潮流控制、电力电子技术领域，特别是一种适用于交流电网的具备多端口主动潮流控制能力的无变压器型广义统一潮流控制器及其控制方法和系统。
背景技术
随着负荷增长及大规模可再生能源的接入，电网结构日趋复杂。一方面，现代电力系统已经发展为大型互联网络，存在着发电机出力和负荷需求不平衡，导致电网潮流分布不均、线路过载、损耗增大，输电量下降等问题。另一方面，高比例的可再生能源的接入和负荷的不断发展，由源荷互动引起的电力系统运行方式多样变化，将导致电力系统潮流分布极为复杂，进而给电力系统的可靠运行带来了巨大的挑战。
为了解决上述问题，通常有两种方案：第一种方案为升级现有输电线路或增设输电线路，增强网架结构，这种方案受输电走廊匮乏、新增变电站征地困难以及经济性等因素的限制而难以实现；第二种方案为通过柔性交流输电装置实现输电线路的主动潮流控制。这种方案可通过电力电子装置对影响功率传输的所有电气参数进行控制，使得电网灵活可控，不仅不需要改变现有电网的结构，还具有灵活调节潮流、动态补偿以及抑制振荡等优点。同时充分利用电力电子装置控制的实时性和快速性，实现输电线上潮流快速动态的调节，从而优化潮流分布。
现有潮流调节功能最全面的潮流控制器主要是广义统一潮流控制器，现有的广义统一潮流控制器典型拓扑结构由一个并联的电压源型换流器和多个串联的电压源型换流器背靠背连接，换流器通过工频隔离变压器和输电线路相连接。通过调节串联侧换流器电压的幅值与相角可独立调节多条输电线路的有功功率和无功功率。然而，该拓扑需要采用昂贵且笨重的工频隔离变压器，这导致装置总体体积大，安装运行和维护的成本很高，同时在拓展设备连接端口时需增加串联工频隔离变压器和三相的电压源型换流器，端口拓展成本高。
发明内容
本部分的目的在于概述本发明的实施案例的一些方面以及简要介绍一些 较佳实施案例。在本部分以及本申请的说明书摘要和发明名称中可能会做些简化或省略以避免使本部分、说明书摘要和发明名称的目的模糊，而这种简化或省略不能用于限制本发明的范围。
鉴于现有技术中存在的问题，提出了本发明。
因此，本发明解决的技术问题是：针对现阶段存在着现有的潮流控制器设备总体体积大，运行维护成本高以及设备体积和运行维护成本降低后与潮流控制器所要达到的功能之间难以权衡的问题，充分考虑潮流控制器的轻便性、经济性和实用性设计了一种无变压器的潮流控制器的新型结构。
为解决上述技术问题，本发明提供如下技术方案：
无变压器型广义统一潮流控制器包括，
无功补偿模块，所述无功补偿模块包括级联桥型逆变器；
潮流调节模块，所述潮流调节模块包括多端口单相MMC；
其中，所述多端口单相MMC与所述级联桥型逆变器进行串联；
所述无功补偿模块为电压源型变流器，具备无功功率双向补偿功能，可以从系统吸收无功，也可以为系统提供无功补偿；
所述潮流调节模块实现输电线有功功率和无功功率的解耦控制。
作为本发明所述的无变压器型广义统一潮流控制器，其中：所述级联桥型逆变器是由多个子模块级联而成。
作为本发明所述的无变压器型广义统一潮流控制器，其中：所述多端口单相MMC包括潮流调节多端口单相MMC和能量平衡多端口单相MMC；
所述能量平衡多端口单相MMC与潮流调节多端口单相MMC并联；
所述级联桥型逆变器与能量平衡多端口单相MMC的交流输出端口相连，实现级联桥型逆变器与多端口单相MMC的串联连接；
所述潮流调节多端口单相MMC的交流输出端口与输电线串联，通过调节串联在输电线上的多端口单相MMC交流输出端口电压的幅值相位，实现输电线有功功率和无功功率的解耦控制。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所述线路潮流控制环的控制目标为：
获取潮流控制输电线的有功功率的参考值和无功功率的参考值
设定线路潮流控制环输出
其中，为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口的输出电压的交流成分的参考值，为与潮流控制输电线相连的潮流调节多端口单相MMC交流输出端口的输出电压的交流成分的参考值，下标i表示第i条输电线为潮流调节平衡输电线，下标j表示第j条潮流控制输电线。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所述级联桥型逆变器控制环包括，
电压控制外环、无功功率控制外环和电流控制内环；
所述级联桥型逆变器控制环的控制目标为潮流调节平衡输电线的无功功率达到参考值和级联桥型逆变器三相电容电压之和稳定为参考值级联桥型逆变器控制环的输出为级联桥型逆变器交流输出端口的电压的交流成分的参考值
所述无功功率控制外环根据潮流调节平衡输电线的无功功率参考值计算潮流调节平衡输电线电流q轴分量参考值
所述电流控制内环在dq坐标系下进行控制，利用比例积分控制器，对潮流调节平衡输电线电流的d轴分量和q轴分量分别控制，数学方程为：
其中，和乘以帕克逆转换矩阵，再乘以-1反相后，得到abc坐标系下的级联桥型逆变器控制环输出参考电压即Vpa、Vpb、Vpc；
其中，VCid和VCiq为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口电压的交流成分的d轴分量和q轴分量，VSMd和VSMq为与级联桥型逆变器相连的能量平衡多端口单相MMC交流输出端口电压的交流成分的d轴分量和q轴分量，kp2为比例积分控制器比例环节增益系数，ki2为比例积分控制器积分环节增益系数，Vid、Viq、VCid、VCiq、VSMd、VSMq为前馈项，作用是增强控制环抗干扰能力，加快控制环响应速度，为解耦项，作用是实现d轴和q轴的解耦控制。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所述公共直流母线电压平衡控制环的控制目标为公共直流母线电压稳定为参考值公共直流母线电压平衡控制环的输出为公共直流母线平衡参考电压
所述公共直流母线电压平衡控制环的控制在abc坐标系下进行，利用比例积分控制器对abc三相的公共直流母线电压进行控制，数学方程为：
其中，Vlinka、Vlinkb、Vlinkc为三相公共直流母线电压，Ipa、Ipb、Ipc为级联桥型逆变器支路三相电流，为前馈的三相参考电压，kp3为比例积分控制器比例环节增益系数，ki3为比例积分控制器积分环节增益系数。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所述环流抑制控制的控制目标为抑制每相的多端口单相MMC之间的环流，环流抑制控制的输出为产生环流的二倍频电压，通过对子模块调制信号进行补偿，实现环流的抑制；
所述环流抑制控制在abc坐标系下进行，利用准比例谐振控制器对abc三相的相内环流进行抑制，数学方程为：
其中，GQPR(s)为准PR控制器的传递函数，ω为谐振频率，ωc为截至频率主要影响系统带宽，kp4为准比例谐振控制器比例环节增益系数，kr为准比例谐振控制器谐振环节增益系数，为与第k条输电线连接的潮流调节多端口单相MMC子模块环流补偿电压，s为拉普拉斯变化下的模型变量，为能量平衡多端口单相MMC子模块环流补偿电压，ilkp和ilkn为与第k条输电线相连的潮流调节多端口单相MMC上桥臂电流和下桥臂电流，下标l为l相的参数。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所述桥臂电压均衡控制包括桥臂电压直流分量调节和注入基频环流调节两种实现方式。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所 述桥臂电压直流分量的调节方式包括，调节上下桥臂直流分量进而控制上下桥臂电容电压均衡，输出为多端口单相MMC上桥臂和下桥臂子模块电压直流分量参考值；
所述桥臂电压均衡控制利用PI控制器对abc三相的多端口单相MMC的桥臂电压直流分量进行控制，数学方程为：
其中，为上桥臂电压直流分量参考值，为下桥臂电压直流分量参考值，为上下桥臂电压均值的参考值，Vaverage,lkp和Vaverage,klp为上桥臂和下桥臂电压的均值，Vlink,l为直流母线电压，下标k为与第条k输电线相连的潮流调节多端口单相MMC的参数，下标l为l相的参数，kp5为比例积分控制器比例环节增益系数，ki5为比例积分控制器积分环节增益系数。
作为本发明所述的无变压器型广义统一潮流控制器的控制方法，其中：所述注入基频环流调节的调节方式包括，
所述基频环流注入调节的桥臂电压均衡控制，通过注入与电压相位相同的基频环流实现上下桥臂电压的均衡，注入基频环流调节的输出为注入的基频环流的参考值，数学方程为：
其中，为与第k条输电线相连的潮流调节多端口单相MMC注入基频环流的参考值，Vaverage,lkp和Vaverage,lkn为潮流调节多端口单相MMC的上下桥臂电压均值，θk为与第k条输电线相连的潮流调节多端口单相MMC输出电压基频分量的相位，kp6为比例积分控制器比例环节增益系数，ki6为比例积分控制器积分环节增益系数。
作为本发明所述的无变压器型广义统一潮流控制器的分配方法，其中：所述基本方程如下：
若第1条输电线为潮流调节平衡输电线，Real为实部，为所述无变压 器型广义统一潮流控制器在第k条输电线上串联补偿电压交流成分的矢量表达式，为实现第k条输电线上目标潮流时所需串联在第1条输电线和第k条输电线之间的串联补偿电压矢量表达式，为与所述级联桥型逆变器相连的所述多端口单相MMC潮流调节模块中的能量平衡多端口单相MMC交流输出端口电压交流成分的矢量表达式，为第k条输电线上的交流电流的共轭矢量表达式，为所述级联桥型逆变器支路的交流电流的共轭矢量表达式，n为通过所述无变压器型广义统一潮流控制器互联的输电线数量。
作为本发明所述的无变压器型广义统一潮流控制器的控制系统，其中：所述控制系统的核心设备为无变压器型广义统一潮流控制器、交流输电线和变电站；
所述无变压器型广义统一潮流控制器安装于多条交流输电线的汇集处；
所述交流输电线与无变压器型广义统一潮流控制器相连，交流输电线可经升压变压器接入高压系统，可经降压变压器接入低压交流系统，低压交流系统可接入低压交流负载、储能设备和电动汽车快充站。
作为本发明所述的无变压器型广义统一潮流控制器的设备保护方法，其中：所述串联在输电线上的电压的过压保护包括保护装置，
所述保护装置与多端口单相MMC潮流调节模块中的潮流调节多端口单相MMC的交流输出端口间并联，实现对串联在输电线上的电压的过压进行保护；
所述保护装置由金属氧化物限压器和晶闸管旁路开关并联组成；
其中，晶闸管旁路开关为反并联晶闸管、阻容回路、静态电阻并联后再与一个饱和电抗器串联；
所述金属氧化物限压器将电压限制在安全电压而晶闸管旁路开关通过将潮流调节多端口单相MMC的交流输出端口旁路，实现过压保护。
作为本发明所述的无变压器型广义统一潮流控制器的设备保护方法，其中：
所述多端口单相MMC子模块的交流输出端口与晶闸管旁路开关并联，使得多端口单相MMC子模块故障时可通过晶闸管旁路开关快速旁路故障的子模块，同时投入冗余的子模块，使得子模块的故障并不影响设备的总体运行；
所述多端口单相MMC子模块的直流侧配有用于电容能量释放的直流卸荷电路，防止过压损坏功率器件。
作为本发明所述的无变压器型广义统一潮流控制器的设备保护方法，其中： 所述级联桥型逆变器子模块的交流端口与快速机械开关并联，使得级联桥型逆变器子模块故障时可迅速切除故障模块；
所述级联桥型逆变器子模块直流侧配有释放电容能量的直流卸荷电路，防止过压损坏功率器件。
本发明的有益效果：现有的级联桥型逆变器只具备无功功率补偿功能，不具备多交流输电线互联和输电线主动潮流解耦控制功能，而本发明通过引入多端口单相MMC潮流调节模块，提供多个交流互联端口，实现多交流输电线互联，并通过调节串联在输电线上的串联补偿电压的幅值相位，可实现输电线有功功率和无功功率解耦的主动控制，和现有统一潮流控制器相比，省去了昂贵且笨重的工频隔离变压器，不仅减小了装置的占地面积，降低了装置安装运行的成本，还加快了装置响应速度，损耗更低。且在拓展潮流控制端口时，传统的广义统一潮流控制器需增加三相的换流器和一台工频隔离变压器，端口拓展成本很高，而本发明中的无变压器型广义统一潮流控制器，只需增加单相小容量的MMC模块数量，可快速、经济地实现潮流控制端口的拓展。
本发明的另外一个有益效果：基于本发明控制器的控制方法可实现控制器的基本功能，保证控制正常运转。
本发明的另外一个有益效果：本发明控制系统的交流输电线不仅可经升压变压器接入高压系统，也可经降压变压器接入低压交流系统，而低压交流系统可接入低压交流负载、储能设备和电动汽车快充站。
本发明的另外一个有益效果：基于本发明控制器的设备保护方法可避免故障情况下换流器内部器件的严重损坏。
附图说明
为了更清楚地说明本发明实施例的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其它的附图。其中：
图1为本发明无变压器型广义统一潮流控制器的拓扑结构与互联多输电线的系统示意图。
图2为本发明无变压器型广义统一潮流控制器省去与级联桥型逆变器相连的能量平衡多端口单相MMC的拓扑结构及其互联多输电线的系统示意 图。
图3为本发明无变压器型广义统一潮流控制器所述的级联桥型逆变器和多端口单相MMC的典型拓扑举例示意图。
图4为本发明无变压器型广义统一潮流控制器所述的多端口单相MMC潮流调节模块的拓扑结构示意图。
图5为本发明无变压器型广义统一潮流控制器的控制方法所述的多端口单相MMC潮流调节模块采用并联两电平单相半桥型子模块的MMC、级联桥型逆变器采用级联全桥拓扑的双端口潮流控制装置的控制方法框图。
图6为本发明无变压器型广义统一潮流控制器的控制系统图。
图7为本发明无变压器型广义统一潮流控制器的控制系统的多端口单相MMC潮流调节模块采用两电平半桥型子模块、级联桥型逆变器采用级联全桥拓扑的双端口潮流控制装置的拓扑结构及其实现两条输电线互联的系统示意图。
图8为本发明无变压器型广义统一潮流控制器的设备保护方法的电压的过压保护方法接线图及保护装置示意图。
图9为本发明无变压器型广义统一潮流控制器的控制系统的多端口单相MMC潮流调节模块采用两电平半桥型子模块、级联桥型逆变器采用级联全桥拓扑的三端口潮流控制装置的拓扑结构及其实现三条输电线互联的系统示意图。
图10为本发明无变压器型广义统一潮流控制器的控制方法的的多端口单相MMC潮流调节模块采用并联两电平单相半桥型子模块的MMC、级联桥型逆变器采用级联全桥拓扑的三端口潮流控制装置的控制方法框图。
图11为本发明无变压器型广义统一潮流控制器、方法及系统的三种工况的仿真各输电线潮流、装置内各电容电压波形图。
具体实施方式
为使本发明的上述目的、特征和优点能够更加明显易懂，下面结合说明书附图对本发明的具体实施方式做详细的说明，显然所描述的实施例是本发明的一部分实施例，而不是全部实施例。基于本发明中的实施例，本领域普通人员在没有做出创造性劳动前提下所获得的所有其他实施例，都应当属于本发明的保护的范围。
在下面的描述中阐述了很多具体细节以便于充分理解本发明，但是本发明还可以采用其他不同于在此描述的其它方式来实施，本领域技术人员可以在不违背本发明内涵的情况下做类似推广，因此本发明不受下面公开的具体实施例的限制。
其次，此处所称的“一个实施例”或“实施例”是指可包含于本发明至少一个实现方式中的特定特征、结构或特性。在本说明书中不同地方出现的“在一个实施例中”并非均指同一个实施例，也不是单独的或选择性的与其他实施例互相排斥的实施例。
本发明结合示意图进行详细描述，在详述本发明实施例时，为便于说明，表示器件结构的剖面图会不依一般比例作局部放大，而且所述示意图只是示例，其在此不应限制本发明保护的范围。此外，在实际制作中应包含长度、宽度及深度的三维空间尺寸。
同时在本发明的描述中，需要说明的是，术语中的“上、下、内和外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。此外，术语“第一、第二或第三”仅用于描述目的，而不能理解为指示或暗示相对重要性。
本发明中除非另有明确的规定和限定，术语“安装、相连、连接”应做广义理解，例如：可以是固定连接、可拆卸连接或一体式连接；同样可以是机械连接、电连接或直接连接，也可以通过中间媒介间接相连，也可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以具体情况理解上述术语在本发明中的具体含义。
实施例1
参照图1～图4为本发明的一个实施例，提供了一种无变压器型广义统一潮流控制器，包括无功补偿模块，具备无功功率双向补偿功能，可以从系统吸收无功，也可以为系统提供无功补偿；潮流调节模块，实现输电线有功功率和无功功率的解耦控制。
具体的，无功补偿模块为电压源型变流器，具备无功功率双向补偿功能，可以从系统吸收无功，也可以为系统提供无功补偿，无功补偿模块包括级联桥型逆变器，级联桥型逆变器是由多个子模块级联而成，如图3为本 发明的控制器中的级联桥型逆变器和多端口单相MMC的典型拓扑举例示意图，级联桥型逆变器的子模块可以是三电平型的，也可以是五电平型的，还可以是其他多电平的子模块。
具体的，潮流调节模块实现输电线有功功率和无功功率的解耦控制，潮流调节模块包括多端口单相MMC，多端口单相MMC与级联桥型逆变器进行串联。
较佳的，如图1为本发明的控制器的拓扑结构及其互联多输电线的系统示意图，多端口单相MMC包括潮流调节多端口单相MMC和能量平衡多端口单相MMC，能量平衡多端口单相MMC与潮流调节多端口单相MMC并联，级联桥型逆变器与能量平衡多端口单相MMC的交流输出端口相连，实现级联桥型逆变器与多端口单相MMC的串联连接，潮流调节多端口单相MMC的交流输出端口与输电线串联，通过调节串联在输电线上的多端口单相MMC交流输出端口电压的幅值相位，实现多端口单相MMC潮流调节模块的公共直流母线电压稳定和输电线有功功率和无功功率的解耦控制。
较佳的，如图2为本发明的控制器省去与级联桥型逆变器相连的能量平衡多端口单相MMC的拓扑结构及其互联多输电线的系统示意图，多端口单相MMC潮流调节模块包括多个共享同一公共直流母线且彼此互相并联的潮流调节多端口单相MMC，潮流调节多端口单相MMC的交流输出端口与输电线串联，通过调节串联在输电线上的潮流调节多端口单相MMC交流输出端口电压的幅值相位，实现输电线有功功率和无功功率的主动控制。
进一步的，如图4为本发明的控制器的多端口单相MMC潮流调节模块的拓扑结构示意图，当多端口单相MMC潮流调节模块仅包括潮流调节多端口单相MMC时，级联桥型逆变器与公共直流母线的正极或负极直接相连，能够实现级联桥型逆变器与多端口单相MMC潮流调节模块的串联，当多端口单相MMC潮流调节模块同时包括潮流调节多端口单相MMC以及能量平衡多端口单相MMC时，级联桥型逆变器的交流输出端口可以与能量平衡多端口单相MMC的交流输出端口相连，同样能够实现级联桥型逆变器与多端口单相MMC潮流调节模块的串联。
进一步的，控制系统使用无变压器型广义统一潮流控制器实现两端输电线潮流控制的装置拓扑和系统连接，无变压器型广义统一潮流控制器包括一个三相级联全桥拓扑的级联桥型逆变器和与之串联的多端口单相 MMC潮流调节模块。
具体的，多端口单相MMC潮流调节模块包含三个共享同一公共直流母线的单相半桥型子模块的MMC，三个单相半桥型子模块的MMC分别与两条交流输电线以及级联桥型逆变器一一相连，并通过调节串联在输电线上的串联补偿电压、与级联桥型逆变器串联的单相半桥型子模块的MMC交流输出端口电压的交流成分、级联桥型逆变器的交流输出端口电压的交流成分的幅值相位，其中，串联补偿电压为串联在输电线上的潮流调节多端口单相MMC交流输出端口电压的交流成分，一方面实现无变压器型广义统一潮流控制器的内部能量平衡，另一方面实现交流输电线上的有功功率和无功功率的主动控制，即实现线路潮流的解耦控制。
实施例2
参照图5，为本发明的一个实施例，提供了一种基于无变压器型广义统一潮流控制器的控制方法，包括：
线路潮流控制环、级联桥型逆变器控制环、公共直流母线电压平衡控制环、环流抑制控制和桥臂电压均衡控制。
进一步的，线路潮流控制环为主要控制包括：
线路潮流控制环的控制目标为潮流控制输电线的有功功率达到参考值和无功功率达到参考值。
较佳的，设定线路潮流控制环输出为
其中，为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口的输出电压的交流成分的参考值，为与潮流控制输电线相连的潮流调节多端口单相MMC交流输出端口的输出电压的交流成分的参考值，下标i表示第i条输电线为潮流调节平衡输电线，下标j表示第j条潮流控制输电线。
具体的，线路潮流控制环首先根据潮流控制输电线的有功功率参考值和无功功率参考值计算潮流控制输电线电流的d轴分量参考值和q轴分量参考值计算方法为解如下方程组：
进一步的，线路潮流控制环在dq坐标系下进行，利用比例积分控制器进行控制，数学方程为：
其中，和乘以帕克逆转换矩阵，得到abc坐标系下的线路潮流控制环输出参考电压即V表示输电线的节点电压，I表示输电线的电流，ω表示输电线的交流频率，L表示输电线的等效电感感值，LPFCM表示多端口单相MMC桥臂的等效电感感值，R表示输电线的等效电阻阻值，V、I、L、R的下标i表示为潮流调节平衡输电线的参数，下标j表示为第j条潮流控制输电线的参数，下标d表示为d轴分量，下标q表示为q轴分量，上标*表示为参考值，kp为比例积分控制器比例环节增益系数，ki为比例积分控制器积分环节增益系数，Vid、Viq、Vjd、Vjq，为前馈项，作用是增强控制环抗干扰能力，加快控制环响应速度，
其中，为解耦项，作用是实现d轴和q轴的解耦控制。
进一步的，级联桥型逆变器控制环为主要控制包括：
电压控制外环、无功功率控制外环和电流控制内环。
具体的，级联桥型逆变器控制环的控制目标为潮流调节平衡输电线的无功功率达到参考值和级联桥型逆变器三相电容电压之和稳定为参考值并输出为级联桥型逆变器交流输出端口的电压的交流成分的参考值
较佳的，无功功率控制外环根据潮流调节平衡输电线的无功功率参考值计算潮流调节平衡输电线电流q轴分量参考值计算公式为：
进一步的，电流控制内环在dq坐标系下进行控制，利用比例积分控制器，对潮流调节平衡输电线电流的d轴分量和q轴分量分别控制，数学方程为：
其中，和乘以帕克逆转换矩阵，再乘以-1反相后，得到abc坐标系下的级联桥型逆变器控制环输出参考电压即Vpa、Vpb、Vpc、VCid、VCiq为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口电压的交流成分的d轴分量和q轴分量，VSMd和VSMq为与级联桥型逆变器相连的能量平衡多端口单相MMC交流输出端口电压的交流成分的d轴分量和q轴分量，kp2为比例积分控制器比例环节增益系数，ki2为比例积分控制器积分环节增益系数，Vid、Viq、VCid、VCiq、VSMd、VSMq为前馈项，作用是增强控制环抗干扰能力，加快控制环响应速度，
其中，为解耦项，作用是实现d轴和q轴的解耦控制。
进一步的，公共直流母线电压平衡控制环为主要控制包括：
公共直流母线电压平衡控制环的控制目标为公共直流母线电压稳定为参考值并输出为公共直流母线平衡参考电压
较佳的，公共直流母线电压平衡控制环的控制在abc坐标系下进行，利用比例积分控制器对abc三相的公共直流母线电压进行控制，数学方程为：
其中，Vlinka、Vlinkb、Vlinkc为三相公共直流母线电压，Ipa、Ipb、Ipc为级联桥型逆变器支路三相电流，为前馈的三相参考电压，kp3为比例积分控制器比例环节增益系数，ki3为比例积分控制器积分环节增益系数。
进一步的，若无变压器型广义统一潮流控制器拓扑中包含与级联桥型逆变器相连的能量平衡多端口单相MMC，得到线路潮流控制环的输出参考电压后，潮流调节多端口单相MMC交流输出端口的参考电压为：
其中，为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流 输出端口的参考电压，为与第j条潮流控制输电线相连的潮流调节多端口单相MMC交流输出端口的参考电压，为潮流控制环的输出电压，为按照本发明提供的一种基于无变压器型广义潮流控制器的分配方法中的任意一种串联补偿电压分配方式计算得到的与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口的参考电压的交流成分，公共直流母线电压平衡控制环中的前馈三相参考电压，等于零，能量平衡多端口单相MMC交流输出端口的参考电压为：
具体的，级联桥型逆变器的交流输出端口的参考电压为：
更进一步的，若无变压器型广义统一潮流控制器拓扑中不包含与级联桥型逆变器相连的能量平衡多端口单相MMC，得到线路潮流控制环的输出参考电压后，潮流调节多端口单相MMC交流输出端口的参考电压为：
其中，为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口的参考电压，为与第j条潮流控制输电线相连的潮流调节多端口单相MMC交流输出端口的参考电压，公共直流母线电压平衡控制环中的前馈三相参考电压，为本发明提供的一种基于无变压器型广义潮流控制器的分配方法中的任意一种串联补偿电压分配方式计算得到的与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口的参考电压的交流成分，级联桥型逆变器控制环中的电流控制内环中的前馈项VSMd和VSMq等于零，级联桥型逆变器的交流输出端口的参考电压为：
具体的，当级联桥型逆变器交流输出端口与公共直流母线负极相连时取加号，当级联桥型逆变器交流输出端口与公共直流母线正极相连时取减号。
进一步的，环流抑制控制包括：
环流抑制控制的控制目标为抑制每相的多端口单相MMC之间的环流，环流抑制控制输出为产生环流的二倍频电压，通过对子模块调制信号进行补偿，实现环流的抑制。
较佳的，环流抑制控制在abc坐标系下进行，利用准比例谐振控制器对abc三相的相内环流进行抑制，数学方程为：
其中，GQPR(s)为准PR控制器的传递函数，ω为谐振频率，ωc为截至频率主要影响系统带宽，kp4为准比例谐振控制器比例环节增益系数，kr为准比例谐振控制器谐振环节增益系数，为与第k条输电线连接的潮流调节多端口单相MMC子模块环流补偿电压，s为拉普拉斯变化下的模型变量，为能量平衡多端口单相MMC子模块环流补偿电压，ilkp和ilkn为与第k条输电线相连的潮流调节多端口单相MMC上桥臂电流和下桥臂电流，下标l为l相的参数，锁相环锁定潮流调节平衡输电线的节点三相电压，获得锁定线路的相位，锁相环输出的相角为abc坐标系到dq坐标系的帕克转换矩阵提供角度。
进一步的，桥臂电压均衡控制包括：
桥臂电压均衡控制为桥臂电压直流分量调节和注入基频环流调节，两种实现方式。
较佳的，桥臂电压直流分量的调节方式包括调节上下桥臂直流分量进而控制上下桥臂电容电压均衡，并输出为多端口单相MMC上桥臂和下桥臂子模块电压直流分量参考值，桥臂电压均衡控制利用PI控制器对abc三相的多端口单相MMC的桥臂电压直流分量进行控制，数学方程为：
其中，为上桥臂电压直流分量参考值，为下桥臂电压直流分量参考值，为上下桥臂电压均值的参考值，Vaverage,lkp和Vaveragelkp为上桥臂和下桥臂电压的均值，Vlink,l为直流母线电压，下标k为与第条k输电线相连的潮流调节多端口单相MMC的参数，下标l为l相的参数，kp5为比例积分控制器比例环节增益系数，ki5为比例积分控制器积分环节增益系数。
较佳的，注入基频环流调节的调节方式包括基频环流注入调节的桥臂电压 均衡控制，通过注入与电压相位相同的基频环流实现上下桥臂电压的均衡，其输出为注入的基频环流的参考值，数学方程为：
其中，为与第k条输电线相连的潮流调节多端口单相MMC注入基频环流的参考值，Vaverage,lkp和Vaverage,lkn为潮流调节多端口单相MMC的上下桥臂电压均值，θk为与第k条输电线相连的潮流调节多端口单相MMC输出电压基频分量的相位，kp6为比例积分控制器比例环节增益系数，ki6为比例积分控制器积分环节增益系数。
实施例3
本实施例为本发明的第三个实施例，提供了一种基于无变压器型广义统一潮流控制器的分配方法，包括：
控制器的分配方法为满足基本条件方程的任何一组的解。
具体的，基本条件方程为：
其中，假设第1条输电线为潮流调节平衡输电线，Real为实部，为无变压器型广义统一潮流控制器在第k条输电线上串联补偿电压交流成分的矢量表达式，为实现第k条输电线上目标潮流时所需串联在第1条输电线和第k条输电线之间的串联补偿电压矢量表达式，为与级联桥型逆变器相连的多端口单相MMC潮流调节模块中的能量平衡多端口单相MMC交流输出端口电压交流成分的矢量表达式，为第k条输电线上的交流电流的共轭矢量表达式，为级联桥型逆变器支路的交流电流的共轭矢量表达式，n为通过无变压器型广义统一潮流控制器互联的输电线数量。
较佳的，适用于交流电网的具备主动潮流控制能力的无变压器型广义统一潮流控制器在配网输电线上串联补偿电压的一种分配方法是其特点为简化性。
较佳的，串联补偿电压的另一种分配方法是即的选取满足从而能够在拓扑上省去与级联桥型逆变器连接的能量平衡多端口单相MMC。
较佳的，串联补偿电压的另一种分配方法是的选取满足取到最小值，从而能够使得单相变流器所需输出电压交流成分幅值最小。
较佳的，串联补偿电压的分配方法还可以是任何一种满足基本条件方程的选取方式。
较佳的，多端口单相MMC潮流调节模块中的单相变流器交流输出端口电压成分中含有控制所需的不同交流成分。
实施例4
参照图6～图7为本发明的一个实施例，提供了一种基于无变压器型广义统一潮流控制器的控制系统，包括：
如图6为本发明的控制系统图，交流电网多输电线潮流控制系统核心设备为无变压器型广义统一潮流控制器，其他组成为交流输电线和变电站。需要说明的是：
无变压器型广义统一潮流控制器安装于多条交流输电线汇集处，交流输电线与无变压器型广义统一潮流控制器相连，交流输电线可以经升压变压器接入高压系统，还可以经降压变压器接入低压交流系统，低压交流系统可以接入低压交流负载或储能设备或电动汽车快充站。
具体的，如图7为本发明控制系统的多端口单相MMC潮流调节模块采用两电平半桥型子模块、级联桥型逆变器采用级联全桥拓扑的双端口潮流控制装置的拓扑结构及其实现两条输电线互联的系统示意图，无变压器型广义统一潮流控制器实现的两端输电线潮流控制系统，无变压器型广义统一潮流控制器内部能量平衡的表现为公共直流母线的电容电压保持稳定以及级联桥型逆变器内的电容电压保持稳定，则要求流入上述电容的有功功率保持为零，即：
其中，第一行的方程表示为流入公共直流母线电容的有功功率为零，第二行的方程表示为流入级联桥型逆变器电容的有功功率为零，表示与输电线1相连的单相半桥型子模块的MMC交流输出端口的电压的交流成分矢量表达式，表示与输电线2相连的单相半桥型子模块的MMC交流输出端口的电压的交流成分矢量表达式，表示与级联桥型逆变器相连的单相半桥型子模块的MMC交流输出端口的电压的交流成分矢量表达式，表示级联桥型逆变器交流输出端口的电压的交流成分矢量表达式，表示输电线1电流的共轭矢量表达式，表示输电线2电流的共轭矢量表达式，表示级联桥型逆变器支路电流的共轭矢量表达式。通过调节与的幅值及大小，使得上述方程成立，即实现无变压器型广义统一潮流控制器的内部能量平衡。
具体的，使用无变压器型广义统一潮流控制器实现三条输电线潮流控制。该实施案例中，无变压器型广义统一潮流控制器包括一个三相级联全桥拓扑的逆变器和与之串联的多端口单相MMC潮流调节模块模块，该多端口单相MMC潮流调节模块模块包含四个共享同一公共直流母线的单相半桥型子模块的MMC，该四个单相半桥型子模块的MMC分别与三条交流输电线以及级联H桥逆变器一一相连，通过调节串联在馈线上的串联补偿电压、与级联桥型逆变器串联的单相半桥型子模块的MMC的交流输出端口电压的交流成分、级联桥型逆变器的交流输出端口电压的交流成分的幅值相位，一方面实现无变压器型广义统一潮流控制器的内部能量平衡，另一方面实现交流馈线上的有功功率和无功功率的主动控制，即实现线路潮流的解耦控制。
实施例5
参照图8，为本发明的一个实施例，提供了控制器的设备保护方法，包括串联在输电线上的电压的过压保护、多端口单相MMC子模块故障旁路保护和级联桥型逆变器子模块保护。
具体的，串联在输电线上的电压的过压保护是通过一个保护装置对串联在输电线上的电压的过压进行保护。
具体的，如图8为本发明的设备保护方法的电压的过压保护方法接线图及保护装置示意图，保护装置由金属氧化物限压器和晶闸管旁路开关并联组成，金属氧化物限压器将电压限制在安全电压，保护装置与多端口单相MMC潮流调节模块中的潮流调节多端口单相MMC的交流输出端口间并联，对串 联在输电线上的电压的过压进行保护。
具体的，多端口单相MMC子模块故障旁路保护包括：
多端口单相MMC子模块通过多端口单相MMC子模块的交流输出端口与晶闸管旁路开关并联，使得多端口单相MMC子模块故障时可通过晶闸管旁路开关快速旁路故障的子模块，同时投入冗余的子模块，使得子模块的故障并不影响设备的总体运行，以及多端口单相MMC子模块的直流侧配有用于电容能量释放的直流卸荷电路，防止过压损坏功率器件，对多端口单相MMC子模块故障旁路进行保护。
具体的，晶闸管旁路开关为反并联晶闸管、阻容回路、静态电阻并联后再与一个饱和电抗器串联，晶闸管旁路开关通过将潮流调节多端口单相MMC的交流输出端口旁路，实现过压保护。
进一步的，级联桥型逆变器子模块保护包括：
级联桥型逆变器子模块通过级联桥型逆变器子模块的交流端口与快速机械开关并联，以及级联桥型逆变器直流侧配有释放电容能量的直流卸荷电路对级联桥型逆变器子模块进行保护。
级联桥型逆变器子模块保护包括级联桥型逆变器子模块的交流端口与快速机械开关并联，使得级联桥型逆变器子模块故障时可迅速切除故障模块。
进一步的，在外部输电线发生故障时，无变压器型广义统一潮流控制器闭锁所有子模块，同时触发保护装置和晶闸管旁路开关，当保护装置触发后，串联在输电线上的电压被钳位至0V左右，并联的级联桥型逆变器闭锁所有的子模块闭锁后，由于则不论电流方向，电容均能进行充电，其中，M为级联桥型逆变器每相子模块数，VC为子模块直流电压，Uphase为电网相电压有效值，Uab为电网线电压有效值。由于每相的电容直流电压之和大于并网点相电压幅值，因此在STATCOM闭锁时，充电回路中电容直流电压之和大于两点充电电压，二极管承受反向压降而关断，无法对电容进行充电，充电电流为零。
实施例6
参照图9～图11，为本发明的另一个实施例，结合上述实施案例，以下采用MATLAB/Simulink软件针对系统进行仿真验证，仿真参数如下表所示：

具体的，由无变压器型广义统一潮流控制器实现柔性互联的三条输电线互联系统，其连接示意图参照图9，为本发明控制系统的的多端口单相MMC潮流调节模块采用两电平半桥型子模块、级联桥型逆变器采用级联全桥拓扑的三端口潮流控制装置的拓扑结构及其实现三条输电线互联的系统示意图。
具体的，仿真实例的控制方法如图10，为本发明的控制方法的的多端口单相MMC潮流调节模块采用并联两电平单相半桥型子模块的MMC、级联桥型逆变器采用级联全桥拓扑的三端口潮流控制装置的控制方法框图，无变压器型广义统一潮流控制器包含四个单相半桥型子模块的MMC，其中与交流输电线相连的三个单相半桥型子模块的MMC控制输电线2、输电线3上的有功功率和无功功率，对应的控制环为线路潮流控制环。
具体的，与级联桥型逆变器相连的单相半桥型子模块的MMC控制公共直流母线电压平衡，对应的控制环为公共直流母线电压平衡控制环。级联桥型逆变器对输电线1上的无功功率进行补偿，对应的控制环为级联桥型逆变器控制环。
具体的，仿真实例的无变压器型广义统一潮流控制器在配网输电线上串联补偿电压的分配方法，考虑优化目标为单相半桥型子模块的MMC所需输 出电压交流成分幅值最小，即的选取满足取到最小值。
进一步的，为验证无变压器型广义统一潮流控制器的主动潮流控制能力，仿真设定了三种运行工况：
工况一：节点1发出0.2p.u.无功功率，节点2吸收0.5p.u.有功功率，发出0.2p.u.无功功率，节点3吸收0.5p.u.有功功率，发出0.2p.u.无功功率。
工况二：节点1发出0.2p.u.无功功率，节点2吸收0.2p.u.有功功率，发出0.2p.u.无功功率，节点3吸收0.8p.u.有功功率，发出0.2p.u.无功功率。
工况三：节点1发出1p.u.无功功率，节点2发出0.2p.u.有功功率，吸收0.2p.u.无功功率，节点3吸收0.5p.u.有功功率，发出0.8p.u.无功功率。
进一步的，如图11为本发明三种工况仿真结果，总共包含11幅波形图，从左到右、从上到下依次为：输电线1有功功率P1波形图、输电线1无功功率Q1波形图、输电线2有功功率P2波形图、输电线2无功功率Q2波形图、输电线3有功功率P3波形图、输电线3无功功率Q3波形图、输电线1相连的多端口单相MMC电容电压波形图、输电线2相连的多端口单相MMC电容电压波形图、输电线3相连的多端口单相MMC电容电压波形图、与级联桥型逆变器相连的多端口单相MMC电容电压波形、级联桥型逆变器电容电压波形。
进一步的，仿真波形结果表明，无变压器型广义统一潮流控制器在互联了三条输电线的情况下，既实现了输电线上的有功功率与无功功率解耦主动潮流控制，同时又保持了装置内部内部能量平衡，即电容电压稳定，具备端口拓展能力。
更进一步的，与现已提出的潮流控制器相比，本发明的拓扑同样具有独立的潮流调节能力。具体的细节对比如下表所示：

传统的统一潮流控制器因包含笨重的工频变压器，设备的总体体积较大，运行维护的成本较高，且在拓展潮流控制端口时需增加串联换流器和工频变压器，使得装置的端口拓展成本较高。T型无变压器型潮流控制器虽然去除了笨重的工频变压器，在体积和成本上具有优势，但其需牺牲一个控制的自由度保持控制器功率的平衡，因而无法控制源端的无功，且T型无变压器型潮流控制器的端口无法扩展。背靠背电压源换流器和基于Hexverter的潮流控制器都为全功率型的拓扑，使得设备的体积较大，且端口拓展的成本较高。本发明提出的潮流控制器具有独立的潮流控制能力，设备体积小，运行安装成本低，且端口易拓展，拓展成本低。
应说明的是，以上实施例仅用以说明本发明的技术方案而非限制，尽管参照较佳实施例对本发明进行了详细说明，本领域的普通技术人员应当理解，可以对本发明的技术方案进行修改或者等同替换，而不脱离本发明技术方案的精神和范围，其均应涵盖在本发明的权利要求范围当中。

Claims (17)

  1. 一种无变压器型广义统一潮流控制器，其特征在于，包括：
    无功补偿模块，所述无功补偿模块包括级联桥型逆变器；
    潮流调节模块，所述潮流调节模块包括多端口单相MMC；
    其中，所述多端口单相MMC与所述级联桥型逆变器进行串联；
    所述无功补偿模块为电压源型变流器，具备无功功率双向补偿功能，可以从系统吸收无功，也可以为系统提供无功补偿；
    所述潮流调节模块实现输电线有功功率和无功功率的解耦控制。
  2. 如权利要求1所述的一种无变压器型广义统一潮流控制器，其特征在于：所述级联桥型逆变器是由多个子模块级联而成。
  3. 如权利要求1所述的一种无变压器型广义统一潮流控制器，其特征在于：
    所述多端口单相MMC包括潮流调节多端口单相MMC和能量平衡多端口单相MMC；
    所述能量平衡多端口单相MMC与潮流调节多端口单相MMC并联；
    所述级联桥型逆变器与能量平衡多端口单相MMC的交流输出端口相连，实现级联桥型逆变器与多端口单相MMC的串联连接；
    所述潮流调节多端口单相MMC的交流输出端口与输电线串联，通过调节串联在输电线上的多端口单相MMC交流输出端口电压的幅值相位，实现输电线有功功率和无功功率的解耦控制。
  4. 一种基于如权利要求1～3任一所述的无变压器型广义统一潮流控制器的控制方法，其特征在于，包括：
    主要控制模块，包括线路潮流控制环、级联桥型逆变器控制环和公共直流母线平衡控制换，实现控制器的基本功能，保证控制正常运转；
    采用环流抑制控制和桥臂电压均衡控制抑制潮流调节模块的环流和电压不均衡的现象，提高控制器的性能；
    锁相环锁定潮流调节平衡输电线的节点三相电压，获得锁定线路的相位，锁相环输出的相角为abc坐标系到dq坐标系的帕克转换矩阵提供角度。
  5. 如权力要求4所述的控制方法，其特征在于：所述线路潮流控制环的控制目标为：
    获取潮流控制输电线的有功功率的参考值和无功功率的参考值
    设定线路潮流控制环输出
    其中，为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口的输出电压的交流成分的参考值，为与潮流控制输电线相连的潮流调节多端口单相MMC交流输出端口的输出电压的交流成分的参考值，下标i表示第i条输电线为潮流调节平衡输电线，下标j表示第j条潮流控制输电线。
  6. 如权力要求4所述的控制方法，其特征在于：所述级联桥型逆变器控制环包括，
    电压控制外环、无功功率控制外环和电流控制内环；
    所述级联桥型逆变器控制环的控制目标为潮流调节平衡输电线的无功功率达到参考值和级联桥型逆变器三相电容电压之和稳定为参考值级联桥型逆变器控制环的输出为级联桥型逆变器交流输出端口的电压的交流成分的参考值
    所述无功功率控制外环根据潮流调节平衡输电线的无功功率参考值计算潮流调节平衡输电线电流q轴分量参考值
    所述电流控制内环在dq坐标系下进行控制，利用比例积分控制器，对潮流调节平衡输电线电流的d轴分量和q轴分量分别控制，数学方程为：
    其中，和乘以帕克逆转换矩阵，再乘以-1反相后，得到abc坐标系下的级联桥型逆变器控制环输出参考电压即Vpa、Vpb、Vpc；
    其中，VCid和VCiq为与潮流调节平衡输电线相连的潮流调节多端口单相MMC交流输出端口电压的交流成分的d轴分量和q轴分量，VSMd和VSMq为与级联桥型逆变器相连的能量平衡多端口单相MMC交流输出端口电压的交流成分的d轴分量和q轴分量，kp2为比例积分控制器比例环节增益系数，ki2为比例积分控制器积分环节增益系数，Vid、Viq、VCid、VCiq、VSMd、VSMq为前馈项，作用是增强控制环抗干扰能力，加快控制环响应速度，为解耦项，作用是实现d轴和q轴的解耦控制。
  7. 如权力要求4所述的控制方法，其特征在于：所述公共直流母线电压平衡控制环的控制目标为公共直流母线电压稳定为参考值公共直流母线电压平 衡控制环的输出为公共直流母线平衡参考电压
    所述公共直流母线电压平衡控制环的控制在abc坐标系下进行，利用比例积分控制器对abc三相的公共直流母线电压进行控制，数学方程为：
    其中，Vlinka、Vlinkb、Vlinkc为三相公共直流母线电压，Ipa、Ipb、Ipc为级联桥型逆变器支路三相电流，为前馈的三相参考电压，kp3为比例积分控制器比例环节增益系数，ki3为比例积分控制器积分环节增益系数。
  8. 如权力要求4所述的控制方法，其特征在于：所述环流抑制控制的控制目标为抑制每相的多端口单相MMC之间的环流，环流抑制控制的输出为产生环流的二倍频电压，通过对子模块调制信号进行补偿，实现环流的抑制；
    所述环流抑制控制在abc坐标系下进行，利用准比例谐振控制器对abc三相的相内环流进行抑制，数学方程为：
    其中，GQPR(s)为准PR控制器的传递函数，ω为谐振频率，ωc为截至频率主要影响系统带宽，kp4为准比例谐振控制器比例环节增益系数，kr为准比例谐振控制器谐振环节增益系数，为与第k条输电线连接的潮流调节多端口单相MMC子模块环流补偿电压，s为拉普拉斯变化下的模型变量，为能量平衡多端口单相MMC子模块环流补偿电压，ilkp和ilkn为与第k条输电线相连的潮流调节多端口单相MMC上桥臂电流和下桥臂电流，下标l为l相的参数。
  9. 如权力要求4所述的控制方法，其特征在于：所述桥臂电压均衡控制包括桥臂电压直流分量调节和注入基频环流调节两种实现方式。
  10. 如权力要求9所述的控制器的控制方法，其特征在于：所述桥臂电压直流分量的调节方式包括调节上下桥臂直流分量进而控制上下桥臂电容电压均衡，输出为多端口单相MMC上桥臂和下桥臂子模块电压直流分量参考值；
    所述桥臂电压均衡控制利用PI控制器对abc三相的多端口单相MMC的桥 臂电压直流分量进行控制，数学方程为：
    其中，V* arm，lkp为上桥臂电压直流分量参考值，为下桥臂电压直流分量参考值，为上下桥臂电压均值的参考值，Vaverage,lkp和Vaverage,klp为上桥臂和下桥臂电压的均值，Vlink,l为直流母线电压，下标k为与第条k输电线相连的潮流调节多端口单相MMC的参数，下标l为l相的参数，kp5为比例积分控制器比例环节增益系数，ki5为比例积分控制器积分环节增益系数。
  11. 如权力要求9所述的控制器的控制方法，其特征在于：所述注入基频环流调节的调节方式包括，
    所述基频环流注入调节的桥臂电压均衡控制，通过注入与电压相位相同的基频环流实现上下桥臂电压的均衡，注入基频环流调节的输出为注入的基频环流的参考值，数学方程为：
    其中，为与第k条输电线相连的潮流调节多端口单相MMC注入基频环流的参考值，Vaverage,lkp和Vaverage,lkn为潮流调节多端口单相MMC的上下桥臂电压均值，θk为与第k条输电线相连的潮流调节多端口单相MMC输出电压基频分量的相位，kp6为比例积分控制器比例环节增益系数，ki6为比例积分控制器积分环节增益系数。
  12. 一种基于如权力要求1～3任一所述的无变压器型广义统一潮流控制器的分配方法，其特征在于，包括：
    所述控制器的分配方法为满足基本条件方程中的任何一组 的解；
    其中，基本方程如下：
    若第1条输电线为潮流调节平衡输电线，Real为实部，为所述无变压器型广义统一潮流控制器在第k条输电线上串联补偿电压交流成分的矢量表 达式，为实现第k条输电线上目标潮流时所需串联在第1条输电线和第k条输电线之间的串联补偿电压矢量表达式，为与所述级联桥型逆变器相连的所述多端口单相MMC潮流调节模块中的能量平衡多端口单相MMC交流输出端口电压交流成分的矢量表达式，为第k条输电线上的交流电流的共轭矢量表达式，为所述级联桥型逆变器支路的交流电流的共轭矢量表达式，n为通过所述无变压器型广义统一潮流控制器互联的输电线数量。
  13. 一种基于如权力要求1～3任一所述的无变压器型广义统一潮流控制器的控制系统，其特征在于，包括：
    所述控制系统的核心设备为无变压器型广义统一潮流控制器、交流输电线和变电站；
    所述无变压器型广义统一潮流控制器安装于多条交流输电线的汇集处；
    所述交流输电线与无变压器型广义统一潮流控制器相连，交流输电线可经升压变压器接入高压系统，可经降压变压器接入低压交流系统，低压交流系统可接入低压交流负载、储能设备和电动汽车快充站。
  14. 一种基于如权力要求1～3任一所述的无变压器型广义统一潮流控制器的设备保护方法，其特征在于，包括：串联在输电线上的电压的过压保护、多端口单相MMC子模块故障旁路保护以及级联桥型逆变器子模块保护，目的是避免故障情况下换流器内部器件的严重损坏；
    所述串联在输电线上的电压的过压保护，通过一个保护装置对串联在输电线上的电压的过压进行保护；
    所述多端口单相MMC子模块通过多端口单相MMC子模块的交流输出端口与晶闸管旁路开关并联，以及多端口单相MMC子模块的直流侧配有用于电容能量释放的直流卸荷电路，防止过压损坏功率器件，对多端口单相MMC子模块故障旁路进行保护；
    所述级联桥型逆变器子模块通过级联桥型逆变器子模块的交流端口与快速机械开关并联，以及级联桥型逆变器直流侧配有释放电容能量的直流卸荷电路对级联桥型逆变器子模块进行保护。
  15. 如权力要求14所述的设备保护方法，其特征在于：所述串联在输电线上的电压的过压保护包括保护装置，
    所述保护装置与多端口单相MMC潮流调节模块中的潮流调节多端口单 相MMC的交流输出端口间并联，实现对串联在输电线上的电压的过压进行保护；
    所述保护装置由金属氧化物限压器和晶闸管旁路开关并联组成；
    其中，晶闸管旁路开关为反并联晶闸管、阻容回路、静态电阻并联后再与一个饱和电抗器串联；
    所述金属氧化物限压器将电压限制在安全电压而晶闸管旁路开关通过将潮流调节多端口单相MMC的交流输出端口旁路，实现过压保护。
  16. 如权力要求14所述的设备保护方法，其特征在于：
    所述多端口单相MMC子模块的交流输出端口与晶闸管旁路开关并联，使得多端口单相MMC子模块故障时可通过晶闸管旁路开关快速旁路故障的子模块，同时投入冗余的子模块，使得子模块的故障并不影响设备的总体运行；
    所述多端口单相MMC子模块的直流侧配有用于电容能量释放的直流卸荷电路，防止过压损坏功率器件。
  17. 如权力要求14所述的设备保护方法，其特征在于：所述级联桥型逆变器子模块的交流端口与快速机械开关并联，使得级联桥型逆变器子模块故障时可迅速切除故障模块；
    所述级联桥型逆变器子模块直流侧配有释放电容能量的直流卸荷电路，防止过压损坏功率器件。
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