2596results about "Flexible AC transmission" patented technology

The present invention provides a method, computer program product, and apparatus and control system and method for providing substantially uninterrupted power to a load. The apparatus includes a control system coupled with an electrical power storage subsystem and a electrical power generator. The control system is configured to provide a plurality of modes of operation including at least a static compensator (STATCOM) mode, an uninterruptible power supply (UPS) mode and a generator mode (gen set), and to control transitions between each of the plurality of modes. In one embodiment, the control system is an integrated closed loop control system that includes a current control system and a voltage control system. The apparatus is capable of operating at least two of the plurality of modes simultaneously, including ramping the gen set mode up and simultaneously ramping the UPS mode down as the gen set mode is ramped down.

The invention provides a method and system for operating a solar farm inverter as a Flexible AC Transmission System (FACTS) device—a STATCOM—for voltage control. The solar farm inverter can provide voltage regulation, damping enhancement, stability improvement and other benefits provided by FACTS devices. In one embodiment, the solar farm operating as a STATCOM at night is employed to increase the connectivity of neighbouring wind farms that produce peak power at night due to high winds, but are unable to connect due to voltage regulation issues. The present invention can also operate during the day because there remains inverter capacity after real power export by the solar farm. Additional auxiliary controllers are incorporated in the solar farm inverter to enhance damping and stability, and provide other benefits provided by FACTS devices.

The power flow model of the multiterminal voltage-source converter-based high voltage DC (M-VSC-HVDC) transmission system for large-scale power systems is studied. The mathematical model is derived using the d-q axis decomposition of HVDC's control parameter. The developed model can be applied to all existing shunt voltage-source converter (VSC) based controllers, including Static Synchronous Compensator (STATCOM), point-to-point HVDC system, back-to-back HVDC system and multiterminal HVDC system. A unified procedure is developed for incorporating the proposed model into the conventional Newton-Raphson power flow solver. The IEEE 300-bus test system embedded with multiple HVDC transmission systems under different configurations are investigated. Simulation results reveal that the proposed model is effective and accuracy in meeting various control objectives.

The invention provides a novel battery energy-storage system and a function integration designing method thereof. The system comprises an energy storage unit and an EMS (energy storage monitoring system); the energy storage unit comprises an EB (energy storage battery unit), an BMS (battery management system) and a PCS (power storage current transformer); the EB is connected with the BMS, the BMS is respectively connected with the EB and the PCS, the input end of the EMS is connected with the output end of the BMS, and the PCS and the EMS are communicated with each other. The method comprises an energy storage battery monitoring and analyzing method achieved through the BMS and the PCS and an energy-storage system monitoring and analyzing method achieved through the PCS and the EMS. In the battery energy-storage system function integration design provided by the invention, all large application occasions of electric power systems are covered, the objective is clear, and various requirements and applications are met.

Floating electrically isolated active impedance modules are formed to attach to power transmission lines without breaking the lines such that the power line forms a secondary of the main transformer of the module. Each module includes an electrical energy storage device and a switching circuit, such as a single phase inverter, connected to the storage device and to the main transformer primary winding. The inverter can be controlled to couple a selected voltage to the transmission line through the main transformer primary winding which can provide effective positive impedance, negative impedance, or a voltage at or near phase quadrature with the line current. Many active impedance modules may be distributed over a power system grid to allow control of the impedance of the power lines in the grid and to steer power through the grid, with each module electrically isolated from ground and from other phase lines of the transmission system.

Systems and methods for supplying power (both active and reactive) at a medium voltage from a DCSTATCOM to an IT load without using a transformer are disclosed. The DCSTATCOM includes an energy storage device, a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and / or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique.

The invention discloses a mixed type power quality controlling device comprising an active part and a passive part, wherein the active part comprises active power filters (APFs) and static var generators (SVGs), the SVGs are used for supplying transient reactive power, and the APFs are used for filtering harmonic waves; the number of the APFs and the SVGs is at least two groups, and the APFs and the SVGs are connected with a three-phase power grid in parallel through a transformer isolation mode; the passive part comprises a static var compensator (SVC) which is used for supplying steady-state var power, wherein the SVC comprises a thirstier switching capacitor (TSC), a thirstier control reactor (TCR), and a fixed capacitance compensator (FC); the TSC, the TCR and the FC are directly connected with the three-phase power grid, the TSC is used for supplying high-capacity capacitive var power, the FC is used for supplying low-capacity var power and is also used as a main subharmonic filtering branch circuit to carry out harmonious comprehensive compensation and harmonic control on a power system.

The supercapacitor-based grid fault ride-through system provides a dynamic model of a wind generation system including a Voltage Source Converter (VSC), which functions as a Static Compensator (STATCOM). The power control capability of the STATCOM is extended by incorporating energy stored in a supercapacitor. The system implements a vector control technique based on the decoupling of real and reactive power. Simulation results show that a fixed speed induction generator is capable of withstanding a significant grid fault when aided by the supercapacitor-based grid fault ride-through system. Moreover, the induction generator regains its pre-fault status immediately after the fault is cleared.

Floating electrically isolated active impedance modules are formed to attach to power transmission lines without breaking the lines such that the power line forms a secondary of the main transformer of the module. Each module includes an electrical energy storage device and a switching circuit, such as a single phase inverter, connected to the storage device and to the main transformer primary winding. The inverter can be controlled to couple a selected voltage to the transmission line through the main transformer primary winding which can provide effective positive impedance, negative impedance, or a voltage at or near phase quadrature with the line current. Many active impedance modules may be distributed over a power system grid to allow control of the impedance of the power lines in the grid and to steer power through the grid, with each module electrically isolated from ground and from other phase lines of the transmission system.

A device and a method for controlling the flow of electric power in a transmission line carrying alternating current, in which a first voltage source converter is connected to the transmission line at a first point and a second voltage source converter is connected to the transmission line at a second point. Further, the first and second voltage source converters have their direct current sides connected to a common capacitor unit. Also included is a by-pass switch connected to the transmission line between the first point and the second point in parallel with the first and second voltage source converters so that the first and second voltage source converters will operate as a back-to-back station when the by-pass switch is open and as two parallel static var compensators when the by-pass switch is closed.

The invention discloses a dynamic power coordination control method for a battery energy storage system. The battery energy storage system comprises a plurality of power converters which supply power to a load and are connected in parallel for operation, and is characterized in that: the power converters connected in parallel for operation are divided into two types, and a master-slave control scheme is adopted, wherein one type comprises only one power converter which adopts a constant voltage constant frequency control mode and is called a master node, and the power converters of the other type adopt a constant power mode with a slight droop characteristic, and serve as slave nodes; generally, a power converter with a high capacity is selected to be the only one master node which is specified by an upper-layer monitoring system, and all the other power converters are the slave nodes; and under a stable state condition, active power and reactive power output by the power converters which serve as the slave nodes are set by a power instruction transmitted by the monitoring system, and the output power of the power converter which serves as the master node is dynamically regulated according to a load condition. The method adopting the master-slave control scheme has the advantages that: on the premise of sufficient power capacity, both the voltage stability and frequency stability of a micro-grid system are easily achieved, anti-load disturbance capability is high, and failure recovery time is short.

The invention relates to a battery energy storage system based power conversion system and a control method thereof. The power conversion system comprises a battery energy storage system, a bidirectional DC / DC (direct-current) converter, a grid-side current transformer, a filter circuit and an isolated voltage transformer. The battery energy storage system is in parallel connection with a direct-current bus of the grid-side current transformer through the bidirectional DC / DC converter; the grid-side current transformer, the filter circuit and the isolated voltage transformer are connected in sequence; and the isolated voltage transformer accesses to a power grid. The control method includes sequentially monitoring the battery energy storage system, the bidirectional DC / DC converter, the grid-side current transformer, the filter circuit and the isolated voltage transformer by a control circuit. Since the battery energy storage system utilizes battery cells connected in series and is in parallel connection with the common direct-current bus through the bidirectional DC / DC converter, circulation among battery packs is avoided, and capacity expansion of the system is facilitated. Further, by the aid of the monitoring control strategy for SOC (super capacitor state of charge) of the battery energy storage system and battery end voltage, excessive charge or discharge state of the battery energy storage system is avoided, service lives of the battery packs are prolonged, and comprehensive service cost is lowered.

A power flow controller responsive to power circulation demand for optimizing power transfer is disclosed. When a power flow controller operates at its rated capacity, it can no longer regulate from-bus voltage set-points, line power flow set-points, or both. In such cases, the power flow controller switches to power circulation set-point control without exceeding the rated capacities of the voltage-sourced converters in the power flow controller. Power-voltage (PV) curves associated with voltage stability analysis for maximizing power transfer can be generated and stored for use with a power flow controller operating in automatic power flow control mode.

A multilevel cascade voltage source inverter having separate DC sources is described herein. This inverter is applicable to high voltage, high power applications such as flexible AC transmission systems (FACTS) including static VAR generation (SVG), power line conditioning, series compensation, phase shifting and voltage balancing and fuel cell and photovoltaic utility interface systems. The M-level inverter consists of at least one phase wherein each phase has a plurality of full bridge inverters equipped with an independent DC source. This inverter develops a near sinusoidal approximation voltage waveform with only one switching per cycle as the number of levels, M, is increased. The inverter may have either single-phase or multi-phase embodiments connected in either wye or delta configurations.

The invention relates to a battery energy storage system peak clipping and valley filling real-time control method based on load prediction and belongs to the field of power system automatic control. The control method provided by the invention comprises the following steps of: firstly searching similar history daily load data, carrying out expanding short-term load prediction by adopting a linear regression analysis method, building a battery energy storage system peak clipping and valley filling real-time optimization model, solving the battery energy storage system peak clipping and valley filling real-time optimization model by adopting a dynamic programming algorithm, and obtaining the output power of a battery energy storage system at each moment. The control method provided by the invention comprises battery charging and discharging frequency constraint and discharge depth constraint in the real-time optimization model, is used for researching relation between battery life and the charging and discharging frequency and the relation between the battery life and the discharge depth and is beneficial to prolonging the battery life. Minimum load variance is taken as a target function, the peak-to-valley of a load curve can be reduced, the load curve is smoother while constraint conditions are met, and the peak clipping and valley filling application requirement can be met. Local part of the load curve can be smoother by adopting load smoothness constraint.

A method for calculating power flow solution of a power transmission network with unified power flow controllers is adapted to calculate the power flow on a large-scale power transmission network. The unified power flow controller has a series transformer, a series converter, a direct current coupling capacitor, a shunt converter, and a series transformer. The shunt transformer is connected electrically to a sending-end bus. The series transformer is connected electrically to the sending-end bus and a receiving-end bus. The unified power flow controller is represented by equivalent active and reactive loads on the sending-end and receiving-end buses of the power transmission network.

A family of power converters has input ac voltage regulation instead of output dc voltage regulation. The bi-directional converters control power flows and maintain the input ac voltage at or close to a certain reference value. These bi-directional power converters handle both active and reactive power while maintaining the input ac voltage within a small tolerance. Use of these converters is favorable for future power grid maintenance in that they (i) ensure the load demand follows power generation and (ii) provide distributed stability support for the power grid. The converters can be used in future smart loads that help stabilize the power grid.

The invention discloses a microgrid energy management system capable of realizing load management. The energy management system comprises a man-machine interaction module, a prediction module, a system analysis module, a dispatching and control module, and a system management module. The system performs collection and monitoring on information of the output power of a distributed power generation unit (including a wind turbine generator, a photovoltaic array and a diesel engine set), the charging-discharging states of a storage battery, the load power, the electric energy quality information of unit nodes, and the like, then carries out data analysis and processing under the condition of satisfying electrical characteristic constraint conditions of operating conditions and physical equipment, formulates a corresponding optimal control strategy according to the current microgrid operating condition and external application requests, coordinates and manages the operations of the distributed power supply, the load and other modules in the microgrid system, optimizes the energy flow and utilization of the microgrid system, outputs by using renewable resources, supplies electric energy capable of satisfying the required quality to user load at the lowest operating cost, and realizes the system optimization and dispatching.

The invention provides a virtual-impedance-based inverter parallel running method, which is characterized by comprising the following steps of: for each inverter, introducing a virtual generator which is connected to a point with the inverter by virtual impedance; performing droop control on the virtual generators, regulating the frequency and voltage amplitude of each virtual generator by utilizing the active power and reactive power of the corresponding inverters respectively, and further calculating voltage directive values of the virtual generators; and based on the voltage directive values, further calculating output voltage directive values of the inverters, and controlling the inverters to output voltages to track the directive values, thereby realizing control over the voltages of the virtual generators and finally realizing the decoupling regulation of the active power and the reactive power. In the method, a control policy for the wireless parallel running of the inverters is realized by utilizing the virtual impedance; and compared with the conventional control methods, the invention is not required to remarkably increase hardware investment, and betters the using effects of droop characteristics to make applicable the droop characteristics to resistive environments.

A method for comprehensively controlling reactive voltage of a wind farm with imported prediction information includes a planning mode, an online mode and an emergency mode. An operation plan of a power grid and power prediction information of the wind farm are imported in the planning mode, safety of the power grid, safety of the wind farm, safety of wind turbines and economical efficiency of the wind farm are comprehensively considered, and a control scheme for scattering and regulating equipment is formulated in advance; the safety of the power grid, the safety of the wind farm, the safety of the wind turbines and the economical efficiency of the wind farm are comprehensively considered on the basis of control of scattering and regulating of the equipment in the online mode, and the regulating quantity for continuously regulating the equipment is computed; and disturbance duration is extremely short during actual operation in the emergency mode, various reactive compensation devices cannot be easily communicated with a comprehensive reactive voltage control system of the wind farm and cannot be controlled by the comprehensive reactive voltage control system of the wind farm, and accordingly, the various reactive compensation devices are reactively locally controlled in the emergency mode in the design. The method has the advantages of robustness in control and high reliability.

The invention discloses a control method of a battery energy storage system for peak clipping and valley filling in a distribution network. The control method comprises the following steps: obtaining a daily load curve on a predicted day according to a load predicating method, and computing the peak value and valley value of the daily load curve; setting a synthesis output valley value after participation of the energy storage system, and setting an initial value of synthesis output peak value; comparing predicated daily load data with the synthesis output valley value and the initial value of synthesis output peak value which have been set, and judging as follows: if the load data is smaller than the synthesis output valley value, charging the energy storage system to complete valley filling; and if the load data is larger than the initial value of synthesis output peak value, discharging the energy storage system to complete peak clipping, so that the synthesis output after energy storage adjustment reaches to the initial value of synthesis output peak value. At the peak and valley moments according to the load curve, the energy storage system is set to be charged once and discharged twice within one day, the requirement of peak clipping and valley filling can be achieved, and charging and discharging balance every day can be kept, so that the service life of the battery is prolonged to the maximum. Moreover, the control method also can ensure safe and stable operation of the energy storage system.

A method to incorporate the steady-state model of the generalized power flow controller into a Newton-Raphson power flow algorithm is disclosed. The disclosed method adopts a flexible steady-state model of the generalized power flow controller, which can be applied to calculate the power flow solution of a power grid embedded with STATCOM, UPFC, GUPFC and the generalized power flow controller in a single framework. The disclosed method only incorporates the control variables of the shunt voltage sourced converter into the state vector of Newton-Raphson power flow algorithm. The increment of state variables due to incorporating the generalized power flow controller is less than the prior art. Further, the method can preserve the quadratic convergence characteristic of the Newton-Raphson power flow algorithm after embedding the generalized power flow controller into a power grid.

A method for calculating power flow solution of a power transmission network with unified power flow controllers is adapted to calculate the power flow on a large-scale power transmission network. The unified power flow controller has a series transformer, a series converter, a direct current coupling capacitor, a shunt converter, and a series transformer. The shunt transformer is connected electrically to a sending-end bus. The series transformer is connected electrically to the sending-end bus and a receiving-end bus. The unified power flow controller is represented by equivalent active and reactive loads on the sending-end and receiving-end buses of the power transmission network.

The present invention provides a power control circuit connectable to a load adapted to receive a power supply, the power control circuit adapted to absorb power from the power supply and adapted to deliver power to the power supply to stabilize at least one electrical parameter of the power supply. The present invention also provides an associated method of stabilizing at least one electrical parameter of a power supply connectable to a load, the method including absorbing power from the power supply or delivering power to the power supply. The at least one electrical parameter of the power supply includes parameters such as voltage and frequency.

Voltage source converter based on a chain-link cell topology including one or more phases, each of the phases having one or more series-connected chain-link cell modules connected to each other. The output voltage of the voltage source converter is controlled by control signals applied to the series-connected chain-link cell modules. In case of failure of a chain-link cell module, that module is controlled, by the control signals, such that zero output voltage is provided at its output voltage AC terminal.

An electrical energy storage unit and control system, and applications thereof. In an embodiment, the electrical energy storage unit (which may also be referred to as a battery energy storage system (“BESS”) includes a battery system controller and battery packs. Each battery pack has battery cells, a battery pack controller that monitors the cells, a battery pack cell balancer that adjusts the amount of energy stored in the cells, and a battery pack charger. The battery pack controller operates the battery pack cell balancer and the battery pack charger to control the state-of-charge of the cells. In an embodiment, the cells are lithium ion battery cells.

The invention discloses a direct current de-icing device based on a full-bridge modular multilevel converter. The full-bridge modular multilevel converter has a three-phase bridge structure, each phase of the converter comprises an upper bridge arm and a lower bridge arm, the upper and lower bridge arms which are respectively formed by serially connecting N full-bridge power modules end to end, and the full-bridge power modules form a chain type multilevel structure, the front ends of the first power modules of the upper bridge arms of all phases are connected to form the positive pole of a public direct current bus; the tail ends of the Nth power modules of all lower bridge arms of all phases are connected to form the negative pole of the public direct current bus; the tail ends of the Nth power modules of all upper bridge arms are connected with the front ends of the first power modules of the respective lower bridge arms of the phases by smoothing reactors; and the center of the electric reactor serves as the alternating current bus of the phase. The device has high high-voltage direct current output capacity and the direct current voltage of the device can be regulated continuously from zero; on the other hand, the fully compatible chain type scalable vector graphics (SVG) topology can realize quick dynamic reactive regulation; and the device has the combined functions of direct current de-icing and alternating current dynamic reactive compensation.

The invention provides a method and system for operating a solar farm inverter as a Flexible AC Transmission System (FACTS) device—a STATCOM—for voltage control. The solar farm inverter can provide voltage regulation, damping enhancement, stability improvement and other benefits provided by FACTS devices. In one embodiment, the solar farm operating as a STATCOM at night is employed to increase the connectivity of neighboring wind farms that produce peak power at night due to high winds, but are unable to connect due to voltage regulation issues. The present invention can also operate during the day because there remains inverter capacity after real power export by the solar farm. Additional auxiliary controllers are incorporated in the solar farm inverter to enhance damping and stability, and provide other benefits provided by FACTS devices.

The invention relates to a micro-grid system, and in particular relates to a micro-grid system for ships. The micro-grid system for the ships comprises a solar photovoltaic power generation system, a wind power generation system, a storage battery energy storage system, an emergency diesel generator, a load, a direct current bus and an alternative current bus, wherein the direct current bus and the alternative current bus are connected together through a bidirectional converter; the direct current bus is connected with the solar photovoltaic power generation system and the storage battery energy storage system; the alternative current bus is respectively connected with the wind power generation system, the emergency diesel generator and the load; and the system is connected with a medium voltage main power grid in the ship through an interconnection switch and a transformer at side where the alternative current bus is positioned. The defect that the new energy distributed type power generation cannot be directly used in a ship power system is overcome, a new offshore energy resource is sufficiently utilized, and the energy conservation and the emission reduction in the field of ocean transportation are realized.