Technology of HVDC based Voltage Source Converter, based on can turning off power electronic devices and voltage source converter (VSC), mostly is BtB
Topological structure also realizes electric energy transmission with buried cable and submarine cable for transmission medium.Wherein voltage source converter (VSC)
It it is the basic component units of this transmission system.The topological structure being applied to Practical Project at present has two level, three level and module
Change the topological structure such as many level.
Multi-terminal HVDC transmission (MTDC) system refers to containing multiple converting plants or the DC transmission system of multiple Inverter Station.It shows
Work feature is to be capable of multiple feed, many drop points by electricity, it is provided that one the most flexibly, power transmission mode efficiently.MTDC
Transmission system is mainly used in: delivered power to multiple load centers in a distant place by multiple Energy Bases；Aerial line can not be used
The big city in corridor, road or the center of industry；DC power transmission line medial fascicle accesses load or power supply；Several isolated exchange systems
DC power transmission line is utilized to realize the non-synchronous contact etc. of electrical network between system.Switching device skill is entirely controlled along with high-power electric and electronic
The further development of art, the research of Novel Control, gradually reducing of direct current transportation cost and carrying that the quality of power supply requires
Height, based on conventional current source converter (csc) (Current Source Converted CSC) and voltage source converter (Voltage
Source Converter VSC) mixing MTDC technology of transmission of electricity, MTDC technology of transmission of electricity based on FACTS, Yi Jiji
Novel MTDC technology in VSC will be rapidly developed, and will be greatly improved the operational reliability of MTDC transmission system
And practicality, expand the range of application of MTDC transmission system, provide more novel interconnection mode for electrical network, for big city
Many drop points of direct current supply are provided new approaches by electricity, and the new forms of energy for other forms access electrical network offer new method, for high-quality electricity
The foundation in energy storehouse provides new way.
Different from traditional C/S C-MTDC system, during the reversion of VSC-MTDC system load flow, DC voltage direction is constant, unidirectional current
Flow path direction inverts, and need not mechanically actuated, and speed, reliability is higher.It is a kind of both had higher reliable
Property there is again flexible and changeable control mode, therefore VSC-MTDC is the suitable scheme building MTDC transmission system in parallel.
VSC-MTDC system at the aspect such as operational flexibility, reliability than two end systems more technical advantage, but its run control
System the most also wants complexity.Control to be the basic control mode in current source type direct current transportation (CSC-HVDC) system with electric current
Equally, the basic controlling during DC voltage control is VSC-HVDC system.In VSC-MTDC system, direct current of sampling
Voltage-controlled current conversion station is equivalent to an active balance node, plays power-balance and the effect of stable DC voltage, and it controls
Performance And Reliability the most just determines operation characteristic and the reliability of whole system.
VSC-MTDC DC voltage and trend coordination control strategy have following several: (1) master-slave mode voltage control method, feature
Being to control simply, controllability is the strongest, however it is necessary that system command is coordinated by high speed communication；(2) voltage descent method, excellent
Point is to need not top level control device to be adjusted value coordination, and the requirement to mutual communication is low, has certain extensibility, lacks
Point is slope configuration complexity, and power flowcontrol is affected by system main electrical scheme and direct current cables parameter, and greatest drawback is accurately to enter
Row power flow control；(3) DC voltage control method for coordinating based on voltage deviation, the feature of the method is only without communication
Vertical regulation, flexible configuration, extensibility are strong, but coordinate and in terms of optimal power flow control, by itself having DC voltage concurrently
The restriction of control structure, its control performance is limited, and wherein second order voltage deviation method automatically cuts off when carrying out voltage deviation control
Power flowcontrol, therefore voltage is coordinated and power flowcontrol can not be carried out simultaneously, and three rank voltage deviation methods there is also this problem,
The control ability in the most each stage is limited.
Summary of the invention
It is an object of the invention to provide a kind of converter Control method of Multi-end flexible direct current transmission system, apply this control method
Inverter and apply the flexible direct current power transmission system of this inverter, in order to solve DC voltage in existing VSC-MTDC system
With trend coordinate control can not carry out simultaneously problem.
For achieving the above object, the solution of the present invention includes: a kind of converter Control method of Multi-end flexible direct current transmission system,
Apply the inverter of this control method and apply the flexible direct current power transmission system of this inverter.
A kind of converter Control method of Multi-end flexible direct current transmission system: when DC bus-bar voltage is on voltage set in advance
Limit value udc_ref_highAnd lower limit udc_ref_lowBetween time, inverter runs on constant dc power control pattern；Work as DC bus-bar voltage
It is in upper voltage limit value u set in advancedc_ref_highAnd lower limit udc_ref_lowTime in addition, inverter runs on dc bus electricity
Pressure control model, when busbar voltage is higher than when setting higher limit, and inverter regulation DC bus-bar voltage is stable at higher limit, when
When busbar voltage is less than lower limit, inverter regulation DC bus-bar voltage is stable at lower limit.
Inverter in this control method uses Direct Current Control method based on rotating coordinate system, and it is based on rotating coordinate system
Outer shroud controls to include for producing watt current instruction idrefPower controller, power controller include meritorious flow controller and
DC voltage controller, when inverter runs on constant dc power control pattern, and power flow control device is output as watt current and refers to
Make idrefInput；When inverter runs on DC bus-bar voltage control model, and DC voltage controller is output as watt current
In this control method, DC voltage controller includes voltage lower bound controller and voltage high limit controller.
Use the inverter of this control method: when DC bus-bar voltage is in upper voltage limit value u set in advancedc_ref_highUnder and
Limit value udc_ref_lowBetween time, inverter runs on constant dc power control pattern；When DC bus-bar voltage is in electricity set in advance
Press limit value udc_ref_highAnd lower limit udc_ref_lowTime in addition, inverter runs on DC bus-bar voltage control model, works as mother
Line voltage is higher than when setting higher limit, and inverter regulation DC bus-bar voltage is stable at higher limit, when busbar voltage is less than lower limit
During value, inverter regulation DC bus-bar voltage is stable at lower limit.
This inverter uses Direct Current Control method based on rotating coordinate system, and its outer shroud based on rotating coordinate system controls to include
For producing watt current instruction idrefPower controller, power controller includes meritorious flow controller and DC voltage control
Device, when inverter runs on constant dc power control pattern, power flow control device is output as watt current instruction idrefInput；
When inverter runs on DC bus-bar voltage control model, DC voltage controller is output as watt current instruction idrefDefeated
The DC voltage controller of this inverter includes voltage lower bound controller and voltage high limit controller.
Use the Multi-end flexible direct current transmission system of this control method: each inverter load importance in this DC transmission system
Different upper voltage limit value u of different setdc_ref_highAnd lower limit udc_ref_low。
The invention has the beneficial effects as follows: use the DC transmission system of this control method and this inverter, inverter can be according to directly
The running status of streaming system automatically switches self operational mode: at one end or will time skew occurs multiterminal element busbar voltage
Running mode switching is by constant dc power control pattern to DC voltage control pattern, by stable for DC bus-bar voltage upper and lower set
In the range of limit, expansion of preventing accident；The voltage bound that different set according to load importance is different can be in straight-flow system
The power supply of critical load is preferentially guaranteed when breaking down.The multi-terminal system DC point using this method is fixed, control structure
Simply, system flexible configuration, extensibility is strong, is suitably applied the distributed multiterminal flexible direct current system of extensive many drop points
Detailed description of the invention
The present invention will be further described in detail below in conjunction with the accompanying drawings.
The structure diagram of Multi-end flexible direct current transmission system is as shown in Figure 1: flow as pros with power from exchanging lateral DC side
To, S1, S3, S4 are power supply, and Load2, Load5 are power load.Fig. 2 a is the flexible direct current power transmission system change of current
The equivalent circuit of device, wherein Ps、QsMeritorious and reactive power, I for ACa1、Ib1、Ic1、Usa、Usb、UscRespectively
For electric current and the voltage of AC three-phase, Uca、Ucb、UccFor the alternating voltage after inverter impedance consumes, Pc、Idc
For power and the electric current of this inverter input direct-current electrical network, to flow as positive direction from the lateral DC side of exchange, UdcFor inverter
DC side terminal voltage, specific works mode does not repeats them here.Fig. 2 b is flexible direct-current transmission converter control block diagram, this control
Constant dc power control mode involved by block diagram processed, the principle of DC voltage control (determining Control of Voltage) mode own, measure and figure
Middle labels etc. belong to prior art, do not repeat them here, and particular content is with reference to paper " flexibility based on dq0 synchronous coordinate
Direct current transportation control strategy and simulation study " (protecting electrical power system and detection, volume 37 22 phase).Increase the mark explanation of each symbol.
The concrete control method of inverter of Multi-end flexible direct current transmission is as follows:
Set higher limit u of inverterdc_ref_highWith lower limit udc_ref_lowAnd rectification and inversion balance function.Properly functioning
Time, busbar voltage is in setting voltage higher limit udc_ref_highWith lower limit udc_ref_lowIn the range of, through weighing the fortune of function
Control inverter after calculation and run on constant dc power control pattern；When DC bus-bar voltage is in upper voltage limit value set in advance
udc_ref_highAnd lower limit udc_ref_lowTime in addition, after the computing of balance function, switch inverter run on dc bus electricity
Pressure control model, when busbar voltage exceedes higher limit, control bus voltage stabilization is in higher limit, when busbar voltage is less than down
During limit value, control bus voltage stabilization is in lower limit.When inverter runs on constant dc power control pattern, active power will be maintained
According to its power command value PorderBeing controlled, the now output of power flow control device instructs as watt current in Fig. 2 b
idrefInput；When inverter runs on DC bus-bar voltage control model, by original for switching by its power command value PorderEnter
Row controls to by d-c bus voltage value UdcBeing controlled, the output of DC voltage controller is as watt current in Fig. 2 b
Instruction idrefInput, in this way, inverter can mutually switch smoothly in two kinds of mode of operations, solves former
The problem that first inverter not only can not be operated in constant dc power control pattern but also be operated in stable DC busbar voltage pattern.Complete
As shown in Figure 3 a, Fig. 3 a is the coordination control proposed based on voltage deviation principle to the power controller control block diagram of mode switching operation
Device structure processed, power controller includes DC voltage control part and relevant power flowcontrol part.Wherein voltage levels limit controls
Device is PI controller, carries out the regulation gained merit thus control DC voltage when DC voltage exceedes deviation range, meritorious
Flow controller is PI controller based on inverse steady state model, and this controller entered when DC voltage is within the scope of high lower bound
The quick trend closed loop control of row；Instruct as watt current owing to three controller outputs are all added by adder, thus
Competition for voltage controller and flow controller creates condition, and weighs function and be namely based on the control of DC voltage high lower bound
Device output result adjusts the output of flow controller, and then carries out DC voltage and effective power flow according to the parameter being pre-configured with
Coordination control, this balance function can carry out different configuration according to the coordination requirement of the DC voltage of system and effective power flow,
Simplest being configured to a constant, this constant and voltage controller output combine, and compare point in flow controller
Analysis, the actual DC busbar voltage in conjunction with current commutation device has the meritorious situation of output, based on DC voltage stability and tide optimization
Distribution principle finally determines the watt current instruction of output.The input of this tuning controller has 5 variablees, respectively voltages
High limit instruction Udc_ref_High, voltage lower bound instruction Udc_ref_Low, active power instruction P_ref, DC bus-bar voltage
Udc and the actual active-power P of inverter AC, be output as the watt current instruction Id_ref of inverter；Wherein voltage levels
The PI parameter of limit controller and power flow control device is configured based on dynamic characteristic by ssystem transfer function；Voltage lower bound control
The output violent change of device processed is the meritorious restriction of rectification that this end inverter participates in coordinating to control, and wherein lower bound Pvdc_Low_lower sets
Being set to zero, the configuration of high limit Pvdc_Low_upper directly determines this end and participates in the rectification that voltage coordinates to control and gain merit ability,
Actual incorporation engineering demand configures；The output violent change of voltage high limit controller is that this end inverter participates in coordinating the inverse of control
Becoming meritorious to limit, the highest limit Pvdc_High_upper is set to zero, and the configuration of lower bound Pvdc_High_lower directly determines
This end participates in the inversion that voltage coordinates to control and gains merit ability, and actual incorporation engineering demand configures；The configuration of balance function
Have various ways, but totally have three kinds of schemes: the first scheme is that DC voltage high lower bound controller is completely preferential, now when
When DC voltage exceedes high limit limit value, effective power flow will be changed meeting DC voltage maximum stability, actual meritorious
Trend and instruction are the most equal；The program is suitable for having the AC network end that the strongest urgent trend supports；First scheme
Preferential for effective power flow, now this end inverter exceedes the high lower bound initial stage at DC voltage to carry out a certain degree of unidirectional current voltage-controlled
System, but owing to balance function is configured to effective power flow preferentially, when carrying out stable state, effective power flow still ensures that and instructs into closed loop
Value, the program can carry out DC voltage control at the dynamic initial stage, still ensures that trend carries after stablizing, and the program is suitable for tool
There is the AC network end that the urgent trend of certain transient state supports；The third scheme is that effective power flow limits coordination mode, the most directly
Stream voltage exceedes height in limited time, and change is also carried out a certain degree of DC voltage support by trend, but also can consider this end trend
Delivery requirements, the AC power flow knots modification caused due to coordinative role under this kind of mode between one, two two schemes,
The program is suitable for inverter and must assure that the AC network end of to a certain degree trend conveying；And last it is to ensure that this end change of current
Device runs under the capacity allowed, and wherein Id_upper is this end inverter maximal integer mass flow watt current limit value, Id_lower
For this end inverter maximum inversion watt current limit value, watt current amplitude limit value is usually set to the Dalian that current transformer allows
Reforwarding row load current.
The external characteristics with the Active Power Controller that DC bus-bar voltage high-low pressure limit controls function meets such as the requirement of Fig. 3 b:
During controlling, when busbar voltage is beyond the upper lower limit value set, power controller is operated in DC voltage control pattern,
Now voltage constant is the corresponding upper lower limit value set；When busbar voltage is in the range of upper lower limit value, switches to and determine merit
Rate control model, now power invariability.
The DC bus-bar voltage high-low pressure limit value of selected each end, each end limit value can be consistent, it is also possible to elects different value as, this limit value
The difference selected will cause trend allocation priority different.In simulations below example, different inverter correspondence loads is set
The upper lower limit value that fixed different priority is the most different.
Effectiveness below by simulating, verifying DC voltage high-low pressure limit control method.
According to above control strategy, in MATLAB/SIMULINK software, build modular multi-level flexible direct current defeated
The phantom of electricity inverter multi-terminal system.This model is by five Converter DC-side concurrent access systems, wiring sketch such as Fig. 4
Shown in.Wherein 1# inverter rated power is the volume that rated power is 100MW, 3# inverter of 350MW, 2# inverter
Determining the rated power that rated power is 200MW, 5# inverter that power is 100MW, 4# inverter is 100MW, direct current
Bus rated voltage is 400kV.1# inverter is for determine DC bus-bar voltage operational mode, and 2 5# inverters are determines power fortune
Row mode.2#, 3#, 4#, 5# are the power controller with DC bus-bar voltage high-low pressure limit control function, wherein 4#
Low pressure is limited to 370kV, remaining low pressure is limited to 380kV.
Emulation one: 1# inverter is for determining DC bus-bar voltage pattern, and busbar voltage instruction is 400kV；2# inverter is from DC side
Taking out power 50MW, 3# inverter takes out power 100MW from DC side, and 4# inverter takes out power 100MW, 5# from DC side
Inverter takes out power 100MW from DC side.During 0.6S, 1# inverter grid side generation three-phase no-voltage falls fault.Fig. 5 a
For 1# inverter alternating voltage waveform, Fig. 5 b is DC bus-bar voltage waveform, and Fig. 5 c is 1 5# inverter DC bus current
Waveform (flows to DC side as positive direction with inverter AC).1# inverter after 0.6S fault is can be seen that from simulation waveform
Out of service, its DC current reduces to 0A, and 2#, 3#, 5# inverter is cut into dc bus electricity by power mode of determining before
Pressure controlled state, and still keep 100MW Power operation by stable for busbar voltage at lower limit 380kV, 4# inverter.
Emulation two: 1# inverter is for determining DC bus-bar voltage pattern, and busbar voltage instruction is 400kV；0.2S2# starts from direct current
Power 100MW is taken out in side, and 3# inverter takes out power 50MW from DC side, and 5# takes out power 100MW from DC side, during 0.5S
4# starts to take out power 150MW from DC side, and during 0.7S, 4# transfers to and send power 100MW to DC side；1.0S2# send to direct current
Power 70MW, 3# send power 70MW, 5# to start to direct current to direct current to send power 70MW, 1.3S4# to send power to direct current
200MW, 1.7S4# transfer to and take out power 20MW from DC side.Fig. 6 a, 6b are the simulation waveform of this test.Can from waveform
During to find out 0.5S limited due to the transmission of 1# power, defeated beyond 1# inverter of power summation that 2 5#4 inverter are taken out
Sending ability, now 1# current conversion station transfers the maximum power output operation of rectification direction to, and DC bus-bar voltage falls, 2#, 3#, 5#
Be cut into DC bus-bar voltage control at 0.5S, by stable for busbar voltage at its lower limit 380kV, as 0.7S 2 5# from
DC side is taken out the summation of power and is transferred 50MW to, and now 1# converter power can meet the service requirement of remaining four inverter,
Busbar voltage is controlled at 400kV by 1# inverter again, and 2#, 3#, 5# transfer original constant dc power control to, its through-put power
Recover to power command value.1.0S2#, 3#, 5# transfer to DC side output, and now 4# is also to DC side output,
4 inverters are 310MW to DC side output summation, and system is properly functioning, and when 1.3S, 4# exports to DC side
Power increases to 200MW and increases 100WM, and now 4 inverters are 410MW to DC side conveying general power, super
Having gone out the transmittability of 1# inverter, now 1# inverter transfers the maximum power output operation of inversion direction, DC bus-bar voltage to
Raising, 2#, 3#, 5#1.3S be cut into DC bus-bar voltage control, by busbar voltage limit value 400kV the most thereon, when
During 1.7S, 2 5# send the summation of power to transfer 190MW to DC side, and now 1# converter power can meet remaining four and changes
The service requirement of stream device, busbar voltage is controlled at 400kV by 1# inverter again, and 2#, 3#, 5# transfer to and original determine power
Controlling, its through-put power is recovered to power command value.
The above simulating, verifying effectiveness of this control method.