CN110912173A - VSC direct-current power grid control method - Google Patents
VSC direct-current power grid control method Download PDFInfo
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- CN110912173A CN110912173A CN201911104248.1A CN201911104248A CN110912173A CN 110912173 A CN110912173 A CN 110912173A CN 201911104248 A CN201911104248 A CN 201911104248A CN 110912173 A CN110912173 A CN 110912173A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The invention relates to a VSC direct current power grid control method, which is characterized in that a first-stage control is defined to be a control adopted by an outermost converter station in a VSC direct current power grid, a second-stage control is defined to be a converter station connected with the first-stage converter station through a high-voltage direct current line, a weak alternating current power grid is connected to an alternating current side of the converter station in the second-stage control, the first-stage control uses direct current voltage control and adopts a feedforward double-closed-loop decoupling control strategy for control, and in the second-stage control, the converter station controls the balance of the flow direction of power and alternating current voltage through a feedforward decoupling control strategy and a phasing angle control. The control method can enable the weak alternating current system in the VSC direct current power grid to stably operate. The weak alternating current system applying the control strategy can stably connect a power feeding station and a power receiving station in a direct current system at the same time, and the alternating current system can carry a certain amount of alternating current load. The hierarchical control strategy provides a solution for multi-converter station control of a direct current power grid.
Description
Technical Field
The invention belongs to the field of parallel operation of alternating current and direct current systems, the field of power grid planning and the field of power system simulation, and relates to a direct current power grid, in particular to a direct current power grid formed on the basis of a voltage source converter station, wherein the alternating current and direct current systems in the power grid are in hybrid connection.
Background
With the improvement of the application technology of power electronic components, direct current transmission and a direct current power grid become important supplements of an alternating current power grid. Direct current transmission has been successfully operated in china for many years to deliver excess electric energy in the middle and western regions to the eastern coastal regions. Meanwhile, the extra-high voltage direct current transmission and the extra-high voltage alternating current transmission are used for continuously transmitting the wind power and the solar power generation in the west and the north to the load center in the east, and the method makes an important contribution to energy conservation and emission reduction of the country.
In urban power distribution networks, most of the power transmission is carried out by cables as media due to limited space. In the long-distance alternating current cable power transmission, the direct current power transmission is better in economy, and the direct current power transmission occupies less space than the alternating current power transmission. The direct current power grid of a voltage source converter station (VSC) has great advantages in the aspect of integrating wind energy and solar energy, can enable the wind energy and the solar energy to be smoothly connected in a power generation mode, and independently controls active power and reactive power. In view of this, a VSC based dc grid can be an important component of the energy internet.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a novel VSC direct current power grid control method which can improve the control stability of a system in a direct current power grid containing more VSCs, particularly the stability of a weak alternating current system directly supplying power by means of VSC inversion.
The technical scheme adopted by the invention for solving the technical problem is as follows:
a VSC direct current power grid control method defines that first-stage control is control adopted by a converter station on the outermost side in a VSC direct current power grid, second-stage control is a converter station connected with the first-stage converter station through a high-voltage direct current line, a weak alternating current power grid is connected to the alternating current side of the converter station in the second-stage control, the first-stage control uses direct current voltage control and adopts a feedforward double-closed-loop decoupling control strategy to control, and in the second-stage control, the converter station controls the flow direction of power and the balance of alternating current voltage through a feedforward decoupling control strategy and phasing angle control.
In the first-stage control, the direct-current voltage is controlled to input parameters to the inner ring through the outer ring PI control, active and reactive parameters are decoupled in the inner ring to obtain a decoupled control signal, parameters in a rotating rectangular coordinate system are converted into coordinate parameters of a three-phase alternating-current system through dq- > abc calculation matrix, and the converter station outputs given direct-current side voltage through the parameters to perform direct-current voltage control.
In the second-stage control, active power is controlled to input parameters to the inner ring through outer ring PI control, active and reactive parameters are decoupled in the inner ring to obtain a decoupled control signal, parameters in a rotating rectangular coordinate system are converted into coordinate parameters of a three-phase alternating current system through dq- > abc calculation matrix, and the converter station outputs given active power through the parameters to perform power control.
In the phasing angle control, the converter station generates a three-phase ac control signal corresponding to the phase angle signal by a given phase angle sum signal generating means, by which the converter station is able to output a voltage of a given phase angle for the phase angle control of the weak ac grid.
And in the direct current power grid containing the weak alternating current system, selecting the shortest path of the converter station connected to the strong power grid, and defining the control level of the converter station as n +1 level control according to the number n of the converter stations separated between a certain converter station and the alternating current strong power grid.
Furthermore, the converter station of the third stage is coupled to the control converter station of the second stage via the weak ac network.
The invention has the advantages and positive effects that:
1. the control method can enable the weak alternating current system in the VSC direct current power grid to stably operate. The weak alternating current system applying the control strategy can stably connect a power feeding station and a power receiving station in a direct current system at the same time, and the alternating current system can carry a certain amount of alternating current load. The hierarchical control strategy provides a solution for multi-converter station control of a direct current power grid.
2. The control method can enable the alternating voltage of the weak alternating current system connected with the power feeding station to have higher stabilizing speed, reduce the stabilizing and balancing time of the system and enable the whole direct current power transmission network to have better dynamic stability. The converter station that delivers electrical energy to the weak ac grid is called the "power feeding station", and the converter station that draws electrical energy from the weak ac grid is called the "power receiving station". According to the alternating current weak power grid in the direct current power grid, the control mode and the control scheme of the converter station connected with the weak power grid are set according to the difference between the power feeding station and the power receiving station, so that the stability of the system can be improved.
3. By using the control method, when the power of the weak alternating current system in the direct current power grid is increased, the power of the voltage control station of the weak alternating current power grid can be reliably reversed, so that the direct current power grid can provide more active power for the weak alternating current system. The direct current power grid can ensure that the middle weak alternating current system can reliably run when the power changes, and the balance station can accurately and timely meet the power change and stability requirements of the middle weak alternating current system.
Drawings
Fig. 1 is a control schematic diagram of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following embodiments, which are illustrative only and not limiting, and the scope of the present invention is not limited thereby.
A VSC direct current power grid control method comprises a converter station VSC1, a VSC2, a VSC3, a VSC4, an alternating current strong power grid, a weak alternating current power grid, a filter in the weak alternating current power grid, a direct current transmission line, a decoupling control strategy, phase angle control (fixed delta), active control (P) and alternating current voltage control (U)rms) And an upper hierarchical control strategy. The AC grid AC exchanges energy with the dc grid via the converter stations VSC1 and VSC 4. In the dc network, a weak ac network is provided, which exchanges energy with the dc network via the VSC2 and the VSC 3. The converter station is controlled through a decoupling control strategy, the decoupling control strategy is adopted, active control and phasing angle control are used for controlling trigger pulses for the converter station, and upper-layer hierarchical control is used for controlling the quantity of the decoupling control strategy.
The converter station VSC1 and the converter station VSC4 are directly connected to the ac grid, so VSC1 and VSC4 belong to the first level of control, VSC2 is connected to VSC1 via a dc cable, what the other side of VSC2 is connected to the ac grid, so the shortest path of connection of VSC2 to the ac grid is connected to the grid through VSC1, i.e. the control level of VSC2 is the second level. Likewise, the control hierarchy of the VSC3 is second level.
Power flows to VSC2 by VSC1, flows to VSC4 by VSC3 again, and the weak electric wire netting load between VSC2 and VSC3 consumes a small part of alternating current power, and weak electric wire netting of interchange is to VSC3 input power simultaneously.
The AC is an alternating current strong power grid, the AC inputs alternating current power into a converter station VSC1, the converter station VSC1 performs switching control through signals sent by a PWM signal generator, a trigger angle of the PWM signal generator is from a calculation matrix of 'dq- > abc', dq parameters are from improved feedforward decoupling control, outer-loop voltage PI control and control signals taken from the AC alternating current power grid are output to the improved feedforward decoupling control to be calculated, and a measured direct current voltage value is compared with a given direct current voltage value and is output to a PI controller of an outer-loop voltage controller.
The VSC1 converts AC power into DC power through DC voltage control of a first stage and then transmits the DC power to the VSC2, the VSC2 adopts constant active power control, the DC current is input to the VSC2, the converter station VSC2 carries out switching control through signals sent by a PWM signal generator, a trigger angle of the PWM signal generator comes from a calculation matrix of 'dq- > abc', dq parameters come from improved feedforward decoupling control, outer-loop active PI control and measurement signals taken from an AC alternating current power grid are output to the improved feedforward decoupling control for calculation, and a measured active power value is compared with a given active power value and output to a PI controller of an outer-loop voltage controller. The VSC2 converts direct current power into alternating current power through constant active power control and outputs the alternating current power to a weak alternating current system.
VSC3 and weak ac system vector, VSC3 performs switching control operations by means of PWM control signals to convert the weak ac system power into dc power to be fed to the dc grid, VSC3 has PWM control signals from a sine signal generator, the sine signal generator signals are from a phasing angle delta control and a given constant voltage control, the constant voltage control signals are from the difference between a given voltage value and a voltage measurement.
The VSC4 converts direct current power into alternating current power and transmits the alternating current power to an alternating current power grid AC, the VSC4 performs switching control through signals sent by a PWM signal generator, a trigger angle of the PWM signal generator is from a calculation matrix of 'dq- > abc', dq parameters are from improved feedforward decoupling control, outer ring voltage PI control and control signals taken from the AC alternating current power grid are output to the improved feedforward decoupling control to be calculated, and a measured direct current voltage value is compared with a given direct current voltage value and is output to a PI controller of the outer ring voltage controller.
The converter station VSC2 control alternating voltage, converter station VSC3 control active power, VSC2 adopts the control mode of phasing angle to produce the pulse of starting, the switch of trigger transistor, VSC1 and VSC4 adopt and decide direct current voltage control, control the first order direct current voltage of whole direct current electric wire netting, guarantee the power transmission of alternating current strong electric wire netting and direct current electric wire netting, carry out the control of converter station trigger pulse through feedforward decoupling control strategy.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept, and these changes and modifications are all within the scope of the present invention.
Claims (6)
1. A VSC direct current power grid control method is characterized in that: the method comprises the steps of defining first-stage control as control adopted by the outermost converter station in a VSC direct-current power grid, defining second-stage control as the converter station connected with the first-stage converter station through a high-voltage direct-current line, wherein the alternating-current side of the converter station in the second-stage control is connected with a weak alternating-current power grid, the first-stage control uses direct-current voltage control and adopts a feedforward double-closed-loop decoupling control strategy for control, and in the second-stage control, the converter station controls the flow direction of power and the balance of alternating-current voltage through the feedforward decoupling control strategy and the phasing angle control.
2. A VSC dc grid control method according to claim 1, characterised in that: in the first-stage control, direct-current voltage is controlled to input parameters to the inner ring through outer ring PI control, active and reactive parameters are decoupled in the inner ring to obtain a decoupled control signal, parameters in a rotating rectangular coordinate system are converted into coordinate parameters of a three-phase alternating-current system through dq- > abc calculation matrix, and the converter station outputs given voltage on a direct-current side through the parameters to perform direct-current voltage control.
3. A VSC dc grid control method according to claim 1, characterised in that: in the second-stage control, active power is controlled to input parameters to the inner ring through outer ring PI control, active and reactive parameters are decoupled in the inner ring to obtain a decoupled control signal, parameters in a rotating rectangular coordinate system are converted into coordinate parameters of a three-phase alternating current system through dq- > abc calculation matrix, and the converter station outputs given active power through the parameters to perform power control.
4. A VSC dc grid control method according to claim 1, characterised in that: in phasing angle control, the converter station generates, via a given phase angle and signal generating means, a three-phase ac control signal corresponding to the phase angle signal, by means of which the converter station is able to output a voltage of the given phase angle for phase angle control of the weak ac power network.
5. A VSC dc grid control method according to claim 1, characterised in that: in a direct current power grid containing a weak alternating current system, the shortest path of a converter station connected to a strong power grid is selected, and the control level of the converter station is defined as n +1 level control according to the number n of converter stations separated between a certain converter station and the alternating current strong power grid.
6. A VSC dc grid control method according to claim 1, characterised in that: and the converter station of the third stage is connected with the control converter station of the second stage through a weak alternating current power grid.
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