CN113852071A - DC side loop closing control method based on double voltage source type converter flexible loop closing device - Google Patents
DC side loop closing control method based on double voltage source type converter flexible loop closing device Download PDFInfo
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- CN113852071A CN113852071A CN202111113716.9A CN202111113716A CN113852071A CN 113852071 A CN113852071 A CN 113852071A CN 202111113716 A CN202111113716 A CN 202111113716A CN 113852071 A CN113852071 A CN 113852071A
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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
- H02J3/007—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources
- H02J3/0073—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing alternative feeding paths between load and source when the main path fails, e.g. transformers, busbars
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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
- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
- H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
- H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
- H02J9/061—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems for DC powered loads
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- 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 direct current side loop closing control method based on the double voltage source type converter flexible loop closing device comprises the steps of closing a live switch, starting the double voltage source type converter flexible loop closing device, adopting a rectification control strategy, adjusting direct current bus voltages on two sides of the direct current side loop closing switch to be equal, closing the direct current side loop closing switch, completing impact-free loop closing, and avoiding loop closing impact to cause protection misoperation of a power distribution system. After the loop closing is finished, the second voltage source type converter adopts an alternating current voltage stabilization control strategy to control the output fundamental wave voltage of the alternating current valve side to be the same as the first power supply voltage, and after the first power supply switch is disconnected, the first load bus voltage is controlled to track the first power supply voltage, so that the quality of the power supply voltage is ensured. And after the voltage of the first load bus is recovered, controlling the voltage of the first load bus to track the voltage of the second power supply, closing the change-over switch after the voltage of the first load bus is equal to the voltage of the second power supply, and quitting the double-voltage-supply type converter flexible loop closing device to finish the uninterrupted load transfer.
Description
Technical Field
The application relates to the technical field of power distribution network closed-loop transfer control, in particular to a direct current side closed-loop control method based on a double-voltage-source converter flexible closed-loop device.
Background
Load transfer, i.e. the redistribution of loads in the grid when there is a local or risk fault in the grid. With the development of the economic society, the national economic construction and the requirements of residential users on power supply reliability and power supply continuity are higher and higher, and the requirement of the users on continuous power supply is difficult to meet by a power failure load transfer mode.
In order to meet the requirements of resident users on continuous power supply and reliable power supply and realize uninterrupted load transfer of a power distribution network, in the prior art, a proper power supply path is selected for the power distribution network to transfer load by a loop closing operation method, wherein the loop closing operation refers to the operation of closing and running a network formed by a circuit, a transformer or a breaker string in the electrical operation of a power system.
However, when the two sides of the loop closing point have different pressure differences and different short-circuit impedances, the above prior art may generate a circular current after the loop closing, and a large impact current may also occur at the moment of the loop closing, and the excessive loop closing impact current may cause the protection action of the power distribution system, and may further affect the safe and stable operation of the power distribution network.
Disclosure of Invention
The application provides a direct current side loop closing control method based on a double voltage source type converter flexible loop closing device, and aims to solve the technical problem that the overlarge loop closing impact current can cause a power distribution system to perform protection action and influence the safe and stable operation of a power distribution network.
In order to solve the technical problem, the embodiment of the application discloses the following technical scheme:
in a first aspect, the embodiment of the application discloses a direct current side loop closing control method based on a double voltage source type converter flexible loop closing device, which comprises the steps of entering a non-impact loop closing stage, electrifying the double voltage source type converter by closing an electrified switch so as to start the double voltage source type converter flexible loop closing device adopting a double closed loop control structure with feedforward decoupling;
by utilizing a rectifier principle and adopting a rectification control strategy, the direct current bus voltages at two sides of a direct current side loop closing switch of a double-voltage-source converter flexible loop closing device are adjusted, when the direct current bus voltages at two sides of the direct current side loop closing switch of the double-voltage-source converter flexible loop closing device are equal, the direct current side loop closing switch of the double-voltage-source converter flexible loop closing device is closed, and the non-impact loop closing stage is completed;
entering a non-power-off negative charge conversion and supply stage, controlling a control strategy of a second voltage source type converter in the double-voltage source type converter flexible loop closing device to be alternating current voltage stabilization control by utilizing feed-forward and single-loop feedback, controlling an output fundamental wave voltage at the side of an alternating current valve to track a first power supply voltage by the alternating current voltage stabilization control strategy of the feed-forward and single-loop feedback, and controlling the output fundamental wave voltage at the side of the alternating current valve to be the same as the first power supply voltage in the double-voltage source type converter flexible loop closing device, wherein the output current at the alternating current side of the double-voltage source type converter flexible loop closing device is zero;
disconnecting a switch of a first power supply in the dual-voltage-source converter flexible loop closing device, enabling the first power supply in the dual-voltage-source converter flexible loop closing device to quit power supply, enabling the voltage of a first load bus in the dual-voltage-source converter flexible loop closing device to be reduced, and controlling the voltage of the first load bus to track the voltage of the first power supply in the dual-voltage-source converter flexible loop closing device through an alternating current voltage stabilizing control strategy of feedforward and single-loop feedback;
after the voltage of the first load bus is recovered, the voltage of the first load bus is controlled to track the voltage of the second power supply by using a slope function switching principle, so that after the voltage of the first load bus is equal to the voltage of the second power supply, the change-over switch is closed, the live switches on two sides of the flexible loop closing device of the double-voltage source type converter are disconnected, the flexible loop closing device of the double-voltage source type converter is quitted from running, the first load power is converted into the second power supply from the first power supply, and the non-power-off negative charge conversion stage is completed.
Optionally, the controlling the first load bus voltage to track the second power supply voltage by using a ramp function switching principle further includes:
the expression formula of the ramp function switching principle is as follows: u shapesd(q)ref＝Us2d(q)+Kp(Us1d(q)-Us2d(q))
Wherein, KpDenotes the slope coefficient, KpSlowly changes from 1 to 0, Us1d(q)Representing the AC-DC-axis voltage, U, of the first power supplys2d(q)Representing the AC-DC-axis voltage, U, of the second power supplysd(q)refAnd the AC-DC component represents the first load voltage adjustment reference value, and finally, the AC-DC component is converted into the three-phase voltage value through d-q inverse transformation.
Optionally, the control strategy of the second voltage source converter in the dual voltage source converter flexible loop closing apparatus is an ac voltage stabilization control using a feedforward plus single loop feedback, and further includes:
the control strategy of the second voltage source type converter in the double-voltage source type converter flexible loop closing device is changed into alternating current voltage stabilization control of feedforward and single-loop feedback from rectification control.
Optionally, the feedforward plus single-loop feedback ac voltage stabilization control strategy controls the ac valve side to output the fundamental voltage to track the first power voltage, further including:
the control object of the feedforward and single-loop feedback alternating current voltage stabilization control is converted into the alternating current valve side output fundamental voltage by the direct current bus voltage on two sides of the direct current side loop closing switch of the double-voltage source type converter flexible loop closing device.
Optionally, the feedforward plus single-loop feedback ac voltage stabilization control strategy controls a first load dc bus voltage to track a first power voltage in the dual-voltage power converter flexible loop closing device, including:
the control object of the feedforward and single-loop feedback alternating current voltage stabilization control is converted into a first load bus voltage by the output fundamental wave voltage of the alternating current valve side.
Optionally, the method enters a non-impact loop closing stage, and before the dual-voltage source type converter is electrified by closing an electrified switch to start the dual-voltage source type converter flexible loop closing device adopting the dual-closed-loop control structure with feedforward decoupling, the method further includes:
the voltage source converters of the double voltage source converter flexible loop closing device all adopt three-phase two-level voltage source converters.
The beneficial effect of this application does:
the embodiment of the application provides a direct current side loop closing control method based on double voltage source type converter flexible loop closing device, including entering the no-impact loop closing stage, through closing the electrified switch, give double voltage source type converter electrification, in order to start the double voltage source type converter flexible loop closing device that adopts the double closed loop control structure who takes feedforward decoupling zero, utilize the rectifier principle, adopt the control strategy of rectification, adjust the direct current bus voltage of double voltage source type converter flexible loop closing device direct current side loop closing switch both sides, the direct current bus voltage of double voltage source type converter flexible loop closing device direct current side loop closing switch both sides is equal, close double voltage source type converter flexible loop closing device direct current side loop closing switch, no-impact loop closing stage is accomplished. Compared with the traditional loop closing device, the flexible loop closing device of the double voltage source type converter has flexible control capability and higher safety; the static synchronous compensator has the function of providing dynamic reactive compensation and stabilizing the voltage of the alternating current bus; by adopting the turn-off device, even if the receiving end alternating current system has serious faults, certain power can be transmitted as long as the alternating current bus of the transformer substation still has voltage; active power and reactive power can be independently adjusted at the same time; the level of harmonics is relatively low; when the current can flow in two directions, the polarity of the direct current voltage can not be changed, and a parallel multi-terminal direct current system is formed, on the premise of keeping the voltage of the multi-terminal direct current system constant, the single-terminal current can be adjusted in the positive direction and the negative direction by changing the direction of the single-terminal current; the occupied area is small. Compared with the method for closing the loop at the alternating current side, the direct current side is closed and the loop is closed only by controlling and adjusting the voltage values of the current converters at the two ends to be equal, so that the difficulty caused by the loop closing operation due to the amplitude value or the phase deviation of the three-phase voltage is avoided, the control is simple to realize, the phenomenon that the impact current of the loop is too large to cause the power distribution system to carry out protection action is avoided, and the influence on the safe and stable operation of the power distribution network is avoided. Entering a non-power-off negative charge conversion and supply stage, controlling a control strategy of a second voltage source type converter in the double voltage source type converter flexible loop closing device to utilize a feedforward and single-ring feedback alternating current voltage stabilization control, controlling an alternating current valve side to output fundamental wave voltage to track a first power supply voltage by the feedforward and single-ring feedback alternating current voltage stabilization control strategy, controlling a first power supply switch in the double voltage source type converter flexible loop closing device when the alternating current valve side output fundamental wave voltage is the same as the first power supply voltage in the double voltage source type converter flexible loop closing device, disconnecting the first power supply switch in the double voltage source type converter flexible loop closing device, stopping power supply of the first power supply in the double voltage source type converter flexible loop closing device, reducing a first load bus voltage in the double voltage source type converter flexible loop closing device, controlling the first load bus voltage to track the first power supply voltage in the double voltage source type converter flexible loop closing device by the feedforward and single-ring feedback alternating current voltage stabilization control strategy, after the voltage of the first load bus is recovered, the voltage of the first load bus is controlled to track the voltage of the second power supply by using a slope function switching principle, so that after the voltage of the first load bus is equal to the voltage of the second power supply, the change-over switch is closed, the live switches on two sides of the flexible loop closing device of the double-voltage source type converter are disconnected, the flexible loop closing device of the double-voltage source type converter is quitted from running, the first load power is converted into the second power supply from the first power supply, and the non-power-off negative charge conversion stage is completed. The final loop closing is realized by the change-over switch, the running loss of the double voltage source type converter flexible loop closing device can be reduced, the loop closing running reliability is improved, the double voltage source type converter flexible loop closing device is protected, the negative charge switching and supplying stage is not interrupted, the integral structure of the controller is not required to be changed, the load switching and supplying without interruption can be realized only by controlling the switching of instructions and controlled voltage signals, the control stability is good, and the electric energy quality requirement can be met while the system power supply continuity is ensured.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic flowchart of a dc-side loop closing control method for a flexible loop closing device based on a dual voltage source type converter according to an embodiment of the present application;
fig. 2 is a schematic structural diagram of a system based on a dual-voltage-source converter flexible loop closing device according to an embodiment of the present application;
fig. 3 is a schematic diagram of a dc-side loop closing process of a flexible loop closing device based on a dual voltage source type converter according to an embodiment of the present application;
fig. 4 is a schematic diagram of a dual closed-loop control structure of a two-side voltage source converter according to an embodiment of the present disclosure;
fig. 5 is a schematic diagram of a strategy adjustment control structure of a second voltage source converter after loop closing according to an embodiment of the present application;
fig. 6 is a schematic diagram illustrating a load-to-power smooth switching control principle provided in an embodiment of the present application;
fig. 7 is a schematic diagram of a simulation waveform of a dc bus voltage provided in an embodiment of the present application;
fig. 8 is a schematic diagram of a dc bus current simulation waveform provided in the embodiment of the present application;
fig. 9 is a schematic diagram of a simulation waveform of a key current in a loop closing process according to an embodiment of the present application;
fig. 10 is a schematic waveform diagram illustrating load transfer power smoothing switching simulation provided in an embodiment of the present application.
Detailed Description
In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, an embodiment of the present application provides a method for controlling a dc-side loop closing device based on a dual voltage source converter, including the following steps:
step S110: and entering a non-impact loop closing stage, and electrifying the double-voltage source type converter by closing an electrified switch so as to start the double-voltage source type converter flexible loop closing device adopting a double-closed-loop control structure with feedforward decoupling.
In some embodiments, before entering the non-impact loop closing stage and charging the dual-voltage-source converter by closing the charging switch to start the dual-voltage-source converter flexible loop closing device adopting the dual-closed-loop control structure with feed-forward decoupling, the method further includes:
the voltage source converters of the double voltage source converter flexible loop closing device all adopt three-phase two-level voltage source converters.
Step S120: by utilizing the principle of a rectifier and adopting a control strategy of rectification, the direct current bus voltages on two sides of a direct current side loop closing switch of a double-voltage-source converter flexible loop closing device are adjusted, when the direct current bus voltages on two sides of the direct current side loop closing switch of the double-voltage-source converter flexible loop closing device are equal, the direct current side loop closing switch of the double-voltage-source converter flexible loop closing device is closed, and the non-impact loop closing stage is completed.
As shown in FIG. 2, the first power source is a main power source, the second power source is a standby power source, Us1、Us2Is the bus voltage on two sides of a DC side loop closing switch of a double voltage source type converter flexible loop closing device, and simultaneously, Us1Is also the first supply voltage, Us2And also as a second power supply voltage, K1 is a first load switch, K4 is a second load switch, in the figure, AC represents alternating current, PT represents a voltage transformer, in a normal state, the first power supply supplies power to the first load, the second power supply supplies power to the second load, and the change-over switch K5 is in an off state when the dual voltage source type converter flexible loop closing device is not put into operation. K2 and K3 are live switches of the double-voltage-source converter, and the live switches K2 and K3 are closed during direct current loop closing so as to start the voltage-source converters on two sides. K6 is DCAnd the side loop closing switch is connected with the voltage source type converters on two sides to form a back-to-back converter based on the double voltage source type converters.
As shown in FIG. 9, Is1aRepresenting the current, I, through the first load switch K11aThe current on the AC side of the second voltage source converter is shown, and the current I on the AC side of the second voltage source converter before and after the loop closing on the DC side of 0.5s can be seen from the figure1aAre very small and the loop has little effect on the ac side current. At 1.2s, the first power supply stops supplying power, and the current I flowing through the first load switch K1s1aReduced to zero, the load current is transferred to the converter formed by the second voltage source type converter, so that the current I on the alternating current side of the second voltage source type converter1aAnd is increased.
Step S130: and entering a non-power-off negative charge conversion and supply stage, controlling a control strategy of a second voltage source type converter in the double-voltage source type converter flexible loop closing device to be alternating current voltage stabilization control by utilizing feed-forward and single-loop feedback, controlling the output fundamental wave voltage of the alternating current valve side to track the first power supply voltage by the alternating current voltage stabilization control strategy of the feed-forward and single-loop feedback, and controlling the output fundamental wave voltage of the alternating current valve side to be the same as the first power supply voltage in the double-voltage source type converter flexible loop closing device, wherein the output current of the alternating current side of the double-voltage source type converter flexible loop closing device is zero.
In some embodiments, the control strategy of the second voltage source converter in the dual voltage source converter flexible loop device is an ac voltage stabilization control using a feedforward plus single loop feedback, further comprising:
the control strategy of the second voltage source type converter in the double-voltage source type converter flexible loop closing device is changed into alternating current voltage stabilization control of feedforward and single-loop feedback from rectification control.
In some embodiments, the ac voltage stabilization control strategy of feed-forward plus single loop feedback controls the ac valve side output fundamental voltage to track the first supply voltage, further comprising:
the control object of the feedforward and single-loop feedback alternating current voltage stabilization control is converted into the alternating current valve side output fundamental voltage by the direct current bus voltage on two sides of the direct current side loop closing switch of the double-voltage source type converter flexible loop closing device.
Step S140: the switch of a first power supply in the double-voltage-source converter flexible loop closing device is disconnected, the first power supply in the double-voltage-source converter flexible loop closing device quits power supply, the voltage of a first load bus in the double-voltage-source converter flexible loop closing device can be reduced, and the alternating current voltage stabilization control strategy of feedforward plus single-loop feedback controls the voltage of the first load bus to track the voltage of the first power supply in the double-voltage-source converter flexible loop closing device.
In some embodiments, a feed-forward plus single loop feedback ac regulated control strategy for controlling a first load bus voltage to track a first supply voltage in a dual voltage supply type converter flexible loop device, comprises:
the control object of the feedforward and single-loop feedback alternating current voltage stabilization control is converted into a first load bus voltage by the output fundamental wave voltage of the alternating current valve side.
Step S150: after the voltage of the first load bus is recovered, the voltage of the first load bus is controlled to track the voltage of the second power supply by using a slope function switching principle, so that after the voltage of the first load bus is equal to the voltage of the second power supply, the change-over switch is closed, the live switches on two sides of the flexible loop closing device of the double-voltage source type converter are disconnected, the flexible loop closing device of the double-voltage source type converter is quitted from running, the first load power is converted into the second power supply from the first power supply, and the non-power-off negative charge conversion stage is completed.
In some embodiments, controlling the first load bus voltage to track the second supply voltage using a ramp function switching principle further comprises:
the expression formula of the ramp function switching principle is as follows: u shapesd(q)ref＝Us2d(q)+Kp(Us1d(q)-Us2d(q))
Wherein, KpDenotes the slope coefficient, KpSlowly changes from 1 to 0, Us1d(q)Representing the AC-DC-axis voltage, U, of the first power supplys2d(q)Representing the AC-DC-axis voltage, U, of the second power supplysd(q)refAnd the AC-DC component represents the first load voltage adjustment reference value, and finally, the AC-DC component is converted into the three-phase voltage value through d-q inverse transformation.
As shown in fig. 4, in a normal state, the first power supply supplies power to the first load, the second power supply supplies power to the second load, the first load switch K1 and the second load switch K4 are closed, in a loop closing process, the live switches K2 and K3 are both used as live switches, and the K6 is used as a loop closing switch, and the specific loop closing and load transferring processes are as follows:
first, the charging switches K2, K3 are closed to charge the two-side voltage source converter. As shown in fig. 4, before loop closing, the first voltage source converter and the second voltage source converter both act as a rectifier, and are used to output a stable dc voltage at the dc side, and when the voltages output from both sides are equal, the loop closing condition is satisfied, and loop closing operation is performed. The control strategies of the rectifier are more, and the most mature double closed-loop control structure formed by current inner loop feedback and voltage outer loop feedback is selected in various control modes. Due to the coupling voltage omega Li under the two-phase rotating coordinate systemsd、ωLisqAnd the network voltage usd、usqFor the influence generated by the d-axis current and the q-axis current, the independent control of the d-axis current and the q-axis current cannot be realized only by means of negative feedback decoupling control, so that the problem is solved by finally adopting a feedforward decoupling control strategy.
The voltage outer ring takes the voltage value preset and output at the direct current side as a direct current voltage reference value udcrefThe actual output voltage value of the DC side is udcWill udcrefAnd udcAfter difference is made, the output current i is controlled by PI (proportional integral)drefAs active reference for the current inner loop, reference current reactive component i qref0. Three-phase current i on current inner ring sampling power supply sidesa、isb、iscConverted into a direct and alternating current component i under a d-q coordinate system through coordinate transformationsd、isqAnd a reference current idref、iqrefObtaining a voltage reference vector value u through inner loop controldrefAnd uqrefThe inner loop control takes into account the coupling voltage ω Lisd、ωLisqAnd the network voltage usd、usqFor d and q axis current generationThe control principle formula of the influence is as follows:
wherein, KiP、KiIIs the regulating parameter of PI control.
And performing d-q coordinate inverse transformation on the voltage reference value to obtain a three-Phase signal wave, controlling the Phase of the output three-Phase signal wave to be consistent with the Phase of the three-Phase power supply voltage by using a Phase Locked Loop (PLL), and comparing the output three-Phase signal wave with a high-frequency carrier wave respectively to further control the working condition of the switching tube, thereby finally achieving the expected control effect.
As shown in fig. 3, the dc-side bus voltage u on both sides of the loop closing switch K6 is adjusted1dcAnd u1dcLet u stand for1dcAnd u1dcAnd the same, realizing loop closing. After the loop closing is finished, the control strategy of the second voltage source type converter is changed from controlling the direct current side bus voltage to controlling the alternating current side output fundamental wave voltage upwmControl so that upwmThe voltage of the first power supply is equal to the voltage of the first power supply to ensure that the output current of the double voltage source type converter flexible loop closing device on the alternating current side is zero, then the first load switch K1 is switched off, the first power supply is powered off, and the voltage U of a first load bus is influenced by the voltage drop of an alternating current inductorL1The voltage feedback quantity is reduced to output the fundamental wave voltage u from the AC sidepwmSwitching to a first load bus voltage UL1And then controlled to track the first supply voltage Us1I.e. to control the first load voltage to be equal to the first supply voltage Us1After the first load bus voltage is recovered, the first load bus voltage U is controlled and adjustedL1Tracking the second supply voltage Us2I.e. to control the first load voltage to be equal to the second supply voltage Us2Wait for the first load voltage and US2When the voltages are equal, the first loadAfter the power is supplied by the second power supply, the change-over switch K5 is closed, the live switches K2 and K3 are disconnected, and the loop closing device is withdrawn, so that the first load is changed to be supplied by the second power supply.
As shown in fig. 5, when the loop closing is completed, the first power supply is about to stop supplying power, and at this time, the control strategy of the second voltage source converter needs to be changed to convert the first load from the first power supply to the second power supply, so as to realize the non-power-cut load conversion. Specifically, after loop closing, the second voltage source converter control strategy converts the controlled dc bus voltage to the controlled ac output voltage, which is embodied as a feedforward plus single loop feedback ac regulated control, as shown in the first PART1 of fig. 5. In order to realize stable switching of the control strategy, the previous operation condition is not changed as much as possible in the switching process, that is, the first load is still powered by the first power supply, so that the alternating current output current of the second voltage source type converter is zero, and the alternating current output fundamental voltage of the second voltage source type converter needs to be controlled to be equal to the first power supply voltage. Fundamental wave voltage u output from AC side of converterpwma、upwmb、upwmcConverted into a quadrature-direct axis component u through d-q coordinate transformationpwmd、upwmqWhile u iss1d、us1qIs the quadrature-direct axis component u of the first supply voltage d-q after coordinate transformations2d、us2qThe output u of the voltage switching module is instructed for the quadrature-direct axis component after the coordinate transformation of the second power voltage d-q before the load is suppliedsdref、usqrefIs a first power supply us1d、us1q. Value u of power supply voltagesdref、usqrefNot only used as a feedforward voltage signal, but also used as a controlled voltage upwmd、upwmqAfter difference is made, a tiny feedback regulation signal is obtained through PI control, and the power supply voltage u is adjustedsdref、usqrefAnd respectively carrying out difference with the feedback adjusting signal, then carrying out d-q coordinate transformation to obtain three-phase signal waves, controlling the phase of the output three-phase signal waves to be consistent with the phase of the three-phase power supply voltage by using phase locking, and then comparing the three-phase signal waves with a high-frequency carrier wave to further control the working condition of the switching tube, thereby finally achieving the desired control effect.
When the first load switch K1 is turned offThe first power supply stops supplying power, the first load current is transferred to the double-voltage-source converter flexible loop closing device, and the fundamental voltage u of the alternating current side PWM wave is controlledpwma、upwmb、upwmcTracking the first supply voltage, the presence of an alternating current inductance causes the voltage of the first load to drop. In order to effectively solve the voltage drop problem, the first load voltage is controlled to track the first power supply voltage, that is, the first load voltage is controlled to be equal to the first power supply voltage, the control is switched as shown in a second PART2 in fig. 5, and the controlled voltage (feedback signal) is switched from the quadrature-axis component u and the direct-axis component u of the PWM fundamental voltagepwmd、upwmqConverted into the quadrature-direct component u of the first load voltageL1d、uL1q. After the first load voltage recovers and stabilizes again, the load is supplied by the second power supply, and the feedforward power supply voltage reference value u needs to be used for supplying power to the first loadsdref、usqrefFrom a first supply voltage us1d、us1qSmoothly switching to a second supply voltage u by a command voltage switching modules2d、us2q. As shown in fig. 6, in order to ensure the continuity of power supply and satisfy the power quality requirement during the power supply switching without power cut and loop closing, the bus voltage is required to be smoothly switched during the power supply switching process, and the power supply is smoothly switched from the first power supply to the second power supply, i.e. the first load voltage UL1Slave and first supply voltage Us1Smooth transition to the second supply voltage Us2A ramp conversion is used. At first, multiplying the initial output value 1 of the ramp function by the difference value between the first power supply and the second power supply, adding the multiplied result to the second power supply voltage value, and at the moment, offsetting the positive and negative second power supply voltage values to obtain the power supply voltage reference value usd(q)refIs the first power supply voltage value us1dThe output value of the ramp function is gradually changed from 1 to 0 along with the adjustment of the ramp function, and the obtained power supply voltage reference value u is obtainedsd(q)refAlso from the first supply voltage value us1d(q)Smooth transition to the second supply voltage value us2d(q)。
As shown in fig. 5, in the whole switching process of the control strategy, the control parameters do not need to be re-set, the overall structure of the controller is not changed, and the control can be realized only by switching the control command and the controlled voltage signal, so that the control stability is good, and the implementation is relatively simple.
As shown in FIGS. 7-8, the 0.1s (second) two-terminal voltage source converter is used as rectifier start to control the DC bus voltage UdcBefore the loop closing for 0.5s, the voltage of the direct-current side bus can quickly reach a stable value, and the current I of the direct-current sidedcIs always very small and almost zero. 0.5s closes the loop closing switch K6, and as can be seen from the figure, the voltage and the current of the direct current bus have almost no change, and the surge-free loop closing is basically realized. And when the power supply of the main power supply is stopped for 1.2s, the first load current is transferred to the flexible loop closing device of the double-voltage-source type converter, so that the direct-current bus current is increased, but the direct-current bus voltage is reduced to some extent due to the disturbance of load transfer, but the voltage is slowly restored to be stable again due to the regulation effect of the control strategy of the converter. 1.4s, in order to solve the problem of load voltage reduction, a control strategy is changed to improve the load voltage, the direct current bus voltage has a very small fluctuation, and the direct current bus current is continuously increased. And 2s, load supply is realized, the load voltage is smoothly transited from the first power supply to the second power supply for supplying power, and the influence on the voltage and the current of the direct current bus is small.
As shown in FIG. 10, the supply of the load is started 2s (seconds), and the first load voltage U is set 2s beforeL1Waveform of (d) and first supply voltage Us12s, the first load voltage waveform begins to smooth towards the second supply voltage waveform Us2And the voltage waveform is quickly overlapped with the voltage waveform of the second power supply, so that the smooth switching of the load power supply voltage is realized.
It can be seen from the foregoing embodiments that, the dc-side loop closing control method based on the dual voltage source type converter flexible loop closing device provided in the embodiments of the present application includes entering an impact-free loop closing stage, charging the dual voltage source type converter by closing the charged switch to start the dual voltage source type converter flexible loop closing device adopting the dual closed loop control structure with feedforward decoupling, adjusting dc bus voltages on both sides of the dc-side loop closing switch of the dual voltage source type converter flexible loop closing device by using a rectifier principle and a control strategy of rectification, closing the dc-side loop closing switch of the dual voltage source type converter flexible loop closing device when the dc bus voltages on both sides of the dc-side loop closing switch of the dual voltage source type converter flexible loop closing device are equal, and completing the impact-free loop closing stage. Compared with the traditional loop closing device, the flexible loop closing device of the double voltage source type converter has flexible control capability and higher safety; the static synchronous compensator has the function of providing dynamic reactive compensation and stabilizing the voltage of the alternating current bus; by adopting the turn-off device, even if the receiving end alternating current system has serious faults, certain power can be transmitted as long as the alternating current bus of the transformer substation still has voltage; active power and reactive power can be independently adjusted at the same time; the level of harmonics is relatively low; when the current can flow in two directions, the polarity of the direct current voltage can not be changed, and a parallel multi-terminal direct current system is formed, on the premise of keeping the voltage of the multi-terminal direct current system constant, the single-terminal current can be adjusted in the positive direction and the negative direction by changing the direction of the single-terminal current; the occupied area is small. Compared with the method for closing the loop at the alternating current side, the direct current side is closed and the loop is closed only by controlling and adjusting the voltage values of the current converters at the two ends to be equal, so that the difficulty caused by the loop closing operation due to the amplitude value or the phase deviation of the three-phase voltage is avoided, the control is simple to realize, the phenomenon that the impact current of the loop is too large to cause the power distribution system to carry out protection action is avoided, and the influence on the safe and stable operation of the power distribution network is avoided. Entering a non-power-off negative charge conversion and supply stage, controlling a control strategy of a second voltage source type converter in the double voltage source type converter flexible loop closing device to utilize a feedforward and single-ring feedback alternating current voltage stabilization control, controlling an alternating current valve side to output fundamental wave voltage to track a first power supply voltage by the feedforward and single-ring feedback alternating current voltage stabilization control strategy, controlling a first power supply switch in the double voltage source type converter flexible loop closing device when the alternating current valve side output fundamental wave voltage is the same as the first power supply voltage in the double voltage source type converter flexible loop closing device, disconnecting the first power supply switch in the double voltage source type converter flexible loop closing device, stopping power supply of the first power supply in the double voltage source type converter flexible loop closing device, reducing a first load bus voltage in the double voltage source type converter flexible loop closing device, controlling the first load bus voltage to track the first power supply voltage in the double voltage source type converter flexible loop closing device by the feedforward and single-ring feedback alternating current voltage stabilization control strategy, after the voltage of the first load bus is recovered, the voltage of the first load bus is controlled to track the voltage of the second power supply by using a slope function switching principle, so that after the voltage of the first load bus is equal to the voltage of the second power supply, the change-over switch is closed, the live switches on two sides of the flexible loop closing device of the double-voltage source type converter are disconnected, the flexible loop closing device of the double-voltage source type converter is quitted from running, the first load power is converted into the second power supply from the first power supply, and the non-power-off negative charge conversion stage is completed. The final loop closing is realized by the change-over switch, the running loss of the double voltage source type converter flexible loop closing device can be reduced, the loop closing running reliability is improved, the double voltage source type converter flexible loop closing device is protected, the negative charge switching and supplying stage is not interrupted, the integral structure of the controller is not required to be changed, the load switching and supplying without interruption can be realized only by controlling the switching of instructions and controlled voltage signals, the control stability is good, and the electric energy quality requirement can be met while the system power supply continuity is ensured.
Since the above embodiments are all described by referring to and combining with other embodiments, the same portions are provided between different embodiments, and the same and similar portions between the various embodiments in this specification may be referred to each other. And will not be described in detail herein.
It is noted that, in this specification, relational terms such as "first" and "second," and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a circuit structure, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such circuit structure, article, or apparatus. Without further limitation, the presence of an element identified by the phrase "comprising an … …" does not exclude the presence of other like elements in a circuit structure, article or device comprising the element.
Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.
The above-described embodiments of the present application do not limit the scope of the present application.
Claims (6)
1. A direct current side loop closing control method based on a double voltage source type converter flexible loop closing device is characterized by comprising the following steps:
entering a non-impact loop closing stage, and electrifying the double-voltage source type converter by closing an electrified switch so as to start the double-voltage source type converter flexible loop closing device adopting a double-loop closing control structure with feedforward decoupling;
by utilizing a rectifier principle and adopting a rectification control strategy, the direct current bus voltages at two sides of a direct current side loop closing switch of the double voltage source type converter flexible loop closing device are adjusted, when the direct current bus voltages at two sides of the direct current side loop closing switch of the double voltage source type converter flexible loop closing device are equal, the direct current side loop closing switch of the double voltage source type converter flexible loop closing device is closed, and the non-impact loop closing stage is completed;
entering a non-power-off negative charge conversion and supply stage, wherein a control strategy of a second voltage source type converter in the double-voltage source type converter flexible loop closing device is alternating current voltage stabilization control by utilizing feed-forward and single-loop feedback, the alternating current voltage stabilization control strategy of the feed-forward and single-loop feedback controls the output fundamental wave voltage at the side of an alternating current valve to track a first power supply voltage, the output fundamental wave voltage at the side of the alternating current valve is the same as the first power supply voltage in the double-voltage source type converter flexible loop closing device, and the output current at the alternating current side of the double-voltage source type converter flexible loop closing device is zero;
disconnecting a switch of a first power supply in the dual-voltage converter flexible loop closing device, wherein the first power supply in the dual-voltage converter flexible loop closing device quits power supply, the voltage of a first load bus in the dual-voltage converter flexible loop closing device can be reduced, and an alternating current voltage stabilizing control strategy of feedforward plus single-loop feedback controls the voltage of the first load bus to track the voltage of the first power supply in the dual-voltage converter flexible loop closing device;
after the first load bus voltage is recovered, the first load bus voltage is controlled to track the second power supply voltage by using a ramp function switching principle, so that after the first load bus voltage is equal to the second power supply voltage, the change-over switch is closed, the live switches on two sides of the double-voltage source type converter flexible loop closing device are disconnected, the double-voltage source type converter flexible loop closing device is quitted from running, the first load power supply is converted into the second power supply from the first power supply, and the non-power-outage negative charge conversion stage is completed.
2. The dual voltage source type converter-based flexible loop closing device direct current side loop closing control method according to claim 1, wherein the controlling the first load bus voltage to track the second power source voltage by using a ramp function switching principle further comprises:
the expression formula of the ramp function switching principle is as follows: u shapesd(q)ref＝Us2d(q)+Kp(Us1d(q)-Us2d(q))
Wherein, KpDenotes the slope coefficient, KpSlowly changes from 1 to 0, Us1d(q)Representing the AC-DC-axis voltage, U, of the first power supplys2d(q)Representing the AC-DC-axis voltage, U, of the second power supplysd(q)refAnd the AC-DC component represents the first load voltage adjustment reference value, and finally, the AC-DC component is converted into the three-phase voltage value through d-q inverse transformation.
3. The dc-side loop closing control method based on the dual voltage source converter flexible loop closing device according to claim 1, wherein the control strategy of the second voltage source converter in the dual voltage source converter flexible loop closing device is an ac voltage stabilization control using a feedforward plus a single loop feedback, further comprising:
and the control strategy of a second voltage source type converter in the double-voltage source type converter flexible loop closing device is changed into alternating current voltage stabilization control of feedforward and single-loop feedback from rectification control.
4. The method for controlling the direct-current side loop closing control based on the dual voltage source type converter flexible loop closing device according to claim 1, wherein the alternating current voltage stabilization control strategy of feed-forward plus single loop feedback controls the output fundamental voltage of the alternating current valve side to track the first power supply voltage, and further comprising:
the control object of the feedforward and single-loop feedback alternating current voltage stabilization control is converted into the alternating current valve side output fundamental voltage by the direct current bus voltage on two sides of the direct current side loop closing switch of the double-voltage source type converter flexible loop closing device.
5. The method for controlling the dc side loop closing control based on the dual voltage source type converter flexible loop closing device according to claim 1, wherein the ac voltage stabilization control strategy of feedforward plus single loop feedback controls the first load bus voltage to track the first power voltage in the dual voltage source type converter flexible loop closing device, and comprises:
the control object of the feedforward and single-loop feedback alternating current voltage stabilization control is converted into a first load bus voltage by the output fundamental wave voltage of the alternating current valve side.
6. The method for controlling the dc side loop closing of the dual voltage source type converter based flexible loop closing device according to claim 1, wherein before entering the non-impact loop closing stage, the dual voltage source type converter is electrified by closing an electrified switch to start the dual voltage source type converter based flexible loop closing device adopting the dual closed loop control structure with feedforward decoupling, the method further comprises:
the voltage source converters of the double voltage source converter flexible loop closing device all adopt three-phase two-level voltage source converters.
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