CN113852071B - Direct-current side loop closing control method based on flexible loop closing device of double-voltage source type converter - Google Patents
Direct-current side loop closing control method based on flexible loop closing device of double-voltage source type converter Download PDFInfo
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- CN113852071B CN113852071B CN202111113716.9A CN202111113716A CN113852071B CN 113852071 B CN113852071 B CN 113852071B CN 202111113716 A CN202111113716 A CN 202111113716A CN 113852071 B CN113852071 B CN 113852071B
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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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- 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 direct current side loop closing control method based on the double-voltage source type converter flexible loop closing device provided by the embodiment of the application comprises the steps of closing an electrified switch, starting the double-voltage source type converter flexible loop closing device, adopting a rectification control strategy, and closing the direct current side loop closing switch when the direct current bus voltages at two sides of the direct current side loop closing switch are equal, so that no-impact loop closing is completed, and the protection misoperation of a power distribution system caused by loop closing impact is avoided. After the loop closing is completed, the second voltage source type converter adopts an alternating current voltage stabilizing 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 second power supply voltage, closing the change-over switch after the voltage of the first load bus is equal to the second power supply voltage, exiting the flexible loop closing device of the double-voltage source type converter, and completing uninterrupted load transfer.
Description
Technical Field
The application relates to the technical field of closed-loop power supply control of power distribution networks, in particular to a direct-current side closed-loop control method based on a flexible closed-loop device of a double-voltage source type converter.
Background
Load transfer, i.e. the redistribution of load in the grid when the grid is locally faulty or at risk of faults. With the development of economy and society, the requirements of national economy construction and resident users on power supply reliability and power supply continuity are higher and higher, and the power failure load transferring mode is difficult to meet the requirements of the users on continuous power supply.
In order to meet the requirements of resident users on continuous power supply and reliable power supply and realize uninterrupted power supply of a power distribution network, in the prior art, the power distribution network selects a proper power supply path to carry out load transfer by a method of loop closing operation, wherein the loop closing operation refers to operation of closing a network formed by a circuit, a transformer or a breaker string in electric operation of a power system.
However, when the pressure difference and the short circuit impedance are different at two sides of the loop closing point, the prior art can generate a circulation after loop closing, and larger impact current can occur at the moment of loop closing, and the overlarge impact current of loop closing can possibly cause a power distribution system to perform protection action, so that the safety and stability operation of the power distribution network can be influenced.
Disclosure of Invention
The application provides a direct-current side loop closing control method based on a flexible loop closing device of a double-voltage source type converter, which aims to solve the technical problem that excessive loop closing impact current can cause protection action of a power distribution system and affect safe and stable operation of a power distribution network.
In order to solve the technical problems, 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 no-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;
the rectifier principle is utilized, a rectification control strategy is adopted, the direct current bus voltages at the two sides of the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter are regulated, and when the direct current bus voltages at the two sides of the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter are equal, the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter is closed, and the loop closing stage without impact is completed;
the control strategy of the second voltage source type converter in the double voltage source type converter flexible loop closing device is alternating current voltage stabilizing control by utilizing a feedforward and single loop feedback, and the alternating current voltage stabilizing control strategy of the feedforward and single loop feedback controls the output fundamental wave voltage of an alternating current valve side to track the first power supply voltage;
switching off a switch of a first power supply in the flexible loop closing device of the double-voltage source type converter, wherein the first power supply in the flexible loop closing device of the double-voltage source type converter exits from power supply, the voltage of a first load bus in the flexible loop closing device of the double-voltage source type converter can drop, and an alternating current voltage stabilizing control strategy of feedforward and single-loop feedback is used for controlling the voltage of the first load bus to track the voltage of the first power supply in the flexible loop closing device of the double-voltage source type converter;
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 by utilizing a slope function switching principle, closing a change-over switch after the voltage of the first load bus is equal to the voltage of the second power supply, opening electrified switches on two sides of the flexible loop closing device of the double-voltage source type converter, and exiting the flexible loop closing device of the double-voltage source type converter to finish the stage of converting the first load power supply from the first power supply to the second power supply without power failure and negative charge transfer.
Optionally, controlling the first load bus voltage to track the second power supply voltage using a ramp function switching principle further includes:
the expression formula of the ramp function switching principle is as follows: u (U) sd(q)ref ＝U s2d(q) +K p (U s1d(q) -U s2d(q) )
Wherein K is p Representing the ramp coefficient, K p Slowly change from 1 to 0,U s1d(q) Representing the AC-DC voltage, U, of a first power supply s2d(q) Represents the AC-DC axis voltage of the second power supply, U sd(q)ref And the alternating-direct axis component representing the first load voltage adjustment reference value is finally converted into a three-phase voltage value through d-q inverse transformation.
Optionally, the control strategy of the second voltage source converter in the flexible loop closing device of the dual voltage source converter is ac voltage stabilizing control using a feedforward plus single loop feedback, and further includes:
the control strategy of the second voltage source type converter in the flexible loop closing device of the double voltage source type converter is changed from rectification control to alternating current voltage stabilizing control of feedforward and single loop feedback.
Optionally, the ac voltage stabilizing control strategy of feedforward plus single loop feedback controls the ac valve side output fundamental voltage to track the first power supply voltage, and further includes:
the control object of the alternating current voltage stabilization control of feedforward and single loop feedback is that the direct current bus voltage at two sides of a direct current side loop closing switch of a flexible loop closing device of a double-voltage source type converter is converted into the alternating current valve side output fundamental wave voltage.
Optionally, the alternating current voltage stabilizing control strategy of feedforward plus single loop feedback controls the first load direct current bus voltage to track the first power supply voltage in the flexible loop closing device of the double voltage source type converter, and the method comprises the following steps:
the control object of the alternating current voltage stabilizing control of feedforward and single loop feedback is converted into a first load bus voltage by the output fundamental wave voltage of an alternating current valve side.
Optionally, before entering the no-impact loop closing stage and powering the dual-voltage source converter by closing the live switch to start the dual-voltage source converter flexible loop closing device adopting the dual-closed loop control structure with feedforward decoupling, the device further comprises:
the voltage source type converters of the flexible loop closing device of the double voltage source type converter adopt three-phase two-level voltage source converters.
The beneficial effects of the application are as follows:
the direct current side loop closing control method based on the double voltage source type converter flexible loop closing device comprises the steps of entering a no-impact loop closing stage, powering on the double voltage source type converter by closing a live switch to start the double voltage source type converter flexible loop closing device with a feedforward decoupling double closed loop control structure, adjusting 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 by using a rectifier principle and adopting a rectifying control strategy, and closing 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 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, wherein the no-impact loop closing stage is completed. 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 static synchronous compensator, can provide dynamic reactive compensation and stabilize the voltage of an alternating current bus; by adopting the turn-off device, even if a 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 regulated simultaneously; the harmonic level is relatively low; the current can flow bidirectionally, the polarity of the direct-current voltage can not be changed, and when the parallel type multi-terminal direct-current system is formed, the single-terminal power flow can be regulated in the forward direction and the reverse direction by changing the direction of the single-terminal current on the premise of keeping the voltage of the multi-terminal direct-current system constant; the occupied area is small. Compared with the loop closing at the alternating current side, the loop closing at the direct current side is realized only by controlling and adjusting the voltage values of the direct current sides of the converters at the two ends to be equal, so that the difficulty brought by the amplitude value or the phase deviation of the three-phase voltage to the loop closing operation is avoided, the control is realized simply, the protection action of a power distribution system caused by the overlarge loop closing impact current is avoided, and the influence on the safe and stable operation of the power distribution network is avoided. The control strategy of the second voltage source type converter in the double voltage source type converter flexible loop closing device is alternating current voltage stabilizing control of feedforward and single loop feedback, the alternating current voltage stabilizing control strategy of feedforward and single loop feedback controls the output fundamental wave voltage of an alternating current valve side to track the first power supply voltage, when the output fundamental wave voltage of the alternating current valve side is identical with the first power supply voltage in the double voltage source type converter flexible loop closing device, the output current of the alternating current side of the double voltage source type converter flexible loop closing device is zero, a switch of the first power supply in the double voltage source type converter flexible loop closing device is opened, the first power supply in the double voltage source type converter flexible loop closing device exits power supply, the voltage of a first load bus in the double voltage source type converter flexible loop closing device drops, the alternating current voltage stabilizing control strategy of feedforward and single loop feedback controls the voltage of the first load bus to track the first power supply voltage in the double voltage source type 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 slope function switching principle, the first load bus voltage is enabled to be equal to the second power supply voltage, the double voltage source type converter flexible loop closing device is opened, the double voltage loop closing device is closed, the power supply is completed, and the double power supply is not powered by the flexible loop closing device, and the power supply of the double voltage source type converter flexible loop closing device is closed, and the power supply is powered by the power supplied by the double voltage. The final loop closing device is realized by the change-over switch, so that the operation loss of the flexible loop closing device of the double-voltage source type converter can be reduced, the loop closing operation reliability is improved, the flexible loop closing device of the double-voltage source type converter is protected, the uninterrupted negative charge transfer stage is not required to be changed, the uninterrupted load transfer can be realized by only switching a control command and a controlled voltage signal, the control stability is good, and the power quality requirement can be met while the power supply continuity of the system 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 as claimed.
Drawings
In order to more clearly illustrate the technical solution of the present application, the drawings that are needed in the embodiments will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.
Fig. 1 is a schematic flow chart of a direct current side loop closing control method based on a flexible loop closing device of a dual-voltage source type converter according to an embodiment of the application;
FIG. 2 is a schematic diagram of a system structure of a flexible ring closing device based on a dual voltage source converter 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 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 application;
fig. 5 is a schematic diagram of a strategy adjustment control structure of a second voltage source converter after ring closing according to an embodiment of the present application;
FIG. 6 is a schematic diagram of a load transfer power smoothing switching control principle according to an embodiment of the present application;
fig. 7 is a schematic diagram of a simulation waveform of a dc bus voltage according to an embodiment of the present application;
FIG. 8 is a schematic diagram of a DC bus current simulation waveform according to an embodiment of the present application;
FIG. 9 is a schematic diagram of a waveform of a key current simulation in a loop closing process according to an embodiment of the present application;
fig. 10 is a schematic diagram of a load-to-power-supply smooth switching simulation waveform according to an embodiment of the present application.
Detailed Description
In order to make the technical solution of the present application better understood by those skilled in the art, the technical solution of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, shall fall within the scope of the present application.
Referring to fig. 1, the embodiment of the application provides a direct current side loop closing control method based on a flexible loop closing device of a double-voltage source type converter, which comprises 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 no-impact loop closing stage and powering the dual voltage source converter by closing the power switch to start the dual voltage source converter flexible loop closing device adopting the dual closed loop control structure with feedforward decoupling, the method further comprises:
the voltage source type converters of the flexible loop closing device of the double voltage source type converter adopt three-phase two-level voltage source converters.
Step S120: the rectifier principle is utilized, a rectification control strategy is adopted, the direct current bus voltages at the two sides of the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter are regulated, and when the direct current bus voltages at the two sides of the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter are equal, the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter is closed, and the loop closing stage without impact is completed.
As shown in FIG. 2, the first power supply is a main power supply, the second power supply is a standby power supply, U s1 、U s2 Bus voltage at two sides of direct-current side loop closing switch of flexible loop closing device of double-voltage source type converter, and U s1 Also being the first supply voltage, U s2 The transformer is also a second power supply voltage, K1 is a first load switch, K4 is a second load switch, AC in the figure represents alternating current, PT represents a voltage transformer, under a normal state, the first power supply supplies power to the first load, the second power supply supplies power to the second load, and when the flexible loop closing device of the double-voltage source type converter is not put into operation, the change-over switch K5 is in an off state. And K2 and K3 are live switches of the double-voltage source type converter, and the live switches K2 and K3 are closed when the direct current is closed, so that the voltage source type converters on two sides are started. K6 is a direct-current side closed loop switch connected with the voltage source converters at two sides to form a back-to-back converter based on the double voltage source converters.
As shown in FIG. 9, in the diagram I s1a Indicating the current through the first load switch K1, I 1a The current I of the alternating current side of the second voltage source type converter before and after the loop closing of the direct current side of 0.5s can be seen from the diagram 1a Are very small and the closed loop has little effect on the ac side current. The first power supply stops supplying power at 1.2s, and the current I flows through the first load switch K1 s1a To zero, the load current is transferred to the converter formed by the second voltage source converter, so that the second voltage source converter ac side current I 1a Increasing.
Step S130: the control strategy of the second voltage source type converter in the double voltage source type converter flexible loop closing device is alternating current voltage stabilizing control by utilizing feedforward and single loop feedback, the alternating current voltage stabilizing control strategy of feedforward and single loop feedback controls the output fundamental wave voltage of an alternating current valve side to track the first power supply voltage, and when the output fundamental wave voltage of the alternating current valve side is identical to the first power supply voltage in the double voltage source type converter flexible loop closing device, 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 flexible loop closing device of the dual voltage source converter is ac voltage stabilizing control using a feedforward plus single loop feedback, and further comprising:
the control strategy of the second voltage source type converter in the flexible loop closing device of the double voltage source type converter is changed from rectification control to alternating current voltage stabilizing control of feedforward and single loop feedback.
In some embodiments, the ac voltage regulation control strategy of feedforward 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 alternating current voltage stabilization control of feedforward and single loop feedback is that the direct current bus voltage at two sides of a direct current side loop closing switch of a flexible loop closing device of a double-voltage source type converter is converted into the alternating current valve side output fundamental wave voltage.
Step S140: and switching off a switch of a first power supply in the flexible loop closing device of the double-voltage source type converter, wherein the first power supply in the flexible loop closing device of the double-voltage source type converter exits power supply, the voltage of a first load bus in the flexible loop closing device of the double-voltage source type converter can drop, and an alternating current voltage stabilizing control strategy of feedforward and single-loop feedback is used for controlling the voltage of the first load bus to track the voltage of the first power supply in the flexible loop closing device of the double-voltage source type converter.
In some embodiments, an ac voltage regulation control strategy for feedforward plus single loop feedback controls a first load bus voltage to track a first supply voltage in a dual voltage source converter flexible loop device, comprising:
the control object of the alternating current voltage stabilizing control of feedforward and single loop feedback is converted into a first load bus voltage by the output fundamental wave voltage of an alternating current valve side.
Step S150: 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 by utilizing a slope function switching principle, closing a change-over switch after the voltage of the first load bus is equal to the voltage of the second power supply, opening electrified switches on two sides of the flexible loop closing device of the double-voltage source type converter, and exiting the flexible loop closing device of the double-voltage source type converter to finish the stage of converting the first load power supply from the first power supply to the second power supply without power failure and negative charge transfer.
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 (U) sd(q)ref ＝U s2d(q) +K p (U s1d(q) -U s2d(q) )
Wherein K is p Representing the ramp coefficient, K p Slowly change from 1 to 0,U s1d(q) Representing the AC-DC voltage, U, of a first power supply s2d(q) Represents the AC-DC axis voltage of the second power supply, U sd(q)ref And the alternating-direct axis component representing the first load voltage adjustment reference value is finally converted into a three-phase voltage value through d-q inverse transformation.
As shown in fig. 4, in the 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 the ring closing process, the live switches K2 and K3 are all live switches, and the K6 is a ring closing switch, and the specific ring closing and load transferring processes are as follows:
first, the charging switches K2 and K3 are closed to charge the voltage source type converters at two sides. The first voltage source type converter and the second voltage source type converter both adopt a rectification control strategy, as shown in fig. 4, and before ring closing, the first voltage source type converter and the second voltage source type converter are both equivalent to a rectifier and are used for outputting a stable direct current voltage on a direct current side, and when the voltage values output from two sides are equal, the ring closing condition is met, and the ring closing operation is carried out. The control strategies of rectifiers are comparatively large, and the control strategies are different from each otherIn the formula, a double closed-loop control structure formed by the most mature current inner loop feedback and the voltage outer loop feedback is selected. Due to coupling voltage ωLi in two-phase rotation coordinate system sd 、ωLi sq Grid voltage u sd 、u sq The influence on d and q axis currents cannot be independently controlled by only negative feedback decoupling control, so that a feedforward decoupling control strategy is finally adopted to solve the problems.
The voltage outer ring takes the voltage value preset and output by the direct current side as a direct current voltage reference value u dcref The voltage actually output on the DC side is u dc Will u dcref And u is equal to dc After the difference is made, the output current i is controlled by PI (proportional integral ) dref As active reference of the current inner loop, reference current reactive component i qref =0. Three-phase current i at current inner loop sampling power supply side sa 、i sb 、i sc Transformed into d-q coordinate system under-crossing direct axis current component i through coordinate transformation sd 、i sq With reference current i dref 、i qref Obtaining a voltage reference vector value u by inner loop control dref And u qref The inner loop control takes into account the coupling voltage ωLi sd 、ωLi sq Grid voltage u sd 、u sq The control principle formula of the influence on d and q axis currents is as follows:
wherein K is iP 、K iI Is the adjustment parameter of PI control.
And (3) reversely transforming d-q coordinates to obtain three-phase signal waves of the voltage reference value, controlling the output three-phase signal waves to be consistent with the three-phase power supply voltage phase by using a PLL (Phase Locked Loop) and comparing the output three-phase signal waves with high-frequency carrier waves respectively, further controlling the working condition of a switching tube, and finally achieving the expected control effect.
As shown in fig. 3, the dc side bus voltage u across the closed loop switch K6 is regulated 1dc And u 1dc Let u 1dc And u 1dc And the two parts are equal to each other, so that the ring closing is realized. After the loop closing is completed, the control strategy of the second voltage source type converter is changed from controlling the busbar voltage at the direct current side to controlling the output fundamental wave voltage u at the alternating current valve side pwm Control is made such that u pwm The first load switch K1 is disconnected after the output current of the alternating current side of the flexible loop closing device of the double-voltage source type converter is ensured to be zero by being equal to the first power supply voltage, the first power supply is stopped from supplying power, and the first load bus voltage U is influenced by the voltage drop of the alternating current inductor L1 The voltage feedback quantity is reduced to output the fundamental wave voltage u from the AC side pwm Switching to the first load bus voltage U L1 And then control it to track the first power supply voltage U s1 I.e. controlling the first load voltage to be equal to the first supply voltage U s1 After the first load bus voltage is recovered, controlling and regulating the first load bus voltage U L1 Tracking a second supply voltage U s2 I.e. controlling the first load voltage to be equal to the second supply voltage U s2 To the first load voltage and U S2 When the voltages are equal, the first load is turned into power supply by the second power supply, the change-over switch K5 is closed, the live switches K2 and K3 are opened, the ring closing device is withdrawn, and the first load is turned into power supply by the second power supply.
As shown in fig. 5, when the loop closing is completed, the first power supply is stopped, and then the control strategy of the second voltage source type converter needs to be changed to change the first load from the first power supply to the second power supply, so as to realize uninterrupted load transfer. Specifically, after loop closing, the control strategy of the second voltage source type converter is changed from the voltage of the direct current control bus to the alternating current control output voltage, and the control strategy is embodied as alternating current voltage stabilizing control of feedforward and single loop feedback, as shown in a first PART PART1 in 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, namely the first load is still supplied by the first power supply, so that the second voltage source type converter is switchedThe output current is zero, and the ac output fundamental voltage of the second voltage source converter needs to be controlled to be equal to the first power supply voltage. Fundamental wave voltage u output from AC side of converter pwma 、u pwmb 、u pwmc Is transformed into an alternating-direct axis component u through d-q coordinate transformation pwmd 、u pwmq At the same time u s1d 、u s1q For the AC-DC axis component after d-q coordinate transformation of the first power supply voltage, u s2d 、u s2q For the AC-DC axis component after the d-q coordinate transformation of the second power supply voltage, before the load is transferred, the output u of the voltage switching module is instructed sdref 、u sqref For the first power supply u s1d 、u s1q . Supply voltage value u sdref 、u sqref As a feed-forward voltage signal and through a controlled voltage u pwmd 、u pwmq After the difference is made, a tiny feedback regulating signal is obtained through PI control, and the power supply voltage u is obtained sdref 、u sqref And respectively differencing the feedback regulation signals, obtaining three-phase signal waves through d-q coordinate transformation, keeping the phase of the three-phase signal waves output by phase-locked control consistent with the phase of the three-phase power supply voltage, comparing the three-phase signal waves with a high-frequency carrier wave, further controlling the working condition of the switching tube, and finally achieving the desired control effect.
When the first load switch K1 is disconnected, the first power supply stops supplying power, the first load current is transferred to the flexible loop closing device of the double-voltage source type converter, and the fundamental wave voltage u of the PWM wave at the alternating current side is controlled pwma 、u pwmb 、u pwmc The first supply voltage is tracked and the presence of the ac inductance causes a drop in the voltage of the first load. In order to effectively solve the problem of voltage drop, the control is changed into the control of the first load voltage to track the first power voltage, i.e. the control of the first load voltage to be equal to the first power voltage, and the control is changed into the control as shown in the second PART2 in fig. 5, and the controlled voltage (feedback signal) is switched by the AC-DC axis component u of the PWM fundamental wave voltage pwmd 、u pwmq The ac-dc axis component u converted into the first load voltage L1d 、u L1q . After the first load voltage is recovered and stabilized, starting the transfer of the load to the second power supplyTo supply the first load, the feed-forward supply voltage reference u is then required sdref 、u sqref From a first supply voltage u s1d 、u s1q Smoothly switching to the second power supply voltage u by the command voltage switching module s2d 、u s2q . As shown in fig. 6, in order to ensure power supply continuity while meeting power quality requirements, the bus voltage is required to be smoothly switched in the process of switching from the first power supply to the second power supply, i.e., the first load voltage U L1 From and to a first supply voltage U s1 Smooth transition to the second supply voltage U s2 A ramp is used. The initial output value 1 of the ramp function is multiplied by the difference value of the first power supply and the second power supply voltage, the multiplied result is added with the second power supply voltage value, at the moment, the positive and negative second power supply voltage values counteract, and the obtained power supply voltage reference value u sd(q)ref Is the first power voltage value u s1d With the adjustment of the ramp function, the output value of the ramp function is gradually changed from 1 to 0, and the obtained power supply voltage reference value u sd(q)ref Also from the first supply voltage value u s1d(q) Smooth transition to the second supply voltage value u s2d(q) 。
As shown in fig. 5, in the switching process of the whole control strategy, the control parameters are not required to be reset, the overall structure of the controller is not changed, and the switching of the control command and the controlled voltage signal is only required, so that the control stability is good and the implementation is relatively simple.
As shown in figures 7-8, the voltage source converter at two ends of 0.1s (second) is used as a rectifier to start, and the DC bus voltage U is controlled dc Before 0.5s of the ring is closed, the voltage of the bus at the direct current side can reach a stable value quickly, and the current I at the direct current side dc Is always very small and almost zero. The 0.5s closed loop switch K6 shows that the voltage and the current of the direct current bus almost have no change, and the impact-free loop closing is basically realized. 1.2s main power supply stops supplying power, the first load current is transferred to the flexible loop closing device of the double-voltage source type converter, so that the current of the direct current bus is increased to some extent, but the voltage of the direct current bus is increased due to the disturbance of load transferThe voltage then slowly returns to steady again due to the regulation of the inverter control strategy. 1.4s to solve the problem of load voltage drop, change control strategy and improve load voltage, direct current bus voltage appears a little fluctuation, direct current bus current continues to increase. And 2s, load transfer is realized, the load voltage is smoothly transited from the first power supply to the second power supply for power supply, and the influence on the voltage and the current of the direct current bus is not great.
As shown in FIG. 10, the load transfer is started for 2 seconds, and the first load voltage U is 2 seconds before L1 Waveform and first power supply voltage U s1 At 2s, the first load voltage waveform begins to smooth to the second supply voltage waveform U s2 And the load power supply voltage is quickly moved to coincide with the waveform of the second power supply voltage, so that the smooth switching of the load power supply voltage is realized.
The embodiment of the application provides 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 no-impact loop closing stage, powering the double voltage source type converter by closing a live 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, adjusting 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 by using a rectifier principle and adopting a rectifying control strategy, and closing 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 when the direct current bus voltages at two sides of the direct current side loop closing switch are equal, wherein the no-impact loop closing stage is completed. 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 static synchronous compensator, can provide dynamic reactive compensation and stabilize the voltage of an alternating current bus; by adopting the turn-off device, even if a 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 regulated simultaneously; the harmonic level is relatively low; the current can flow bidirectionally, the polarity of the direct-current voltage can not be changed, and when the parallel type multi-terminal direct-current system is formed, the single-terminal power flow can be regulated in the forward direction and the reverse direction by changing the direction of the single-terminal current on the premise of keeping the voltage of the multi-terminal direct-current system constant; the occupied area is small. Compared with the loop closing at the alternating current side, the loop closing at the direct current side is realized only by controlling and adjusting the voltage values of the direct current sides of the converters at the two ends to be equal, so that the difficulty brought by the amplitude value or the phase deviation of the three-phase voltage to the loop closing operation is avoided, the control is realized simply, the protection action of a power distribution system caused by the overlarge loop closing impact current is avoided, and the influence on the safe and stable operation of the power distribution network is avoided. The control strategy of the second voltage source type converter in the double voltage source type converter flexible loop closing device is alternating current voltage stabilizing control of feedforward and single loop feedback, the alternating current voltage stabilizing control strategy of feedforward and single loop feedback controls the output fundamental wave voltage of an alternating current valve side to track the first power supply voltage, when the output fundamental wave voltage of the alternating current valve side is identical with the first power supply voltage in the double voltage source type converter flexible loop closing device, the output current of the alternating current side of the double voltage source type converter flexible loop closing device is zero, a switch of the first power supply in the double voltage source type converter flexible loop closing device is opened, the first power supply in the double voltage source type converter flexible loop closing device exits power supply, the voltage of a first load bus in the double voltage source type converter flexible loop closing device drops, the alternating current voltage stabilizing control strategy of feedforward and single loop feedback controls the voltage of the first load bus to track the first power supply voltage in the double voltage source type 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 slope function switching principle, the first load bus voltage is enabled to be equal to the second power supply voltage, the double voltage source type converter flexible loop closing device is opened, the double voltage loop closing device is closed, the power supply is completed, and the double power supply is not powered by the flexible loop closing device, and the power supply of the double voltage source type converter flexible loop closing device is closed, and the power supply is powered by the power supplied by the double voltage. The final loop closing device is realized by the change-over switch, so that the operation loss of the flexible loop closing device of the double-voltage source type converter can be reduced, the loop closing operation reliability is improved, the flexible loop closing device of the double-voltage source type converter is protected, the uninterrupted negative charge transfer stage is not required to be changed, the uninterrupted load transfer can be realized by only switching a control command and a controlled voltage signal, the control stability is good, and the power quality requirement can be met while the power supply continuity of the system is ensured.
Since the foregoing embodiments are all described in other modes by reference to the above, the same parts are provided between different embodiments, and the same and similar parts are provided between the embodiments in the present specification. And will not be described in detail herein.
It should be 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. Moreover, 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 statement "comprises" or "comprising" a … … "does not exclude that an additional identical element is present in a circuit structure, article or apparatus that comprises the element.
Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure of the application herein. This application is intended to cover any variations, uses, or adaptations of the application 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 application 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 embodiments of the present application described above do not limit the scope of the present application.
Claims (6)
1. A direct-current side loop closing control method based on a flexible loop closing device of a double-voltage source type converter 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-closed loop control structure with feedforward decoupling;
the method comprises the steps of utilizing a rectifier principle, adopting a rectifying control strategy to regulate the voltages of direct current buses at two sides of a direct current side loop closing switch of a flexible loop closing device of the double-voltage source type converter, and closing the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter when the voltages of the direct current buses at two sides of the direct current side loop closing switch of the flexible loop closing device of the double-voltage source type converter are equal, so that the loop closing stage without impact is completed;
the control strategy of the second voltage source type converter in the double voltage source type converter flexible loop closing device is alternating current voltage stabilizing control by utilizing feedforward and single loop feedback, the alternating current voltage stabilizing control strategy of the feedforward and the single loop feedback controls the output fundamental wave voltage of an alternating current valve side to track the first power supply voltage, and when the output fundamental wave voltage of the alternating current valve side is the same as the first power supply voltage in the double voltage source type converter flexible loop closing device, the output current of the alternating current side of the double voltage source type converter flexible loop closing device is zero;
switching off a switch of a first power supply in the flexible loop closing device of the double-voltage source type converter, wherein the first power supply in the flexible loop closing device of the double-voltage source type converter exits from power supply, the voltage of a first load bus in the flexible loop closing device of the double-voltage source type converter can drop, and an alternating current voltage stabilizing control strategy of feedforward and single-loop feedback is used for controlling the voltage of the first load bus to track the voltage of the first power supply in the flexible loop closing device of the double-voltage source type converter;
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 by using a slope function switching principle, closing a change-over switch after the voltage of the first load bus is equal to the voltage of the second power supply, opening electrified switches on two sides of the flexible loop closing device of the double-voltage source type converter, and exiting the flexible loop closing device of the double-voltage source type converter to operate so as to complete the conversion of the first load power supply from the first power supply to the second power supply without power failure and negative charge transfer.
2. The direct current side loop closing control method based on the flexible loop closing device of the dual voltage source converter according to claim 1, wherein the controlling the first load bus voltage to track the second power voltage by using a ramp function switching principle further comprises:
the expression formula of the ramp function switching principle is as follows: u (U) sd(q)ref = U s2d(q) + K p （U s1d(q) - U s2d(q) ）
Wherein K is p Representing the ramp coefficient, K p Slowly change from 1 to 0,U s1d(q） Representing the AC-DC voltage, U, of a first power supply s2d(q） Represents the AC-DC axis voltage of the second power supply, U sd(q)ref And the alternating-direct axis component representing the first load voltage adjustment reference value is finally converted into a three-phase voltage value through d-q inverse transformation.
3. The method for controlling the direct current side loop closing based on the flexible loop closing device of the dual-voltage source converter according to claim 1, wherein the control strategy of the second voltage source converter in the flexible loop closing device of the dual-voltage source converter is alternating current voltage stabilizing control by using a feedforward and single loop feedback, and the method further comprises the following steps:
the control strategy of the second voltage source type converter in the flexible loop closing device of the double voltage source type converter is changed from rectification control to alternating current voltage stabilizing control of feedforward and single loop feedback.
4. The direct current side loop closing control method based on the double voltage source converter flexible loop closing device according to claim 1, wherein the alternating current voltage stabilizing control strategy of feedforward and single loop feedback controls an alternating current valve side output fundamental wave voltage to track the first power supply voltage, further comprising:
the control object of the alternating current voltage stabilization control of feedforward and single loop feedback is that the direct current bus voltage at two sides of a direct current side loop closing switch of a flexible loop closing device of a double-voltage source type converter is converted into the alternating current valve side output fundamental wave voltage.
5. The method for controlling the direct current side loop closing of the flexible loop closing device of the double-voltage source type converter according to claim 1, wherein the alternating current voltage stabilizing control strategy of feedforward and single loop feedback is used for controlling the first load bus voltage to track the first power voltage in the flexible loop closing device of the double-voltage source type converter, and the method comprises the following steps:
the control object of the alternating current voltage stabilizing control of feedforward and single loop feedback is converted into a first load bus voltage by the output fundamental wave voltage of an alternating current valve side.
6. The method for controlling the direct current side loop closing of the flexible loop closing device based on the dual voltage source converter according to claim 1, wherein before the step of entering the no-impact loop closing stage and charging the dual voltage source converter by closing the charging switch to start the flexible loop closing device of the dual voltage source converter adopting the dual closed loop control structure with feedforward decoupling, the method further comprises:
the voltage source type converters of the flexible loop closing device of the double voltage source type converter adopt three-phase two-level voltage source converters.
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