CN111786396B - Phase-change failure suppression method for high-voltage direct-current transmission system based on energy storage type chained STATCOM - Google Patents
Phase-change failure suppression method for high-voltage direct-current transmission system based on energy storage type chained STATCOM Download PDFInfo
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
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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
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/10—Flexible AC transmission systems [FACTS]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The invention discloses a method for inhibiting commutation failure of a high-voltage direct-current power transmission system based on an energy storage type chained STATCOM, wherein the power transmission system comprises a power transmission end power grid; the transmitting end power grid is connected with the receiving end power grid through a direct current transmission line; the energy storage type chained STATCOM is connected in parallel to an alternating current bus of the receiving-end power grid. According to the invention, an energy storage technology is combined with a reactive compensation technology by adopting an energy storage type chained STATCOM device, so that an effective supporting effect can be provided for the voltage of a receiving bus of a high-voltage direct-current power transmission system when the receiving alternating-current power grid fails, the commutation failure probability of the HVDC system is reduced, and the running stability of the alternating-current direct-current system is improved; and the damping of the interconnected system can be obviously enhanced, the power oscillation is restrained, and the power recovery of the direct current transmission system after the fault is promoted.
Description
Technical Field
The invention relates to a direct current transmission system, in particular to a high-voltage direct current transmission system commutation failure inhibition method based on an energy storage type chained STATCOM.
Background
Commutation failure, which is the most typical system fault of a direct current transmission system (HVDC), is one of the major difficulties faced by the development of a high-voltage direct current transmission system. Short circuit faults of the direct current falling point near-area receiving end alternating current system can cause voltage drop of a bus of the high-voltage direct current inversion station, and if the faults are not cleared in time, commutation failure of the direct current transmission system can be caused. In addition, once the high-voltage direct current system fails to cause locking, the instant shortage of the power supply of the power grid of the receiving end is caused, the power balance and normal power supply of the receiving end system are greatly influenced, and the frequency instability of the alternating current system of the receiving end is easily caused.
Currently, in high voltage ac transmission systems, synchronous regulators (SC), static Var Compensators (SVC) and advanced static var generators (STATCOM) are three main dynamic reactive compensation devices. The SC has strong short-time overload capacity and a certain inertial supporting function, but belongs to rotary machinery, and has complex operation and maintenance and high investment and operation and maintenance cost, which limits the application of the synchronous speed regulator in the HVDC system. SVC output reactive power is adjustable, and the loss is little, the maintenance is simple, the reliability is high, obtains a large amount of applications in the electric wire netting, but it has that dynamic response speed is relatively slow, output reactive power is influenced by electric wire netting voltage fluctuation greatly, easily produces a large amount of harmonic pollution etc. defect, leads to SVC to use less in HVDC system commutation failure suppression field. The STATCOM has the advantages of high response speed, wide operation range, multiple functions, small device size, easiness in maintenance, capability of rapidly and effectively improving the voltage quality of an access point, and is an ideal reactive compensation device for inhibiting commutation failure in a high-voltage direct-current transmission system, but the reactive compensation quality of the STATCOM is greatly influenced by a direct-current side capacitance value and capacitance voltage, and the reactive output capacity is greatly influenced by power grid voltage fluctuation.
In recent years, with the improvement of the performance and the reduction of the cost of the energy storage battery, the energy storage battery has been widely applied due to the characteristics of high energy density, small self-discharge, less pollution and long cycle life. The battery energy storage is gradually combined with a power electronic technology and is applied to the improvement of the electric energy quality and the stability of a power grid, wherein a novel FACTS (flexible alternating current transmission system) device combining the energy storage technology with a reactive compensation technology, namely an energy storage type STATCOM, is a typical application of the battery energy storage.
When the existing chained STATCOM structure is applied to a high-voltage direct-current transmission system, the problems that excessive reactive power output causes severe double frequency fluctuation of the capacitance voltage of the submodule, the voltage equalizing control strategy of each level of unit capacitance is complex, and the supporting effect of only compensating the voltage of a reactive power grid is limited exist.
Disclosure of Invention
The invention aims to solve the technical problems of providing a high-voltage direct-current power transmission system commutation failure suppression method based on an energy storage type chained STATCOM (static synchronous compensator) aiming at the defects of the prior art, so that the probability of the HVDC system commutation failure is reduced, and the running stability of an alternating-current and direct-current system is improved.
In order to solve the technical problems, the invention adopts the following technical scheme: the high-voltage direct-current transmission system based on the energy storage type chained STATCOM comprises a transmitting-end power grid; the transmitting end power grid is connected with the receiving end power grid through a direct current transmission line; the energy storage type chained STATCOM is connected in parallel to an alternating current bus of the receiving-end power grid.
The energy storage type chained STATCOM is used in a high-voltage direct-current transmission system, the problems that the voltage doubling fluctuation of the STATCOM submodule capacitor is serious, the voltage equalizing control strategy of each cascade unit capacitor is complex and the supporting effect of only compensating reactive power grid voltage is limited due to the existence of excessive reactive power output can be avoided, and the energy storage chained STATCOM has the advantages of maintaining the steady voltage of a bus, inhibiting the voltage sag level, damping the power oscillation and inhibiting the phase jump.
The three phases of the energy storage type chained STATCOM adopt a star connection method; each phase comprises a plurality of cascaded sub-modules; the submodule comprises an energy storage unit; the energy storage unit is connected with the DC/DC converter, the direct current capacitor and the direct current side of the H-bridge single-phase AC/DC converter in parallel in sequence. Each phase of the energy storage type chained STATCOM is connected in parallel to an alternating current bus of the receiving end power grid through a reactor, an equivalent loss resistor and an alternating current transformer in sequence. The energy storage type chained STATCOM adopts a chained structure, so that a large number of storage batteries can be prevented from being concentrated in series-parallel connection, the energy storage unit is connected with the direct current side of the H-bridge single-phase AC/DC converter in parallel after performing voltage-current closed-loop control through the DC/DC converter, the voltage stability of the storage batteries and the reliability of the system can be effectively improved, and the energy storage chained STATCOM is easy to expand to high voltage and high power, so that the energy storage unit is applied to the field of high-voltage direct current transmission commutation failure inhibition.
The invention also provides a commutation failure suppression method of the HVDC system, which comprises the following steps:
1) At the starting point of each sampling period, outputting three-phase current i to energy storage type chained STATCOM sx Three-phase voltage v of secondary side of AC transformer sx Sampling; x=a, b, c;
2) Using ac power transformationThree-phase voltage v of secondary side of pressure device sx Calculating a power grid voltage phase theta and a power grid voltage angular frequency omega;
3) By means of three-phase current i sx Three-phase voltage v of secondary side of AC transformer sx Acquiring current i under dq coordinate system by power grid voltage phase theta and voltage angular frequency omega sy Voltage v sy ；y＝d,q；
4) After the grid voltage angular frequency omega is subjected to a first-order low-pass filtering link, the grid voltage angular frequency omega is matched with the rated grid voltage angular frequency omega * Making difference, and then obtaining d-axis active current instruction through adjustment of a proportional controllerAccording to the control mode of the energy storage type chained STATCOM, a q-axis reactive current instruction is determined>
5) Using the current i in the dq coordinate system after the first order low pass filtering sy Voltage v sy D-axis active current commandQ-axis reactive current command->Calculating to obtain output modulation voltage v under dq coordinate system my And modulating said output modulation voltage v my Transforming to the abc coordinate system to obtain the output modulation voltage v in the abc coordinate system mx ；
6) Modulating the output voltage v in abc coordinate system mx And modulating by a monopole frequency multiplication CPS-SPWM (carrier phase shift sine wave pulse width modulation technology) to obtain an H-bridge single-phase AC/DC converter driving signal in the energy storage type chained STATCOM submodule.
The reactive compensation and energy storage technology are combined, namely, in the step 4) and the step 5), a reactive current control loop exists, and an active current control loop based on frequency deviation control exists. When the receiving end alternating current power grid fails, the method not only can provide an effective supporting function for the receiving end busbar voltage of the high-voltage direct current power transmission system, but also can reduce the commutation failure probability of the HVDC system and improve the running stability of the alternating current direct current system; and the damping of the interconnected system can be obviously enhanced, the power oscillation is restrained, and the power recovery of the direct current transmission system after the fault is promoted.
In step 4), a q-axis reactive current command is determinedThe specific implementation process of (1) comprises the following steps: if the energy storage type chained STATCOM is in a constant reactive power control mode, a reactive power instruction value Q * Multiplying by a coefficient->Get q-axis reactive current command +.>v sd The d-axis voltage of the secondary side of the alternating current transformer; if the energy storage type chained STATCOM is in a steady-state voltage regulation control mode, the secondary side voltage peak value v of the alternating current transformer s After the first-order low-pass filtering link, the voltage is equal to rated alternating voltage +.>Making difference, and then regulating by a proportional controller to obtain a q-axis reactive current instruction +.>If the energy storage type chained STATCOM is in the transient voltage control mode, the turn-off angle signal gamma in the power transmission system is subjected to a first-order low-pass filtering link and then is combined with a rated turn-off angle instruction gamma * The difference is made, and the difference is added into an alternating voltage difference value of a steady-state voltage regulation control mode after being regulated by a proportional controller, and then q-axis reactive current instruction +.>
And if the energy storage type chained STATCOM is in the locking control mode, locking power device driving signals of all the energy storage type chained STATCOM sub-modules. In the transient voltage control mode, more reactive compensation can be provided in a short time by adding an off angle coordination control structure into the energy storage type chained STATCOM alternating voltage outer ring, and commutation failure can be well restrained.
In order to judge the fault level of the receiving end by detecting the instantaneous drop amplitude and drop rate of the voltage of the alternating current bus of the receiving end, the corresponding control strategy is switched according to the severity of the fault, and the control mode of the energy storage type chained STATCOM comprises the following steps: a steady-state voltage regulation control mode, a steady-state constant reactive control mode, a transient voltage control mode and a lockout control mode; the four mode switching logics include:
1) The voltage of the alternating voltage is higher than 0.9p.u and lower than 1.1p.u., the voltage change rate of the power transmission system is not higher than a set threshold value (set as 2000) and the energy storage type chain STATCOM steady-state constant reactive power control mode action is judged if a constant reactive power control command signal is received; p.u. is per unit value;
2) The voltage of the alternating voltage is higher than 0.9p.u and lower than 1.1p.u., the voltage change rate of the power transmission system is not higher than a set threshold value (set as 2000) and the energy storage type chain type STATCOM steady-state voltage regulating mode action is judged if a steady-state voltage regulating control command signal is received;
3) The voltage of the alternating current is reduced to 0.9p.u. and is larger than 0.4p.u., or the voltage change rate of the power transmission system is higher than a threshold value (the invention is set to 2000), and the operation of the energy storage type chained STATCOM transient voltage control mode is judged;
4) And (3) judging that the energy storage type chained STATCOM locking control mode acts when the alternating current is lower than 0.4p.u.
To further suppress commutation failure, the method of the present invention further includes a DC/DC converter control section; the DC/DC converter control section includes:
1) At the starting point of each sampling period, the DC capacitor voltage u of the energy storage type chained STATCOM submodule dc Output current I of energy storage unit o Sampling;
2) Rated direct current of the energy storage type chained STATCOM submoduleVoltage valueSubtracting the submodule direct-current capacitance voltage measurement u dc The difference value is regulated by a proportional-integral controller to generate a current instruction value; preferably, the value current command is limited to a maximum charge/discharge current ± I limit Inside;
3) Will instruct the current value I ref Subtracting the energy storage unit output current measurement I o After being regulated by a proportional-integral controller, the DC/DC converter driving signal in the energy storage type chained STATCOM submodule is obtained through PWM modulation;
4) If the state of charge SOC of the energy storage unit is smaller than SOC min And the current is the discharging direction of the energy storage battery, and sends out a DC/DC converter locking signal to make I ref Setting 0, and discharging is not performed any more; if the state of charge SOC of the energy storage battery is smaller than SOC max When the current is in the charging direction of the energy storage battery, a DC/DC converter locking signal is sent out to send I ref Setting 0, and not charging; wherein SOC is min ＝20％；SOC max ＝80％。
As an inventive concept, the invention also provides a commutation failure suppression system of the high-voltage direct-current transmission system of the energy storage type chained STATCOM, which comprises an AC/DC converter control module; the AC/DC converter control module is programmed or configured to perform the steps of the AC/DC converter control method of the present invention.
As an inventive concept, the invention also provides a commutation failure suppression system of the high-voltage direct-current transmission system of the energy storage type chained STATCOM, which comprises a DC/DC converter control module; the DC/DC converter control module is programmed or configured to perform the steps of:
1) At the starting point of each sampling period, the DC capacitor voltage u of the energy storage type chained STATCOM submodule dc Output current I of energy storage unit o Sampling;
2) Rated direct-current voltage value of the energy-storage type chained STATCOM submoduleSubtracting the submodule direct-current capacitance voltage measurement u dc The difference value is regulated by a proportional-integral controller to generate a current instruction value; preferably, the value current command is limited to a maximum charge/discharge current ± I limit Inside;
3) Will instruct the current value I ref Subtracting the energy storage unit output current measurement I o After being regulated by a proportional-integral controller, the DC/DC converter driving signal in the energy storage type chained STATCOM submodule is obtained through PWM modulation;
4) If the state of charge SOC of the energy storage unit is smaller than SOC min And the current is the discharging direction of the energy storage battery, and sends out a DC/DC converter locking signal to make I ref Setting 0, and discharging is not performed any more; if the state of charge SOC of the energy storage battery is smaller than SOC max When the current is in the charging direction of the energy storage battery, a DC/DC converter locking signal is sent out to send I ref Setting 0, and not charging; wherein SOC is min ＝20％；SOC max ＝80％。
Compared with the prior art, the invention has the following beneficial effects: according to the invention, an energy storage technology is combined with a reactive compensation technology by adopting an energy storage type chained STATCOM device, so that an effective supporting effect can be provided for the voltage of a receiving bus of a high-voltage direct-current power transmission system when the receiving alternating-current power grid fails, the commutation failure probability of the HVDC system is reduced, and the running stability of the alternating-current direct-current system is improved; and the damping of the interconnected system can be obviously enhanced, the power oscillation is restrained, and the power recovery of the direct current transmission system after the fault is promoted. In the transient voltage control mode, more reactive compensation can be provided in a short time by adding an off angle coordination control structure into the energy storage type chained STATCOM alternating voltage outer ring, and commutation failure can be well restrained.
Drawings
Fig. 1 is a block diagram of a hvdc transmission system including an energy storage type chained STATCOM according to an embodiment of the present invention;
FIG. 2 is a main circuit block diagram of an energy storage chained STATCOM according to an embodiment of the invention;
fig. 3 is a block diagram of a control system for suppressing commutation failure of a hvdc transmission based on an energy storage type chained STATCOM according to an embodiment of the present invention;
fig. 4 is a power coordination control mode switching logic diagram of an energy storage chained STATCOM according to an embodiment of the present invention.
Detailed Description
Referring to fig. 1, in an embodiment of the present invention, a structure diagram of a high-voltage direct-current power transmission system including an energy storage type chained STATCOM is connected to a receiving-end ac bus of the high-voltage direct-current power transmission system in a boosting and parallel manner through an ac transformer after passing through a connection reactor and an equivalent loss resistor.
Referring to fig. 2, a main circuit structure diagram of an energy storage type chained STATCOM according to an embodiment of the present invention includes an energy storage unit, a DC/DC converter, a DC capacitor, an H-bridge single-phase AC/DC converter, a connection reactor, an equivalent loss resistor, and an AC transformer; the energy storage unit is sequentially connected with the DC/DC converter, the direct-current capacitor and the direct-current side of the H-bridge single-phase AC/DC converter in parallel to form an energy storage chain type STATCOM submodule; the energy storage type chained STATCOM submodules form a cascading type multi-level inverter through multi-module cascading; the three phases of the energy storage type chained STATCOM are connected in a star connection mode, and after the three phases are connected with the reactor and the equivalent loss resistor, the three phases are connected in parallel through boosting of an alternating current transformer to be connected into an alternating current bus.
Referring to fig. 3, in the high-voltage direct-current transmission commutation failure suppression control block diagram based on an energy storage chain type STATCOM according to an embodiment of the present invention, an AC/DC control module part mainly comprises a phase-locked loop module, an active adjustment module based on frequency deviation, a constant reactive control module, a steady-state voltage adjustment module, a transient voltage control module and a current inner loop decoupling control module, and a DC/DC control module part mainly comprises a voltage and current double closed loop control and an energy storage unit SOC judgment module, and the specific control method comprises:
AC/DC control section:
1) At the starting point of each sampling period, outputting three-phase current i to the energy storage type chained STATCOM sx (x=a, b, c), ac transformer secondary side three-phase voltage v sx (x=a, b, c) sampling；
2) Sampling the secondary side three-phase voltage v of the alternating current transformer obtained in the step 1) sx (x=a, b, c) is sent to a PLL module to obtain a grid voltage phase θ and a voltage angular frequency ω, where the conversion formula of the abc/αβ module is:
3) Outputting three-phase current i by the energy storage type chained STATCOM obtained by sampling in the step 1) sx (x=a, b, c), ac transformer secondary side three-phase voltage v sx (x=a, b, c), and the grid voltage phase theta obtained in the step 2) is sent to an abc/dq conversion module to obtain current i under the dq coordinate system sy (y=d, q) and voltage v sy (y=d, q), wherein the abc/dq block conversion formula is as follows:
4) After the grid voltage angular frequency omega obtained in the step 2) is subjected to a first-order low-pass filtering link, the grid voltage angular frequency omega is matched with the rated grid voltage angular frequency omega * Making difference, and then obtaining d-axis active current instruction through adjustment of a proportional controller
5) If the energy storage type chained STATCOM is in a constant reactive power control mode, a reactive power instruction value Q * Multiplying by a coefficientGet q-axis reactive current command +.>Wherein v is sd The d-axis voltage of the secondary side of the alternating current transformer obtained in the step 3);
6) If the energy storage type chained STATCOM is in a steady-state voltage regulation control mode, the secondary side voltage peak value v of the alternating current transformer s After the first-order low-pass filtering link, the voltage is equal to rated alternating voltageMaking difference, and then regulating by a proportional controller to obtain a q-axis reactive current instruction +.>Wherein v is s The calculation formula is as follows:
wherein v is sα 、v sβ For the secondary side three-phase voltage v of the AC transformer in step 2) sx (x=a, b, c) into the abc/αβ module;
7) If the energy storage type chained STATCOM is in the transient voltage control mode, the turn-off angle signal gamma in the high-voltage direct-current transmission system is subjected to a first-order low-pass filtering link and then is combined with a rated turn-off angle instruction gamma * Making difference, adding the difference into the alternating voltage difference of the steady-state regulation control mode in the step 6) after the adjustment of the proportional controller, and obtaining a q-axis reactive current instruction after the adjustment of the proportional controller
8) Current i in dq coordinate system obtained in step 3) sy (y=d, q) and voltage v sy (y=d, q) after first order low pass filtering, and the d-axis active current command obtained in step 4)And q-axis reactive current instruction ++obtained in step 5) or step 6) or step 7)>Sending the modulation voltage into a current inner loop decoupling control module to obtain an output modulation voltage v under a dq coordinate system my (y=d, q), the specific calculation formula is as follows:
wherein L is the inductance value of the connecting reactor, omega is the PLL output angular frequency, k ipd 、k iid Respectively the proportional and integral coefficients, k of the d-axis PI controller ipq 、k iiq Proportional and integral coefficients of the q-axis PI controller respectively;
9) Modulating the modulation voltage v in the dq coordinate system obtained in the step 8) my (y=d, q) is sent to a dq/abc conversion module to obtain an output modulation voltage v in an abc coordinate system mx (x=a, b, c), wherein the dq/abc module conversion formula is as follows:
10 (ii) modulating the output modulation voltage v in the abc coordinate system obtained in step 9) mx And (x=a, b, c) is subjected to unipolar frequency multiplication CPS-SPWM modulation to obtain an H-bridge single-phase AC/DC converter driving signal in the energy storage type chained STATCOM submodule. The triangular carrier signals of the AC/DC inverter bridge modules in the same phase are staggered in sequence according to a cascading sequence to form pi/N angles, wherein N is the number of chain links;
11 If the energy storage type chained STATCOM is in the locking control mode, locking IGBT driving signals of all the energy storage type chained STATCOM submodules.
DC/DC control section:
1) At the starting point of each sampling period, the DC capacitor voltage u of the energy storage type chained STATCOM submodule dc Output current I of energy storage unit o Sampling;
2) Rated direct-current voltage value of the energy-storage type chained STATCOM submoduleSubtracting the sub-module DC capacitance voltage measurement u sampled in step 12) dc Then, the current command value is generated by the regulation of the proportional-integral controller, and the current command value is limited to the maximum charge and discharge current + -I limit Inside;
3) Current command I generated in step 2) ref Subtracting the energy storage unit output current measurement I o After being regulated by a proportional-integral controller, the DC/DC converter driving signal in the energy storage type chained STATCOM submodule is obtained through PWM modulation;
4) If the state of charge SOC of the energy storage unit is smaller than SOC min =20%, and when the current is in the discharge direction of the energy storage battery, a DC/DC converter locking signal is sent out to make I ref Setting to 0, and discharging is not performed any more; if the state of charge SOC of the energy storage battery is smaller than SOC max When the current is 80%, and the current is in the charging direction of the energy storage battery, a DC/DC converter locking signal is sent out to enable I ref Set to 0 and no longer charge.
Referring to fig. 4, in an embodiment of the present invention, a power coordination control mode switching logic diagram of an energy storage type chained STATCOM is divided into four control modes: the method comprises a steady-state voltage regulation control mode, a steady-state constant reactive power control mode, a transient voltage control mode and a locking control mode, wherein the receiving end fault level is judged by detecting the instantaneous drop amplitude and drop rate of the voltage of the receiving end alternating current bus, and corresponding control strategies are switched according to the fault severity, and the switching logic of each mode is as follows:
1) The voltage of the alternating voltage is higher than 0.9p.u and lower than 1.1p.u., the system voltage change rate is not higher than a set threshold value (set as 2000) and the energy storage type chain type STATCOM constant reactive power control mode action is judged if a constant reactive power control command signal is received; p.u. is per unit value;
2) The voltage of the alternating voltage is higher than 0.9p.u and lower than 1.1p.u., the system voltage change rate is not higher than a set threshold value (set as 2000) and if a steady-state voltage regulation control command signal is received, the steady-state voltage regulation mode action of the energy storage type chain type STATCOM is judged;
3) The alternating voltage is reduced to 0.9p.u. and is larger than 0.4p.u., or the voltage change rate is higher than a threshold value (set as 2000) and the transient voltage control mode action of the energy storage type chained STATCOM is judged;
4) And (3) judging that the energy storage type chained STATCOM locking control mode acts when the alternating current is lower than 0.4p.u. In addition, the energy storage type chained STATCOM can be manually locked through manual intervention.
The lockout control mode is higher in priority than the transient voltage control mode, and the transient voltage control mode is higher in priority than the steady-state mode.
Claims (9)
1. A commutation failure suppression method of a high-voltage direct-current transmission system comprises a transmitting end power grid; the transmitting end power grid is connected with the receiving end power grid through a direct current transmission line; the energy storage type chained STATCOM is connected in parallel to an alternating current bus of the receiving-end power grid; the method is characterized by comprising the following steps of:
1) At the starting point of each sampling period, outputting three-phase current i to energy storage type chained STATCOM sx Three-phase voltage v of secondary side of AC transformer sx Sampling; x=a, b, c;
2) By means of the three-phase voltage v of the secondary side of an ac transformer sx Calculating a power grid voltage phase theta and a power grid voltage angular frequency omega;
3) By means of three-phase current i sx Three-phase voltage v of secondary side of AC transformer sx Acquiring current i under dq coordinate system by power grid voltage phase theta and voltage angular frequency omega sy Voltage v sy ；y＝d,q；
4) After the grid voltage angular frequency omega is subjected to a first-order low-pass filtering link, the grid voltage angular frequency omega is matched with the rated grid voltage angular frequency omega * Making difference, and then obtaining d-axis active current instruction through adjustment of a proportional controllerAccording to the control mode of the energy storage type chained STATCOM, a q-axis reactive current instruction is determined>
5) Using the current i in the dq coordinate system after the first order low pass filtering sy Voltage v sy D-axis active current commandQ-axis reactive current command->Calculating to obtain output modulation voltage v under dq coordinate system my And modulating said output modulation voltage v my Transforming to the abc coordinate system to obtain the output modulation voltage v in the abc coordinate system mx ；
6) Modulating the output voltage v in abc coordinate system mx And obtaining an H-bridge single-phase AC/DC converter driving signal in the energy storage type chained STATCOM submodule through unipolar frequency multiplication CPS-SPWM modulation.
2. The method of claim 1, wherein in step 4), a q-axis reactive current command is determinedThe specific implementation process of (1) comprises the following steps: if the energy storage type chained STATCOM is in a constant reactive power control mode, a reactive power instruction value Q * Multiplying by a coefficient->Get q-axis reactive current command +.>v sd The d-axis voltage of the secondary side of the alternating current transformer; if the energy storage type chained STATCOM is in a steady-state voltage regulation control mode, the secondary side voltage peak value v of the alternating current transformer s After the first-order low-pass filtering link, the voltage is equal to rated alternating voltage +.>Making difference, and then regulating by a proportional controller to obtain a q-axis reactive current instruction +.>If the energy storage type chained STATCOM is in the transient voltage control mode, the turn-off angle signal gamma in the power transmission system is subjected to a first-order low-pass filtering link and then is combined with a rated turn-off angle instruction gamma * The difference is made,
the q-axis reactive current instruction is obtained by adjusting the voltage of the power supply through the proportional controller and then adding the voltage to the alternating voltage difference value of the steady-state voltage-adjusting control mode after the adjustment of the proportional controller
3. Method according to claim 1 or 2, characterized in that if the energy storage chain STATCOM is in a latch control mode, the power device drive signals of all energy storage chain STATCOM sub-modules are latched.
4. A method according to claim 1 or 2, characterized in that the control mode of the energy storing chain STATCOM comprises: a steady-state voltage regulation control mode, a steady-state constant reactive control mode, a transient voltage control mode and a lockout control mode; the four mode switching logics include:
1) The voltage of the alternating voltage is higher than 0.9p.u. and lower than 1.1p.u., the voltage change rate of the power transmission system is not higher than a set threshold value, and if a constant reactive power control command signal is received, the energy storage type chained STATCOM steady-state constant reactive power control mode action is judged; p.u. is per unit value;
2) The voltage of the alternating voltage is higher than 0.9p.u and lower than 1.1p.u., the voltage change rate of the power transmission system is not higher than a set threshold value, and if a steady-state voltage regulation control command signal is received, the steady-state voltage regulation mode action of the energy storage type chained STATCOM is judged;
3) The voltage of the alternating current is reduced to 0.9p.u. and is larger than 0.4p.u., or the voltage change rate of the power transmission system is higher than a threshold value, and the operation of the energy storage type chained STATCOM transient voltage control mode is judged;
4) And (3) judging that the energy storage type chained STATCOM locking control mode acts when the alternating current is lower than 0.4p.u.
5. The method according to claim 1 or 2, further comprising a DC/DC converter control section; the DC/DC converter control section includes:
1) At the starting point of each sampling period, the DC capacitor voltage u of the energy storage type chained STATCOM submodule dc Output current I of energy storage unit o Sampling;
2) Rated direct-current voltage value of the energy-storage type chained STATCOM submoduleSubtracting the submodule direct-current capacitance voltage measurement u dc The difference value is regulated by a proportional-integral controller to generate a current instruction value;
3) Will instruct the current value I ref Subtracting the energy storage unit output current measurement I o After being regulated by a proportional-integral controller, the DC/DC converter driving signal in the energy storage type chained STATCOM submodule is obtained through PWM modulation;
4) If the state of charge SOC of the energy storage unit is smaller than SOC min And the current is the discharging direction of the energy storage battery, and sends out a DC/DC converter locking signal to make I ref Setting 0, and discharging is not performed any more; if the state of charge SOC of the energy storage battery is smaller than SOC max In the time-course of which the first and second contact surfaces,
and at this time, the current is in the charging direction of the energy storage battery, and then a DC/DC converter locking signal is sent out to make I ref Setting 0, and not charging; wherein SOC is min ＝20％；SOC max ＝80％。
6. The method according to claim 1, wherein the current command value is limited to a maximum charge and discharge current ± I limit Inside.
7. The method according to claim 1, wherein the energy storage type chained STATCOM is connected between three phases by star connection; each phase comprises a plurality of cascaded sub-modules; the submodule comprises an energy storage unit; the energy storage unit is connected with the DC/DC converter, the direct current capacitor and the direct current side of the H-bridge single-phase AC/DC converter in parallel in sequence.
8. The method according to claim 1, wherein each phase of the energy storage type chained STATCOM is connected in parallel to an ac bus of the receiving power grid through a reactor, an equivalent loss resistor and an ac transformer in sequence.
9. The commutation failure suppression system of the high-voltage direct-current transmission system based on the energy storage type chained STATCOM is characterized by comprising an AC/DC converter control module; the AC/DC converter control module is configured for performing the steps of the method of one of claims 1 to 8.
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