CN113595404A - Back-to-back converter control method of new energy traction power supply system - Google Patents

Back-to-back converter control method of new energy traction power supply system Download PDF

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CN113595404A
CN113595404A CN202110767266.9A CN202110767266A CN113595404A CN 113595404 A CN113595404 A CN 113595404A CN 202110767266 A CN202110767266 A CN 202110767266A CN 113595404 A CN113595404 A CN 113595404A
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power
converter
current
power supply
voltage
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CN113595404B (en
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戴朝华
廉静如
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Southwest Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • 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
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
    • 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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

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  • Inverter Devices (AREA)

Abstract

The invention discloses a back-to-back converter control method of a new energy traction power supply system, which comprises the steps of monitoring load active power and renewable energy output power of two power supply arms in real time, dynamically distributing a charging and discharging power given value of an energy storage system, and calculating reference power at two sides of a back-to-back converter according to a negative sequence compensation principle; the energy storage system controls the output voltage of the energy storage system by adopting a constant voltage control method and obtains the voltage of the direct current side of the back-to-back converter; calculating reference currents on two sides of the back-to-back converter according to the acquired reference power and the power supply; and controlling the back-to-back converter to follow the reference current by adopting a double-vector model predictive control algorithm. The invention aims to solve the problems of poor dynamic response, large error and incapability of fully exerting the negative sequence compensation advantage of the back-to-back converter in the prior art.

Description

Back-to-back converter control method of new energy traction power supply system
Technical Field
The invention belongs to the technical field of new energy traction power supply, and particularly relates to a back-to-back converter control method of a new energy traction power supply system.
Background
By the end of 2020, the total business mileage of the electrified railway in China reaches 14.6 kilometers, and the total business mileage of the high-speed rail reaches 3.8 kilometers. The electricity consumption of the railway reaches as much as 900 hundred million kWh in 2020, wherein the traction energy consumption accounts for more than 50% of the total railway energy consumption. Electrified railways are one of the key areas of carbon emissions. In order to realize the vision of 'carbon neutralization', realize the aim of 'energy conservation and emission reduction', promote high permeability and high-efficiency utilization of new energy, domestic and foreign scholars actively explore and practice novel power supply modes such as multi-energy complementation, micro-grid and energy Internet.
In the aspect of electrified railways, a new power supply mode of integrating a renewable energy power generation system and an energy storage system through a back-to-back converter device is proposed at present. The system can be used for improving the electric energy quality problems of a traction power supply system, such as negative sequence, harmonic wave, idle work and the like; the energy storage unit can be connected to improve the utilization efficiency of renewable braking energy, and the system operation cost is effectively saved; and the renewable energy power generation unit can be connected to realize energy conservation and emission reduction of the system, and the toughness and the power supply reliability of the system are improved. However, most of the current researches are focused on the feasible architecture, compensation principle, negative sequence and harmonic detection, upper-layer energy management and the like of the system, and the research on the control strategy of the back-to-back converter is less. The common control strategy is hysteresis control, but the hysteresis control has larger tracking error and slow dynamic response speed.
Therefore, the prior art cannot fully exert the negative sequence compensation capability of the railway power regulator on the system; and when the system frequently switches the working modes, the stability of the system may be affected when the dynamic response speed is slow, the error is large and the system is serious.
Disclosure of Invention
In order to solve the problems, the invention provides a back-to-back converter control method of a new energy traction power supply system, and aims to solve the problems that the dynamic response is poor, the error is large, and the negative sequence compensation advantage of the back-to-back converter cannot be fully exerted in the prior art.
In order to achieve the purpose, the invention adopts the technical scheme that: a back-to-back converter control method of a new energy traction power supply system comprises the following steps:
s100, dynamically distributing a given value of charging and discharging power of an energy storage system by monitoring load active power and renewable energy source output power of two power supply arms in real time, and calculating reference power on two sides of a back-to-back converter according to a negative sequence compensation principle;
s200, calculating reference currents on two sides of the back-to-back converter according to the acquired reference power;
and S300, controlling the back-to-back converter to follow the reference current by adopting a double-vector model predictive control algorithm.
Further, in the step S100, load active power, renewable energy output power, and charge and discharge power of the energy storage system of the two power supply arms are monitored in real time; the output power of the renewable energy source and the energy storage system offsets part of the load power, and then the reference power of the back-to-back converters on the left side and the right side is solved according to the negative sequence compensation principle of the railway power regulator.
Further, in step S100, by monitoring the load active power and the renewable energy output power of the two power supply arms in real time, dynamically allocating a given value of the charging and discharging power of the energy storage system, and calculating the reference power on both sides of the back-to-back converter according to the negative sequence compensation principle, the method includes the steps of:
s101, monitoring the active power of the load of the two power supply arms to be P in real timeLα、PLβRenewable energy output power of PrenThe charging and discharging power of the energy storage system is Pess；
S102, calculating reference power P at two sides of the back-to-back converter according to the negative sequence compensation principle* c1、P* c2、Q* c1、Q* c2Respectively expressed as:
Figure BDA0003152263570000021
further, in the step S200, according to the characteristics of the three-phase inverter in the dq coordinate system, the current of the three-phase inverter is reversely solved according to the active power and reactive power calculation formula; and performing coordinate inverse transformation to solve the current in the abc coordinate system, and taking the a-phase current as reference currents on two sides of the back-to-back converter.
Further, in the step S200, calculating the reference currents at two sides of the back-to-back converter according to the reference power includes the steps of:
s201, according to the characteristics of the three-phase inverter in the dq coordinate system, if the d axis is taken as the alternating-current side voltage vector synthesis direction, eq0; the active power P and the reactive power Q of the converter are obtained as follows:
Figure BDA0003152263570000031
s202, when the voltage of the alternating current side of the back-to-back converter is consistent with the voltage of a large power grid during networking, edE is the large grid potential;
s203, substituting the reference power into the formula to reversely calculate the current i of the three-phase inverterd，iq(ii) a Then inverse coordinate transformation is carried out to solve the current in the abc coordinate system, and then the a-phase current i is takena1And ia2Respectively as reference current i of left and right side convertersref1，iref2。
Further, in step S300, a dual-vector model predictive control algorithm is used to control the back-to-back converter to follow the reference current, and the specific control algorithm is as follows: constructing virtual double vectors according to a switching function, and determining the action time of each vector according to a modulation method; and constructing an objective function, and obtaining an optimal switch control signal according to the minimum principle of the objective function.
Further, in the step S300, the dual vector model predictive control algorithm includes the steps of:
s301, combining the output voltages of the single-phase current transformer in pairs to construct 9 virtual vectors; u. of1s,i(i＝1,2,…,9)：
(uout1，uout1)，(uout1，uout2)，(uout1，uout3)，(uout2，uout1)，(uout2，uout2)，(uout2，uout3)，(uout3，uout1)，(uout3，uout2)，(uout3，uout3)；
The relationship between the synthesized virtual voltage and the base voltage is:
Figure BDA0003152263570000032
in the formula uoutm，uoutn(m, n is 1,2,3) represents three states of converter output voltage, t1,mAnd t1,nRespectively represents uoutm、uoutnThe action time of (c);
s302, predicting the current of the converter at the moment k +2 to be i1(k +2) is represented by:
i1(k+2)＝i1(k+1)+fm(k)t1,m+fn(k)t1,n；
in the formula i1(k +1) represents the predicted converter output current at the sampling moment of k + 1; f. ofm(k)、fn(k) Respectively represents uoutm、uoutnThe corresponding current derivative;
output voltage uoutiThe corresponding derivative of the current being given the sign fi(k) Represents:
Figure BDA0003152263570000033
in the formula, e1(k) Represents the voltage of the secondary side of the step-down transformer at the k sampling time, i1(k) Representing the converter output current at the sampling instant k, L1Representing the filter inductance, R, of the converter1Representing the equivalent impedance of the current transformer;
s303, setting a target function g, traversing and optimizing all target functions, searching a virtual vector combination corresponding to the minimum target function value and action time corresponding to the virtual vector combination, and converting the virtual vector combination into a corresponding switching sequence to be used as a switching signal of the next period;
g＝|i1ref(k+2)-i1(k+2)|；
in the formula i1ref(k +2) denotes the reference current at time k +2, i1And (k +2) represents the converter output current at the moment k + 2.
Further, the t is1,mAnd t1,nRespectively represents uoutm、uoutnThe formula of the action time of (1) is as follows:
Figure BDA0003152263570000041
in the formula, TsRepresents a sampling period; gm、GnRespectively represents uoutm、uoutnA corresponding voltage objective function;
wherein the voltage objective function is defined as Gp(p＝1,2,3)；
Gp＝|u1ref(k+1)-uouti|；
In the formula u1ref(k +1) is the reference voltage for k +1 sampling periods, uouti(i ═ 1,2,3) represents three basic voltage vectors.
Furthermore, the new energy traction power supply system with the back-to-back converter comprises a traction power supply system, a back-to-back converter system and a control system thereof, an energy storage system, a renewable energy system and a control unit, wherein the direct current sides of inverters on two sides of the back-to-back converter are connected to a common capacitor side together, the common capacitor side is connected with the energy storage system and the renewable energy system in parallel, and the alternating current side of the back-to-back converter is connected to the traction power supply system through a step-down transformer.
The beneficial effects of the technical scheme are as follows:
the method does not need a PWM module, reduces the calculated amount of the model and has simple control method; virtual dual-vector control is adopted, so that output current ripples are small, and the switching frequency is constant in one period; and the energy storage module is adopted to control the direct-current side voltage of the back-to-back converter, so that the direct-current side voltage fluctuation caused by system mode switching can be reduced, the current control of the inverter is influenced, and the dynamic response of the system is enhanced.
Drawings
Fig. 1 is a schematic flow chart of a back-to-back converter control method of a new energy traction power supply system according to the present invention.
Fig. 2 is a topological diagram of a traction power supply system in which renewable energy and stored energy are connected through a back-to-back converter in the embodiment of the present invention.
Fig. 3 is a main circuit topology structure diagram of the back-to-back converter in the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described with reference to the accompanying drawings.
In specific implementation, renewable energy and stored energy are built as shown in fig. 2 and are connected to a traction power supply system model through a back-to-back converter, and the model mainly comprises a traction power supply system, a back-to-back converter system and a control system thereof, an energy storage system, a renewable energy system and a control unit. The traction power supply system comprises a 220kV power system, a V/V traction transformer and a 27.5kV traction network.
The new energy traction power supply system with the back-to-back converter comprises a traction power supply system, the back-to-back converter system and a control system, an energy storage system, a renewable energy system and a control unit thereof, wherein the DC sides of inverters on two sides of the back-to-back converter are connected to a public capacitor side together, the public capacitor side is connected with the energy storage system and the renewable energy system in parallel, and the AC side of the back-to-back converter is connected to the traction power supply system through a step-down transformer.
The direct current sides of the single-phase inverters on the left side and the right side of the back-to-back converter are connected to the public capacitor side together, and the alternating current sides are connected to a traction network through a step-down transformer. The specific equivalent topological diagram is shown in fig. 3, and the traction network is equivalent to a large power grid from the perspective of a back-to-back converter. The left and right alternating current sides are connected into a large power grid through series filter inductors and equivalent impedance. The currents of two arms of the traction power supply system are compensated, so that primary side three-phase currents of the traction transformer are symmetrical, and negative sequence currents are eliminated.
A storage battery in the energy storage system is connected to a common capacitor on the direct current side in parallel through a bidirectional DC/DC converter, and the DC/DC converter supports the voltage of a direct current bus by adopting a constant voltage control algorithm to realize surplus and shortage regulation of electric quantity.
In this embodiment, referring to fig. 1, the invention provides a method for controlling a back-to-back converter of a new energy traction power supply system, which includes steps S100 to S300.
And S100, dynamically distributing a charging and discharging power given value of the energy storage system by monitoring the load active power and the renewable energy source output power of the two power supply arms in real time, and calculating reference power on two sides of the back-to-back converter according to a negative sequence compensation principle.
Monitoring load active power, renewable energy source output power and energy storage system charge and discharge power of the two power supply arms in real time; the output power of the renewable energy source and the energy storage system offsets part of the load power, and then the reference power of the back-to-back converters on the left side and the right side is solved according to the negative sequence compensation principle of the railway power regulator.
The specific embodiment comprises the following steps:
real-time monitoring of load active power P of two power supply armsLα、PLβAnd calculating the power P of the demand side of the traction power supply systemL，PLIs PLαAnd PLβSumming;
real-time monitoring renewable energy output power PrenAnd setting the renewable energy output time PrenGreater than 0, P when renewable energy does not output powerren0 (renewable energy output, P)renIs greater than 0; when the renewable energy source is not available, Pren0; ) (ii) a The charging and discharging power of the energy storage system is PessAnd setting P when the energy storage system is chargedess< 0, P when the energy storage system is dischargedrenGreater than 0 (when the energy storage system is charged, PessLess than 0; when the energy storage system is discharged, Pren＞0；)；
Reference power P of back-to-back converter* c1、P* c2、Q* c1、Q* c2Respectively expressed as:
Figure BDA0003152263570000061
the left side of the converter sends out reactive power, the right side of the converter absorbs the reactive power, and after reactive compensation, primary side three-phase currents of the traction transformer are symmetrical.
And S200, calculating reference currents on two sides of the back-to-back converter according to the acquired reference power.
According to the characteristics of the three-phase inverter in the dq coordinate system, reversely calculating and solving the current of the three-phase inverter according to an active power and reactive power calculation formula; and performing coordinate inverse transformation to solve the current in the abc coordinate system, and taking the a-phase current as reference currents on two sides of the back-to-back converter.
The specific embodiment comprises the following steps:
s201, according to the characteristics of the three-phase inverter in the dq coordinate system, if the d axis is taken as the alternating-current side voltage vector synthesis direction, eq0; the active power P and the reactive power Q of the converter are obtained as follows:
Figure BDA0003152263570000062
s202, when the voltage of the alternating current side of the back-to-back converter is consistent with the voltage of a large power grid during networking, edE is the large grid potential;
s203, substituting the reference power into the formula to reversely calculate the current i of the three-phase inverterd，iq(ii) a Then inverse coordinate transformation is carried out to solve the current in the abc coordinate system, and then the a-phase current i is takena1And ia2Respectively as reference current i of left and right side convertersref1，iref2。
S300, controlling the back-to-back converter to follow the reference current i by adopting a double-vector model predictive control algorithmref1，iref2。
As shown in the main circuit topology diagram of the back-to-back converter in fig. 3, L1 represents the filter inductance on the left side of the converter, and R1 represents the equivalent impedance on the left side of the converter. Detecting output voltage u1(k), current i1(k) and voltage e1(k) on the low-voltage side of the step-down transformer at the sampling moment k in real time;
(1) obtaining output current i of current transformer k-1 at sampling moment1(k-1), converter output voltage uout(k-1)；
(2) Solving the reference current i at the moment k +1 and the moment k +2 by adopting a Lagrange extrapolation algorithm1ref(k +1) and i1ref(k+2)
Figure BDA0003152263570000071
In the formula i1ref(k-2) denotes the reference current at the sampling instant k-2, i1ref(k-1) denotes the reference current at the sampling instant k-1, i1ref(k) A reference current representing the sampling instant k;
(3) estimating the output current i of the converter at the sampling moment of k +1 by using an estimation and prediction delay compensation method1(k+1)
Figure BDA0003152263570000072
In the formula, TsRepresents a sampling period;
(4) according to the dead beat idea, calculating the reference voltage u of k +1 sampling periods1ref(k+1)
Figure BDA0003152263570000073
In the formula i1(k +2) represents the converter output current at the sampling moment of k +2, and the secondary side voltage e of the step-down transformer at the moment of k +1 can be approximately considered in prediction considering that the grid voltage changes slowly1(k+1)＝e1(k)。
The double-vector model predictive control algorithm comprises the following steps:
s301, the output voltage of the single-phase two-level converter has three states, namely the output voltage is equal to 0, the output voltage is equal to the voltage of a direct-current bus, and the output voltage is outputThe output voltage is equal to the negative DC bus voltage and is respectively set as uout1＝0、uout2＝udc、uout3＝-udc(ii) a Therefore, the output voltages of the single-phase current transformer are combined in pairs, and 9 virtual vectors can be constructed; u. of1s,i(i＝1,2,…,9)：
(uout1，uout1)，(uout1，uout2)，(uout1，uout3)，(uout2，uout1)，(uout2，uout2)，(uout2，uout3)，(uout3，uout1)，(uout3，uout2)，(uout3，uout3)；
The relationship between the synthesized virtual voltage and the base voltage is:
Figure BDA0003152263570000074
in the formula uoutm，uoutn(m, n is 1,2,3) represents three states of converter output voltage, t1,mAnd t1,nRespectively represents uoutm、uoutnThe action time of (1).
S302, predicting the current of the converter at the moment k +2 to be i1(k +2) is represented by:
i1(k+2)＝i1(k+1)+fm(k)t1,m+fn(k)t1,n；
in the formula i1(k +1) represents the predicted converter output current at the sampling moment of k + 1; f. ofm(k)、fn(k) Respectively represents uoutm、uoutnThe corresponding current derivative;
said t is1,mAnd t1,nRespectively represents uoutm、uoutnThe formula of the action time of (1) is as follows:
Figure BDA0003152263570000081
in the formula, TsRepresents a sampling period; gm、GnRespectively represents uoutm、uoutnA corresponding voltage objective function;
wherein the voltage objective function is defined as Gp(p＝1,2,3)；
Gp＝|u1ref(k+1)-uouti|；
In the formula u1ref(k +1) is the reference voltage for k +1 sampling periods, uouti(i ═ 1,2,3) represents three basic voltage vectors.
Output voltage uoutiThe corresponding derivative of the current being given the sign fi(k) Represents:
Figure BDA0003152263570000082
in the formula, e1(k) Represents the voltage of the secondary side of the step-down transformer at the k sampling time, i1(k) Representing the converter output current at the sampling instant k, L1Representing the filter inductance, R, of the converter1Representing the equivalent impedance of the current transformer.
S303, setting a target function g, traversing and optimizing all target functions, searching a virtual vector combination corresponding to the minimum target function value and action time corresponding to the virtual vector combination, and converting the virtual vector combination into a corresponding switching sequence to be used as a switching signal of the next period;
g＝|i1ref(k+2)-i1(k+2)|；
in the formula i1ref(k +2) denotes the reference current at time k +2, i1And (k +2) represents the converter output current at the moment k + 2.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (9)

1. A back-to-back converter control method of a new energy traction power supply system is characterized by comprising the following steps:
s100, dynamically distributing a given value of charging and discharging power of an energy storage system by monitoring load active power and renewable energy source output power of two power supply arms in real time, and calculating reference power on two sides of a back-to-back converter according to a negative sequence compensation principle;
s200, calculating reference currents on two sides of the back-to-back converter according to the acquired reference power;
and S300, controlling the back-to-back converter to follow the reference current by adopting a double-vector model predictive control algorithm.
2. The method for controlling the back-to-back converter of the new energy traction power supply system according to claim 1, wherein in the step S100, load active power, renewable energy output power and energy storage system charge and discharge power of two power supply arms are monitored in real time; the output power of the renewable energy source and the energy storage system offsets part of the load power, and then the reference power of the back-to-back converters on the left side and the right side is solved according to the negative sequence compensation principle of the railway power regulator.
3. The method as claimed in claim 2, wherein in step S100, the reference power at two sides of the back-to-back converter is calculated according to the negative sequence compensation principle by monitoring the load active power and the renewable energy output power of the two power supply arms in real time, dynamically allocating the charging and discharging power set value of the energy storage system, and including the steps of:
s101, monitoring the active power of the load of the two power supply arms to be P in real timeLα、PLβRenewable energy output power of PrenThe charging and discharging power of the energy storage system is Pess；
S102, calculating two back-to-back converters according to the negative sequence compensation principleSide reference power of P* c1、P* c2、Q* c1、Q* c2Respectively expressed as:
Figure FDA0003152263560000011
4. the back-to-back converter control method of the new energy traction power supply system according to claim 1, wherein in the step S200, according to the characteristics of the three-phase inverter in the dq coordinate system, the current of the three-phase inverter is reversely solved according to the active power and reactive power calculation formula; and performing coordinate inverse transformation to solve the current in the abc coordinate system, and taking the a-phase current as reference currents on two sides of the back-to-back converter.
5. The method as claimed in claim 4, wherein in step 2300, the reference current on both sides of the back-to-back converter is calculated according to the reference power, and the method comprises the steps of:
s201, according to the characteristics of the three-phase inverter in the dq coordinate system, if the d axis is taken as the alternating-current side voltage vector synthesis direction, eq0; the active power P and the reactive power Q of the converter are obtained as follows:
Figure FDA0003152263560000021
s202, when the voltage of the alternating current side of the back-to-back converter is consistent with the voltage of a large power grid during networking, edE is the large grid potential;
s203, substituting the reference power into the formula to reversely calculate the current i of the three-phase inverterd，iq(ii) a Then inverse coordinate transformation is carried out to solve the current in the abc coordinate system, and then the a-phase current i is takena1And ia2As parameters of left and right convertersTest current iref1，iref2。
6. The method according to claim 1, wherein in step S300, a double-vector model predictive control algorithm is used to control the back-to-back converter to follow the reference current, and the specific control algorithm is: constructing virtual double vectors according to a switching function, and determining the action time of each vector according to a modulation method; and constructing an objective function, and obtaining an optimal switch control signal according to the minimum principle of the objective function.
7. The method for controlling the back-to-back converter of the new energy traction power supply system according to claim 6, wherein in the step S300, the bi-vector model predictive control algorithm comprises the steps of:
s301, combining the output voltages of the single-phase current transformer in pairs to construct 9 virtual vectors; u. of1s,i(i＝1,2,…,9)；
The relationship between the synthesized virtual voltage and the base voltage is:
Figure FDA0003152263560000022
in the formula uoutm，uoutn(m, n is 1,2,3) represents three states of converter output voltage, t1,mAnd t1,nRespectively represents uoutm、uoutnThe action time of (c);
s302, predicting the current of the converter at the moment k +2 to be i1(k +2) is represented by:
i1(k+2)＝i1(k+1)+fm(k)t1,m+fn(k)t1,n；
in the formula i1(k +1) represents the predicted converter output current at the sampling moment of k + 1; f. ofm(k)、fn(k) Respectively represents uoutm、uoutnThe corresponding current derivative;
output ofVoltage uoutiThe corresponding derivative of the current being given the sign fi(k) Represents:
Figure FDA0003152263560000031
in the formula, e1(k) Represents the voltage of the secondary side of the step-down transformer at the k sampling time, i1(k) Representing the converter output current at the sampling instant k, L1Representing the filter inductance, R, of the converter1Representing the equivalent impedance of the current transformer;
s303, setting a target function g, traversing and optimizing all target functions, searching a virtual vector combination corresponding to the minimum target function value and action time corresponding to the virtual vector combination, and converting the virtual vector combination into a corresponding switching sequence to be used as a switching signal of the next period;
g＝|i1ref(k+2)-i1(k+2)|；
in the formula i1ref(k +2) denotes the reference current at time k +2, i1And (k +2) represents the converter output current at the moment k + 2.
8. The method as claimed in claim 7, wherein t is the control of the back-to-back converter of the new energy traction power supply system1,mAnd t1,nRespectively represents uoutm、uoutnThe formula of the action time of (1) is as follows:
Figure FDA0003152263560000032
in the formula, TsRepresents a sampling period; gm、GnRespectively represents uoutm、uoutnA corresponding voltage objective function;
wherein the voltage objective function is defined as Gp(p＝1,2,3)；
Gp＝|u1ref(k+1)-uouti|；
In the formula u1ref(k +1) is a parameter of k +1 sampling periodsExamination voltage uouti(i ═ 1,2,3) represents three basic voltage vectors.
9. The back-to-back converter control method of the new energy traction power supply system according to any one of claims 1 to 8, wherein the new energy traction power supply system with the back-to-back converter comprises a traction power supply system, a back-to-back converter system and a control system thereof, an energy storage system, a renewable energy system and a control unit, the dc sides of inverters at two sides of the back-to-back converter are commonly connected to a common capacitor side, the common capacitor side is connected with the energy storage system and the renewable energy system in parallel, and the ac side of the back-to-back converter is connected to the traction power supply system through a step-down transformer.
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