Energy management method for through-type flexible traction power supply system

Abstract

The present application relates to a kind of through flexible traction power supply system energy management method, belong to electric traction technical field.The technical scheme: by arranging the weight level of negative sequence compensation, power fusion and voltage deviation compensation, combine the real-time residual capacity threshold of back-to-back converter, build from compensation to fusion to step type control logic of voltage regulation;Based on capacity threshold constraint and priority, realize multi-objective hierarchical control;First, eliminate negative sequence hazards using all or part of capacity;Second, according to the residual capacity to perform power fusion, realize the use of regenerative braking energy;Finally, try to compensate voltage deviation using the final residual capacity.The present application considers the capacity threshold of back-to-back converter, gradient type calculation reference power, improves the capacity utilization of back-to-back converter, reduces investment cost;Consider the three-phase voltage deviation of point of common coupling, realize the comprehensive management of three-phase voltage deviation, three-phase voltage unbalance and effective power factor and other power quality at point of common coupling.

Description

Technical Field

[0001] This invention relates to an energy management method for a through-type flexible traction power supply system, belonging to the field of electric traction technology. Background Technology

[0002] By the end of 2025, the total mileage of my country's high-speed railways will exceed 50,000 kilometers, with the "eight vertical and eight horizontal" high-speed railway network becoming a crucial pillar for ensuring national economic and social development. Currently, high-speed railway traction power supply systems generally adopt a single-phase AC power supply system at industrial frequency, requiring electrical phase separation in the overhead contact line. When trains pass through these phase separations, power is cut off for coasting, leading to a series of problems such as speed reduction and transient overvoltage. Furthermore, current train braking generally employs regenerative braking, where the onboard motors are converted to generator operation during braking, feeding regenerative energy back into the power supply system. How to eliminate electrical phase separation in the overhead contact line and fully utilize the regenerative energy generated by trains to reduce railway operating costs has become a research hotspot in the field of high-speed railway traction power supply. Chinese Patent CN202410857201.7 discloses a flexible through-type traction power supply system and control method, which can effectively solve the above problems. However, the energy management strategy in the control method of the through-type flexible traction power supply system proposed in this technical solution has technical defects such as ignoring the capacity threshold of back-to-back converters and not considering the three-phase voltage deviation at the point of common coupling, resulting in problems such as low voltage level at the point of common coupling, insufficient capacity utilization of back-to-back converters, and high investment costs. Summary of the Invention

[0003] This invention proposes an energy management method for a through-type flexible traction power supply system. It fully considers the capacity constraints of back-to-back converters and the voltage deviation at the point of common coupling (PCC). By constructing a multi-objective hierarchical control model based on priority ranking, it maximizes the capacity potential of back-to-back converters while ensuring safe and stable system operation. It prioritizes negative-sequence compensation, achieves power sharing, and utilizes remaining capacity to compensate for three-phase voltage deviations, effectively improving the voltage level at the PCC. This optimizes converter capacity configuration efficiency, reduces back-to-back converter investment costs, and enhances the overall performance of the through-type flexible traction power supply system. It addresses the problems of low voltage levels at the PCC, affecting power quality and system stability, and insufficient back-to-back converter capacity utilization, leading to wasted equipment investment and reduced operational economy in existing through-type flexible traction power supply systems.

[0004] The technical solution of this invention is:

[0005] An energy management method for a through-type flexible traction power supply system is proposed. This method constructs a stepped control logic from compensation to balancing to voltage regulation by arranging the weight levels of negative sequence compensation, power balancing, and voltage deviation compensation, combined with the real-time remaining capacity threshold of back-to-back converters. Based on capacity threshold constraints and priority allocation, multi-objective hierarchical control is achieved. First, all or part of the capacity is utilized to eliminate the harm of negative sequence. Second, power balancing is performed based on the remaining capacity to utilize regenerative braking energy. Finally, the final remaining capacity is used to compensate for voltage deviations as much as possible. This method thoroughly solves the problems of low capacity utilization, neglect of voltage deviation compensation, and substandard voltage levels at the point of common coupling, achieving the dual benefits of maximizing converter capacity utilization and optimizing comprehensive power quality compensation.

[0006] This invention does not calculate all power requirements at once, but rather in stages: first, it satisfies the highest priority negative sequence compensation and accurately calculates the remaining capacity after consumption; then, it uses this remaining capacity as a constraint condition for the next stage of power facilitation; finally, it utilizes the remaining threshold space after completing the first two functions to compensate for the three-phase voltage deviation as much as possible. The step-by-step algorithm maximizes the potential of the converter.

[0007] The through-type flexible traction power supply system includes a central traction substation (CTS) and multiple ordinary traction substations (TSS). Each ordinary traction substation (TSS) contains a single-phase traction transformer. The primary side of the single-phase traction transformer is connected to the three-phase AC busbar of the central traction substation (CTS), and the secondary side is connected to the overhead contact line. The central traction substation (CTS) includes a single-phase traction transformer and a power flow control system. The primary side of the single-phase traction transformer is connected to the three-phase AC busbar of the central traction substation (CTS), and the secondary side is connected to the overhead contact line. The power flow control system includes a compensation system, an energy storage system, and an energy feedback system. The compensation system includes a Scott transformer and back-to-back converters. The Scott transformer consists of two sets of single-phase transformers, named T1 and T2 respectively. The back-to-back converters consist of two sets of converters connected in parallel on their DC sides, named VSC1 and VSC2 respectively. The primary side of T2 is connected to the two-phase AC busbars of the single-phase traction transformer, and the secondary side is connected to the AC side of VSC2. One end of the primary side of T1 is connected to the unpowered phase AC busbar of the single-phase traction transformer, and the other end is connected to the center tap of T2. The secondary side is connected to the AC side of VSC2. The energy storage system includes an energy storage medium and a DC-DC converter. The high-voltage side of the DC-DC converter is connected to the DC side of the back-to-back converter, and the low-voltage side is connected to the energy storage medium. The energy feed system includes a three-phase grid-connected inverter. The DC side of the three-phase grid-connected inverter is connected to the DC side of the back-to-back converter, and the AC side is connected to the distribution network in the central traction substation (CTS).

[0008] The specific steps are as follows:

[0009] Step 1: Set the power flow control system operating parameters: VSC i (i = 1, 2) Rated capacity S i_max Rated power P of energy storage system SC_max Lower limit of the safe threshold for the state of charge of energy storage medium in SoC min With security threshold upper limit SoC max The rated power P of the energy feed system F_max The short-circuit capacity S of the external power grid referred to the point of common coupling G ;

[0010] Step 2: Calculate the negative sequence complex power S at the point of common coupling. - Total traction load active power P LM Total traction load reactive power Q LM 10kV power distribution network distribution load P LD . Regulations: P LM Q LM and P LD The positive direction is from the power supply network to the load;

[0011] Step 3: Calculate the reference power P of the energy feeder system F_ref and the reference power P of the energy storage system SC_ref

[0012] 1) If P LM ≥0 and SoC≤SoC min

[0013] (1)

[0014] 2) If P LM ≥0 and SoC>SoC min

[0015] (2)

[0016] 3) If P LM <0 and SoC≥SoC max

[0017] (3)

[0018] 4) If P LM <0 and SoC <SoC max

[0019] (4)

[0020] In the formula: SoC is the state of charge of the energy storage medium collected in real time; min() is to take the minimum value of the multiple data in parentheses.

[0021] Rule: P F_ref The positive direction is from the DC side of the three-phase grid-connected inverter to the AC side; P SC_ref The positive direction is the flow into the energy storage medium;

[0022] Step 4: Calculate the VSC when the compensation system acts as an energy exchange medium. i Reference power S i,B_ref for

[0023] (5)

[0024] In the formula: || represents taking the absolute value; when P F_ref +P SC_ref When d1 > 0, d1 = 1; otherwise, d1 = -1.

[0025] Step 5: Calculate VSC when the compensation system performs negative sequence compensation. i Required capacity S N_ref for

[0026] (6)

[0027] (7)

[0028] In the formula: angle() represents the phase angle of the vector in parentheses; e is the base; j is the complex unit; r i For T i Wiring angle.

[0029] Therefore, VSC is used for negative order compensation. i Reference power S i,N_ref for

[0030] (8)

[0031] Calculate the three-phase voltage imbalance e after negative sequence compensation u

[0032] (9)

[0033] If e u = 0%, then proceed to Step 6; if e u If the deviation is greater than 2%, proceed to Step 7; otherwise, set the three-phase voltage deviation compensation power Q. i,ref = 0, proceed to Step 8;

[0034] Step 6: Calculate Q i,ref for

[0035] (10)

[0036] (11)

[0037] (12)

[0038] In the formula: R G With X G These are the equivalent resistance and equivalent reactance of the external power grid referred to the point of common coupling, respectively.

[0039] Step 7: Order

[0040] (13)

[0041] Calculate S i,N_ref for

[0042] (14)

[0043] Calculate P F_ref and P SC_ref for:

[0044] If SoC≤SoC min

[0045] (15)

[0046] on the contrary

[0047] (16)

[0048] Step 8: Calculate VSC i Total reference power S i,ref for

[0049] (17)

[0050] S i,ref P F_ref and P SC_ref It is transmitted to the converter control layer.

[0051] The core difference between this invention and the prior art (CN202410857201.7) lies in the priority logic of the control strategy and the dynamic capacity allocation mechanism.

[0052] (1) Improvement of algorithm logic (from "single function" to "multi-objective collaboration"):

[0053] The shortcomings of the comparative document are that its control method only considers single or parallel functional requirements and lacks a prioritization of the importance of different functions. This "indiscriminate" approach can easily lead to back-to-back converters being unable to cope with all situations due to capacity contention when dealing with complex operating conditions, especially neglecting compensation for voltage deviations at the point of common coupling.

[0054] The innovation of this invention lies in its proposal of a capacity hierarchical control method based on priority ranking. This invention is the first to prioritize negative-sequence compensation, power leeway, and voltage deviation compensation according to their importance. Through strict priority division, it ensures that converter capacity is used preferentially where it is most needed, avoiding conflicts in control objectives.

[0055] (2) Improvement in capacity utilization (from "hard constraints" to "dynamic margin calculation"):

[0056] The shortcomings of the comparison document are that it only treats the converter capacity as a fixed threshold. When multiple target demands exceed the total capacity, it can only passively fail or reduce performance, resulting in low capacity utilization and wasted equipment investment.

[0057] The innovation of this invention lies in the introduction of a "dynamic reallocation of remaining capacity" mechanism. Instead of calculating all power demand at once, this invention performs the calculation in stages: first, it satisfies the highest priority negative-sequence compensation, accurately calculating the remaining capacity after consumption; then, it uses this remaining capacity as a constraint for the next stage (power balancing); finally, it utilizes the remaining threshold space after completing the first two functions to compensate for three-phase voltage deviations as much as possible. This "step-by-step" algorithm maximizes the potential of the converter.

[0058] This invention abandons the general power coordination control strategy in the prior art. Compared with the prior art, the beneficial effects of this invention are: 1) It considers the capacity threshold of back-to-back converters and calculates the reference power in a gradient manner, which improves the capacity utilization of back-to-back converters, reduces investment costs, and enhances economic efficiency; 2) It considers the three-phase voltage deviation at the point of common coupling and realizes the comprehensive management of power quality such as three-phase voltage deviation, three-phase voltage imbalance, and effective power factor at the point of common coupling. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the electrical structure of the through-type flexible traction power supply system according to an embodiment of the present invention;

[0060] Figure 2 This is a flowchart illustrating the energy management method of the through-type flexible traction power supply system according to an embodiment of the present invention. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0062] The through-type flexible traction power supply system in the embodiment is as follows: Figure 1As shown, it includes one central traction substation (CTS) and multiple ordinary traction substations (TSS). The ordinary traction substations (TSS) primarily consist of single-phase traction transformers. The primary side of each single-phase traction transformer is connected to the three-phase AC busbar of the central traction substation (CTS), and the secondary side is connected to the overhead contact line. The central traction substation (CTS) includes single-phase traction transformers and a power flow control system. The primary side of each single-phase traction transformer is connected to the three-phase AC busbar of the central traction substation (CTS), and the secondary side is connected to the overhead contact line. The power flow control system includes a compensation system, an energy storage system, and an energy feeder system. The compensation system includes Scott transformers and back-to-back converters. The Scott transformer consists of two sets of single-phase transformers, named T1 and T2 respectively; the back-to-back converters consist of two sets of converters connected in parallel on their DC sides, named VSC1 and VSC2 respectively. The primary side of T2 is connected to the two-phase AC busbars of the single-phase traction transformer, and the secondary side is connected to the AC side of VSC2. One end of the primary side of T1 is connected to the unpowered phase AC busbar of the single-phase traction transformer, and the other end is connected to the center tap of T2. The secondary side is connected to the AC side of VSC2. The energy storage system includes an energy storage medium and a DC-DC converter. The high-voltage side of the DC-DC converter is connected to the DC side of the back-to-back converter, and the low-voltage side is connected to the energy storage medium. The energy feed system includes a three-phase grid-connected inverter. The DC side of the three-phase grid-connected inverter is connected to the DC side of the back-to-back converter, and the AC side is connected to the railway 10kV distribution network in the central traction substation (CTS). (See diagram: P) LM With Q LM These represent the total traction load active power and the total traction load reactive power, respectively; S i_ref For VSC i (i = 1, 2) Complex power reference values; P SC_ref With P F_ref These are the active power reference values ​​for the energy storage system and the energy feeder system, respectively. It is stipulated that the positive direction of the above power values ​​is... Figure 1 The middle arrow indicates direction.

[0063] An energy management method for a through-type flexible traction power supply system, such as Figure 2 As shown, it includes:

[0064] Step 1: Set the power flow control system operating parameters: VSC i (i = 1, 2) Rated capacity S i_max Rated power P of energy storage system SC_max Lower limit of the safe threshold for the state of charge of energy storage medium in SoC min With security threshold upper limit SoC max The rated power P of the energy feed system F_max The short-circuit capacity S of the external power grid referred to the point of common coupling G ;

[0065] Step 2: Calculate the negative sequence complex power S at the point of common coupling. - Total traction load active power P LM Total traction load reactive power Q LM With the 10kV distribution network distribution load P LD . Regulations: P LD The positive direction is from the power supply network to the load;

[0066] Step 3: Calculate P F_ref and P SC_ref

[0067] 1) If P LM ≥0 and SoC≤SoC min

[0068] (1)

[0069] 2) If P LM ≥0 and SoC>SoC min

[0070] (2)

[0071] 3) If P LM <0 and SoC≥SoC max

[0072] (3)

[0073] 4) If P LM <0 and SoC <SoC max

[0074] (4)

[0075] In the formula: SoC is the state of charge of the energy storage medium collected in real time; min() is to take the minimum value of the multiple data in parentheses.

[0076] Step 4: Calculate the VSC when the compensation system acts as an energy exchange medium. i Reference power S i,B_ref for

[0077] (5)

[0078] In the formula: || represents taking the absolute value; when P F_ref +P SC_ref When d1 > 0, d1 = 1; otherwise, d1 = -1.

[0079] Step 5: Calculate VSC when the compensation system performs negative sequence compensation. i Required capacity SN_ref for

[0080] (6)

[0081] (7)

[0082] In the formula: angle() represents the phase angle of the vector in parentheses; e is the base; j is the complex unit; r i For T i Wiring angle.

[0083] Therefore, VSC is used for negative order compensation. i Reference power S i,N_ref for

[0084] (8)

[0085] Calculate the three-phase voltage imbalance e after negative sequence compensation u

[0086] (9)

[0087] If e u = 0%, then proceed to Step 6; if e u If the deviation is greater than 2%, proceed to Step 7; otherwise, set the three-phase voltage deviation compensation power Q. i,ref = 0, proceed to Step 8;

[0088] Step 6: Calculate Q i,ref for

[0089] (10)

[0090] (11)

[0091] (12)

[0092] In the formula: R G With X G These are the equivalent resistance and equivalent reactance of the external power grid referred to the point of common coupling, respectively.

[0093] Step 7: Order

[0094] (13)

[0095] Calculate S i,N_ref for

[0096] (14)

[0097] Calculate P F_ref and PSC_ref for:

[0098] If SoC≤SoC min

[0099] (15)

[0100] on the contrary

[0101] (16)

[0102] Step 8: Calculate S i,ref for

[0103] (17)

[0104] S i,ref P F_ref and P SC_ref It is transmitted to the converter control layer.

[0105] This invention abandons the general power coordination control strategy in existing technologies and creatively proposes a priority-based, multi-objective hierarchical control method based on capacity threshold constraints. This method constructs a "compensation-coupling-voltage regulation" stepped control logic by arranging the weight levels of negative sequence compensation, power balancing, and voltage deviation compensation, combined with the real-time remaining capacity threshold of back-to-back converters. First, it utilizes all or part of the capacity to eliminate the harm of negative sequence; second, it performs power balancing based on the remaining capacity to realize the utilization of regenerative energy; finally, it uses the final remaining capacity to compensate for voltage deviations as much as possible. This mechanism completely solves the problems of low capacity utilization, neglect of voltage deviation compensation, and substandard voltage levels at the point of common coupling in the comparative documents, achieving the dual benefits of maximizing converter capacity utilization and optimizing comprehensive power quality compensation.

Claims

1. An energy management method for a through-type flexible traction power supply system, characterized in that: By arranging the weight levels of negative sequence compensation, power facilitation, and voltage deviation compensation, and combining the real-time remaining capacity threshold of back-to-back converters, a step-by-step control logic is constructed from compensation to facilitation to voltage regulation; multi-objective hierarchical control is achieved based on capacity threshold constraints and priority division; firstly, all or part of the capacity is used to eliminate the harm of negative sequence. Secondly, power switching is performed based on the remaining capacity to utilize regenerative braking energy; finally, the remaining capacity is used to compensate for voltage deviations as much as possible.

2. The energy management method for a through-type flexible traction power supply system according to claim 1, characterized in that: This method does not calculate all power demand at once, but calculates it in stages: first, it satisfies the highest priority negative sequence compensation and accurately calculates the remaining capacity after consumption; then, it uses this remaining capacity as a constraint condition for the next stage of power facilitation; finally, it uses the remaining threshold space after completing the first two functions to compensate for the three-phase voltage deviation as much as possible. The step-by-step algorithm maximizes the potential of the converter.

3. The energy management method for a through-type flexible traction power supply system according to claim 1 or 2, characterized in that: The continuous flexible traction power supply system includes a central traction substation (CTS) and multiple ordinary traction substations (TSS). Each ordinary traction substation (TSS) contains a single-phase traction transformer. The primary side of the single-phase traction transformer is connected to the three-phase AC busbar of the central traction substation (CTS), and the secondary side is connected to the overhead contact line. The central traction substation (CTS) includes single-phase traction transformers and a power flow control system. The primary side of the single-phase traction transformer is connected to the three-phase AC busbar of the central traction substation (CTS), and the secondary side is connected to the overhead contact line. The power flow control system includes a compensation system, an energy storage system, and an energy feedback system. The compensation system includes Scott transformers and back-to-back converters. The Scott transformer consists of two sets of single-phase transformers, named T1. The back-to-back converter consists of two sets of converters connected in parallel on the DC side, named VSC1 and VSC2 respectively. The primary side of T2 is connected to the two-phase AC busbars powered by the single-phase traction transformer, and the secondary side is connected to the AC side of VSC2. One end of the primary side of T1 is connected to the unpowered phase AC busbar of the single-phase traction transformer, and the other end is connected to the center tap position of T2. The secondary side is connected to the AC side of VSC2. The energy storage system includes an energy storage medium and a DC-DC converter. The high-voltage side of the DC-DC converter is connected to the DC side of the back-to-back converter, and the low-voltage side is connected to the energy storage medium. The energy feed system includes a three-phase grid-connected inverter. The DC side of the three-phase grid-connected inverter is connected to the DC side of the back-to-back converter, and the AC side is connected to the distribution network in the central traction substation (CTS).

4. The energy management method for a through-type flexible traction power supply system according to claim 3, characterized in that... The specific steps are as follows: Step 1: Set the power flow control system operating parameters: VSC i (i = 1, 2) Rated capacity S i_max Rated power P of energy storage system SC_max Lower limit of the safe threshold for the state of charge of energy storage medium in SoC min With security threshold upper limit SoC max The rated power P of the energy feed system F_max The short-circuit capacity S of the external power grid referred to the point of common coupling G ; Step 2: Calculate the negative sequence complex power S at the point of common coupling. - Total traction load active power P LM Total traction load reactive power Q LM 10kV distribution network distribution load P LD ; stipulate: P LM Q LM and P LD The positive direction is from the power supply network to the load; Step 3: Calculate the reference power P of the energy feeder system F_ref and the reference power P of the energy storage system SC_ref 1) If P LM ≥0 and SoC≤SoC min （1） 2) If P LM ≥0 and SoC>SoC min （2） 3) If P LM <0 and SoC≥SoC max （3） 4) If P LM <0 and SoC <SoC max （4） In the formula: SoC is the state of charge of the energy storage medium collected in real time; min() is to take the minimum value of the multiple data in parentheses; Rule: P F_ref The positive direction is from the DC side of the three-phase grid-connected inverter to the AC side; P SC_ref The positive direction is the flow into the energy storage medium; Step 4: Calculate the VSC when the compensation system acts as an energy exchange medium. i Reference power S i,B_ref for （5） In the formula: || represents taking the absolute value; when P F_ref +P SC_ref When d1 > 0, d1 = 1; otherwise, d1 = -1. Step 5: Calculate VSC when the compensation system performs negative sequence compensation. i Required capacity S N_ref for （6） （7） In the formula: angle() represents the phase angle of the vector in parentheses; e is the base; j is the complex unit; r i For T i Wiring angle; Therefore, VSC is used for negative order compensation. i Reference power S i,N_ref for （8） Calculate the three-phase voltage imbalance e after negative sequence compensation u （9） If e u = 0%, then proceed to Step 6; if e u If the deviation is greater than 2%, proceed to Step 7; otherwise, set the three-phase voltage deviation compensation power Q. i,ref = 0, proceed to Step 8; Step 6: Calculate Q i,ref for （10） （11） （12） In the formula: R G With X G These are the equivalent resistance and equivalent reactance of the external power grid referred to the point of common coupling, respectively. Step 7: Order （13） Calculate S i,N_ref for （14） Calculate P F_ref and P SC_ref for: If SoC≤SoC min （15） on the contrary （16） Step 8: Calculate VSC i Total reference power S i,ref for （17） S i,ref P F_ref and P SC_ref It is transmitted to the converter control layer.

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