A coordinated control method for energy storage railway power regulator

Abstract

The present invention provides a coordinated control method for an energy storage railway power regulator, which is used to enhance the robust stability of the energy storage railway power regulator when the power flows in both directions. The method includes: building a traction power supply system model of an energy storage railway power regulator using a V / v traction transformer; applying an energy storage railway power regulator to manage negative sequence current; and controlling the energy storage railway power regulator using a coordinated control method; the proposed coordinated control method can solve the fluctuation of the DC voltage of the reverse power flow under parameter perturbation, thereby improving the system robustness and enhancing the power quality of the traction system.

Description

Technical Field

[0001] The invention belongs to the field of power quality and energy storage type railway power regulator control, and relates to a coordinated control method of an energy storage type railway power regulator. Background Art

[0002] Railway Power Conditioner (RPC) is a comprehensive compensation device used in railway power quality management. It balances the grid current and manages power quality by transferring active power and reactive power. Energy Storage Type Railway Power Conditioner (ESS-RPC) adds an energy storage system (ESS) to the two-port RPC system and expands it to three ports. Compared with the original RPC system, ESS-RPC can use energy storage to absorb regenerative braking energy, perform peak shaving and valley filling, and smooth out fluctuations.

[0003] However, the existing control methods do not consider the stability of ESS-RPC when managing the power quality of traction loads. Due to the random fluctuations in the loads of the two power supply arms, ESS-RPC often switches the power transmission direction between the two arms. Studies have found that the ESS-RPC back-to-back system has a high power consumption when the active power is transferred from the VSC to the VSC. β (β-side voltage source converter) to VSC α The DC voltage transferred (power forward flow) by the (α-side voltage source converter) remains stable under the perturbation of the system parameters (inductance L). However, the active power from the VSC α To VSC β The perturbation of the transfer inductance L (when power flows in the reverse direction) will cause the DC voltage to fluctuate, thus affecting the power quality of the traction power supply system. Therefore, a new coordinated control method needs to be proposed to ensure the stability of the ESS-RPC system. Summary of the invention

[0004] The present invention provides a coordinated control method for an energy storage railway power regulator, which is used to solve the DC voltage stability difference caused by the impedance mismatch of the ESS-RPC DC terminal when power flows in both directions under parameter perturbation. This DC voltage fluctuation will cause negative sequence and harmonics in the ESS-RPC transfer current, thereby affecting the power quality of the traction system.

[0005] The specific method is to coordinate the control of ESS-RPC when power flows in both directions, and use VSC when power flows in the forward direction. α Stabilize DC voltage. When power flows in the reverse direction, ESS is used to stabilize DC voltage first, and then VSC is switched after the voltage stabilizes. βThe DC voltage is controlled and the cycle repeats itself.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions, including:

[0007] S1. Build a model of energy storage railway power conditioner traction power supply system using V / v traction transformer;

[0008] S2. Use energy storage railway power regulator to balance the left and right power supply arms and manage the negative sequence current of the three-phase power grid;

[0009] S3. A new coordinated control method is used to control the energy storage railway power regulator. When the power flows forward, the VSC α Using voltage control, VSC β The ESS uses power control, and when the power flows in the reverse direction, the VSC α Switch to power control, VSC β Power control is used first, while ESS uses voltage control. After a delay, the VSC is turned on after the DC voltage stabilizes. β Using voltage control, VSC α The power control adopted with ESS ensures that the ESS-RPC system always works under the positive power flow;

[0010] The patent of this invention has the following advantages over the prior art:

[0011] The proposed three-port coordinated control enhances the system robustness and can maintain the DC impedance matching of the ESS-RPC system regardless of the forward and reverse power flow, so that the system DC voltage remains stable, thereby ensuring the stability of the traction power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the ESS-RPC circuit topology;

[0013] Figure 2 It is the negative sequence current compensation vector diagram of energy storage type railway power regulator;

[0014] Figure 3 Railway power conditioner VSC control block diagram (a) VSC α Control block diagram (b) VSC β Control block diagram;

[0015] Figure 4 It is a bidirectional DC-DC control block diagram;

[0016] Figure 5 This is the block diagram of the new coordinated control strategy;

[0017] Figure 6(a) L = 1p.u power switching DC voltage (b) L = 1.2pu power switching DC voltage under conventional control;

[0018] Figure 7 Under conventional control (a) L = 1p.u power switching grid three-phase current (b) L = 1.2pu power switching grid three-phase current;

[0019] Figure 8 Under coordinated control (a) L = 1p.u power switching DC voltage (b) L = 1.2pu power switching DC voltage;

[0020] Fig. 9 Under coordinated control (a) L = 1p.u power switching grid three-phase current (b) L = 1.2pu power switching grid three-phase current;

[0021] Fig.10 Switching DC voltage for power L=1.2pu under conventional control;

[0022] Fig.11 The power switching grid current is L=1.2pu under conventional control;

[0023] Fig.12 The DC voltage waveform is switched for L=1.2pu power under coordinated control;

[0024] Fig.13 To switch the grid current under coordinated control, L = 1.2 pu power; DETAILED DESCRIPTION

[0025] The present invention proposes a coordinated control method for an energy storage type railway power regulator. In order to better demonstrate the innovation and stability of the present invention, the coordinated control method for an energy storage type railway power regulator is explained in detail below in conjunction with the accompanying drawings and embodiments:

[0026] Table 1 shows the physical meanings of the variables of the present invention, wherein the subscript x={α, β} represents the left and right power supply arms of the RPC respectively.

[0027]

[0028] S1. Build a model of energy storage railway power conditioner traction power supply system using V / v traction transformer;

[0029] In specific implementation, the ESS-RPC circuit system proposed by the present invention is as follows: Figure 1As shown, it includes a V / v traction transformer, an α power supply arm, a β power supply arm, an α side step-down transformer, a β side step-down transformer, a railway power conditioner and an energy storage system. The railway power conditioner is connected in parallel between the α power supply arm and the β power supply arm through the α side step-down transformer and the β side step-down transformer respectively, and the energy storage system is connected to the DC link of the railway power conditioner.

[0030] The energy storage railway power conditioner is composed of a back-to-back converter, a step-down transformer, a super capacitor, a DC capacitor, and a line inductor. The back-to-back converter includes an α-side voltage source converter and a β-side voltage source converter. The two converters are connected through a DC capacitor and are respectively connected to the step-down transformers on both sides through line inductors. The energy storage device and the bidirectional DC-DC system are connected to the railway power conditioner.

[0031] S2. Use energy storage railway power regulator to balance the left and right power supply arms and manage the negative sequence current of the three-phase power grid;

[0032] Figure 2 This is the negative sequence current compensation vector diagram of the energy storage railway power conditioner. In specific implementation, the energy storage railway power conditioner is used to transfer active power and reactive power to balance the left and right power supply arms. The energy storage railway power conditioner transfers part of the active power of the heavy-load arm to the light-load arm through the voltage source inverter, so that the active load of the two arms is balanced, and then compensates a certain amount of reactive current, so that the three-phase current on the primary side of the V / v transformer is symmetrical and in phase with the voltage, thereby eliminating the negative sequence current and achieving balance. At the same time, the ESS is controlled to absorb regenerative braking energy and supply the stored energy to the traction power supply system.

[0033] S3. Control method of each converter of ESS-RPC;

[0034] Since ESS-RPC is a single-phase system, the static-synchronous coordinate transformation formula cannot be directly used. The single-phase AC quantity can be constructed as a pair of orthogonal AC quantities in the static αβ coordinate system through the construction method, and then the system mathematical model in the dq coordinate system is established through the αβ-dq coordinate transformation. After the coordinate transformation, the βα coordinate system is transformed into a dq coordinate system that rotates synchronously with the base frequency of the power grid. The base frequency model in the two-phase dq rotating coordinate system is:

[0035]

[0036] Figure 3 This is a control block diagram of a voltage source converter (VSC). VSC can use voltage and current dual closed-loop control or power and current dual closed-loop control. Figure 4 This is a bidirectional DC-DC control block diagram, which can also adopt voltage and current dual closed-loop control or power and current dual closed-loop control.

[0037] S4. Use coordinated control method to control the energy storage railway power regulator;

[0038] The coordinated control method proposed in this paper is as follows Figure 5 As shown in FIG. 1 , the specific method is to coordinate the control of ESS-RPC when power flows in both directions. α Using voltage control, VSC β When power control is adopted, the active power is transferred from VSC to β To VSC α The transfer is a positive power flow, that is, the active power is transferred from the power control side to the voltage control side. The active power flows in a positive direction. α To VSC β The transfer is a reverse flow of power, that is, the transfer of active power from the power control side to the voltage control side is a reverse flow.

[0039] The above method is used to distinguish the positive and negative power flows, and the coordinated control is for the VSC when the power flows forward. α Using voltage control, VSC β The ESS uses power control, and when the power flows in the reverse direction, the VSC α Switch to power control, VSC β First, power control is used, while ESS uses voltage control. After a delay, VSC β Using voltage control, VSC α The power control adopted with ESS ensures that the ESS-RPC system always works under the positive power flow.

[0040] The present invention is further described below by specific examples:

[0041] In this embodiment of the present invention, the conventional control method and the coordinated control method are compared. First, an energy storage railway power regulator system is built in MATLAB / Simulink, and the coordinated control method is simulated and compared with the conventional control method. Then, the two control methods are compared in the experimental platform, where pu is the per-unit value.

[0042] Simulation platform:

[0043] Under conventional control method, the power switching DC voltage diagram when the VSC AC inductance is L=1p.u under conventional control is as follows: Figure 6 (a), it is observed that there is no fluctuation in the DC voltage whether the power flows in the forward or reverse direction. Figure 6 (b) is the DC voltage waveform when the VSC AC inductance is L = 1.2pu under the conventional control strategy. When the power is transmitted in the forward direction, the ESS-RPC DC voltage is stable at 2000V, and the entire system operates stably. After 0.5s, the active power flows in the reverse direction, and the DC voltage will slowly oscillate, with an oscillation amplitude of about 120V, which shows that the conventional control strategy has poor robustness and stability.

[0044] Figure 7 (a) is the three-phase current of the power grid with L=1p.u under conventional control. The three-phase current remains symmetrical regardless of the forward or reverse power flow. 7(b) is the three-phase current diagram of the power grid with L=1.2pu. The three-phase current is symmetrical before 0-0.5s, and harmonics are found in the three-phase current after 0.5s, which will affect the power quality of the grid.

[0045] Figure 8 is the DC side voltage of ESS-RPC when L=1p.u and L=1.2pu under coordinated control. Figure 8 (a) Power switching is performed at 1s. Power flows forward from 1 to 1.5s, and VSC is used at this time. α The DC voltage is controlled and stabilized at 2000V. After the power switching is performed at 1.5s, the DC voltage produces a maximum overshoot of 139V, which is 6.95%, which is 81V less than the overshoot of conventional control. The power switching is performed again at 2s, and the VSC β Control the DC voltage. At this time, an overshoot of 166V is generated, which is 54V less than that of conventional control, and the DC voltage will not oscillate even if the power is reversed. Figure 8 (b) is the DC voltage diagram after the inductance L increases to 1.2pu. At 1s, an overshoot of 195V is generated. At 1.5s, the power switching generates an overshoot of 137V. Then the DC voltage stabilizes. At 2s, a secondary switching is performed, generating an overshoot of 168V. Comparing 8(a) and 8(b), it is found that the coordinated control strategy can keep the DC voltage stable when the inductance is perturbed, and the overshoot during power switching is smaller than that of the conventional control strategy. In summary, coordinated control under parameter perturbation can ensure the stability of the DC voltage of the cascade system, thereby ensuring the stability of the power transfer of the entire system, and has better robust stability.

[0046] Fig. 9 The three-phase current waveform of the power grid before and after the perturbation of L is shown in Figure 1. The control strategy is the same as the conventional control strategy when the power flows in the forward direction from 1 to 1.5 seconds. After 1.5 seconds, the DC voltage is controlled by energy storage, and it is found that the perturbation of L has almost no effect on the power grid current.

[0047] Experimental platform:

[0048] Fig.10 This is the experimental waveform of active power from positive to negative observed by the oscilloscope under the conventional control strategy L = 1.2pu. Fig.10 It is observed that the power flows in the forward direction from 0 to 0.2s, and the DC voltage is stable at 5V. After 0.2s, the power transmission direction changes, and the DC voltage keeps oscillating. Fig.11 The grid current diagram shows that the three-phase current oscillates after 0.03s.

[0049] Fig.12This is the experimental waveform of DC voltage with L=1.2pu under coordinated control. It can be found that the voltage is stable at 5V when the power flows forward. The DC voltage is also stable when the power flows in the reverse direction. Fig.13 It is found that the three-phase current is symmetrical.

[0050] The present invention aims at the phenomenon that the DC voltage of ESS-RPC fluctuates when the power flows bidirectionally under parameter perturbation of ESS-RPC: when the active power flows from VSC β To VSC α During the transfer, the ESS-RPC DC voltage remains stable, and when the active power is transferred from the VSC α To VSC β During the transfer, the ESS-RPC DC voltage oscillates, which in turn affects the system compensation performance and reduces the power quality.

[0051] The proposed new coordinated control method is used to solve this problem. Finally, the effectiveness of the proposed coordinated control method is verified through simulation and experiments. It is found that the coordinated control strategy eliminates the oscillation of the DC voltage of the traditional control strategy when the active power transmission direction changes, and finally stabilizes the DC voltage.

Claims

1. A coordinated control method for an energy storage railway power regulator, characterized in that: include: S1. Build a model of energy storage railway power conditioner traction power supply system using V / v traction transformer; S2. Use energy storage railway power regulator to balance the left and right power supply arms and manage the negative sequence current of the three-phase power grid; S3. The energy storage railway power conditioner is controlled by a coordinated control method. The coordinated control method is to coordinately control each converter so that the energy storage railway power conditioner always works in the power forward flow mode; the control method of each converter is that the voltage source converter at one end adopts voltage control, and the voltage source converter at the other side adopts power control, and the energy storage system adopts power control or voltage control; the power forward flow is the transfer of active power from the power control side to the voltage control side; the power reverse flow is the transfer of active power from the voltage control side to the power control side. The above method is used to distinguish the forward and reverse flows of power. When the coordinated control is the power forward flow, the VSC α Using voltage control, VSC β The ESS uses power control, and when the power flows in the reverse direction, the VSC α Switch to power control, VSC β First, power control is used, while ESS uses voltage control. After a delay, VSC β Using voltage control, VSC α The power control adopted with ESS ensures that the ESS-RPC system always works under the positive power flow.

2. A coordinated control method for energy storage railway power regulator according to claim 1, characterized in that S1 The model includes a V / v traction transformer, an α power supply arm, a β power supply arm, an α side step-down transformer, a β side step-down transformer, a railway power conditioner and an energy storage system; the railway power conditioner is connected in parallel between the α power supply arm and the β power supply arm through the α side step-down transformer and the β side step-down transformer respectively; the energy storage system is connected to the DC link of the railway power conditioner; the energy storage type railway power conditioner is composed of a back-to-back converter, a step-down transformer, a super capacitor, a DC capacitor, and a line inductor; the back-to-back converter includes an α side voltage source converter and a β side voltage source converter; the two converters are connected through a DC capacitor, and are respectively connected to the step-down transformers on both sides through line inductors; the super capacitor and the bidirectional DC-DC form an energy storage system connected to the railway power conditioner.

3. A coordinated control method for energy storage type railway power regulator according to claim 1, characterized in that S2 The energy storage railway power conditioner described in the invention transfers active power and reactive power to balance the left and right power supply arms; the energy storage railway power conditioner transfers part of the active power of the heavy-loaded arm to the light-loaded arm through the voltage source inverter, so that the active loads of the two arms are balanced, and then compensates for a certain reactive current, so that the three-phase current on the primary side of the V / v transformer is symmetrical and in phase with the voltage, thereby eliminating the negative sequence current and achieving balance, and at the same time controlling the ESS to absorb regenerative braking energy and supplying the stored energy to the traction power supply system.

4. According to a coordinated control method for an energy storage railway power conditioner according to any one of claims 1 to 3, the ESS-RPC system can be guaranteed to work in the forward direction regardless of the forward or reverse power flow, so that even if the parameters are perturbed, the DC voltage will not fluctuate, thereby solving the problem of DC voltage fluctuation caused by reverse power flow under parameter perturbation, thereby improving the robustness of the system.

Images