Hybrid energy storage type railway power conditioner virtual machine control method

Abstract

This invention relates to a hybrid energy storage railway power regulator technology under a virtual motor control system. It introduces a virtual inertial element into the current compensation strategy of the railway power regulator and employs virtual DC motor control in the hybrid energy storage system. Power quality is managed through the railway power regulator, and regenerative braking energy is recovered and utilized by connecting to the hybrid energy storage device. A segmented adaptive power allocation strategy based on the filtering time constant of the energy storage unit's state of charge and a dynamic adjustment strategy for limited power within the hybrid energy storage system are adopted. By adjusting the filtering time constant, "shallow charging and discharging" of the battery is ensured, with the supercapacitor handling the remaining power after the battery bears part of the load. A virtual inertial element is introduced to provide inertial support compared to the traditional control of railway power regulators, and virtual DC motor control is used for the hybrid energy storage system. This results in frequency stability under load fluctuations, as well as better dynamic performance and anti-interference capabilities.

Description

Technical Field

[0001] This invention relates to a control method based on an energy storage type railway power regulator, and more particularly to a virtual motor control method for a hybrid energy storage type railway power regulator. Background Technology

[0002] With the development of high-speed railways in my country, harmonics and reactive power continue to affect the safety and stability of railway traffic, and the problem of negative sequence is becoming increasingly serious, posing a severe challenge to the healthy and safe operation of railway power supply systems. For example, the Sichuan-Tibet Railway, which is currently under construction, experiences extreme changes in traction power due to factors such as large altitude differences and numerous long and steep sections, posing a significant challenge to the power supply capacity of the traction system.

[0003] Because traction power supply systems widely adopt a three-phase to two-phase power supply method, supplying power to single-phase power supply arms via the secondary side, it is difficult for the traction load in the power supply section to be in a balanced state. The three-phase side is prone to imbalance, leading to a large amount of negative sequence components entering the power supply system and affecting the safe operation of the power system. Simultaneously, electric locomotives, as high-power loads, also affect the balance of the power supply system; negative sequence currents can cause damage to motors in the power grid and malfunctions in relay protection devices. Similarly, the presence of harmonic components also causes additional power losses to electrical equipment.

[0004] The Sichuan-Tibet Railway traverses a region of varying altitudes and numerous long, steep slopes, generating significant regenerative braking energy during high-speed train operation. A large portion of this regenerative braking energy is fed back into the power grid. Furthermore, because this energy contains substantial negative-sequence and harmonic components, its feedback negatively impacts the stability of the power system. Therefore, power companies have implemented a "reverse feedback, positive accounting" system, charging for regenerative braking energy as if it were consumed electricity. This results in substantial economic losses for the railway system. Therefore, addressing energy consumption issues and improving the utilization rate of regenerative braking energy is crucial.

[0005] Domestic and international research has been conducted on power quality management related to traction power supply systems, and solutions can be divided into two categories. The first is external compensation devices, such as static var compensators (SVCs) for dynamic reactive power compensation, or passive filters for harmonic elimination and reactive power compensation. The second is optimization of the power supply system itself, such as traction network expansion or new in-phase power supply technologies. However, the first method has limitations in power quality management, and the second method involves traction network reconstruction, which is costly and impractical. To simultaneously achieve functions such as harmonic suppression, power factor improvement, and negative sequence component suppression, thereby improving power quality, equipment combinations must be considered. After 1980, Japanese scholars proposed the Railway Power Conditioner (RPC), which can achieve comprehensive compensation for the traction power supply system and solve almost all power quality problems. Simultaneously, energy storage devices can be added to the DC side of the RPC to utilize regenerative braking energy. Currently, there are many RPC control methods. Domestic research teams have proposed deadbeat control based on repetitive prediction and a dual closed-loop control based on real-time current detection, both of which can achieve power quality management. However, the traction power supply system, as a weak AC system, has poor damping and inertia. Under these control methods, due to the relatively small inertia exhibited by the RPC, it cannot provide damping and inertial support under dynamic traction network conditions, and the system cannot maintain stability. Therefore, this invention proposes a virtual inertial control based on traditional dual closed-loop control to provide damping and inertial support for the system, thereby improving the stability of the traction power supply system under dynamic loads.

[0006] Regarding external energy storage devices, the main energy storage components currently used include batteries and supercapacitors. Among these, battery energy storage has advantages such as high energy density, relatively low cost, and long lifespan, while supercapacitor energy storage has advantages such as high power density and fast charge / discharge response. Both types of energy storage have their own advantages. Therefore, this invention, tailored to the characteristics of the Sichuan-Tibet railway line, adopts a hybrid energy storage device connected to the DC bus side of the railway power regulator. Based on the traditional power control of the energy storage components, virtual motor control is introduced to further improve the system's damping and inertial support, thereby enhancing the reliability of the traction power supply system and the railway power regulator. This makes it suitable for various extreme operating conditions in the traction network. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by proposing a virtual motor control method for a hybrid energy storage type railway power regulator, comprising the following steps:

[0008] Establish a general current compensation strategy to achieve comprehensive compensation for negative sequence, reactive, and harmonic currents;

[0009] By using a segmented adaptive power allocation based on the filtering time constant of the energy storage unit's state of charge to smooth the power of the hybrid energy storage system, the power fluctuations are divided into high-frequency components and low-frequency components, which are handled by supercapacitors and batteries respectively, thus achieving energy complementarity in hybrid energy storage.

[0010] A hybrid energy storage system with dynamic adjustment of limited power is adopted, in which the battery first bears the limited power, and then the supercapacitor bears the remaining power.

[0011] A VDCM control system is established for hybrid energy storage to simulate the inertia and damping of a DC motor.

[0012] A virtual inertial control system is established. Based on the original current compensation and DC voltage regulation control, a virtual inertial element is introduced to replace the voltage phase-locked loop of the railway power regulator, thereby achieving frequency stability under load fluctuations.

[0013] Based on the above scheme, the current compensation strategy is specifically as follows:

[0014] Active power compensation: Assuming α arm is the light load side and β arm is the heavy load side, half of the current difference between the two phases is transferred to β arm through the railway power regulator, so that the active current components of the two phases are consistent.

[0015] As shown in equations (1) and (2), the currents of phase A and phase B after compensation are:

[0016]

[0017]

[0018] Reactive current compensation: Through active current compensation, the current amplitudes of phases A and B are equal. The reactive current that leads phases A and B by 90 degrees is compensated respectively, as shown in equation (3). The reactive current amplitude used for compensation is:

[0019] I Aactive =I Breactive =I' A tan30° (3)

[0020] Harmonic current compensation: A compensation current with the same magnitude but opposite phase to the harmonic current of the locomotive load is generated by the railway power regulator to counteract the harmonic current generated by the locomotive load, as shown in equation (4):

[0021]

[0022] In the formula, I Lh I Rh The effective value of the h-th harmonic current of the left and right power supply arms; φ Lh φ RhThese represent the h-th harmonic current phases of the left and right power supply arms, respectively.

[0023] Based on the above scheme, the power fluctuation is specifically divided into high-frequency components and low-frequency components as follows:

[0024] The low-frequency power command handled by the battery is as follows:

[0025]

[0026] T is the filtering time constant in the filter, P HESS This represents the power fluctuation value.

[0027] P HESS The remaining high-frequency power is supplied by the supercapacitor, whose instructions are as follows:

[0028]

[0029] When the energy storage unit is in the charging state, first determine whether the SOC is low and charge more. If the SOC of the supercapacitor is small, increase T, then ΔT is positive; if the battery should be charged more, decrease T, then ΔT is negative.

[0030]

[0031] When the two energy storage units discharge, if the supercapacitor has a high SOC, then ΔT is positive; if the battery has a high SOC, then ΔT is negative; the larger SOC is used as the adjustment ratio.

[0032]

[0033] Based on the above scheme, the internal coordination control strategy of the hybrid energy storage system is specifically as follows:

[0034] The output power of the battery is the minimum of the rated discharge power and the target power; as shown in equation (9):

[0035] P bat (k)=min{P' bat (k),P cmax_bat} (9)

[0036] The discharge power of a supercapacitor is the minimum of its rated discharge power and remaining power, as shown in equation (10):

[0037] P SC (k)=min{|P ESref (k)-P bat (k)|,P cmax_SC} (10)

[0038] Based on the above scheme, the VDCM control specifically includes:

[0039] Equation (16) is the mechanical equation of the synchronous motor. The synchronous angular frequency ω of the control system is generated by the expected active power, thereby replacing the traditional voltage phase-locked loop and realizing RPC control in the form of a power phase-locked loop.

[0040]

[0041] In the formula, ω is the angular velocity of the DC motor, ω N Where J is the rated angular velocity of the DC motor, and T is the moment of inertia. m T e These are mechanical and electromagnetic torques, respectively.

[0042]

[0043]

[0044] E=C T Φω (19)

[0045] In the formula, CT is the torque coefficient of the DC motor, and Ф is the magnetic flux per pole of the DC motor;

[0046] Based on the above scheme, the virtual inertial control specifically refers to:

[0047] The desired power P is taken as the mechanical power P. m The output power is the electromagnetic power P. e ;

[0048] Based on equations (17), (18), and (19) to simulate the inertia and damping characteristics of a DC motor, the armature current I is obtained. bat_ref The duty cycle is obtained through the inner current loop;

[0049] The control signal for the switching transistor is obtained through PWM modulation.

[0050] The beneficial effects of this invention are:

[0051] This invention achieves energy complementarity among energy storage components through a hybrid energy storage system and power distribution control, maximizing the utilization of regenerative braking energy while improving power quality in the traction power supply system. Compared to traditional control strategies, this invention proposes a virtual motor control system applied to the RPC and energy storage device. This strategy provides inertial and damping support to the system through a virtual inertial element and VDCM control strategy, smoothing DC bus disturbances and maintaining power transmission balance, thereby enhancing the stability of the entire system. Furthermore, under traction load fluctuations, it can ensure the frequency and power stability of the traction power supply system, improving the overall system's anti-disturbance performance. Attached Figure Description

[0052] The present invention includes the following figures:

[0053] Figure 1 System equivalent model

[0054] Figure 2 RPC compensation principle phasor diagram

[0055] Figure 3 Hybrid Energy Storage Equivalent Model

[0056] Figure 4 Adaptive power allocation algorithm diagram for energy storage units

[0057] Figure 5 Internal Coordination Control Strategy of Hybrid Energy Storage System

[0058] Figure 6 Virtual inertial control topology

[0059] Figure 7 VDCM control topology

[0060] Figure 8 Comparison of dynamic control effects after introducing a virtual motor control system (left arm abruptly changes from 5MW to 20MW in 0.5s). Detailed Implementation

[0061] The following combination Figure 1-8 The present invention will be described in further detail below.

[0062] A virtual motor control method for a hybrid energy storage type railway power regulator includes the following steps:

[0063] Step 1: Topology of hybrid energy storage railway power regulator and comprehensive compensation for negative sequence and harmonic currents;

[0064] like Figure 1 As shown, the system mainly consists of three parts: a three-phase V / V traction power supply system, a railway power regulator, and a hybrid energy storage device.

[0065] The key principle of RPC compensation lies in detecting the command current required for RPC power quality management, thereby controlling the inverter current to track the reference current in real time. Its compensation includes two parts: negative sequence and harmonic current compensation.

[0066] Negative sequence current compensation:

[0067] The principle of RPC negative sequence current compensation is as follows: Based on the energy flow characteristics of RPC, active and reactive power compensation is performed on the current of the left and right power supply arms of the traction power supply system respectively to achieve power balance of the two power supply arms, so that the three-phase current on the grid side of the V / V transformer is completely symmetrical and the three-phase power factor is 1, thus eliminating the negative sequence component.

[0068] like Figure 2It can be seen that the three-phase current on the primary side is unbalanced and has obvious negative sequence components.

[0069] Active current compensation: such as Figure 2 As shown in (b), active current compensation can make the two active loads equal. Assuming that arm α is the light load side and arm β is the heavy load side, in order to balance the supply current of the two arms, the RPC needs to transfer half of the current difference between the two phases to arm β, so that the active current components of the two phases are consistent. Finally, the current amplitudes of phases A and B are equal. As shown in equations (1) and (2), the currents of phases A and B after compensation are:

[0070]

[0071]

[0072] Reactive current compensation: While active current compensation results in phases A and B having equal current amplitudes, phase C's current differs from the other two phases, requiring compensation for both phase and amplitude. Therefore, reactive current compensation is necessary for correction. For example... Figure 2 As shown in (c), reactive current leading by 90 degrees is compensated for in phases A and B respectively, and the amplitude of the reactive current used for compensation is:

[0073] I Aactive =I Breactive =I' A tan30° (3)

[0074] like Figure 1 As shown in (c), after compensation, the amplitudes of the three-phase currents A, B, and C are consistent, and they are in phase with the three-phase voltages respectively.

[0075] Harmonic current compensation:

[0076] Because the load of electrified railway locomotives generates harmonics, harmonic current compensation is required. A compensation current, equal in magnitude but opposite in phase to the harmonic current of the locomotive load, is generated by an RPC to counteract the harmonic current generated by the locomotive load, as shown in equation (4):

[0077]

[0078] In the formula, I Lh I Rh The effective value of the h-th harmonic current of the left and right power supply arms; φ Lh φ Rh These represent the h-th harmonic current phases of the left and right power supply arms, respectively.

[0079] Step 2: Power allocation strategy based on low-pass filter and internal coordination control strategy of hybrid energy storage system based on dynamic adjustment of limiting power;

[0080] like Figure 3The diagram illustrates a hybrid energy storage topology. To fully utilize the energy characteristics of different types of energy storage devices in a hybrid energy storage system, power distribution needs to be considered in a system composed of batteries and supercapacitors. Based on the respective advantages of supercapacitors and batteries, a low-pass filter is used to smooth the power of the hybrid energy storage system. For traditional hybrid energy storage power distribution control strategies, when regenerative braking energy is recovered, a low-pass filter can separate power fluctuations into high-frequency and low-frequency components, which are handled by the supercapacitor and battery respectively. The low-frequency power command handled by the battery is as follows:

[0081]

[0082] T is the filtering time constant in the filter, P HESS This represents the power fluctuation value. P HESS The remaining high-frequency power is supplied by the supercapacitor, whose instructions are as follows:

[0083]

[0084] At this point, the control strategy block diagram of the low-pass filter power allocation algorithm is as follows: Figure 4 As shown in (a).

[0085] A larger T results in a smaller cutoff frequency and narrower passband of the low-pass filter, leading to less power allocated to the battery and a greater power load on the supercapacitor. Conversely, a smaller T results in more power allocated to the battery and less power allocated to the supercapacitor. Therefore, by setting an appropriate T, energy management optimization of the energy storage unit can be achieved, such as... Figure 4 As shown in (b), by comprehensively considering the SOC of the battery and the supercapacitor, the time constant is dynamically adjusted, exhibiting self-adaptability.

[0086] When the energy storage unit is charging, first determine whether to charge more if the SOC is low. If the supercapacitor's SOC is low, then T should be increased, and ΔT should be positive. Furthermore, a larger SOC weight should be selected as the adjustment ratio to speed up the adjustment process. If the battery needs more charging, then T should be decreased, and ΔT should be negative.

[0087]

[0088] When both energy storage units discharge, the one with the higher SOC should discharge more. If the supercapacitor has a higher SOC, then ΔT is positive; if the battery has a higher SOC, then ΔT is negative. The adjustment ratio is based on the larger SOC.

[0089]

[0090] like Figure 5The diagram shows the internal coordination control strategy of the hybrid energy storage system. To achieve the goal of limiting battery power, the output value of the battery should be the minimum of the rated discharge power value and the target power value, as shown in equation (9):

[0091] P bat (k)=min{P' bat (k),P cmax_bat} (9)

[0092] After the battery bears part of the power, the remaining power is borne by the supercapacitor. Similarly, the discharge power of the supercapacitor should be the minimum of the supercapacitor's rated discharge power and remaining power, as shown in equation (10):

[0093] P SC (k)=min{|P ESref (k)-P bat (k)|,P cmax_SC} (10)

[0094] The depth of charge and discharge of a battery has a significant impact on its cycle life; an increased depth of charge and discharge leads to a shorter lifespan. Therefore, charge and discharge control should adhere to the "shallow charge and shallow discharge" principle as much as possible. This paper proposes an energy management control strategy based on a dynamic adjustment of the limiting power of the battery's SOC value, taking into account a deviation of 50% from the battery's SOC value. When the battery's SOC value is close to 50% and within its optimal operating range, the battery's output is limited to its maximum rated power, with the remaining power handled by the supercapacitor. When the battery's SOC value deviates from 50% and is within the charge and discharge warning zone, the limiting power borne by the battery is reduced, and the remaining power is handled by the supercapacitor.

[0095] 1) Battery charging power

[0096] At this time P ESref (k)<0,P' bat (k)<0,P cmax_bat If the value is less than 0, the limit should be set to a larger value. Its charging power is:

[0097]

[0098]

[0099] When SOC bat The greater the deviation from 50%, the smaller the value of λ, and the smaller the output power that the battery can bear.

[0100] 2) Supercapacitor charging power

[0101] At this time P ESref (k)<0,P bat (k)<0,Pcmax_bat If the value is less than 0, the limit should be set to a larger value. When the battery only provides partial power, the supercapacitor charging power is:

[0102] P SC (k)=max{P ESref (k)-P bat (k),P cmax_SC} (13)

[0103] 3) Battery discharge power

[0104] At this time P ESref (k)>0,P' bat (k)>0,P dmax_bat If the value is greater than 0, the limiting value should be larger. Its discharge power is:

[0105]

[0106] 4) Supercapacitor charging power

[0107] At this time P ESref (k)>0,P bat (k)>0,P dmax_bat >0, the limiting value should be a larger value. When the battery only bears part of the power, the discharge power of the supercapacitor is:

[0108] P SC (k)=min{P ESref (k)-P bat (k),P dmax_SC} (15)

[0109] Step 3: Construct an RPC system based on virtual inertial control and a hybrid energy storage system based on VDCM control:

[0110] like Figure 6 The diagram shows the RPC control block diagram with the introduction of a virtual inertial element. Equation (14) is the mechanical equation of the synchronous motor. By simulating this equation, the synchronous angular frequency ω of the control system is generated through the desired active power, thus replacing the traditional voltage phase-locked loop and realizing RPC control in the form of a power phase-locked loop.

[0111]

[0112] In the formula, ω is the angular velocity of the DC motor, ω N Where J is the rated angular velocity of the DC motor, and T is the moment of inertia. m T e These are mechanical and electromagnetic torque, respectively.

[0113]

[0114]

[0115] E=C T Φω (19)

[0116] In the formula C T Φ is the torque coefficient of the DC motor, and Ф is the magnetic flux per pole of the DC motor.

[0117] like Figure 7 The diagram shown is a VDCM control block diagram for an energy storage system. The desired power P is taken as the mechanical power P. m The output power is the electromagnetic power P. e Based on the mechanical rotation equation (17) and the armature circuit electromotive force balance equations (18) and (19), the inertia and damping characteristics of the DC motor are simulated, and the armature current I is obtained. bat_ref The duty cycle is obtained through the inner current loop, and finally the control signal for the switching transistor is obtained through PWM modulation. When the traction load power output fluctuates, the energy storage converter using the VDCM control strategy can quickly adjust the angular velocity ω, and then regulate the armature electromotive force.

[0118] Step 4: Simulation Verification

[0119] The correctness of the conclusions was verified by simulation using the MATLAB / Simulink platform.

[0120] like Figure 8 The image shows a comparison of the control effects of an energy storage-type RPC under a virtual motor control system. Figure 8 (a) A comparison was made between the energy storage converter VDCM and the traditional PI control. The VDCM control provides inertial damping support, which reduces the output power regulation time by 30% and allows for flexible changes in response regulation.

[0121] Figure 8 (b) shows a comparison of the RPC results of virtual inertial link control and traditional control. It can be seen that under a 0.5s load change, the RPC output frequency fluctuation under traditional control will last for a long time and deviate from the normal frequency by up to -1.5Hz. However, the RPC with virtual inertia added has a stable output frequency of 50Hz and has better stability.

[0122] The above embodiments are for illustrative purposes only and are not intended to limit the scope of this invention. Those skilled in the art can make various changes and modifications without departing from the essence and scope of this invention. Therefore, all equivalent technical solutions also fall within the scope of this invention, and the patent protection scope of this invention should be defined by the claims. Content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A virtual motor control method for a hybrid energy storage type railway power regulator, characterized in that, Includes the following steps: Establish a general current compensation strategy to achieve comprehensive compensation for negative sequence, reactive, and harmonic currents; By using a segmented adaptive power allocation based on the filtering time constant of the energy storage unit's state of charge to smooth the power of the hybrid energy storage system, the power fluctuations are divided into high-frequency components and low-frequency components, which are handled by supercapacitors and batteries respectively, thus achieving energy complementarity in hybrid energy storage. A hybrid energy storage system with dynamic adjustment of limited power is adopted, in which the battery first bears the limited power, and then the supercapacitor bears the remaining power. A VDCM control system is established for hybrid energy storage to simulate the inertia and damping of a DC motor. A virtual inertial control is established. Based on the original current compensation and DC voltage regulation control, a virtual inertial element is introduced to replace the voltage phase-locked loop of the railway power regulator, so as to achieve frequency stability under load fluctuations. The current compensation strategy is specifically as follows: Active power compensation: Assuming α arm is the light load side and β arm is the heavy load side, half of the current difference between the two phases is transferred to β arm through the railway power regulator, so that the active current components of the two phases are consistent. As shown in equations (1) and (2), the currents of phase A and phase B after compensation are: ; ; Reactive current compensation: Through active current compensation, the current amplitudes of phases A and B are equal. The reactive current that leads phases A and B by 90 degrees is compensated respectively, as shown in equation (3). The reactive current amplitude used for compensation is: ; Harmonic current compensation: A compensation current with the same magnitude but opposite phase to the harmonic current of the locomotive load is generated by the railway power regulator to counteract the harmonic current generated by the locomotive load, as shown in equation (4): ; In the formula, I Lh I Rh The effective value of the h-th harmonic current of the left and right power supply arms; These are the phases of the h-th harmonic currents of the left and right power supply arms, respectively. The specific internal coordination and control strategy of the hybrid energy storage system is as follows: The output power of the battery is the minimum of the rated discharge power and the target power; as shown in equation (9): ; The discharge power of a supercapacitor is the minimum of its rated discharge power and remaining power, as shown in equation (10): ; The VDCM control specifically refers to: Equation (16) is the mechanical equation of the synchronous motor. The synchronous angular frequency ω of the expected active power generation control system replaces the traditional voltage phase-locked loop and realizes RPC control in the form of a power phase-locked loop. ; In the formula, ω is the angular velocity of the DC motor, ω N Where J is the rated angular velocity of the DC motor, and T is the moment of inertia. m T e These are mechanical and electromagnetic torques, respectively. ; ; ; In the formula C T Φ is the torque coefficient of the DC motor, and Ф is the magnetic flux per pole of the DC motor.

2. The virtual motor control method for a hybrid energy storage type railway power regulator as described in claim 1, characterized in that, The power fluctuation is divided into high-frequency components and low-frequency components, specifically: The low-frequency power command handled by the battery is as follows: ; T is the filtering time constant in the filter, P HESS This represents the power fluctuation value. P HESS The remaining high-frequency power is supplied by the supercapacitor, whose instructions are as follows: ; When the energy storage unit is in the charging state, first determine whether the SOC is low and charge more. If the SOC of the supercapacitor is small, increase T, then ΔT is positive; if the battery should be charged more, decrease T, then ΔT is negative. ; When both energy storage units discharge, if the supercapacitor has a high SOC, then ΔT is positive; if the battery has a high SOC, then ΔT is negative; the larger SOC is used as the adjustment ratio. 。 3. The virtual motor control method for a hybrid energy storage type railway power regulator as described in claim 2, characterized in that, The virtual inertial control specifically refers to: The desired power P is taken as the mechanical power P. m The output power is the electromagnetic power P. e ; Based on equations (17), (18), and (19), the armature current I is obtained by simulating the inertia and damping characteristics of a DC motor. bat_ref The duty cycle is obtained through the inner current loop; The control signal for the switching transistor is obtained through PWM modulation.

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