A static SVG device suitable for heavy-duty locomotive loads

Abstract

The application provides a static SVG device suitable for heavy load of a locomotive, relates to the field of railway power supply, and comprises a three-phase MMC converter, the three-phase MMC converter comprises three-phase bridge arms, each phase bridge arm is composed of an upper bridge arm and a lower bridge arm, the upper bridge arm comprises a plurality of cascaded half-bridge sub-modules, and the lower bridge arm comprises a plurality of cascaded half-bridge sub-modules, wherein the energy storage elements of the half-bridge sub-modules at least comprise super capacitors; further comprising: a voltage balancing module, which is used for determining the number of real-time input half-bridge sub-modules of the upper bridge arm and the lower bridge arm of each phase bridge arm, and determining the real-time input half-bridge sub-modules of the upper bridge arm and the lower bridge arm of each phase bridge arm based on the number of real-time input half-bridge sub-modules of the upper bridge arm and the lower bridge arm of each phase bridge arm; a network-forming voltage source control module, which is used for active control, reactive control and virtual impedance control, has the advantages of adapting to heavy load of a locomotive and improving the stability of power system operation.

Description

Technical Field

[0001] This invention relates to the field of railway power supply, and in particular to a static SVG device suitable for heavy-load locomotive loads. Background Technology

[0002] In the current wave of energy transition and transportation electrification, the new power system is facing numerous challenges. On the one hand, the large-scale and high-proportion integration of renewable energy into the grid, with its inherent intermittency and volatility, increases the difficulty of power grid power balancing. On the other hand, the grid connection of high-power impact loads such as heavy-haul railways brings strong power surges to the grid. The combined effect of these two factors leads to a series of problems in the grid, such as three-phase imbalance, phase flicker, and short-term frequency / voltage drops, seriously affecting the stable operation of the grid and power quality.

[0003] In existing technologies, rotating synchronous condensers are key equipment for ensuring grid stability and providing instantaneous energy support. However, with the increasing demands for response speed and regulation capacity in new power systems, existing rotating synchronous condensers have gradually revealed significant shortcomings. Their construction and maintenance costs are high, increasing the overall economic burden on the power system; furthermore, when faced with rapidly changing power demands, their response speed is slow, making it difficult to provide sufficient energy support in a short period and failing to fully meet the urgent needs of new power systems for instantaneous energy support.

[0004] Therefore, there is a need to provide a static SVG device suitable for heavy-load locomotive loads, in order to adapt to heavy-load locomotive loads and improve the stability of power system operation. Summary of the Invention

[0005] This invention provides a static SVG device suitable for heavy-duty locomotive loads, comprising a three-phase MMC converter, wherein the three-phase MMC converter includes three-phase bridge arms, each phase bridge arm consisting of an upper bridge arm and a lower bridge arm, the upper bridge arm including multiple cascaded half-bridge sub-models, and the lower bridge arm including multiple cascaded half-bridge sub-modules, wherein the energy storage element of each half-bridge sub-module includes at least a supercapacitor; further comprising: a voltage balancing module, used to determine the number of half-bridge sub-modules activated in real time in the upper and lower bridge arms of each phase bridge arm, and based on the number of half-bridge sub-modules activated in real time in the upper and lower bridge arms of each phase bridge arm, to determine the number of half-bridge sub-modules activated in real time in the upper and lower bridge arms of each phase bridge arm; and a grid-type voltage source control module, used for active power control, reactive power control, and virtual impedance control.

[0006] Furthermore, the energy storage element includes a supercapacitor and a thin-film capacitor connected in parallel.

[0007] Furthermore, the voltage balancing module is further used to: determine the number of half-bridge sub-modules to be put into operation in real time for the upper and lower arms of each phase bridge arm based on the DC side voltage value, the nominal voltage value of the energy storage element of the half-bridge sub-module, the reference voltage of each phase, and the compensation amount of each phase.

[0008] Furthermore, the voltage balancing module is further used to determine the number of half-bridge sub-modules engaged in real time for the upper and lower bridge arms of each phase arm based on the following formula:

[0009] N AP =V DC / (2*V 1 )-round((V A +HL A ) / V 1 )；

[0010] N AL =V DC / (2*V 1 )+round((V A -HL A ) / V 1 )；

[0011] N BP =V DC / (2*V 1 )-round((V B +H LB ) / V 1 )；

[0012] N BL =V DC / (2*V 1 )+round((V B -H LB ) / V 1 )；

[0013] N CP=V DC / (2*V 1 )-round((V C +H LC ) / V 1 )；

[0014] N CL =V DC / (2*V 1 )+round((V C -H LC ) / V 1 )；

[0015] in, N AP This refers to the number of half-bridge submodules that are deployed in real time for the upper arm of phase A. V DC This is the DC bus voltage. V 1 This is the rated voltage of the half-bridge submodule. V A This is the AC reference phase voltage of phase A. HL A This is the command signal for the A-phase circulating current. N AL This refers to the number of half-bridge submodules that are deployed in real time for the lower arm of phase A. N BP The number of half-bridge submodules deployed in real time for the upper arm of phase B bridge arm. V B This is the AC reference phase voltage of phase B. H LB This is the command signal for the B-phase circulating current. N BL This refers to the number of half-bridge submodules that are deployed in real time for the lower arm of phase B bridge arm. N CP The number of half-bridge submodules deployed in real time for the upper arm of the C-phase bridge arm. V C The AC reference phase voltage for phase C. H LC This is the command signal for the C-phase circulating current. N CL The number of half-bridge sub-modules that are put into operation in real time for the lower arm of the C-phase bridge arm.

[0016] Furthermore, the voltage balancing module is further used to: for the upper arm of each phase bridge arm, when the real-time activated half-bridge sub-module of the upper bridge arm is greater than 0 and less than the number of half-bridge sub-modules included in the upper bridge arm, determine the real-time activated half-bridge module of the upper bridge arm based on the direction of the bridge arm current and the state of the supercapacitor of each half-bridge sub-module included in the upper bridge arm.

[0017] For each phase bridge arm, when the number of half-bridge submodules put into operation in real time in the lower bridge arm is greater than 0 and less than the number of half-bridge submodules included in the lower bridge arm, the number of half-bridge submodules put into operation in real time in the lower bridge arm is determined based on the direction of the bridge arm current and the energy state and stress state of the supercapacitor of each half-bridge submodule included in the lower bridge arm.

[0018] Furthermore, the voltage balancing module is further used to: for each half-bridge submodule included in the upper bridge arm, calculate the comprehensive ranking index of the half-bridge submodule based on the port voltage of the half-bridge submodule, the remaining energy state of the supercapacitor of the half-bridge submodule, and the voltage change rate; and determine the real-time commissioning half-bridge submodules of the upper bridge arm and the commissioning or disconnection order of the half-bridge submodules included in the upper bridge arm based on the comprehensive ranking index of each half-bridge submodule.

[0019] Furthermore, the voltage equalization module is further used to calculate the comprehensive ranking index of the half-bridge submodules based on the following formula:

[0020] ,

[0021] in, For the first The comprehensive ranking index of each half-bridge sub-module , and As weight, , Let be the port voltage of the i-th half-bridge submodule. Let represent the current direction sign of the bridge arm containing the i-th half-bridge submodule. Let represent the remaining energy state of the supercapacitor in the i-th half-bridge submodule. Let be the voltage change rate of the supercapacitor in the i-th half-bridge submodule.

[0022] Furthermore, the voltage equalization module is further used to: adjust the voltage deviation amplitude based on the voltage deviation amplitude of each half-bridge submodule included in the bridge arm. The values ​​of β and γ are adjusted based on the load power, the rate of change of the bridge arm current, and the voltage fluctuation rate of each half-bridge submodule included in the bridge arm.

[0023] Furthermore, the grid-type voltage source control module is further used to: dynamically adjust the virtual rotational inertia coefficient based on the energy of the supercapacitor; and perform active power control based on the virtual rotational inertia coefficient.

[0024] Furthermore, the network-type voltage source control module is further used to: perform virtual impedance control based on a frequency segmentation adaptive algorithm.

[0025] Compared with existing technologies, the static SVG device provided by this invention, suitable for heavy-duty locomotive loads, has at least the following beneficial effects:

[0026] 1. Supercapacitors are used as the energy storage elements in the half-bridge sub-modules. Supercapacitors have high power density and fast charging and discharging characteristics, enabling them to quickly respond to power fluctuations in heavy-haul locomotive loads, effectively compensate for reactive power, and improve power quality. Thin-film capacitors enhance the stability and reliability of energy storage. The voltage balancing module can accurately determine the number of sub-modules to be engaged in real time for each phase arm and, based on various factors, determine the specific sub-modules to be engaged, avoiding overcharging and over-discharging of sub-modules, extending equipment lifespan, ensuring stable operation of the equipment under complex working conditions, and providing reliable power support for heavy-haul locomotives.

[0027] 2. Active power control based on dynamic adjustment of the virtual moment of inertia coefficient using supercapacitor energy enhances the system's ability to cope with power surges and maintains frequency stability. Virtual impedance control employing a frequency-segmented adaptive algorithm automatically adjusts impedance parameters according to system frequency changes, optimizing power distribution. The voltage balancing module accurately selects the input sub-modules through comprehensive ranking indicators, reducing voltage deviation and fluctuations, improving output voltage quality, effectively improving the power supply environment for heavy-duty locomotives, and reducing the impact on the power grid.

[0028] 3. The number and sequence of submodules are determined by comprehensively considering various factors to adapt to different operating conditions and load changes of heavy-duty locomotives. By adjusting the weighting coefficients, the control strategy can be flexibly optimized according to actual needs, enhancing the equipment's adaptability to complex environments. Simultaneously, reasonable voltage balance control avoids damage to submodules caused by uneven voltage, reducing equipment failure rates and lowering maintenance frequency and costs. Attached Figure Description

[0029] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0030] Figure 1 This is a schematic diagram of a stationary SVG device suitable for heavy-duty locomotive loads, according to some embodiments of this specification.

[0031] Figure 2This is a circuit diagram of a half-bridge sub-module according to some embodiments of this specification;

[0032] Figure 3 This is a circuit diagram of a half-bridge submodule according to other embodiments of this specification.

[0033] Figure 4 This is a schematic diagram of the operation of a half-bridge submodule in a locked state according to some embodiments of this specification;

[0034] Figure 5 This is a schematic diagram of the operation of a half-bridge submodule in the engaged state, according to some embodiments of this specification;

[0035] Figure 6 This is a schematic diagram illustrating the operation of a half-bridge submodule in a disconnected state according to some embodiments of this specification;

[0036] Figure 7 This is a load power variation diagram showing the energy storage element as a thin-film capacitor according to some embodiments of this specification;

[0037] Figure 8 This is a load power variation diagram showing the energy storage element as a supercapacitor according to some embodiments of this specification;

[0038] Figure 9 This is a load power variation diagram of the energy storage element being a thin-film capacitor connected in parallel with a supercapacitor, as shown in some embodiments of this specification;

[0039] Figure 10 This is a frequency component analysis diagram shown according to some embodiments of this specification. Detailed Implementation

[0040] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0041] Figure 1 This is a circuit diagram of a stationary SVG device suitable for heavy-duty locomotive loads, as shown in some embodiments of this specification. Figure 1 As shown, it includes a three-phase MMC converter, a voltage balancing module, and a grid-type voltage source control module.

[0042] A three-phase MMC converter consists of three phase arms, each consisting of an upper arm and a lower arm. The upper arm comprises multiple cascaded half-bridge sub-modules, and the lower arm comprises multiple cascaded half-bridge sub-modules. For example, each phase arm consists of 22 half-bridge sub-modules.

[0043] Figure 2 This is a circuit diagram of a half-bridge submodule shown in some embodiments of this specification, such as... Figure 2 As shown, this half-bridge submodule mainly consists of two transistors (VT) with anti-parallel diodes and an energy storage element, which is a supercapacitor. The input signal "PWM" undergoes AND and NOT operations to control the on / off states of the two VTs, thereby achieving precise control of the submodule's output state. When the two VTs are on or off, the half-bridge submodule can be connected to the circuit or bypassed, thus flexibly adjusting the output voltage and current of the three-phase MMC converter. The half-bridge submodule stores and releases energy through the charging and discharging of the capacitors. During normal operation, it can be orderly connected or disconnected according to system requirements, thereby constructing a near-sinusoidal multi-level voltage waveform, effectively reducing the harmonic content of the output voltage and improving power quality.

[0044] Figure 3 This is a circuit diagram of a half-bridge submodule shown according to other embodiments of this specification, such as... Figure 3As shown, in some embodiments, the energy storage element includes a supercapacitor and a thin-film capacitor connected in parallel. This parallel combination fully leverages the advantages of both, exhibiting superior performance in multiple aspects. From a frequency band shunting perspective, the two constitute a "physical filter." The thin-film capacitor has an extremely low equivalent series resistance (ESR) and strong high-frequency ripple current capability, enabling it to quickly respond to high-frequency ripple and fast voltage spikes in the μs to ms range. While the supercapacitor has a high energy density and a significantly higher ESR and moderate high-frequency ripple current capability, it can handle large energy and low-frequency pulsations (ms to s). In this way, high frequencies flow through the low-ESR channel of the thin-film capacitor, while low frequencies flow through the high-capacity channel of the supercapacitor, achieving a natural and efficient frequency band shunting. Regarding supercapacitor protection, high-frequency, large ripple currents can cause heating and ESR aging in the internal electrolytic system of the supercapacitor, leading to a significant decrease in cycle life. With the thin-film capacitor connected in parallel, the high-frequency ripple is absorbed by the thin-film capacitor, and the supercapacitor only needs to handle low-frequency energy, resulting in a significant reduction in its temperature rise and stress. Actual measurements show that the lifespan of supercapacitors can be increased from tens of thousands of cycles to hundreds of thousands of cycles, effectively extending their service life. The voltage ripple of the half-bridge submodule is mainly caused by bridge arm current pulsations, submodule connection / disconnection transients, and DC bus disturbances. After connecting a film capacitor in parallel, high-frequency components are absorbed by the film capacitor, while the supercapacitor handles the slowly changing voltage offset, reducing the submodule voltage ripple by 20-60%. When a peak occurs in the bridge arm current, if only the supercapacitor is used, the current rushing in directly will lead to ESR losses and temperature rise; after connecting a film capacitor in parallel, its extremely low ESR first absorbs the peak value, while the supercapacitor only handles the smoother component, making the three-phase MMC converter more stable, control easier to converge, and the bus more stable.

[0045] Furthermore, in the mid-frequency range (100Hz–1kHz), supercapacitors have higher impedance, while thin-film capacitors have lower impedance. Parallel connection of these capacitors reduces the equivalent impedance and improves stability. This not only increases the dynamic voltage control bandwidth of the submodule but also enhances the transient stability of VSG-based control. Parallel connection of supercapacitors and thin-film capacitors offers significant advantages in improving supercapacitor lifespan, reducing submodule voltage ripple, enhancing device safety, and improving dynamic performance and grid support capabilities.

[0046] like Figure 4As shown, both VT1 and VT2 are locked, which is similar to the blocking state of a two-level converter. This occurs when the modular multilevel converter is in a fault state, such as a severe DC-side short-circuit fault, but this mode does not exist during normal operation. When current flows from the positive bus to the AC output, it flows from the upper freewheeling diodes VD1 through the submodule capacitors to the AC output, charging the half-bridge submodule capacitors. When current flows from the AC output to the positive bus, it flows from the lower freewheeling diodes VD2 without passing through the submodule capacitors, bypassing the submodule capacitors. In this case, the submodule capacitors are bypassed. When both VTs are locked, only the half-bridge submodule capacitors are charged, with no possibility of discharge.

[0047] like Figure 5 As shown, with VT1 on and VT2 off, the current can still flow bidirectionally. When the current flows from the positive DC bus to the AC output terminal, the current will gradually flow from each freewheeling diode VD1 through the capacitor of the half-bridge sub-module to the AC output terminal, at which time the capacitor of the half-bridge sub-module will be charged. When the current flows from the AC output terminal to the positive DC bus, the current will gradually flow from the capacitor of each half-bridge sub-module through VT1 to the positive DC bus, at which time the capacitor of the half-bridge sub-module will be discharged.

[0048] like Figure 6 As shown, with VT1 off and VT2 on, the current can still flow bidirectionally. When the current flows from the positive DC bus to the AC output terminal, VT2 flows to the AC output terminal without passing through the capacitor of the half-bridge submodule, and the capacitor voltage of the half-bridge submodule is not affected. When the current flows from the AC output terminal to the positive DC bus, the current flows from each of the lower freewheeling diodes VD2 to the positive DC bus without passing through the capacitor of the half-bridge submodule, and the capacitor voltage of the half-bridge submodule is also not affected.

[0049] like Figure 1 As shown, a static SVG device suitable for heavy-duty locomotive loads may further include a voltage balancing module for determining the number of half-bridge sub-modules that are put into operation in real time for the upper and lower bridge arms of each phase arm, and determining the number of half-bridge sub-modules that are put into operation in real time for the upper and lower bridge arms of each phase arm based on the number of half-bridge sub-modules that are put into operation in real time for the upper and lower bridge arms of each phase arm.

[0050] Preferably, the voltage equalization module is further used for:

[0051] Based on the DC side voltage value, the nominal voltage value of the energy storage element of the half-bridge submodule, the reference voltage of each phase, and the compensation amount of each phase, the number of half-bridge submodules put into operation in real time for the upper and lower bridge arms of each phase is determined.

[0052] Specifically, the voltage balancing module is further used to determine the number of half-bridge sub-modules to be engaged in real time for the upper and lower arms of each phase arm based on the following formula:

[0053] N AP =V DC / (2*V 1 )-round((V A +HL A ) / V 1 )；

[0054] N AL =V DC / (2*V 1 )+round((V A -HL A ) / V 1 )；

[0055] N BP =V DC / (2*V 1 )-round((V B +H LB ) / V 1 )；

[0056] N BL =V DC / (2*V 1 )+round((V B -H LB ) / V 1 )；

[0057] N CP =V DC / (2*V 1 )-round((V C +H LC ) / V1 )；

[0058] N CL =V DC / (2*V 1 )+round((V C -H LC ) / V 1 )；

[0059] in, N AP This refers to the number of half-bridge submodules that are deployed in real time for the upper arm of phase A. V DC This is the DC bus voltage. V 1 This is the rated voltage of the half-bridge submodule. V A This is the AC reference phase voltage of phase A. HL A This is the command signal for the A-phase circulating current. N AL This refers to the number of half-bridge submodules that are deployed in real time for the lower arm of phase A. N BP The number of half-bridge submodules deployed in real time for the upper arm of phase B bridge arm. V B This is the AC reference phase voltage of phase B. H LB This is the command signal for the B-phase circulating current. N BL This refers to the number of half-bridge submodules that are deployed in real time for the lower arm of phase B bridge arm. N CP The number of half-bridge submodules deployed in real time for the upper arm of the C-phase bridge arm. V C The AC reference phase voltage for phase C. H LC This is the command signal for the C-phase circulating current. N CL The number of half-bridge sub-modules that are put into operation in real time for the lower arm of the C-phase bridge arm.

[0060] The voltage balancing module can determine the real-time activated half-bridge submodules for each phase arm based on the number of real-time activated half-bridge submodules in the upper and lower arms of each phase arm in any way. For example, it can directly use the bubble sort method to determine the real-time activated half-bridge submodules for each phase arm based on the number of real-time activated half-bridge submodules in the upper and lower arms of each phase arm. As an example only, for the upper arm, if the number of real-time activated half-bridge submodules in the upper arm is less than or equal to 0, then none of the half-bridge submodules in the upper arm are activated; if the number of real-time activated half-bridge submodules in the upper arm is greater than or equal to the total number of submodules included in the upper arm, then all of them are activated. If the number of real-time activated half-bridge submodules in the upper arm is greater than 0 and less than the total number of submodules included in the upper arm, then the activation strategy is determined according to the current direction ip of the arm. When ip>0, the current discharges the capacitor. To prevent the low-voltage half-bridge submodule from being too low, the submodules with the lowest voltage are selected and put into operation based on the number of half-bridge submodules put into operation in real time on the upper bridge arm. When ip≤0, the current charges the capacitor. To avoid the high-voltage submodule from being too high, the submodules with the highest voltage are selected and put into operation based on the number of half-bridge submodules put into operation in real time on the upper bridge arm.

[0061] The control logic of the lower bridge arm is similar to that of the upper bridge arm, and will not be elaborated here. In this way, a suitable half-bridge submodule can be selected from the sorted half-bridge submodules for operation based on real-time demand and current direction, achieving dynamic configuration of the half-bridge submodules in both the upper and lower bridge arms. This not only meets the system's power output requirements but also effectively balances the capacitor voltage of each half-bridge submodule, preventing damage to individual half-bridge submodules due to overcharging or over-discharging, thus improving the reliability and stability of the entire system.

[0062] Preferably, the voltage equalization module is further used for:

[0063] For the upper arm of each phase bridge arm, when the real-time activated half-bridge submodule of the upper bridge arm is greater than 0 and less than the number of half-bridge submodules included in the upper bridge arm, the real-time activated half-bridge submodule of the upper bridge arm is determined based on the direction of the bridge arm current and the state of the supercapacitor of each half-bridge submodule included in the upper bridge arm.

[0064] For each phase bridge arm, when the number of half-bridge submodules put into operation in real time in the lower bridge arm is greater than 0 and less than the number of half-bridge submodules included in the lower bridge arm, the number of half-bridge submodules put into operation in real time in the lower bridge arm is determined based on the direction of the bridge arm current and the energy state and stress state of the supercapacitor of each half-bridge submodule included in the lower bridge arm.

[0065] Specifically, the voltage balancing module is further used for:

[0066] For each half-bridge submodule included in the upper arm, a comprehensive ranking index of the half-bridge submodule is calculated based on the port voltage of the half-bridge submodule, the remaining energy state of the supercapacitor of the half-bridge submodule, and the voltage change rate.

[0067] Based on the comprehensive ranking index of each half-bridge submodule, the real-time deployment order of the half-bridge submodules in the upper arm and the deployment or removal order of the half-bridge submodules included in the upper arm are determined.

[0068] For example, the voltage balancing module is further used to calculate the overall ranking index of the half-bridge sub-modules based on the following formula:

[0069] ,

[0070] in, For the first The comprehensive ranking index of each half-bridge sub-module , and As weight, , Let be the port voltage of the i-th half-bridge submodule. Let represent the current direction sign of the bridge arm containing the i-th half-bridge submodule. Let represent the remaining energy state of the supercapacitor in the i-th half-bridge submodule. Let be the voltage change rate of the supercapacitor in the i-th half-bridge submodule.

[0071] The half-bridge sub-modules included in the upper arm can be sorted according to comprehensive ranking indicators, and the top ones can be selected. N AP Each half-bridge sub-module serves as a real-time input half-bridge module for the upper bridge arm.

[0072] The method for determining the real-time activation of the half-bridge sub-modules of the lower bridge arm is the same as the method for determining the real-time activation of the half-bridge sub-modules of the upper bridge arm, and will not be repeated here.

[0073] Preferably, the voltage equalization module is further used for:

[0074] The value of α is adjusted based on the voltage deviation amplitude of each half-bridge submodule included in the bridge arm;

[0075] The values ​​of β and γ are adjusted based on the load power, the rate of change of the bridge arm current, and the voltage fluctuation rate of each half-bridge submodule included in the bridge arm.

[0076] Specifically, the adjustment of the α value is mainly based on the voltage deviation amplitude of each half-bridge submodule in the bridge arm. When a submodule voltage deviation is large, it means that the system voltage balance is threatened, and the weight of α is increased. This is because a higher α will make the sorting algorithm focus more on the submodule voltage balance target, prioritizing the submodules that can quickly restore voltage balance and put them into operation, thereby effectively correcting voltage deviations and ensuring system stability. When the submodule voltage is within the allowable deviation range, the value of α is appropriately reduced, giving more control freedom to the energy regulation target, enabling the system to better achieve energy management while ensuring basic voltage balance.

[0077] The adjustment of β and γ values ​​needs to comprehensively consider the load power, the rate of change of the bridge arm current, and the voltage fluctuation rate of each half-bridge submodule. When the system detects sudden changes in load power, a bridge arm current rate of change exceeding a set threshold, or a significant increase in the voltage fluctuation rate of a submodule, the controller automatically enters the impact support mode, correspondingly increasing the weight ratio of β and γ. The purpose of this is to prioritize the operation of submodules with high supercapacitor energy margins and low current stress levels, ensuring that the impact energy is primarily borne by the supercapacitor channels, fully leveraging the advantages of rapid charging and discharging of supercapacitors. Meanwhile, the thin-film capacitors can focus on suppressing high-frequency voltage ripple, improving the system's ability to cope with complex operating conditions and its stability, ensuring safe and reliable system operation.

[0078] For example, setting , and Value constraints: ,in, for The minimum value, for The maximum value, for The minimum value, for The maximum value, for The minimum value, for The maximum value that can be obtained.

[0079] The following formula can be used to... The value needs to be adjusted:

[0080] ,

[0081] ,

[0082] in, For time t Values, This is the maximum voltage difference. Preset voltage Let be the average voltage of all half-bridge submodules in the arm containing the i-th half-bridge submodule. This represents the total number of half-bridge sub-modules included in the bridge arm.

[0083] Define impact strength index (normalized):

[0084] ,

[0085] in: For impact strength, Sudden changes in load power; : Rate of change of bridge arm current; : Voltage change rate of supercapacitor , and As weight, , The baseline value for power surge. : Reference value for rate of change of current : Voltage change rate reference value.

[0086] Define the activation function for the impact support mode. for:

[0087] ,

[0088] in, : Preset impact strength.

[0089] The value can be adjusted according to the following formula:

[0090] ,

[0091] ,

[0092] in, For time t Values, For time t Values.

[0093] Therefore, the voltage equalization module can calculate the comprehensive ranking index of the half-bridge sub-modules based on the following formula:

[0094] .

[0095] like Figure 1 As shown, a static SVG device suitable for heavy-duty locomotive loads can also be configured with a grid-type voltage source control module for active power control, reactive power control, and virtual impedance control.

[0096] Specifically, the active power control of the grid-type voltage source control module simulates the inertial characteristics of a synchronous generator. The rotor of a synchronous generator possesses inertia, and its inertial equation is:

[0097] ,

[0098] in, It is the moment of inertia, which reflects the magnitude of the rotor's inertia; It is the rotor angular velocity; Mechanical power is the power that drives the generator to rotate. It is electromagnetic power, which is the electrical power output by the generator; It is the damping coefficient; That is the rated angular velocity.

[0099] At the same time, it possesses the characteristic of active droop, and the equation is:

[0100] ,

[0101] in, It is a reference mechanical power. This is the active power droop coefficient, which allows adjustment of the mechanical power input based on the frequency deviation. Solving the two equations above, we can obtain the equation regarding... The expression:

[0102] ,

[0103] Based on this, the module can automatically adjust the output active power according to changes in the grid frequency, simulating the inertial response and primary frequency regulation function of a synchronous generator to maintain the stability of the grid frequency.

[0104] Reactive power control is achieved through the reactive power droop characteristic equation, namely:

[0105] ,

[0106] in, It is the output voltage amplitude; It is the amplitude of the no-load voltage; It is the Laplace operator; and It is the reactive power droop coefficient; It is the reference voltage amplitude; It is the rated voltage amplitude; It is a reference reactive power; This refers to the actual reactive power output. The grid-type voltage source control module can dynamically adjust the amplitude of the output voltage based on voltage and reactive power deviations, thereby regulating the output reactive power, achieving stable voltage control, and meeting the system's reactive power requirements.

[0107] Under non-decoupling conditions, the expression for virtual impedance control is:

[0108] ,

[0109] in, It is the reference current; It is a virtual inductance; It is the voltage at the point of common coupling; It is a virtual resistance. Through this control equation, the grid-connected voltage source control module simulates the characteristics of physical impedance at the control level, which can improve the dynamic performance of the equipment, suppress circulating current, improve the stability and reliability of the system, and enable the equipment to better adapt to changes in the power grid when operating in grid-connected mode.

[0110] As a preferred embodiment, the grid-type voltage source control module is further used for:

[0111] The virtual rotational inertia coefficient is dynamically adjusted based on the energy of the supercapacitor.

[0112] Active power control is performed based on the virtual rotational inertia coefficient.

[0113] Specifically, when the system experiences abnormal situations such as rapid frequency changes or sudden changes in active power, if the supercapacitor's energy margin is detected to be sufficient, the module will promptly increase the virtual rotational inertia coefficient. Because supercapacitors possess the characteristic of providing real energy support on a millisecond scale and can discharge rapidly, increasing the virtual rotational inertia coefficient enhances the transient active power support capability of the grid-type voltage source, effectively addressing sudden power changes in the system and maintaining system frequency stability.

[0114] When the supercapacitor's energy approaches its lower limit, the module automatically reduces its virtual rotational inertia coefficient to prevent DC voltage instability caused by over-discharge of the submodule. This is because thin-film capacitors can only handle high-frequency ripple and cannot provide inertia support. If a high virtual rotational inertia coefficient is maintained, the supercapacitor's continuous high-power output may cause problems such as DC-side voltage collapse.

[0115] Active power control is achieved based on dynamically adjusted virtual moment of inertia coefficients. By closely linking the energy state of supercapacitors with the virtual moment of inertia coefficients, the active power output of the grid-type voltage source can be adjusted in real time according to the energy status of the supercapacitors. This fully leverages the rapid response advantage of supercapacitors while ensuring the safe and stable operation of the system. Without supercapacitors, this "inertia-adaptive" regulation would lack a physical basis, making it difficult to achieve effective active power support and system stability control.

[0116] As a preferred embodiment, the grid-type voltage source control module is further used for:

[0117] Virtual impedance control is performed based on a frequency segmentation adaptive algorithm.

[0118] Specifically, in the high-frequency range (e.g., above 200Hz), the grid-type voltage source control module accurately determines the operating condition by monitoring the rate of change of current or voltage harmonics. Once the high-frequency range is entered, the grid-type voltage source control module increases the equivalent resistance component in the virtual impedance. At this time, it works in conjunction with the film capacitor in the half-bridge sub-module. The film capacitor, with its fast response characteristics, can effectively absorb high-frequency voltage and current ripple, reducing its impact on the system and ensuring the stable operation of the system under high-frequency disturbances. The high-frequency range refers to the operating range where the disturbance time scale is less than a single grid cycle and is mainly characterized by the rate of change of current or higher harmonics.

[0119] In the low-frequency (e.g., 0.1Hz~20Hz) and impulse power ranges, the grid-type voltage source control module reduces virtual impedance. Since supercapacitors have the capability to provide real energy support at the millisecond level, they undertake the primary energy exchange task in this range. Reducing virtual impedance avoids significant voltage drops caused by excessive virtual impedance, ensuring that the supercapacitor's energy can be output efficiently and stably, meeting the system's energy demands during low-frequency and high-power impulses. The low-frequency and impulse power ranges refer to operating intervals with disturbance timescales exceeding several grid cycles, characterized primarily by sudden changes in active power or frequency shifts.

[0120] For example, in the high-frequency band, the equivalent resistance component in the virtual impedance is increased according to the following formula:

[0121] ,

[0122] ,

[0123] in:

[0124] ,

[0125] in, For the complex frequency domain of virtual impedance, For frequency The equivalent resistance component in a changing virtual impedance. This refers to the equivalent inductance component in the virtual impedance. For complex variables in the complex frequency domain, This is the minimum value of the equivalent resistance. This is the maximum value of the equivalent resistance. This is the judgment coefficient for high-frequency operating conditions. A positive constant parameter is used to adjust the sensitivity of high-frequency operating condition determination. This is the absolute value of the rate of change of current.

[0126] For example, in the low-frequency impulse range, the virtual impedance can be reduced according to the following formula:

[0127] ,

[0128] in, This is the minimum value of the equivalent resistance. This is the minimum value of the equivalent inductance component in the virtual impedance, reducing the virtual impedance voltage drop and releasing the real energy channel of the supercapacitor.

[0129] The grid-type voltage source control module integrates the virtual inertia, reactive power droop, and virtual impedance parameters from the grid-type VSG control with the composite energy storage characteristics formed by the parallel connection of thin-film capacitors and supercapacitors within the half-bridge submodule. This integration subjects the dynamic external characteristics of the grid-type voltage source to online constraints based on actual available energy capacity, enabling the system to dynamically adjust its virtual impedance according to its own energy reserves and grid operating conditions. This significantly improves the system's stable operation under impact loads and weak grid conditions.

[0130] The following section, based on experiments, explains the beneficial effects of a stationary SVG device suitable for heavy-duty locomotive loads.

[0131] Under the same test conditions, the load power changes for energy storage elements of thin-film capacitors, supercapacitors, and parallel supercapacitors are categorized as follows: Figure 7 , Figure 8 ,and Figure 9 As shown, by Figure 7 , Figure 8 ,and Figure 9 It is known that while film capacitors can handle high-frequency ripple, their ability to buffer large energy changes when faced with sudden changes in load power is limited, resulting in poor power fluctuation suppression. Supercapacitors, due to their high ESR, generally have limited high-frequency ripple current capability, leading to internal heating and affecting lifespan, and their response to high-frequency power changes is not rapid enough. However, when a film capacitor is connected in parallel with a supercapacitor, during sudden load decreases of 1 second and increases of 1.8 seconds, the film capacitor quickly absorbs the high-frequency power changes, while the supercapacitor handles low-frequency, large energy fluctuations. The synergistic effect of the two effectively suppresses ripple caused by power surges, reduces the stress on each capacitor, extends the supercapacitor's lifespan, and improves stability and the ability to respond to power changes.

[0132] like Figure 10 As shown, a voltage balancing module, a three-phase MMC converter, and a grid-type voltage source control module of a static SVG device suitable for heavy-haul locomotive loads are combined to effectively reduce the load voltage THD (Total Harmonic Distortion) to 1.83%, significantly improving the system voltage quality and grid-type support capability, and fully verifying the excellent performance of this device in harmonic suppression and power quality improvement.

[0133] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A static SVG device suitable for heavy-duty locomotive loads, characterized in that, The device includes a three-phase MMC converter, wherein the three-phase MMC converter includes three-phase bridge arms, each bridge arm consists of an upper bridge arm and a lower bridge arm, the upper bridge arm includes multiple cascaded half-bridge sub-models, and the lower bridge arm includes multiple cascaded half-bridge sub-modules, wherein the energy storage element of the half-bridge sub-module includes at least a supercapacitor. Also includes: The voltage balancing module is used to determine the number of half-bridge sub-modules that are put into operation in real time for the upper and lower bridge arms of each phase bridge arm, and to determine the number of half-bridge sub-modules that are put into operation in real time for the upper and lower bridge arms of each phase bridge arm based on the number of half-bridge sub-modules that are put into operation in real time for the upper and lower bridge arms of each phase bridge arm. A grid-type voltage source control module is used for active power control, reactive power control, and virtual impedance control. The voltage equalization module is further used for: Adjust based on the voltage deviation amplitude of each half-bridge submodule included in the bridge arm. The value of ; Based on the load power, the rate of change of the bridge arm current, and the voltage fluctuation rate of each half-bridge submodule included in the bridge arm, adjust... and The value of ; The overall ranking index of the half-bridge submodule is calculated based on the following formula: ， in, Let be the comprehensive ranking index for the i-th half-bridge submodule. , and As weight, , Let be the port voltage of the i-th half-bridge submodule. Let represent the current direction sign of the bridge arm containing the i-th half-bridge submodule. Let represent the remaining energy state of the supercapacitor in the i-th half-bridge submodule. Let be the voltage change rate of the supercapacitor in the i-th half-bridge submodule; Based on the comprehensive ranking index of each half-bridge submodule, the real-time deployment order of the half-bridge submodules in the upper arm and the deployment or removal order of the half-bridge submodules included in the upper arm are determined.

2. A static SVG device suitable for heavy-duty locomotive loads according to claim 1, characterized in that, The energy storage elements include supercapacitors and thin-film capacitors connected in parallel.

3. A static SVG device suitable for heavy-duty locomotive loads according to claim 1 or 2, characterized in that, The voltage equalization module is further used for: Based on the DC bus voltage, the rated voltage of the half-bridge submodule, the AC side reference phase voltage of each phase, and the command signal of the circulating current of each phase, the number of half-bridge submodules put into operation in real time for the upper and lower bridge arms of each phase is determined.

4. A static SVG device suitable for heavy-duty locomotive loads according to claim 3, characterized in that, The voltage balancing module is further used to determine the number of half-bridge sub-modules to be engaged in real time for the upper and lower bridge arms of each phase arm based on the following formula: ； ； ； ； ； ； Among them, N AP This refers to the number of half-bridge submodules that are deployed in real time for the upper arm of phase A. V DC This is the DC bus voltage. V 1 This is the rated voltage of the half-bridge submodule. V A This is the AC reference phase voltage of phase A. HL A This is the command signal for the A-phase circulating current. N AL This refers to the number of half-bridge submodules that are deployed in real time for the lower arm of phase A. N BP The number of half-bridge submodules deployed in real time for the upper arm of phase B bridge arm. V B This is the AC reference phase voltage of phase B. H LB This is the command signal for the B-phase circulating current. N BL This refers to the number of half-bridge submodules that are deployed in real time for the lower arm of phase B bridge arm. N CP The number of half-bridge submodules deployed in real time for the upper arm of the C-phase bridge arm. V C The AC reference phase voltage for phase C. H LC This is the command signal for the C-phase circulating current. N CL The number of half-bridge sub-modules that are put into operation in real time for the lower arm of the C-phase bridge arm.

5. A static SVG device suitable for heavy-duty locomotive loads according to claim 4, characterized in that, The voltage equalization module is further used for: For the upper arm of each phase bridge arm, when the real-time activated half-bridge submodule of the upper bridge arm is greater than 0 and less than the number of half-bridge submodules included in the upper bridge arm, the real-time activated half-bridge submodule of the upper bridge arm is determined based on the direction of the bridge arm current and the state of the supercapacitor of each half-bridge submodule included in the upper bridge arm. For each phase bridge arm, when the number of half-bridge submodules put into operation in real time in the lower bridge arm is greater than 0 and less than the number of half-bridge submodules included in the lower bridge arm, the number of half-bridge submodules put into operation in real time in the lower bridge arm is determined based on the direction of the bridge arm current and the energy state and stress state of the supercapacitor of each half-bridge submodule included in the lower bridge arm.

6. A static SVG device suitable for heavy-duty locomotive loads according to claim 1 or 2, characterized in that, The grid-type voltage source control module is further used for: The virtual rotational inertia coefficient is dynamically adjusted based on the energy of the supercapacitor. Active power control is performed based on the virtual rotational inertia coefficient.

7. A static SVG device suitable for heavy-duty locomotive loads according to claim 6, characterized in that, The grid-type voltage source control module is further used for: Virtual impedance control is performed based on a frequency segmentation adaptive algorithm.

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