An electrified railway flexible converter parameter optimization design method based on double-frequency energy optimal distribution

Abstract

The application relates to an electrified railway flexible converter parameter optimization design method, device, equipment, medium and program product based on double-frequency energy optimized distribution. The method comprises the following steps: determining double-frequency energy according to the instantaneous characteristics of single-phase modular multilevel converter corresponding single-phase side output power; obtaining a double-frequency energy distribution result by cooperatively distributing the double-frequency energy according to a distribution ratio; determining the module parameter mapping relationship of a three-phase modular multilevel converter, a single-phase modular multilevel converter and a DC bus respectively based on the double-frequency energy distribution result; under a preset operation constraint condition, based on a preset design target, the module parameter mapping relationship of the three-phase modular multilevel converter, the single-phase modular multilevel converter and the DC bus is used to jointly optimize the design parameters of the distribution ratio and a power supply system to obtain target design parameters of the power supply system. The method can improve the economy of parameter design.

Description

Technical Field

[0001] This application relates to the fields of power electronic conversion and rail transit traction power supply technology, and in particular to a method, device, computer equipment, computer-readable storage medium and computer program product for optimizing the parameters of a flexible converter for electrified railways based on second harmonic energy optimization allocation. Background Technology

[0002] With the development of high-speed railways, intercity railways, and heavy-haul railways, traction loads exhibit characteristics such as large capacity, rapid fluctuations, strong impact, and complex operating conditions. Traditional power supply methods using power frequency traction transformers are gradually showing limitations in adaptability, regulation capability, and power quality. Therefore, flexible power supply systems for electrified railways based on power electronics technology are receiving increasing attention. One typical structure is a back-to-back flexible power supply device formed by coupling three-phase modular multilevel converters and single-phase modular multilevel converters via a DC bus. This type of device connects to the public power grid on the three-phase side and the traction network on the single-phase side, enabling controllable energy conversion between the three-phase grid and the single-phase traction load. This not only improves the negative sequence effect on the grid side but also enhances active and reactive power regulation capabilities, improves regenerative braking energy feedback levels, and to a certain extent enhances the flexibility and controllability of the traction power supply system. However, current parameter designs for flexible converters in electrified railways result in poor overall system economy. Summary of the Invention

[0003] Therefore, it is necessary to provide a method, apparatus, computer equipment, computer-readable storage medium, and computer program product for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy optimization allocation, which can improve the economic efficiency of parameter design.

[0004] In a first aspect, this application provides a parameter optimization design method for flexible converters in electrified railways based on second-harmonic energy optimization allocation, applicable to a power supply system including a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus connecting the three-phase modular multilevel converter and the single-phase modular multilevel converter; the method includes:

[0005] Based on the instantaneous characteristics of the single-phase output power of the single-phase modular multilevel converter, the second harmonic energy to be processed is determined.

[0006] According to the allocation ratio, the second-harmonic energy is coordinated and distributed to the three-phase modular multilevel converter, the single-phase modular multilevel converter and the DC bus to obtain the second-harmonic energy allocation result;

[0007] Based on the second harmonic energy allocation results, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are determined respectively.

[0008] Under preset operating constraints and based on preset design objectives, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are jointly optimized according to the allocation ratio and the design parameters of the power supply system to obtain the target design parameters of the power supply system.

[0009] Secondly, this application also provides a parameter optimization design device for flexible converters in electrified railways based on second-harmonic energy optimization allocation, applied to a power supply system including a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus connecting the three-phase modular multilevel converter and the single-phase modular multilevel converter; the device includes:

[0010] The second harmonic energy determination module is used to determine the second harmonic energy to be processed based on the instantaneous characteristics of the output power of the single-phase side of the single-phase modular multilevel converter.

[0011] The energy distribution module is used to distribute the second-harmonic energy to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the distribution ratio, so as to obtain the second-harmonic energy distribution result.

[0012] The mapping relationship determination module is used to determine the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus respectively based on the second harmonic energy allocation results.

[0013] The joint optimization module is used to perform joint optimization of the power supply system under preset operating constraints, based on preset design goals, the module parameter mapping relationship of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus, and the allocation ratio and the design parameters of the power supply system, to obtain the target design parameters of the power supply system.

[0014] Thirdly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the method provided in the first aspect above.

[0015] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method provided in the first aspect above.

[0016] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps in the method provided in the first aspect above.

[0017] The aforementioned method, apparatus, computer equipment, computer-readable storage medium, and computer program product for optimizing the parameter design of flexible converters for electrified railways based on second-harmonic energy allocation determine the second-harmonic energy to be processed based on the instantaneous characteristics of the single-phase output power of the single-phase modular multilevel converter. This energy is then collaboratively allocated to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio. This collaboratively distributes the inherent pulsating energy, which was originally passively borne by a single component, effectively reducing the energy burden on the single-phase side. Based on the second-harmonic energy allocation results, the module parameter mapping relationships of each module in the power supply system are determined. Under preset operating constraints, and based on preset design goals and the module parameter mapping relationships of each module, joint optimization is performed on the allocation ratio and the design parameters of the power supply system to obtain the target design parameters. The allocation ratio and design parameters can be used as adjustment variables. Joint optimization based on the design goals under operating constraints avoids the additional costs caused by a single component passively increasing the design margin to absorb second-harmonic energy, thus effectively improving the economic efficiency of the parameter design of flexible converters for electrified railways. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a parameter optimization design method for a flexible converter in electrified railways based on second-harmonic energy optimization allocation in one embodiment.

[0020] Figure 2 This is a flowchart illustrating the process of determining the module parameter mapping relationship in one embodiment;

[0021] Figure 3 This is a schematic diagram of the topology of a flexible power supply system for electrified railways in one embodiment;

[0022] Figure 4 This is a schematic diagram of the instantaneous power and second harmonic energy swing on the single-phase side in one embodiment;

[0023] Figure 5 This is a schematic diagram illustrating the principle of second harmonic energy distribution in one embodiment;

[0024] Figure 6 This is a flowchart illustrating the parameter optimization design method for a flexible converter in electrified railways based on second harmonic energy optimization allocation in yet another embodiment.

[0025] Figure 7 This is a structural block diagram of a parameter optimization design device for a flexible converter in an electrified railway based on second harmonic energy optimization allocation in one embodiment.

[0026] Figure 8 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0028] It should be noted that the terms "first," "second," etc., used in this application can be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from the second element. The terms "comprising" and "having," and any variations thereof, used in this application, are intended to cover non-exclusive inclusion. The term "multiple" used in this application refers to two or more. The term "and / or" used in this application refers to one of the embodiments, or any combination of multiple embodiments.

[0029] While traditional power supply methods are structurally mature and widely used in engineering, they are essentially relatively rigid electromagnetic coupling power supply modes. They lack sufficiently flexible active control methods for issues such as power matching between three-phase and single-phase traction networks, negative sequence control, flexible power flow regulation, and regenerative braking energy utilization. Especially when operating under conditions of significant load fluctuations, frequent regenerative energy generation, and weak grids, traditional solutions struggle to simultaneously ensure power quality, equipment utilization, and system dynamic performance. Therefore, flexible power supply systems for electrified railways based on power electronics technology are receiving increasing attention. Back-to-back flexible power supply devices formed by coupling three-phase modular multilevel converters and single-phase modular multilevel converters via a DC bus are considered one of the important technical routes for flexible power supply in electrified railways due to the advantages of modular multilevel converters, such as strong adaptability to high voltage levels, good output waveform quality, high modularity, and flexible expansion.

[0030] However, unlike the power characteristics of the three-phase side, the instantaneous power output of the single-phase traction side naturally includes a second harmonic pulsating component. In other words, during the transmission of single-phase power to the traction network, there is inevitably a pulsating power varying at twice the power frequency and a corresponding energy oscillation within the system. This second harmonic energy is not an additional disturbance generated under accidental operating conditions, but rather an inherent structural problem in single-phase power transmission. If the carrying and distribution methods of this second harmonic energy are not specifically addressed during the system design phase, it can often only be passively absorbed by increasing the margin of local components. This leads to an increase in the capacitance of the single-phase submodule, an enhancement of the second harmonic circulating current in the bridge arm, and an increase in the rated current of the bridge arm, further resulting in adverse consequences such as increased component losses, increased thermal design pressure, and increased equipment size and cost.

[0031] In traditional technologies, parameter design for single-phase MMCs (Modular Multilevel Converters) typically starts from the individual converter body, configuring parameters such as capacitance, current, voltage, and reactors. For the single-phase side frequency harmonic problem, a common approach is to assume that the single-phase MMC itself absorbs this energy, i.e., by increasing the capacitance of the single-phase submodule and increasing the arm current margin to meet operational requirements. While this method is easy to implement, it is often conservative from a system perspective. Essentially, it concentrates the frequency harmonic energy, which could be optimized and distributed across multiple stages, onto the single-phase converter, resulting in insufficient economic efficiency. Furthermore, existing solutions generally lack a unified approach to parameter co-design of the three-phase MMC, single-phase MMC, and DC bus, and have not yet developed a systematic parameter design method for distributing, mapping, and optimizing frequency harmonic energy across different energy storage modules.

[0032] Therefore, for flexible power supply systems in electrified railways, and specifically for back-to-back flexible power supply devices composed of three-phase modular multilevel converters (MMCs), single-phase modular multilevel converters (MMCs), and DC buses, it is necessary to propose a new design method. This method should not merely rely on empirical selection of local parameters, but should identify the essential source of the second harmonic energy on the single-phase side at the system level, using it as the main design principle. A reasonable allocation should be made among the single-phase MMC, three-phase MMC, and DC bus, and combined with constraints such as ripple, current stress, voltage fluctuation, fault ride-through, and overload capacity, to obtain parameter configuration results with better overall performance and economy. The parameter optimization design method for flexible converters in electrified railways based on optimized allocation of second harmonic energy provided in this application can be applied to in-phase power supply systems in electrified railways, flexible traction substations, flexible power supply devices in sectioning stations, regenerative braking energy feedback scenarios, and other flexible power supply systems that require high-quality AC power from a three-phase grid to a single-phase traction network.

[0033] The parameter optimization design method for flexible converters in electrified railways based on second-harmonic energy optimization allocation provided in this application can be executed independently by a computer device such as a terminal or server, or jointly by a terminal and a server. The terminal can be, but is not limited to, various personal computers, laptops, smartphones, tablets, drones, low-altitude aircraft, IoT devices, and portable wearable devices. IoT devices can include smart speakers, smart TVs, smart air conditioners, smart vehicle equipment, projection equipment, etc. Portable wearable devices can include smartwatches, smart bracelets, head-mounted devices, etc. Head-mounted devices can be virtual reality (VR) devices, augmented reality (AR) devices, smart glasses, etc. The server can be a standalone physical server, a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services.

[0034] In one exemplary embodiment, such as Figure 1 As shown, a parameter optimization design method for flexible converters in electrified railways based on second harmonic energy optimization allocation is provided. In this embodiment, the method is applied to computer equipment as an example for illustration, including the following steps 102 to 108. Wherein:

[0035] Step 102: Determine the second harmonic energy to be processed based on the instantaneous characteristics of the single-phase output power of the single-phase modular multilevel converter.

[0036] Among them, the flexible power supply system for electrified railways is an architecture used for traction power supply of electrified railways. The system includes a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus connecting the three-phase modular multilevel converter and the single-phase modular multilevel converter, forming a back-to-back topology. This allows the power from the three-phase public grid to be converted into power suitable for the single-phase traction network. It can also actively regulate power flow, suppress negative sequence, and regenerate regenerative braking energy, thereby improving power supply quality and flexibility.

[0037] A three-phase modular multilevel converter (MMC) is a modular multilevel converter connected to a three-phase AC power grid. It consists of multiple cascaded sub-modules, each of which is typically a half-bridge or full-bridge structure. A single-phase modular multilevel converter (MMC) is a modular multilevel converter connected to a single-phase traction network. It is the main source of double-frequency energy. The DC bus is the DC voltage bus that connects the three-phase MMC and the single-phase MMC.

[0038] In the flexible power supply system of electrified railways, when a single-phase side outputs AC power, both its output voltage and current are sinusoidal. The waveform of the instantaneous power (voltage multiplied by current) not only contains a constant average power but also inevitably includes a pulsating component that fluctuates at twice the power frequency. The amplitude of this pulsating component is equal to the apparent power S. This is a unique and unavoidable second-harmonic power pulsation characteristic of a single-phase system. Based on the sampled or effective values ​​of the single-phase output voltage and current, the second-harmonic energy to be processed can be determined. This second-harmonic energy is caused by the instantaneous characteristics of the single-phase output power; it is the amplitude of the pulsating energy that the system must periodically absorb and release within one second-harmonic cycle (i.e., half of the power frequency cycle).

[0039] For example, a computer device can determine the instantaneous characteristics of the single-phase output power of a single-phase modular multilevel converter, and determine the second harmonic energy to be processed in a flexible power supply system for electrified railways based on these instantaneous characteristics. For instance, the computer device can acquire the operating parameters of the single-phase modular multilevel converter in the flexible power supply system for electrified railways, such as the output voltage and output current on the single-phase side. The computer device can establish an instantaneous power model based on the output voltage and output current to determine the instantaneous output power on the single-phase side, and extract the pulsation component based on the instantaneous output power, thereby determining the second harmonic energy to be processed.

[0040] Step 104: According to the allocation ratio, the second-harmonic energy is collaboratively allocated to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus to obtain the second-harmonic energy allocation result.

[0041] The allocation ratio is a quantization coefficient used to divide the second harmonic energy generated on the single-phase side among the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus. The allocation ratio can include a set of three non-negative values, and to satisfy energy conservation, the sum of the three values ​​is normalized to 1. The allocation ratio determines how much second harmonic energy each module in the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus needs to handle. For example, the allocation ratio can be... =0.6, =0.2, =0.2 indicates that the single-phase MMC handles 60% of the second harmonic energy, the three-phase MMC and the DC bus each handle 20%, and the sum of the three ratios is 1. This allocation ratio reflects that most of the second harmonic energy is still handled by the single-phase MMC, while the other two modules share the remaining part to reduce the burden on the single-phase MMC.

[0042] The second harmonic energy allocation result can include the specific energy values ​​allocated to the three-phase MMC, single-phase MMC, and DC bus according to the allocation ratio. For example, the second harmonic energy allocation result can include a set of three scalars, each with an energy unit, such as joules or kilojoules. For instance, if the second harmonic energy is 63.7 kilojoules, the allocation ratio is... =0.6, =0.2, =0.2. The computer equipment multiplies the second harmonic energy by 0.6, 0.2 and 0.2 respectively, and obtains the following second harmonic energy distribution results: 38.22 kJ of energy is allocated to the single-phase MMC, 12.74 kJ of energy is allocated to the three-phase MMC, and 12.74 kJ of energy is allocated to the DC bus.

[0043] Optionally, the computer device can obtain the allocation ratio, which can be preset manually or derived from the current value dynamically adjusted by the optimization algorithm in subsequent optimization loops. Based on the allocation ratio and the second harmonic energy, the computer device performs a multiplication-based collaborative allocation process. Specifically, since the allocation ratio contains three components and satisfies the normalization condition, the computer device can multiply the second harmonic energy by each component of the allocation ratio to generate three new energy data: the first energy allocated to the single-phase MMC, the second energy allocated to the three-phase MMC, and the third energy allocated to the DC bus. These three energy data together constitute the second harmonic energy allocation result.

[0044] Step 106: Based on the second harmonic energy allocation results, determine the module parameter mapping relationships for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus, respectively.

[0045] The module parameter mapping relationship describes the quantitative correlation rules or mathematical expressions between the electrical characteristic parameters of each module (three-phase modular multilevel converter, single-phase modular multilevel converter, DC bus) in the power supply system and the allocated second harmonic energy. The module parameter mapping relationship determines the minimum requirements or design criteria that a module must meet for its key physical parameters after undertaking a specific share of second harmonic energy. The module parameter mapping relationship can include one or more mathematical inequalities, equations, or lookup table rules, such as the proportional relationship between the minimum value of the submodule capacitance and energy, or the functional relationship between the effective value of the bridge arm current and energy.

[0046] For example, for each module in a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus, the computer equipment can invoke a pre-set module parameter mapping relationship generation rule that matches the characteristics of that module. Based on this rule and the second harmonic energy allocated to each module, the computer equipment obtains the respective module parameter mapping relationship for each module. Taking a single-phase modular multilevel converter as an example, the computer equipment can substitute its allocated first energy into a preset formula to generate a mapping relationship inequality specifically for the sub-module capacitors of that module. Similarly, for the DC bus, the computer equipment substitutes its allocated second energy into another formula to generate a mapping relationship for the DC bus capacitors. Furthermore, for a three-phase modular multilevel converter, the computer equipment can generate a mapping relationship regarding its arm current margin or additional energy storage requirements based on its allocated third energy.

[0047] Step 108: Under preset operating constraints, based on preset design objectives, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are used to jointly optimize the allocation ratio and the design parameters of the power supply system to obtain the target design parameters of the power supply system.

[0048] Operating constraints are boundary limitations that the power supply system must meet during the design phase. They can specify physical or engineering limits that parameter values ​​cannot exceed. Operating constraints can originate from various aspects such as electrical safety, equipment withstand voltage, thermal tolerance, grid connection specifications, and fault ride-through requirements. In some embodiments, the computer equipment can pre-obtain operating constraints from user input, design specification libraries, or system operating experience data. Operating constraints can exist in the form of inequalities or equations, such as a voltage fluctuation amplitude not exceeding a set value, a current effective value not exceeding the thermal tolerance, and specific parameters must remain within allowable ranges during low-voltage ride-through. Design objectives are a set of performance or economic indicators expected to be achieved during the optimization process. Design objectives determine the quality evaluation criteria. Design objectives can be singular (e.g., minimizing the total system energy storage capacity) or a weighted combination of multiple objectives (e.g., a weighted sum of total system energy storage capacity, bridge arm current stress, device losses, and DC bus voltage fluctuation amplitude). The computer equipment can obtain preset design objectives from user requirements (e.g., "desiring the equipment size to be as small as possible") or pre-set optimization strategies.

[0049] Design parameters are physical quantities whose specific values ​​need to be determined during the power supply system design process. Design parameters can be quantitative representations of the inherent physical characteristics of each module in a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus. For example, design parameters may include, but are not limited to, at least one of the following parameters: submodule capacitance value, arm rated current value, DC bus capacitance value, number of submodules, arm reactor value, and rated voltage level. Different modules can be associated with different design parameters. For example, for a single-phase modular multilevel converter, the associated design parameters may include the capacitance value of each submodule, arm rated current, number of submodules, and arm reactor value; for a three-phase modular multilevel converter, the associated design parameters may include the capacitance value of each submodule, arm rated current, arm reactor value, and control margin-related setpoints; for a DC bus, the associated design parameters may include the DC bus capacitance value and allowable voltage fluctuation range. The target design parameters are a set of design parameters that are output after joint optimization, satisfy the operational constraints, and optimize the design objective. The target design parameters may include the final determined allocation ratio and the design parameters associated with each module.

[0050] Optionally, the computer device can acquire preset operational constraints and design objectives. It can unify the allocation ratio and power supply system design parameters as decision variables, and under the constraints of the operational constraints, perform joint optimization based on the design objectives and the mapping relationship between the module parameters of each module. For example, the computer device can use numerical optimization algorithms (such as sequential quadratic programming, genetic algorithms, or particle swarm optimization) for joint optimization. In each iteration, the algorithm can try new allocation ratios and design parameters, call the module parameter mapping relationship to calculate whether the corresponding operational constraints are satisfied, and evaluate the objective function value. When the algorithm converges to a set of feasible solutions that are optimal for the design objectives, the computer device stops iterating and obtains the target design parameters of the power supply system based on the allocation ratio and design parameters corresponding to the optimal solution.

[0051] In the above-mentioned parameter optimization design method for flexible converters in electrified railways based on the optimized allocation of second harmonic energy, the second harmonic energy to be processed is determined according to the instantaneous characteristics of the output power of the single-phase side of the single-phase modular multilevel converter. This second harmonic energy is then collaboratively allocated to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio. This collaboratively distributes the inherent pulsating energy, which was originally passively borne by a single component, effectively reducing the energy load on the single-phase side. Based on the second harmonic energy allocation results, the module parameter mapping relationship of each module in the power supply system is determined. Under preset operating constraints, based on the preset design goals and the module parameter mapping relationship of each module, joint optimization is performed on the allocation ratio and the design parameters of the power supply system to obtain the target design parameters. The allocation ratio and design parameters can be used as adjustment variables. Under operating constraints, joint optimization is performed based on the design goals, avoiding the additional costs caused by a single component passively increasing the design margin to absorb second harmonic energy. This effectively improves the economic efficiency of the parameter design of flexible converters in electrified railways.

[0052] In an exemplary embodiment, determining the second harmonic energy to be processed based on the instantaneous characteristics of the output power of the single-phase side of the single-phase modular multilevel converter includes: determining the instantaneous output power of the single-phase side based on the output voltage and output current of the single-phase side of the single-phase modular multilevel converter; determining the active power and reactive power based on the instantaneous output power, and obtaining the apparent power based on the active power and reactive power; and determining the second harmonic energy to be processed based on the apparent power.

[0053] In the flexible power supply system of electrified railways, the single-phase side is the electrical side, consisting of the AC output port of a single-phase modular multilevel converter and the traction power supply network connected to it. Output voltage Output voltage is the single-phase AC voltage presented at the port on the single-phase side. It can be a continuous time function, a discrete data sequence consisting of sampling times and corresponding voltage values, or a set of effective parameters describing its amplitude and phase. Output current... This refers to the current flowing from the single-phase side to the traction network. Similar to the output voltage, the output current can be expressed analytically, as a discrete sampling sequence, or as an effective value phase parameter. Instantaneous output power. It is the power value transmitted on the single-phase side at every instant, which is physically equal to the product of the instantaneous value of the output voltage and the instantaneous value of the output current, i.e. Instantaneous output power can be a function that varies with continuous time or a sequence of power values ​​at discrete time points.

[0054] Active power measures the net energy transferred on average over a complete cycle on a single-phase side, reflecting the power component that actually does work. From the perspective of instantaneous power composition, active power equals the DC component of the instantaneous power. Computer equipment can obtain active power by integrating and averaging the instantaneous power values ​​over the cycle, or by multiplying the effective voltage value, effective current value, and the cosine of the power factor. Reactive power represents the power component that exchanges energy between a single-phase side and the grid without consuming energy. Reactive power does not do work on the load but causes voltage drop and current increase in the line. Computer equipment can obtain it by the amplitude of the orthogonal component in the instantaneous power, or by calculating it using the effective value and phase relationship. For example, computer equipment can obtain it from the instantaneous power expression... Identify the constant term That is, active power, extracted from the instantaneous power expression. coefficient before As reactive power; for example, computer equipment can sum the instantaneous power array collected for an entire cycle and divide by the number of sampling points to obtain the average active power. Computer equipment can also obtain the reactive power value based on the product of the effective voltage value, effective current value, and the sinusoidal term of the power factor. Apparent power is the total power capacity required to be provided by a single-phase power source; it is a vector synthesis of active and reactive power. For example, apparent power... It can be a scalar, and can be expressed by the formula The calculation yielded, where Active power The apparent power is the reactive power, and its amplitude directly determines the swing amplitude of the second harmonic energy.

[0055] Optionally, the computer equipment can acquire the output voltage and output current of the single-phase side of the single-phase modular multilevel converter. The output voltage and output current can be continuous functional expressions, discrete sampling sequences, or RMS values ​​and phase parameters. Based on the physical definition of instantaneous power, the computer equipment can perform multiplication operations on the output voltage and output current at the same moment or under the same time reference. If the output voltage and output current are analytical expressions, the computer equipment can directly derive the mathematical function of instantaneous output power; if the output voltage and output current are discrete sampling points, the computer equipment can perform point-by-point multiplication to generate an instantaneous output power sequence corresponding to time or sampling points.

[0056] Computer equipment can separate active power from instantaneous output power. and reactive power Depending on the form in which instantaneous output power is expressed, different separation methods can be used. For example, for analytical expressions, computer equipment can directly identify the DC term with a frequency of 0 as active power. and The coefficients of the terms are combined to form reactive power. For example, for a discrete instantaneous power sequence, computer equipment can perform Fourier analysis on the sequence to extract the amplitudes of the DC component and the second harmonic component, and then solve for the active power using trigonometric relationships. and reactive power Alternatively, the active power can be calculated using an orthogonal decomposition algorithm. and reactive power In obtaining active power and reactive power Afterwards, the computer device can perform square and square root operations. The apparent power is obtained. Computer equipment can determine the second harmonic energy to be processed based on the apparent power. For example, computer equipment can use the basic physical relationships of the power system to combine the apparent power with the system angular frequency to calculate the second harmonic energy that the system needs to absorb or release every half power frequency cycle.

[0057] In some embodiments, the computer device can establish a single-phase second-harmonic pulsating power model based on the instantaneous characteristics of the single-phase output power. If the single-phase output voltage and output current are respectively as follows:

[0058]

[0059]

[0060] in, This refers to the output voltage on the single-phase side. This is the effective value of the output voltage on the single-phase side. The system angular frequency is expressed in rad / s. This refers to the output current on the single-phase side. This is the effective value of the output current on the single-phase side; The power factor angle is the phase difference between the output voltage and the output current, measured in radians or degrees.

[0061] The instantaneous output power of a single phase can then be expressed as follows:

[0062]

[0063] in, This refers to the instantaneous output power on the single-phase side. Active power This refers to reactive power.

[0064] As can be seen from the above formula, the instantaneous output power of a single-phase side, in addition to the average power, also contains a second harmonic ripple term, the amplitude of which is the apparent power. As shown in the following formula:

[0065]

[0066] Furthermore, the energy oscillation amplitude (second harmonic energy) corresponding to the second harmonic pulsating power can be expressed as follows:

[0067]

[0068] in, The amplitude of the pulsating energy that the system needs to absorb and release within one harmonic cycle is the harmonic energy to be processed.

[0069] In this embodiment, the instantaneous output power is determined based on the output voltage and output current of the single-phase side, the active power and reactive power are determined based on the instantaneous output power, the apparent power is determined based on the active power and reactive power, and the second harmonic energy is determined based on the apparent power. The second harmonic energy can be accurately determined based on electrical relationships, ensuring the accuracy of the second harmonic energy.

[0070] In an exemplary embodiment, the second-harmonic energy is collaboratively distributed to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio to obtain the second-harmonic energy allocation result. This includes: determining the allocation ratio configured for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus respectively; and performing collaborative allocation based on the allocation ratio and the second-harmonic energy to obtain the second-harmonic energy allocation result for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus.

[0071] Optionally, the computer equipment can determine the allocation ratio, which can be derived from a preset initial configuration. For example, during system initialization, the computer equipment can directly read the preset allocation ratio. Alternatively, the allocation ratio can be calculated by an optimization algorithm running on the computer equipment. This algorithm, while satisfying subsequent constraints, dynamically solves for an optimal allocation ratio with the goal of minimizing the total system energy storage or the arm current. In iterative design, the allocation ratio can also come from correction instructions after multi-condition verification. The computer equipment automatically adjusts the original allocation ratio based on the verification results (such as single-phase arm current exceeding the limit). The allocation ratio can include the allocation ratios of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus, and the sum of the allocation ratios of the three modules is 1.

[0072] Computer equipment can perform mathematical calculations based on the second harmonic energy and the allocation ratio, outputting the second harmonic energy allocation results for a three-phase modular multilevel converter (MMC), a single-phase modular multilevel converter (MMC), and a DC bus. In some embodiments, a second harmonic energy allocation mechanism is introduced to collaboratively allocate the second harmonic energy among the single-phase MMC, three-phase MMC, and DC bus according to the allocation ratio. Specifically, the following is defined: The proportion of second harmonic energy carried by single-phase MMC. The proportion of second harmonic energy carried by the three-phase MMC. The proportion of second harmonic energy carried by the DC bus, i.e., the distribution ratio, may include... , as well as Then we have the following formula:

[0073]

[0074] Therefore, the second harmonic energy allocated to each carrying module is as follows:

[0075]

[0076]

[0077]

[0078] in, The second harmonic energy to be processed; To allocate the second harmonic energy to the single-phase MMC; The second harmonic energy allocated to the three-phase MMC; The second harmonic energy is allocated to the DC bus. Therefore, the result of the second harmonic energy allocation can include... , as well as .

[0079] In this embodiment, by determining the allocation ratios for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus configuration, and then coordinating the allocation to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratios, the second harmonic energy can be transformed from a local forced burden to a global collaborative burden. This effectively avoids the problem of over-design on the single-phase side and helps to upgrade the system parameter design from independent design of a single component to system-level collaborative design, effectively improving economy while ensuring performance.

[0080] In one exemplary embodiment, the frequency doubling energy allocation result includes a first energy allocated to the single-phase modular multilevel converter, a second energy allocated to the DC bus, and a third energy allocated to the three-phase modular multilevel converter; such as Figure 2 As shown, the process of determining the module parameter mapping relationship, namely, based on the second harmonic energy allocation result, determines the module parameter mapping relationship of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus respectively, including steps 202 to 206. Wherein:

[0081] Step 202: Based on the first energy, determine the module parameter mapping relationship between the required energy storage capacity of the sub-modules included in the single-phase modular multilevel converter and the first energy.

[0082] The first energy is the second harmonic pulsating energy allocated from the total second harmonic energy according to the allocation ratio in the second harmonic energy distribution result, and distributed to the single-phase modular multilevel converter (MMC). Optionally, the computer equipment can determine the first energy that needs to be absorbed and released by the single-phase MMC from the second harmonic energy distribution result. Based on the principles of energy conservation and capacitor energy storage, the computer equipment can establish a quantitative correspondence between the first energy and the required energy storage capacity of the sub-modules included in the single-phase MMC, thereby obtaining the module parameter mapping relationship of the single-phase modular multilevel converter. For example, the total energy storage change of all sub-modules in the four arms of the single-phase MMC needs to be able to cover the first energy, thus forming an inequality relationship: "the number of sub-modules in four arms multiplied by the capacitance of a single sub-module multiplied by the square of the rated voltage multiplied by twice the allowable ripple coefficient should not be less than the first energy." The computer equipment can regard this inequality as a module parameter mapping relationship, where the required energy storage capacity of the sub-module can be reflected as the lower limit of the sub-module capacitance value, or as the lower limit of the number of sub-modules required under a given capacitance value. Based on the first energy level and combined with parameters such as the rated voltage of the submodule, the number of bridge arm submodules, and the allowable voltage ripple coefficient preset in the system or input by the user, the computer equipment can calculate the minimum value or adjustment suggestions that the submodule capacitor should meet through the module parameter mapping relationship. In this way, the abstract energy index can be directly quantified into specific component parameter requirements, giving the design of single-phase MMC a clear and quantitative basis.

[0083] Step 204: Based on the second energy, determine the module parameter mapping relationship between the required buffer capacity of the DC bus capacitor and the second energy.

[0084] The second energy, in this context, is the portion of the total second-harmonic energy allocated to the DC bus based on a predetermined distribution ratio. For example, a computer device can acquire this second energy, which needs to be buffered by the DC bus through its capacitor voltage fluctuations. The computer device can establish a mapping relationship between the second energy and the required buffer capacity of the DC bus capacitor based on the relationship between capacitor energy storage and voltage changes. This mapping relationship of the DC bus module parameters allows for the transformation of bus capacitor design, which previously required empirical estimation, into precise calculations based on quantified energy allocation.

[0085] Step 206: Based on the third energy, determine the module parameter mapping relationship between the equivalent available additional energy storage of the three-phase modular multilevel converter and the third energy.

[0086] The third energy, in this context, is the second-harmonic pulsation energy allocated from the total second-harmonic energy according to the allocation ratio, and distributed to the three-phase modular multilevel converter (MMC). Optionally, the computer equipment can determine the third energy that the three-phase MMC needs to buffer through its internal energy storage redundancy and regulation capabilities. Since the three-phase MMC itself does not generate second-harmonic pulsations, the computer equipment needs to establish a mapping relationship between the third energy and the equivalent available additional energy storage of the three-phase MMC, thereby obtaining the module parameter mapping relationship of the three-phase modular multilevel converter. For example, the module parameter mapping relationship can be a simple "equivalent available additional energy storage should not be less than the third energy," or it can be further decomposed into more detailed mapping relationships such as the additional energy storage of the three-phase MMC sub-module capacitors, the margin of the bridge arm current, and the circulating current regulation capability. After obtaining the third energy, the computer equipment can combine it with the design parameters of the three-phase MMC (such as the number of sub-modules, rated voltage, allowable ripple, etc.) to calculate the percentage of additional energy storage capacity or rated current margin required, thereby forming a guideline for parameter adjustment.

[0087] In some embodiments, a second harmonic energy allocation mechanism is established. After obtaining the second harmonic energy allocation result, a module parameter mapping relationship between the second harmonic energy and system parameters can also be established. For example, if a single-phase MMC consists of four bridge arms, each bridge arm contains... Each submodule has a rated capacitor of [number]. Rated voltage is The allowable voltage ripple factor is The effective second-harmonic energy storage provided by a single-phase MMC approximately satisfies the following equation:

[0088]

[0089] in, This is the initial energy allocated to the single-phase MMC. Therefore, the single-phase MMC submodule capacitor should satisfy the following formula:

[0090]

[0091] in, The proportion of second harmonic energy carried by single-phase MMC; This refers to the rated apparent power on the single-phase side. It is the power frequency angular frequency.

[0092] Meanwhile, the second harmonic energy allocated to a single-phase MMC will also manifest in the bridge arm current design through circulating current. For a single-phase MMC, the effective value of its second harmonic circulating current can be approximated as follows:

[0093]

[0094] in, The effective value of the second harmonic circulating current flowing through a single-phase MMC bridge arm is given. This circulating current is generated by the flow of second harmonic energy between the bridge arms and is an important factor affecting the bridge arm current design. This is the rated voltage of the DC bus. The effective value of the rated AC current on the single-phase side is as follows:

[0095]

[0096] in, This is the effective value of the rated AC current on the single-phase side, that is, the effective value of the rated current output by the single-phase MMC on the AC side; This is the effective value of the rated voltage on the single-phase side. The rated current on the DC side is then given by the following formula:

[0097]

[0098] in, It is the rated current on the DC side, that is, the DC current flowing through the DC bus in a back-to-back system when the rated active power is applied. This is the rated active power. Therefore, the rated current of a single-phase MMC arm can be determined using the following approximate formula:

[0099]

[0100] in, This is the effective value of the rated current of a single-phase MMC bridge arm. When designing, the rated capacity of the bridge arm current should be at least greater than or equal to this value, and overload margin should be considered.

[0101] For DC buses, if DC bus capacitors are used and allowable voltage fluctuation amplitude To receive the allocated second harmonic energy, the following equation must be satisfied:

[0102]

[0103] in, To distribute the double-frequency energy to the DC bus; This is the rated voltage of the DC bus.

[0104] when When the above formula is used, it can be approximated as the following formula:

[0105]

[0106] Therefore, the lower limit for DC bus capacitor design is obtained as follows:

[0107]

[0108] in, The proportion of second harmonic energy carried by the DC bus; This is the rated apparent power for a single phase. It is the power frequency angular frequency.

[0109] For a three-phase MMC, the second-harmonic energy allocated to it does not represent its inherent second-harmonic power pulsation, but rather the selective absorption or release of a portion of the second-harmonic energy transferred from the single-phase side through its internal energy storage redundancy, arm circulating current regulation capability, and power control margin. Therefore, in parameter design, the equivalent available additional energy storage of the three-phase MMC can satisfy the following equation:

[0110]

[0111] in, The equivalent available additional energy storage that a three-phase MMC can provide represents the additional energy capacity that a three-phase MMC can absorb or release through the energy storage redundancy of submodule capacitors, bridge arm current margin, and control degrees of freedom. It can be used as an equivalent design constraint; To allocate the double-frequency energy to the three-phase MMC; The proportion of second harmonic energy carried by the three-phase MMC; This is for the second harmonic energy to be processed. Simultaneously, the rated current and capacitor design of the three-phase MMC arms must meet the corresponding energy storage and regulation margin requirements.

[0112] In this embodiment, by mapping the first energy, the second energy, and the third energy to the sub-module energy storage capacity of the single-phase MMC, the bus capacitor buffer capacity of the DC bus, and the equivalent available additional energy storage of the three-phase MMC, a direct and quantified module parameter mapping relationship is established between the energy undertaken by each module and its own parameters. Based on the module parameter mapping relationship, the conversion from energy allocation to parameter constraints can be completed efficiently, which is beneficial to improving the accuracy of parameter design.

[0113] In an exemplary embodiment, under preset operating constraints, based on preset design goals and the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus, joint optimization is performed on the allocation ratio and the design parameters of the power supply system to obtain the target design parameters of the power supply system. This includes: under preset operating constraints, based on preset design goals and the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus, joint optimization is performed on the allocation ratio and the design parameters of the power supply system to obtain candidate design parameters of the power supply system; based on the candidate design parameters, performance verification is performed under at least one operating condition to obtain verification results; if the verification results do not meet the operating constraints, the allocation ratio is adjusted, and the process returns to the step of coordinating the second harmonic energy allocation to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio to obtain the second harmonic energy allocation results, until the obtained verification results meet the operating constraints. Based on the candidate design parameters corresponding to meeting the operating constraints, the target design parameters of the power supply system are obtained.

[0114] Among them, the candidate design parameters are the intermediate design results obtained after joint optimization. The candidate design parameters may include the allocation ratio, that is, the specific values ​​of the second harmonic energy allocation among the single-phase modular multilevel converter, the three-phase modular multilevel converter and the DC bus. The candidate design parameters may also include system design parameters mapped from the second harmonic energy allocation results, such as the submodule capacitance value and bridge arm rated current value of the single-phase modular multilevel converter, the capacitance value of the DC bus, and the energy storage redundancy of the three-phase modular multilevel converter.

[0115] At least one operating condition is a set of non-rated operating scenarios used to verify the feasibility of candidate design parameters. At least one operating condition can correspond to operating parameters that can represent various severe or special conditions that may be encountered in the actual operation of the power supply system. For example, it may include operating parameters such as voltage drop depth, overload multiple, power feedback direction, and load change rate. At least one operating condition can be extracted from the engineering experience of electrified railway traction power supply, such as including but not limited to low voltage ride-through condition (e.g., grid-side voltage drops to 20% and lasts for 200 milliseconds), traction load sudden increase and decrease condition (e.g., load increases from 0 to full load within 1 second), regenerative braking energy feedback condition (e.g., power flow reverses), short-time overload condition (e.g., 1.2 times rated power for 10 seconds), and weak grid operation condition (e.g., low short-circuit capacity ratio).

[0116] The verification result is the judgment information output after the performance evaluation under a certain working condition is completed. The verification result can be used to determine whether the iteration process should be terminated. If the verification results of all working conditions meet the preset operating constraints, then the candidate design parameters are confirmed as the final target design parameters. If the verification result of any working condition does not meet the operating constraints, the allocation ratio can be adjusted according to the specific degree of exceeding the limit, and the joint optimization and verification steps can be re-executed until the target design parameters of the power supply system are obtained.

[0117] For example, the computer device can obtain preset operating constraints from storage or user input. These constraints may include, but are not limited to, at least one of various constraints such as the upper limit of capacitor voltage ripple coefficient of a single-phase modular multilevel converter submodule, the upper limit of arm current, the allowable range of DC bus voltage fluctuation, modulation ratio limits, and overcurrent requirements during low-voltage ride-through. The computer device can obtain preset design objectives, such as using one or more weighted factors as optimization directions, including minimum total energy storage capacity, minimum arm current stress, minimum device losses, or minimum DC voltage fluctuation.

[0118] The computer equipment can read the established module parameter mapping relationship, which quantitatively describes the mathematical relationship between the second harmonic energy undertaken by each module and its corresponding parameters. For example, the submodule capacitance of a single-phase modular multilevel converter is proportional to the allocated energy, and the DC bus capacitance is also proportional to the allocated energy. The computer equipment can use the allocation ratio and the design parameters of the power supply system (such as the capacitance value and rated current value of each module) as optimization variables. Under the premise of satisfying all operating constraints, it can find a set of variable values ​​that optimize the design objective by solving an optimization problem (e.g., using linear programming or gradient descent algorithms). This set of optimal variable values ​​becomes the candidate design parameters, which is the best design result under rated operating conditions, but has not yet been widely verified in operation.

[0119] After obtaining the candidate design parameters, the computer equipment can substitute them into at least one preset operating condition model for performance verification. The computer equipment can read parameters for at least one operating condition from the operating condition library one by one. For example, under the low voltage ride-through condition, the grid voltage is set to 20% of the rated value and maintained for 300 milliseconds; or under the traction load change condition, the power is increased from 0 to 120% within 0.1 seconds. For each operating condition, the computer equipment can calculate the response of each key point of the power supply system under that condition based on the circuit model or analytical formula, such as the peak arm current of the single-phase modular multilevel converter, the maximum fluctuation amplitude of the submodule capacitor voltage, and the DC bus voltage drop depth. The computer equipment can compare these calculated values ​​with preset operating constraints. If all monitored values ​​are within the constraint range, the verification result for that operating condition is "satisfied"; if any value exceeds the limit, the verification result is "unsatisfied," and the specific item and value of the exceeded limit are recorded.

[0120] After receiving the verification results, the computer equipment can determine whether all preset operating constraints are met. If any conditions are not met, the computer equipment cannot directly adopt the current candidate design parameters. In this case, the computer equipment can, according to the return instruction, return to the step of coordinating the second-harmonic energy distribution to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio, to obtain the second-harmonic energy distribution result. Upon returning, the computer equipment can adjust the specific values ​​of the allocation ratio based on the over-limit information given in the verification results. For example, if the DC bus voltage fluctuation exceeds the limit, the computer equipment can reduce the allocation ratio borne by the DC bus and correspondingly increase the allocation ratio borne by the single-phase or three-phase modular multilevel converter; if the bridge arm current is too large, the allocation ratio borne by the corresponding converter can be reduced. After adjustment, the computer equipment can re-execute the joint optimization step to obtain a new set of candidate design parameters, and then perform performance verification for at least one operating condition again until the verification results for all operating conditions meet the operating constraints. When all verification results are met, the last obtained candidate design parameters can be used as the target design parameters for the power supply system.

[0121] In some embodiments, the computer device can construct a comprehensive constraint system for parameter design. This constraint system includes, but is not limited to, single-phase MMC submodule capacitor voltage ripple constraints, single-phase MMC arm rated current constraints, three-phase MMC arm current constraints, three-phase MMC internal circulating current and modulation margin constraints, DC bus voltage fluctuation constraints, arm voltage constraints, arm reactor constraints, and additional constraints under low voltage ride-through, overload operation, and weak grid conditions. Based on this, a weighted combination of the total system energy storage capacity, arm current stress, device losses, and DC bus voltage fluctuation amplitude is used as the optimization objective. For example, the design objective can be constructed as follows:

[0122]

[0123] in, The objective function value corresponding to the design objective; This represents the total energy storage capacity of the system. For bridge arm current stress; For device losses; This represents the voltage fluctuation amplitude of the DC bus. , , , These are weighting coefficients, obtained by adjusting... By solving the system together with relevant parameters, the optimal design result of the system under constraints can be obtained, that is, the target design parameters.

[0124] After obtaining the candidate design parameters under rated operating conditions, a multi-condition verification and iterative correction process is further introduced. Specifically, the obtained candidate design parameters are simulated or analytically verified under low voltage ride-through conditions, traction load change conditions, regenerative braking energy feedback conditions, short-term overload conditions, and weak network operation conditions. If it is found that there are issues such as excessive arm current, excessive DC fluctuations, insufficient local energy storage, or insufficient modulation margin under a certain operating condition, the second harmonic energy allocation ratio and candidate design parameters are readjusted, and the solution is re-performed under constraints to obtain the final parameter design results that can meet the requirements of multiple operating scenarios. This yields the target design parameters of the power supply system, thus forming a complete parameter design process from second harmonic energy identification, system-level allocation, parameter mapping, comprehensive optimization to multi-condition correction.

[0125] In this embodiment, the allocation ratio and design parameters are jointly optimized under operating constraints and design objectives. At least one operating condition is introduced to verify the performance of candidate design parameters. When the verification result does not meet the operating constraints, the allocation ratio is adjusted and the optimization iteration is repeated until the target design parameters are obtained, thereby enhancing the scenario adaptability and reliability of parameter design.

[0126] In an exemplary embodiment, the operating constraints include at least one of the following: capacitor voltage ripple coefficient constraints of the sub-modules included in the single-phase modular multilevel converter, arm current constraints of the sub-modules included in the single-phase modular multilevel converter, arm current constraints of the three-phase modular multilevel converter, internal circulating current and modulation margin constraints of the three-phase modular multilevel converter, DC bus voltage fluctuation constraints, arm voltage constraints, arm reactor constraints, and additional constraints under low voltage ride-through, overload operation, and weak grid conditions; the design objectives include at least one of the following: total system energy storage capacity, arm current stress, device losses, and DC bus voltage fluctuation amplitude.

[0127] Among them, the capacitor voltage ripple coefficient constraint of the sub-modules included in the single-phase modular multilevel converter is a limitation set on the fluctuation range of the voltage across the capacitor of each sub-module in the single-phase modular multilevel converter; the arm current constraint is an upper limit set on the peak or effective value of the current flowing through each converter arm; the internal circulating current constraint is a limitation on the circulating current flowing inside the three-phase converter arm that does not flow through the AC side and DC side; the modulation margin constraint is the minimum difference or ratio that needs to be maintained between the DC bus voltage and the peak voltage of the AC side to ensure that the three-phase converter can output the desired AC voltage waveform; the voltage fluctuation constraint is a limit set on the allowable fluctuation range of the DC bus voltage; the arm voltage constraint is the upper and lower limit conditions that the sum of the instantaneous output voltages of all sub-modules on each arm must meet; the arm reactor constraint is a limitation set on the inductance value and current withstand capability of the reactors connected in the arm; the additional constraints are not constraints on the power supply system under steady-state rated operating conditions, but rather constraints to ensure that the power supply system can continue to operate or safely overcome adverse conditions such as grid faults and load surges.

[0128] The total energy storage capacity of the system is the sum of the capacitance values ​​of all energy storage elements (mainly the capacitors of all sub-modules and the DC bus capacitor) in the entire flexible power supply system, or the equivalent total energy storage capacity; the bridge arm current stress is the effective value or peak value of the current flowing through all bridge arm power devices; device loss refers to the total power consumption generated by all power semiconductor devices in the power supply system; the DC bus voltage fluctuation amplitude is the minimum allowable DC bus voltage fluctuation.

[0129] In this embodiment, various operational constraints and design objectives can be flexibly configured to ensure the global optimality of system parameter design. Furthermore, the optimization objectives and constraints can be mapped to specific physical quantities, thereby improving the economic efficiency of the parameter design for the flexible power supply system of electrified railways.

[0130] This application also provides an application scenario in which the above-mentioned method for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy allocation is applied. Specifically, the application of this method for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy allocation in this scenario is as follows:

[0131] The purpose of this application is to provide a parameter optimization design method for flexible converters in electrified railways based on second-harmonic energy optimization allocation. This method addresses the problems in traditional technologies where second-harmonic energy on the single-phase side is typically passively handled by the single-phase MMC, leading to excessively large single-phase submodule capacitors, conservative bridge arm current design, and uneconomical overall system parameter configuration. The parameter design method of this application allows for a re-evaluation and rational allocation of second-harmonic pulsating energy generated on the single-phase side from a holistic system perspective. This prevents this energy from being solely handled by a single module, instead coordinating its distribution among the single-phase MMC, three-phase MMC, and DC bus modules based on system structure, operational constraints, and optimization objectives. Furthermore, the allocation results are used to determine key parameters such as submodule capacitors, bridge arm rated current, internal energy storage margin, DC bus capacitor, and allowable voltage fluctuation range. This enables the entire flexible power supply system to achieve a more economical and reasonable design while meeting traction power supply performance requirements, fault ride-through requirements, and multi-condition operation requirements.

[0132] Based on this, this application proposes a parameter design method suitable for flexible power supply systems in electrified railways. The system employs a back-to-back topology formed by connecting three-phase modular multilevel converters and single-phase modular multilevel converters via a DC bus. The three-phase side is connected to the public power grid, and the single-phase side is connected to the traction network to provide single-phase AC power to the traction load. For example... Figure 3 The diagram shows the topology of a flexible power supply system for electrified railways, illustrating the connections between the three-phase power grid, three-phase MMC (Multi-Level Converter), DC bus, single-phase MMC, traction network, and traction loads. The three-phase power grid (e.g., 110 kV) is stepped down by a three-phase transformer and connected to the AC side of the three-phase modular multi-level converter. The DC side of the three-phase converter is connected back-to-back to the DC side of the single-phase modular multi-level converter via a DC bus, forming a bidirectional energy flow channel. The AC side of the single-phase modular multi-level converter is then connected to the single-phase traction network via a single-phase transformer, thus providing single-phase AC power to traction loads such as electric locomotives on the traction network.

[0133] like Figure 4 The diagram shows the instantaneous power and second harmonic energy oscillation on the single-phase side, illustrating the existence of second harmonic pulsations in the single-phase output power and the resulting periodic energy oscillations within the system. The single-phase output voltage... and output current Both are standard sine waves, and there is a phase difference between them. According to instantaneous power theory, the instantaneous power of a single-phase system... It can be decomposed into two parts: one part is the constant average power (i.e., active power). The other part is pulsating power that fluctuates sinusoidally at twice the power frequency, the amplitude of which is determined by the apparent power. The instantaneous power waveform oscillates around the average power line at a frequency twice the grid frequency (i.e., 100Hz or 120Hz), which is a key characteristic distinguishing single-phase systems from three-phase systems. Due to the fluctuations in instantaneous power, the system needs to periodically absorb and release energy within a second harmonic cycle, and the amplitude of this energy oscillation... It can be derived from the formula The calculation yielded the result.

[0134] Based on this, the parameter design method provided in this application can obtain the basic input parameters and constraints required for system design, including the rated voltage, frequency, and capacity of the three-phase and single-phase sides, the rated voltage and allowable fluctuation range of the DC bus, the rated voltage of the submodules, the allowable capacitor voltage ripple coefficient, the upper limit of the rated current of the bridge arm, the modulation ratio constraint, the design range of the bridge arm voltage and bridge arm reactor, and engineering requirements such as low voltage ride-through, overload operation, and adaptability to weak power grids. Figure 5 The diagram illustrates the principle of second harmonic energy distribution, illustrating how the total second harmonic energy is proportionally distributed among the single-phase MMC, three-phase MMC, and DC bus. The total second harmonic energy... It is calculated from the apparent power and grid angular frequency on the single-phase side; The corresponding branch points to the single-phase MMC carrier unit, indicating that this part of the energy is carried out through submodule capacitor energy storage and a second-harmonic circulation path, and the first energy carried is... ; The corresponding branch points to the three-phase MMC load-bearing unit, indicating that this part of the energy is absorbed by the internal energy storage redundancy and bridge arm circulating current / control margin of the three-phase MMC, and the corresponding third energy is... ; The corresponding branch points to the DC bus carrying unit, indicating that this part of the energy is buffered by the allowable voltage fluctuation of the bus capacitor, and the corresponding second energy it bears is .

[0135] like Figure 6 The diagram illustrates the parameter design process for second-harmonic energy optimization allocation, encompassing a complete workflow from inputting system parameters, establishing a second-harmonic model, setting energy allocation, establishing parameter constraints, joint optimization solution, to multi-condition verification and correction. Specifically, the computer equipment can acquire pre-set system basic input parameters, including rated voltage, rated frequency, and rated capacity for both three-phase and single-phase sides, rated DC bus voltage and its allowable fluctuation range, as well as threshold values ​​for various operating constraints, such as capacitor voltage ripple coefficient constraints for single-phase submodules, arm current constraints, DC bus voltage fluctuation constraints, arm voltage constraints, arm reactor constraints, and additional constraints under low-voltage ride-through, overload operation, and weak grid conditions. These input data constitute the boundaries and prerequisites for subsequent design.

[0136] Computer equipment can derive the instantaneous power expression for a single-phase side based on the instantaneous expressions of the output voltage and current. It can identify the average power and the power term pulsating at twice the power frequency, thereby establishing a second-harmonic pulsating power model. Based on this model, the computer equipment can calculate the amplitude of the pulsating energy fluctuation within one second-harmonic cycle. This yields the second harmonic energy to be processed. The computer equipment can initialize a set of allocation ratios, or directly solve for the optimal allocation ratios using subsequent optimization algorithms. These three allocation coefficients ( , as well as The numbers () represent the proportions of second harmonic energy carried by single-phase MMC, three-phase MMC, and DC bus, respectively, and satisfy the following conditions: .

[0137] Once the allocation ratio is determined, the computer equipment can execute three parameter mapping paths in parallel. The first path is to establish a single-phase MMC parameter mapping, which the computer equipment can do based on the energy allocated to the single-phase MMC. Based on parameters such as the number of sub-modules in a single-phase MMC, the rated voltage of the sub-modules, and the capacitor voltage ripple factor, according to the formula... The minimum value of the submodule capacitor is determined, and the rated current of the bridge arm is determined based on the circulating current approximation formula and the bridge arm current synthesis formula. The second path is to establish a three-phase MMC parameter mapping, whereby the computer equipment allocates energy to the three-phase MMC. This is mapped to the requirements of its internal energy storage redundancy and bridge arm current margin. The third path is to establish a DC bus parameter mapping, whereby the computer equipment determines the parameters based on the energy allocated to the DC bus. Combined with the allowable voltage fluctuation range, according to the formula Determine the minimum value of the DC bus capacitance.

[0138] After completing the mapping of the three parameters, the computer device can construct a comprehensive objective function that includes multiple optimization objectives, such as... ,in The total energy storage capacity of the system. For bridge arm current stress, For device losses, This represents the DC bus voltage fluctuation amplitude. Simultaneously, the computer equipment can integrate all previously input operational constraints (such as capacitor voltage ripple coefficient constraints, arm current constraints, internal circulating current and modulation margin constraints, voltage fluctuation constraints, arm voltage constraints, arm reactor constraints, and additional constraints related to low voltage ride-through, overload operation, and weak grid conditions) into the feasible region boundary of this optimization problem. The computer equipment can then utilize mathematical optimization algorithms to allocate the proportions within the feasible region defined by the constraints. The system's specific design parameters (such as submodule capacitance, bridge arm rated current, and DC bus capacitance) are jointly solved to search for the optimal combination of parameters that minimizes the objective function, thereby obtaining candidate design parameters.

[0139] After optimization, the computer equipment can substitute the obtained candidate design parameters into at least one operating condition for performance verification. These operating conditions include low voltage ride-through, traction load change, regenerative braking energy feedback, short-time overload, and weak grid operation. During the verification process, the computer equipment needs to evaluate whether all operating constraints are met. If the verification result is satisfactory, i.e., all constraints are met under all operating conditions, the computer equipment determines the current candidate design parameters as the target design parameters for the power supply system. If the verification result is unsatisfactory, for example, if the arm current exceeds the limit or the DC bus voltage fluctuation exceeds the standard under a certain operating condition, the process returns to the setting / optimization stage via a feedback arrow. The computer equipment can adjust the allocation ratio and repeat subsequent parameter mapping, objective function construction, joint optimization and multi-condition verification steps to form a closed loop iteration until the verification is passed and the target design parameters of the power supply system are obtained.

[0140] Compared to traditional technologies, the parameter design method provided in this application changes the traditional approach of assuming all second harmonic energy on the single-phase MMC body is applied. Instead, it elevates the second harmonic pulsating energy to a system-level design object, establishing a collaborative allocation mechanism among the single-phase MMC, three-phase MMC, and DC bus. Through this mechanism, this application can optimize the allocation of second harmonic energy based on the energy storage characteristics, fluctuation tolerance, and parameter costs of different carrying units, thereby reducing the problem of overly conservative local design on the single-phase side. For engineering applications, this means that the submodule capacitor configuration and bridge arm current design values ​​of the single-phase MMC can be effectively compressed while meeting performance requirements, resulting in a corresponding reduction in device stress and losses, and optimization of equipment size and cost.

[0141] Furthermore, this application does not simply transfer second-harmonic energy from one component to another, but rather seeks the comprehensive optimal result under constraints, thus achieving a more reasonable balance between economy and performance. By incorporating the DC bus capacitance and voltage fluctuations, the internal energy storage redundancy and control margin of the three-phase MMC, and the energy storage and current capacity of the single-phase MMC into the same design framework, collaborative design of system parameters is achieved. This not only improves the problem of excessive local parameter redundancy but also enhances the adaptability of the flexible power supply device under complex operating conditions such as severe fluctuations in traction load, frequent feedback of regenerative braking energy, fault ride-through, and weak network operation. Overall, this application enables the flexible power supply system for electrified railways to achieve better overall cost, lower component stress, better operational performance, and stronger engineering applicability.

[0142] The following example, using a 40MVA (Mega Volt-Ampere) electrified railway flexible power supply system, further illustrates this application. This example is only used to illustrate the design concept and implementation process of this application and does not constitute a limitation on the scope of protection of this application. The system in this example adopts a back-to-back structure formed by connecting three-phase MMCs and single-phase MMCs via a DC bus. The three-phase MMCs are connected to a three-phase public power grid, and the single-phase MMCs are connected to a 27.5kV traction network. The system rated capacity is 40MVA, the power frequency is 50Hz, and the DC bus rated voltage is 60kV. For ease of explanation, the following parameter design is based on the single-phase side rated operating condition and operating condition near unity power factor. The single-phase side rated voltage is 27.5kV, and the rated apparent power is... The effective value of the rated current on the single-phase side is (install).

[0143] Under this rated operating condition, the amplitude of the second harmonic pulsation energy on the single-phase side is from Confirmed. Since the system frequency is 50Hz, that is... Therefore, (kilojoules). This means that for a 40MVA single-phase traction side, the system needs to handle approximately 63.7kJ of oscillation energy per second harmonic cycle.

[0144] To reflect the allocation concept of this application, this embodiment does not adopt the traditional method of "all borne by single-phase MMC", but instead sets a set of cooperative allocation ratios. As a preferred embodiment, take... Therefore, the second harmonic energy allocated to the single-phase MMC, three-phase MMC, and DC bus is as follows:

[0145]

[0146]

[0147]

[0148] Based on this, the parameters of the single-phase MMC are first designed. Assume the single-phase MMC adopts a four-arm structure, with each arm configured with... Each submodule has a rated voltage of [value missing]. The submodule capacitor voltage ripple coefficient is allowed to be taken as... The single-phase energy storage design relationship according to this application is as follows:

[0149]

[0150] Substituting the above parameters, we can obtain (Law), meaning the capacitance of a single submodule of a single-phase MMC is at least approximately (millifarads). Considering discrete device selection, aging margin, and fault condition correction, this embodiment can take the single-phase MMC submodule capacitor as... .

[0151] Next, check the rated current of the single-phase MMC bridge arm. Assume the rated active power condition... (megawatts), then the rated current on the DC side is The effective value of the circulating current corresponding to the second harmonic energy allocated to the single-phase MMC is approximately as follows:

[0152]

[0153] Therefore, the rated current of a single-phase MMC bridge arm can be estimated using the following formula:

[0154]

[0155] Thus obtain Considering certain overload and design margin, the rated current of the single-phase MMC bridge arm in this embodiment can be taken as 900A to 1000A.

[0156] Then, the parameters of the DC bus are designed. Assuming the rated voltage of the DC bus is 60kV, the allowable voltage fluctuation amplitude caused by the second harmonic is controlled within... That is, approximately 5% of the rated value. The approximate design relationship for the DC bus carrying second-harmonic energy is as follows:

[0157]

[0158] Substituting the parameters, we get the following formula:

[0159]

[0160] That is, the theoretical lower limit of DC bus capacitance is approximately (microfarads). Considering bus transients, voltage control, and engineering margins, this embodiment can design the equivalent capacitance of the DC bus as follows: .

[0161] For a three-phase MMC, the second harmonic energy it handles in this embodiment is 12.7 kJ. This energy does not mean that the three-phase side inherently has a second harmonic output, but rather that the three-phase MMC needs to selectively absorb and release some of the energy fluctuations introduced from the single-phase side through the bridge arm current margin, internal energy storage redundancy, and control freedom. In engineering design, the submodule capacitors, bridge arm rated currents, and control margins of the three-phase MMC can be modified based on the conventional three-phase MMC design. For example, if each bridge arm of the three-phase MMC is configured with 40 submodules, and the rated voltage of the submodules is also taken as 1.7 kV, then the submodule capacitors can be increased by 5% to 15% on the conventional baseline value as additional energy storage redundancy, and the bridge arm rated current can reserve about 10% dynamic adjustment margin to handle the 12.7 kJ of second harmonic energy allocated in this embodiment.

[0162] To illustrate the effectiveness of the method presented in this application, we can further examine the traditional design approach, where the second harmonic energy is entirely handled by a single-phase MMC, i.e., taking... At this point, the capacitor design formula for the single-phase MMC submodule becomes... Substituting the same parameters, we can obtain As can be seen, compared with the traditional solution where the entire process is handled by a single-phase MMC, this embodiment adopts... After the allocation method is changed, the capacitance of a single submodule of the single-phase MMC is reduced from about 34.5mF to about 20.7mF, a reduction of about 40%. Correspondingly, the design values ​​of the second harmonic circulating current and bridge arm current of the single-phase MMC also decrease, while the DC bus and the three-phase MMC only need to bear a small proportion of the second harmonic energy to complete the buffering, thereby achieving better overall economy.

[0163] After obtaining the initial parameters mentioned above, this embodiment further performs operating condition verification. For electrified railway scenarios, the verification focuses on conditions such as sudden increases and decreases in traction load, regenerative braking power feedback, short-term overload, and voltage dips on the grid side. If the verification reveals that the single-phase MMC arm current is close to the upper limit or the DC bus voltage fluctuation is too large, the current can be appropriately reduced. And increase or If the single-phase MMC capacitor configuration is found to be too large, it can be appropriately increased. or Simultaneously, the constraints on the three-phase side and the DC side are checked to ensure they are met. Through iterative adjustment of the above allocation coefficients, this embodiment can obtain a design parameter combination with better overall cost and performance while meeting the requirements of rated operating conditions and fault operating conditions.

[0164] Therefore, this application does not simply provide a fixed formula, but rather offers a complete design method for "identification-allocation-mapping-optimization-verification" around second harmonic energy. An example using a 40MVA electrified railway flexible power supply system demonstrates that this application can significantly reduce the energy storage and current pressure on single-phase MMCs, making parameter configuration more economical, while preserving the system's controllability and adaptability under multiple operating conditions.

[0165] The parameter design method provided in this application is applied to back-to-back flexible power supply devices consisting of three-phase modular multilevel converters, single-phase modular multilevel converters, and DC buses. It belongs to the overall parameter design method for three-phase / single-phase MMC back-to-back systems in electrified railways. Specifically, a second-harmonic pulsating power expression is established based on the instantaneous power model of the single-phase side, and the corresponding second-harmonic energy swing amplitude is further determined. This second-harmonic energy is used as the core input quantity for system parameter design, elevating the naturally existing second-harmonic energy on the single-phase side from an "implicit influencing factor" to an "explicit design object." Regarding the design mechanism for the coordinated distribution of second-harmonic energy among the single-phase MMC, three-phase MMC, and DC bus, by setting the proportions of single-phase MMC, three-phase MMC, and DC bus, the total second-harmonic energy is distributed among multiple energy storage units, satisfying a normalization relationship where the sum of each distribution proportion is 1. Specifically, the second-harmonic energy allocated to the single-phase MMC is mapped to the design parameters of the single-phase MMC's submodule capacitors, number of submodules, bridge arm rated current, bridge arm circulating current margin, and bridge arm reactors. This ensures that the key parameters of the single-phase MMC are no longer roughly selected based on experience, but are quantitatively determined by the second-harmonic energy allocation results. Furthermore, a DC bus parameter mapping relationship is established based on the second-harmonic energy allocation results. This maps the second-harmonic energy allocated to the DC bus to the design parameters such as DC bus capacitors, allowable voltage fluctuation range, and transient voltage deviation range. This allows the DC bus to participate in the second-harmonic energy reception as a system buffer, thereby reducing the local energy storage pressure on the single-phase MMC.

[0166] Furthermore, under constraints such as ripple constraints, current constraints, voltage fluctuation constraints, modulation ratio constraints, bridge arm voltage constraints, bridge arm reactor constraints, as well as fault ride-through, overload operation, and weak network operation, the second harmonic energy allocation ratio and various key parameters are jointly solved, enabling system-level parameter collaborative design under multiple constraints. Specifically, with the goal of minimizing total capacitance, minimizing bridge arm current stress, minimizing device losses, minimizing DC bus voltage fluctuation, minimizing equipment size, minimizing overall cost, or optimizing overall system performance, the second harmonic energy allocation ratio and system parameters are jointly optimized, thereby achieving a comprehensive improvement in economy and performance through optimization.

[0167] The parameter design method provided in this application further verifies and iteratively corrects the design results under rated operating conditions by combining multiple operating conditions such as low voltage ride-through, traction load mutation, regenerative braking energy feedback, short-term overload, and weak network operation. This achieves closed-loop correction capability from rated operating conditions to complex operating conditions, ensuring that the designed parameters are feasible and adaptable under typical operating scenarios of electrified railways.

[0168] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages in other steps. It is understood that the steps in different embodiments can be freely combined as needed, and all non-contradictory solutions formed by such combinations are within the scope of protection of this application.

[0169] Based on the same inventive concept, this application also provides a device for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy optimization allocation, used to implement the aforementioned method for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy optimization allocation. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of the device for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy optimization allocation provided below can be found in the limitations of the method for optimizing the parameters of a flexible converter for electrified railways based on second-harmonic energy optimization allocation described above, and will not be repeated here.

[0170] In one exemplary embodiment, such as Figure 7 As shown, a parameter optimization design device 700 for flexible converters in electrified railways based on second-harmonic energy optimization allocation is provided. This device is applied to a power supply system including a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus connecting the three-phase modular multilevel converter and the single-phase modular multilevel converter. The parameter optimization design device 700 for flexible converters in electrified railways based on second-harmonic energy optimization allocation includes: a second-harmonic energy determination module 702, an energy allocation module 704, a mapping relationship determination module 706, and a joint optimization module 708, wherein:

[0171] The second harmonic energy determination module 702 is used to determine the second harmonic energy to be processed based on the instantaneous characteristics of the output power of the single-phase side of the single-phase modular multilevel converter.

[0172] The energy distribution module 704 is used to distribute the second harmonic energy to the three-phase modular multilevel converter, the single-phase modular multilevel converter and the DC bus according to the distribution ratio, so as to obtain the second harmonic energy distribution result.

[0173] The mapping relationship determination module 706 is used to determine the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus respectively based on the second harmonic energy allocation results.

[0174] The joint optimization module 708 is used to perform joint optimization on the allocation ratio and the design parameters of the power supply system under preset operating constraints and based on preset design goals, the module parameter mapping relationship of the three-phase modular multilevel converter, the single-phase modular multilevel converter and the DC bus, and to obtain the target design parameters of the power supply system.

[0175] In some embodiments, the second harmonic energy determination module 702 is further configured to determine the instantaneous output power of the single-phase side based on the output voltage and output current of the single-phase side of the single-phase modular multilevel converter; determine the active power and reactive power based on the instantaneous output power, and obtain the apparent power based on the active power and reactive power; and determine the second harmonic energy to be processed based on the apparent power.

[0176] In some embodiments, the energy distribution module 704 is further configured to determine the distribution ratios for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus configuration, respectively; and to perform coordinated distribution based on the distribution ratios and the second harmonic energy to obtain the second harmonic energy distribution results for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus.

[0177] In some embodiments, the second-harmonic energy allocation result includes a first energy allocated to the single-phase modular multilevel converter, a second energy allocated to the DC bus, and a third energy allocated to the three-phase modular multilevel converter; the mapping relationship determination module 706 is further configured to determine, based on the first energy, a module parameter mapping relationship between the required energy storage capacity of the sub-modules included in the single-phase modular multilevel converter and the first energy; based on the second energy, a module parameter mapping relationship between the required buffer capacity of the DC bus capacitor and the second energy; and based on the third energy, a module parameter mapping relationship between the equivalent available additional energy storage of the three-phase modular multilevel converter and the third energy.

[0178] In some embodiments, the joint optimization module 708 is further configured to, under preset operating constraints, based on preset design goals and the respective module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus, jointly optimize the allocation ratio and the design parameters of the power supply system to obtain candidate design parameters of the power supply system; based on the candidate design parameters, perform performance verification under at least one operating condition to obtain verification results; if the verification results do not meet the operating constraints, adjust the allocation ratio and return to execute the step of coordinating the second harmonic energy allocation to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio to obtain the second harmonic energy allocation results, until the obtained verification results meet the operating constraints, and obtain the target design parameters of the power supply system according to the candidate design parameters corresponding to meeting the operating constraints.

[0179] In some embodiments, the operating constraints include at least one of the following: capacitor voltage ripple coefficient constraints of the sub-modules included in the single-phase modular multilevel converter, arm current constraints of the sub-modules included in the single-phase modular multilevel converter, arm current constraints of the three-phase modular multilevel converter, internal circulating current and modulation margin constraints of the three-phase modular multilevel converter, DC bus voltage fluctuation constraints, arm voltage constraints, arm reactor constraints, and additional constraints under low voltage ride-through, overload operation, and weak grid conditions; the design objectives include at least one of the following: total system energy storage capacity, arm current stress, device losses, and DC bus voltage fluctuation amplitude.

[0180] The modules in the aforementioned electrified railway flexible converter parameter optimization design device based on second-harmonic energy optimization allocation can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0181] In one exemplary embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 8As shown, the computer device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides the environment for the operating system and computer programs stored in the non-volatile storage media. The database stores various data related to the parameter optimization design method for flexible converters in electrified railways based on second-harmonic energy optimization allocation. The I / O interfaces are used for information exchange between the processor and external devices. The communication interface is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements a parameter optimization design method for flexible converters in electrified railways based on second-harmonic energy optimization allocation.

[0182] Those skilled in the art will understand that Figure 8 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0183] In one embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0184] In one embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0185] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0186] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0187] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0188] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0189] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A parameter optimization design method for flexible converters in electrified railways based on second harmonic energy optimization allocation, characterized in that, The method is applied to a power supply system comprising a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus connecting the three-phase modular multilevel converter and the single-phase modular multilevel converter; the method includes: Based on the instantaneous characteristics of the single-phase output power of the single-phase modular multilevel converter, the second harmonic energy to be processed is determined. According to the allocation ratio, the second-harmonic energy is collaboratively distributed to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus to obtain the second-harmonic energy allocation result; Based on the second harmonic energy allocation results, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are determined respectively. Under preset operating constraints and based on preset design objectives, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are jointly optimized with respect to the allocation ratio and the design parameters of the power supply system to obtain the target design parameters of the power supply system.

2. The method according to claim 1, characterized in that, The step of determining the second harmonic energy to be processed based on the instantaneous characteristics of the single-phase output power of the single-phase modular multilevel converter includes: The instantaneous output power of the single-phase side is determined based on the output voltage and output current of the single-phase modular multilevel converter. The active power and reactive power are determined based on the instantaneous output power, and the apparent power is obtained based on the active power and the reactive power. The second harmonic energy to be processed is determined based on the apparent power.

3. The method according to claim 1, characterized in that, The process of allocating the second-harmonic energy to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio yields the second-harmonic energy allocation result, including: The allocation ratios for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus configuration are determined respectively. Based on the allocation ratio and the second harmonic energy, a coordinated allocation is performed to obtain the second harmonic energy allocation result for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus.

4. The method according to claim 1, characterized in that, The second-harmonic energy allocation result includes a first energy allocated to the single-phase modular multilevel converter, a second energy allocated to the DC bus, and a third energy allocated to the three-phase modular multilevel converter. The step of determining the module parameter mapping relationships for the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus based on the second-harmonic energy allocation results includes: Based on the first energy, determine the module parameter mapping relationship between the required energy storage capacity of the sub-modules included in the single-phase modular multilevel converter and the first energy; Based on the second energy, determine the module parameter mapping relationship between the required buffer capacity of the DC bus capacitor and the second energy; Based on the third energy, determine the module parameter mapping relationship between the equivalent available additional energy storage of the three-phase modular multilevel converter and the third energy.

5. The method according to claim 1, characterized in that, Under preset operating constraints and based on preset design objectives, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are jointly optimized with respect to the allocation ratio and the design parameters of the power supply system to obtain the target design parameters of the power supply system, including: Under preset operating constraints and based on preset design objectives, the module parameter mapping relationships of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus are jointly optimized with respect to the allocation ratio and the design parameters of the power supply system to obtain candidate design parameters of the power supply system. Based on the candidate design parameters, performance verification is performed under at least one operating condition to obtain the verification results; If the verification result does not meet the operating constraints, the allocation ratio is adjusted, and the process returns to the step of coordinating the second harmonic energy allocation to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the allocation ratio to obtain the second harmonic energy allocation result, until the obtained verification result meets the operating constraints. Based on the candidate design parameters corresponding to meeting the operating constraints, the target design parameters of the power supply system are obtained.

6. The method according to any one of claims 1 to 5, characterized in that, The operating constraints include at least one of the following: capacitor voltage ripple coefficient constraints of the sub-modules included in the single-phase modular multilevel converter, arm current constraints of the sub-modules included in the single-phase modular multilevel converter, arm current constraints of the three-phase modular multilevel converter, internal circulating current and modulation margin constraints of the three-phase modular multilevel converter, voltage fluctuation constraints of the DC bus, arm voltage constraints, arm reactor constraints, and additional constraints under low voltage ride-through, overload operation, and weak grid conditions. The design objectives include at least one of the following: total system energy storage capacity, bridge arm current stress, device losses, and voltage fluctuation amplitude of the DC bus.

7. A parameter optimization design device for flexible converters in electrified railways based on second harmonic energy optimization allocation, characterized in that, The device is applied to a power supply system including a three-phase modular multilevel converter, a single-phase modular multilevel converter, and a DC bus connecting the three-phase modular multilevel converter and the single-phase modular multilevel converter; the device includes: The second harmonic energy determination module is used to determine the second harmonic energy to be processed based on the instantaneous characteristics of the output power of the single-phase side of the single-phase modular multilevel converter. The energy distribution module is used to distribute the second-harmonic energy to the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus according to the distribution ratio, so as to obtain the second-harmonic energy distribution result. The mapping relationship determination module is used to determine the module parameter mapping relationship of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus respectively based on the second harmonic energy allocation result. The joint optimization module is used to perform joint optimization of the module parameter mapping relationship of the three-phase modular multilevel converter, the single-phase modular multilevel converter, and the DC bus under preset operating constraints and based on preset design goals, with regard to the allocation ratio and the design parameters of the power supply system, to obtain the target design parameters of the power supply system.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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