A method for eliminating DC secondary ripple in a through-type traction device based on multi-port collaboration

Abstract

This invention provides a method for eliminating DC secondary ripple in a through-type traction device based on multi-port collaboration, comprising: acquiring electrical quantities at three ports; constructing a second harmonic power component model for each port based on the electrical quantities at the three ports; constructing a secondary ripple elimination optimization model based on the second harmonic power component model, using the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables, with the objective function of minimizing the total second harmonic power on the DC side; solving the secondary ripple elimination optimization model to generate collaborative modulation control commands. This invention requires no additional hardware and can actively suppress DC-side secondary ripple simply by optimizing the control strategy. It can reduce DC bus voltage fluctuations, lower the requirements for supporting capacitor configuration, and is of great significance for improving the operational stability, power quality, and engineering application value of the new through-type traction power supply system.

Description

Technical Field

[0001] This invention relates to the field of electrified railway power control technology, and in particular to a method for eliminating DC secondary ripple in a through traction device based on multi-port coordination. Background Technology

[0002] A continuous traction power supply system utilizes power electronic converters to flexibly adjust the voltage amplitude and phase of the traction network. This eliminates phase-splitting elements in the traction network while improving traction power quality, enabling continuous power supply and thus enhancing the power quality and operational reliability of the electrified railway power supply system. To reduce equipment investment and engineering modification difficulty, existing technologies have proposed a novel continuous traction power supply device based on a "two-phase AC input—single-phase AC output" conversion unit, such as... Figure 1 As shown in the figure. This device makes full use of existing traction transformers and achieves efficient and reliable through-line power supply without changing the main structure of the traditional traction power supply system, showing good prospects for engineering applications.

[0003] However, the submodules of this type of novel through-type traction power supply device typically contain multiple single-phase conversion ports, with each port achieving energy coupling via a common DC bus. Since single-phase AC power inevitably generates second-harmonic pulsating power during transmission, both the input-side single-phase rectifier port and the output-side single-phase inverter port inject secondary ripple power into the DC bus. When the secondary ripple power from multiple ports is superimposed on the DC side, it causes DC bus voltage fluctuations, forming significant secondary ripple. This DC voltage secondary ripple not only increases the DC-side capacitor requirements, leading to increased device size and cost, but also increases voltage and current stress on power devices, adversely affecting system operational stability and output power quality. Therefore, reducing the transmission and superposition of secondary ripple power from each port to the DC side, and lowering DC bus voltage fluctuations, has become a key technical problem to be solved in this novel through-type traction power supply device.

[0004] To address the aforementioned issues, traditional solutions typically reduce DC voltage secondary ripple by increasing the DC-side capacitor capacity or adding a DC filter. However, these methods significantly increase device size and investment costs, limiting their widespread application in engineering projects. In contrast, suppressing DC-side secondary ripple through software control strategies requires no additional hardware and thus has greater engineering application value. However, most existing control methods focus on secondary ripple regulation at the input ports, primarily addressing the mutual compensation of secondary ripple power between input ports, while neglecting the impact of secondary ripple introduced by the single-phase inverter port on the output side. In reality, even if some secondary ripple on the input side can be offset to a certain extent on the DC side, the output port will still continuously inject secondary ripple power into the DC bus when transmitting single-phase power to the traction network, resulting in noticeable secondary ripple on the DC side. Summary of the Invention

[0005] This invention provides a method for eliminating DC secondary ripple in a through-type traction device based on multi-port collaboration. To solve the above-mentioned technical problems, this invention adopts the following technical method: This invention provides a method for eliminating DC secondary ripple in a through-type traction device based on multi-port cooperation, comprising: Acquire three-port electrical quantities; Based on the three-port electrical quantities, construct the second harmonic power component model for each port; Based on the aforementioned second harmonic power component model, a quadratic ripple elimination optimization model is constructed with the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables, and the objective function being the minimum total second harmonic power on the DC side. Solve the secondary ripple elimination optimization model to generate cooperative modulation control commands.

[0006] Optionally, the three-port electrical quantities include the instantaneous value of the first input voltage, the instantaneous value of the first input current, the phase angle of the first input voltage, and the phase angle of the first input current at the first input port; the instantaneous value of the second input voltage, the instantaneous value of the second input current, the phase angle of the second input voltage, and the phase angle of the second input current at the second input port; and the instantaneous value of the output voltage, the instantaneous value of the output current, the phase angle of the output voltage, and the phase angle of the output current at the output port.

[0007] Optionally, the second harmonic power component model of each port includes a first input port second harmonic power component model, a second input port second harmonic power component model, and an output port second harmonic power component model. The construction of the second harmonic power component model for each port based on the three-port electrical quantities includes: Based on the instantaneous value of the first input voltage, the instantaneous value of the first input current, the phase angle of the first input voltage, and the phase angle of the first input current, the second harmonic power component model of the first input port is determined; Based on the instantaneous value of the second input voltage, the instantaneous value of the second input current, the phase angle of the second input voltage, and the phase angle of the second input current, the second input port second harmonic power component model is determined; Based on the instantaneous values ​​of the output voltage, the instantaneous values ​​of the output current, the phase angle of the output voltage, and the phase angle of the output current, the second harmonic power component model of the output port is determined.

[0008] Optionally, based on the second harmonic power component model, a quadratic ripple elimination optimization model is constructed with the objective function of minimizing the total second harmonic power on the DC side, using the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables; including: Based on the second harmonic power component model, the adjustment function of each port is determined; The adjustment functions of each port are combined for DC-side second harmonic power synthesis. The reactive power of the first input port, the reactive power of the second input port, and the voltage phase of the output port are used as optimization variables to construct a quadratic ripple elimination optimization model with the objective function of minimizing the total DC-side second harmonic power.

[0009] Optionally, the adjustment function for each port includes a reactive power adjustment function for the first input port, a reactive power adjustment function for the second input port, and a voltage phase adjustment function for the output port. Determining the adjustment function for each port based on the second harmonic power component model includes: Based on the second harmonic power component model of the first input port, the reactive power adjustment function of the first input port is determined; Based on the second input port second harmonic power component model, determine the reactive power regulation function of the second input port; Based on the second harmonic power component model of the output port, the voltage phase adjustment function of the output port is determined.

[0010] Optionally, the constraints of the quadratic ripple elimination optimization model include the following: Output port voltage constraints, output port phase constraints, input port current constraints, port capacity constraints, port power balance constraints, and grid-side power quality constraints.

[0011] Optionally, the coordinated modulation control command includes a first input port reactive power regulation amount, a second input port reactive power regulation amount, and an output port target voltage phase.

[0012] The present invention has the following beneficial effects: The method proposed in this invention does not require additional hardware. It can actively suppress DC-side secondary ripple by optimizing the control strategy. This not only reduces DC bus voltage fluctuations and lowers the requirements for supporting capacitor configuration, but also has significant implications for improving the operational stability, power quality, and engineering application value of the new through-type traction power supply system. Attached Figure Description

[0013] Figure 1 A structural diagram of a novel through-type traction power supply device provided in an embodiment of the present invention; Figure 2 A flowchart illustrating the DC secondary ripple elimination method for a through-type traction device based on multi-port collaboration provided in an embodiment of the present invention. Figure 3 The DC-side capacitor voltage waveform diagram of the through-traction power supply device provided in the embodiment of the present invention; Figure 4The voltage and current waveform diagram of the first input port α of the through traction power supply device provided in the embodiment of the present invention; Figure 5 The voltage and current waveform diagram of the second input port β of the through traction power supply device provided in the embodiment of the present invention; Figure 6 The output port γ voltage and current waveform diagram of the through traction power supply device provided in the embodiment of the present invention; Figure 7 The grid-side current waveform diagram is provided for an embodiment of the present invention. Detailed Implementation

[0014] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0015] To solve the above technical problems, such as Figure 2 As shown, this invention proposes a method for eliminating DC secondary ripple in a through-type traction device based on multi-port collaboration. This method is applied to applications such as... Figure 1 The novel through-type traction power supply device shown is The device includes a first input port α, a second input port β, a common DC bus, and an output port γ. The first input port α and the second input port β are connected to the secondary side of an existing traction transformer, and the output port γ is connected to the traction network. The traction transformer transmits the three-phase grid voltage... Converted into two-phase voltages with equal amplitude and a phase difference of 60° or 90°. , and will , The voltage is input to the two input ports of the two-phase to single-phase converter unit, and after conversion, it is output from a single output port. The first input port α and the second input port β transfer energy to the DC side through a single-phase rectifier unit, while the output port γ outputs energy to the traction network through a single-phase inverter unit. Since each port is a single-phase power port, double-frequency pulsating power is generated during power transmission and is coupled and superimposed on the DC side.

[0016] The specific implementation steps of the method of the present invention include: Step S201: Collect three-port electrical quantities; The operating status of the first input port α, the second input port β, and the output port γ are monitored in real time, and the instantaneous value of the first input voltage at the first input port is collected. Instantaneous value of the first input current Phase angle of the first input voltage Phase angle with the first input current Instantaneous value of the second input voltage at the second input port Instantaneous value of the second input current Phase angle of the second input voltage Phase angle of second input current Instantaneous output voltage value at the output port Instantaneous value of output current Output voltage phase angle and output current phase angle The instantaneous voltage and current values ​​mentioned above can be acquired in real time by voltage and current sensors, and the phase angle can be obtained through synchronous detection or phase-locked loop extraction.

[0017] Step S202: Based on the three-port electrical quantities, construct the second harmonic power component model for each port; Based on the aforementioned collected three-port voltage, current, and phase angle information, the active and reactive power of each port are calculated, and the power factor angle of each port is obtained. For any port... k ( k =α, β, γ), active power reactive power and power factor angle They are represented as follows: (1) In the formula, and Ports k The effective values ​​of voltage and current.

[0018] For any port, for any port k Its instantaneous voltage and instantaneous current are expressed as follows: (2) The instantaneous power at the port can then be expressed as the sum of the average power component and the second harmonic power component, i.e.: (3) Considering as well as Further, each port can be obtained k The second harmonic power component model is rewritten as follows: (4) In equation (4) k By replacing them with the corresponding first input port α, second input port β, and output port γ, we can obtain the second harmonic power component model of the first input port, the second harmonic power component model of the second input port, and the second harmonic power component model of the output port corresponding to each port.

[0019] As can be seen from equation (4), the amplitude and phase of the second harmonic power component at the port are related to the active power, reactive power and phase of the port voltage.

[0020] Step S203: Based on the second harmonic power component model, with the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables, construct a quadratic ripple elimination optimization model with the objective function of minimizing the total second harmonic power on the DC side. Since the voltage phases of the first and second input ports are fixed and the active power is given, the second harmonic power component model of the first and second input ports can be expressed as the reactive power adjustment functions of the first and second input ports, respectively, as shown in the following equations: (5) In the formula, and These are the adjusted reactive power obtained after optimization from the first input port α and the second input port β, respectively.

[0021] For the output port γ, its active power is determined by the traction load power demand, and its reactive power must meet the traction network operation requirements; neither is considered an independent optimization variable. Therefore, the output port second harmonic power component model can be expressed as the output port voltage phase adjustment function as shown in the following equation: (6) In the formula, The output port γ is the regulated voltage phase obtained after optimization.

[0022] Based on the energy transmission relationship of the hybrid through-type traction power supply device, the first input port α and the second input port β transfer double-frequency power to the DC side during rectification and power delivery, while the output port γ absorbs double-frequency power from the DC side during inverter power supply. Therefore, the total double-frequency power on the DC side can be expressed as: (7) Substituting equations (5) and (6) into equation (7), we get: (8) Since the amplitude of the second harmonic ripple of the DC bus voltage is positively correlated with the amplitude of the pulsation of the synthesized second harmonic power on the DC side, an optimization model for eliminating the second harmonic ripple is constructed with the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables. The objective function is to minimize the total second harmonic power on the DC side, as shown in the following equation: (9) In the formula, T This is the period corresponding to the second harmonic power pulsation.

[0023] Based on the above objective function, to ensure that the secondary ripple elimination process meets the system operation requirements and that the electrical quantities at each port are within a safe and feasible range, further constraints need to be introduced to limit the optimization variables. The constraints of the secondary ripple elimination optimization model include: output port voltage constraints, output port phase constraints, input port current constraints, port capacity constraints, port power balance constraints, and grid-side power quality constraints.

[0024] Output port voltage constraint. To ensure that the output port voltage does not compromise the traction network voltage level requirements during secondary ripple cancellation, the voltage at output port γ should meet the traction network power supply requirements, denoted as: (10) In the formula, and These are the upper and lower limits of the effective value of the allowable output voltage of the traction network, respectively.

[0025] Output port phase constraint. To ensure that the output voltage can achieve secondary ripple elimination while still meeting the synchronization requirements for full-line operation, the voltage phase of the optimized output port γ is... It must meet the requirements of continuous power supply or same-phase closing, and its target phase is denoted as . Then there is an output phase synchronization constraint: (11) In the formula, This represents the upper limit of the allowable phase deviation.

[0026] Input port current constraint. To prevent overcurrent caused by excessive adjustment of the reactive power or current phase at the input port, the current at the first input port α is constrained. Current at the second input port β The value should not exceed the rated allowable value of the device and system: (12) In the formula, and These are the upper limits of the effective current values ​​at the first input port α and the second input port β, respectively.

[0027] Port capacity constraints. To ensure that the optimization results do not exceed the device design capacity, the actual power handled by each port should meet the converter's rated capacity limit: (13) In the formula, , and These are the rated capacity limits for the first input port α, the second input port β, and the output port γ, respectively.

[0028] Port power balance constraint. To ensure normal energy transfer within the device, the total active power on the input side should meet the power demand of the output load, denoted as: (14) In the formula, and These are the active power at the first input port α and the second input port β, respectively. This represents the active power at the output port γ.

[0029] Power quality constraints on the grid side. First, to ensure that the operation of the input port meets the power quality requirements of the traction transformer input side, the power factor on the input side should meet the allowable range, denoted as: (15) In the formula, This is the lower limit of the input-side power factor.

[0030] Furthermore, to ensure the symmetry of the three-phase currents on the grid side, the negative sequence current on the grid side should also meet the allowable range. Taking a V / V traction transformer as an example, based on the mapping relationship between the input port α and β currents and the three-phase currents on the grid side, the allowable range for the negative sequence current on the grid side can be obtained as follows: (16) In the formula, n This refers to the turns ratio coefficient of the traction transformer. This is the upper limit of the allowable negative sequence current on the grid side.

[0031] Step S204: Solve the secondary ripple elimination optimization model to generate cooperative modulation control commands.

[0032] The objective function is solved using numerical or nonlinear optimization methods to generate corresponding coordinated modulation control commands, which are then sent to the input and output stage converters. Specifically, for the input-side rectifier stage, the reactive power regulation at the first input port obtained through optimization is... Second input port reactive power regulation This is converted into a rectifier stage current inner loop reference value, used to update the current control commands for the first input port α and the second input port β. For the output-side inverter stage, the optimized solution of the output port target voltage phase is then applied. The phase command, serving as the inverter output reference voltage, is used to update the voltage reference signal at the output port γ. Through the execution of these control commands, the second harmonic power phasors on the input and output sides gradually approach the optimal matching relationship, thereby reducing DC-side secondary ripple.

[0033] Experimental verification In this embodiment, to verify the effectiveness of the proposed DC secondary ripple elimination method, a simulation model of a novel through-type traction power supply device was built in the MATLAB / Simulink platform. The simulation parameters are shown in Table 1. It should be noted that in practical engineering applications, a two-phase to single-phase converter unit is typically composed of multiple cascaded single-phase full-bridge submodules to meet the system voltage level and power capacity requirements. For example, each phase can use 25 submodules for cascaded operation, corresponding to a traction load of approximately 25 MW. Under this operating condition, the power undertaken by each submodule is basically evenly distributed, and the transmission power of a single submodule is approximately 1 MW. To facilitate the analysis of the control mechanism of the method of this invention, a single equivalent submodule is used for modeling and simulation analysis in this embodiment. Since the control strategies of each submodule are consistent, their operating characteristics are similar; therefore, this equivalent modeling method does not affect the verification of the effectiveness of the method of this invention.

[0034] Table 1 Simulation Parameters of the New Type of Through Traction Power Supply Device ; New type of through traction power supply device t The DC secondary ripple elimination method described in this invention was not used during the period from 0 to 0.2 s. t The method is used when the time is 0.2 s. Figure 3 It can be seen that, without using the method of this invention, the submodule The DC bus voltage exhibits significant secondary ripple, with a maximum DC voltage of approximately 2180 V and a minimum of approximately 1800 V. Compared to the rated DC voltage of 2000 V, the upper deviation is approximately 180 V, the lower deviation is approximately 200 V, and the peak-to-peak ripple value is approximately 380 V. t When the method of this invention is applied at 0.2 s, the DC voltage quickly stabilizes after a brief dynamic adjustment, with a maximum value of approximately 2008 V and a minimum value of approximately 1990 V. The upper deviation from the rated value of 2000 V is approximately 8 V, and the lower deviation is approximately 10 V. The peak-to-peak ripple value is reduced to approximately 18 V. This comparison shows that the secondary ripple of the DC voltage is reduced by 95.3% after applying the method of this invention, indicating that the method of this invention can significantly eliminate the secondary ripple of the DC voltage and improve the stability of the DC-side voltage of the device.

[0035] Depend on Figure 4 and Figure 5 It can be seen that, without using the method of the present invention, the first input port With the second input port The current waveforms are basically in phase with the corresponding port voltage waveforms, indicating that the input port is mainly operating in a state of approximately unity power factor. When the method of this invention is used, the first input port... With the second input port The phase of the current is significantly adjusted relative to the voltage at each port, as indicated by the phase difference shown in the figure. and This indicates that the input current is no longer strictly in phase with the port voltage, but rather exhibits a controlled phase shift. Therefore, the method of this invention, without altering the predetermined active power transmission requirements of the input port, achieves the reconstruction of the input current phase and current vector through reactive power adjustment on the input side, thereby changing the synthesis relationship of the second harmonic power component on the DC side of the input port.

[0036] Furthermore, by Figure 6 It can be seen that after adopting the method of the present invention, the output port The voltage and current amplitudes remain essentially constant, indicating that the power transmission state at the output port is generally stable and can meet the normal power supply requirements of the traction load. A magnified view shows that after implementing the method of this invention, the output port voltage phase is adjusted to a certain extent, and the output current phase shifts synchronously accordingly. This is because, during the implementation of the method of this invention, the active and reactive power at the output port remain essentially constant. Under the condition that the output voltage amplitude remains essentially constant, when the output voltage phase is adjusted, the output current needs to maintain the original power transmission relationship through a synchronous phase change. This demonstrates that the method of this invention, by coordinating the output-side voltage phase, changes the phase characteristics of the second harmonic power component at the output port on the DC side, thereby cooperating with the input side to achieve DC voltage secondary ripple elimination.

[0037] In addition, by Figure 7 It can be seen that after adopting the method of the present invention, the grid-side current waveform maintains good periodicity and symmetry, and no obvious distortion or instability occurs. This indicates that the method of the present invention does not introduce additional adverse effects while adjusting the reactive power on the input side and the voltage phase on the output side, and the overall system operates stably.

[0038] In summary, the method proposed in this invention coordinates the transmission and superposition of the second harmonic power components at the input and output ports on the DC side through input-side reactive power regulation and output-side voltage phase angle regulation. This effectively reduces the DC-side synthesized second harmonic power pulsation and significantly eliminates secondary ripple in the DC bus voltage. Simultaneously, it maintains normal power transmission, meets the power supply requirements of traction loads, and ensures operational stability and power quality. This invention requires no additional hardware; it actively suppresses secondary ripple on the DC side simply by optimizing the control strategy. This not only reduces DC bus voltage fluctuations and lowers the requirements for supporting capacitor configuration, but also has significant implications for improving the operational stability, power quality, and engineering application value of the new through-type traction power supply system.

[0039] In some embodiments, the present invention also provides a computer system 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-described method embodiments.

[0040] The present invention also provides a computer-readable storage medium for storing a computer program. This computer-readable storage medium can be applied to a computer device, and the computer program causes the computer device to perform the corresponding processes in the methods described above in the embodiments of the present invention; for the sake of brevity, further details are omitted here.

[0041] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0042] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this document. Those skilled in the art should recognize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for eliminating DC secondary ripple in a through-type traction device based on multi-port collaboration, characterized in that, include: The system collects three-port electrical quantities, including the instantaneous values ​​of the first input voltage, the first input current, the first input voltage phase angle, and the first input current phase angle of the first input port; the instantaneous values ​​of the second input voltage, the second input current, the second input voltage phase angle, and the second input current phase angle of the second input port; and the instantaneous values ​​of the output voltage, the output current, the output voltage phase angle, and the output current phase angle of the output port. Based on the three-port electrical quantities, a second harmonic power component model for each port is constructed; the second harmonic power component model for each port includes a first input port second harmonic power component model, a second input port second harmonic power component model, and an output port second harmonic power component model. Based on the aforementioned second harmonic power component model, a quadratic ripple elimination optimization model is constructed with the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables, and the objective function being the minimum total second harmonic power on the DC side. Solve the aforementioned secondary ripple elimination optimization model to generate cooperative modulation control commands; The step of constructing a second harmonic power component model for each port based on the three-port electrical quantities includes: Based on the instantaneous value of the first input voltage, the instantaneous value of the first input current, the phase angle of the first input voltage, and the phase angle of the first input current, the second harmonic power component model of the first input port is determined; Based on the instantaneous values ​​of the second input voltage, the second input current, the phase angle of the second input voltage, and the phase angle of the second input current, the second input port second harmonic power component model is determined: ； In the formula, The second harmonic power component model is for the first input port. The second input port is the second harmonic power component model. The active power at the first input port. The adjusted reactive power obtained after optimization at the first input port α. The active power at the second input port. The optimized reactive power obtained from the second input port β is... The angular frequency of the power grid. For time, The phase angle of the first input voltage. The phase angle of the second input voltage; Based on the instantaneous values ​​of the output voltage, the instantaneous values ​​of the output current, the phase angle of the output voltage, and the phase angle of the output current, the second harmonic power component model of the output port is determined.

2. The method according to claim 1, characterized in that, The second harmonic power component model, using the reactive power at the first input port, the reactive power at the second input port, and the voltage phase at the output port as optimization variables, constructs a quadratic ripple elimination optimization model with the objective function of minimizing the total second harmonic power on the DC side; including: Based on the second harmonic power component model, the adjustment function of each port is determined; The adjustment functions of each port are combined for DC-side second harmonic power synthesis. The reactive power of the first input port, the reactive power of the second input port, and the voltage phase of the output port are used as optimization variables to construct a quadratic ripple elimination optimization model with the objective function of minimizing the total DC-side second harmonic power.

3. The method according to claim 2, characterized in that, The adjustment functions for each port include a reactive power adjustment function for the first input port, a reactive power adjustment function for the second input port, and a voltage phase adjustment function for the output port. The determination of the adjustment function for each port based on the second harmonic power component model includes: Based on the second harmonic power component model of the first input port, the reactive power adjustment function of the first input port is determined; Based on the second input port second harmonic power component model, determine the reactive power regulation function of the second input port; Based on the second harmonic power component model of the output port, the voltage phase adjustment function of the output port is determined.

4. The method according to claim 3, characterized in that, The constraints of the quadratic ripple elimination optimization model include the following: Output port voltage constraints, output port phase constraints, input port current constraints, port capacity constraints, port power balance constraints, and grid-side power quality constraints.

5. The method according to claim 4, characterized in that, The coordinated modulation control command includes a first input port reactive power adjustment amount, a second input port reactive power adjustment amount, and an output port target voltage phase.

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