A resonant impedance reshaping device for electrified railways and a control strategy

Abstract

The application discloses a kind of electrified railway resonance impedance remodeling device and control strategy, it is related to electrified railway traction power supply technical field.Resonance impedance remodeling device is composed of cascaded H bridge type converter CHC, electric reactor L and measurement and control device MCD.Cascaded H bridge type converter CHC is connected with contact line T on the secondary side of traction substation TS through electric reactor L at any position;Measurement and control device MCD sends the DC side voltage of cascaded H bridge type converter CHC, traction network voltage and the AC side current of cascaded H bridge type converter CHC measured into controller CD, and controller CD sends output signal into cascaded H bridge type converter CHC to carry out real-time control to traction network voltage, forms virtual resistance to remodel impedance under the resonance frequency of electrified railway, to avoid the purpose that resonance overvoltage caused by harmonic current generated by electric locomotive EL.

Description

Technical Field

[0001] This invention relates to the field of traction power supply technology for electrified railways, and in particular to an electrified railway resonant impedance reshaping device and control strategy based on virtual resistance. Background Technology

[0002] Due to limited space in electric locomotives, filtering devices are generally not installed on them. Therefore, electric locomotives inevitably inject harmonic currents into the system during operation. Currently, electric locomotives are mainly AC-DC and AC-DC-AC types. AC-DC locomotives mainly generate low-order harmonics such as the 3rd, 5th, and 7th, while AC-DC-AC locomotives mainly generate high-order harmonics around the 50th or even 100th. When the harmonic current matches the existing resonant point of the electrified railway traction power supply system, a resonant overvoltage phenomenon will occur. This often causes the contact wire or roof surge arrester to burn out or explode, and the lighting electrical appliances in the traction substation to burn out, posing a serious threat to traffic safety. Current research on resonance suppression has led domestic and international scholars to propose resonance suppression measures for electrified railways, primarily based on passive and active filters. These measures all start by filtering out harmonic currents. However, if the harmonic current at the resonant frequency is not completely filtered out, it will inevitably cause resonant overvoltage. If the existing resonant point of the traction power supply system disappears, then harmonic currents at any frequency will not be able to cause a resonance accident. Therefore, this invention starts by changing the impedance frequency characteristics of the traction power supply system. By introducing a virtual impedance at the resonant frequency, the impedance of the electrified railway system is changed to make the existing resonant point disappear, thereby achieving the purpose of avoiding resonance accidents. Summary of the Invention

[0003] The purpose of this invention is to provide a resonant impedance reshaping device and control strategy for electrified railways, which can effectively solve the technical problem of resonant overvoltage phenomenon.

[0004] The objective of this invention is achieved through the following technical solution: an electrified railway resonant impedance reshaping device, comprising a cascaded H-bridge converter CHC, a reactor L, and a measurement and control device MCD; the cascaded H-bridge converter CHC is connected to any position on the contact line T on the secondary side of the traction substation TS via the reactor L; the measuring terminals of the measurement and control device MCD are respectively connected to the voltage terminal of the DC-side capacitor of the cascaded H-bridge converter CHC, the traction network voltage terminal, and the AC-side current terminal of the cascaded H-bridge converter CHC; the measurement and control device MCD measures... Voltage and current signals are sent to the controller CD. The output signal of the controller CD is connected to the cascaded H-bridge converter CHC to control the traction network resonant overvoltage caused by the harmonic current generated by the electric locomotive EL in real time. The cascaded H-bridge converter CHC consists of n single-phase H-bridge converters HC. The size of n is determined by the voltage level of the insulated gate bipolar transistor and the power supply mode of the electrified railway traction power supply system. Each H-bridge is a unit, and the units are cascaded to achieve high voltage and multi-level output.

[0005] The resonant impedance reshaping device is applicable to electrified railways under direct power supply, AT power supply, or any power supply method.

[0006] A virtual resistor is formed in parallel with the traction network by a resonant impedance reshaping device to change the impedance of the electrified railway at the existing resonant frequency. The MCD measurement and control device is used to collect the traction network voltage and the AC side current signal of the cascaded H-bridge converter CHC. A hierarchical control strategy is adopted to prevent the electrified railway from resonant overvoltage accidents. The control strategy includes three control modes: the first control mode is global DC voltage control, the second control mode is traction network harmonic voltage control, and the third control mode is DC voltage equalization control. The first-level global DC voltage control is to calculate the average voltage of the DC side capacitor of each unit and the difference with the reference value of the DC side capacitor voltage. After adjustment by the proportional-integral controller, the difference is multiplied by the unit sinusoidal value of the traction network voltage to obtain the reference value of the active current of the cascaded H-bridge converter CHC AC side.

[0007] A control strategy for a resonant impedance reshaping device for electrified railways, wherein the second-layer traction network harmonic voltage control process is as follows: First, the acquired traction network voltage is subjected to a fast Fourier transform to decompose the traction network voltage into harmonic signals of orders h1-h2. The amplitude of each harmonic signal is sent to a judgment module to obtain the amplitude of the resonant voltage signal. Then, the traction network resonant voltage is formed by an inverse fast Fourier transform. The result obtained by dividing by the virtual resistance is used as the reference value of the AC side resonant current of the cascaded H-bridge converter CHC. The reference value of the AC side active current of the cascaded H-bridge converter CHC is obtained by subtracting the reference value of the AC side resonant current of the cascaded H-bridge converter CHC. Finally, the difference between the reference value of the AC side current of the cascaded H-bridge converter CHC and the acquired AC side current of the cascaded H-bridge converter CHC is sent to a proportional-integral controller to obtain the original modulation wave of the cascaded H-bridge converter CHC.

[0008] The specific steps for the judgment module to obtain the amplitude of the resonant voltage signal in the second-layer traction network harmonic voltage control process are as follows: determine whether the amplitude of each harmonic voltage is greater than or equal to the harmonic voltage set value. If yes, output the corresponding harmonic voltage amplitude; if no, output 0. The harmonic voltage set value needs to be determined according to the traction network harmonic voltage threshold.

[0009] The virtual resistance involved in the second-layer traction network harmonic voltage control process adopts an adaptive form. First, the root mean square of each resonant voltage component output by the judgment module is calculated. The difference between the root mean square and the harmonic voltage set value is sent to the proportional-integral controller. Finally, the reciprocal of the virtual resistance is obtained through the limiting function. The reciprocal of the virtual resistance is limited to the range [y1, y2]. The values ​​of y1 and y2 are determined according to the power supply voltage of the electrified railway traction power supply system and the capacity of the cascaded H-bridge converter CHC.

[0010] The third-layer DC voltage equalization control employs a modulation wave reconstruction method. The AC side current of the cascaded H-bridge converter CHC is divided by its amplitude to obtain the adjustment signal. The average DC side voltage is subtracted from the DC side voltages of units 1 to (n-1) and then fed into a proportional-integral controller (PIC). The output of the PIC is multiplied by the adjustment signal, and the result is used as the modulation wave fine-tuning amount for units 1 to (n-1). Then, the negative of the sum of the modulation wave fine-tuning amounts of the first (n-1) units is taken as the modulation wave fine-tuning amount for the nth unit. Finally, the original modulation wave obtained from the second-layer traction network harmonic voltage control is superimposed with the modulation wave fine-tuning amounts of each unit to obtain a new modulation wave for each unit, which is then fed into the pulse width modulation (PWM) module. Compared with existing technologies, the beneficial effects of this invention are:

[0011] I. This invention can change the impedance at the resonant point of the traction power supply system of electrified railways, fundamentally avoiding the occurrence of resonant overvoltage.

[0012] Second, this invention only controls the voltage at the resonant point and has no effect on the fundamental voltage or current.

[0013] Third, this invention can reshape the resonant impedance of the traction power supply system under different operating conditions by adjusting the controller parameters according to the operating status of the traction power supply system (changes in locomotive model, changes in power supply operating mode, etc.). Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the topology of the electrified railway resonant impedance reshaping device integrated into the traction power supply system as described in Embodiment 1 of the present invention.

[0015] Figure 2 This is a schematic diagram of the cascaded H-bridge converter and reactor of the resonant impedance reshaping device described in Embodiment 2 of the present invention.

[0016] Figure 3 This is a schematic diagram of the overall control strategy of the resonant impedance reshaping device described in Embodiment 3 of the present invention. Detailed Implementation

[0017] To better understand the inventive concept of this invention, its working principle is briefly described below: To prevent resonant overvoltage accidents in the traction power supply system of electrified railways, a resonant impedance reshaping device is connected in parallel to the traction network to control the voltage of the traction network, thereby changing the impedance at the resonant point of the traction power supply system. The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] Example 1

[0019] like Figure 1 As shown, this embodiment of the invention provides a resonant impedance reshaping strategy device for electrified railways, including a cascaded H-bridge converter CHC, a reactor L, and a measurement and control device MCD; the cascaded H-bridge converter CHC is connected to any position on the contact line T on the secondary side of the traction substation via the reactor L; the measurement and control device MCD measures the voltage u of the DC-side capacitor of the cascaded H-bridge converter CHC. dc traction network voltage u T AC side current i of cascaded H-bridge converter CHC AD The signal is fed into the controller CD, which then sends the output signal to the cascaded H-bridge converter CHC to adjust the traction network voltage u. T Real-time control is performed to address the resonant overvoltage caused by harmonic currents generated by the electric locomotive EL.

[0020] Example 2

[0021] like Figure 2 As shown in the diagram, this embodiment of the invention provides a topology diagram of a cascaded H-bridge converter. The cascaded H-bridge converter CHC is composed of n single-phase H-bridge converters HC (HC1 to HC2). n Each H-bridge is a unit, and different units are cascaded to achieve high voltage and multi-level output. The specific number n of single-phase H-bridge converters (HC) is determined by the voltage level of the insulated-gate bipolar transistors (IGBTs) and the power supply method of the electrified railway traction power supply system. This structure also ensures that the resonant impedance reshaping strategy device can be connected to electrified railways under any power supply method, including direct power supply, BT power supply, and AT power supply.

[0022] Example 3

[0023] like Figure 3 As shown, based on an electrified railway resonant impedance reshaping device, a control strategy for the resonant impedance reshaping device is proposed: the measurement and control device MCD collects the traction network voltage and the AC side current of the cascaded H-bridge converter CHC, and through the control strategy, the electrified railway avoids the occurrence of resonant overvoltage accidents. The control strategy includes three control modes: the first control mode is global DC voltage control, the second control mode is traction network harmonic voltage control, and the third control mode is DC voltage equalization control.

[0024] The first-level global DC voltage control controls the voltage u of the DC-side capacitors in each unit. dc(k) After being fed into the summation module, the average DC-side voltage is obtained by dividing by the total number of cells, n. This average is then compared with the reference voltage value of the DC-side capacitor. The difference is calculated, and after adjustment by the proportional-integral controller, it is multiplied by the unit sinusoidal value of the traction network voltage to obtain the reference value of the active current on the AC side of the cascaded H-bridge converter CHC.

[0025] The second layer of traction network harmonic voltage control involves controlling the collected traction network voltage u. T A Fast Fourier Transform (FFT) is performed to decompose the traction network voltage into harmonic signals of orders 2-100. The amplitude of each harmonic signal is then fed into a judgment module to obtain the amplitude of the resonant voltage signal. Finally, an inverse FFT is performed to form the traction network resonant voltage u. Tr , let u Tr Divide by virtual resistance R AD Obtain the reference value of the resonant current on the AC side of the cascaded H-bridge converter CHC. The reference value of the active current on the AC side of the cascaded H-bridge converter CHC is compared with the reference value of the resonant current on the AC side of the cascaded H-bridge converter CHC. The AC side current reference value of the cascaded H-bridge converter CHC is obtained by subtraction. Finally, the AC side current reference value of the cascaded H-bridge converter CHC is... The AC side current i of the cascaded H-bridge converter CHC is collected. AD The difference is fed into the proportional-integral controller to obtain the original modulation wave of the cascaded H-bridge converter CHC. The specific steps for the judgment module to obtain the amplitude of the resonant voltage signal in the second-layer traction network harmonic voltage control process are as follows: determine whether the amplitude of each harmonic voltage is greater than or equal to the harmonic voltage set value. If yes, output the corresponding harmonic voltage amplitude; if no, output 0. The harmonic voltage set value needs to be determined according to the traction network harmonic voltage threshold.

[0026] The harmonic voltage setting value needs to be determined based on the traction network harmonic voltage threshold. The virtual resistor R in the traction network harmonic voltage control... AD Adaptive approach is adopted. First, the root mean square (RMS) of each resonant voltage component output by the judgment module is calculated, and then the RMS is compared with the harmonic voltage setpoint u. ε The difference is fed into a proportional-integral controller, and finally, the virtual resistance R is obtained through a limiting function. AD The reciprocal of the virtual resistance. The function of the limiting function is to limit the reciprocal of the virtual resistance to the range [y1, y2]. The values ​​of y1 and y2 are determined based on the power supply voltage of the electrified railway traction power supply system and the capacity of the cascaded H-bridge converter CHC.

[0027] The third-level DC voltage equalization control adopts the form of modulation wave reconstruction to convert the AC side current i of the cascaded H-bridge converter CHC. AD Dividing its amplitude by the average voltage of the DC-side capacitor is used as the adjustment signal. The difference between the voltages of the DC-side capacitors of units 1 to (n-1) is calculated and then fed into a proportional-integral (PI) controller. The output of the PPI controller is multiplied by the adjustment signal to obtain the modulation wave fine-tuning amount Δu for units 1 to (n-1). AD To ensure that the third-layer DC voltage equalization control does not affect the first-layer global DC voltage control, the negative of the sum of the modulation wave fine-tuning values ​​of the previous n-1 units is taken as the modulation wave fine-tuning value Δu of the nth unit. AD(n) Finally, the original modulated wave obtained by controlling the harmonic voltage of the traction network is... The modulated wave is superimposed on the fine-tuning amount of the modulation wave of each unit and sent to the PWM modulation module as a new modulation wave for each unit.

Claims

1. A control strategy for a resonant impedance reshaping device for electrified railways, comprising a cascaded H-bridge converter CHC, a reactor L, and a measurement and control device MCD; characterized in that: The cascaded H-bridge converter CHC is connected to any position on the contact line T on the secondary side of the traction substation TS via reactor L. The measuring terminals of the measurement and control device MCD are connected to the voltage terminals of the DC-side capacitor, the traction network voltage terminal, and the AC-side current terminal of the cascaded H-bridge converter CHC, respectively. The voltage and current signals measured by the measurement and control device MCD are sent to the controller CD. The output signal of the controller CD is connected to the cascaded H-bridge converter CHC to perform real-time control of the traction network resonant overvoltage caused by the harmonic current generated by the electric locomotive EL. The cascaded H-bridge converter CHC includes... n It consists of a single-phase H-bridge converter HC. n The size is determined by the voltage level of the insulated gate bipolar transistor and the power supply method of the electrified railway traction power supply system. Each H-bridge is a unit, and the units are cascaded to achieve high voltage and multi-level output. A virtual resistor is formed in parallel with the traction network by a resonant impedance reshaping device to change the impedance of the electrified railway at the existing resonant frequency. The MCD measurement and control device is used to collect the traction network voltage and the AC side current signal of the cascaded H-bridge converter CHC. A hierarchical control strategy is adopted to prevent the electrified railway from resonant overvoltage accidents. The hierarchical control strategy includes a first layer of global DC voltage control, a second layer of traction network harmonic voltage control, and a third layer of DC voltage equalization control. The first layer of global DC voltage control is to calculate the average voltage of the DC side capacitor of each unit and the difference with the reference value of the DC side capacitor voltage. After adjustment by a proportional-integral controller, the difference is multiplied by the unit sinusoidal value of the traction network voltage to obtain the reference value of the active current of the cascaded H-bridge converter CHC AC side. The second-layer traction network harmonic voltage control is as follows: First, the acquired traction network voltage is subjected to a fast Fourier transform, decomposing the traction network voltage into... h 1- h The second harmonic signal is obtained, and the amplitude of each harmonic signal is sent to the judgment module to obtain the amplitude of the resonant voltage signal. Then, the resonant voltage of the traction network is formed by inverse fast Fourier transform. The result obtained by dividing by the virtual resistance is used as the reference value of the resonant current on the AC side of the cascaded H-bridge converter CHC. The reference value of the active current on the AC side of the cascaded H-bridge converter CHC is obtained by subtracting the reference value of the resonant current on the AC side of the cascaded H-bridge converter CHC. Finally, the difference between the reference value of the AC side current of the cascaded H-bridge converter CHC and the acquired AC side current of the cascaded H-bridge converter CHC is sent to the proportional-integral controller to obtain the original modulation wave of the cascaded H-bridge converter CHC.

2. The control strategy for an electrified railway resonant impedance reshaping device according to claim 1, characterized in that: The resonant impedance reshaping device is applicable to electrified railways under direct power supply, AT power supply, or any power supply method.

3. The control strategy for an electrified railway resonant impedance reshaping device according to claim 1, characterized in that: The specific steps for the judgment module to obtain the amplitude of the resonant voltage signal in the second-layer traction network harmonic voltage control are as follows: determine whether the amplitude of each harmonic voltage is greater than or equal to the harmonic voltage set value. If yes, output the corresponding harmonic voltage amplitude; if no, output 0. The harmonic voltage set value needs to be determined according to the traction network harmonic voltage threshold.

4. The control strategy for an electrified railway resonant impedance reshaping device according to claim 1, characterized in that: The virtual resistance involved in the second-layer traction network harmonic voltage control adopts an adaptive form. First, the root mean square (RMS) of each resonant voltage component output by the judgment module is calculated. The difference between the RMS and the harmonic voltage setpoint is then sent to the proportional-integral controller. Finally, the reciprocal of the virtual resistance is obtained through a limiting function, where the reciprocal of the virtual resistance is limited to a range of […]. y 1, y 2] or less, y 1. y The value of 2 is determined based on the power supply voltage of the electrified railway traction power supply system and the capacity of the cascaded H-bridge converter CHC.

5. The control strategy for an electrified railway resonant impedance reshaping device according to claim 1, characterized in that: The third-level DC voltage equalization control adopts a modulated wave reconstruction method, using the AC side current of the cascaded H-bridge converter CHC divided by its amplitude as the adjustment signal, and the average DC side voltage is compared with the first to the second... n The DC-side voltage of unit -1 is calculated by subtracting the input voltage and then fed into the proportional-integral controller. The output of the proportional-integral controller is multiplied by the regulation signal, and the result is used as the first to second voltages. n The modulation wave fine-tuning amount of unit -1, then take the previous value. n The negative of the sum of the modulation wave fine-tuning values ​​of -1 units is used as the first... n The modulation wave fine-tuning amount of each unit is then used to superimpose the original modulation wave obtained from the harmonic voltage control of the second-layer traction network with the modulation wave fine-tuning amount of each unit, and send it as the new modulation wave of each unit into the pulse width modulation module (PWM).

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