High voltage circuit system and control method thereof

Abstract

The application discloses a high-voltage circuit system and a control method thereof. The high-voltage circuit system comprises a main isolation contactor KM1, a low-pass filter unit comprising a filter support capacitor FC and a filter reactor FL, one end of the filter support capacitor FC being connected to the filter reactor FL, an IGBT electronic switch KMQ, one end of the IGBT electronic switch KMQ being connected to the filter reactor FL, and the other end of the IGBT electronic switch KMQ being connected to the main isolation contactor KM1. When high voltage is applied to the high-voltage circuit system, the IGBT electronic switch KMQ and the main isolation contactor KM1 are closed, the filter support capacitor FC starts to charge, the voltage of the filter support capacitor FC rises, and when the voltage difference between the voltage of the filter support capacitor FC and the battery voltage reaches a preset voltage difference, it is determined that the filter support capacitor FC completes pre-charging, the IGBT electronic switch KMQ is disconnected, and the filter support capacitor FC stops charging.

Description

Technical Field

[0001] This application relates to the field of high-voltage circuits for urban rail vehicles, and more particularly to a high-voltage circuit system and its control method. Background Technology

[0002] High-voltage electrical systems in rail transit typically consist of a high-voltage input stage and a converter load stage. The converter stage generally comprises three-phase inverters, DC / DC converters, and rectifiers, all composed of power electronic devices such as IGBTs, diodes, and MOSFETs. This stage is highly sensitive to voltage and current surges from the high-voltage input stage and is easily damaged. Correspondingly, the high-voltage stage mainly consists of high-voltage protection devices, which serve to buffer and isolate the intermediate surge energy between the power grid and the downstream converter system, provide pre-charging support capacitors, and facilitate power mode switching.

[0003] The high-voltage electrical topology of rail transit vehicles is generally as follows: Figure 1 As shown, the high-voltage input stage typically consists of a grid voltage sensor TV0, a ​​grid current sensor TA1, a main isolation contactor KM1, a pre-charging contactor KM2, a pre-charging resistor R1, a filter reactor FL, a filter support capacitor FC, and an FC capacitor voltage sensor TV1. FL and FC form a low-pass filter unit; FC is typically 4mF and FL is typically 4mH. KM1, KM2, and R1 form a high-voltage disconnect switch and provide pre-charging for the FC capacitor; R1 is typically 150 ohms. The existing topology has the following drawbacks:

[0004] 1. The high-voltage input stage has a large number of components, a complex structure, and a high cost. The pre-charging time is too long, generally exceeding 2 seconds.

[0005] 2. The coordination relationship between KM1, KM2 and R1 is complex and requires multiple mechanical actions, which has a significant impact on the life of the contactor. The failure rate of pre-charging problems is significantly higher than that of other components, causing vehicles to fail to start normally or even the train to be taken off the line after passengers are cleared.

[0006] 3. During the pre-charging period, resistor R1 must withstand heat of up to 5kJ or even higher within 0.1s. The requirements for short-term overload of the resistor are very high. Improper calculation and control of the accumulated energy of the resistor often leads to the resistor burning out or short circuit, causing serious operational failures.

[0007] 4. KM1 acts as an electrical isolating switch for the high-voltage system, disconnecting the grid high voltage from the inverter in the event of a system fault, providing slow isolation protection. KM2 and R1 are only used for current-limiting pre-charging of the FC capacitor, preventing the grid from directly charging the capacitor through the FL reactor. Faults in TV0 and TV1 sensors, as well as faults in the R1 pre-charging resistor, can lead to abnormal pre-charging processes. Uncontrollable overcharging can damage the capacitor and the KM1 main contactor, and the resulting oscillating voltage can damage the relatively fragile three-phase inverter. Furthermore, the operation of KM1 and KM2 is controlled by the difference between the FC voltage and the grid voltage. If the difference is too large, KM1 cannot close; if the difference exceeds 2 seconds, a pre-charging fault will be reported, causing the system to lock up. Grid voltage fluctuations and sensor zero drift can also cause the system to lock up.

[0008] 5. KM1 is a mechanically operated switch with a response time of up to 100ms. It has a long isolation time for the downstream inverter system and can only be used for IGBT overheating faults with short protection time. The risk of downstream system being affected is relatively high.

[0009] Therefore, while traditional high-voltage input structures are relatively mature, they also suffer from drawbacks such as high cost and high failure rate, and cannot provide rapid protection for downstream systems. To address this, a new high-voltage topology and its control method are needed that can enable unlimited pre-charging of the system in terms of time and number of cycles, possess high reliability, and provide rapid grid disconnection for weak downstream power electronic systems. Summary of the Invention

[0010] This application provides a high-voltage circuit system and its control method, which at least solves the problems of a large number of high-voltage input stage devices, complex structure, high cost, excessively long pre-charging time, high risk of system oscillation, short service life, high failure rate, and low efficiency of mechanical switch protection circuit.

[0011] This invention provides a high-voltage circuit system and its control method, the high-voltage circuit system comprising:

[0012] Main isolating contactor KM1;

[0013] A low-pass filter unit includes a filter support capacitor FC and a filter reactor FL, wherein one end of the filter capacitor FC is connected to the filter reactor FL;

[0014] The IGBT electronic switch KMQ has one end connected to the filter reactor FL and the other end connected to the main isolation contactor KM1.

[0015] When high voltage is applied to the high voltage circuit system, the IGBT electronic switch KMQ and the main isolation contactor KM1 are closed, and the filter support capacitor FC begins to charge, causing the voltage of the filter support capacitor FC to rise. When the voltage difference between the voltage of the filter support capacitor FC and the battery voltage reaches a preset voltage difference, it is determined that the filter support capacitor FC has completed pre-charging, and the IGBT electronic switch KMQ is opened, causing the filter support capacitor FC to stop charging.

[0016] The aforementioned high-voltage circuit system also includes:

[0017] Grid voltage sensor TV0;

[0018] The grid current sensor TA1 has one end connected to one end of the grid voltage sensor TV0 and the other end connected to the main isolation contactor KM1.

[0019] An FC capacitor voltage sensor, one end of which is connected to the filter reactor FL;

[0020] A three-phase inverter is connected to the filter support capacitor FC.

[0021] When high voltage is applied to the high voltage circuit system, the main isolation contactor KM1 and the IGBT electronic switch KMQ are closed. Current flows from the voltage source DC through the grid current sensor TA1, the main isolation contactor KM1, the IGBT electronic switch KMQ, the filter reactor FL, and the filter support capacitor FC. After the current flows through the positive terminal of the filter support capacitor FC, it is shunted and flows into the high voltage circuit branch.

[0022] The high-voltage circuit system described above includes a first high-voltage circuit branch and a second high-voltage circuit branch.

[0023] Wherein, after the current flows into the first high-voltage circuit branch, it flows to the three-phase inverter, and flows out from the negative terminal of the inverter back to GND;

[0024] The current flows into the second high-voltage circuit branch and then to the filter support capacitor FC, charging the filter support capacitor FC. The current then flows out from the negative terminal of the filter support capacitor FC and back to GND.

[0025] The present invention also provides a high-voltage circuit system control method, characterized in that the high-voltage circuit system control method includes a direct charging pre-charge control method, a modulation-free pre-charge control method based on an LC model, a pre-charge control method based on an exponential function, and a power grid overvoltage cut-off protection control method.

[0026] In the above-mentioned high-voltage circuit system control method, the direct charging pre-charge control method includes:

[0027] When high voltage is applied to the high voltage circuit system, the main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge.

[0028] In the above-mentioned high-voltage circuit system control method, the modulation-free pre-charge control method based on the LC model includes:

[0029] A simulation model of the first high-voltage circuit system based on the LC model was established using simulation tools, and the optimal switching width and frequency were preset.

[0030] In the above-mentioned high-voltage circuit system control method, the modulation-free pre-charge control method based on the LC model further includes:

[0031] When high voltage is applied to the high voltage circuit system, according to the preset optimal switching width and preset frequency, the IGBT electronic switch KMQ is alternately turned on using the first high voltage circuit system simulation model. The main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge.

[0032] Determine whether the pre-charging of the filter support capacitor FC is complete. If the result is that the pre-charging of the filter support capacitor FC is complete, the state of the IGBT electronic switch KMQ changes from interleaved conduction to constant conduction.

[0033] In the above-mentioned high-voltage circuit system control method, the pre-charge control method based on the exponential function includes:

[0034] A simulation model of the second high-voltage circuit system based on the exponential function is established using the simulation tool, and the first nonlinear exponential coefficient and the second nonlinear exponential coefficient are selected using the simulation tool according to the principle of minimizing impact.

[0035] In the above-mentioned high-voltage circuit system control method, the pre-charge control method based on the exponential function includes:

[0036] When the high voltage is applied to the high voltage circuit system, according to the first nonlinear exponential coefficient and the second nonlinear exponential coefficient, the second high voltage circuit system simulation model is used to perform nonlinear interleaved conduction of the IGBT electronic switch KMQ. The main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge.

[0037] Determine whether the pre-charging of the filter support capacitor FC is complete. If the result is that the pre-charging of the filter support capacitor FC is complete, the state of the IGBT electronic switch KMQ changes from non-linear interleaved conduction to constant conduction.

[0038] In the above-mentioned high-voltage circuit system control method, the power grid overvoltage cutoff protection control method includes:

[0039] When the grid voltage sensor detects that the voltage difference of the high-voltage circuit system exceeds the standard voltage difference, it closes the IGBT electronic switch KMQ and then detects the voltage difference of the high-voltage circuit system again. When the voltage difference decreases to the standard voltage difference, it opens the IGBT electronic switch KMQ to realize the overvoltage cut-off protection of the high-voltage circuit system.

[0040] Compared to related technologies, this invention proposes a high-voltage circuit system and its control method, which presents an electrical topology for a train traction high-voltage system with series power electronic switches in the high-voltage circuit. This topology has fewer components, lower cost, higher pre-charging efficiency, and lower failure rate. This invention determines the pre-charging control strategy through numerical calculation or model simulation, and formulates direct charging or multi-pulse control strategies based on data. This invention proposes a design method for the multi-pulse pre-charging control strategy, including an implementable simulation model, pulse sequence, and control cycle, and proposes a simple fixed-pulse-width multi-pulse sequence method. This invention proposes a multi-pulse pre-charging control strategy based on an exponential function, providing a specific formula for the nonlinear exponential function. The exponential function control parameters are optimized through a more intuitive simulation model. The non-pre-emptive multi-pulse sequence has a good matching relationship with the new circuit structure, enabling uniform and rapid completion of the pre-charging process. This invention also proposes a single-pulse pre-transfer grid overvoltage cutoff protection strategy, identifying the voltage difference between KMQ and CE when the grid is overvoltaged to determine the cutoff strategy. If the voltage difference exceeds a threshold, a short pre-transfer of KMQ single pulse is proposed to reduce the KMQ voltage difference before quickly cutting off the grid for rapid protection.

[0041] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description

[0042] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0043] Figure 1 This is a prior art high-voltage circuit topology based on the embodiments of this application;

[0044] Figure 2 This is a high-voltage circuit topology according to an embodiment of this application;

[0045] Figure 3 It is an equivalent second-order circuit of the high-voltage circuit according to the embodiments of this application;

[0046] Figure 4 This is a MATLAB simulation model of an RLC series equivalent second-order circuit according to an embodiment of this application.

[0047] Figure 5 These are MATLAB simulation waveforms under harsh working conditions according to embodiments of this application;

[0048] Figure 6 These are MATLAB simulation waveforms under suitable operating conditions according to embodiments of this application;

[0049] Figure 7 The waveform simulated in MATLAB when the pulse width is greater than a quarter cycle according to the embodiments of this application;

[0050] Figure 8 The waveform simulated in MATLAB according to the embodiments of this application has a pulse width less than and close to a quarter cycle.

[0051] Figure 9 The waveform simulated in MATLAB according to the embodiments of this application has a pulse width that is less than and far from a quarter cycle.

[0052] Figure 10 These are MATLAB simulation waveforms under fixed narrow pulse width and multiple cycles according to embodiments of this application.

[0053] Figure 11 This is a MATLAB simulation model of pre-charge control based on an exponential function according to an embodiment of this application;

[0054] Figure 12 This is a MATLAB simulation waveform of precharge control based on an exponential function according to an embodiment of this application;

[0055] Figure 13 This is a single-pulse pre-transfer type power grid overvoltage cutoff protection according to an embodiment of this application.

[0056] The attached figures are labeled as follows:

[0057] TV0: Mains voltage sensor;

[0058] TA1: Network current sensor;

[0059] KM1: Main isolating contactor;

[0060] KMQ: IGBT electronic switch;

[0061] FL: Filter reactor;

[0062] FC: Filter support capacitor;

[0063] TV1: FC capacitor voltage sensor;

[0064] CTU: U-phase current sensor;

[0065] CTW: W-phase current sensor;

[0066] M: Traction motor. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to 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. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0068] Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0069] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0070] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application refers to two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following objects are in an "or" relationship. The terms "first," "second," and "third" used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0071] This invention proposes a high-voltage circuit system and its control method, which realizes unlimited pre-charging of the system in terms of time and number of times, has high reliability, and provides a fast grid disconnection action for the weak power electronic system in the downstream stage.

[0072] The embodiments of this application will be described below using a high-voltage circuit system and its control method as an example.

[0073] Example 1

[0074] This embodiment provides a high-voltage circuit system and its control method. Please refer to... Figure 2 , Figure 2 This is a high-voltage circuit topology according to an embodiment of this application, such as... Figure 2 As shown, the high-voltage circuit system includes:

[0075] Main isolating contactor KM1;

[0076] The low-pass filter unit includes a filter support capacitor FC and a filter reactor FL, with one end of the filter capacitor FC connected to the filter reactor FL.

[0077] The IGBT electronic switch KMQ has one end connected to the filter reactor FL and the other end connected to the main isolation contactor KM1.

[0078] When high voltage is applied to the high voltage circuit system, the IGBT electronic switch KMQ and the main isolation contactor KM1 are closed, and the filter support capacitor FC begins to charge, causing the voltage of the filter support capacitor FC to rise. When the voltage difference between the filter support capacitor FC and the battery voltage reaches the preset voltage difference, it is determined that the filter support capacitor FC has completed pre-charging, and the IGBT electronic switch KMQ is opened, so that the filter support capacitor FC stops charging.

[0079] In this embodiment, the high-voltage circuit system further includes:

[0080] Grid voltage sensor TV0;

[0081] The grid current sensor TA1 has one end connected to one end of the grid voltage sensor TV0 and the other end connected to the main isolation contactor KM1.

[0082] An FC capacitor voltage sensor, one end of which is connected to the filter reactor FL;

[0083] A three-phase inverter is connected to the filter support capacitor FC.

[0084] When high voltage is applied to the high voltage circuit system, the main isolation contactor KM1 and the IGBT electronic switch KMQ are closed, and the current flows from the voltage source DC through the grid current sensor TA1, the main isolation contactor KM1, the IGBT electronic switch KMQ, the filter reactor FL, and the filter support capacitor FC. After the current flows through the positive terminal of the filter support capacitor FC, it is shunted and flows into the high voltage circuit branch.

[0085] The high-voltage circuit branch includes a first high-voltage circuit branch and a second high-voltage circuit branch.

[0086] Wherein, after the current flows into the first high-voltage circuit branch, it flows to the three-phase inverter, and flows out from the negative terminal of the inverter back to GND;

[0087] The current flows into the second high-voltage circuit branch and then to the filter support capacitor FC, charging the filter support capacitor FC. The current then flows out from the negative terminal of the filter support capacitor FC and back to GND.

[0088] In a specific embodiment, the new high-voltage circuit consists of TV0, TA1, KM1, KMQ, FL, TV1, FC, a three-phase inverter, CTU, CTW, M, etc.; TV0, TA1, KM1, KMQ, FL, TV1, and FC together form the high-voltage input stage circuit. The high-voltage measurement of TV0 is connected to the DC+ of the high-voltage input power supply, and the high-voltage measurement of TV0 is connected to the GND of the high-voltage input power supply. The "+" terminal of KM1 is connected to the DC+ of the high-voltage input power supply, and the "-" terminal of KM1 is sequentially connected to the C terminal of IGBT KMQ. The C terminal of IGBT KMQ is connected to the "+" terminal of FL, and the "-" terminal of FL is sequentially connected to the "+" terminal of FC. The "-" terminal of FC is connected to the GND of the high-voltage input power supply, the high-voltage measurement of TV1 is connected to the "+" terminal of FC, and the high-voltage measurement of TV1 is connected to the "-" terminal of FC or the GND of the high-voltage input power supply. The measurement hole of TA1 is threaded through the wire between the "+" terminal of KM1 and the DC+ of the high-voltage power supply. The FC terminal "+" is connected to the high-voltage input terminal "+" of the three-phase inverter via a low-inductance busbar, and the FC terminal "-" is connected to the high-voltage input terminal "-" of the three-phase inverter via a low-inductance busbar. The three-phase output of the three-phase inverter is connected to the three-phase input terminal of M. The measuring holes of CTU and CTW are respectively threaded onto the U-phase and W-phase conductors between the three-phase inverter and M.

[0089] Among them, TV0: grid voltage sensor; TA1: grid current sensor; KM1: main isolation contactor; KMQ: IGBT electronic switch; FL: filter reactor; FC: filter support capacitor; TV1: FC capacitor voltage sensor; CTU: U-phase current sensor; CTW: W-phase current sensor; M: traction motor.

[0090] High-voltage circuit working principle: When KM1 and KMQ are both closed and conducting, the high-voltage input stage circuit is in a fully conducting state in both forward and reverse directions. When energy flows in the forward direction, the current flows from DC+ through TA1, KM1, KMQ, FL, and FC in the main circuit. After passing through the "+" of FC, it splits into two branches. The first branch flows to the three-phase inverter and returns to GND from the negative terminal of the inverter. The second branch flows out from the "-" of FC through capacitor FC and returns to GND. The capacitor charges, and the capacitor voltage TV1 rises. If the inverter stops working, the first branch stops working and there is no current. If the grid voltage TV0 and the FC voltage TV2 have the same amplitude and phase, the second branch stops working and there is no current, thus forming a complete return loop. When energy flows in the reverse direction, the current flows in the completely opposite direction. The first and second branches merge and flow in reverse to DC+. The capacitor FC discharges, and the capacitor voltage TV1 drops. In addition, there will be circulating current in FC and inside the three-phase inverter. The direction of the circulating current is either positive or negative depending on the operating state.

[0091] When KM1 is on and KMQ is off, the circuit is partially closed, and only reverse energy flow is possible, such as the negative half-wave during oscillation.

[0092] When KM1 is off and KMQ is on, the circuit is completely shut down, with no current flow and no energy exchange.

[0093] Example 2

[0094] Please refer to Figures 3 to 13 , Figure 3 It is an equivalent second-order circuit of the high-voltage circuit according to the embodiments of this application; Figure 4 This is a MATLAB simulation model of an RLC series equivalent second-order circuit according to an embodiment of this application. Figure 5 These are MATLAB simulation waveforms under harsh working conditions according to embodiments of this application; Figure 6 These are MATLAB simulation waveforms under suitable operating conditions according to embodiments of this application; Figure 7 The waveform simulated in MATLAB when the pulse width is greater than a quarter cycle according to the embodiments of this application; Figure 8 The waveform simulated in MATLAB according to the embodiments of this application has a pulse width less than and close to a quarter cycle. Figure 9 The waveform simulated in MATLAB according to the embodiments of this application has a pulse width that is less than and far from a quarter cycle. Figure 10 These are MATLAB simulation waveforms under fixed narrow pulse width and multiple cycles according to embodiments of this application. Figure 11 This is a MATLAB simulation model of pre-charge control based on an exponential function according to an embodiment of this application; Figure 12 This is a MATLAB simulation waveform of precharge control based on an exponential function according to an embodiment of this application; Figure 13 This is a single-pulse pre-transfer type power grid overvoltage cutoff protection according to an embodiment of this application. For example... Figures 3 to 13 As shown, the high-voltage circuit system control method of the invention is applicable to the above-mentioned high-voltage circuit system, and the high-voltage circuit system control method includes:

[0095] Direct charging pre-charge control method, modulation-free pre-charge control method based on LC model, pre-charge control method based on exponential function and grid overvoltage cut-off protection control method.

[0096] In this embodiment, the direct charging pre-charge control method includes:

[0097] When high voltage is applied to the high voltage circuit system, the main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, current flows into the second branch, and the filter support capacitor FC begins to charge.

[0098] In practical implementation, there are two control strategies for KMQ: one is no control, where the FC capacitor is directly charged through the reactor; the other is to apply control, where no control strategy is applied, keeping the IGBT KMQ always on. The high-voltage circuit is equivalent to a second-order RLC series circuit, such as... Figure 3 As shown; where RFL is the equivalent resistance of the reactor FL and the line, which is generally small for traction systems, about 100-200 milliohms; DC is the standard voltage source. Urban rail transit typically uses two voltage sources: DC 750V and DC 1500V. When KM1 is closed, the system is equivalent to the step response of an RLC series second-order circuit. When selecting the LC for the traction system... Therefore, it is an underdamped system. The current and FC voltage responses of the series system are as follows:

[0099]

[0100]

[0101] in,

[0102] Resonant angular frequency L is the inductance value (H), and C is the capacitance value (F);

[0103] Attenuation factor R is the equivalent resistance of the line (Ω), which is the internal resistance of the reactor and the line resistance.

[0104] The system's inherent oscillation period is T = 2π / ω0;

[0105] A represents the power supply amplitude, and ω represents the power supply frequency. For this system, the fundamental frequency dominates, and other frequencies are ignored; therefore, ω = ω0. Calculations show that the peak value of the line current i and the capacitor voltage u... c The peak values ​​are very high, with FC having C = 4000uF, FL having L = 4mH, and R... FL Taking R = 100mΩ and DC power supply A = 1500V as an example, during the first 1 / 4 cycle of the fundamental frequency:

[0106] i max =1387.6A;

[0107] u max =2895V;

[0108] It can be seen that the peak current and peak voltage are extremely high, far exceeding the range that the system devices can withstand.

[0109] Numerical calculations using formulas are not intuitive enough. This invention recommends using simulation software such as MATLAB to create more intuitive timing diagrams. The MATLAB simulation model of the RLC series equivalent second-order circuit is shown below. Figure 4As shown; simulation provides a clear view of the system's timing waveforms, and the simulated waveforms closely resemble the actual waveforms. The MATLAB simulation waveforms under harsh operating conditions are shown below. Figure 5 As shown;

[0110] Under certain suitable operating conditions, a simple direct-charging control strategy can also be adopted, which is often used in systems with low operating voltage, small LC filtering, low output power, and high switching frequency. For example, FC has C=400uF, FL has L=3mH, and R... FL Taking R = 200mΩ and DC power supply A = 750V as an example, the MATLAB simulation waveform under suitable operating conditions is as follows: Figure 6 As shown in the waveform, under suitable operating conditions, the peak values ​​of the first voltage and the first current during the step response are not very high, and most devices can withstand them for a short period of time, making it suitable for a direct charging control strategy.

[0111] Therefore, when designing the program, this invention needs to determine the control strategy of KMQ through numerical calculation or model simulation. If the result is suitable, a simple direct charging strategy can be adopted, while a multi-level pre-charging control strategy based on the LC model can be adopted when conditions are adverse.

[0112] The implementation steps of the direct charging pre-charge control method without applying control are as follows:

[0113] Step 1: System Preparation;

[0114] Step 2: Apply high voltage to the power grid, and both KM1 and KMQ are opened;

[0115] Step 3: KMQ is closed, and direct charging control is applied without control.

[0116] Step 4: KM1 is closed, the circuit is connected, the second branch is working, and FC charging begins;

[0117] Step 5: Pre-charging complete, KM1 and KMQ status maintained, system is about to start formal operation.

[0118] In this embodiment, the modulation-free precharge control method based on the LC model includes:

[0119] A simulation model of the first high-voltage circuit system based on the LC model was established using simulation tools, and the optimal switching width and frequency were preset.

[0120] When high voltage is applied to the high voltage circuit system, according to the preset optimal switching width and preset frequency, the IGBT electronic switch KMQ is alternately turned on by the first high voltage circuit system simulation model. The main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge.

[0121] Determine whether the pre-charging of the filter support capacitor FC is completed. When the determination result is that the pre-charging of the filter support capacitor FC is completed, the state of the IGBT electronic switch KMQ changes from interleaved conduction to constant conduction.

[0122] In a specific implementation, when the switch pulse width T purse > T / 4, the voltage and current peaks cross the highest point of the free oscillation. And since the oscillation has formed, the reactor current shows a negative oscillation. Only part of the energy is stored in FC, resulting in a significant reduction in the charging effect. More seriously, due to the peak of the free oscillation, it causes a large impact on the device. This pulse width is not suitable for high-voltage and large FC value occasions. As Figure 7 shown in the matlab simulation waveform when the pulse width is greater than one-quarter of the period.

[0123] When the switch pulse width T purse < T / 4, this pulse width is relatively close to T / 4. The voltage and current peaks do not completely cross the highest point of the free oscillation, only forming a 1 / 4 oscillation waveform. The reactor current does not show a negative oscillation, and all the oscillation energy is stored in FC, and the charging effect is very good. However, due to being close to the peak of the free oscillation, it causes a large impact on the device. This pulse width is not suitable. As Figure 8 shown in the matlab simulation waveform when the pulse width is less than and close to one-quarter of the period [[ID=##]] [[ID=##]]

[0124] When the switch pulse width T purse < T / 4, this pulse width is about T / 12. The voltage and current peaks are far from the highest point of the free oscillation, only forming a partial initial oscillation waveform. The reactor current does not show a negative oscillation, and all the oscillation energy is stored in FC, and the charging effect is good. Since it is far from the peak of the free oscillation, it will not cause a large impact on the device. This pulse width is relatively suitable. As Figure 9 shown in the matlab simulation waveform when the pulse width is less than and far from one-quarter of the period.

[0125] From the above analysis, when the control pulse width is less than 1 / 4 of the natural oscillation period, the amplitudes of the peak charging current and peak voltage decrease with the decrease of the pulse width. However, the charging energy of each pulse will also decrease accordingly, and the number of pulses to be charged will increase. A series of pulse control strategies are required. To avoid oscillation, the switching frequency f > 2*f0 but within the tolerable range of KMQ. This method is suitable for medium and low voltage occasions that can withstand a certain current impact and cannot apply complex control strategies, and the effect is better than the direct charging pre-charging strategy without control.

[0126] The specific implementation steps of the unmodulated pre-charging control method based on the LC model are as follows:

[0127] Step 1: Establish a system simulation model and determine the optimal switching width and frequency;

[0128] Step 2: System preparation and device initialization;

[0129] Step 3: Apply high voltage to the power grid, and both KM1 and KMQ are opened;

[0130] Step 4: KM1 closes;

[0131] Step 5: KMQ closes, implements a fixed pulse width modulation-free control strategy based on the LC model, the circuit conducts for a short time, the second branch works, and FC starts charging;

[0132] Step 6: Determine if pre-charging is complete. If not, repeat step 5. If complete, proceed to step 7.

[0133] Step 7: Pre-charging ends, KMQ switches from interleaved conduction to constant conduction;

[0134] Step 8: Pre-charging complete, KM1 and KMQ status maintained, system is about to start formal operation.

[0135] In this embodiment, the pre-charge control method based on the exponential function includes:

[0136] A simulation model of the second high-voltage circuit system based on the exponential function was established using simulation tools. The first nonlinear exponential coefficient and the second nonlinear exponential coefficient were selected using simulation tools according to the principle of minimizing impact.

[0137] When high voltage is applied to the high voltage circuit system, according to the first nonlinear exponent coefficient and the second nonlinear exponent coefficient, the IGBT electronic switch KMQ is nonlinearly interleaved and turned on using the simulation model of the second high voltage circuit system. The main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge.

[0138] Determine whether the pre-charging of the filter support capacitor FC is complete. When the pre-charging of the filter support capacitor FC is complete, the state of the IGBT electronic switch KMQ changes from non-linear interleaved conduction to normally on.

[0139] In practical implementation, the switching pulse width T purse Taking T / 12 and a switching frequency f = 2.5 * f0 as an example, the peak voltage and current are far from the highest point of free oscillation, and the peak gradually decreases as the FC charging charge accumulates. The pre-charging time is only 0.2s, which is much shorter than the charging time through resistor current limiting, resulting in significant optimization. Figure 10 The waveform shown is a MATLAB simulation waveform under a fixed narrow pulse width and multiple cycles.

[0140] The aforementioned fixed pulse width modulation method is too simplistic, resulting in excessively high energy in the initial pulse segment and insufficient energy in the latter half, leading to low pulse utilization throughout the entire duration. This invention proposes a modulation method based on a nonlinear exponential function, u = k² * e k1*x This achieves stable growth in the early stages and rapid growth in the later stages, resulting in a uniform distribution of activation energy. For example... Figure 11 The figure shows a MATLAB simulation model of precharge control based on an exponential function.

[0141] By carefully adjusting the parameters k1 and k2 using simulation tools such as MATLAB, the energy distribution is made as uniform as possible. A larger k1 parameter results in a longer pre-charge time and higher peak current and voltage values; a larger k2 parameter results in a higher peak value in the initial pulse. The uniformity of the pulse energy distribution can be adjusted using k2. The MATLAB simulation waveform of pre-charge control based on an exponential function, using k1=5 and k2=0.5 as an example, is shown below. Figure 12 As shown.

[0142] As can be seen, the waveform is significantly more uniform, and the current and voltage pulses are much reduced. The pre-charge time is approximately 0.25 seconds, close to that of a fixed pulse, which is significantly better than the traditional pre-charge resistor method. However, it effectively reduces the switching stress on each device, improving safety. This method is suitable for high-voltage pre-charge applications and is the most effective among all strategies.

[0143] The specific implementation steps of the pre-charge control method based on the exponential function are as follows:

[0144] Step 1: Establish a system simulation model and select appropriate nonlinear exponential coefficients k1 and k2 according to the principle of minimizing impact;

[0145] Step 2: System preparation and device initialization;

[0146] Step 3: Apply high voltage to the power grid, and both KM1 and KMQ are opened;

[0147] Step 4: KM1 closes;

[0148] Step 5: KMQ is closed, and a pre-charge control strategy based on an exponential function is applied. The circuit is briefly turned on, the second branch is activated, and FC begins charging.

[0149] Step 6: Determine if pre-charging is complete. If not, repeat step 5. If complete, proceed to step 7.

[0150] Step 7: Pre-charging ends, KMQ switches from non-linear interleaved conduction to constant conduction;

[0151] Step 8: Pre-charging complete, KM1 and KMQ status maintained, system is about to start formal operation.

[0152] In this embodiment, the power grid overvoltage tripping protection control method includes:

[0153] When the grid voltage sensor detects that the voltage difference of the high-voltage circuit system exceeds the standard voltage difference, it closes the IGBT electronic switch KMQ and then detects the voltage difference of the high-voltage circuit system again. When the voltage difference drops to the standard voltage difference, it opens the IGBT electronic switch KMQ to realize the overvoltage cut-off protection of the high-voltage circuit system.

[0154] In practical implementation, traditional topologies, due to the slow operation of contactors, cannot effectively disconnect when the grid voltage rises rapidly. They can only rely on downstream power electronic devices with weaker voltage resistance to withstand excessive voltage stress, which can easily cause device damage. This invention uses IGBTs or equivalent power electronic devices (KMQ) as line switches, which can quickly disconnect the grid to achieve downstream protection.

[0155] However, KMQ is also an electronic device. If the voltage between CE is too high during shutdown, it will not only fail to provide protection but will also be damaged. Therefore, to further optimize the fast protection, this invention proposes a pulse pre-transfer type KMQ shutdown. When TV0 detects overvoltage, KMQ is first quickly turned on, and then quickly turned off when the KMQ voltage difference is acceptable. If KMQ is in a conducting state before the overvoltage, the turn-on time only needs to be appropriately extended. The extension time depends on whether the KMQ voltage difference meets the safety requirements. In railway standards, the maximum grid voltage is U. max3 For Un = DC 1500V, U max3 =DC2540V, which exceeds the active clamping threshold of the IGBT driver board. Continuous operation will severely damage the driver board and IGBTs. Therefore, the voltage between KMQ and CE needs to be limited to around 2200V. The worst-case scenario is that the FC voltage is 0, and there can only be one pulse. The turn-on time should be based on the worst-case scenario where Umax3 and FC are 0. Figure 13 The diagram shows a single-pulse pre-loaded overvoltage disconnection protection for the power grid.

[0156] As can be seen, the voltage difference is reduced to below 2200V, and downstream equipment is protected. The KMQ peak value is relatively large, but this fault is a serious system fault and rarely occurs. Occasionally using it within the safety zone of twice the IGBT current is highly recommended. The protection process is as follows: direct shutdown for small voltage differences, and single-pulse protection for large voltage differences. This method is suitable for transient cut-off and fast protection of high-voltage circuit faults, offering faster protection speed than the KM1 mechanical contactor and greater safety.

[0157] The specific implementation steps of the single-pulse pre-transfer type fast protection control method for overvoltage disconnection of power grid are as follows:

[0158] Step 1: System preparation complete, KM1 and KMQ closed and connected;

[0159] Step 2: The system is working normally and is monitoring the grid voltage TV0 in real time;

[0160] Step 3: If TV0 is normal, proceed to step 2; if TV0 detects overvoltage, proceed to step 4.

[0161] Step 4: If the voltage difference across KMQ (ΔU=TV0-TV1) exceeds the safe tolerance value of KMQ, proceed to step 5; otherwise, proceed to step 7.

[0162] Step 5: KMQ closes or opens with a delay (depending on the previous state of KMQ), apply a single pulse, the circuit briefly turns on or turns off with a delay, the second branch works or turns off with a delay, FC starts charging, and the voltage difference across KMQ begins to decrease;

[0163] Step 6: Determine whether the voltage difference across KMQ meets the safety requirements. If not, delay and continue conducting after step 5. If completed, proceed to step 7.

[0164] Step 7: Quick protection ends, KMQ changes from on to off;

[0165] Step 8: Rapid protection complete, KM1 and KMQ status maintained, system enters fault handling procedure.

[0166] In summary, this invention presents a high-voltage circuit system and its control method. It deeply analyzes the characteristics of traditional high-voltage circuits and proposes an electrical topology for a train traction high-voltage system with series-connected power electronic switches in the high-voltage circuit. This topology results in fewer components, a simpler structure, lower cost, shorter pre-charging time, and a lower failure rate. This invention develops direct charging or LC-based multi-pulse control strategies for the new high-voltage circuit. These strategies eliminate mechanical movements, do not rely on sensors, are insensitive to grid voltage fluctuations, and do not involve complex logical coordination relationships, significantly improving reliability and lifespan. This invention proposes a design method for a multi-pulse pre-charging control strategy, greatly reducing pre-charging time and lowering the risk of system oscillation. This invention also proposes a multi-pulse pre-charging control strategy based on exponential functions, resulting in more uniform charging pulse energy, further reducing the impact on device current and voltage, improving lifespan, and lowering the failure rate. Finally, this invention proposes a single-pulse pre-transfer type grid overvoltage cutoff protection strategy, achieving rapid overvoltage protection for downstream systems. Compared to mechanical switch protection, the method proposed in this invention is faster and provides better protection.

[0167] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 patent application should be determined by the scope of the appended claims.

Claims

1. A high-voltage circuit system, characterized in that, The high-voltage circuit system includes: Main isolating contactor KM1; A low-pass filter unit includes a filter support capacitor FC and a filter reactor FL, wherein one end of the filter capacitor FC is connected to the filter reactor FL; IGBT electronic switch KMQ, one end of which is connected to the filter reactor FL, and the other end of which is connected to the main isolation contactor KM1; The grid voltage sensor TV0 is connected in parallel between the positive and negative terminals of the high-voltage circuit; When high voltage is applied to the high voltage circuit system, the IGBT electronic switch KMQ and the main isolation contactor KM1 are closed, and the filter support capacitor FC starts to charge, causing the voltage of the filter support capacitor FC to rise. When the voltage difference between the voltage of the filter support capacitor FC and the grid voltage reaches a preset voltage difference, it is determined that the filter support capacitor FC has completed pre-charging, and the IGBT electronic switch KMQ is opened, so that the filter support capacitor FC stops charging. When the grid voltage sensor TV0 detects overvoltage in the high-voltage circuit system and detects that the voltage difference across the IGBT electronic switch KMQ exceeds the standard voltage difference, the IGBT electronic switch KMQ is closed, and the voltage difference across the IGBT electronic switch KMQ is detected again. When the voltage difference across the IGBT electronic switch KMQ decreases to the standard voltage difference, the IGBT electronic switch KMQ is opened, thereby realizing overvoltage cut-off protection of the high-voltage circuit system.

2. The high-voltage circuit system according to claim 1, characterized in that, Also includes: The grid current sensor TA1 has one end connected to one end of the grid voltage sensor TV0 and the other end connected to the main isolation contactor KM1. An FC capacitor voltage sensor, one end of which is connected to the filter reactor FL; A three-phase inverter is connected to the filter support capacitor FC. When high voltage is applied to the high voltage circuit system, the main isolation contactor KM1 and the IGBT electronic switch KMQ are closed. Current flows from the voltage source DC through the grid current sensor TA1, the main isolation contactor KM1, the IGBT electronic switch KMQ, the filter reactor FL, and the filter support capacitor FC. After the current flows through the positive terminal of the filter support capacitor FC, it is shunted and flows into the high voltage circuit branch.

3. The high-voltage circuit system according to claim 2, characterized in that, The high-voltage circuit branch includes a first high-voltage circuit branch and a second high-voltage circuit branch. Wherein, after the current flows into the first high-voltage circuit branch, it flows to the three-phase inverter, and flows out from the negative terminal of the inverter back to GND; The current flows into the second high-voltage circuit branch and then to the filter support capacitor FC, charging the filter support capacitor FC. The current then flows out from the negative terminal of the filter support capacitor FC and back to GND.

4. A control method for a high-voltage circuit system, applied to the high-voltage circuit system as described in any one of claims 1-3, characterized in that, The high-voltage circuit system control methods include a direct charging pre-charge control method, a modulation-free pre-charge control method based on an LC model, a pre-charge control method based on an exponential function, and a power grid overvoltage cut-off protection control method. The power grid overvoltage disconnection protection control method includes: When the grid voltage sensor TV0 detects overvoltage in the high-voltage circuit system and detects that the voltage difference across the IGBT electronic switch KMQ exceeds the standard voltage difference, the IGBT electronic switch KMQ is closed, and the voltage difference across the IGBT electronic switch KMQ is detected again. When the voltage difference across the IGBT electronic switch KMQ decreases to the standard voltage difference, the IGBT electronic switch KMQ is opened, thereby realizing overvoltage cut-off protection of the high-voltage circuit system.

5. The high-voltage circuit system control method according to claim 4, characterized in that, The direct charging pre-charging control method includes: When high voltage is applied to the high voltage circuit system, the main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, current flows into the second branch, and the filter support capacitor FC begins to charge.

6. The high-voltage circuit system control method according to claim 5, characterized in that, The modulation-free precharge control method based on the LC model includes: A simulation model of the first high-voltage circuit system based on the LC model was established using simulation tools, and the optimal switching width and frequency were preset.

7. The high-voltage circuit system control method according to claim 6, characterized in that, The modulation-free precharge control method based on the LC model further includes: When high voltage is applied to the high voltage circuit system, according to the preset optimal switching width and preset frequency, the IGBT electronic switch KMQ is alternately turned on using the first high voltage circuit system simulation model. The main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge. Determine whether the pre-charging of the filter support capacitor FC is complete. If the result is that the pre-charging of the filter support capacitor FC is complete, the state of the IGBT electronic switch KMQ changes from interleaved conduction to constant conduction.

8. The high-voltage circuit system control method according to claim 5, characterized in that, The pre-charge control method based on the exponential function includes: A simulation model of the second high-voltage circuit system based on an exponential function is established using simulation tools. The first nonlinear exponential coefficient and the second nonlinear exponential coefficient are selected using the simulation tools according to the principle of minimizing impact.

9. The high-voltage circuit system control method according to claim 8, characterized in that, The pre-charge control method based on the exponential function includes: When the high voltage is applied to the high voltage circuit system, according to the first nonlinear exponential coefficient and the second nonlinear exponential coefficient, the second high voltage circuit system simulation model is used to perform nonlinear interleaved conduction of the IGBT electronic switch KMQ. The main isolation contactor KM1 and the IGBT electronic switch KMQ are both closed, the current flows into the second branch, and the filter support capacitor FC begins to charge. Determine whether the pre-charging of the filter support capacitor FC is complete. If the result is that the pre-charging of the filter support capacitor FC is complete, the state of the IGBT electronic switch KMQ changes from non-linear interleaved conduction to constant conduction.

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