A broadband impedance modeling method for an extra-high voltage converter valve hall

Abstract

The application discloses a wideband impedance modeling method for an extra-high voltage converter valve hall, and the method comprises the following steps: establishing an IGBT wideband impedance model based on the physical structure of an insulated gate bipolar transistor (IGBT) and the frequency response characteristics in the off state; testing the IGBT wideband impedance, identifying and optimizing the model parameters; establishing an MMC sub-module equivalent impedance model according to the current path and the conduction characteristics of the switching devices in different working states of the MMC sub-module; combining the MMC topological structure, the bridge arm reactor, the sub-module capacitor and the internal module connection relationship of the valve hall to construct a wideband impedance equivalent model which is expanded layer by layer from the device level, the sub-module level, the bridge arm level to the valve hall level; and analyzing the wideband conduction interference characteristics of the valve hall. The application can accurately represent the impedance characteristics and the electromagnetic interference propagation law of the extra-high voltage converter valve hall in a wideband range, and provides a model basis for the electromagnetic compatibility analysis of the valve hall, the insulation coordination design, the transient characteristic research and the optimization of the suppression measures.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic compatibility and broadband modeling of ultra-high voltage flexible DC transmission systems, and in particular to impedance modeling of converter valve halls based on voltage source converters (VSCs). Specifically, it relates to a broadband impedance modeling method for ultra-high voltage converter valve halls. Background Technology

[0002] The converter valve hall is a core facility in ultra-high voltage flexible direct current (UHVDC) transmission projects, a massive enclosed structure housing tens of thousands of submodules, their control equipment, cooling systems, connecting busbars, and supporting structures. Inside, modular multilevel converters (MMCs) composed of power semiconductor devices such as insulated-gate bipolar transistors (IGBTs) operate at high frequencies under high voltage and high current conditions. In this complex electromagnetic environment, the switching process excites broadband electromagnetic energy ranging from several kHz to hundreds of MHz, causing strong electromagnetic interference (EMI). This broadband EMI can severely impact secondary measurement, control, and protection equipment within and adjacent to the valve hall, leading to electromagnetic compatibility (EMC) problems, such as measurement signal distortion, malfunction or failure of protection systems, and even threatening the safe and stable operation of the entire transmission system. Therefore, accurate broadband impedance modeling and analysis of the valve hall is a crucial prerequisite for EMC prediction, insulation coordination optimization, and system transient characteristic assessment.

[0003] Currently, besides the impedance modeling approach discussed in this invention, several other methods exist for modeling and analyzing UHV converter valve halls, including circuit simulation: This method simulates the dynamic response of various components in the valve hall by building a simulation model of the converter valve circuit. While this method can effectively reflect the time-domain performance of the converter valve, it has limitations in frequency-domain characteristic analysis. Another method is finite element analysis (FEA): Especially in electromagnetic field analysis, the finite element method is widely used in the study of converter valve heat dissipation, electric field and magnetic field distribution. Although this method has advantages in handling complex geometries and local electromagnetic effects, it consumes significant computational resources and is generally difficult to handle broadband characteristic analysis.

[0004] In summary, traditional modeling methods often employ lumped parameter simplification or topological equivalent models, which are difficult to accurately characterize the high-frequency impedance characteristics of power electronic devices such as IGBTs, resulting in significant deviations between simulation results and actual operating conditions. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a broadband impedance modeling method for ultra-high voltage converter valve halls, which can solve the technical problem that traditional modeling methods often use lumped parameter simplification or topological equivalent models, making it difficult to accurately characterize the high-frequency impedance characteristics of power electronic devices such as IGBTs, resulting in a large deviation between simulation results and actual operating conditions.

[0006] Technical solution: The present invention provides a broadband impedance modeling method for ultra-high voltage converter valve halls, comprising:

[0007] Based on the physical structure of the insulated gate bipolar transistor (IGBT) and its capacitance effect and dielectric loss characteristics in the off-state, an equivalent impedance model for IGBT with wideband impedance is established.

[0008] Wideband impedance testing was performed on an insulated gate bipolar transistor (IGBT) in the off-conducting state to obtain the impedance amplitude-frequency and phase-frequency characteristics of the IGBT. Based on the impedance amplitude-frequency and phase-frequency characteristics, the parameters in the wideband impedance equivalent model of the IGBT were identified and optimized to obtain the parameters of the IGBT.

[0009] A sub-module of a modular multilevel converter (MMC) is constructed using IGBT parameters. Based on the different conduction paths of the MMC sub-module in the on and off states, an equivalent impedance model of the MMC sub-module is established. In the equivalent impedance model of the MMC sub-module, the IGBT off state is represented by a wideband impedance equivalent model, and the IGBT on state is represented by an equivalent resistance model.

[0010] Based on the topology of the modular multilevel converter (MMC), the equivalent impedance model of the MMC submodule is extended step by step to the bridge arm stage and the converter valve stage. Combining the bridge arm reactor, the MMC submodule capacitor, and the activation method of the redundant spare MMC submodule, a broadband impedance equivalent model of the converter valve is constructed.

[0011] Based on the broadband impedance equivalent model of the converter valve, and combined with the connection relationship and electromagnetic coupling path between converter valve modules inside the UHV converter valve hall, a broadband impedance model at the valve hall level is established to analyze the broadband conducted interference characteristics and impedance distribution law inside the UHV converter valve hall.

[0012] Furthermore, the IGBT broadband impedance equivalent model satisfies the following formula:

[0013] ;

[0014] in, The total impedance of the IGBT; Angular frequency, The imaginary unit, and These are the stray resistance and stray inductance of the lead wire, respectively; The equivalent capacitance formed by the PN junction in the off state; This is the equivalent resistance corresponding to the internal buffer layer and drift region; This is the equivalent capacitance of an anti-parallel diode; This is the equivalent resistance of the dielectric loss of the PN junction; This is the equivalent resistance of the dielectric loss of the anti-parallel diode; , and A wideband model for forming elastically press-fit IGBTs. and A broadband equivalent model of anti-parallel diodes.

[0015] Furthermore, the insulated-gate bipolar transistor (IGBT) in the non-conducting state undergoes a wideband impedance test to obtain its impedance amplitude-frequency and phase-frequency characteristics. Based on these characteristics, the parameters in the IGBT's wideband impedance equivalent model are identified and optimized to obtain the IGBT's parameters, including:

[0016] A DC bias voltage is applied to an insulated gate bipolar transistor (IGBT) in the off state, and an AC small signal is superimposed on the DC bias voltage to perform a wideband impedance test. This ensures that the IGBT is in the off state during the test and meets the small-signal response conditions. Based on the impedance amplitude-frequency and phase-frequency characteristics obtained from the test, the parameters in the IGBT wideband impedance equivalent model are identified and optimized using a parameter fitting method to obtain the IGBT parameters.

[0017] Furthermore, the modular multilevel converter (MMC) submodule includes two IGBTs connected in series, a diode connected in antiparallel to each IGBT, and a submodule capacitor C0 connected in parallel across the two IGBTs. Based on the port voltage and port current relationship of the modular multilevel converter (MMC) submodule, and based on the Thevenin equivalent principle, the circuit of the modular multilevel converter (MMC) submodule is equivalent to a two-port network consisting of an equivalent resistor and an equivalent voltage source connected in series. This two-port network serves as the equivalent circuit of the MMC submodule.

[0018] Furthermore, the Modular Multilevel Converter (MMC) consists of multiple bridge arms, each containing multiple MMC sub-modules, which are directly connected in series. After obtaining the equivalent circuit of the MMC sub-module using the Thevenin equivalent principle, the equivalent circuits of multiple MMC sub-modules are connected in series again according to the Thevenin equivalent principle to obtain the equivalent circuit of the bridge arm.

[0019] Furthermore, the wideband impedance equivalent model of the converter valve is established based on the MMC three-phase symmetrical topology. Each phase includes an upper arm and a lower arm, and each arm includes multiple MMC sub-modules and arm reactors. The multiple MMC sub-modules are connected in series and then connected in series with the arm reactors.

[0020] Furthermore, by adjusting the number of MMC sub-modules put into operation on the bridge arm, the operating conditions of the UHV converter valve hall under different voltage and power levels are simulated.

[0021] Furthermore, when the MMC system is running, if any submodule on any of the bridge arms fails, the faulty submodule can be directly replaced by the redundant backup submodule equipped in the modular multilevel converter (MMC).

[0022] Furthermore, during the establishment of the valve hall-level broadband impedance model, the influence of the leakage inductance and large capacitance values ​​of the converter valve module on the electromagnetic interference of the valve hall is considered.

[0023] Furthermore, in the MMC three-phase symmetrical topology, the three-phase AC side is connected to the power grid or load, and the DC side forms a DC bus through the common terminal of the upper and lower bridge arms.

[0024] Beneficial Effects: Compared with existing technologies, the significant technical effects of this invention are as follows: This invention considers the electrical characteristics and dynamic response of each component within the converter valve. By establishing a wideband impedance equivalent model of the IGBT, the behavior of the VSC valve hall under different operating conditions can be effectively described and analyzed. This method not only improves the accuracy of the model but also provides a solid foundation for subsequent system simulation and control strategy optimization. Using the IGBT wideband impedance equivalent model for modeling allows for flexible analysis of system characteristics in both the frequency and time domains, achieving an accurate description of complex nonlinear behavior. Through this technology, the dynamic characteristics of the VSC valve hall can be better understood, thereby optimizing the design and operation of flexible DC transmission systems. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process of the present invention;

[0026] Figure 2 The diagram shows the broadband impedance equivalent model of an IGBT.

[0027] Figure 3 The IGBT wideband test curve (10V DC bias) is shown in the off state.

[0028] Figure 4 A schematic diagram illustrating different working states of the MMC submodule;

[0029] Figure 5 This is based on the Thevenin equivalent MMC impedance equivalent model;

[0030] Figure 6 MMC impedance models under different operating conditions;

[0031] Figure 7 MMC topology diagram;

[0032] Figure 8 The equivalent circuit diagram of the converter valve module is shown below.

[0033] Figure 9 This diagram illustrates the electromagnetic interference coupling method in the VSC valve hall. Detailed Implementation

[0034] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0035] like Figure 1 As shown, a broadband impedance modeling method for an ultra-high voltage converter valve hall according to the present invention includes the following steps:

[0036] S1. Based on the physical structure of the Insulated Gate Bipolar Transistor (IGBT) and its capacitance effect and dielectric loss characteristics in the off-state, establish an equivalent impedance model for the IGBT wideband impedance.

[0037] The specific implementation process of step S1 is as follows:

[0038] Based on the physical structure of the Insulated Gate Bipolar Transistor (IGBT) (such as leads, buffer layer, drift region, PN junction, etc.) and its physical characteristics in the off-state (such as capacitance effect and dielectric loss), an equivalent circuit is constructed through circuit theory analysis, and a broadband impedance equivalent model of IGBT is derived.

[0039] like Figure 2 The figure shows the broadband impedance equivalent model of an insulated gate bipolar transistor (IGBT) in the off state.

[0040] In this embodiment, the IGBT broadband impedance equivalent model satisfies the following formula:

[0041] ;

[0042] in, The total impedance of the IGBT; Angular frequency, The imaginary unit; and These are the stray resistance and stray inductance of the lead wire, respectively; The equivalent capacitance formed by the PN junction in the off state; This is the equivalent resistance corresponding to the internal buffer layer and the drift region; This is the equivalent capacitance of the anti-parallel diode (including parasitic capacitance); This is the equivalent resistance of the dielectric loss of the PN junction; This is the equivalent resistance for the dielectric loss of the anti-parallel diode; , and A wideband model for forming elastically press-fit IGBTs. and A broadband equivalent model of anti-parallel diodes.

[0043] The above IGBT wideband impedance equivalent model not only considers the physical structure of the IGBT, but also its physical characteristics in the off state. Compared with the traditional model, it can more accurately simulate the electrical characteristics of the IGBT at different frequencies.

[0044] S2. Perform wideband impedance testing on the insulated gate bipolar transistor (IGBT) in the non-conducting state to obtain the impedance amplitude-frequency characteristics and phase-frequency characteristics of the IGBT. Based on the impedance amplitude-frequency characteristics and phase-frequency characteristics, identify and optimize the parameters in the wideband impedance equivalent model of the IGBT to obtain the parameters of the IGBT.

[0045] The specific implementation process of step S2 is as follows:

[0046] A DC bias voltage is applied to an insulated gate bipolar transistor (IGBT) in the off state, and an AC small signal is superimposed on the DC bias voltage to perform a wideband impedance test. This ensures that the IGBT device is in the off state during the test and meets the small signal response conditions. Based on the impedance amplitude-frequency characteristics and phase-frequency characteristics obtained from the test, the parameters in the IGBT wideband impedance equivalent model are identified and optimized using a parameter fitting method to obtain the IGBT parameters.

[0047] In this embodiment, to obtain the wideband impedance characteristics of the Insulated Gate Bipolar Transistor (IGBT), an impedance analyzer is used to test the IGBT in its off-state. The IGBT in its off-state is considered an impedance, and its on-state is considered a short circuit, neglecting the influence of parasitic parameters. Unlike testing passive components, when performing wideband testing on an IGBT in its off-state (i.e., off-state) using an impedance analyzer, a DC bias voltage of a certain amplitude needs to be applied across the IGBT. A small AC signal is then superimposed on this voltage to perform a frequency sweep test on the component, ensuring that the test signal applied to the device under test is always positive. The impedance analyzer is then used to test the IGBT module. During testing, the DC bias voltage is 10V, and the AC signal amplitude is 200mV. A small AC signal amplitude should be used during testing to ensure that the applied AC signal meets the requirements of small-signal testing. The test results are as follows. Figure 3 As shown, Figure 3 Figure (a) in the figure is the amplitude-frequency response curve of the IGBT. Figure 3 Figure (b) in the figure is the phase frequency characteristic curve of the IGBT.

[0048] The measured impedance-frequency characteristics show that the module as a whole exhibits capacitor-like characteristics. In the low-frequency range, the components consistently exhibit capacitive characteristics. The phase-frequency characteristic curve shows that the phase angle remains at -90°. When the frequency reaches 10MHz, resonance occurs.

[0049] To obtain a more accurate IGBT wideband impedance, the LM algorithm was used to fit its impedance parameters, and the parameter values ​​are shown in Table 1 below.

[0050] Table 1. Parameters of the broadband equivalent model

[0051]

[0052] S3. Construct sub-modules of the Modular Multilevel Converter (MMC) using IGBT parameters; establish an equivalent impedance model for the MMC sub-module based on the different conduction paths of the sub-modules in the on and off states. In the equivalent impedance model of the MMC sub-module, the IGBT off state is represented by a wideband impedance equivalent model, and the IGBT on state is represented by an equivalent resistance model.

[0053] like Figure 5 As shown, Figure 5 Figure (a) shows the MMC submodule circuit. Figure 5 Figure (b) shows the equivalent circuit of the MMC submodule. Figure 5 Figure (c) shows the equivalent circuit of the bridge arm. Among them, Indicates the current of the MMC submodule. Indicates the bridge arm current. Indicates the capacitor current of the submodule. Indicates the voltage of the MMC submodule. Indicates the capacitor voltage of the submodule. This represents the equivalent resistance of the MMC submodule. This indicates the equivalent voltage source of the MMC submodule. Indicates the equivalent resistance of the bridge arm. This indicates the equivalent voltage source of the bridge arm.

[0054] Figure 5As shown in Figure (a), the Modular Multilevel Converter (MMC) submodule consists of two IGBTs (T1 and T2), two diodes (D1 and D2), and a submodule capacitor C0. The two IGBTs (T1 and T2) are connected in series, with one diode connected in anti-parallel to each IGBT. The submodule capacitor C0 is connected in parallel across the two series-connected IGBTs. The submodule is configured based on the port voltage of the Modular Multilevel Converter (MMC) submodule. Port current Based on Thevenin's equivalence principle, the modular multilevel converter (MMC) submodule circuit can be equivalent to an circuit consisting of an equivalent resistance. With equivalent voltage source A two-port network connected in series serves as the equivalent circuit for the MMC submodule. Figure 5 As shown in Figure (b), the equivalent circuits of multiple MMC sub-modules are then connected in series according to the Thevenin equivalence principle to obtain the bridge arm equivalent circuit, as shown in Figure (b). Figure 5 As shown in Figure (c).

[0055] The MMC submodule has three operating states: the latched state, the engaged state, and the disengaged state. The latched state is an abnormal operating state and is not considered in the modeling. Based on the current direction of the upper and lower arms in each phase unit of the MMC, and the switching states of switching devices T1 and T2 within the MMC submodule, the MMC submodule can be divided into six different operating modes.

[0056] Figure 4 Figure (a) shows the working state of the MMC submodule when the current is in the positive direction of the latched state; Figure 4 Figure (b) shows the working state of the MMC submodule when the current is reversed in the locked state; Figure 4 Figure (c) shows the working state of the MMC submodule when it is in the positive direction of the current. Figure 4 Figure (d) in the figure is a schematic diagram of the working state of the MMC submodule when the current is reversed in the input state; Figure 4 Figure (e) in the figure is a schematic diagram of the working state of the MMC submodule when the current is in the positive direction of the cut-off state; Figure 4 Figure (f) in the diagram is a schematic diagram of the working state of the MMC submodule when the current is reversed in the cut-off state.

[0057] like Figure 4 As shown, when the MMC submodule is in the latched state, a turn-off signal is applied to both switching devices T1 and T2, at which point both switching devices T1 and T2 are in the off state. When the current flow direction is positive, i.e., the current flow direction is as follows... Figure 4When the current direction is as marked in Figure (a), the reverse freewheeling diode D1 conducts. At this time, current flows through the reverse freewheeling diode D1 to charge the MMC submodule capacitor; when the current flow direction is reversed, i.e., the current flow direction is as shown in Figure (a), the reverse freewheeling diode D1 conducts. Figure 4 When the current direction is indicated by the symbol in Figure (b), the reverse freewheeling diode D2 conducts. Current flows through the reverse freewheeling diode D2, bypassing the MMC submodule capacitor. The MMC submodule latch-up state is an abnormal operating state. This state is used to charge the MMC submodule capacitor or to disconnect the MMC submodule capacitor when a fault occurs in the MMC system. During normal operation of the MMC system, the MMC submodule is not allowed to be in a latch-up state.

[0058] When the MMC submodule is in the active state, an on signal is applied to switch T1 and an off signal is applied to switch T2. At this time, switch T1 is in the on state and switch T2 is in the off state. When the current flow direction is positive, i.e., the current flow direction is as follows... Figure 4 In the direction marked in Figure (c), the reverse freewheeling diode D1 is turned on. Although an on-signal is applied to the switching device T1, T1 is always in the off state because it is always subjected to a reverse voltage. At this time, current flows through the reverse freewheeling diode D1 to charge the MMC submodule capacitor; when the current flow direction is reversed, i.e., the current flow direction is as shown in Figure (c), the reverse freewheeling diode D1 is turned on. Figure 4 In the direction marked in Figure (d), switch T1 is in a conducting state because an on signal has been applied to it. At this time, the MMC submodule capacitor will discharge itself through switch T1.

[0059] When the MMC submodule is in the active state, the MMC submodule capacitor will always participate in the operation of the MMC, and will charge or discharge according to the direction of current flow. The output voltage of the MMC submodule is always the capacitor voltage of the MMC submodule.

[0060] When the MMC submodule is in the disconnected state, a turn-off signal is applied to switch T1 and an turn-on signal is applied to switch T2. At this time, switch T1 is in the off state and switch T2 is in the on state. When the current flow direction is positive, that is, the current flow direction is as follows: Figure 4 When the direction marked in diagram (e) is met, switching device T2 is turned on. Current flows through switching device T2, bypassing the MMC submodule capacitor; when the current flow direction is reversed, i.e., the current flow direction is as shown in the diagram... Figure 4In the direction marked in Figure (f), the reverse freewheeling diode D2 is turned on. Although an on signal is applied to the switching device T2, it is always in the off state because it is always subjected to a reverse voltage. At this time, current flows through the reverse freewheeling diode D2, bypassing the MMC submodule capacitor.

[0061] When the MMC submodule is in the disconnected state, the MMC submodule capacitor is always disconnected from the main circuit, and the output voltage of the MMC submodule is always zero.

[0062] The IGBT cutoff state is characterized using a wideband impedance equivalent model, and a wideband equivalent circuit model for the sub-module is constructed based on the Thevenin equivalence principle, as detailed below:

[0063] Based on the different operating modes of the aforementioned MMC submodules, consider the MMC impedance equivalent model based on Thevenin's equivalent, such as... Figure 5 As shown,

[0064] A Modular Multilevel Converter (MMC) consists of multiple bridge arms, each containing multiple MMC sub-modules, which are directly connected in series. After obtaining the equivalent circuit of each MMC sub-module using Thevenin's equivalence principle, the equivalent circuits of multiple MMC sub-modules are then connected in series again, according to Thevenin's equivalence principle, to obtain the equivalent circuit of each bridge arm, as shown below. Figure 5 As shown in Figure (c).

[0065] exist Figure 5 middle, This refers to the current flowing into the MMC submodule; the operating state of the submodule determines the current flowing into the capacitor. Size and output voltage of MMC submodule The size is as follows:

[0066]

[0067] When considering the on-state voltage drop of the IGBT At that time, the output voltage of the MMC submodule This can be further expressed as:

[0068]

[0069] Calculating the change in capacitor voltage of the MMC submodule, we have:

[0070]

[0071] Wherein, the simulation step size is , The positive direction is defined as the direction in which the capacitor flows into the positive plate of the submodule capacitor. The capacitance value of the submodule is C. Let... The voltage of the submodule capacitor is obtained:

[0072]

[0073] Accordingly, Figure 5 In the simulation model, voltage and resistance can be represented as:

[0074]

[0075] in, This is the equivalent on-resistance of the IGBT in the on-state.

[0076]

[0077] As shown in the above equation, the equivalent circuit of the bridge arm of the MMC submodule can be encapsulated into a submodule bridge arm equivalent processing module. The bridge arm equivalent processing module greatly improves the calculation speed of the simulation model. The bridge arm equivalent processing module only needs to obtain the reference values ​​of the upper and lower bridge arm currents and modulation voltages from the outside, and can calculate the equivalent voltages of the upper and lower bridge arms using the above relationship.

[0078] Therefore, it can be seen that Figure 6 Ignoring abnormal operating states, i.e., locked states, the remaining two states and four modes of the MMC submodules are represented by the Thevenin equivalents, where Zoff uses... Figure 2 The impedance model of the IGBT under the cutoff state is replaced by a pure resistance module in Zon. Figure 6 Figure (a) shows a schematic diagram of the MMC impedance model under the positive direction of the input current; Figure 6 Figure (b) shows a schematic diagram of the MMC impedance model under the negative direction of the input current; Figure 6 Figure (c) in the diagram is a schematic diagram of the MMC impedance model under the positive direction of the cut-off state current; Figure 6 Figure (d) in the diagram is a schematic diagram of the MMC impedance model under the negative direction of the cut-off state current.

[0079] S4. Based on the topology of the modular multilevel converter (MMC), the equivalent impedance model of the MMC submodule is extended step by step to the bridge arm stage and the converter valve stage. Combining the bridge arm reactor, the MMC submodule capacitor, and the activation method of the redundant spare MMC submodule, a broadband impedance equivalent model of the converter valve is constructed.

[0080] The broadband impedance equivalent model of the converter valve is established based on the three-phase symmetrical topology of the MMC (Modular Multilevel Converter). Each phase includes an upper arm and a lower arm, and each arm includes multiple MMC submodules and an arm reactor. These MMC submodules are connected in series with the arm reactor. By adjusting the number of MMC submodules in operation on each arm, the operating conditions of the UHV converter valve hall under different voltage and power levels are simulated. When the MMC system is running, if a submodule on any arm fails, the faulty submodule is directly replaced by the redundant backup submodules provided by the modular multilevel converter (MMC). In the three-phase symmetrical topology of the MMC, the three-phase AC side is connected to the grid or load, and the DC side forms a DC bus through the common terminal of the upper and lower arms.

[0081] like Figure 7 The diagram shows the rectifier-side topology of the MMC, with point 0 representing the zero-potential reference point. The MMC consists of three-phase units, each phase containing upper and lower arms. Each arm comprises N submodules and an AC reactor L0 connected in series. The DC voltage is supported by the three parallel-connected phase units of the MMC. To ensure DC voltage stability, the number of submodules in each of the three phase units must be equal. Therefore, we can conclude that:

[0082]

[0083] Taking phase a unit as an example, when all the upper bridge arm submodules of phase a unit are removed, we can obtain:

[0084]

[0085] If the MMC needs to output its rated DC voltage, then all N sub-modules in the lower bridge arm of phase a need to be put into operation by the MMC. Since the three phase units of the MMC are symmetrical, the total DC current... The DC current is evenly distributed among the three phase units, and the current in each phase unit is... Since the AC reactors L0 of the upper and lower bridge arms are equal, the AC current... The current is evenly distributed between the upper and lower bridge arms. Therefore, the current in the upper and lower bridge arms of phase a is:

[0086]

[0087] When the MMC needs to output different voltage and power levels, it can adjust the number of operational submodules in each bridge arm to meet different operational requirements. When the MMC system is running, if a submodule on any bridge arm fails, the redundant backup submodules provided with the MMC can directly replace the faulty submodule without requiring system downtime for repair or replacement, thus increasing the fault tolerance of the MMC system.

[0088] S5. Based on the equivalent model of wideband impedance of converter valve, and combined with the connection relationship and electromagnetic coupling path between converter valve modules inside the UHV converter valve hall, a wideband impedance model at the valve hall level is established to analyze the wideband conducted interference characteristics and impedance distribution law inside the UHV converter valve hall.

[0089] In establishing the wideband impedance model at the valve hall level, the influence of the leakage inductance and large capacitance values ​​of the converter valve module on the electromagnetic interference (EMI) in the valve hall is considered. Specifically, based on the wideband equivalent circuit at the converter valve module level, the wideband impedance model at the valve hall level further considers the influence of the leakage inductance and large capacitance parameters of the converter valve module, as well as the coupling path between modules, on the propagation of EMI. This model is used to analyze the EMI coupling characteristics between converter valve modules and the wideband conducted interference characteristics of the valve hall.

[0090] The converter valve module is the smallest unit in the VSC valve hall, mainly composed of IGBTs, protection thyristors, diodes, capacitors, a control unit, and a bypass switch. Therefore, when modeling impedance, the leakage inductance and the value of the large capacitor in the module are considered to affect the electromagnetic interference (EMI) of the valve hall. This is combined with a broadband EMI model at the converter valve module level (see...). Figure 8 This allows for the analysis of the impact of internal capacitance and bridge arm reactance of the converter valve module on conducted interference. The VSC valve hall consists of hundreds of high-power converter valve modules. Based on the broadband impedance equivalent model of the converter valve, and combined with the UHV converter valve hall topology, a broadband impedance model at the VSC valve hall level is established to study the electromagnetic interference coupling characteristics between converter valve modules (e.g., Figure 9 ), and analyze the electromagnetic interference characteristics of the VSC valve hall.

[0091] This invention establishes a wideband impedance model for IGBTs based on their physical structure and frequency response characteristics in the off-state. Wideband impedance tests are performed on the IGBT modules, and the model parameters are identified and optimized based on the test results. An equivalent impedance model for the MMC submodule is established based on the current path and switching device conduction characteristics under different operating states. Furthermore, considering the MMC topology, bridge arm reactors, submodule capacitors, and the internal module connections within the valve hall, a wideband impedance equivalent model is constructed, progressively expanding from the device level, submodule level, bridge arm level to the valve hall level. Finally, the wideband conducted interference characteristics of the valve hall are analyzed by considering the electromagnetic coupling relationships between the converter valve modules.

[0092] The method proposed in this invention can accurately characterize the impedance characteristics and electromagnetic interference propagation law of UHV converter valve halls over a wide frequency range, providing a model basis for valve hall electromagnetic compatibility analysis, insulation coordination design, transient characteristic research, and suppression measure optimization.

[0093] This invention, based on impedance modeling, constructs an impedance network by disassembling core components such as IGBT modules and buffer circuits, and combining the device's physical characteristics and frequency response characteristics. This enables precise equivalence from the device level to the valve hall level. This modeling approach effectively captures high-frequency harmonic propagation paths and impedance matching characteristics, solving the accuracy limitations of traditional models in EMC analysis and transient characteristic simulation. It represents a key technological direction for current UHV VSC converter valve hall modeling.

Claims

1. A broadband impedance modeling method for ultra-high voltage converter valve halls, characterized in that, include: Based on the physical structure of the insulated gate bipolar transistor (IGBT) and its capacitance effect and dielectric loss characteristics in the off-state, an equivalent impedance model for IGBT with wideband impedance is established. Wideband impedance testing was performed on an insulated gate bipolar transistor (IGBT) in the off-conducting state to obtain the impedance amplitude-frequency and phase-frequency characteristics of the IGBT. Based on the impedance amplitude-frequency and phase-frequency characteristics, the parameters in the wideband impedance equivalent model of the IGBT were identified and optimized to obtain the parameters of the IGBT. A sub-module of a modular multilevel converter (MMC) is constructed using IGBT parameters. Based on the different conduction paths of the MMC sub-module in the on and off states, an equivalent impedance model of the MMC sub-module is established. In the equivalent impedance model of the MMC sub-module, the IGBT off state is represented by a wideband impedance equivalent model, and the IGBT on state is represented by an equivalent resistance model. Based on the topology of the modular multilevel converter (MMC), the equivalent impedance model of the MMC submodule is extended step by step to the bridge arm stage and the converter valve stage. Combining the bridge arm reactor, the MMC submodule capacitor, and the activation method of the redundant spare MMC submodule, a broadband impedance equivalent model of the converter valve is constructed. Based on the broadband impedance equivalent model of the converter valve, and combined with the connection relationship and electromagnetic coupling path between converter valve modules inside the UHV converter valve hall, a broadband impedance model at the valve hall level is established to analyze the broadband conducted interference characteristics and impedance distribution law inside the UHV converter valve hall.

2. The broadband impedance modeling method for UHV converter valve hall according to claim 1, characterized in that, The equivalent impedance model of the IGBT broadband satisfies the following formula: ； in, The total impedance of the IGBT; Angular frequency, The imaginary unit, and These are the stray resistance and stray inductance of the lead wire, respectively; The equivalent capacitance formed by the PN junction in the off state; This is the equivalent resistance corresponding to the internal buffer layer and drift region; This is the equivalent capacitance of an anti-parallel diode; This is the equivalent resistance of the dielectric loss of the PN junction; This is the equivalent resistance of the dielectric loss of the anti-parallel diode; , and A wideband model for forming elastically press-fit IGBTs. and A broadband equivalent model of anti-parallel diodes.

3. The broadband impedance modeling method for UHV converter valve hall according to claim 1, characterized in that, The method involves performing a wideband impedance test on an insulated-gate bipolar transistor (IGBT) in its non-conductive state to obtain the impedance amplitude-frequency and phase-frequency characteristics of the IGBT. Based on these characteristics, the parameters in the wideband impedance equivalent model of the IGBT are identified and optimized to obtain the IGBT parameters, including: A DC bias voltage is applied to an insulated gate bipolar transistor (IGBT) in the off state, and an AC small signal is superimposed on the DC bias voltage to perform a wideband impedance test. This ensures that the IGBT is in the off state during the test and meets the small-signal response conditions. Based on the impedance amplitude-frequency and phase-frequency characteristics obtained from the test, the parameters in the IGBT wideband impedance equivalent model are identified and optimized using a parameter fitting method to obtain the IGBT parameters.

4. The broadband impedance modeling method for UHV converter valve hall according to claim 1, characterized in that: The modular multilevel converter (MMC) submodule includes two IGBTs connected in series, a diode connected in antiparallel to each IGBT, and a submodule capacitor C0 connected in parallel across the two IGBTs. Based on the port voltage and port current relationship of the modular multilevel converter (MMC) submodule, and based on the Thevenin equivalent principle, the circuit of the modular multilevel converter (MMC) submodule is equivalent to a two-port network consisting of an equivalent resistor and an equivalent voltage source connected in series. This two-port network serves as the equivalent circuit of the MMC submodule.

5. The broadband impedance modeling method for UHV converter valve hall according to claim 4, characterized in that: The Modular Multilevel Converter (MMC) consists of multiple bridge arms, each containing multiple MMC sub-modules. The MMC sub-modules are directly connected in series. After obtaining the equivalent circuit of the MMC sub-module using Thevenin's equivalence principle, the equivalent circuits of the multiple MMC sub-modules are connected in series again according to Thevenin's equivalence principle to obtain the equivalent circuit of the bridge arm.

6. The broadband impedance modeling method for UHV converter valve hall according to claim 1, characterized in that: The broadband impedance equivalent model of the converter valve is established based on the MMC three-phase symmetrical topology. Each phase includes an upper arm and a lower arm. Each arm includes multiple MMC sub-modules and an arm reactor. The multiple MMC sub-modules are connected in series and then connected in series with the arm reactor.

7. The broadband impedance modeling method for UHV converter valve hall according to claim 6, characterized in that: By adjusting the number of MMC sub-modules put into operation on the bridge arm, the operating conditions of the UHV converter valve hall under different voltage and power levels are simulated.

8. The broadband impedance modeling method for UHV converter valve hall according to claim 6, characterized in that: When the MMC system is running, if any submodule on any of the bridge arms fails, the faulty submodule can be directly replaced by the redundant backup submodule provided by the modular multilevel converter (MMC).

9. The broadband impedance modeling method for UHV converter valve hall according to claim 1, characterized in that, In the process of establishing the wideband impedance model of the valve hall, the influence of the leakage inductance and large capacitance values ​​of the converter valve module on the electromagnetic interference of the valve hall is considered.

10. The broadband impedance modeling method for UHV converter valve hall according to claim 6, characterized in that: In the MMC three-phase symmetrical topology, the three-phase AC side is connected to the power grid or load, and the DC side forms a DC bus through the common terminal of the upper and lower bridge arms.

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