A modular multilevel converter

Abstract

The application discloses a modular multilevel converter, which comprises a plurality of cascaded converter sub-modules; the converter sub-module comprises an IGCT power module and an IGBT power module; the IGCT power module comprises a direct-current capacitor, a first fully-controlled switch module, a second fully-controlled switch module, a buffer circuit and a discharge resistor; the direct-current capacitor is connected in parallel with the discharge resistor and the buffer circuit respectively; the buffer circuit is connected with the first fully-controlled switch module and the second fully-controlled switch module which are connected in series; the second fully-controlled switch module is connected in parallel with an output end of the IGCT power module; the first fully-controlled switch module and the second fully-controlled switch module each comprise an IGCT device and a diode connected in anti-parallel with the IGCT device. By mixing the IGBT power module and the IGCT power module in the modular multilevel converter, the applicability and reliability of the modular multilevel converter are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more particularly to a modular multilevel converter. Background Technology

[0002] High-voltage direct current voltage source converters (HVDC-VSCs) are widely used for renewable energy grid connection due to their advantages such as flexible regulation, low harmonics, and high efficiency. Modular multilevel converters (MMCs) are one of the commonly used topologies of HVDC-VSC technology and have great application prospects in the converter field.

[0003] Currently, Insulated Gate Bipolar Transistors (IGBTs) are widely used in MMCs due to their advantages such as high withstand voltage, high current carrying capacity, high switching frequency, low switching losses, and acceptable conduction losses. Integrated gate commutated thyristors (IGCTs) integrate the thyristor chip and gate drive circuitry, connecting them externally to the gate drive unit in a low-inductance manner. This achieves both the stable turn-off capability of a transistor and the low conduction losses of a thyristor. IGCTs offer advantages such as high current carrying capacity, high blocking voltage, high switching frequency, high reliability, compact structure, and low conduction losses. Furthermore, they are low-cost and have a high yield, making them promising candidates for high-voltage, high-capacity converter applications. Summary of the Invention

[0004] This invention provides a modular multilevel converter that allows for the mixed use of IGCT power modules and IGBT power modules.

[0005] According to one aspect of the present invention, a modular multilevel converter is provided, the modular multilevel converter comprising a plurality of cascaded converter sub-modules; the converter sub-modules comprising an IGCT power module and an IGBT power module;

[0006] The IGCT power module includes a DC capacitor, a first fully controlled switch module, a second fully controlled switch module, a buffer circuit, and a discharge resistor; the DC capacitor is connected in parallel with the discharge resistor and the buffer circuit respectively; the buffer circuit is connected in parallel with the first fully controlled switch module and the second fully controlled switch module which are connected in series; the second fully controlled switch module is connected in parallel with the output terminal of the IGCT power module; both the first fully controlled switch module and the second fully controlled switch module include an IGCT device and a diode connected in antiparallel with it.

[0007] Optionally, the insulation voltage of the IGCT device is V. DRM V DRM >1.6*U dc The rated on-state current of the IGCT device is I. T(RMS) I T(RMS) >1.6*I rms ;

[0008] Among them, U dc I is the rated operating voltage of the IGCT power module. rms This is the rated operating current of the IGCT power module.

[0009] Optionally, the diode is a fast recovery diode;

[0010] The insulation voltage of the diode is V. RRM V RRM =V DRM The average forward current of the diode is I. F(AV) I F(AV) >I rms .

[0011] Optionally, the capacitance of the DC capacitor is C0.

[0012] In the formula, P dc The power on the DC side of the modular multilevel converter. ε is the average value of the operating voltage of the DC capacitor, ε is the percentage fluctuation of the operating voltage of the DC capacitor, m is the modulation ratio, and ω is the average value of the operating voltage of the DC capacitor. N Where is the angular frequency, and n is the number of converter submodules in a single bridge arm of the modular multilevel converter. The angle represents the power factor between active and reactive power.

[0013] Optionally, the resistance value of the discharge resistor is R.

[0014] In the formula, C0 is the capacitance value of the DC capacitor, and t is the discharge time of the DC capacitor after the IGCT power module is shut down.

[0015] Optionally, the latch-up loss of the IGBT power module is P. IGBT The latch-up loss of the IGCT power module is P. IGCT P IGBT =P IGCT ;

[0016] The latch-up loss of the IGCT power module includes power supply loss and discharge resistance loss; the power supply discharge loss is P. IGCT-loss1 The discharge resistor loss is

[0017]

[0018] In the formula, R is the average value of the operating voltage of the DC capacitor, and R is the resistance value of the discharge resistor.

[0019] Optionally, the buffer circuit includes an anode counteractor;

[0020] The first end of the anode countermeasure is electrically connected to the first end of the DC capacitor and the first end of the discharge resistor, respectively; the second end of the anode countermeasure is electrically connected to the anode of the first fully controlled switch module; the cathode of the first fully controlled switch module is electrically connected to the anode of the second fully controlled switch module; the cathode of the second fully controlled switch module is electrically connected to the second end of the DC capacitor and the second end of the discharge resistor, respectively.

[0021] In the IGCT power module, the inductance value of the circuit containing the anode reactor is L1.

[0022] In the formula, U dc The rated operating voltage of the IGCT power module is denoted as , and di / dt is the critical rate of change of current for the first fully controlled switching module and the second fully controlled switching module.

[0023] Optionally, the inductance value of the anode counter is L0.

[0024] Among them, L loop This refers to the loop inductance of the IGCT power module.

[0025] Optionally, the buffer circuit further includes a clamping resistor, a clamping diode, and a clamping capacitor;

[0026] The first terminal of the clamping resistor is electrically connected to the first terminal of the DC capacitor and the first terminal of the anode countermeasure, respectively; the second terminal of the clamping resistor is electrically connected to the first terminal of the clamping capacitor and the cathode of the clamping diode, respectively; the anode of the clamping diode is electrically connected to the second terminal of the anode countermeasure and the anode of the first fully controlled switch module, respectively; the second terminal of the clamping capacitor is electrically connected to the second terminal of the DC capacitor, the second terminal of the discharge resistor, and the cathode of the second fully controlled switch module, respectively.

[0027] The capacitance of the clamping capacitor is C. CL , 3≤A≤5;

[0028] In the formula, I rms U is the rated operating current of the IGCT power module. block t is the unlocked overvoltage threshold of the IGCT power module. f The current drop time is the time when the second fully controlled switch module is turned off.

[0029] Optionally, the resistance value of the clamping resistor is R. S , 3≤B≤5;

[0030] In the formula, T on This refers to the conduction time of the second fully controlled switch module.

[0031] Optionally, the clamping diode is a fast recovery diode;

[0032] The insulation voltage of the clamping diode is V. DCL-RRM V DCL-RRM =V RRM .

[0033] Optionally, the IGCT power module further includes a bypass switch; the bypass switch is electrically connected to the output terminal.

[0034] The rated operating voltage of the bypass switch is greater than the unlocked overvoltage threshold U of the IGCT power module. block The rated operating current of the bypass switch is greater than the rated operating current of the IGCT power module.

[0035] The technical solution of this invention, by using IGBT power modules and IGCT power modules in a modular multilevel converter, enables the modular multilevel converter to be applicable to high-voltage, high-frequency, and low-frequency application scenarios. It solves the problems of low current density and poor overcurrent protection performance of IGBT modules, and also avoids the problems of slow switching speed and low voltage density caused by using only IGCT modules, thereby improving the applicability and reliability of the modular multilevel converter.

[0036] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a topology diagram of a modular multilevel converter provided in an embodiment of the present invention;

[0039] Figure 2 This is a topology diagram of an IGBT power module provided in an embodiment of the present invention;

[0040] Figure 3 This is a topology diagram of an IGCT power module provided in an embodiment of the present invention. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0043] Figure 1 This is a topology diagram of a modular multilevel converter provided in an embodiment of the present invention. Figure 2 This is a topology diagram of an IGBT power module provided in an embodiment of the present invention. Figure 3 This is a topology diagram of an IGCT power module provided in an embodiment of the present invention. (Reference) Figures 1-3 The modular multilevel converter 01 includes six bridge arms, each connected to an AC side port and a DC side port respectively. Corresponding upper and lower bridge arms are connected to the same AC side port, all upper bridge arms are connected to the same DC side port, and all lower bridge arms are connected to the same DC side port. Each bridge arm includes multiple cascaded converter sub-modules 02. The converter sub-module 02 can be an IGBT power module 021 or an IGCT power module 022. The modular multilevel converter 01 provided in this embodiment of the invention includes both IGBT power module 021 and IGCT power module 022.

[0044] It should be noted that the embodiments of the present invention are only illustrated using a modular multilevel converter with a three-phase six-arm structure as an example. The modular multilevel converter can also be a two-phase four-arm or other structures, and the embodiments of the present invention do not limit this.

[0045] Continue to refer to Figure 2 The IGBT power module 021 includes a DC capacitor C1, two IGBT devices (T1 and T2), and two diodes (D1 and D2) connected in anti-parallel to the two IGBT devices. The IGBT power module 021 features high switching speed, is suitable for high-frequency operation, and its manufacturing technology is relatively mature, leading to widespread application and low maintenance costs. However, the IGBT power module 021 is limited by current density; high-current applications require additional parallel operation or larger modules, making it unsuitable for high-voltage applications.

[0046] Continue to refer to Figure 3 The IGCT power module 022 includes a DC capacitor C2, a first fully controlled switch module 041, a second fully controlled switch module 042, a buffer circuit 03, and a discharge resistor R. The first fully controlled switch module 041 includes an IGCT device T3 and a diode D3 connected in antiparallel to it. The second fully controlled switch module 042 includes an IGCT device T4 and a diode D4 connected in antiparallel to it. The anode of the IGCT device T3 and the cathode of the diode D3 are electrically connected to the first terminal of the DC capacitor C2, the first terminal of the discharge resistor R, and the first terminal of the buffer circuit 03. The cathode of the IGCT device T3 and the anode of the diode D3 are electrically connected to the anode of the IGCT device T4 and the cathode of the diode D3. The cathode of the IGCT device T4 and the anode of the diode D3 are electrically connected to the second terminal of the DC capacitor C2, the second terminal of the discharge resistor R, and the second terminal of the buffer circuit 03. The output terminal of the IGCT power module 022 is connected in parallel with the second fully controlled switch module 042.

[0047] Specifically, when IGCT device T3 or diode D3 is turned on, DC capacitor C2 can charge or discharge after IGCT power module 022 is connected to the bridge arm. At this time, IGCT power module 022 is working. When IGCT power module 022 is working normally, the voltage across DC capacitor C2 is the actual operating voltage of IGCT power module 022, which is generally the rated operating voltage of IGCT power module 022. When IGCT device T4 or diode D4 is turned on, IGCT power module 022 is not working, DC capacitor C2 is bypassed, and IGCT power module 022 has no effect on the operation of modular multilevel converter 01. Buffer circuit 03 can effectively suppress the rate of increase of current or voltage on the first fully controlled switch module 041 and / or the second fully controlled switch module 042 when IGCT power module 022 is working, protecting the IGCT device from damage. Discharge resistor R can release the energy of DC capacitor C when modular multilevel converter 01 is shut down.

[0048] The IGCT power module 022 has high voltage withstand capability, making it suitable for high-voltage applications. It can also withstand significant overcurrent surges, providing better overcurrent protection. Furthermore, the IGCT power module 022 has low switching losses, making it suitable for low-frequency operation. However, its relatively slow switching speed makes it unsuitable for high-frequency operation, and its current applications are limited.

[0049] In summary, by using both IGBT power modules and IGCT power modules in a modular multilevel converter, the modular multilevel converter can be applied to high-voltage, high-frequency, and low-frequency applications simultaneously. This solves the problems of low current density and poor overcurrent protection performance of IGBT modules, and avoids the problems of slow switching speed and low voltage density caused by using only IGCT modules, thus improving the applicability and reliability of the modular multilevel converter.

[0050] In an optional embodiment, the rated operating voltage of the IGCT power module 022 is the same as that of the IGBT power module 021, both being U. dc The rated operating current of IGCT power module 022 is the same as that of IGBT power module 021, both being I... rms Alternatively, depending on the actual required voltage and power level, the rated operating voltage of the IGCT power module 022 may differ from that of the IGBT power module 021, and the rated operating current of the IGCT power module 022 may also differ from that of the IGBT power module 021. By combining these components, the required voltage and power level can be achieved, thereby improving the flexibility and applicability of the modular multilevel converter 01.

[0051] To ensure the proper functioning of the IGCT devices in the modular multilevel converter 01 and to improve the reliability of the IGCT power module 022, the insulation voltage V of the IGCT devices (T3, T4) is... DRM >1.6*U dc The on-state rated current I of IGCT devices (T3, T4) T(RMS) >1.6*I rms U dc I is the rated operating voltage of the IGCT power module. rms This is the rated operating current of the IGCT power module.

[0052] Among them, the insulation voltage V of the IGCT device DRM Insulation voltage refers to the electrical insulation class that an IGCT device can safely withstand. It indicates the device's insulation performance; that is, when a voltage less than or equal to this value is applied across the IGCT device, the insulating material can effectively isolate the voltage difference. For an IGCT device, the insulation voltage is the highest voltage that its insulating components can withstand. Exceeding this voltage may lead to insulation failure or electric shock. The on-state rated current I of the IGCT device is also mentioned. T(RMS) This refers to the current that the device can continuously withstand under normal operating conditions. It also refers to the maximum current that the IGCT device can operate at for an extended period under specific temperature and other operating parameters. Exceeding this rated current may damage the IGCT device or degrade its performance. The insulation voltage V of the IGCT device is set accordingly. DRM >1.6*U dc The on-state rated current I of the IGCT device T(RMS) >1.6*I rms This allows the IGCT devices (T3, T4) to operate at the insulation voltage V. DRM and on-state rated current I T(RMS) Within the specified range, to ensure the reliability and safety of IGCT devices (T3, T4).

[0053] Optionally, the insulation voltage V of the diodes (D3, D4) RRM =V DRM >1.6*U dc The average forward current I of diodes (D3, D4) F(AV) >I rms .

[0054] Among them, diodes (D3 and D4) are fast recovery diodes, possessing a rapid recovery speed, which is beneficial for the rapid switching of the operating state of the IGCT power module 022. The insulation voltage VRRM of diodes (D3 and D4) refers to the maximum voltage that the diodes (D3 and D4) can withstand when operating in reverse; exceeding this voltage will cause the diodes to break down. The average forward current I of diodes (D3 and D4) is... F(AV) This refers to the average current that a diode (D3, D4) can continuously conduct under forward energization. Exceeding this current may cause the diode to overheat or be damaged.

[0055] Taking the modular multilevel converter 01 with a three-phase six-arm structure as an example, when the IGCT power module 022 is working normally, the power of a single IGCT power module 022 is the integral of the voltage and current entering and exiting the power module, the power of a single arm is the integral of the voltage and current of that arm, the power of each phase (including the upper and lower arms) is one-third of the power of the modular multilevel converter 01, and the change in energy stored in a single arm is...

[0056] Among them, P dc The DC-side power of the modular multilevel converter 01 is given by m, where m is the modulation ratio and ω is the input voltage. N ω is the angular frequency. N = 2πf, where f is the operating frequency, typically 50Hz. The angle represents the power factor between active and reactive power.

[0057] The energy of a single IGCT power module 022 is the energy stored in DC capacitor C2, i.e. The average value of the operating voltage of DC capacitor C2; the percentage fluctuation of the operating voltage of DC capacitor C2 is ε, i.e. n represents the number of converter submodules 02 in a single arm of the modular multilevel converter 01. This number can be obtained using the formula for the change in energy stored in a single arm, ΔW(m). Set the capacitance of the DC capacitor in the IGCT power module 022 to... This enables the IGCT power module 022 to be used in the modular multilevel converter 01, allowing for the mixed use of the IGBT power module 021 and the IGCT power module 022.

[0058] Furthermore, the discharge resistor R must release the energy stored in the DC capacitor C2 within time t after the modular multilevel converter 01 stops. This requires that the discharge energy of the discharge resistor R within time t be greater than or equal to the energy stored in the DC capacitor C2. Right now

[0059] In this way, it can be ensured that after the modular multilevel converter 01 is shut down, the discharge resistor R can quickly release the energy stored in the DC capacitor C2, avoiding sudden current changes, abnormal voltage, etc. when the modular multilevel converter 01 is restarted, which would affect the operation of the modular multilevel converter 01. It can also prevent the IGCT power module 022 from being placed in a dangerous environment, which would affect the performance and lifespan of the equipment.

[0060] In an optional embodiment, the discharge resistor R includes a first discharge resistor R1 and a second discharge resistor R2. The resistance value of the first resistor R1 is equal to the resistance value of the second resistor R2, both being R0. That is, the resistance value of the discharge resistor R is... Right now

[0061] Optionally, the latch-up loss P of the IGCT power module 022 IGCT Equal to the latch-up loss P of IGBT power module 021 IGBT The latch-up loss of IGBT power module 022 is P IGCT-loss1 , P is the average value of the operating voltage of the DC capacitor. IGCT-loss1 The power discharge loss of the IGCT power module 022, i.e., the discharge resistance. Then according to The resistance value of the discharge resistor R can be determined.

[0062] In this way, the latch-up loss P of the IGCT power module 022 can be reduced. IGCT It can be equal to the latch-up loss P of the IGBT power module 021. IGBT This enables balanced current distribution among various converter submodules 02, ensuring the performance and stability of the modular multilevel converter 01; it also enables balanced load distribution, reducing unbalanced losses in the locked-out state.

[0063] Optional, continue to refer to Figure 3 The buffer circuit 03 includes an anode reactor L1; the first terminal of the anode reactor L1 is electrically connected to the first terminal of the DC capacitor C2 and the first terminal of the discharge resistor R, respectively; the second terminal of the anode reactor L1 is electrically connected to the anode of the first fully controlled switch module 041; the cathode of the first fully controlled switch module 041 is electrically connected to the anode of the second fully controlled switch module 042; the cathode of the second fully controlled switch module 042 is electrically connected to the second terminal of the DC capacitor C2 and the second terminal of the discharge resistor R, respectively. The inductance of the circuit containing the anode reactor L in the IGCT power module 22... U dcdenoted as the rated operating voltage of the IGCT power module, and di / dt as the critical rate of change of current for the first fully controlled switch module 41 and the second fully controlled switch module 42.

[0064] The critical rate of change of current refers to the maximum rate of change of current that a device can withstand. When the rate of change of current in a device exceeds the critical rate of change of current, it will lead to a large induced voltage inside the device, which will exceed the device's withstand voltage capability. This will result in additional power loss and excessively high device temperature, which will easily cause breakdown and damage to the device.

[0065] For example, the anode reactor L includes an inductor, which can reduce the rate of increase of the current in the critical rate of change of the current of the first fully controlled switching module 041, preventing the switching process speed of the first fully controlled switching module 041 from being too fast, causing the rate of change of the current to exceed the critical rate of change of the current of the first fully controlled switching module 041, thus damaging the first fully controlled switching module 041. The inductance value of the circuit containing the anode reactor L in the IGCT power module 022. The rate of change of current in the first fully controlled switch module 041 can be limited to within the critical rate of change of current, thus protecting the first fully controlled switch module 041 and / or the second fully controlled switch module 042 from damage.

[0066] Optional, the inductance value of the anode counter L L loop This is to address the loop inductance of the IGCT power module. Thus, during normal operation of the modular multilevel converter, the rate of change of current can be limited to the critical rate of change of current in the first fully controlled switch module 41 and the second fully controlled switch module 42. This ensures the switching speed of the IGCT power module while minimizing damage to the first and second fully controlled switch modules 41 and 42. It also prevents the inductance value L0 of the anode reactor L from being too large, which would lead to an excessively large inductance value L1 in the circuit containing the anode reactor L, thus reducing the switching speed of the IGCT power module.

[0067] In an optional embodiment, the inductance value of the circuit containing the anode reactor L in the IGCT power module 022 di T / dt represents the critical rate of change of current for the IGCT device. This prevents fluctuations in the actual operating voltage of the IGCT power module 022 from causing the rate of change of current to exceed the critical rate of change of current for the IGCT device, thus damaging the IGCT device.

[0068] Optional, continue to refer to Figure 3 The buffer circuit 03 also includes a clamping resistor R. S Clamping diode D CL and clamping capacitor C CL Clamping resistor R SThe first terminal is electrically connected to the first terminal of DC capacitor C2 and the first terminal of anode resistor L, respectively; clamping resistor R S The second end is connected to the clamping capacitor C. CL The first terminal and clamping diode D CL Cathode electrical connection; clamping diode D CL The anodes are electrically connected to the second terminal of the anode countermeasure L and the anode of the first fully controlled switch module 041, respectively; clamping capacitor C CL The second terminal is electrically connected to the second terminal of DC capacitor C2 and the cathode of the second fully controlled switch module 042.

[0069] Among them, the clamping capacitor C CL The capacitance value is 3≤A≤5, I rms U is the rated operating current of the IGCT power module. block t is the unlocked overvoltage threshold of the IGCT power module 022. f This refers to the current drop time when the second fully controlled switch module 042 is turned off. The unlocked overvoltage threshold U... block This refers to a preset voltage protection value for the IGCT power module that is higher than its rated operating voltage. When the actual operating voltage of the IGCT power module exceeds this voltage protection value, the system will activate the protection mechanism and put the IGCT power module 022 into the unlocked state. At this time, the IGCT power module 022 is turned off to avoid negative impacts on other power modules or modular multilevel converter 01 due to excessively high output voltage, thereby protecting the normal operation of the system.

[0070] Specifically, clamping resistor R S Connecting it in parallel with the anode reactor L provides a path for the anode reactor L, reducing the voltage spike when the IGCT device is turned off. This prevents the anode reactor L from being open-circuited when the IGCT device is turned off, which would result in a large voltage spike on the IGCT device and cause it to break down and be damaged. Clamping diode D CL When the IGCT device is turned on, it can prevent current from flowing from the clamping resistor R. S Current flows through, avoiding clamping resistor R S The effect of the anode reactor L is weakened. Clamping capacitor C CL This can accelerate the absorption of turn-on energy from the IGCT power module during the turn-on process of the IGCT device, preventing excessive turn-on energy from causing the actual operating voltage of the IGCT power module to exceed the unlocked overvoltage threshold U. block .

[0071] For example, when the IGCT power module is turned on, due to the certain conduction delay of the IGCT device, sufficient turn-on energy needs to be provided during the turn-on process of the IGCT device T3 to overcome the energy barrier of the blocking layer during the conduction process of the fully controlled switching module of the IGCT device T3. This will lead to an increase in the actual operating voltage of the IGCT power module and the clamping capacitance C. CL The voltage across the terminals increases, and the actual operating voltage of the IGCT power module is equal to the clamping capacitor C. CL The voltage across the terminals. When the IGCT power module is turned on, the clamping capacitor C... CL The voltage across the terminals rises to the unlocked overvoltage threshold U. block time To prevent the IGCT power module from entering a latch-up state during the turn-on process, clamping capacitor C... CL The voltage across the terminals rises to the unlocked overvoltage threshold U. block Time T rise When the second fully controlled switch module is turned off, the current fall time t f 3-5 times that, i.e., T rise =A*t f 3≤A≤5, from which the clamping capacitor can be obtained. A value of 3≤A≤5 is preferred. This way, when the second fully controlled switch module 042 is turned off and the first fully controlled switch module 041 is turned on, the IGCT power module can be prevented from entering a locked state during the turn-on process, which would prevent the IGCT power module from working properly.

[0072] Optional, clamping resistor R S resistance value 3≤B≤5, T on This refers to the conduction time of the second fully controlled switch module 042.

[0073] Specifically, when the second fully controlled switch module 042 is turned on, the clamping capacitor C... CL The discharge time constant is T RC =R S *C CL At clamping capacitor C CL Discharge time constant T RC Within 3-5 times the time, the clamping capacitor C CL The voltage across the terminals drops to almost zero, meaning that in order to ensure the clamping capacitor C... CL The voltage across the terminals drops to zero, B*T RC <T on ,Right now 3≤B≤5. Clamping capacitor C CL The maximum energy of the discharge is the energy stored in the anode reactor L, which is L0 is the inductance value of the anode counteractor L, I rmsThis is the rated operating current of the IGCT power module.

[0074] Optional, clamping diode D CL For a fast recovery diode, the insulation voltage of the clamping diode is V. DCL-RRM V DCL-RRM =V RRM >1.6*U dc It can have a fast recovery speed and is not easily damaged by penetration.

[0075] For example, when the second fully controlled switch module 042 is turned off, current flows through the clamping diode D. CL The maximum approximation of the current is I rms The time it takes for the flow to pass is A*t. f Therefore, current flows through clamping diode D CL The effective value of the current is 3≤A≤5, t f T is the current fall time when the second fully controlled switch module 042 is turned off. s This refers to the switching cycle of the second fully controlled switch module 042.

[0076] In an optional embodiment, clamping diode D CL The forward average current is greater than I rms This causes the clamping diode D to... CL Not easily damaged.

[0077] Optional, continue to refer to Figure 3 The IGCT power module 022 also includes a bypass switch S; the bypass switch S is electrically connected to the output terminal of the IGCT power module 022; the rated operating voltage of the bypass switch S is greater than the unlocked overvoltage threshold U of the IGCT power module 022. block The rated operating current of the bypass switch S is greater than the rated operating current of the IGCT power module.

[0078] The bypass switch S can be a mechanical switch or a semiconductor switch, etc., and the embodiments of the present invention do not limit it.

[0079] For example, when the actual operating voltage of the IGCT power module 022 is greater than the unlocked overvoltage threshold U block When the bypass switch S closes normally, it protects the IGCT power module 022 from damage. The rated operating voltage of the bypass switch S is greater than the unlocked overvoltage threshold U of the IGCT power module 022. block This allows the bypass switch S to operate within a higher operating voltage range. On one hand, this prevents damage to the bypass switch S; on the other hand, it ensures that the actual operating voltage of the IGCT power module 022 exceeds the unlocked overvoltage threshold U. blockEven when the bypass switch S is unlocked, it can still operate normally. The rated operating voltage of the bypass switch S can be the overvoltage threshold U in the unlocked state. block The rated operating current of the bypass switch S is 1.2-1.5 times that of the IGCT power module 022, which is greater than the effective value of the bridge arm current. This ensures that the bypass switch S is not easily damaged and can work effectively in the modular multilevel converter.

[0080] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A modular multilevel converter, characterized in that, The modular multilevel converter includes multiple cascaded converter sub-modules; the converter sub-modules include IGCT power modules and IGBT power modules; The IGCT power module includes a DC capacitor, a first fully controlled switch module, a second fully controlled switch module, a buffer circuit, and a discharge resistor. The DC capacitor is connected in parallel with the discharge resistor and the buffer circuit. The buffer circuit is connected in parallel with the first fully controlled switch module and the second fully controlled switch module, which are connected in series. The second fully controlled switch module is connected in parallel with the output terminal of the IGCT power module. Both the first fully controlled switch module and the second fully controlled switch module include an IGCT device and a diode connected in antiparallel to it. The insulation voltage of the IGCT device is VDRM. The rated on-state current of the IGCT device is: , ;in, The rated operating voltage of the IGCT power module is [voltage value missing]. This refers to the rated operating current of the IGCT power module; The buffer circuit includes an anode counteractor; the first end of the anode counteractor is electrically connected to the first end of the DC capacitor and the first end of the discharge resistor, respectively; the second end of the anode counteractor is electrically connected to the anode of the first fully controlled switch module; the cathode of the first fully controlled switch module is electrically connected to the anode of the second fully controlled switch module; the cathode of the second fully controlled switch module is electrically connected to the second end of the DC capacitor and the second end of the discharge resistor, respectively. In the IGCT power module, the inductance value of the circuit containing the anode counter is L1. In the formula, The rated operating voltage of the IGCT power module is [voltage value missing]. The current critical rate of change is defined for the first fully controlled switch module and the second fully controlled switch module.

2. The modular multilevel converter according to claim 1, characterized in that, The diode is a fast recovery diode; The insulation voltage of the diode is , The average forward current of the diode is , .

3. The modular multilevel converter according to claim 1, characterized in that, The capacitance value of the DC capacitor is C0. ; In the formula, The power on the DC side of the modular multilevel converter. This represents the average value of the operating voltage of the DC capacitor. The percentage fluctuation of the operating voltage of the DC capacitor is denoted by , where m is the modulation ratio. Where is the angular frequency, and n is the number of converter submodules in a single bridge arm of the modular multilevel converter. The angle represents the power factor between active and reactive power.

4. The modular multilevel converter according to claim 3, characterized in that, The resistance value of the discharge resistor is R. In the formula, C0 is the capacitance value of the DC capacitor, and t is the discharge time of the DC capacitor after the IGCT power module is shut down.

5. The modular multilevel converter according to claim 4, characterized in that, The latch-up loss of the IGBT power module is PIGBT, and the latch-up loss of the IGCT power module is... , ; The latch-up loss of the IGCT power module includes power supply loss and discharge resistance loss; the power supply loss is... The discharge resistor loss is , ; In the formula, R is the average value of the operating voltage of the DC capacitor, and R is the resistance value of the discharge resistor.

6. The modular multilevel converter according to claim 1, characterized in that, The inductance value of the anode counter is L0. ; in, This refers to the loop inductance of the IGCT power module.

7. The modular multilevel converter according to claim 1, characterized in that, The buffer circuit also includes a clamping resistor, a clamping diode, and a clamping capacitor; The first terminal of the clamping resistor is electrically connected to the first terminal of the DC capacitor and the first terminal of the anode countermeasure, respectively; the second terminal of the clamping resistor is electrically connected to the first terminal of the clamping capacitor and the cathode of the clamping diode, respectively; the anode of the clamping diode is electrically connected to the second terminal of the anode countermeasure and the anode of the first fully controlled switch module, respectively; the second terminal of the clamping capacitor is electrically connected to the second terminal of the DC capacitor, the second terminal of the discharge resistor, and the cathode of the second fully controlled switch module, respectively. The capacitance of the clamping capacitor is , 3≤A≤5; In the formula, This refers to the rated operating current of the IGCT power module. This is the unlocked overvoltage threshold of the IGCT power module. The current drop time is the time when the second fully controlled switch module is turned off.

8. The modular multilevel converter according to claim 7, characterized in that, The resistance value of the clamping resistor is RS. , ; In the formula, This refers to the conduction time of the second fully controlled switch module.

9. The modular multilevel converter according to claim 7, characterized in that, The clamping diode is a fast recovery diode; The insulation voltage of the clamping diode is , .

10. The modular multilevel converter according to claim 7, characterized in that, The IGCT power module also includes a bypass switch; the bypass switch is electrically connected to the output terminal. The rated operating voltage of the bypass switch is greater than the unlocked overvoltage threshold of the IGCT power module. The rated operating current of the bypass switch is greater than the rated operating current of the IGCT power module.

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