A system and method for obtaining a bridge arm current of a soft direct current converter valve

Abstract

This invention provides a system and method for acquiring the arm current of a flexible DC converter valve. The system includes a converter valve control system, a submodule controller, and an IGBT driver. The IGBT driver is connected to the control terminals of each IGBT in the submodule of the flexible DC converter valve. The IGBT driver is communicatively connected to the submodule controller, and the submodule controller is communicatively connected to the converter valve control system. By real-time acquisition of the voltage between the collector and emitter of the IGBT and its case temperature data, combined with the collector-emitter voltage and collector current relationship curves of different types of IGBT devices at various junction temperatures, the theoretical value of the flexible DC converter valve arm current is calculated. Combined with the IGBTs that actually carry the arm current, the current direction and current amplitude of the flexible DC converter valve arm current are obtained. This can be used as a basis for judging the fault of the current transformer, providing technical support for the reliability and stability of the flexible DC transmission system.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, specifically to a system and method for obtaining the arm current of a flexible DC converter valve. Background Technology

[0002] In flexible DC transmission systems, the control system needs to use the current of each arm of the converter valve to achieve functions such as submodule capacitor voltage balance control, circulating current suppression, and converter valve overcurrent protection. Therefore, timely and accurate acquisition of the arm current is crucial for ensuring the safe and stable operation of the flexible DC converter valve.

[0003] Currently, most flexible DC projects use current transformers (CTs) located on the bridge arms of the converter valve to collect bridge arm currents. This current information is then transmitted via fiber optic cables through a merging unit to the various control units of the converter valve. However, this approach has several problems in practical applications: First, when the current data collected by the CTs is inaccurate or contains errors, the upper-level controller struggles to identify the fault due to a lack of effective judgment methods. In practice, numerous instances have occurred where CT failures prevented the upper-level controller from recognizing the fault, leading to widespread failures in converter valve submodules and ultimately system shutdowns. Second, the sampling delay of the bridge arm current collected by the CTs is significant, typically greater than 60 microseconds. Flexible DC systems have extremely high requirements for link delay in bridge arm overcurrent protection. This excessive sampling delay makes it difficult to configure protection settings for the flexible DC system, severely impacting the system's operational safety margin and fault ride-through capability. Furthermore, since the CTs are usually located close to the bridge arm reactors, they cannot identify the fault current in cases of internal converter valve tower faults, such as valve tower flashovers, thus failing to provide protection criteria for the upper-level control system. Summary of the Invention

[0004] Therefore, in order to accurately and quickly obtain the bridge arm current of the converter valve, the present invention provides a system and method for obtaining the bridge arm current of a flexible DC converter valve.

[0005] In a first aspect, the present invention provides a system for acquiring the arm current of a flexible DC converter valve, comprising: a converter valve control system, a submodule controller, and an IGBT driver;

[0006] The IGBT driver is connected one-to-one with the control terminals of each IGBT tube in the sub-module of the flexible DC converter valve.

[0007] The IGBT driver is connected to the submodule controller, and the submodule controller is connected to the converter valve control system.

[0008] The IGBT driver is used to acquire the voltage between the collector and emitter of the IGBT connected to it in real time, and calculate the theoretical value of the bridge arm current based on the voltage.

[0009] The submodule controller is used to collect the theoretical values ​​of the voltage between the collector and emitter of the IGBT transistors and the bridge arm current sent by all IGBT drivers in this submodule, and send them to the converter valve control system in a unified manner.

[0010] The converter valve control system is used to determine the IGBT that actually carries the bridge arm current in the current control cycle and the direction of the bridge arm current, based on the voltage between the collector and emitter of the received IGBT and the submodule control command issued in the previous control cycle. It also calculates the theoretical value of the bridge arm current corresponding to all IGBTs that carry the bridge arm current in the current control cycle, and takes the average value as the bridge arm current amplitude for the current cycle.

[0011] Optionally, the converter valve control system is also used to calculate the correction factor for the arm current and send the correction factor to the IGBT driver;

[0012] The IGBT driver is also used to correct the current amplitude of the arm current according to a correction factor.

[0013] Optionally, the IGBT driver includes: an analog signal acquisition unit, a data storage unit, a communication unit, a programmable logic unit, and a digital signal processor; wherein:

[0014] The analog acquisition unit is used to acquire the voltage between the collector and emitter of the corresponding IGBT and its case temperature data, and send them to the digital signal processor and programmable logic unit.

[0015] The digital signal processor is used to calculate the theoretical value of the flexible DC converter valve arm current based on the data sent by the analog acquisition unit and the collector-emitter voltage and collector current relationship curve data of different types of IGBT devices at various junction temperatures stored in the data storage unit, and send it to the programmable logic control unit and the data storage unit.

[0016] The data storage unit is used to store data sent by the digital signal processor, as well as the collector-emitter voltage and collector current relationship curves of different types of IGBT devices at various junction temperatures.

[0017] The programmable logic unit (PLU) is used to receive data sent by the analog signal acquisition unit and the digital signal processor, and generate corresponding control commands to send to the corresponding IGBT and the digital signal processor to control the corresponding IGBT and IGBT driver.

[0018] The communication unit is used to enable information exchange between the IGBT driver and the upper-level control unit.

[0019] Optionally, the IGBT driver may also include: a fault monitoring unit, a power amplification unit, and an isolated power supply unit; wherein:

[0020] The fault monitoring unit is communicatively connected to the programmable logic unit (PLU) to monitor the fault status information of the IGBT driver and the IGBT transistors connected to it, and sends the fault status information to the PLU, which then protects the IGBT driver and the corresponding IGBT transistors.

[0021] The power amplifier unit is used to amplify the output capability of the control commands of the programmable logic unit before outputting them to the corresponding IGBT transistor.

[0022] The isolated power supply unit is used to provide power supply voltage to the IGBT driver.

[0023] Secondly, the present invention provides a method for obtaining the arm current of a flexible DC-DC converter valve, applied to the flexible DC-DC converter valve arm current acquisition system described in the first aspect, the method comprising:

[0024] The IGBT driver acquires the voltage between the collector and emitter of the upper and lower IGBT transistors in each submodule of the flexible DC converter valve in real time, and calculates the theoretical value of the bridge arm current based on the voltage.

[0025] The submodule controller collects the theoretical values ​​of the voltage between the collector and emitter of the IGBT transistors and the bridge arm current sent by all IGBT drivers in this submodule, and sends them to the converter valve control system in a unified manner.

[0026] The converter valve control system determines the IGBT that actually carries the current in the current control cycle of each bridge arm based on the voltage between the collector and emitter of the IGBT and the submodule control command issued in the previous control cycle, and obtains the current direction of the bridge arm.

[0027] The converter valve control system calculates the theoretical value of the arm current corresponding to all IGBT transistors that pass through the arm current in this control cycle, and takes the average value as the arm current amplitude for this cycle.

[0028] Optionally, after calculating the bridge arm current amplitude for this cycle, the calculation also includes:

[0029] The converter valve control system calculates the correction coefficient for the bridge arm current based on the submodule capacitor voltage;

[0030] The IGBT driver corrects the current amplitude of the bridge arm current based on a correction factor.

[0031] Optionally, the converter valve control system calculates the correction factor for the arm current based on the submodule capacitor voltage, including:

[0032] The converter valve control system collects the change in the voltage of the sub-module capacitor according to a preset period, and calculates the effective value of the bridge arm current based on the change in the voltage of the sub-module capacitor.

[0033] The converter valve control system receives the IGBT collector current collected by the IGBT driver within a preset period to obtain the calibration value of the bridge arm current.

[0034] The converter valve control system divides the effective value of the arm current by the calibrated value of the arm current to obtain the correction factor.

[0035] Optionally, the effective value of the bridge arm current is calculated based on the change in the submodule capacitor voltage, including:

[0036] The converter valve control system calculates the instantaneous value of the bridge arm current based on the integral relationship between the bridge arm current and the capacitance value of the submodule, combined with the change in the voltage of the submodule capacitor, and then calculates the effective value of the bridge arm current based on the instantaneous value.

[0037] Optionally, the formula for calculating the instantaneous value is:

[0038]

[0039] in, This represents the instantaneous value of the bridge arm current. This represents the instantaneous value of the charging current of the nth submodule, where N is the total number of submodules engaged in a single control cycle of any bridge arm.

[0040] Optionally, the formula for calculating the effective value of the bridge arm current based on the instantaneous value is as follows:

[0041]

[0042] in, is the effective value of the bridge arm current, and T is the preset period.

[0043] Optionally, the IGBT driver corrects the current amplitude of the bridge arm current according to a correction factor, including:

[0044] The IGBT driver collects the case temperature of each IGBT in real time and calculates the junction temperature of the corresponding IGBT based on the case temperature.

[0045] The IGBT driver multiplies the junction temperature by a correction factor to obtain the corrected junction temperature;

[0046] Based on the corrected junction temperature, the IGBT driver determines the relationship curve between the voltage between the collector and emitter of the IGBT transistor and the bridge arm current, and obtains the current amplitude of the corrected bridge arm current according to the relationship curve.

[0047] Optionally, the converter valve control system determines, based on the voltage and the submodule control command issued in the previous control cycle, the IGBT transistors that actually carry the bridge arm current in the current control cycle in each bridge arm, including:

[0048] If the control command for the submodule in the previous control cycle was to cut off, and the voltage between the collector and emitter of the lower IGBT of the submodule is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, then it is determined that the upper IGBT of the submodule in the current control cycle is actually carrying the bridge arm current, and the direction of the bridge arm current in this control cycle is determined to be negative.

[0049] If the submodule control command in the previous control cycle was "engaged", and the voltage between the collector and emitter of the upper IGBT of the submodule is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, then it is determined that the lower IGBT of the submodule that is in the "disabled" state in the current control cycle is actually carrying bridge arm current, and the direction of the bridge arm current in this control cycle is determined to be positive.

[0050] The technical solution of this invention has the following advantages:

[0051] 1. The system and method for acquiring the arm current of a flexible DC converter valve provided by this invention acquires the voltage between the collector and emitter of the upper and lower IGBTs in each sub-module of the flexible DC converter valve in real time through an IGBT driver, and calculates the theoretical value of the arm current based on the voltage. The converter valve control system determines the IGBT that actually carries the arm current in the current control cycle and determines the direction of the arm current based on the voltage between the collector and emitter of the IGBT and the sub-module control command issued in the previous control cycle. Finally, the converter valve control system calculates the theoretical value of the arm current corresponding to all IGBTs that carry the arm current in the current control cycle, and takes the average value as the arm current amplitude for the current cycle. This method effectively solves the problems of relying solely on the arm current acquisition by the arm CT and the inability to identify abnormal faults in the CT device, leading to converter valve failure. It provides accurate, fast, and effective acquisition of the arm current, which can also serve as a basis for judging current transformer faults, providing technical support for the reliability and stability of flexible DC transmission systems.

[0052] 2. The IGBT driver provided by this invention acquires the voltage between the collector and emitter of the IGBT tube and its case temperature data in real time. Combined with the collector-emitter voltage and collector current relationship curve data of different types of IGBT devices at various junction temperatures, the theoretical value of the flexible DC converter valve arm current is calculated, which reduces the calculation burden of the converter valve control system and enables accurate, fast and effective acquisition of the arm current. Attached Figure Description

[0053] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0054] Figure 1 This is a schematic diagram of the structure of a flexible DC converter valve provided in an embodiment of the present invention;

[0055] Figure 2 A schematic diagram of one embodiment of the IGBT driver provided in this invention;

[0056] Figure 3 This is a schematic diagram of another embodiment of the IGBT driver provided in this invention.

[0057] Figure 4 A schematic diagram of a system for acquiring the arm current of a flexible DC converter valve provided in an embodiment of the present invention;

[0058] Figure 5 A flowchart illustrating a method for obtaining the arm current of a flexible DC converter valve, provided in an embodiment of the present invention. Detailed Implementation

[0059] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the system or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0061] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0063] Existing flexible DC converter valves (referred to as flexible DC converter valves) mostly adopt a half-bridge structure sub-module (such as... Figure 1 SM1-SM N As shown in the figure, its structural diagram is as follows: Figure 1 As shown, based on the series connection characteristics of the sub-modules of the converter valve, the inventors discovered that the current in each arm of the converter valve is approximately equal to the current Ic flowing through the collector of the IGBT device that is turned on at the same time in the same arm. The voltage Vce between the collector and emitter of the IGBT device can accurately reflect this current. Therefore, by accurately monitoring the voltage between the collector and emitter of the turned-on IGBT through the IGBT driver, the arm current can be accurately obtained.

[0064] However, flexible DC transmission projects involve thousands of sub-modules, which doubles the number of IGBTs. The converter station control system or converter valve control system cannot calculate the collector current of all IGBTs. Therefore, the IGBT driver at the bottom level is required. Traditional drivers are usually implemented by pure analog circuits or programmable logic units containing only a few logic gates as the core processing unit, which cannot implement complex algorithms.

[0065] Based on this, the present invention provides an IGBT driver, the structural schematic of which is shown below. Figure 2 As shown, it includes: an analog signal acquisition unit, a data storage unit, a communication unit, a programmable logic unit, and a digital signal processor. (The analog signal acquisition unit is used to acquire data from the corresponding IGBT transistor (e.g., ...) Figure 2The data acquisition unit (shown in the IGBT device) collects and transmits the voltage between the collector and emitter and the case temperature data to a digital signal processor (DSP) and a programmable logic unit (PLU). The DSP calculates the theoretical value of the flexible DC converter valve arm current based on the data from the analog acquisition unit and the collector-emitter voltage versus collector current curves of different types of IGBT devices at various junction temperatures stored in the data storage unit. This theoretical value is then sent to the PLU and the data storage unit. The collector-emitter voltage refers to the voltage between the collector and emitter of the IGBT. The data storage unit stores the data from the DSP and the collector-emitter voltage versus collector current curves of different types of IGBT devices at various junction temperatures. The PLU receives the data from the analog acquisition unit and the DSP, generates corresponding control commands, and sends them to the corresponding IGBT and the DSP to control the IGBT and its driver. Specifically, controlling the IGBT can include turning it on or off, and controlling the IGBT driver can involve implementing core control, protection, and communication functions such as driver fault monitoring, device protection, and communication coding. These adjustments can be made according to the specific application. The communication unit is used to realize information interaction between the IGBT driver and the upper control unit. In practical applications, the upper control unit can be the converter valve control system and sub-module controller in the flexible DC converter valve arm current acquisition system, as shown in the following embodiments.

[0066] like Figure 1 As shown, each submodule of the converter valve includes an upper IGBT, a lower IGBT, and a submodule capacitor (such as...). Figure 1 (As shown in the figure, the capacitors connected in parallel across the upper and lower IGBTs are both equipped with reverse diodes; based on this, each IGBT driver can be configured to independently control one IGBT.)

[0067] Since the relationship between collector current and collector-emitter voltage varies with the junction temperature of the device, the above-mentioned IGBT driver can be used to collect the voltage between the collector and emitter of the corresponding IGBT and its case temperature data. Combined with the collector-emitter voltage and collector current relationship curve data of different types of IGBT devices at various junction temperatures, the theoretical value of the flexible DC converter valve arm current can be calculated, reducing the computational burden of the converter valve control system.

[0068] In one specific embodiment, the IGBT driver may further include a fault monitoring unit, a power amplification unit, and an isolated power supply unit, as shown in the schematic diagram below. Figure 3 As shown.

[0069] Specifically, the fault monitoring unit communicates with the programmable logic unit (PLU) to monitor the fault status information of the IGBT driver and its connected IGBTs, and sends the fault status information to the PLU. The PLU then protects the IGBT driver and the corresponding IGBTs themselves. Fault statuses can include, but are not limited to, undervoltage supply, short-circuit faults, overcurrent faults, and abnormal IGBT trigger commands. The power amplification unit amplifies the control command output of the PLU before outputting it to the corresponding IGBT to meet the power requirements of the IGBT driver. The isolated power supply unit provides the power supply voltage to the IGBT driver.

[0070] like Figure 4 As shown, this embodiment of the invention also provides a system for acquiring the arm current of a flexible DC converter valve, including: a converter valve control system (VBC), a submodule controller (SMC), and an IGBT driver. Figure 4 Only the upper IGBT driver and the lower IGBT driver are shown in the text. The structure of the IGBT driver is similar to that of the lower IGBT driver, so it will not be described in detail.

[0071] Among them, the IGBT driver and the sub-module within the flexible DC converter valve (such as...) Figure 1 SM1-SM N The control terminals of each IGBT (as shown) are connected one-to-one; the IGBT driver is connected to the submodule controller, and the submodule controller is connected to the converter valve control system; the IGBT driver is used to acquire the voltage between the collector and emitter of the IGBT connected to it in real time, and calculate the theoretical value of the bridge arm current based on the voltage; the submodule controller is used to collect the theoretical values ​​of the voltage between the collector and emitter of the IGBT and the bridge arm current sent by all IGBT drivers in this submodule, and send them to the converter valve control system; the converter valve control system is used to determine the IGBT that actually carries the bridge arm current in the current control cycle in each bridge arm, and determine the direction of the bridge arm current, based on the received voltage between the collector and emitter of the IGBT and the submodule control command issued in the previous control cycle, and calculate the theoretical value of the bridge arm current corresponding to all IGBTs that carry the bridge arm current in this control cycle, and take the average value as the bridge arm current amplitude of this cycle.

[0072] Specifically, the communication methods between the various modules within the system can be selected according to the actual application situation without specific limitations. For example, fiber optic communication with Manchester encoding as the protocol format can be selected.

[0073] During each control cycle, the bridge arm current has four possible paths to flow through the submodule: through the upper IGBT, the upper diode, the lower IGBT, and the lower diode.

[0074] Therefore, after receiving the SMC information uploaded by all submodules in each bridge arm, the VBC begins to determine the current direction of each bridge arm. For example, if the Vce uploaded by the lower IGBT driver of a disconnected submodule in the bridge arm is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, it indicates that the bridge arm current flows through the lower diode, and the bridge arm current direction for this control cycle is determined to be negative. Alternatively, if the Vce uploaded by the upper IGBT driver of a connected submodule in the bridge arm is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, the bridge arm current direction for this control cycle is determined to be positive. After determining the current direction, the IGBTs for which the bridge arm current needs to be calculated can be selected according to the different current directions. When the current direction is positive, the bridge arm current flows through the lower IGBT that is turned on; when the current direction is negative, the bridge arm current flows through the upper IGBT that is turned on. By averaging the collector current values ​​corresponding to the above IGBTs, the current direction and current amplitude of the bridge arm current for this cycle can be obtained.

[0075] The aforementioned IGBT driver, SMC, and VBC processing architecture is suitable for flexible DC transmission. This IGBT driver possesses the capability for accurate analog data acquisition and complex algorithm implementation. It achieves precise calculation of collector current at the bottom-level control unit of the converter valve and uses VBC for logic judgment and data selection. By combining edge computing with top-level logic judgment, the computational burden on the upper-level control system is reduced. This effectively solves the problems of relying solely on the arm current acquisition via the arm CT and the inability to identify abnormal faults in the CT device, leading to converter valve failures. Simultaneously, it reduces the sampling delay for acquiring arm current and allows flexible DC transmission systems to configure higher overcurrent protection settings, effectively improving system operating margin and fault ride-through capability.

[0076] In one specific embodiment, based on the same inventive concept as the above-mentioned flexible DC converter valve arm current acquisition system, considering that the IGBT junction temperature data obtained by the IGBT driver from the device case temperature acquisition has a certain deviation, which affects the accuracy of the acquired collector current, a correction coefficient is introduced to correct the junction temperature in real time.

[0077] Therefore, the converter valve control system is also used to calculate the correction factor for the arm current and send the correction factor to the IGBT driver; the IGBT driver is also used to correct the current amplitude of the arm current according to the correction factor. For details on how to calculate the correction factor for the arm current, please refer to the following embodiments, which will not be repeated here.

[0078] like Figure 5 As shown in the figure, this embodiment of the invention also provides a method for obtaining the arm current of a flexible DC converter valve, the method comprising the following steps:

[0079] Step S1: The IGBT driver acquires the voltage between the collector and emitter of the upper and lower IGBT transistors in each submodule of the flexible DC converter valve in real time, and calculates the theoretical value of the bridge arm current based on the voltage.

[0080] As described in the above embodiments, one IGBT driver is connected to one IGBT device. The IGBT driver acquires the voltage between the collector and emitter of the upper and lower IGBT transistors in each submodule of the flexible DC converter valve in real time. Then, each IGBT driver calculates the theoretical value of the corresponding bridge arm current based on the collector-emitter voltage it has acquired. The specific calculation process is as follows: the case temperature, collector-emitter voltage, and collector current of the IGBT device are acquired in real time. Then, based on the device characteristics of the IGBT, the curve relationship between the collector-emitter voltage and the collector current at a certain temperature is used to obtain the theoretical value of the corresponding bridge arm current based on the collector-emitter voltage.

[0081] In step S2, the submodule controller collects the theoretical values ​​of the voltage between the collector and emitter of the IGBT transistors and the bridge arm current sent by all IGBT drivers in the submodule, and sends them to the converter valve control system.

[0082] Step S3: The converter valve control system determines the IGBT that actually carries the current in the current control cycle of each bridge arm based on the voltage between the collector and emitter of the IGBT and the submodule control command issued in the previous control cycle, and also determines the current direction of the bridge arm.

[0083] After the IGBT driver calculates the theoretical value of the bridge arm current, it uploads it along with the collected collector-emitter voltage value to the submodule controller (SMC). The SMC collects the information uploaded by the upper and lower IGBT drivers of the submodule and uploads it to the converter valve control system (VBC). The VBC collects the collector voltages of the upper and lower IGBTs of all submodules and, in conjunction with the submodule control commands issued in the previous control cycle, determines the IGBT in each bridge arm that actually carries the bridge arm current in the current control cycle.

[0084] In actual operation, only the designated submodule will be turned on in each control cycle, and the location of the submodule turned on is different in each control cycle. In addition, depending on the direction of the bridge arm current, there are four paths for the bridge arm current to flow through the upper IGBT of the submodule, the lower IGBT, the upper anti-parallel diode, and the lower anti-parallel diode. Therefore, in each control cycle, it is necessary to find the IGBT that actually flows through the bridge arm current as the basis for the acquisition and judgment of the bridge arm current.

[0085] Specifically, the VBC process for determining the actual IGBT current flowing through the bridge arm is as follows: Assuming the direction of the current flowing into the converter valve via the bridge arm reactor is the positive direction of the bridge arm current, the submodule with the lower IGBT turned on is defined as disconnected, and the submodule with the upper IGBT turned on is defined as connected. Therefore, if the submodule control command in the previous control cycle was disconnected, and the voltage between the collector and emitter of the lower IGBT in the submodule is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, it is determined that the upper IGBT of the submodule currently connected in the current control cycle is actually flowing through the bridge arm current, and the direction of the bridge arm current in this control cycle is determined to be negative; if the submodule control command in the previous control cycle was connected, and the voltage between the collector and emitter of the upper IGBT in the submodule is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, it is determined that the lower IGBT of the submodule currently disconnected in the current control cycle is actually flowing through the bridge arm current, and the direction of the bridge arm current in this control cycle is determined to be positive.

[0086] Step S4: The converter valve control system calculates the theoretical value of the arm current corresponding to all IGBT transistors that pass through the arm current in this control cycle, and takes the average value as the arm current amplitude for this cycle.

[0087] The method for obtaining the arm current of the flexible DC converter valve provided in this embodiment can accurately, quickly and reliably obtain the arm current of the flexible DC converter valve. It effectively solves the problems of relying solely on the arm current acquisition by the arm CT and the inability to identify abnormal faults in the CT device, which leads to converter valve failure. At the same time, the sampling delay of the arm current obtained by this method is much lower than that of the CT device. Furthermore, it allows the flexible DC transmission system to be configured with higher overcurrent protection settings, effectively improving the system's operating margin and fault ride-through capability.

[0088] In one specific embodiment, to ensure the accuracy of the obtained bridge arm current, the following step is included after step S3:

[0089] Step S5: The converter valve control system calculates the correction coefficient of the bridge arm current based on the submodule capacitor voltage.

[0090] Specifically, the calculation process is as follows:

[0091] In step S51, the converter valve control system collects the change in the submodule capacitor voltage according to a preset period, and calculates the effective value of the bridge arm current based on the change in the submodule capacitor voltage. In actual applications, the preset period can be adjusted according to the actual situation, for example, it can be 20ms.

[0092]

[0093] Where i is the instantaneous value of the charging current of any submodule, C is the submodule capacitance, T is the control step size (control cycle) of the control system, and ΔU is the change in the submodule capacitor voltage within the control step size.

[0094] Since the charging and discharging current of the submodule capacitor is approximately equal to the bridge arm current, the instantaneous value of the bridge arm current can be obtained from the change in the submodule capacitor voltage. The calculation formula is as follows:

[0095]

[0096] in, This represents the instantaneous value of the bridge arm current. This represents the instantaneous value of the charging current of the nth submodule detected within 20ms, where N is the total number of submodules engaged in a single control cycle of any bridge arm.

[0097] It should be noted that since the sub-modules switched on and off for each control step are different, VBC needs to first determine which sub-modules are switched on before calculating the instantaneous value of the arm current, and then calculate the instantaneous value of the arm current for each of these switched sub-modules in accordance with the above method.

[0098] After obtaining the instantaneous values ​​of the bridge arm currents, sum and average the obtained instantaneous values ​​to obtain the effective value of the bridge arm currents within 20ms. The specific calculation formula is as follows:

[0099]

[0100] Where T is 20ms.

[0101] In summary, the converter valve control system calculates the instantaneous value of the bridge arm current based on the integral relationship between the bridge arm current and the capacitance value of the submodule, combined with the change in the voltage of the submodule capacitor, and then calculates the effective value of the bridge arm current based on the instantaneous value.

[0102] In step S52, the converter valve control system receives the IGBT collector current collected by the IGBT driver within a preset period and obtains the calibration value of the bridge arm current.

[0103] In step S53, the converter valve control system divides the effective value of the arm current by the calibrated value of the arm current to obtain the correction coefficient. Then, step S5 is executed.

[0104] Step S6: The IGBT driver corrects the current amplitude of the bridge arm current according to the correction factor.

[0105] After obtaining the correction factor, the VBC sends the factor to each IGBT driver. The IGBT driver then calibrates the junction temperature data calculated in real time based on the correction factor. The specific process is as follows:

[0106] Step S61: The IGBT driver collects the case temperature of each IGBT in real time and calculates the junction temperature of the corresponding IGBT based on the case temperature.

[0107] In step S62, the IGBT driver multiplies the junction temperature by the correction factor to obtain the corrected junction temperature.

[0108] In step S63, the IGBT driver determines the relationship curve between the voltage between the collector and emitter of the IGBT transistor and the bridge arm current based on the corrected junction temperature, and obtains the current amplitude of the corrected bridge arm current according to the relationship curve.

[0109] In short, the IGBT driver acquires the IGBT collector-emitter voltage and IGBT case temperature in real time. It calculates the junction temperature of the device in real time using the IGBT case temperature, multiplies the junction temperature by the correction factor issued by VBC to obtain the corrected junction temperature, and uses the Vce and Ic relationship curve at this junction temperature to obtain the real-time calculated current value by looking up a table. That is, it obtains the corrected bridge arm current amplitude.

[0110] By using the above method, the bridge arm current obtained from the submodule voltage fluctuation is periodically corrected to improve the accuracy of the collector current calculation, thereby improving the accuracy of the obtained bridge arm current.

[0111] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A system for acquiring the arm current of a flexible DC converter valve, characterized in that, include: Converter valve control system, submodule controller and IGBT driver; The IGBT driver is connected one-to-one with the control terminals of each IGBT tube in the sub-module of the flexible DC converter valve. The IGBT driver is communicatively connected to the submodule controller, and the submodule controller is communicatively connected to the converter valve control system; The IGBT driver is used to acquire the voltage between the collector and emitter of the IGBT connected to it in real time, and calculate the theoretical value of the bridge arm current based on the voltage. The submodule controller is used to collect the theoretical values ​​of the voltage between the collector and emitter of the IGBT transistor and the bridge arm current sent by all IGBT drivers in this submodule, and send them to the converter valve control system in a unified manner. The converter valve control system is used to determine the IGBT that actually carries the bridge arm current in the current control cycle and the direction of the bridge arm current in each bridge arm based on the voltage between the collector and emitter of the received IGBT and the submodule control command issued in the previous control cycle. It also calculates the theoretical value of the bridge arm current corresponding to all IGBTs that carry the bridge arm current in the current control cycle, takes the average value as the bridge arm current amplitude of the current cycle.

2. The system for acquiring the bridge arm current of the flexible DC converter valve according to claim 1, characterized in that, The converter valve control system is also used to calculate the correction coefficient of the bridge arm current and send the correction coefficient to the IGBT driver; The IGBT driver is also used to correct the current amplitude of the bridge arm current according to the correction factor.

3. The system for acquiring the bridge arm current of the flexible DC converter valve according to claim 1, characterized in that, The IGBT driver includes: an analog signal acquisition unit, a data storage unit, a communication unit, a programmable logic unit, and a digital signal processor; wherein: The analog signal acquisition unit is used to acquire the voltage and case temperature data between the collector and emitter of the corresponding IGBT, and send them to the digital signal processor and programmable logic unit. The digital signal processor is used to calculate the theoretical value of the flexible DC converter valve arm current based on the data sent by the analog acquisition unit and the collector-emitter voltage and collector current relationship curve data of different types of IGBT devices at various junction temperatures stored in the data storage unit, and send it to the programmable logic control unit and the data storage unit. The data storage unit is used to store the data sent by the digital signal processor, as well as the collector-emitter voltage and collector current relationship curves of different types of IGBT devices at various junction temperatures. The programmable logic unit is used to receive data sent by the analog signal acquisition unit and the digital signal processor, and generate corresponding control commands to send to the corresponding IGBT and the digital signal processor to control the corresponding IGBT and the IGBT driver itself. The communication unit is used to enable information interaction between the IGBT driver and the upper-level control unit.

4. The system for obtaining the bridge arm current of the flexible DC converter valve according to claim 3, characterized in that, The IGBT driver further includes: a fault monitoring unit, a power amplification unit, and an isolated power supply unit, wherein: The fault monitoring unit is communicatively connected to the programmable logic unit and is used to monitor the fault status information of the IGBT driver and the IGBT tube connected thereto, and send the fault status information to the programmable logic unit, so that the programmable logic unit can protect the IGBT driver itself and the corresponding IGBT tube. The power amplifier unit is used to amplify the control command output capability of the programmable logic unit and then output it to the corresponding IGBT tube; The isolated power supply unit is used to provide power supply voltage to the IGBT driver.

5. A method for obtaining the arm current of a flexible DC converter valve, characterized in that, The method for obtaining the bridge arm current of the flexible DC converter valve as described in any one of claims 1-4 includes: The IGBT driver acquires the voltage between the collector and emitter of the upper and lower IGBT transistors in each submodule of the flexible DC converter valve in real time, and calculates the theoretical value of the bridge arm current based on the voltage. The submodule controller collects the theoretical values ​​of the voltage between the collector and emitter of the IGBT transistors and the bridge arm current sent by all IGBT drivers in this submodule, and sends them to the converter valve control system. The converter valve control system determines the IGBT that actually carries the current in the current control cycle of each bridge arm, and determines the direction of the current in the bridge arm, based on the voltage between the collector and emitter of the IGBT and the submodule control command issued in the previous control cycle. The converter valve control system calculates the theoretical value of the arm current corresponding to all IGBT transistors that pass through the arm current in this control cycle, and takes the average value as the arm current amplitude for this cycle.

6. The method for obtaining the bridge arm current of the flexible DC converter valve according to claim 5, characterized in that, After calculating the bridge arm current amplitude for this cycle, the following steps are also included: The converter valve control system calculates the correction coefficient for the bridge arm current based on the submodule capacitor voltage; The IGBT driver corrects the current amplitude of the bridge arm current according to the correction factor.

7. The method for obtaining the bridge arm current of the flexible DC converter valve according to claim 6, characterized in that, The converter valve control system calculates the correction coefficient for the bridge arm current based on the submodule capacitor voltage, including: The converter valve control system collects the change in the voltage of the sub-module capacitor according to a preset period, and calculates the effective value of the bridge arm current based on the change in the voltage of the sub-module capacitor. The converter valve control system receives the IGBT collector current collected by the IGBT driver within a preset period to obtain the calibration value of the bridge arm current. The converter valve control system divides the effective value of the arm current by the calibrated value of the arm current to obtain the correction coefficient.

8. The method for obtaining the bridge arm current of the flexible DC converter valve according to claim 7, characterized in that, The calculation of the effective value of the bridge arm current based on the change in the capacitor voltage of the submodule includes: The converter valve control system calculates the instantaneous value of the bridge arm current based on the integral relationship between the bridge arm current and the capacitance value of the submodule, combined with the change in the voltage of the submodule capacitor, and calculates the effective value of the bridge arm current based on the instantaneous value. The formula for calculating the instantaneous value is: in, This represents the instantaneous value of the charging current of the nth submodule, where N is the total number of submodules engaged in a single control cycle of any bridge arm.

9. The method for obtaining the bridge arm current of the flexible DC converter valve according to claim 8, characterized in that, The formula for calculating the effective value of the bridge arm current based on the instantaneous value is as follows: in, is the effective value of the bridge arm current, and T is the preset control period.

10. The method for obtaining the bridge arm current of the flexible DC converter valve according to claim 6, characterized in that, The IGBT driver corrects the current amplitude of the bridge arm current according to the correction factor, including: The IGBT driver collects the case temperature of each IGBT in real time and calculates the junction temperature of the corresponding IGBT based on the case temperature. The IGBT driver multiplies the junction temperature by the correction factor to obtain the corrected junction temperature; Based on the corrected junction temperature, the IGBT driver determines the relationship curve between the voltage between the collector and emitter of the IGBT transistor and the bridge arm current, and obtains the current amplitude of the corrected bridge arm current according to the relationship curve.

11. The method for obtaining the bridge arm current of a flexible DC converter valve according to any one of claims 5-10, characterized in that, The converter valve control system, based on the voltage and the submodule control commands issued in the previous control cycle, determines the IGBTs in each bridge arm that actually carry the bridge arm current during the current control cycle, including: If the control command for the submodule in the previous control cycle was to cut off, and the voltage between the collector and emitter of the lower IGBT of the submodule is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, then it is determined that the upper IGBT of the submodule in the current control cycle is actually carrying the bridge arm current, and the direction of the bridge arm current in this control cycle is determined to be negative. If the submodule control command in the previous control cycle was "engaged", and the voltage between the collector and emitter of the upper IGBT of the submodule is negative and equal to the forward voltage drop of the diode connected in parallel with the IGBT, then it is determined that the lower IGBT of the submodule that is in the "disabled" state in the current control cycle is actually carrying bridge arm current, and the direction of the bridge arm current in this control cycle is determined to be positive.

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