A reverse recovery period protection device based on a high voltage direct current transmission system

Abstract

This invention provides a reverse recovery period protection device for high-voltage direct current (HVDC) transmission systems, used for the protection of converter valve thyristors in HVDC transmission systems. It acquires the operating parameters of each switching transistor in the optical pulse module through a compensation module to determine the aging degree of each switching transistor based on the operating parameters, and then obtains a compensation value for each switching transistor based on the aging degree. A compensation current is generated based on the compensation value of each switching transistor, and when the optical pulse module enters the next protection window, the compensation current is injected into the compensation terminal of each switching transistor. This invention can reduce the impact of analog circuit hardware aging on the protection response speed, ensure the timeliness of the protection, and thus guarantee the long-term reliability of the protection.

Description

Technical Field

[0001] This invention relates to the field of power technology, and in particular to a reverse recovery period protection device based on a high-voltage direct current transmission system. Background Technology

[0002] Converter valves are core equipment in high-voltage direct current (HVDC) transmission systems, undertaking the key function of converting AC to DC power. They are widely used in ultra-high voltage projects, new energy grid connection, and inter-regional power grid interconnection.

[0003] When a thyristor in a converter valve ring switches from on to off, there is a reverse recovery period. During the reverse recovery period, a positive voltage spike will appear. The high slope of the positive voltage spike will cause the thyristor to break down. Therefore, in the prior art, a reverse recovery period protection unit (RPU) is set up to monitor the rate of rise of the positive voltage (du / dt) across the thyristor in real time. When the threshold is exceeded (usually 100V / μs for a single thyristor, and the threshold is added together when multiple thyristors are connected in series), a trigger pulse is immediately output to turn the thyristor back on, eliminate the positive voltage, and avoid damage to the thyristor.

[0004] Traditional RPUs use analog circuits for fast response, but the components in analog circuits are significantly affected by aging, causing the actual trigger threshold to deviate, resulting in insufficient long-term reliability of the protection. Therefore, in some technical practices, digital circuits are chosen. However, digital circuits require converting analog signals to digital signals, and analog-to-digital conversion and digital processing introduce new delays, resulting in slower response. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a reverse recovery period protection device based on a high voltage direct current transmission system, so as to solve the problems that the analog circuit of the traditional RPU is significantly affected by aging, resulting in insufficient long-term reliability of protection, while the digital circuit will cause delays in analog-to-digital conversion and data processing, and slow response.

[0006] This invention provides a reverse recovery period protection device for a high-voltage direct current (HVDC) transmission system, used for the protection of the thyristors in the converter valve of the HVDC transmission system. The reverse recovery period protection device includes an energy harvesting module, a sampling module, an optical pulse module, and a compensation module connected in parallel between the positive and negative busbars.

[0007] The energy harvesting module is used to draw power from the power grid to supply power to other modules;

[0008] The sampling module is used to sample the rate of rise of the forward voltage of the thyristor in the converter valve during the reverse recovery period;

[0009] The optical pulse module is used to output an optical pulse when entering the protection window period and when the positive voltage rise rate reaches the protection threshold, so as to isolate the conduction of each thyristor in the converter valve.

[0010] The compensation module is used for:

[0011] The operating parameters of each switching transistor in the optical pulse module are collected to obtain the aging degree of each switching transistor based on the operating parameters, and the compensation value of each switching transistor is obtained based on the aging degree of each switching transistor.

[0012] A compensation current is generated based on the compensation value of each of the switching transistors, and when the optical pulse module enters the protection window period again, the compensation current is injected into the compensation terminal of each of the switching transistors to counteract the effects of aging.

[0013] Optionally, the compensation module is further configured to:

[0014] The input and output voltages of the target switching transistor are collected to obtain the conduction state of the target switching transistor.

[0015] The conduction delay of the target switching transistor is obtained based on the timestamp of the enable signal and the conduction state toggle time of the target switching transistor.

[0016] The aging degree of the target switching transistor is obtained by comparing the conduction delay with a preset standard delay.

[0017] Optionally, the compensation module is further configured to: obtain an aging trend based on historical data of the aging degree of the target switching transistor, and obtain a compensation current of the target switching transistor in the next protection window period based on the aging trend.

[0018] Optionally, the compensation module is further configured to: obtain a correction coefficient based on the difference between the compensated turn-on delay of the target switching transistor and a preset standard delay, and correct the compensation current of the target switching transistor in the next protection window period based on the correction coefficient.

[0019] Optionally, the sampling module includes a sampling resistor, the optical pulse module further includes a PNP transistor, and the compensation module is further configured to: acquire the voltage drop of the sampling resistor to obtain the actual peak voltage of the sampling resistor, and obtain a second compensation current based on the difference between the actual peak voltage and a preset expected peak voltage, so as to compensate the sampling resistor based on the second compensation current, so that the actual peak voltage in the next protection window period is consistent with the expected peak voltage.

[0020] Optionally, the compensation module is further configured to: obtain the changing trend of the second compensation current based on the historical data of the second compensation current, so as to obtain the predicted value of the second compensation current in the next protection window period, and compensate the sampling resistor according to the predicted value of the second compensation current in the next protection window period.

[0021] Optionally, the optical pulse module includes a first control loop, a second control loop, and a third control loop respectively connected between the positive bus and the negative bus, wherein,

[0022] A first switching transistor is connected in series in the first control loop. The first switching transistor is used to turn on the first control loop when entering the protection window period.

[0023] A second switching transistor is connected in series in the second control loop, and the control terminal of the second switching transistor is connected to the first voltage divider node in the first control loop;

[0024] The third control loop contains a light pulse diode and a third switching transistor connected in series, and the control terminal of the third switching transistor is connected to the second voltage divider node in the second control loop.

[0025] Optionally, the sampling node for obtaining the conduction state of the first switching transistor and the third switching transistor includes the input terminal of the first switching transistor and the input terminal of the third switching transistor.

[0026] The reverse recovery period protection device based on the high-voltage direct current (HVDC) transmission system provided by this invention is used to protect the thyristors of the converter valve in the HVDC transmission system. It collects the operating parameters of each switching transistor in the optical pulse module through a compensation module to obtain the aging degree of each switching transistor based on the operating parameters, and obtains the compensation value of each switching transistor based on the aging degree. A compensation current is generated based on the compensation value of each switching transistor, and when the optical pulse module enters the protection window period again, the compensation current is injected into the compensation terminal of each switching transistor accordingly. This reduces the impact of hardware aging on the response speed of the protection, ensures the timeliness of the protection, and thus ensures the long-term reliability of the protection. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the installation of the reverse recovery period protection device in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the module structure of the reverse recovery period protection device in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the optical pulse module of the reverse recovery period protection device in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the energy harvesting module of the reverse recovery period protection device in an embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the sampling module of the reverse recovery period protection device in an embodiment of the present invention.

[0032] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0034] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] like Figure 1 As shown, the reverse recovery period protection device 100 is connected in series with the equalizing capacitor C0 across the two ends of the valve section. The valve section is connected in series with an inductor and multiple thyristors. In response to the rate of rise of the forward voltage at the positive terminal of the thyristor string, a displacement current is generated on the equalizing capacitor C0. The larger the rate of rise of the forward voltage, the larger the displacement current. The reverse recovery period protection device 100 determines whether the rate of rise of the forward voltage exceeds a threshold based on the magnitude of the displacement current. If the threshold is exceeded, the protection is triggered, and an optical pulse is output to isolate and control the thyristors in the valve section to conduct for a period of time to eliminate the forward voltage spike.

[0037] like Figure 2As shown, in this embodiment, the reverse recovery period protection device 100 includes an energy harvesting module 110, a sampling module 120, an optical pulse module 130, and a compensation module 140 disposed between its positive bus A and negative bus K. The energy harvesting module is used to draw power from the power grid to supply power to other modules; the sampling module 120 is used to sample the forward voltage rise rate of the thyristor in the converter valve during the reverse recovery period; the optical pulse module 130 is used to output an optical pulse when the forward voltage rise rate reaches the protection threshold to isolate and control the conduction of each thyristor in the converter valve.

[0038] The compensation module 140 is used to collect the operating parameters of each switching transistor in the optical pulse module 130, so as to obtain the aging degree of each switching transistor according to the operating parameters, and obtain the compensation value of each switching transistor according to the aging degree of each switching transistor. Then, a compensation current is generated according to the compensation value of each switching transistor. When the optical pulse module enters the protection window period again, the compensation current is injected into the compensation terminal of each switching transistor to offset the aging effect, ensure the response speed of the optical pulse module 130, and ensure the protection effect.

[0039] To facilitate the acquisition of the aging degree of the switching transistor, in this embodiment, the compensation module 140 is further configured to: acquire the input voltage and output voltage of the target switching transistor to obtain the conduction state of the target switching transistor; obtain the conduction delay of the target switching transistor based on the timestamp of the enable signal of the target switching transistor and the conduction state toggling time; and obtain the aging degree of the target switching transistor based on the comparison between the conduction delay and a preset standard delay.

[0040] The conduction state transition time can be obtained from the state transition time of the input and output voltages of the target switching transistor, which can reduce the requirements for high-frequency sampling and reduce power consumption.

[0041] In this embodiment, as Figure 3 and Figure 5 As shown, the sampling module 120 converts the displacement current into voltage through the sampling resistor 121, forming a sampling voltage between the positive bus A and the negative bus K. The optical pulse module 130 responds to the sampling voltage and outputs an optical pulse when the sampling voltage reaches a preset threshold.

[0042] The optical pulse module 130 includes a first switching transistor Q1, a second switching transistor Q2, and a third switching transistor Q3, which are connected between the positive bus A and the negative bus K through a first control loop, a second control loop, and a third control loop, respectively. The control terminal of the second switching transistor Q2 is connected to the first voltage divider node in the first control loop. Optical pulse diodes (D4, D5) are connected in series in the third control loop. The control terminal of the third switching transistor Q3 is connected to the second voltage divider node in the second control loop, forming a control link from the first switching transistor Q1, the second switching transistor Q2, to the third switching transistor Q3.

[0043] When entering the protection window, the host computer controls the first switching transistor Q1 to turn on via optocoupler isolation, and the first control loop is turned on. The voltage across the fourth resistor R4 in the first control loop responds to the sampling voltage. When the sampling voltage is greater than the threshold, the voltage across the fourth resistor R4 simultaneously reaches the turn-on condition of the second switching transistor Q2 (PNP transistor). The second switching transistor Q2 turns on, the second control loop is turned on, and the voltage of the second voltage divider node of the second control loop is pulled up, driving the third switching transistor Q3 to turn on, and then turning on the third control loop, driving the photopulse diode in the third control loop to emit a photopulse.

[0044] To reduce sampling costs, in this embodiment, the sampling nodes for obtaining the conduction states of the first switching transistor Q1 and the third switching transistor Q3 include a first node P1 located at the input terminal of the first switching transistor Q1, a second node P2 located at the input terminal of the third switching transistor Q3, and a third node P3. The third node P3 is located on the negative bus K, and the low-voltage side sampling nodes of the first switching transistor Q1 and the third switching transistor Q3 share the third node P3.

[0045] Before the first switching transistor Q1 and the third switching transistor Q3 are turned on, the voltages of the first node P1 and the second node P2 are pulled up to the positive bus A through the first control loop and the third control loop. When they are turned on, the voltages of the first node P1 and the second node P2 drop. Simultaneously, the compensation module 140 also collects the voltage drop across the sampling resistor, corresponding to the voltage at the positive bus A. By reasonably allocating the voltage division ratio, before the voltages of the first node P1 and the second node P2 drop, the first voltage obtained from the voltage division of the sampling resistor 121 is less than the second and third voltages obtained from the voltage division of the first node P1 and the second node P2; after the voltages of the first node P1 and the second node P2 drop, the first voltage is greater than the second and third voltages. Therefore, the on-state switching detection of the first switching transistor Q1 and the third switching transistor Q3 can be achieved through a comparator, reducing the need for analog-to-digital conversion and lowering costs.

[0046] For PNP transistors, the collector is the output terminal, and the conduction state can be detected by detecting whether the collector voltage is pulled up.

[0047] In an optional embodiment, for the third switching transistor Q3, the output potential of the second switching transistor Q2 is flipped as the first control signal to determine that the gate of the third switching transistor Q3 has received a conduction drive. The input potential of the third switching transistor Q3 is pulled down as the second control signal to determine the conduction of the third switching transistor Q3. The first control signal is used as the start signal of the integrating capacitor, and the second control signal is used as the end signal of the integrating capacitor. The conduction delay of the third switching transistor Q3 is obtained through the integrated voltage of the integrating capacitor. The conduction delay time is converted into voltage, which avoids the need for direct time monitoring of the effective moment of the gate drive signal and the moment of conduction state flip, and eliminates the need for time monitoring with high time resolution.

[0048] The compensation current injection terminals include the control terminals of the first switching transistor Q1 and the third switching transistor Q3. In this embodiment, the first switching transistor Q1 and the third switching transistor Q3 are NMOS transistors, and the compensation current is injected into their gates. The second switching transistor Q2 is a PNP transistor, and its compensation current is injected into its base. For NMOS transistors, their turn-on delay can also be monitored using a ring oscillator. By connecting the gate and source of the NMOS transistor to a ring oscillator, the turn-on delay can be obtained by monitoring the oscillation frequency.

[0049] To improve the compensation effect, the compensation module 140 is also used to obtain the aging trend based on the historical data of the aging degree of the target switching transistor, and to obtain the compensation current of the target switching transistor in the next protection window period based on the aging trend.

[0050] To ensure the compensation effect, the compensation module is also used to: obtain a correction coefficient based on the difference between the compensated on-time delay of the target switching transistor and the preset standard delay, and correct the compensation current of the target switching transistor in the next protection window period based on the correction coefficient. When the on-time delay is greater than the standard delay, the correction coefficient is increased, and the compensation current is increased. The larger the difference, the larger the correction coefficient. The specific specifications are determined based on the specific hardware characteristics.

[0051] Since the reverse recovery period protection device 100 monitors displacement current, it converts the displacement current into a sampling voltage by sampling resistor 121 through sampling module 120. The optical pulse module 130 responds to this sampling voltage. When sampling resistor 121 ages, its resistance value typically increases. Under a small displacement current, the sampling voltage may reach the protection threshold, leading to false triggering of protection. If the aging resistance decreases, the protection may fail to function properly. To avoid false triggering or inadequate protection, in this embodiment, the compensation module is further configured to: collect the voltage drop across the sampling resistor to obtain the actual peak voltage of the sampling resistor, and obtain a second compensation current based on the difference between the actual peak voltage and a preset expected peak voltage. This second compensation current is used to compensate the sampling resistor so that the actual peak voltage in the next protection window period matches the expected peak voltage. When the actual peak voltage is greater than the expected peak voltage, the second compensation current is negative; when the actual peak voltage is less than the expected peak voltage, the second compensation current is positive.

[0052] The compensation module 140 is also used to: obtain the changing trend of the second compensation current based on historical data of the second compensation current, so as to obtain the predicted value of the second compensation current in the next protection window period, and to compensate the sampling resistor according to the predicted value of the second compensation current in the next protection window period. This ensures that compensation is provided in every protection window period, guaranteeing the compensation effect.

[0053] The main power-consuming module of the reverse recovery protection device 100 is the compensation module 140. To ensure the power supply for the compensation module 140, such as... Figure 4 As shown, the energy harvesting module 110 includes a first resistor R1 and a first diode D1 connected in series on the positive bus A. A third diode D3, a third resistor R3, a second diode D2, and a second resistor R2 are connected in series between the negative bus K and the anode of the first diode D1. During the positive half-cycle of the AC current in the valve section, the current is transmitted through the first diode D1 by the back-end sampling module 120. During the negative half-cycle, the current is transmitted through the third diode D3, the third resistor R3, the second diode D2, and the second resistor R2. An energy storage capacitor bank is connected in parallel on the third resistor R3. Power is harvested according to the current during the negative half-cycle to provide a 3.3V DC power supply.

[0054] The energy storage capacitor bank is also connected to transient voltage suppressor diodes (TVS) to regulate and protect the 3.3V power supply. The specific parameters of each component in the energy harvesting module 110 can be designed according to actual power supply requirements, and this application does not impose any special limitations on them.

[0055] Two transient voltage suppressor diodes (TVS) are connected in reverse series between the positive bus A and the negative bus K to provide overvoltage protection.

[0056] In this embodiment, the functions of the compensation module 140 include data acquisition, data processing, and compensation current generation. Data processing can be implemented by a microcontroller or a programmable logic controller, some data acquisition is implemented by an analog-to-digital converter, and the compensation current is provided by a digital-to-analog converter.

[0057] The reverse recovery period protection device based on the high voltage direct current transmission system provided by this invention is used to protect the thyristors of the converter valve in the high voltage direct current transmission system. By monitoring the aging degree of each switching transistor in the optical pulse module, the compensation current of each switching transistor is obtained. When the optical pulse module enters the protection window period again, the compensation current is injected into the compensation terminal of each switching transistor to offset the impact of the aging of the analog circuit hardware on the response speed of the protection, ensuring the timeliness of the protection, and thus ensuring the long-term reliability of the protection.

[0058] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0059] The embodiments described above are merely illustrative of several specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of protection of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A reverse recovery period protection device based on a high-voltage direct current (HVDC) transmission system, used for the protection of the thyristor in the converter valve of the HVDC transmission system, characterized in that, The reverse recovery period protection device is equipped with an energy harvesting module, a sampling module, an optical pulse module, and a compensation module connected in parallel between the positive and negative busbars. The energy harvesting module is used to draw power from the power grid to supply power to other modules; The sampling module is used to sample the rate of rise of the forward voltage of the thyristor in the converter valve during the reverse recovery period; The optical pulse module is used to output an optical pulse when entering the protection window period and when the positive voltage rise rate reaches the protection threshold, so as to isolate the conduction of each thyristor in the converter valve. The compensation module is used for: The operating parameters of each switching transistor in the optical pulse module are collected to obtain the aging degree of each switching transistor based on the operating parameters, and the compensation value of each switching transistor is obtained based on the aging degree of each switching transistor. A compensation current is generated based on the compensation value of each of the switching transistors, and when the optical pulse module enters the protection window period for the next time, the compensation current is injected into the compensation terminal of each of the switching transistors to counteract the aging effect. The compensation module is also used for: The input and output voltages of the target switching transistor are collected to obtain the conduction state of the target switching transistor. The conduction delay of the target switching transistor is obtained based on the timestamp of the enable signal and the conduction state toggle time of the target switching transistor. The aging degree of the target switching transistor is obtained by comparing the conduction delay with a preset standard delay; The aging trend is obtained based on historical data of the aging degree of the target switching transistor, and the compensation current of the target switching transistor in the next protection window period is obtained based on the aging trend. The sampling module includes a sampling resistor, the optical pulse module includes a PNP transistor, and the compensation module is further used to: collect the voltage drop of the sampling resistor to obtain the actual peak voltage of the sampling resistor, and obtain a second compensation current based on the difference between the actual peak voltage and the preset expected peak voltage, so as to compensate the sampling resistor according to the second compensation current, so that the actual peak voltage in the next protection window period is consistent with the expected peak voltage. The optical pulse module includes a first control circuit, a second control circuit, and a third control circuit connected between the positive bus and the negative bus, respectively. A first switching transistor is connected in series in the first control circuit. The first switching transistor is used to turn on the first control circuit when entering the protection window period. A second switching transistor is connected in series in the second control circuit. The control terminal of the second switching transistor is connected to the first voltage divider node in the first control circuit. An optical pulse diode and a third switching transistor are connected in series in the third control circuit. The control terminal of the third switching transistor is connected to the second voltage divider node in the second control circuit.

2. The reverse recovery period protection device based on a high-voltage direct current transmission system according to claim 1, characterized in that, The compensation module is further configured to: obtain a correction coefficient based on the difference between the compensated on-time delay of the target switching transistor and a preset standard delay, and correct the compensation current of the target switching transistor in the next protection window period based on the correction coefficient.

3. The reverse recovery period protection device based on a high-voltage direct current transmission system according to claim 1, characterized in that, The compensation module is further configured to: obtain the changing trend of the second compensation current based on the historical data of the second compensation current, so as to obtain the predicted value of the second compensation current in the next protection window period, and compensate the sampling resistor based on the predicted value of the second compensation current in the next protection window period.

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