A commutation failure rapid prediction method and device for a hybrid commutation converter

Abstract

The application provides a commutation failure fast prediction method and device for a hybrid commutation converter, which comprises the following steps: whenever a bridge arm in the hybrid commutation converter is turned on according to a trigger angle instruction and starts to commutate, taking the turning-on time as a starting point, combining a set bridge arm delay turn-off time, the commutation is divided into three stages, the first stage is a natural commutation stage of the hybrid commutation converter, the time experienced in this stage is the delay turn-off time of the bridge arm, the second and third stages are forced commutation stages of the hybrid commutation converter, the second stage ends and the third stage starts when the phase of the commutation voltage starts to exceed 180°; the current value in the turned-off bridge arm at the end of each stage is predicted respectively, and whether the hybrid commutation converter will have a commutation failure is determined according to the prediction values one by one. The application can quickly obtain the result of whether the hybrid commutation converter has a commutation failure after the bridge arm is triggered, which helps the DC power transmission system to identify the risk in advance.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current transmission technology, and in particular to a method for rapid prediction of commutation failure in hybrid commutation converters. Background Technology

[0002] High-voltage direct current (HVDC) transmission systems employing grid-commutated converters (LCC-HVDC) have been widely and extensively used in inter-regional power transmission due to their advantages such as large transmission capacity, rapid and controllable power output, and low cost. However, because LCC-HVDCs use semi-controlled thyristors as commutation elements, commutation failure is highly likely to occur if the receiving-end AC system experiences a fault. In recent years, with the rapid development of fully controlled power electronic devices, some scholars have proposed using fully controlled power electronic devices to modify converters and force current cut-off to complete commutation in case of commutation anomalies, thus combining natural and forced commutation. Therefore, the State Grid Corporation of China has proposed a controllable commutation converter topology based on a hybrid parallel connection of thyristors and IGBTs. In this topology, the bridge arm is divided into two sub-branches: a main branch consisting of thyristors and IGBTs connected in series to carry large currents; and an auxiliary branch consisting of IGBTs connected in parallel with the main branch to transfer current and cut off the commutation current in case of commutation anomalies. Considering that IGCTs are fully controlled devices developed based on thyristors, and possess high surge current withstand capability and low losses, Tsinghua University proposed a hybrid commutation converter (HCC) that proportionally replaces the thyristors in the bridge arms with RB-IGCTs. The advantages of the hybrid commutation converter are mainly reflected in two aspects: First, the control of the hybrid commutation converter is simpler, unlike controllable commutation converters which require current transfer before forced commutation, thus reducing reliability; second, the hybrid commutation converter uses RB-IGCTs to replace the original thyristors in the bridge arms proportionally, resulting in lower costs and lower long-term operating losses, thus demonstrating strong economic efficiency.

[0003] However, the commutation failure resilience of a hybrid commutation converter is directly proportional to the replacement ratio of RB-IGCTs; the more RB-IGCTs replaced, the stronger the commutation failure resilience. Taking a single-phase ground fault in AC as an example, relevant studies show that the critical inductance for commutation failure in a traditional LCC is 0.86–1.23H. When the RB-IGCT configuration ratio is 30%, this critical inductance drops to 0.3H; when the ratio reaches 50%, it further drops to 0.16H. With further improvements in the configuration of RB-IGCTs and surge arresters, as long as the protection voltage generated by the surge arrester during active shutdown is not lower than the peak AC line voltage, the hybrid commutation converter can successfully complete commutation under any severity of AC fault. Therefore, within the allowable design range, the hybrid commutation converter can force commutation by actively shutting off the current flowing through the fully controlled device, thereby preventing commutation failure.

[0004] In practical applications, if the RB-IGCT replaces thyristors only at a small ratio for economic reasons, then if an AC system fault occurs exceeding the design target range corresponding to that replacement ratio, the hybrid commutation converter faces the risk of commutation failure. Alternatively, in extreme cases, long-term operation may lead to a decline in the performance of the RB-IGCT and surge arresters, thereby affecting the hybrid commutation converter's ability to withstand commutation failure, thus also posing a risk of commutation failure. However, since the commutation failure of a hybrid commutation converter is not affected by the turn-off angle, its commutation failure mechanism is completely different from that of an LCC. Therefore, traditional methods for rapid prediction and identification of commutation failure used in LCCs will all fail for hybrid commutation converters. Currently, there is a lack of rapid prediction and identification methods for commutation failure specifically for hybrid commutation converters and their characteristics, a problem that urgently needs to be solved. Summary of the Invention

[0005] To address the technical problem that traditional LCC commutation failure prediction and identification methods are not applicable to hybrid commutation converters, this invention provides a method and apparatus for rapid prediction of commutation failure in hybrid commutation converters. This method can quickly obtain the result of whether the hybrid commutation converter has failed after the bridge arm is triggered, which helps the DC transmission system to identify risks in advance, take countermeasures, and ensure the stable and reliable operation of the system.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical method: a method for rapid prediction of commutation failure in a hybrid commutation converter. Whenever a bridge arm in the hybrid commutation converter is turned on and begins commutation according to the trigger angle command, the commutation is divided into three stages, starting from the turn-on time and combined with the set bridge arm delay turn-off time. The first stage is the natural commutation stage of the hybrid commutation converter, and the time experienced in this stage is the bridge arm delay turn-off time. The second and third stages are the forced commutation stages of the hybrid commutation converter. When the commutation voltage phase begins to exceed 180°, the second stage ends and the third stage begins. The current value in the bridge arm that is turned off at the end of each stage is predicted, and the hybrid commutation converter is determined successively based on the predicted values ​​to determine whether commutation failure will occur.

[0007] Furthermore, at the end of the first phase, the current value in the switched-off arm is predicted using the following formula:

[0008] (1)

[0009] In the formula, This is the predicted value of the current in the bridge arm that was turned off at the end of the first phase; The initial value of the current in the switched-off arm; This refers to the commutation voltage in the commutation circuit. Angular frequency, Commutation time; The equivalent inductance of the commutation circuit; The trigger angle; The angle corresponding to the delayed turn-off time of the bridge arm;

[0010] like If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the result is greater than 0, then proceed to the second stage of prediction and judgment.

[0011] Furthermore, at the end of the second phase, the current value in the switched-off arm is predicted using the following formula:

[0012] (2)

[0013] In the formula, The predicted value of the current in the shut-off arm at the end of the second phase; This is the protection voltage of the surge arrester;

[0014] like If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the value is greater than 0, then proceed to the third stage of prediction and judgment.

[0015] Furthermore, at the end of the third stage, the current value in the switched-off arm is predicted using the following formula:

[0016] (3)

[0017] (4)

[0018] In the formula, The predicted value of the current in the shut-off arm at the end of the third stage; This is from the perspective of the third stage.

[0019] like If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the value is greater than 0, it is determined that the hybrid commutation converter will fail to commutate.

[0020] In another aspect of the present invention, a device for rapid prediction of commutation failure in a hybrid commutation converter includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the aforementioned method for rapid prediction of commutation failure in a hybrid commutation converter.

[0021] In another aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the aforementioned method for rapid prediction of commutation failure in a hybrid commutation converter.

[0022] As another aspect of the present invention, a computer program product includes a computer program that, when executed by a processor, implements the aforementioned method for rapid prediction of commutation failure in a hybrid commutation converter.

[0023] This invention provides a method and apparatus for rapid prediction of commutation failure in hybrid commutation converters. When a fault is detected in the AC grid on the inverter side of a DC transmission system, the method proposed in this invention can predict and identify whether commutation failure has occurred. Specifically, whenever an arm of the hybrid commutation converter is turned on and begins commutation according to the trigger angle command, the current value in the switched-off arm is predicted in three stages, starting from that moment, depending on the different conditions of the commutation process. The prediction results at each stage are then used to determine whether commutation failure is about to occur in the hybrid commutation converter. This method for rapid prediction of commutation failure in hybrid commutation converters, combined with the working principle of the hybrid commutation converter, allows for rapid determination of commutation failure by predicting the current in the switched-off arm after the arm is triggered. This helps the DC transmission system identify risks in advance, take countermeasures, and ensure the stable and reliable operation of the system. Attached Figure Description

[0024] Figure 1 This is a structural diagram of the high-voltage direct current transmission system (HCC-HVDC) employing a hybrid commutation converter involved in this invention;

[0025] Figure 2 This is an equivalent circuit diagram of the commutation process of the hybrid commutator in this invention;

[0026] Figure 3 This is a flowchart of the method for rapid prediction of commutation failure in a hybrid commutation converter as described in this invention.

[0027] Figure 4 This is a current waveform diagram of the bridge arm Y5 during commutation under a 0.15H fault in the simulation experiment of this invention;

[0028] Figure 5 This is the simulation experiment of the present invention after natural commutation. The actual value and Comparison chart;

[0029] Figure 6 This is the actual value of the total commutation time in the simulation experiment of this invention. Compared with the predicted value Comparison chart;

[0030] Figure 7 This is the simulation experiment of the present invention under a 0.15H fault condition. and Comparison chart;

[0031] Figure 8 This is a current waveform diagram of bridge arm Y5 during commutation under a 0.08H fault in the simulation experiment of this invention;

[0032] Figure 9 This is the simulation experiment of the present invention under a 0.08H fault condition. and Comparison chart;

[0033] Figure 10 This is the simulation experiment of the present invention under a 0.08H fault condition. and The comparison chart. Detailed Implementation

[0034] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0035] It is worth noting that the topology of the hybrid commutator involved in this invention is described in [reference needed]. Figure 1 In order to predict in advance whether there are any risks during commutation of this type of hybrid commutation converter, the present invention conducts an in-depth study on the working principle of the hybrid commutation converter as follows:

[0036] First, Kirchhoff's voltage equations are written for the commutation circuit of the hybrid commutator, resulting in:

[0037] (5)

[0038] in, The current in the switched-off bridge arm; This represents the current currently flowing in the bridge arm; Commutation voltage, It is angular frequency. Commutation time; This is the equivalent inductance of the commutation circuit.

[0039] like Figure 2 As shown, the DC current during commutation is... ,comprehensive , And equation (5), integrating both sides of the equation, we get:

[0040] (6)

[0041] in, It corresponds to the angle that has been partially completed during the commutation process; and They are and place value, The trigger angle.

[0042] Let equation (6) be Let it represent the actual commutation area that the commutation voltage can provide. If the commutation process can be completed during the natural commutation phase, then... Then the right side of equation (6) is:

[0043] (7)

[0044] Therefore, equation (7) is defined as the commutation area required to complete the commutation. ,definition For a hybrid commutator, the fixed angle from the start of commutation to the execution of forced commutation corresponds to the phase angle. When At this time, forced commutation is not necessary; commutation can be completed on its own. However, when... When forced commutation is required, the commutation area provided by the forced commutation process must be utilized. for:

[0045] (8)

[0046] According to equation (8), when entering forced commutation... The larger the value, the more difficult it is to complete the commutation. And only when... The value must be reduced to 0 before the commutation process of the next sequence begins in order to complete forced commutation and avoid commutation failure.

[0047] As can be seen from the above analysis, after triggering, Make predictions based on When the current drops to 0, a rapid prediction and identification of commutation failure can be made. To this end, this invention proposes to predict the current value in the turned-off bridge arm in three stages, starting from the turn-on moment and combining the set bridge arm delay turn-off time, when the bridge arm in the hybrid commutation converter is turned on according to the trigger angle command and starts commutation. Based on the prediction result, it is determined whether the hybrid commutation converter will experience commutation failure.

[0048] The first stage of prediction is performed, which is the natural commutation stage of the hybrid commutator. The time elapsed in this stage is the delayed turn-off time of the bridge arm, corresponding to the angle of... . The rate of change during this phase is: Substitute the relevant data and use equation (1) to... Predict the current value after the first stage ends;

[0049] (1)

[0050] In the formula, This is the predicted value of the current in the bridge arm that was turned off at the end of the first phase; This is the initial value of the current in the switched-off bridge arm.

[0051] At this time, if If the value is less than or equal to 0, it indicates that the commutation process can be completed through only the first-stage bridge arm, and it can be directly determined that the hybrid commutation converter will not experience commutation failure; if If the result is greater than 0, then proceed to the second stage of prediction and judgment.

[0052] In the second stage, the hybrid commutation converter enters the forced commutation stage. In this stage... The rate of change is: ,in, This is the protection voltage of the surge arrester. During this stage, and All are positive values, working together to promote The decline. But It will continue to decline, therefore the end point of this stage is... The zero-crossing point. Substituting the relevant data, using equation (2) to... Predict the current value after the second stage ends:

[0053] (2)

[0054] In the formula, , For the prediction in the second phase The decrease value, The predicted value of the current in the switched-off arm at the end of the second phase.

[0055] At this time, if If the value is less than or equal to 0, it indicates that the commutation process can be completed through the second-stage bridge arm, and it can be directly determined that the hybrid commutation converter will not experience commutation failure; if If the value is greater than 0, then proceed to the third stage of prediction and judgment.

[0056] The third stage is also a forced commutation stage, but after entering the third stage, Turning it negative will hinder... The decline. Therefore, in this stage The rate of change is: .once Less than ,but The rate of change is positive. It will increase again, and a commutation phenomenon will occur, which will inevitably lead to commutation failure. Let... The third stage is a continuous perspective, which can be obtained from equation (4). Starting from the zero point, satisfying Substitute the relevant data and apply equation (3) to... Predict the current value after the third stage ends:

[0057] (3)

[0058] (4)

[0059] In the formula, , For prediction in the third stage The decrease value, The predicted value of the current in the bridge arm that was turned off at the end of the third phase.

[0060] At this time, if If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the value is greater than 0, it is determined that the hybrid commutation converter will fail to commutate.

[0061] In summary, this invention provides a method for rapid prediction of commutation failure in hybrid commutation converters. (See also...) Figure 3 The steps of this method are as follows:

[0062] Step S1: Detect whether the AC grid on the inverter side of the DC transmission system has a fault. If yes, proceed to step S2. If no, there is no need to determine whether the hybrid commutation converter will fail to commutate.

[0063] Step S2: Whenever the bridge arm in the hybrid commutator is turned on and starts commutation according to the trigger angle command, the calculation of relevant parameters is initiated, and the three-stage prediction and identification of commutation failure risk in steps S3-S5 is performed.

[0064] Step S3, First stage prediction: Calculate the current value in the switched-off arm at the end of the first stage of commutation according to formula (1). Determine the current value If the value is greater than 0, it is determined that the hybrid commutation converter will not fail to commutate; if it is, proceed to step S4.

[0065] Step S4, Second Stage Prediction: Calculate the current value in the switched-off arm at the end of the second stage of commutation according to formula (2). Determine the current value If the value is greater than 0, it is determined that the hybrid commutation converter will not fail to commutate; if it is, proceed to step S5.

[0066] Step S5, Third Stage Prediction: Calculate the current value in the switched-off arm at the end of the third stage of commutation according to formula (3). Determine the current value If the value is greater than 0, it is determined that the hybrid commutation converter will not fail to commutate; if it is, it is determined that the hybrid commutation converter will fail to commutate.

[0067] To verify the effectiveness and accuracy of this invention, based on the CIGRE standard model in PSCAD / EMTDC software, some thyristors were replaced with RB-IGCTs at a certain ratio to construct a model as follows. Figure 1 The high-voltage direct current transmission system using HCC is shown. At the same time, the traditional inverter-side constant turn-off angle controller in the standard model is replaced with a constant voltage controller. The system is simulated for different AC bus faults.

[0068] I. Verifying the predictions of this invention The effectiveness and accuracy of [the system / mechanism].

[0069] A single-phase 0.15H ground fault is set on the AC bus, with a duration of 3.0s-3.1s. The time-delay shutdown time is set to 0.0008s after the start of commutation. Taking one of the bridge arms Y5 as an example, bridge arm Y5 underwent a total of 5 commutations during the fault. Figure 4 The current value during commutation of bridge arm Y5 During the fault, the bridge arm in the HCC did not experience commutation failure. Figure 5 The current value in bridge arm Y5 at the end of the first stage under this operating condition. Compared with the predicted value Comparison chart, Figure 6 This is a comparison chart of the actual and predicted total commutation time under this operating condition. Figure 5 and Figure 6 It can be seen that the present invention predicts Both the total commutation time and the overall commutation time have high accuracy.

[0070] II. To verify the effectiveness and accuracy of the present invention in predicting the risk of commutation failure.

[0071] When the aforementioned single-phase 0.15H ground fault occurs on the AC bus, the present invention is first activated to perform the first stage of prediction, based on... Figure 5 It can be seen that the current in bridge arm Y5 is greater than zero after the first stage, so the second stage prediction is required. Figure 7 Showing and The comparison between them shows that due to Greater than ,therefore If the value is less than zero, according to the prediction method proposed by this invention, it can be directly determined that there is no risk of commutation failure, which is consistent with... Figure 4 This is consistent with the actual situation.

[0072] III. Verify the effectiveness and accuracy of the present invention in scenarios where commutation failure occurs in hybrid commutation converters.

[0073] A three-phase 0.08H ground fault is set on the AC bus, with a duration of 3.0s-3.1s. The time-delay shutdown time is set to 0.0008s after the start of commutation. Taking one of the bridge arms Y5 as an example, bridge arm Y5 underwent a total of 5 commutations during the fault. Figure 8 The current value during commutation of bridge arm Y5 It can be seen that the bridge arm failed to commutate during the first commutation process. For this invention, when an AC system fault occurs, the invention first initiates a first-stage prediction process, such as... Figure 9 As shown, after the first phase is completed If the value is greater than zero, a second-stage prediction is required. From Figure 9 As can be seen from this, during the first commutation process of bridge arm Y5, Greater than ,therefore If the value is greater than zero, it is determined that commutation cannot be completed in the second stage. At this point, a third stage prediction is required, calculating the limiting phase at which the hybrid commutation converter will not fail to commutate. ,right The prediction was made, and the result was as follows: Figure 10 As shown. According to Figure 10 It can be seen that during the first commutation process of bridge arm Y5, Greater than ,therefore Greater than zero, which means Since it cannot be reduced to 0 before the limiting phase, the method according to the present invention can quickly predict that the first commutation after a fault in a hybrid commutator will fail, and according to... Figure 9 and Figure 10 It can be seen that other commutation processes will not occur, which is related to Figure 8 The actual results are completely consistent.

[0074] Therefore, the rapid prediction method for commutation failure of hybrid commutator proposed in this invention has high accuracy. In addition, the prediction results of this invention can be obtained at the beginning of commutation. Compared with the method of predicting and identifying commutation failure after the inflection point, the prediction efficiency of this invention is higher and has the characteristic of speed.

[0075] Based on the same principle as the rapid prediction method for commutation failure in hybrid commutated converters described in the above embodiments, this invention also provides a device for rapid prediction of commutation failure in hybrid commutated converters. This device includes a memory, a processor, and a computer program stored in the memory. The processor executes the computer program to implement the rapid prediction method for commutation failure in hybrid commutated converters described in the above embodiments. Specifically, the device can be an electronic computer or tablet computer, the processor can be a CPU, GPU, etc., and the memory can be RAM, ROM, EEPROM, CDROM, disk storage media, or any other medium capable of carrying or storing the computer program and readable by a computer; no limitation is made herein.

[0076] On the other hand, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for rapid prediction of commutation failure in a hybrid commutation converter as described in the above embodiments. Specifically, the computer-readable storage medium may be RAM, ROM, EEPROM, SSD, CDROM, DVD, USB flash drive, or any other medium capable of carrying or storing a computer program and capable of being read by a computer.

[0077] On the other hand, the present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the method for rapid prediction of commutation failure in a hybrid commutation converter as described in the above embodiments.

[0078] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0079] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for rapid prediction of commutation failure in a hybrid commutator, characterized in that: Whenever an arm in the hybrid commutator is turned on and begins commutation according to the trigger angle command, the commutation is divided into three stages, starting from the turn-on time and combined with the set arm delay turn-off time. The first stage is the natural commutation stage of the hybrid commutator, and the time experienced in this stage is the arm delay turn-off time. The second and third stages are the forced commutation stages of the hybrid commutator. When the commutation voltage phase begins to exceed 180°, the second stage ends and the third stage begins. The current value in the arm that is turned off at the end of each stage is predicted, and the hybrid commutator is determined to be likely to fail to commutate based on the predicted values. At the end of the first phase, the current value in the switched-off bridge arm is predicted using the following formula: （1） In the formula, This is the predicted value of the current in the bridge arm that was turned off at the end of the first phase; The initial value of the current in the switched-off arm; This refers to the commutation voltage in the commutation circuit. Angular frequency, Commutation time; The equivalent inductance of the commutation circuit; The trigger angle; The angle corresponding to the delayed turn-off time of the bridge arm; like If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the result is greater than 0, then proceed to the second stage of prediction and judgment.

2. The method for rapid prediction of commutation failure in a hybrid commutator according to claim 1, characterized in that: At the end of the second phase, the current value in the switched-off bridge arm is predicted using the following formula: （2） In the formula, The predicted value of the current in the shut-off arm at the end of the second phase; This is the protection voltage of the surge arrester; like If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the value is greater than 0, then proceed to the third stage of prediction and judgment.

3. The method for rapid prediction of commutation failure in a hybrid commutator according to claim 2, characterized in that: At the end of the third stage, the current value in the switched-off bridge arm is predicted using the following formula: （3） （4） In the formula, The predicted value of the current in the shut-off arm at the end of the third stage; This is from the perspective of the third stage. like If the value is less than or equal to 0, it is determined that the hybrid commutation converter will not experience commutation failure; if... If the value is greater than 0, it is determined that the hybrid commutation converter will fail to commutate.

4. A device for rapid prediction of commutation failure in a hybrid commutation converter, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: The processor executes the computer program to implement the method for rapid prediction of commutation failure in a hybrid commutation converter as described in any one of claims 1-3.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that: When executed by a processor, the computer program implements the method for rapid prediction of commutation failure for hybrid commutated converters as described in any one of claims 1-3.

6. A computer program product, comprising a computer program, characterized in that: When executed by a processor, the computer program implements the method for rapid prediction of commutation failure for hybrid commutated converters as described in any one of claims 1-3.

Images