Trigger optimization operation method suitable for hybrid grid commutator converter

Abstract

The application discloses a trigger optimization operation method suitable for a hybrid power grid commutation converter. When detecting that a fault occurs in an inverter-side alternating current system, a synchronous commutation voltage phase value corresponding to a current to-be-conducted bridge arm is assumed as a trigger angle to trigger, then a prediction means is used to obtain specific conditions of a supplied commutation area and a demanded commutation area in a next commutation process after triggering, and whether triggering is executed at present is judged based on the specific conditions. If the specific conditions do not satisfy preset optimal trigger conditions, a pulse signal is blocked, phase value updating is waited for, and the same operation of the new trigger angle corresponding to the phase value is executed until the preset conditions are satisfied. When the conditions are satisfied, a trigger pulse signal is directly sent to perform actual triggering, so that an optimal trigger time is found. The application can significantly improve the power transmission capacity of a direct current power transmission system during a fault in the inverter-side alternating current system, and improve the ability of the hybrid power grid commutation converter to resist commutation failure.

Description

Technical Field

[0001] This invention relates to the field of high-voltage direct current transmission technology, and in particular to a triggering optimization method for a hybrid grid phase-commutation converter. Background Technology

[0002] LCC-HVDC transmissions have been widely used for a long time in high-voltage, high-capacity, long-distance power transmission due to their advantages such as low loss, low cost, and mature technology. However, because they use thyristors, they require a certain level of commutation support from the AC system, making commutation failure unavoidable. Commutation failure leads to a rapid increase in DC current, a rapid decrease in DC voltage and transmission power, and in severe cases, DC system shutdown. Especially with the increasing number of DC drop points at load centers, the probability of commutation failure and cascading faults in multi-infeed DC transmission systems has risen sharply, becoming a major challenge threatening the safe and stable operation of AC / DC systems.

[0003] To address the aforementioned issues, relevant research has primarily focused on two aspects of modifying LCC-HVDC converters. One approach targets the control and protection system, such as improving the early trigger control strategy (CFPREV) from different angles to obtain more voltage time area and maximize the ability to withstand commutation failures. However, such methods have limited effectiveness under severe fault conditions and can increase reactive power consumption, leading to further drops in AC voltage and potentially worsening the commutation process. In contrast, topology modifications to the LCC have received significant attention and development due to their more pronounced effects. Existing HVDC converters based on capacitor rectifier converters (CCCs) increase the steady-state commutation angle by inserting a fixed series capacitor between the transformer secondary winding and the converter arm. However, the addition of the capacitor increases current harmonics in the DC system and may trigger charging overvoltage, causing the inverter to lose its self-recovery capability. Controlled series capacitor converter (CSCC) changes the position of the series capacitor between the system and the converter transformer, but its topology harmonic characteristics are complex and there is a risk of resonance; similar is the enhanced capacitor rectifier converter (ELCC), but it has the disadvantage of reducing the commutation voltage in the initial stage of capacitor installation.

[0004] Compared to capacitor modules, the application of fully controlled power electronic devices for modification offers a significant advantage in fundamentally resolving commutation failures, and current topology modification research is moving in this direction. The direct adoption of LCC-MMC dual-ended hybrid DC transmission has already been applied in engineering projects. This involves modifying the inverter side of an LCC to use a modular multilevel converter (MMC) structure based on fully controlled IGBTs. However, the MMC technology route for UHV and above still requires series full-bridge modules to solve DC-side fault isolation problems. This approach suffers from high equipment costs, low power density, high losses, large size, significant difficulty in increasing IGBT capacity, prominent power matching contradictions, and complex control and protection coordination between converters with different characteristics, all of which diminish the advantages of this technology route. The approach of using fully controlled devices to modify the LCC inverter-side converter arms to construct a hybrid grid commutation converter not only maximizes the advantages of LCC transmission but also solves the shortcomings of dual-ended hybrid DC transmission. Existing typical hybrid grid commutation converters include the following types: One type replaces the bridge arm with a structure composed of semi-controlled and fully controlled devices connected in series. The fully controlled devices use IGBTs with anti-parallel diodes, but the characteristic differences between IGBTs and thyristors cause new problems during turn-off. Another type is a controlled commutation converter (CLCC) structure based on a hybrid parallel connection of thyristors and IGBTs in two branches. In this topology, the bridge arm is divided into two sub-branches. The thyristor and IGBT are connected in series to form the main branch to carry large currents; the other auxiliary branch, composed of IGBTs, is connected in parallel with the main branch to interrupt large currents. However, this topology requires adding an extra branch in each bridge arm, resulting in low device utilization and fundamentally increasing the power loss and modification cost of the hybrid grid commutation converter. A third type replaces the thyristors in the bridge arm with RB-IGCTs in series at a certain ratio. However, regardless of the type of hybrid grid phase-commutation converter, its commutation principle and overall process are not fundamentally different from those of LCC, with the only difference being the method of shutdown.

[0005] However, current research on hybrid grid commutation converters focuses on their turn-off characteristics, mainly to turn off the bridge arm when it cannot be turned off and commutation failure is imminent, using fully controlled devices. Although this can greatly alleviate or suppress commutation failure, it does not fully utilize its ability to regulate reactive power to enhance fault ride-through and suppress commutation failure. Therefore, hybrid grid commutation converters currently lack more targeted trigger control strategies. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a triggering optimization operation method suitable for hybrid power grid commutation converters, which addresses the shortcomings of the existing technology and improves the ability of hybrid power grid commutation converters to suppress commutation failures.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a triggering optimization operation method applicable to a hybrid power grid commutator converter, the method comprising: when a fault occurs in the AC system on the inverter side of the converter, assuming that the synchronous commutation voltage phase value corresponding to the current bridge arm to be turned on is used as the triggering angle for triggering, and predicting the supply commutation area and the demand commutation area at the time corresponding to the minimum turn-off angle after triggering;

[0008] Calculate the difference between the supply commutation area and the demand commutation area. If the difference meets the set conditions, that is, the difference changes from decreasing to increasing, or the difference is zero, then send a square wave trigger pulse signal to the switching device of the bridge arm to be turned on.

[0009] This invention starts by optimizing the triggering time of the hybrid grid phase converter and proposes a virtual flexible triggering optimization method. By selecting a more suitable triggering time during AC system faults, reactive power consumption is reduced, and the transmission power of the DC system is effectively maintained, thereby further ensuring the performance recovery and safety and stability of the AC systems at both ends. At the same time, it can also improve the ability of the hybrid grid phase converter to suppress commutation failures and reduce related modification costs and overall operating losses.

[0010] In this invention, before triggering by using the phase value of the synchronous commutation voltage corresponding to the currently conducting bridge arm as the trigger angle, the method further includes: defining the selection range of subsequent trigger angles. The specific implementation process includes:

[0011] The commutation voltage of the bridge arm to be turned on is used as the input of the phase-locked loop (PLL), and the output of the PLL and the set minimum firing angle are used as the input. As the input of the first two-input comparator, the output of the first two-input comparator is connected to the control terminal of the first two-input data selector. The first input terminal of the first two-input data selector is the output of the phase-locked loop, and the second input terminal is 0.

[0012] The output of the first two-input data selector is connected to one input of the second two-input comparator and one input of the second two-input data selector. The other input of the second two-input comparator is the set maximum firing angle. The output of the second two-input comparator is connected to the control terminal of the second two-input data selector;

[0013] The output of the second two-input data selector is sampled to obtain the firing angle signal for the bridge arm to select.

[0014] In this invention, if the difference does not meet the set conditions, the pulse signal is blocked, and the synchronous commutation voltage phase value is updated. The prediction operation is then performed on the trigger angle corresponding to the next moment until the set conditions are met.

[0015] The specific implementation process of predicting the supply commutation area and demand commutation area at the moment corresponding to the minimum turn-off angle after triggering includes: determining the instantaneous rate of change of commutation voltage E and DC current. The calculation formula is as follows: , ;in DC power at trigger time, For the trigger angle, U G Let L be the effective value of the phase voltage of the AC system, ΔU be the longitudinal component of the voltage, δU be the transverse component of the voltage, and L be the effective value of the phase voltage. s For the equivalent inductance of the AC bus, To absorb reactive power in the converter, U c This is the average voltage of the DC line's equivalent capacitance to ground.

[0016] set up , As a prediction error correction coefficient, the commutation voltage E and the rate of change of DC current after the previous commutation process are then used. The actual values ​​are substituted into the formulas for calculating the instantaneous rate of change of commutation voltage and DC current, respectively, to calculate M and N. M and N are updated after each commutation process.

[0017] The calculated M, N, and firing angle are... During the commutation process, the reactive power supplied by the AC system power supply to the converter bus... Substitute into the formula , and In the middle, the commutation voltage for the next commutation process DC current change rate DC current Make predictions; where U d R is the DC voltage at the inverter side port. d I is the equivalent resistance of the receiving end line. d To obtain the measured DC current, The time difference between the trigger moment and the minimum shut-off angle moment;

[0018] Using the predicted commutation voltage and DC current Calculate the supply-transformation area and the demand-transformation area.

[0019] This invention utilizes the completed commutation process to obtain the prediction error correction coefficient, which is then used to predict the next commutation process. This allows for the selection of the optimal triggering time, significantly improving the power transmission capability of the DC transmission system during AC system faults on the inverter side.

[0020] In this invention, the commutation area S is supplied. G The calculation formula is: Where α is the firing angle, μ is the commutation angle, and L is the firing angle. c To replace the equivalent inductance of the phase, Commutation voltage, This is the angular frequency of the power grid.

[0021] The required commutation area S for the next commutation process N The calculation formula is:

[0022] Where α is the firing angle, μ is the commutation angle, and I... d For direct current, L c This is the equivalent inductance for phase commutation.

[0023] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention enables reactive power regulation, significantly improving the power transmission capacity of the DC transmission system during AC system faults on the inverter side, reducing the impact on the AC system, and having a positive impact on the performance recovery of the receiving-end system and the stable and secure access of new energy sources to the sending-end system. This invention improves the ability of hybrid grid commutator converters to withstand commutation failures, effectively reducing the hybrid ratio of fully controlled devices in the bridge arm under the same fault level, thus reducing modification costs and daily operating losses. Attached Figure Description

[0024] Figure 1 These are two typical topologies for hybrid power grid phase-commutation converters;

[0025] Figure 2 A flowchart illustrating a virtual flexible triggering method for a specific bridge arm;

[0026] Figure 3 Commutation process on the LCC inverter side;

[0027] Figure 4 This relates to the relationship between the two commutation areas after triggering.

[0028] Figure 5 A comparison of the firing angles under two firing methods in the event of a single-phase fault;

[0029] Figure 6 A comparison of DC quantities under two triggering methods in the case of a single-phase fault;

[0030] Figure 7 A comparison of power output under two triggering methods in the event of a single-phase fault;

[0031] Figure 8 A comparison of inverter-side AC voltage under two triggering methods in the case of a single-phase fault;

[0032] Figure 9 A comparison of rectifier-side AC voltage under two triggering methods in the case of a single-phase fault;

[0033] Figure 10 A comparison of the triggering angles under two triggering methods in the case of a three-phase fault;

[0034] Figure 11 A comparison of DC quantities under two triggering methods in the case of a three-phase fault;

[0035] Figure 12 A comparison of power output under two triggering methods in the case of a three-phase fault;

[0036] Figure 13 A comparison of inverter-side AC voltage under two triggering methods in the case of a three-phase fault;

[0037] Figure 14 A comparison of rectifier-side AC voltage under two triggering methods in the case of a three-phase fault;

[0038] Figure 15 This study compares the commutation failure suppression capabilities of different models using different triggering methods. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. 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.

[0040] Example 1

[0041] Embodiment 1 of this invention, based on the CIGRE standard model in PSCAD / EMTDC software, takes a more intuitive series-connected RB-IGCT hybrid power grid commutator topology as an example, namely... Figure 1 The series connection type in the present invention is used to verify the triggering optimization method proposed in the embodiments of the present invention.

[0042] Figure 1 Two typical hybrid grid phase-commutation converter topologies are presented. In the operation method of this embodiment, when the inverter-side AC system is normal, the hybrid grid phase-commutation converter on the inverter side of the high-voltage direct current transmission system adopts the same triggering mode as the grid phase-commutation converter (LCC), which is provided by the original control and protection system; when a fault is detected in the inverter-side AC system, the triggering of the hybrid grid phase-commutation converter is switched to a method called virtual flexible triggering.

[0043] The specific execution steps of this virtual flexible triggering method are as follows: Figure 2 This flowchart illustrates the method using a single hybrid bridge arm as an example of virtual flexible triggering; the specific operations for the remaining 11 hybrid bridge arms are the same. First, the control system uses a phase-locked loop to obtain the synchronous phase value of the commutation voltage corresponding to the bridge arm to be activated, and sets the minimum trigger angle. With the maximum trigger angle This determines the selection range of the subsequent firing angle. Specifically, a two-input magnitude comparison module (a and b represent two input quantities) controls the switch to select the signal. Figure 2 In the two-input comparator U1, one input a corresponds to The other input b of U1 corresponds to the commutation voltage phase of bridge arm Y1. When a ≥ b, U1 outputs a high level, and the output of the two-input data selector U2 is the output of the phase-locked loop (PLL). Otherwise, the output of U2 is 0. One input a of the two-input comparator U3 corresponds to the output of the two-input data selector U2, and the other input b corresponds to... When a≥b, the two-input comparator U3 outputs a high level, and the output of the two-input data selector U4 is the same as the output of U3. Otherwise, the output of U4 is 0. Sampling the output of U4 yields the firing angle signal selectable by bridge arm Y1; where U VTIY Here, PH_Y1 represents the commutation voltage of bridge arm Y1, AOI_Y1 represents the phase of the commutation voltage of bridge arm Y1, and AOI_Y1 represents the generated firing angle signal selectable by bridge arm Y1. Simultaneously, the synchronization phase value is updated according to the set sampling frequency. Figure 2 Part ① of the text. Once the phase value of the commutation grid corresponding to the arm to be energized enters the selection range, it is assumed that triggering will occur at the current trigger angle. Then, through prediction, the required commutation area and the supplied commutation area in the next commutation process after triggering are determined. Figure 2 Parts ② and ③ in the text. Figure 2 middle, It is the predicted commutation voltage on bridge arm Y1, Puse_Y6 is the trigger pulse for bridge arm Y6, L cf For equivalent commutation inductance, It is the predicted DC current on bridge arm Y1. This represents the difference between the two commutation areas corresponding to the commutation process of arm Y1. The criterion for determining whether triggering should occur at that moment is to use the time corresponding to the minimum shut-off angle as a reference, and to use the required commutation area S predicted at that time. N With the commutation supply area S G The difference between This is used to characterize the relationship between positive and negative returns after triggering, and the minimum value of this difference is defined as the optimal commutation area difference. Figure 3 This describes three possible relationships between the two commutation areas under different conditions after triggering. When When the value changes from decreasing to increasing or becomes zero, the optimal triggering condition is considered met. If the optimal triggering condition is not met, the pulse signal is blocked, waiting for an update, and the same prediction operation is performed on the trigger angle corresponding to the next moment until the setting condition is met. If the setting condition is met, a trigger pulse signal is directly issued for actual triggering. Figure 2 Part ④ of the text. Only when a fault signal (Fault) is detected in the inverter-side AC system will the control and protection system use the virtual flexible triggering method's trigger pulse Flex_Y1 instead of the original trigger pulse LCC_Y1 for triggering. Figure 2 Part ⑤ of the above, thereby achieving optimized operation of the hybrid power grid phase converter.

[0044] To anticipate the impact of a change in the firing angle on the next commutation process of a hybrid power grid commutator, it is necessary to predict the rate of change of the commutation voltage and DC current after the firing angle change. The optimized triggering time is determined. Since existing formulas for the rate of change of commutation voltage and DC current cannot be directly used to calculate the relationship between the two after a certain time interval, this invention provides a convenient prediction method based on an error correction coefficient. First, the commutation voltage E and the reactive power Q absorbed by the converter are... s The instantaneous relationships are as follows:

[0045] (1)

[0046] in This refers to the DC power at which the commutation process is triggered. For the selected trigger angle; U G The effective value of the phase voltage of the AC system; ΔU is the longitudinal component of the voltage; δU is the transverse component of the voltage; L s This is the equivalent inductance of the AC bus.

[0047] The instantaneous rate of change of direct current can be expressed by the following formula:

[0048] (2)

[0049] Among them U c U is the average voltage of the DC line's equivalent capacitance to ground. d L is the DC voltage at the inverter side port. d With R d These are the equivalent inductance and resistance of the receiving-end line, respectively.

[0050] First, in the above two formulas and The prediction error correction coefficients M and N are used to represent the values ​​of M and N respectively. Then, the actual values ​​of the commutation voltage and DC current change rate after the previous commutation process are used as the results of equations (1) and (2) and other known parameters to inversely calculate the values ​​of M and N. Subsequently, these M, N, and firing angle are used to calculate the values ​​of M and N. Substituting the values ​​of other relevant parameters at the current moment into the following two equations, we can obtain the commutation voltage for the next commutation process. With DC current change The prediction of DC current allows for the determination of the supply and demand commutation areas. Furthermore, M and N are updated after each actual commutation process is completed.

[0051]

[0052]

[0053]

[0054] The supply commutation area S can be calculated using the predicted commutation voltage and DC current change rate, respectively, by the following formula. G Area S commutated to demand N :

[0055]

[0056] (Completed commutation process)

[0057] (Next commutation process)

[0058] Where α is the firing angle; μ is the commutation angle; I d For direct current; L c The equivalent inductance for commutation; commutation area difference =S N - S G .

[0059] The main difference between the different hybrid methods lies in the different shutdown processes. The series method directly uses fully controlled devices for shutdown, while the parallel method transfers the current from one branch to another before being shut down by fully controlled devices. The shutdown method in both cases uses fully controlled devices to shut down the aforementioned two types of current. Therefore, both hybrid grid commutation converters and LCCs are based on the natural commutation process of thyristors, differing only in the final commutation termination method. Thus, the overall principle of the commutation process is not fundamentally different from that of an LCC. Therefore, taking the commutation process from VT6 to VT2 on the LCC inverter side as an example, the equivalent circuit of the converter at this time is as follows: Figure 3As shown. The KVL equations for the commutation circuits at this point are:

[0060] (3)

[0061] Where u b u c These are the AC phase B and C voltages, respectively; L c For the equivalent inductance of the commutation phase; and These are the currents flowing through VT2 and VT6, respectively.

[0062] Let the commutation voltage provided by the AC side be During commutation, the DC current is Substituting both into equation (3) and integrating both sides of the equation, we get:

[0063] (4)

[0064] Where α is the firing angle and μ is the commutation angle.

[0065] The right side of equation (4) is defined as the required commutation area of ​​the converter during the commutation process:

[0066] (5)

[0067] The left side of equation (4) is defined as the actual commutation area that the AC side voltage can provide during the commutation process:

[0068] (6)

[0069] In this embodiment, the trigger angle is During the commutation process, the reactive power supplied by the AC system power supply to the converter bus... The calculation process is as follows:

[0070] The total reactive power Q consumed by the inverter i It can be represented as:

[0071]

[0072] in DC power; The fundamental power factor angle; The DC voltage is the voltage across the two bridges connected in series. It is the fundamental power factor angle of the inverter ( (For trigger angle)

[0073] The reactive power compensation of AC filters and capacitor banks is...

[0074] Considering the reactive power balance at the AC bus, we have:

[0075]

[0076] Q s The reactive power supplied by the AC system power supply to the inverter station converter bus.

[0077] The following compares the performance of hybrid grid phase-commutation converters under the same AC-side inductive ground fault with those without considering firing angle optimization and those with the firing angle optimization strategy proposed in this embodiment of the invention. Case 1 is the one without optimization, and Case 2 is the one with optimization, as detailed below:

[0078] (1) Assuming the inductance of a single-phase ground fault on the AC bus is 0.1H and the fault duration is 3.0s-3.08s, the RB-IGCT hybrid replacement ratio adopted in Case 1 and Case 2 is 65%. During the fault, the triggering optimization operation method proposed in this embodiment of the invention is used to optimize the triggering angle given by the original control and protection system. Therefore, the hybrid grid phase-change converter as a whole exhibits a delayed triggering state. The comparison of the changes in the triggering angle is shown in the attached figure. Figure 5 As shown. By Figure 6 As shown in Figure 7, both schemes successfully suppressed commutation failure, but the optimized method effectively stabilized DC voltage and current fluctuations during the fault period, thus significantly maintaining DC power transmission, reducing the power deficit from 26.88% to 9.07%. Furthermore, it reduced the reactive power absorbed by the inverter-side converter from the AC bus, thereby contributing to maintaining the inverter-side bus voltage and the performance recovery of the receiving-end system. Figure 8 As shown in the attached figure; during the fault, the THD of the three-phase voltage of the receiving-end AC bus decreased from 23.2%, 25.5%, and 26.57% to 9.72%, 9.9%, and 15.07%, respectively. Simultaneously, the peak overvoltage excess in the sending-end system also decreased from 26.37% to 3.53%, as shown in the attached figure. Figure 9 As shown, this is beneficial to the safety and stability of the sending-end system, especially when there is a high proportion of new energy sources connected.

[0079] (2) Assume the inductance of the three-phase ground fault on the AC bus is 0.3H, the fault duration is 3.0s-3.08s, and the RB-IGCT hybrid replacement ratio is 65% for both Case 1 and Case 2. The change in the triggering angle after adopting the trigger-optimized operation method during the fault is shown in the attached figure. Figure 10 As shown. By Figure 11As can be seen from Figures 12, 13, and 14, similar to the effect of single-phase grounding, the optimization method can also achieve the expected results. During the fault, the DC power transmission deficit decreased from 24.02% to 7.23%; the THD of the three-phase voltage of the receiving-end AC bus decreased from 22.19%, 22.88%, and 24.19% to 11.67%, 10.96%, and 10.98%, respectively; and the peak overvoltage excess in the sending-end system decreased from 19.08% to 3.18%.

[0080] Secondly, the critical fault inductance values ​​that can trigger commutation failure in different models were investigated. Case 1 represents the CIGRE standard model, Case 2 represents a model with a 30% RB-IGCT mixing ratio, Case 3 represents a model with a 50% RB-IGCT mixing ratio, and Case 4 represents a model with a 30% RB-IGCT mixing ratio that also employs the optimization method of this invention. A single-phase ground fault was set on the AC bus, with a fault duration of 0.5 seconds and an interval of 18° between fault moments. The results are as follows: Figure 15 As shown in the figure, the results demonstrate that the hybrid grid commutation converter with RB-IGCTs connected in series in the bridge arm significantly improves the resistance to commutation failure, and the higher the series ratio, the stronger the resistance. Furthermore, after adding the triggering optimization method proposed in this embodiment to the 30% mixing ratio, the critical fault inductance is close to that of the 50% mixing ratio and is better than that of the hybrid grid commutation converter with only a 30% mixing ratio. This shows that the triggering optimization operation method proposed in this embodiment can enhance the ability of the hybrid grid commutation converter to resist commutation failure during AC-side faults, based on the original triggering method. Therefore, when dealing with the same AC-side fault level, the optimization method of this embodiment can reduce the mixing ratio of RB-IGCTs compared to the original method, thereby reducing the modification cost and operating losses, and improving economic efficiency.

[0081] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0082] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A trigger-optimized operation method for phase-commutator converters in hybrid power grids, characterized in that, The method includes: When a fault occurs in the AC system on the inverter side of the converter, assuming that the phase value of the synchronous commutation voltage corresponding to the currently conducting bridge arm is used as the triggering angle, the supply commutation area and the demand commutation area at the time corresponding to the minimum turn-off angle after triggering are predicted. Calculate the difference between the supply commutation area and the demand commutation area. If the difference meets the set conditions, that is, the difference changes from decreasing to increasing, or the difference is zero, then send a square wave trigger pulse signal to the switching device of the bridge arm to be turned on. The specific implementation process of predicting the supply commutation area and demand commutation area at the time corresponding to the minimum shut-off angle after the trigger is obtained includes: Determine the instantaneous rate of change of commutation voltage E and DC current. The calculation formula is as follows: , ; U is the DC power triggered during the commutation process. G U is the effective value of the phase voltage of the AC system, ΔU is the longitudinal component of the voltage, and U d The DC voltage at the inverter side port is δU, where δU is the transverse voltage component, and L is the voltage across the inverter side. s For the equivalent inductance of the AC bus, To absorb reactive power in the converter, U c This is the average voltage of the DC line's equivalent capacitance to ground. L is the angular frequency of the power grid. d The equivalent inductance of the receiving end line; set up , As a prediction error correction coefficient, the instantaneous change rate of the commutation voltage E and the DC current after the previous commutation process is then used. Substitute the actual values ​​into and In the calculation formula, M and N are calculated in reverse, and M and N are updated after each commutation process is completed; The calculated M, N, and firing angle are... The reactive power delivered by the AC system power supply to the converter bus during the commutation process Substitute into the formula , and In the middle, the commutation voltage for the next commutation process DC current change rate DC current at the minimum turn-off angle Make a prediction; where R d This is the equivalent resistance of the receiving-end line. The DC current is assumed to be measured at the trigger moment. The time difference between the trigger moment and the minimum shut-off angle moment; The trigger angle is assumed to be at the triggering moment; Using the predicted commutation voltage and DC current Calculate the supply-transformation area and the demand-transformation area.

2. The trigger-optimized operation method for hybrid power grid phase converters according to claim 1, characterized in that, Assuming that the synchronous commutation voltage phase value corresponding to the currently conducting bridge arm is used as the trigger angle before triggering, the process also includes: defining the selection range of subsequent trigger angles. The specific implementation process includes: The commutation voltage of the bridge arm to be turned on is used as the input of the phase-locked loop (PLL), and the output of the PLL and the set minimum firing angle are used as the input. As the input of the first two-input comparator, the output of the first two-input comparator is connected to the control terminal of the first two-input data selector. The first input terminal of the first two-input data selector is the output of the phase-locked loop, and the second input terminal is 0. The output of the first two-input data selector is connected to one input of the second two-input comparator and one input of the second two-input data selector. The other input of the second two-input comparator is the set maximum firing angle. The output of the second two-input comparator is connected to the control terminal of the second two-input data selector; The output of the second two-input data selector is sampled to obtain the firing angle signal for the bridge arm to select.

3. The trigger-optimized operation method for hybrid power grid phase converters according to claim 1, characterized in that, If the difference does not meet the set conditions, the pulse signal is blocked, and the synchronous commutation voltage phase value is updated. The prediction operation is then performed on the trigger angle corresponding to the next moment until the set conditions are met.

4. The trigger-optimized operation method for hybrid power grid phase converters according to any one of claims 1 to 3, characterized in that, Supply commutation area S G The calculation formula is: Where α is the firing angle and μ is the commutation angle. Here, E is the commutation voltage.

5. The trigger-optimized operation method for hybrid power grid commutator converters according to claim 4, characterized in that, The required commutation area S for the next commutation process N The calculation formula is: Where α is the firing angle, μ is the commutation angle, and I... d For direct current, L c This is the equivalent inductance for phase commutation.

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