Calculation method for harmonic waves of controllable power grid commutation converter

Abstract

The invention provides a method for calculating harmonic waves of a controllable power grid commutation converter. The method comprises the following steps: detecting a three-phase alternating voltage of the controllable power grid commutation converter; based on the three-phase alternating voltage, judging whether the controllable power grid commutation converter fails in commutation or not; and if yes, calculating transient harmonics. According to the method provided by the invention, the influence of the change of voltage and current in the commutation process and the action process of the lightning arrester is considered, and compared with an approximate analysis method based on switching characteristics or traditional LCC characteristics, the accuracy is higher.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic power control, in particular to a calculation method of controllable line-commutated converter (CLCC) harmonics. BACKGROUND

[0002] In the field of DC power transmission, the traditional line-commutated converter (LCC) has been widely used in China's ultra-high voltage long-distance power transmission projects due to its low loss, large transmission capacity, and long transmission distance. However, during the fault of the receiving end AC system, the LCC is prone to commutation failure due to insufficient commutation voltage, which seriously threatens the safe and stable operation of the power grid. To fundamentally solve the problem of commutation failure, relevant scholars have proposed a controllable line-commutated converter (CLCC) topology structure based on the consideration of engineering feasibility and economy. The controllable line-commutated converter can completely solve the problem of commutation failure and provide reactive power support by increasing the trigger angle during transient operation. However, the increase in the trigger angle also prolongs the arrester action time and induces additional harmonics. To date, there is no relevant literature on the calculation method of CLCC harmonics.

[0003] As a new type of topology, the controllable line-commutated converter is still mostly analyzed using the LCC theory, such as approximating the CLCC characteristics based on the LCC characteristics and analyzing the variation of active power and reactive power with the trigger angle α. However, the harmonic characteristics are not mentioned. Harmonics in power systems can cause equipment failure, power quality degradation, increased line loss, electromagnetic interference, and other negative effects. Given that the controllable line-commutated converter changes the harmonic characteristics of the original LCC, it is necessary to reanalyze the harmonics of the new converter to facilitate the design of AC filters.

[0004] Currently, the analysis of controllable line-commutated converter harmonics does not fully consider the influence of the arrester dynamic process, leading to a lack of theoretical guidance for optimized design of filter parameters. SUMMARY

[0005] The present application provides a calculation method of controllable line-commutated converter harmonics. To solve the above technical problems, the present application adopts the following technical method: In a first aspect, the present application provides a calculation method of controllable line-commutated converter harmonics, comprising: detecting the three-phase AC voltage of the controllable line-commutated converter; based on the three-phase AC voltage, determining whether the controllable line-commutated converter has failed to commutate; if so, calculating the forced commutation angle of the controllable line-commutated converter; Calculate the commutation current and commutation DC voltage of a controllable power grid commutator at different commutation stages; The transient harmonics are calculated based on the forced commutation angle, the commutation current, and the commutation DC voltage.

[0006] Optionally, determining whether the controllable grid commutator has failed to commutate based on the three-phase AC voltage includes: The three-phase AC voltage is subjected to After coordinate transformation, the three-phase voltages are obtained. Axial components and Axis components; based on the Axial components and the The axis component is used to determine whether the commutation of the controllable grid commutator has failed.

[0007] Optionally, the one based on the Axial components and the The shaft component is used to determine whether a controllable power grid commutator has failed to commutate, including: Based on the above Axial components and the Shaft components determine three-phase voltage Axial components and The combined amplitude of the axial components; Based on the synthesized amplitude, it is determined whether the controllable grid commutator has failed to commutate.

[0008] Optionally, determining whether the controllable grid commutator has failed to commutate based on the synthesized amplitude includes: Obtain three-phase voltage Axial components and Reference value for the synthesis of axial components; Determine whether the synthesized amplitude is less than the synthesized reference value; If so, the controllable grid commutator has failed to commutate.

[0009] Optionally, the calculation of the forced commutation angle of the controllable grid commutator includes: Obtain the trigger angle and the natural commutation angle; Based on the trigger angle and the natural commutation angle, the forced commutation angle of the controllable grid commutation converter is calculated.

[0010] Optionally, the commutation current includes natural commutation current and forced commutation current; the natural commutation current includes natural commutation rising current and natural commutation falling current; the forced commutation current includes forced commutation rising current and forced commutation falling current; and the commutation DC voltage includes natural commutation DC voltage, forced commutation DC voltage, and uncommutated DC voltage.

[0011] Optionally, the transient harmonics include the transient harmonic current amplitude and the transient harmonic voltage amplitude; the calculation of transient harmonics based on the forced commutation angle, the commutation current, and the commutation DC voltage includes: The commutation current and the forced commutation angle are expanded segment by segment using Fourier series to obtain the cosine component and sine component of the valve-side transient current of the controllable grid commutation converter. The commutation DC voltage and the forced commutation angle are expanded segment by segment using Fourier series to obtain the cosine component and sine component of the transient DC voltage of the controllable grid commutation converter. The amplitude of the transient harmonic current is determined based on the cosine component and the sinusoidal component of the valve-side transient current. The amplitude of the transient harmonic voltage is determined based on the cosine component and the sinusoidal component of the transient DC voltage.

[0012] Secondly, this application also provides a computer system, comprising: Memory is used to store instructions that can be executed by the processor; A processor for executing the instructions to implement the method as described in any of the first aspects.

[0013] Thirdly, this application also provides a computer-readable medium storing computer program code that, when executed by a processor, implements the method as described in any of the first aspects.

[0014] This application has the following beneficial effects: The method proposed in this application takes into account the changes in voltage and current during the commutation process and the influence of the surge arrester's operation, and has higher accuracy than methods based on switching characteristics or traditional LCC characteristics for approximate analysis. Attached Figure Description

[0015] Figure 1 A flowchart illustrating a method for calculating harmonics in a controllable power grid phase-commutation converter, provided in an embodiment of this application; Figure 2 This is a schematic diagram of the external topology of a controllable power grid phase-commutation converter provided in an embodiment of this application; Figure 3 This is a schematic diagram of the internal topology of a controllable power grid phase-commutation converter provided in an embodiment of this application; Figure 4 A comparison chart of harmonic simulation and calculation results of a controllable power grid phase-commutation converter provided in the embodiments of this application; Figure 4 (a) is a diagram showing the simulation and calculation results of harmonics of AC current in a controllable power grid phase-commutation converter; Figure 4 (b) is a diagram showing the simulation and calculation results of the harmonics of the DC voltage of the controllable grid phase converter. Detailed Implementation

[0016] To facilitate understanding by those skilled in the art, the present application will be further described below in conjunction with embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present application.

[0017] To solve the above technical problems, such as Figure 1 As shown, this application proposes a method for calculating harmonics in a controllable power grid commutator, including: Step S101: Detect the three-phase AC voltage of the controllable grid phase-commutation converter; The schematic diagram of the external topology of the controllable power grid phase-commutator used in this application is as follows: Figure 2 As shown, the three-phase AC voltage is , , ; commutation reactance is Alternating current is , , DC voltage is VT1~VT6 correspond to six controllable commutation valves.

[0018] The topology diagram of the controllable power grid phase converter used in this application is as follows: Figure 3 As shown, it is divided into a main branch and an auxiliary branch. The main branch is responsible for long-term current carrying, while the auxiliary branch is responsible for active turn-off. During transient periods, after the auxiliary branch's insulated-gate bipolar transistor (IGBT) is actively turned off, the valve current is transferred to the surge arrester. This is the operating voltage of the surge arrester, used to provide commutation voltage to assist commutation.

[0019] The AC voltage on the valve side is distorted during commutation, which affects subsequent derivation. Therefore, this step selects to detect the three-phase AC voltage. , , .

[0020] Step S102: Based on the three-phase AC voltage, determine whether the controllable grid phase-commutation converter has failed to commutate; If so, proceed to step S103.

[0021] This step determines whether the controllable grid commutator has failed to commutate based on the collected three-phase AC voltage. The specific determination is as follows: First, the three-phase AC voltage is... After coordinate transformation, the three-phase voltages are obtained. Axial components and The transformation process for the axis components is shown in the following equation: (1) In the formula, , These are the three-phase voltages. Axial components and Axial components.

[0022] Furthermore, based on the three-phase voltage Axial components and Shaft components are used to determine the three-phase voltage. Axial components and Component amplitude of axis components As shown in the following formula: (2) Furthermore, based on To determine whether the controllable power grid commutator has failed to commutate, i.e., to obtain the three-phase voltage. Axial components and Composite reference value of axial components (Given manually), synthesize reference values. With composite amplitude Compare, if the synthesized amplitude Less than the synthetic reference value If the condition is not met, it is assumed that a three-phase fault has occurred in the receiving-end AC power grid, and the next step of transient harmonic analysis calculation is performed. If the condition is not met, it is determined that no three-phase fault has occurred at the receiving end, the harmonic optimization control system does not operate, and the firing angle is maintained. Phase angle exchanged with nature .

[0023] Step S103: Calculate the forced commutation angle of the controllable grid commutator; When calculating transient harmonics, the firing angle Phase angle exchanged with nature It is a controllable variable, while the forced commutation angle needs to be calculated. The calculation process is as follows: The commutation overlap angle of a controllable power grid commutator can be classified into natural commutation angle based on whether the surge arrester operates. Forced phase change In parameter design, the natural commutation angle is a preset value; the forced commutation angle needs to be calculated, and this value is mainly related to parameters such as AC line voltage and surge arrester. Given that CLCCs do not have commutation failure issues, the forced commutation angle can be derived based on this characteristic. The parsing expression.

[0024] If no commutation failure occurs, the forced commutation process ends (i.e., When ), the current of the valve should be At this point, obtain the trigger angle. Exchange phase angle with nature Substituting both into the following formula, the forced commutation angle can be calculated. : (3) In the formula, This is the effective value of the valve side line voltage; It is the commutation overlap angle, and .

[0025] Step S104: Calculate the commutation current and commutation DC voltage of the controllable grid commutator at different commutation stages; After calculating the forced commutation angle, the commutation current and commutation DC voltage of the controllable grid commutation converter at different commutation stages are calculated.

[0026] Controllable grid commutated converters exhibit corresponding commutation current and commutation DC voltage characteristics at different commutation stages. The commutation current is divided into two categories: natural commutation current and forced commutation current. Natural commutation current is further subdivided into natural commutation rising current and natural commutation falling current; forced commutation current includes forced commutation rising current and forced commutation falling current. The commutation DC voltage encompasses three types: natural commutation DC voltage, forced commutation DC voltage, and uncommutated DC voltage.

[0027] Forced commutation accelerates current transfer, necessitating the construction of a new analytical model for the valve-side current. During the commutation from valve 5 to valve 1, in the rising phase of natural commutation, the commutation voltage is provided by the line voltages of phases A and C. At this time, the valve VT1 current, i.e., the rising current of natural commutation, is... It can be represented as: (4) In the formula, The frequency of the controllable grid phase-commutation converter; During the forced commutation rising phase, the commutation voltage is provided by the line voltages of phases A and C and the surge arrester voltage. At this time, the forced commutation rising current... It can be represented as: (5) Because the current during commutation is symmetrical, the commutation current from VT1 to VT3 can be directly derived from the rising current from VT5 to VT1. The natural commutation current decreasing at valve VT1... and forced commutation drop current It can be represented as: (6) (7) If the DC voltage of a controllable grid-commutated converter is under metastable conditions... If it is periodic, then its harmonic spectrum does not contain Secondary component.

[0028] During natural commutation, the commutation process of phases A and C causes a voltage drop, at which point the natural commutation DC voltage... The expression is as follows: (8) In the formula, The line voltages of phases a and b can be expressed as: ; The line voltages of phases c and b can be expressed as: ; During the forced commutation phase, the surge arrester operation will raise the DC voltage, at which point the forced commutation DC voltage will increase. It can be represented as: (9) In the non-commutation stage, the non-commutated DC voltage Line voltage can be expressed as: (10) Step S105: Calculate transient harmonics based on the forced commutation angle, the commutation current, and the commutation DC voltage.

[0029] Finally, based on the forced commutation angle, the commutation current, and the commutation DC voltage, the transient harmonics are calculated. The transient harmonics include the amplitude of the transient harmonic current and the amplitude of the transient harmonic voltage. The specific calculation process is as follows: First, perform Fourier series expansion on the commutation current and forced commutation angle segment by segment to obtain the cosine component of the valve-side transient current of the controllable grid commutated converter. and the sinusoidal component of the transient current on the valve side As shown in the following formula: (11) (12) From equations (11) and (12), it can be seen that when the harmonic order n = 6k, Therefore, it does not contain the 6k harmonic, and considering that the valve-side current does not contain the 2k harmonic, the current at this time consists only of the n=6k±1 harmonic. Since the denominator contains an (n-1) term during integration, the cosine component of the fundamental frequency current... With sinusoidal components It must be solved separately, and the result can be given by the following formula: (13) (14) For a system employing a 12-pulse controllable grid-commutated converter, the harmonic order of the valve-side AC current is: .

[0030] Secondly, Fourier series expansions are performed segment by segment on the commutation DC voltage and the forced commutation angle to obtain the transient DC voltage cosine component of the controllable grid commutation converter. With the sinusoidal component of transient DC voltage As shown in the following formula: (15) (16) For the above formula, when hour Therefore, the CLCC DC voltage, after taking forced commutation into account, only contains Secondary harmonics.

[0031] For a 12-pulse converter consisting of a controllable grid-commutated converter, the harmonic order is... .

[0032] Finally, based on the cosine component of the transient current on the valve side and the sinusoidal component of the transient current on the valve side Determine the amplitude of transient harmonic current As shown in the following formula: (17) Based on the cosine component of transient DC voltage With the sinusoidal component of transient DC voltage Determine the amplitude of transient harmonic voltage As shown in the following formula: (18) Simulation Experiment To verify the effectiveness of the method proposed in this application, a receiving-end CLCC model was built based on the PSCAD / EMTDC simulation platform. The effective value of the valve-side line voltage was 168.1kV, the commutation reactance was 4.279Ω, the DC current was 5kA, and the surge arrester voltage was 235kV. Figure 4 Figure (4)a shows a comparison of the simulation and calculation results of harmonics in a controllable grid phase-commutation converter. From Figure (4), it can be seen that the theoretical calculation value of the CLCC valve-side current is basically consistent with the simulation results. Since the DC current remains stable during the simulation, its harmonic spectrum strictly follows the n=6k±1 order characteristic distribution. Figure 4 (b) It can be seen that the commutation inductor has insufficient clamping effect on the AC voltage in the simulation, which leads to the distortion of the secondary voltage during the commutation process, resulting in a small number of non-characteristic harmonics of the n=6k±2th order. However, the theoretical calculation value of the n=6kth order characteristic harmonic in the CLCC DC voltage is still in good agreement with the simulation results, and the harmonic components generated by the distortion can be ignored.

[0033] In summary, the method proposed in this application takes into account the changes in voltage and current during commutation and the impact of the surge arrester's operation, and has higher accuracy than methods based on switching characteristics or traditional LCC characteristics for approximate analysis.

[0034] In some embodiments, this application also provides a computer system including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0035] This application also provides a computer-readable storage medium for storing a computer program. This computer-readable storage medium can be applied to a computer device, and the computer program causes the computer device to execute the corresponding processes in the methods described above in the embodiments of this application; for brevity, further details are omitted here.

[0036] The above embodiments are preferred implementations of this application. In addition, this application can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this application.

[0037] To facilitate understanding by those skilled in the art of the improvements made by this application compared to 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 application.

Claims

1. A method for calculating harmonics in a controllable power grid commutator, characterized in that, include: Detecting the three-phase AC voltage of a controllable power grid phase-commutation converter; Based on the three-phase AC voltage, determine whether the controllable grid phase-commutation converter has failed to commutate; If so, calculate the forced commutation angle of the controllable power grid commutator; Calculate the commutation current and commutation DC voltage of a controllable power grid commutator at different commutation stages; The transient harmonics are calculated based on the forced commutation angle, the commutation current, and the commutation DC voltage.

2. The method according to claim 1, characterized in that, The step of determining whether the controllable grid phase-commutation converter has failed based on the three-phase AC voltage includes: The three-phase AC voltage is subjected to After coordinate transformation, the three-phase voltages are obtained. Axial components and Axis components; based on the Axial components and the The axis component is used to determine whether the commutation of the controllable grid commutator has failed.

3. The method according to claim 2, characterized in that, The basis of Axial components and the The shaft component is used to determine whether a controllable power grid commutator has failed to commutate, including: Based on the above Axial components and the Shaft components determine three-phase voltage Axial components and The combined amplitude of the axial components; Based on the synthesized amplitude, it is determined whether the controllable grid commutator has failed to commutate.

4. The method according to claim 3, characterized in that, The step of determining whether the controllable power grid commutator has failed to commutate based on the synthesized amplitude includes: Obtain three-phase voltage Axial components and Reference value for the synthesis of axial components; Determine whether the synthesized amplitude is less than the synthesized reference value; If so, the controllable grid commutator has failed to commutate.

5. The method according to claim 1, characterized in that, The calculation of the forced commutation angle of the controllable grid commutator includes: Obtain the trigger angle and the natural commutation angle; Based on the trigger angle and the natural commutation angle, the forced commutation angle of the controllable grid commutation converter is calculated.

6. The method according to claim 1, characterized in that, The commutation current includes natural commutation current and forced commutation current; the natural commutation current includes natural commutation rising current and natural commutation falling current; the forced commutation current includes forced commutation rising current and forced commutation falling current; the commutation DC voltage includes natural commutation DC voltage, forced commutation DC voltage and uncommutated DC voltage.

7. The method according to claim 6, characterized in that, The transient harmonics include the transient harmonic current amplitude and the transient harmonic voltage amplitude; the calculation of transient harmonics based on the forced commutation angle, the commutation current, and the commutation DC voltage includes: The commutation current and the forced commutation angle are expanded segment by segment using Fourier series to obtain the cosine component and sine component of the valve-side transient current of the controllable grid commutation converter. The commutation DC voltage and the forced commutation angle are expanded segment by segment using Fourier series to obtain the cosine component and sine component of the transient DC voltage of the controllable grid commutation converter. The amplitude of the transient harmonic current is determined based on the cosine component and the sinusoidal component of the valve-side transient current. The amplitude of the transient harmonic voltage is determined based on the cosine component and the sinusoidal component of the transient DC voltage.

8. A computer system, characterized in that, include: Memory is used to store instructions that can be executed by the processor; A processor for executing the instructions to implement the method as described in any one of claims 1 to 7.

9. A computer-readable medium, characterized in that, The system contains computer program code that, when executed by a processor, implements the method as described in any one of claims 1 to 7.

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