High-voltage direct-current power transmission system simulation model and construction method

Abstract

The invention discloses a high-voltage direct-current power transmission system simulation model and a construction method, and relates to the technical field of system-level model construction, and the model comprises a primary topology module and a secondary control module. The primary topology module comprises a first power supply module and a rectifier station module at a rectifier side, a direct current power transmission module, and an inverter station module and a second power supply module at an inverter side; the input end of the rectifier station module is electrically connected with the first power supply module, the input end of the DC power transmission module is electrically connected with the output end of the rectifier station module, the output end is connected with the input end of the inverter station module, and the output end of the inverter station module is electrically connected with the second power supply module; and the secondary control module is used for controlling the current, voltage and power of the rectification side and the inversion side based on PID control logic. The primary topology adopts symmetrical single pole wiring, the HVDC is embedded into an alternating current power grid, and the influence of a transformer substation of the alternating current power grid on an HVDC converter station is researched.

Description

Technical Field

[0001] The present invention relates to the technical field of system-level model building, and in particular to a high-voltage direct current transmission system simulation model and a building method. Background Art

[0002] The High Voltage Direct Current (HVDC) system includes DC transmission projects and converter stations. The converter station includes a rectifier station and an inverter station. The place where the sending end performs rectification and conversion is called a rectifier station, and the place where the receiving end performs inversion and conversion is called an inverter station. The devices that realize rectification and inversion conversion are called rectifiers and inverters respectively, and they are collectively called converters.

[0003] In a high-voltage direct current transmission system, electrical energy is extracted from one point of the three-phase AC grid, converted into DC at a rectifier station, and transmitted to the receiving point through overhead lines or cables. After the DC is converted into AC at the inverter station, it enters the AC grid of the receiving party. The rated power of DC transmission is usually greater than 100 MW, and many are between 1000-3000 MW. It is usually used to build a system simulation model to intuitively understand some of the operating characteristics of HVDC.

[0004] In terms of simulation model construction, traditional HVDC is directly separated from two large AC power grids, and the impact of the AC power grid substation on the HVDC converter station cannot be considered. Summary of the invention

[0005] The embodiment of the present invention provides a high-voltage direct current transmission system simulation model, which solves the problem that the traditional HVDC is directly separated from two large alternating current grids and the influence of the substation of the alternating current grid on the HVDC converter station cannot be considered.

[0006] The present invention provides a high-voltage direct current transmission system simulation model, comprising a primary topology module and a secondary control module, wherein the primary topology module comprises a first power module and a rectifier station module on a rectifier side, a direct current transmission module, and an inverter station module and a second power module on an inverter side;

[0007] The first power supply module and the second power supply module both use power supplies with negative feedback regulation characteristics, and are used to simulate two AC power grids;

[0008] The input end of the rectifier station module is electrically connected to the first power module, and the rectifier station module is used to convert the alternating current of the first power module into direct current;

[0009] The DC power transmission module input end is electrically connected to the rectifier station module output end, and the output end is connected to the inverter station module input end. The DC power transmission module is used to transmit the DC power converted by the rectifier station module to the inverter station module.

[0010] The output end of the inverter station module is electrically connected to the second power supply module, and the inverter station module is used to convert direct current into alternating current and input the converted alternating current into the second power supply module;

[0011] The secondary control module is based on PID control logic and is used to control the current, voltage and power on the rectifier side and the inverter side.

[0012] Preferably, the rectifier station module includes an AC filter and a rectifier converter, and the inverter station module includes an AC filter and an inverter; the AC filter adopts 3 groups of BP11 / BP13 filters, 3 groups of HP24 / 36 filters and 2 groups of HP3 filters; the rectifier converter and the inverter both adopt 12-pulse converters, and the midpoint of the 12-pulse converter of the inverter is grounded.

[0013] Preferably, three groups of BP11 / BP13 filters, three groups of HP24 / 36 filters and two groups of HP3 filters are connected in parallel at the AC busbars on the rectifier side and the inverter side.

[0014] Preferably, the rectifier station module and the inverter station module further include a converter transformer, and the converter transformers are of a single-phase double-winding type.

[0015] Preferably, the DC power transmission module includes a main line connection module, and the DC connection module adopts a symmetrical single-pole connection based on a 12-pulse converter valve.

[0016] Preferably, the DC power transmission module further includes a DC filter and two DC stages. The DC filter on the rectifier side uses a group of 6 / 12 filters connected between two DC poles; each DC stage on the inverter side is configured with a group of 6 / 12 filters connected between the DC pole and the ground.

[0017] Preferably, constant current control is adopted on the rectifier side, and Amax angle and constant current control are adopted on the inverter side; both the rectifier side and the inverter side are equipped with a closed-loop current controller, a voltage controller and a low-voltage current limiting control link.

[0018] Preferably, the high-voltage direct current transmission system has a transmission power of 1200MW, a rated direct current voltage of ±200kV, a transmission distance of about 111km, and neither the rectifier station module nor the inverter station module is provided with a grounding electrode or a grounding electrode line.

[0019] Preferably, in the high-voltage direct current transmission system simulation model, the odd-order harmonic distortion rate of the AC bus voltage under steady-state operating conditions does not exceed 1.25%, the even-order harmonic distortion rate does not exceed 0.5%, the total harmonic distortion rate does not exceed 1.75%, and the telephone harmonic waveform coefficient does not exceed 1.0%.

[0020] A method for constructing a high voltage direct current transmission system simulation model comprises the following steps:

[0021] Obtain HVDC design parameters, and construct rectifier station modules, DC transmission modules, and inverter station modules according to the HVDC design parameters;

[0022] A power supply with negative feedback regulation characteristics is used to construct a first power supply module and a second power supply module;

[0023] The first power module, the rectifier station module, the DC transmission module, the inverter station and the second power module are electrically connected in sequence to obtain a primary topology module;

[0024] Based on PID control logic, build secondary control module;

[0025] A simulation model of a high-voltage direct current transmission system is constructed by combining the primary topology module and the secondary control module.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The primary topology module of the present invention includes a first power module and a rectifier station module on the rectifier side, a DC transmission module, and an inverter station module and a second power module on the inverter side, wherein the first power module and the second power module simulate an AC power grid, and the primary topology adopts symmetrical monopole wiring, and the converter station and the substation are jointly constructed, so as to embed the HVDC into the AC power grid. A secondary control module is also provided, which considers the construction of a system-level model operating under multiple working conditions from aspects such as the primary topology of the system and the construction of the secondary control module. It can be used to intuitively understand some operating characteristics of HVDC, study the impact of the substation of the AC power grid on the HVDC converter station, and use the secondary control module to stably operate the HVDC near the rated working condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A flow chart for constructing a high voltage direct current power transmission system simulation model of the present invention;

[0030] Figure 2 A primary topological diagram of the present invention;

[0031] Figure 3 It is a schematic diagram of the configuration of the AC filter of the present invention;

[0032] Figure 4 It is a schematic diagram of the configuration of the DC filter of the present invention;

[0033] Figure 5 It is a schematic diagram of a power module of the present invention;

[0034] Figure 6 It is a block diagram of the secondary control system of the present invention;

[0035] Figure 7 It is a schematic diagram of the trigger angle of the rectifier side of the present invention;

[0036] Figure 8 It is a schematic diagram of the inverter side trigger angle of the present invention;

[0037] Fig. 9 It is a schematic diagram of the rectifier side simulation system of the present invention;

[0038] Fig.10 It is a schematic diagram of the inverter side simulation system of the present invention;

[0039] Fig.11 It is a schematic diagram of simulation results of the DC current and voltage on the upstream side of the present invention;

[0040] Fig.12 It is a schematic diagram of the simulation results of the DC current and voltage on the upstream side of the present invention. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The invention provides a high voltage direct current transmission system simulation model, comprising a primary topology module and a secondary control module.

[0043] The primary topology module includes the first power module and the rectifier station module on the rectifier side, the DC transmission module, and the inverter station module and the second power module on the inverter side. The rated transmission power of the DC transmission project is 1200MW, the rated DC voltage is ±200kV, the transmission distance is about 111km, and the rectifier station and the inverter station are not equipped with grounding electrodes and grounding electrode lines. Among them, the rectifier station and the converter station are collectively referred to as the converter station.

[0044] Reference Figure 5The first power supply module and the second power supply module both use power supplies with negative feedback regulation characteristics to simulate two AC power grids. The first power supply module is the output end, and the second power supply module is the load. A power supply with negative feedback regulation characteristics is used to ensure that the voltage stability can be maintained under various conditions.

[0045] The DC transmission module includes a main line connection module, and the DC connection module adopts a symmetrical single-pole connection based on a 12-pulse converter valve.

[0046] Reference Figure 2 The DC wiring module adopts a symmetrical unipolar wiring based on 12-pulse converter valves. Each converter station is composed of a single converter or multiple converters in parallel. The DC side circuit of the 12-pulse symmetrical unipolar mode consists of positive and negative poles. Only the neutral point of one end of the converter station is grounded. The earth, metal neutral line or other lines cannot be used as normal or backup current circuits. Considering the use of 12 pulses, since the structure of the most basic phase-commutating converter is a three-phase Graetz bridge, also called a six-pulse bridge converter, which contains 6 power electronic switches, each of which connects one phase of the AC and a DC end. For a 6-pulse converter, the phase angle between each pulse differs by 60°. In actual engineering, certain harmonic distortion is inevitably generated at both the AC and DC ends. An improvement measure is to increase the phase difference between the number of pulses, thereby reducing the output voltage fluctuation range, that is, using 12 valves to obtain a 12-pulse waveform.

[0047] The DC side circuit is composed of positive and negative pole conductors. Each station has a 12-pulse converter. Only the midpoint of the 12-pulse converter at the inverter side converter station is grounded. The earth, metal neutral wire or other lines cannot be used as normal or backup current circuits. The topology construction is shown in Figure 2 .

[0048] The rectifier station module includes an AC filter and a rectifier converter, and the inverter station module includes an AC filter and an inverter converter. The AC filter uses 3 groups of BP11 / BP13 filters, 3 groups of HP24 / 36 filters, and 2 groups of HP3 filters, which are connected to the AC bus and wired in parallel. Figure 3 .

[0049] The DC transmission module also includes a DC filter. The DC filter is configured with a set of 6 / 12 filters, connected between the DC poles. Each pole on the inverter side is configured with a set of 6 / 12 filters, connected between the DC pole and the ground. Figure 4 .

[0050] The secondary control module is based on control logic, using fixed-point current control on the rectifier side and Amax angle control based on a fixed turn-off angle on the inverter side.

[0051] The present invention provides a method for constructing an "embedded" high-voltage direct current transmission system simulation model, comprising the following steps:

[0052] Step 1: Determine the complete HVDC design, which includes the DC system main wiring scheme design, AC / DC filter design, and power supply design.

[0053] For the design of the main connection scheme of the DC system, a symmetrical unipolar connection based on 12-pulse converter valves is adopted. Each converter station is composed of a single converter or multiple converters in parallel. The DC voltage output from the two DC terminals of the converter is equal in magnitude and opposite in polarity. Considering the use of 12 pulses, since the structure of the most basic phase-commutating converter is a three-phase Graetz bridge, also called a six-pulse bridge converter, which contains 6 power electronic switches, each of which connects one phase of the AC and a DC terminal. For a 6-pulse converter, the phase angle between each pulse differs by 60°. In actual engineering, certain harmonic distortion is inevitably generated at both the AC and DC ends. An improvement measure is to increase the phase difference between the number of pulses and reduce the output voltage fluctuation range, that is, to obtain a 12-pulse waveform using 12 valves. The converter transformer of the sending and receiving converter station adopts a single-phase double-winding type. The DC side circuit is composed of positive and negative pole conductors, with a 12-pulse converter at each station. Only the midpoint of the 12-pulse converter at the receiving end converter station is grounded. The earth, metal neutral wire or other lines cannot be used as normal or backup current circuits. The topology construction is shown in Figure 2 .

[0054] For AC / DC filter design, it is necessary to consider the design of the AC filter, which should ensure that the AC bus voltage distortion rate and telephone waveform distortion coefficient of the converter station are limited to a certain level under various steady-state operating conditions of the DC system. Specifically, it includes:

[0055] Single harmonic distortion

[0056] When the harmonic impedance of the AC system is calculated at the impedance point with the maximum harmonic distortion within the specified harmonic impedance envelope, the harmonic distortion rate of the AC busbar of the converter station shall not exceed 1.25% for odd orders and 0.5% for even orders.

[0057] Total harmonic distortion

[0058] For the two harmonic orders that cause the highest total distortion, the harmonic impedance of the AC system takes the value within the specified harmonic impedance envelope. For other harmonic components, the harmonic impedance of the AC system is considered to be an open circuit. The calculated total harmonic distortion rate should not be greater than 1.75%.

[0059] Telephone Harmonic Form Factor

[0060] For the two harmonic orders that result in the highest telephone harmonic waveform coefficient, the AC system harmonic impedance adopts the value within the specified harmonic impedance envelope, while for the remaining harmonic components, the system harmonic impedance is considered to be an open circuit, and the calculated telephone harmonic waveform coefficient THF.F. should not be greater than 1.0%.

[0061] The AC filter uses 3 groups of BP11 / BP13 filters, 3 groups of HP24 / 36 filters, and 2 groups of HP3 filters, which are connected to the AC bus and wired in parallel. Figure 3 The DC filter is configured with a set of 6 / 12 filters, connected between the DC poles. Each pole on the inverter side is configured with a set of 6 / 12 filters, connected between the DC pole and the ground, see Figure 4 .

[0062] For power supply design, the power supply is equivalent to the AC power grid. A power supply with negative feedback regulation characteristics is used to ensure that the voltage stability can be maintained under various conditions. The voltage reference value on the rectifier side is set to 230kV. The AC three-phase voltage in the system is measured in real time, and its error value is controlled through the PID control link to achieve a stable level. Among them, P represents proportional regulation, which is based on the size of the deviation and plays a role in stabilizing the voltage in automatic regulation; I represents integral action, which is based on whether the deviation exists and plays a role in eliminating the residual error in automatic regulation; D represents differential action, which is based on the speed of deviation change and plays a role in leading regulation in automatic regulation. See Figure 5 The voltage level of the system fluctuates continuously under various operating conditions, and the power supply voltage level is automatically calibrated through PID negative feedback regulation.

[0063] Step 2: Construct a HVDC control model for the high voltage direct current transmission system.

[0064] Under normal operating conditions, the rectifier side quickly adjusts the alpha angle to keep the DC current constant. The inverter side fast adjustment strategy is to maintain the gamma angle constant at 17°. Under normal operating conditions, the rectifier side tap controls the alpha angle to 15°+2.5°, and the inverter side tap controls the DC voltage to be constant.

[0065] First, design the control block diagram. The secondary control model is based on the control logic. According to the measured value, it sends a trigger pulse to the converter valve of the DC transmission system to adjust the voltage, current and power transmission of the DC transmission system. In the DC transmission system control system constructed in this model, there are two control modes on the inverter side: constant current control and fixed trigger angle control. Different control modes are selected according to the measurement results to control the trigger angle and control the operation of the DC transmission system. In addition to constant current control, there is also constant γ control. The input of γ must take the minimum value of a cycle. As long as the detected minimum value is greater than a certain value, it can be guaranteed that there will be no commutation failure. The low-voltage current limiting control (VDCOL) feature means that in certain fault conditions, when the DC voltage is found to be lower than a certain value, the setting value of the DC current regulator is automatically reduced. After the DC voltage is restored, the control function of the setting value is automatically restored to limit the short-circuit current during a fault. See Figure 6 .

[0066] The rectifier side adopts constant current control, where the control angle waveform is as follows Figure 7 shown.

[0067] The inverter side adopts Amax control and constant current control, where the control angle waveform is as follows Figure 8 In order to improve stability, the inverter side Amax control (modified constant gamma angle control) is used to modify the characteristics of the inverter end so that it has a positive slope or zero slope in transient conditions, that is, when the DC current is between the inverter side current constant and the rectifier side current constant, the trigger angle is reduced according to the current difference, so that the external characteristics of the inverter end become a positive slope.

[0068] Step 3: Combine the topology and control system once, and debug whether the HVDC can operate normally given the corresponding operating conditions.

[0069] The overall simulation diagram is as follows Fig. 9 and Fig.10 shown.

[0070] First, observe the operation of the rectifier side. During the start-up of the DC transmission system to establish the DC voltage and current, the overshoot is small, the steady-state DC voltage and steady-state DC current are established quickly, and the control system characteristics of the DC transmission system meet the requirements. Fig.11 shown.

[0071] Then observe the operation of the inverter side. Similar to the operation of the rectifier side, the overshoot is small during the startup process, and the DC current and voltage reach steady-state operation quickly. The DC transmission system control system meets the rapidity requirements. Fig.12 shown.

[0072] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0073] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high voltage direct current transmission system simulation model, comprising a primary topology module and a secondary control module, characterized in that: The primary topology module includes a first power module and a rectifier station module on the rectifier side, a DC transmission module, and an inverter station module and a second power module on the inverter side; The first power supply module and the second power supply module both use power supplies with negative feedback regulation characteristics, and are used to simulate two AC power grids; The input end of the rectifier station module is electrically connected to the first power module, and the rectifier station module is used to convert the alternating current of the first power module into direct current; The DC power transmission module input end is electrically connected to the rectifier station module output end, and the output end is connected to the inverter station module input end. The DC power transmission module is used to transmit the DC power converted by the rectifier station module to the inverter station module. The output end of the inverter station module is electrically connected to the second power supply module, and the inverter station module is used to convert direct current into alternating current and input the converted alternating current into the second power supply module; The secondary control module is based on PID control logic and is used to control the current, voltage and power on the rectifier side and the inverter side.

2. A high voltage direct current transmission system simulation model as claimed in claim 1, characterized in that: The rectifier station module includes an AC filter and a rectifier converter, and the inverter station module includes an AC filter and an inverter; the AC filter adopts 3 groups of BP11 / BP13 filters, 3 groups of HP24 / 36 filters and 2 groups of HP3 filters; the rectifier converter and the inverter both adopt 12-pulse converters, and the midpoint of the 12-pulse converter of the inverter is grounded.

3. A high voltage direct current transmission system simulation model as claimed in claim 2, characterized in that: Three groups of BP11 / BP13 filters, three groups of HP24 / 36 filters and two groups of HP3 filters are connected in parallel at the AC busbars on the rectifier side and the inverter side.

4. A high voltage direct current transmission system simulation model as claimed in claim 1, characterized in that: The rectifier station module and the inverter station module also include a converter transformer, and the converter transformer is a single-phase double-winding type.

5. A high voltage direct current transmission system simulation model as claimed in claim 1, characterized in that: The DC power transmission module comprises a main line connection module, and the DC connection module adopts a symmetrical single-pole connection based on a 12-pulse converter valve.

6. A high voltage direct current transmission system simulation model as claimed in claim 5, characterized in that: The DC power transmission module also includes a DC filter and two DC stages. The DC filter on the rectifier side uses a group of 6 / 12 filters connected between two DC poles; each DC stage on the inverter side is configured with a group of 6 / 12 filters connected between the DC pole and the ground.

7. A high voltage direct current transmission system simulation model as claimed in claim 1, characterized in that: Constant current control is adopted on the rectifier side, and Amax angle and constant current control are adopted on the inverter side; both the rectifier side and the inverter side are equipped with closed-loop current controller, voltage controller and low-voltage current limiting control link.

8. A high voltage direct current transmission system simulation model as claimed in claim 1, characterized in that: The high-voltage direct current transmission system has a transmission power of 1200MW, a rated direct current voltage of ±200kV, a transmission distance of about 111km, and no grounding electrodes or grounding electrode lines are provided in the rectifier station modules and the inverter station modules.

9. A high voltage direct current transmission system simulation model as claimed in claim 1, characterized in that: The harmonic distortion rate of each harmonic of the AC bus voltage of the high-voltage direct current transmission system simulation model under steady-state operation conditions does not exceed 1.25% for odd orders and 0.5% for even orders, the total harmonic distortion rate does not exceed 1.75%, and the telephone harmonic waveform coefficient does not exceed 1.0%.

10. A method for constructing a high voltage direct current transmission system simulation model according to claim 1, characterized in that: The following steps are involved: Obtain HVDC design parameters, and construct rectifier station modules, DC transmission modules, and inverter station modules according to the HVDC design parameters; A power supply with negative feedback regulation characteristics is used to construct a first power supply module and a second power supply module; The first power module, the rectifier station module, the DC transmission module, the inverter station and the second power module are electrically connected in sequence to obtain a primary topology module; Based on PID control logic, build secondary control module; A simulation model of a high-voltage direct current transmission system is constructed by combining the primary topology module and the secondary control module.

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