A simulation method and system for the electromechanical transient multi-rate of a flexible DC system

Abstract

The present invention provides a simulation method and system for the electromechanical transient multi-rate of a flexible DC system, including: setting the AC network interface position in the flexible DC system as the converter voltage modulation point; simulating the DC network and the converter in the flexible DC system with an hourly time step to obtain the vector of the internal potential of the converter; obtaining the average value of the internal potential in each hourly time step according to the voltage amplitude and phase angle of the internal potential of the converter in each hourly time step of the DC network, and using the average value as the interface variable; and obtaining the injected current of the DC network; incorporating the parallel equivalent impedance into the AC network so that the DC side transfers the interface variable to the AC side, thereby completing the simulation of the electromechanical transient multi-rate of the flexible DC system. The problem of poor accuracy of the existing electromechanical transient multi-rate simulation in the scenario of a passive network accessing a flexible DC system is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply for passive networks and simulation technology for flexible DC systems for new energy transmission, and particularly relates to a simulation method and system for the electromechanical transient multi-rate of a flexible DC system. Background Art

[0002] A prominent advantage of flexible DC transmission is that it can perform passive inversion, that is, its power sending and receiving ends can be power grids without AC synchronous power sources. Power supply for passive networks refers to power supply to urban load centers or to passive islands, and the new energy transmission system refers to new energy units being connected to the power grid through a flexible DC system. Both require the flexible DC system to provide a synchronous AC power source.

[0003] When one end of a flexible DC transmission system is a passive network, the converter at that end needs to establish a synchronous AC power source. In actual engineering, the voltage amplitude and frequency targets of the AC side of the AC transformer valve need to be given, and the AC voltage is maintained through devices such as control, triggering, and turn-off thyristors. Compared with the traditional line-commuted converter (LCC) DC transmission method, flexible DC transmission can control the modulation voltage amplitude and phase by controlling the opening and closing of the control valves, increasing the control freedom of the modulation quantity from one to two, that is, two of the electrical quantities such as AC voltage amplitude, phase, frequency, active power, reactive power, and DC voltage can be controlled simultaneously. For an electrical island without a synchronous AC power source, the flexible DC undertakes the function of controlling the AC voltage amplitude and frequency, and thus has no ability to control other electrical quantities. The active and reactive powers absorbed by the converter are uncontrollable and are determined by the phasor difference between the modulation voltage and the grid voltage. At the same time, it is necessary for the converter station of the flexible DC system on the electrical island with an AC power source to undertake the task of controlling the DC voltage.

[0004] When jointly simulating an AC power grid, a flexible DC converter, and a DC power grid, it is not necessary to adopt exactly the same simulation step size because the primary and secondary systems of the converter station of the flexible DC transmission system have a much higher response speed than that of the AC power grid. If a relatively large simulation step size is adopted as a whole, the characteristics of the fast regulation of the converter station controller and the high-speed switching of the converter valve of the flexible DC transmission system cannot be accurately reflected; if a relatively small simulation step size is adopted as a whole, the calculation speed drops significantly and the calculation time is prolonged. In fact, the electromechanical equipment in the AC power grid has a large time constant, and adopting too small a simulation step size will cause waste of computing resources. At the same time, in the traditional scheme, the power on the valve side of the transformer of the passive network (new energy) in the power supply for passive networks and the flexible DC system for new energy transmission is used as the interface of the AC network. This interface method ignores the characteristics of the converter on the passive side (new energy side) to control the voltage amplitude and frequency of its AC side, resulting in insufficient accuracy. Summary of the Invention

[0005] To solve the above problems, the present invention provides a simulation method for the electromechanical transient multi-rate of a flexible DC system, including:

[0006] Set the AC network interface position in the flexible DC system as the converter voltage modulation point;

[0007] Simulate the DC network and the converter in the flexible DC system with a small time step to obtain the vector of the internal potential of the converter;

[0008] According to the voltage amplitude and phase angle of the internal potential of the converter at each small time step of the DC network, obtain the average value of the internal potential at each small time step, and use the average value as the interface variable; and obtain the injection current of the DC network;

[0009] Incorporate the parallel equivalent impedance into the AC network to transfer the interface variable from the DC side to the AC side, and complete the simulation of the electromechanical transient multi-rate of the flexible DC system.

[0010] Further, according to the voltage amplitude and phase angle of the internal potential of the converter at each small time step of the DC network, obtaining the average value of the internal potential at each small time step and using the average value as the interface variable includes:

[0011] Through small time step simulation, obtain the vector U of the internal potential of the converter ck ;

[0012] According to the voltage amplitude and phase angle formula, use the average value of the internal potential at each small time step as the interface variable. The voltage amplitude and phase angle formula is specifically

[0013]

[0014]

[0015] In the above formula, |U c | k and θ ck respectively represent the voltage amplitude and phase angle of the internal potential of the converter at each small time step of the DC power grid; |U c | N and θ cN respectively represent the voltage amplitude and phase angle of the internal potential of the converter output at this time step.

[0016] Further, for the converter, the dq decoupling control method is adopted to convert each control quantity and controlled quantity into variables represented under the dq axis;

[0017] For the converter valve of the converter, an average value model is adopted. The structure of the average value model is: on the AC side, the converter is simulated as an ideal voltage source containing only fundamental components, and on the DC side, the converter is simulated as an ideal current source and a concentrated capacitor;

[0018] According to the average value model, the per-unit current equations of the converter in the d,q coordinates of the converter valve are as follows:

[0019]

[0020] U sd and U sq are the voltage components in the d-axis and q-axis respectively, and I sd and I sq are the components of the current injected by the converter into the AC side in the d-axis and q-axis respectively. L and R are the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer;

[0021] According to the amplitude |U s | and phase angle θ s of U s , the voltage component in the RI axis can be obtained. When transforming from the dq axis to the RI coordinates, the matrix T is used, where δ is the voltage phase angle calculated and output by the converter frequency regulator. The specific matrix T is:

[0022]

[0023] Furthermore, the converter adopts a voltage-frequency control mode, and the control mode includes an inner loop control and an outer loop control.

[0024] The present invention also provides a simulation system for the electromechanical transient multi-rate of a flexible DC system, including:

[0025] An interface position setting unit for setting the AC network interface position in the flexible DC system as the converter voltage modulation point;

[0026] A vector acquisition unit for simulating the DC network and the converter in the flexible DC system with a small time step to obtain the vector of the internal potential of the converter;

[0027] An interface variable acquisition unit for obtaining the average value of the internal potential for each time step according to the voltage amplitude and phase angle of the internal potential of the converter in the DC network at each time step, using the average value as the interface variable; and obtaining the injected current of the DC network;

[0028] A simulation unit for incorporating the parallel equivalent impedance into the AC network to transfer the interface variable from the DC side to the AC side, thereby completing the simulation of the electromechanical transient multi-rate of the flexible DC system.

[0029] Furthermore, the interface variable acquisition unit includes:

[0030] A vector acquisition subunit for obtaining the vector U ck of the internal potential of the converter through small time step simulation;

[0031] An interface variable acquisition subunit, which is used to take the average value of the potential in each hourly step as an interface variable according to the voltage amplitude and phase angle formula. The specific voltage amplitude and phase angle formula is as follows:

[0032]

[0033]

[0034] In the above formula, |U c | k and θ ck respectively represent the voltage amplitude and phase angle of the potential in the converter within each hourly step of the DC power grid; |U c | N and θ cN respectively represent the voltage amplitude and phase angle of the potential in the converter output in this hourly step.

[0035] Furthermore, the converter adopts a dq decoupling control method to convert each control quantity and controlled quantity into variables represented under the dq axes;

[0036] The converter valve of the converter adopts an average value model. The structure of the average value model is: on the AC side, the converter is simulated as an ideal voltage source containing only the fundamental component, and on the DC side, the converter is simulated as an ideal current source and a concentrated capacitor; 4

[0037] According to the average value model, the per-unit current equation of the converter in the d, q coordinates of the converter valve is as follows:

[0038]

[0039] U sd and U sq are respectively the voltage components under the d and q axes, I sd and I sq are respectively the components of the current injected by the converter into the AC side under the d and q axes; L and R are respectively the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer;

[0040] According to the amplitude |U s | and phase angle θ s | of U s the voltage component under the RI axis can be obtained. When transforming from the dq axes to the RI coordinates, the matrix T is used, where δ is the voltage phase angle calculated and output by the converter frequency regulator. The specific matrix T is as follows:

[0041]

[0042] Furthermore, the converter adopts a voltage-frequency control mode, and the control mode includes an inner loop control and an outer loop control.

[0043] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned methods are implemented.

[0044] The present invention also provides a readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of any one of the above-mentioned methods are implemented.

[0045] The present invention provides a simulation method and system for the electromechanical transient multi-rate of a flexible DC system. By changing the AC network interface position in the flexible DC system powered by a passive network and sending out new energy to the converter voltage modulation point, and combining the multi-rate simulation technology, the accuracy of the electromechanical transient simulation is improved by simulating the actual control process of the converter, and the problem of poor accuracy of the existing electromechanical transient multi-rate simulation in the scenario of a flexible DC system connected to a passive network is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a schematic flow chart of a simulation method for the electromechanical transient multi-rate of a flexible DC system provided by an embodiment of the present invention;

[0047] Figure 2 is a schematic structural diagram of a flexible DC system powered by a passive network and sending out new energy related to an embodiment of the present invention;

[0048] Figure 3 is a schematic diagram of the multi-rate simulation principle of an AC-DC hybrid power grid related to an embodiment of the present invention;

[0049] Figure 4 is a block diagram of the multi-rate simulation calculation of an AC-DC hybrid power grid related to an embodiment of the present invention;

[0050] Figure 5 is a structural diagram of the AC system after the improved interface Norton equivalence related to an embodiment of the present invention;

[0051] Figure 6 is an outer loop control block diagram related to an embodiment of the present invention;

[0052] Figure 7 is a block diagram of the DC network hourly step simulation calculation related to an embodiment of the present invention;

[0053] Figure 8 is a schematic structural diagram of a simulation system for the electromechanical transient multi-rate of a flexible DC system provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0055] As Figure 1 shown, the present invention provides a simulation method for the electromechanical transient multi-rate of a flexible DC system, including the following steps:

[0056] Step S101, set the AC network interface position in the flexible DC system as the converter voltage modulation point.

[0057] In the traditional scheme, the power on the valve side of the converter transformer in the passive network power supply and new energy output flexible DC system is used as the AC network interface. This interface method ignores the characteristics of the converter on the passive side (new energy side) to control the voltage amplitude and frequency of its AC side, resulting in insufficient accuracy. In the present invention, this AC network interface technology is improved, and the interface position is modified from the valve side of the converter transformer to the converter voltage modulation point. In actual engineering, the AC voltage control target needs to be given, and the AC voltage and frequency are maintained through devices such as control, triggering, and turn-off thyristors. This control method of the converter is called the AC side voltage and frequency control method. The structural schematic diagram of the system is as shown in the appendix Figure 2 shown.

[0058] Step S102, simulate the DC network and the converter in the flexible DC system with a small time step to obtain the vector of the internal potential of the converter.

[0059] Through small time step simulation, obtain the vector U of the internal potential of the converter ck ;

[0060] According to the voltage amplitude and phase angle formula, take the average value of the internal potential in each small time step as the interface variable. The voltage amplitude and phase angle formula is specifically

[0061]

[0062]

[0063] In the above formula, |U c | k , θ ck respectively represent the voltage amplitude and phase angle of the internal potential of the converter in each small time step of the DC power grid; |U c | N , θ cN respectively represent the voltage amplitude and phase angle of the internal potential of the converter output in this time step.

[0064] Step S103: Obtain the average value of the internal potential within each hour step based on the amplitude and phase angle of the internal potential voltage in the DC network for each hour step, and use this average value as the interface variable; and obtain the injected current of the DC network.

[0065] The internal potential vector U is obtained through hourly step simulation ck After that, based on the voltage amplitude and phase angle formula, use the average value of the internal potential within each hour step as the interface variable, and obtain the DC network injected current I through Norton equivalent c .

[0066] For the converter, adopt the dq decoupling control method to convert each control quantity and the quantity to be controlled into variables represented under the dq axes;

[0067] For the converter valve of the converter, adopt the average value model. The structure of the average value model is: on the AC side, the converter is simulated as an ideal voltage source containing only the fundamental component, and on the DC side, the converter is simulated as an ideal current source and a concentrated capacitor;

[0068] According to the average value model, the per-unit current equation of the converter in the d and q coordinates of the converter valve is as follows,

[0069]

[0070] U sd 、U sq are the voltage components under the d and q axes respectively, and I sd 、I sq are the components of the current injected by the converter into the AC side under the d and q axes respectively. L and R are the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer;

[0071] According to the amplitude |U s | and phase angle θ s of U s , the voltage component under the RI axis can be obtained. When transforming from the dq axes to the RI coordinates, the matrix T is used, where δ is the voltage phase angle calculated and output by the converter frequency regulator. The specific matrix T is,

[0072]

[0073] For the converter, adopt the voltage-frequency control mode, and this control mode includes inner-loop control and outer-loop control.

[0074] To achieve a constant voltage source on the AC side, the outer-loop control strategy can be simply designed as: use a PI controller to make U sd obtained by calculating the phase angle output by the converter frequency regulator follow the reference value U sdref , and output I sdref to control the voltage amplitude; also use a PI controller to make U sq constantly follow the specified value Usqref = 0 to maintain a constant frequency, output I sdref . I sdref and I sqref are the input parameters for the inner loop control. When input, I sdref is limited by an upper limit I dmax as shown in the attached Figure 6 outer loop control mode.

[0075] The function of the inner loop controller is to adjust the common-mode and differential-mode voltage values so that I sq and I sd track the current reference values I sqref and I sdref input from the outer loop to achieve the corresponding mode of the outer loop control. The response controller involved in the inner loop controller already has a relatively mature electromechanical transient simulation method. Since the AC control point is the busbar on the grid side of the converter transformer, but the control system senses the voltage at the control point not as the primary voltage, but as the secondary voltage processed through input links such as measurement and filtering, therefore, during simulation, the measurement is simulated using a first-order inertia link, and the filtering is simulated using a second-order low-pass filter. The inner loop controller gives the DC-side voltage reference values U cdref and U cqref based on the current reference values input from the outer loop. After passing through the delay link of the analog modulation process, the obtained U cd and U cq are obtained so that I sd and I sq track I sdref and I sqref as shown in the inner loop control part of the attachment Figure 6 .

[0076] In the inner loop and outer loop controls, U sd , U sq are the voltage components in the d and q axes respectively;

[0077] U sdref , U sqref = 0 represent the input reference values corresponding to the outer loop controller and U sd , U sq respectively, and are given known parameters;

[0078] I sd , I sq are the components of the current injected into the AC side of the converter in the d and q axes respectively;

[0079] I sdref , I sqref represent the output reference values corresponding to the outer loop controller and I sd , I sq respectively, and are provided for use by the inner loop controller;

[0080] U cdref and U cqref respectively represent the inner loop controller and U cd and U cq corresponding output reference values, which are provided to the converter valve.

[0081] Step S104, incorporate the parallel equivalent impedance into the AC network to transfer the interface variables from the DC side to the AC side, and complete the electromechanical transient multi-rate simulation of the flexible DC system.

[0082] Meanwhile, incorporate the parallel equivalent impedance Z eq into the AC network to complete the interface process of transferring variables from the DC side to the AC side. Its equivalent form is as shown in the appendix Figure 5 shown. Obviously, when using this interface method, the valve-side voltage of the converter transformer does not need to be used as a constant voltage frequency source.

[0083] Specifically, the multi-rate electromechanical transient simulation scheme is as follows:

[0084] The application scenario of this patent is the electromechanical transient simulation scheme of the converter on the passive side (new energy side) of the flexible DC system for power supply from a passive network and new energy transmission.

[0085] The multi-rate AC-DC hybrid power grid electromechanical transient simulation refers to a method in which the AC power grid uses a large time step T ac , the DC power grid and its converters use a small time step T dc for simulation, and T ac / T dc ∈N + , where N + is the set of positive integers. During the calculation, the AC power grid is integrated with a large time step, the valve-side voltage vector of the converter transformer is transmitted into the DC power grid through the DC network interface, the DC power grid is integrated with a small time step and the variables are transmitted back through the AC network interface, and finally, AC-DC iteration is performed to ensure accuracy. Its basic steps are as follows:

[0086] a) At the Nth time step, the simulation of the AC power grid starts, and the small time step loop parameter k = 0 is set;

[0087] b) Let the DC network interface value U sN(k) = U sN-1 , where: U sN(k) is the iteration quantity of the valve-side voltage vector of the converter transformer at the small time step, and U sN-1 is the iteration quantity of the valve-side voltage vector of the converter transformer determined at the previous large time step of the AC power grid.

[0088] c) According to the ratio of the large and small time steps N stp as shown in Equation (1), between U sN(k) and U sN-1Perform linear interpolation, solve the converter and the corresponding DC grid using hourly step integration, obtain the current injected into the AC grid, and transfer it to the AC grid through the AC grid interface; at the same time, integrate each dynamic element in the AC grid by one step to obtain the injected current;

[0089]

[0090] d) Solve the DC grid interface value U according to the current injected into the AC grid by the DC converter and the current injected by the dynamic elements of the AC grid sN(k+1) ;

[0091] e) Let k = k + 1, and iterate steps c)-d) until |U sN(k+1) -U sN(k) | is less than the set error eps;

[0092] f) Enter the large hourly step simulation of the N+1 AC grid.

[0093] Appendix Figure 3 is a conceptual diagram of multi-rate simulation calculation. The dashed arrows in the figure correspond to the iterative process in step e). The simulation calculation block diagram of the AC-DC hybrid grid is as shown in Appendix Figure 4 shown.

[0094] In traditional electromechanical simulation, the AC grid interface position in step c) is the valve side point of the converter transformer, and the interface variable is the power P s +jQ s transported by the passive side (new energy side). During electromechanical simulation, the valve side voltage U s of the converter transformer needs to be regarded as a constant voltage frequency source at each hourly step of the DC grid. The injected power obtained by calculation at the k-th hourly step is P k +jQ k , and the specific calculation formula is as shown in Equation (2).

[0095]

[0096] After the calculation is completed, calculate the average value of the power at each hourly step according to Equation (3) and inject the current into the AC grid.

[0097]

[0098] The present invention improves this AC grid interface technology, modifies the interface position from the valve side of the converter transformer to the voltage modulation point of the converter, and uses the amplitude and phase angle of the internal potential U c inside the modulation point converter as the interface variables. After obtaining the internal potential vector U ck through hourly step simulation, use the average value of the internal potential at each hourly step as the interface variables according to Equations (4) and (5), and obtain the DC grid injected current I c through Norton equivalent. At the same time, use the parallel equivalent impedance Z eqThe interface process of incorporating into the AC network to complete the transfer of variables from the DC side to the AC side, and its equivalent form is as shown in the appendix. Figure 5 Obviously, when adopting this interface method, the valve-side voltage of the converter transformer does not need to be used as a constant voltage frequency source.

[0099]

[0100]

[0101] In the formula, |U c | k and θ ck respectively represent the amplitude and phase angle of the internal potential voltage of the converter within each hour step of the DC grid. |U c | N and θ cN respectively represent the amplitude and phase angle of the internal potential voltage of the converter output at this time step.

[0102] The converter controller of the flexible DC transmission system adopts the dq decoupling control method. Therefore, each control quantity and the controlled quantity need to be converted into variables represented under the dq axis. In the electromechanical transient simulation, the converter valve adopts the average value model. The structure of the average value model is: on the AC side, the converter is simulated as an ideal voltage source containing only the fundamental component, and on the DC side, the converter is simulated as an ideal current source and a concentrated capacitor. According to this model, the per-unit current equation of the converter in the d, q coordinates of the converter valve is as shown in Equation (6).

[0103]

[0104] U sd and U sq are respectively the voltage components under the d and q axes, I sd and I sq are respectively the components of the current injected by the converter into the AC side under the d and q axes, and L and R are respectively the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer. The two fractional expressions are respectively the dynamic equations of the d and q axis converters obtained according to the average value model, and the electrical quantities involved in the formula are all phasors. According to the amplitude |U s | and phase angle θ s of U s , the voltage component under the RI axis can be obtained. When transforming from the dq axis to the RI coordinate, matrix (7) is adopted, where δ is the voltage phase angle calculated and output by the converter frequency regulator.

[0105]

[0106] The converter involved in the present invention adopts a voltage - frequency control mode. There are many ways to design and implement the controller under the voltage - frequency control mode. The present invention needs to protect any control type that can perform electromechanical transient simulation using the interface method proposed in this patent. Here, common voltage - frequency control strategies are given. The control mode of the converter includes inner - loop control and outer - loop control. Their simulation methods are introduced specifically respectively.

[0107] To achieve a constant - voltage source on the AC side, the outer - loop control strategy can be simply designed as follows: Use a PI controller to make the U obtained by calculating the phase angle output by the converter frequency regulator sd follow the reference value U sdref , and output I sdref to control the voltage amplitude; also use a PI controller to make U sq constantly follow the specified value U sqref = 0 to maintain a constant frequency, and output I sdref . I sdref and I sqref are the input parameters of the inner - loop control. When inputting, perform an upper - limit I sdref limitation on I dmax , as shown in the outer - loop control mode in the appendix Figure 6 .

[0108] The function of the inner - loop controller is to adjust the common - mode and differential - mode voltage values, so that I sq and I sd track the current reference values I sqref and I sdref input from the outer - loop to achieve the corresponding mode of the outer - loop control. The response controller involved in the inner - loop controller already has a relatively mature electromechanical transient simulation method. Since the AC control point is the busbar on the grid side of the converter transformer, but the control - system - perceived control - point voltage is not the primary voltage, but the secondary voltage processed through input links such as measurement and filtering, during simulation, the measurement is simulated using a first - order inertia link, and the filtering is simulated using a second - order low - pass filter. The inner - loop controller gives the DC - side voltage reference values U cdref and U cqref of the converter valve according to the current reference values input from the outer - loop, and then through the delay link of the analog modulation process, the U cd and U cq in Equation (1) are obtained, so that I sd and I sq track I sdref and I sqref , as shown in the inner - loop control part in the appendix Figure 6 .

[0109] U sd 、U sq are the voltage components under the d - axis and q - axis respectively;

[0110] Usdref , U sqref = 0 respectively represent the input reference values corresponding to the outer - loop controller and U sd , U sq respectively, which are given known parameters;

[0111] I sd , I sq are respectively the components of the current injected by the converter into the AC side under the d - and q - axes;

[0112] I sdref , I sqref respectively represent the output reference values corresponding to the outer - loop controller and I sd , I sq respectively, which are provided for the inner - loop controller to use;

[0113] U cdref and U cqref respectively represent the output reference values corresponding to the inner - loop controller and U cd and U cq respectively, which are provided for the converter valve.

[0114] The above is the simulation model of the DC converter and its controller. The simulation steps with a small time step (i.e., the simulation steps of the DC power grid with a small time step in the attachment Figure 3 ) are as follows:

[0115] a) Obtain the AC - side interface data;

[0116] b) Check whether the DC network protection acts;

[0117] c) Update the DC network current source and the equivalent conductance matrix;

[0118] d) Convert the measured quantity to the dq - axis through Equation (7);

[0119] e) Calculate the outer - loop control;

[0120] f) Calculate the inner - loop control;

[0121] g) Obtain U cdref and U cqref and obtain U cd and U cq after passing through the delay link representing the modulation process;

[0122] h) Calculate I sd and I sq ;

[0123] i) Iterate the DC network until the accuracy requirement is met and solve the current injected into the AC network.

[0124] The corresponding block diagram is as shown in the attachment Figure 7 .

[0125] Based on the same inventive concept, the present invention also provides a simulation system for the electromechanical transient multi-rate of a flexible DC system. As Figure 8 shown, it includes:

[0126] An interface position setting unit 810, configured to set the AC network interface position in the flexible DC system as the converter voltage modulation point;

[0127] A vector acquisition unit 820, configured to simulate the DC network and the converter in the flexible DC system by small time steps to obtain the vector of the internal potential of the converter;

[0128] An interface variable acquisition unit 830, configured to obtain the average value of the internal potential in each time step according to the voltage amplitude and phase angle of the internal potential of the converter in each time step of the DC network, and use the average value as the interface variable; and obtain the injected current of the DC network;

[0129] A simulation unit, configured to incorporate the parallel equivalent impedance into the AC network so that the DC side transfers the interface variable to the AC side to complete the electromechanical transient multi-rate simulation of the flexible DC system.

[0130] Furthermore, the interface variable acquisition unit includes:

[0131] A vector acquisition subunit, configured to obtain the vector U of the internal potential of the converter through small time step simulation ck ;

[0132] An interface variable acquisition subunit, configured to use the average value of the internal potential in each time step as the interface variable according to the voltage amplitude and phase angle formula, and the voltage amplitude and phase angle formula is specifically

[0133]

[0134]

[0135] In the above formula, |U c | k , θ ck respectively represent the voltage amplitude and phase angle of the internal potential of the converter in each time step of the DC power grid; |U c | N , θ cN respectively represent the voltage amplitude and phase angle of the internal potential of the converter output in this time step.

[0136] Furthermore, the converter adopts a dq decoupling control method to convert each control quantity and controlled quantity into variables represented under the dq axis;

[0137] The converter valve of the converter adopts an average value model, and the structure of the average value model is as follows: on the AC side, the converter is simulated as an ideal voltage source containing only fundamental components, and on the DC side, the converter is simulated as an ideal current source and a concentrated capacitor; 11

[0138] According to the average value model, the per-unit current equations of the converter in the d and q coordinates of the converter valve are as follows,

[0139]

[0140] U sd and U sq are the voltage components in the d and q axes respectively, and I sd and I sq are the components of the current injected by the converter into the AC side in the d and q axes respectively. L and R are the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer;

[0141] According to the amplitude |U s | of U s and the phase angle θ s of U

[0142]

[0143] Further, the converter adopts a voltage-frequency control mode, and the control mode includes an inner-loop control and an outer-loop control.

[0144] The present invention provides a method and system for electromechanical transient multi-rate simulation of a flexible DC system. When performing electromechanical transient simulation on a flexible DC system for power supply from a passive network and new energy output, the AC network interface position is changed from the valve side of the converter transformer to the voltage modulation point of the converter, and the interface variables are changed from power values to the amplitude and phase angle of the internal electromotive force of the converter. At the same time, a multi-rate simulation technology is combined to improve the simulation efficiency and accuracy.

[0145] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0146] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce means for implementing the functions specified in the process Figure 1 one process or multiple processes and / or blocks Figure 1 means for implementing the functions specified in one block or multiple blocks.

[0147] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that implement the functions specified in the process Figure 1 one process or multiple processes and / or blocks Figure 1 means for implementing the functions specified in one block or multiple blocks.

[0148] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operating steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in the process Figure 1 one process or multiple processes and / or blocks Figure 1 means for implementing the functions specified in one block or multiple blocks.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the specific implementation manners of the present invention can still be modified or equivalently replaced. Any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A simulation method for the electromechanical transient multi-rate of a flexible DC system, Characterized in that, It includes: Set the AC network interface position in the flexible DC system as the converter voltage modulation point; Simulate the DC network and the converter in the flexible DC system with a small time step to obtain the vector of the internal potential of the converter; According to the voltage amplitude and phase angle of the converter's internal potential in each time step of the DC network, obtain the average value of the internal potential in each time step, and use the average value as the interface variable; and obtain the injection current of the DC network; Incorporate the shunt equivalent impedance into the AC network to enable the DC side to transfer the interface variable to the AC side, and complete the electromechanical transient multi-rate simulation of the flexible DC system; The converter adopts the dq decoupling control method to convert each control quantity and controlled quantity into variables represented under the dq axis; The converter valve of the converter adopts an average value model, and the structure of the average value model is: the converter on the AC side is simulated as an ideal voltage source containing only fundamental components, and the converter on the DC side is simulated as an ideal current source and a concentrated capacitor; According to the average value model, the per-unit current equation of the converter in the d and q coordinates of the converter valve is as follows, U sd and U sq are the voltage components under the d- and q-axes respectively, and I sd and I sq are the components of the current injected by the converter into the AC side under the d- and q-axes respectively. L and R are the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer; According to U s amplitude |U s | and phase angle θ s the voltage component under the RI axis can be obtained. When performing the dq-axis to RI coordinate transformation, the matrix T is used, where δ is the voltage phase angle calculated and output by the converter frequency regulator. The specific matrix T is as follows:

2. The method according to claim 1, Characterized in that, According to the voltage amplitude and phase angle of the converter's internal potential in each time step of the DC network, obtain the average value of the internal potential in each time step, and use the average value as the interface variable, including: Through hourly step simulation, the vector U of the internal potential of the converter is obtained ck ; According to the voltage amplitude and phase angle formula, use the average value of the internal potential in each time step as the interface variable, and the voltage amplitude and phase angle formula is specifically, In the above formula, |U c | k , θ ck respectively represent the amplitude and phase angle of the potential voltage in the converter for each hour step of the DC power grid; |U c | N , θ cN respectively represent the amplitude and phase angle of the potential voltage in the converter output at this time step.

3. The method according to claim 1, Characterized in that, The converter adopts a voltage-frequency control mode, and the control mode includes an inner loop control and an outer loop control.

4. A simulation system for the electromechanical transient multi-rate of a flexible DC system, Characterized in that, It includes: An interface position setting unit for setting the AC network interface position in the flexible DC system as the converter voltage modulation point; A vector acquisition unit for simulating the DC network and the converter in the flexible DC system with a small time step to obtain the vector of the internal potential of the converter; An interface variable acquisition unit for obtaining the average value of the internal potential in each time step according to the voltage amplitude and phase angle of the converter's internal potential in each time step of the DC network, and using the average value as the interface variable; and obtaining the injection current of the DC network; A simulation unit for incorporating the shunt equivalent impedance into the AC network to enable the DC side to transfer the interface variable to the AC side, and complete the electromechanical transient multi-rate simulation of the flexible DC system; The converter adopts the dq decoupling control method to convert each control quantity and controlled quantity into variables represented under the dq axis; The converter valve of the converter adopts an average value model, and the structure of the average value model is: the converter on the AC side is simulated as an ideal voltage source containing only fundamental components, and the converter on the DC side is simulated as an ideal current source and a concentrated capacitor; According to the average value model, the per-unit current equation of the converter in the d and q coordinates of the converter valve is as follows, U sd and U sq are the voltage components under the d-axis and q-axis respectively, and I sd and I sq are the components of the current injected by the converter into the AC side under the d-axis and q-axis respectively. L and R are the equivalent inductance and resistance from the voltage modulation point to the valve side of the converter transformer; According to the amplitude of U s |U s | and the phase angle θ s the voltage component under the RI axis can be obtained. When performing the dq-axis to RI coordinate transformation, the matrix T is used, where δ is the voltage phase angle calculated and output by the converter frequency regulator. The specific form of the matrix T is as follows:

5. The system according to claim 4, Characterized in that, The interface variable acquisition unit includes: A vector acquisition subunit, configured to obtain a vector U of the internal potential of a converter through hourly-step simulation ck ; An interface variable acquisition subunit, configured to use the voltage amplitude and phase angle formula to take the average value of the potential within each hour step as the interface variable, and the voltage amplitude and phase angle formula is specifically as follows: In the above formula, |U c | k , θ ck respectively represent the amplitude and phase angle of the potential voltage in the converter for each hour step of the DC grid; |U c | N , θ cN respectively represent the amplitude and phase angle of the potential voltage in the converter output at this time step.

6. The system according to claim 4, wherein, the converter adopts a voltage-frequency control mode, and the control mode includes an inner loop control and an outer loop control.

7. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein, when the processor executes the computer program, the steps of the method according to any one of claims 1 to 3 are implemented.

8. A readable storage medium, having a computer program stored thereon, wherein, when the computer program is executed by the processor, the steps of the method according to any one of claims 1 to 3 are implemented.

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