Real-time simulation modeling method and device for power electronic converter, medium and equipment
The state-space approach with improved Euler's method for power converters addresses transient errors and virtual power losses, achieving efficient and accurate simulation by reducing the admittance matrix order and decoupling direct and alternating current sides.
Patent Information
- Application Number
- CN202510313391.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-17
- Publication Date
- 2025-07-15
AI Technical Summary
When the existing power electronic converter simulation method is modeled through L/C equivalent, it leads to simulation errors and virtual power loss, and the higher harmonics cannot be characterized and cannot meet the needs of real-time simulation.
The improved Euler's discrete state space equation is adopted, the capacitance voltage and inductor current are selected as state variables, the model is established in combination with the switching function, and the controlled power supply and equivalent resistance are equivalent to reduce the model order and avoid the use of energy storage components.
Low-order modeling is realized, the order of the admission matrix is reduced, the simulation efficiency is improved, the virtual power loss and oscillation error are eliminated, and the simulation accuracy is ensured.
Smart Images
Figure CN120317205A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of power system simulation, and in particular to a real-time simulation modeling method, device, medium and equipment for a power electronic converter. Background Art
[0002] Real-time simulation of electromagnetic transients is the guarantee for the safe operation of power systems and the construction of power engineering projects. It is often used for hardware-in-the-loop semi-physical testing and to promote the digital transformation of power systems. In recent years, with the widespread application of power electronic equipment in offshore wind power, distributed power generation, and new energy grid-connected projects, the trend of power electronics in power systems has become increasingly rapid, the complexity of power grids has increased, and fast and slow dynamic characteristics are coupled with each other, resulting in new oscillation and stability problems. Back-to-back voltage source converters are an important part of new power systems. They contain a large number of switching devices, a large number of nodes, a high model order, and a large amount of calculation for inverting the admittance matrix, which seriously restricts the simulation efficiency and cannot meet the needs of real-time simulation in actual projects. The traditional modeling method usually uses the discretization based on the L / C equivalent adjoint circuit to equate the switch to a capacitor and inductor related to the step size, and uses reasonable assignments to keep the admittance matrix unchanged in the simulation, but the number of nodes before and after the equivalent remains unchanged, the order of the model is not reduced, and virtual power loss and transient errors are introduced. There are also studies that use the average value model to equate the port characteristics of the device. This method reduces the order of the model, but ignores high-order harmonics, and the simulation accuracy is limited. Summary of the invention
[0003] The technical problems to be solved by the present invention are:
[0004] For converters, the common existing simulation method is to replace the switching device with L / C for equivalent modeling, and to set appropriate LC parameters to achieve the effect of constant admittance matrix. This method is widely used in current simulation software, which is equivalent to power electronic device level. The order of the model before and after the equivalent remains unchanged, and capacitors and inductors are introduced into the circuit. After the switching action, oscillation will occur, resulting in obvious transient errors. As energy storage elements, the charging and discharging of capacitors and inductors will generate virtual power loss, leading to simulation errors. This problem is aggravated with the increase of switching frequency. The average value model can reduce the model order with the external characteristics of the controlled source equivalent device, but there is a problem that high-order harmonics cannot be represented.
[0005] The present invention adopts the following technical solutions to solve the above technical problems:
[0006] First, for the DC - side capacitor and AC - side inductor of the back - to - back voltage - source converter, select the capacitor voltage and inductor current as state variables, establish the state - space equation and combine it with the power - electronic switch states. Secondly, discretize the state - space equation using the improved Euler method to obtain the discrete - form equation expression, where the variables involved can be divided into the current - step variable values and historical values. Then, represent each historical value with a controlled source and the current - step values with an additional equivalent resistance to obtain the low - order equivalent circuit model in the simulation.
[0007] As a further improvement of the present invention, the state - space equation established using the switching function is:
[0008]
[0009] Among them, the subscripts 1 and 2 are used to distinguish the two AC systems connected to the back - to - back voltage - source converter, namely AC system 1 and AC system 2, v cap_p and v cap_n are the upper and lower capacitor voltages on the DC side respectively, i s is the AC - side inductor current, v s is the grid - side voltage on the AC side, abc represent the three - phase phases respectively, i s1,abc is the column vector composed of the three - phase inductor currents of AC system 1, i s2,abc is the column vector composed of the three - phase inductor currents of AC system 2, v s1,abc is the column vector composed of the three - phase grid - side voltages of AC system 1, v s2,abc is the column vector composed of the three - phase grid - side voltages of AC system 2. Matrices A and B are respectively:
[0010]
[0011] Among them, (1 / L) in matrix B is a 3×3 diagonal matrix, and the element values on the main diagonal are 1 / L. SW upj and SW lowj are the switching states of the upper and lower bridge arms in the j - phase, j = a, b, c. When the switch is on, it is 1, and when it is off, it is 0.
[0012] As a further improvement of the present invention, the discrete form obtained by using the improved Euler method is
[0013]
[0014] Among them, is the predicted value, x V represents the capacitor voltage, x I represents the AC - side inductor current, u V represents the grid - side voltage of the AC system. Matrices A and B are the same as above. After organizing the formula (4), we get
[0015]
[0016] wherein and E is the identity matrix.
[0017] As a further improvement of the present invention, the calculations related to the historical values (at the k-th step) in Equation (5) are combined to obtain an equation in the form of an adjoint circuit:
[0018]
[0019] wherein, (Ts / 2L) is a 3×3 diagonal matrix, and the element values on the main diagonal are Ts / 2L.
[0020] The coefficient matrix of the second term on the right side of Equation (6) related to the variables at the current step is a diagonal matrix, and this matrix is constant under a fixed step size. It shows that the AC-side current is only related to the AC-side voltage, the capacitor voltage value is obtained in the calculation, and the admittance matrix of this simulation model remains unchanged during the simulation, having the characteristic of constant admittance.
[0021] As a further improvement of the present invention, during the calculation, all historical values are stored in advance, the relevant calculations are completed in the form of functions and are equivalent by the method of controlled source assignment. After the current step calculation is completed, the value of the current step is stored as the historical value for the next step calculation. That is, the first term on the right side of Equation (6) is completed in the calculation file and is characterized by a controlled source in the equivalent model, wherein, V comp_his and V comn_his are the combined historical values of the two capacitors on the DC side, and i com11abc_his and i com22abc_his are respectively the combined historical values of the three-phase currents of AC system 1 and AC system 2.
[0022] As a further improvement of the present invention, when calculating the state variables at the current step, the influence of the input variables at the current step is characterized in the equivalent circuit by a parallel equivalent resistance R eq , and the resistance value is twice the AC-side inductance value divided by the simulation step size.
[0023] As a further improvement of the present invention, the AC side of the equivalent model is characterized by an equivalent current source, the DC-side external voltage is obtained during the calculation, and it can be directly interfaced with the external circuit without using a controlled source for equivalence. Through the equivalence, the number of nodes of the back-to-back voltage source converter is reduced from 15 to 7, significantly reducing the order of the admittance matrix.
[0024] The present invention also includes a real-time simulation modeling device for a power electronic converter with multi-stage energy conversion, using the above method, including:
[0025] Acquisition and construction module: For the DC-side capacitor and AC-side inductor of the back-to-back voltage source converter, the capacitor voltage and inductor current are selected as state variables, and the state space equation describing the external characteristics is established by combining the switching function.
[0026] Discretization and assignment module: Based on the improved Euler method, the discrete form equation expression is obtained, and each historical value in the equation is characterized by a controlled power source, and the value of the current step is equivalent in the form of an additional equivalent resistance to obtain a low-order equivalent circuit model in the simulation.
[0027] The present invention also includes a computer storage medium, characterized in that a computer program is stored thereon, and when the computer program is executed by a processor, the steps of the above-described method are implemented.
[0028] The present invention also includes an electronic device, characterized in that it includes a memory and one or more processors, the memory is used to store one or more programs; when the one or more programs are executed by the one or more processors, the above-described method is implemented.
[0029] Compared with the prior art by adopting the above technical solutions, the present invention has the following technical effects:
[0030] The low-order modeling of the back-to-back voltage source converter is realized. Compared with the traditional model, the order of the admittance matrix is greatly reduced, and the simulation efficiency is greatly improved while ensuring the accuracy. The equivalent model is equivalent to the port characteristics, and the AC-side output characteristics are characterized by an equivalent current source. The DC-side external voltage is directly obtained during the calculation process without being characterized by a voltage source, and the AC and DC sides are completely decoupled. In addition, no energy storage devices such as capacitors and inductors are introduced during the equivalent process, and there is no virtual power loss and oscillation error. Description of the drawings
[0031] Figure 1 is the traditional discretization based on the L / C equivalent adjoint circuit.
[0032] Figure 2 is the low-order modeling method of the back-to-back voltage source converter based on improved Euler discretization. Detailed implementation manners
[0033] The technical solutions of the present invention will be further described in detail below with reference to the drawings:
[0034] As Figure 1As shown, the currently common simulation method is based on the adjoint circuit model equivalent to L / C. The switching device in the on state is equivalent to a resistor, and the switching device in the off state is equivalent to a capacitor. When the relationship between the capacitance value, inductance value, and simulation step size satisfies that the simulation step size divided by twice the capacitance value is equal to twice the inductance value divided by the simulation step size, the equivalent resistance values of the capacitance and inductance after simulation discretization are equal, and the admittance matrix during the simulation can be kept constant. However, this method is an equivalent at the power electronic device level, the order of the model remains unchanged before and after the equivalence, and capacitors and inductors are introduced into the circuit. After the switch action, it will cause oscillations and obvious transient errors. Moreover, as energy storage elements, the charging and discharging of capacitors and inductors will generate virtual power losses, resulting in simulation errors.
[0035] As Figure 2 shown, the present invention proposes a low-order modeling method for a back-to-back voltage source converter based on the discretization of the improved Euler method. Selecting the capacitor voltage and inductor current as state variables and combining with the switching function, the state space equation is established as follows:
[0036]
[0037] Among them, the subscripts 1 and 2 are used to distinguish the two AC systems connected to the back-to-back voltage source converter, namely AC System 1 and AC System 2. v cap_p and v cap_n are respectively the upper and lower capacitor voltages on the DC side, i s is the inductor current on the AC side, v s is the grid-side voltage on the AC side, abc respectively represent the three-phase phases, i s1,abc is the column vector composed of the three-phase inductor currents of AC System 1, i s2,abc is the column vector composed of the three-phase inductor currents of AC System 2, v s1,abc is the column vector composed of the three-phase grid-side voltages of AC System 1, v s2,abc is the column vector composed of the three-phase grid-side voltages of AC System 2. The matrices A and B are respectively:
[0038]
[0039] Among them, (1 / L) in the B matrix is a 3×3 diagonal matrix, and the element values on the main diagonal are 1 / L. SW upj and SW lowj are the switching states of the upper and lower bridge arms in the j phase. When the switch is on, it is 1, and when it is off, it is 0, j = a, b, c.
[0040] Discretizing the above equations with Ts as the step size using the improved Euler method, we can obtain:
[0041]
[0042] Among them, is the predicted value, x V represents the capacitor voltage, x I represents the inductor current on the AC side, u V represents the grid-side voltage of the AC system. The matrices A and B are the same as above. After organizing this formula, we get:
[0043]
[0044] Among them and E is the identity matrix.
[0045] Combining the calculations related to the historical value (at the k-th step) variables in the formula, we obtain an equation in the form of an adjoint circuit:
[0046]
[0047] Among them, (Ts / 2L) is a 3×3 diagonal matrix, and the element values on the main diagonal are Ts / 2L.
[0048] When the equivalent model calculates the state variables, all historical values are stored in advance, and the relevant calculations are completed in the form of functions and equivalent by the method of controlled source assignment. After the current step calculation is completed, the value of the current step is stored as the historical value for the next step calculation. That is, the first term on the right side of equation (6) is completed in the calculation file and characterized by a controlled source in the equivalent model. Among them, V comp_his and V comn_his are the combined historical values of the two capacitors on the DC side, i com11abc_his and i com22abc_his are the combined historical values of the three-phase currents of AC system 1 and AC system 2 respectively.
[0049] When calculating the state variables of the current step, the influence of the input variables of the current step is characterized by a parallel equivalent resistance R eq in the equivalent circuit, and the resistance value is twice the value of the AC-side inductor divided by the simulation step size.
[0050] For the second term on the right side of equation (6), the coefficient matrix of the variables related to the current step is a diagonal matrix, and this matrix is constant under a fixed step size. This indicates that the AC-side current is only related to the AC-side voltage, the capacitor voltage value is obtained in the calculation, and the admittance matrix remains unchanged during the simulation. The AC side of the equivalent model is characterized by an equivalent current source. After the DC-side external voltage is obtained during the calculation, it can be directly interfaced with the external circuit without using a controlled source for equivalence. Through equivalence, the number of nodes of the back-to-back voltage source converter is reduced from 15 to 7, significantly reducing the order of the admittance matrix.
Claims
1. A real-time simulation modeling method for a power electronic converter, characterized in that: For the DC-side capacitor and AC-side inductor of a back-to-back voltage source converter, the capacitor voltage and inductor current are selected as state variables, and a state space equation describing the external characteristics is established by combining with the switching function. Based on the improved Euler method, the discrete form equation expression is obtained, and each historical value in the equation is characterized by a controlled power source, and the value of the current step is equivalent in the form of an additional equivalent resistance, so as to obtain a low-order equivalent circuit model in the simulation.
2. The real-time simulation modeling method of the power electronic converter according to claim 1, characterized in that: Taking the capacitor voltage and inductor current as state variables, a state space equation is written by combining with the switching function, and the expression of the state space equation is: Among them, the subscripts 1 and 2 are used to distinguish the two AC systems connected to the back-to-back voltage source converter, namely AC system 1 and AC system 2, v cap_p and v cap_n are the upper and lower capacitor voltages on the DC side respectively, i s is the inductor current on the AC side, v s is the grid-side voltage on the AC side, abc respectively represent the three-phase phases, i s1,abc is the column vector composed of the three-phase inductor currents of AC system 1, i s2,abc is the column vector composed of the three-phase inductor currents of AC system 2, v s1,abc is the column vector composed of the three-phase grid-side voltages of AC system 1, v s2,abc is the column vector composed of the three-phase grid-side voltages of AC system 2; the matrices A and B are respectively: Among them, 1 / L in matrix B is a 3×3 diagonal matrix, and the element values on the main diagonal are 1 / L; SW upj and SW lowj are the switching states of the upper and lower bridge arms of phase j, where j = a, b, c.
3. The real-time simulation modeling method of the power electronic converter according to claim 2, characterized in that: Using the improved Euler method, the state space equation is discretized with a step size of T s to obtain: Among them, is the predicted value for the next step, x V represents the capacitor voltage, x I represents the inductor current on the AC side, u V represents the grid-side voltage of the AC system; after combination, it is written as: wherein and E is the identity matrix.
4. The real-time simulation modeling method of the power electronic converter according to claim 3, characterized in that: The calculations related to the historical value of the k-th step in the equation are combined to obtain an equation in the form of an adjoint circuit: Among them, Ts / 2L is a 3×3 diagonal matrix, and the element values on the main diagonal are Ts / 2L; in the first term, V comp_his and V comn_his are the historical values after combining the two capacitors on the DC side, and i com11abc_his and i com22abc_his are the historical values after combining the three-phase currents of AC system 1 and AC system 2 respectively. The coefficient matrix of the second term on the right side of the equal sign is a diagonal matrix; the AC-side current is only related to the AC-side voltage, and the capacitor voltage value is obtained in the calculation.
5. The real-time simulation modeling method of the power electronic converter according to claim 4, characterized in that: When calculating the current step, all historical values are stored in advance, the relevant calculations are completed in the form of a function and equivalent by the method of assigning a controlled power source. After the current step calculation is completed, the value of the current step is stored as the historical value for the next step calculation, that is, the first term on the right side of equation (6) is completed in the calculation file and characterized by a controlled power source in the equivalent model.
6. The real-time simulation modeling method of the power electronic converter according to claim 5, characterized in that: When calculating the state variables of the current step, the influence of the input variables of the current step is characterized by a parallel equivalent resistance R in the equivalent circuit. eq The resistance value is twice the value of the AC-side inductor divided by the simulation step size.
7. The real-time simulation modeling method of the power electronic converter according to claim 6, characterized in that: The AC side of the equivalent model is characterized by an equivalent current source, and the DC side external voltage is obtained during the calculation process, which can be directly interfaced with the external circuit without using a controlled source for equivalence; through equivalence, the number of nodes of the back-to-back voltage source converter is reduced from 15 to 7, reducing the order of the admittance matrix.
8. A real-time simulation modeling device for a power electronic converter, characterized in that The method adopted is as described in any one of claims 1-7, including An acquisition and construction module: For the DC-side capacitor and AC-side inductor of a back-to-back voltage source converter, the capacitor voltage and inductor current are selected as state variables, and a state space equation describing the external characteristics is established by combining with the switching function. A discretization and assignment module: Based on the improved Euler method, the discrete form equation expression is obtained, and each historical value in the equation is characterized by a controlled power source, and the value of the current step is equivalent in the form of an additional equivalent resistance, so as to obtain a low-order equivalent circuit model in the simulation.
9. A computer storage medium, characterized in that, On which a computer program is stored, and when the computer program is executed by a processor, the steps of the method described in any one of claims 1 to 7 are implemented.
10. An electronic device, characterized in that, It includes a memory and one or more processors, and the memory is used to store one or more programs; when the one or more programs are executed by the one or more processors, the method described in any one of claims 1 to 7 is implemented.