Thermal-electrical real-time simulation method for hybrid DC circuit breaker with superconducting current limiter

Abstract

A thermal-electric combined real-time simulation technology for a hybrid DC circuit breaker containing a superconducting current limiter. The hybrid DC circuit breaker (DCCB) mainly consists of three branches consisting of a fast mechanical circuit breaker, a power electronic switch and an MOV. The three parallel branches are respectively called a main branch, a transfer branch and an energy release branch. The main branch is composed of a fast mechanical circuit breaker, a superconducting current limiter and a power electronic switch in series. The working current flows through the main branch for power transmission, and the superconducting current limiter limits the fault current. In order to accurately simulate the real-time simulation performance of a hybrid DCCB with a superconducting current limiter, the present invention proposes a thermal-electric coupled real-time simulation technology for a hybrid DC circuit breaker (DCCB) containing a superconducting current limiter. The heat of the superconducting current limiter is calculated by real-time simulation to obtain the real-time resistance value of the superconducting current limiter, and the resistance value of the superconducting current limiter in the electromagnetic transient simulation is updated. The simulation accuracy is improved through thermal-electric combined simulation.

Description

Technical Field

[0001] The present invention relates to a real-time simulation technology of a hybrid direct current circuit breaker, and in particular to a thermal-electrical combined real-time simulation method of a hybrid direct current circuit breaker (DCCB) containing a superconducting current limiter. Background Art

[0002] With the rapid development of new sources and loads such as wind power, photovoltaics, energy storage, and electric vehicles, DC microgrids, DC distribution networks, and DC transmission networks are developing rapidly. However, once a fault occurs in a DC grid, its current rises quickly, and it is difficult to break the DC current. Fast mechanical DC circuit breakers are difficult to break, and power electronic devices break quickly. Therefore, the use of fast hybrid DC circuit breakers to suppress fault current and clear faults is an important means to ensure the safe operation of the DC grid.

[0003] In order to accurately analyze the electromagnetic transient (EMT) characteristics of fast hybrid DCCB, it is necessary to simulate and model the fast hybrid DCCB. The response of devices containing nonlinear components, represented by DCCB, is more complex, with a time scale of milliseconds or even microseconds. The key to achieving nonlinear real-time simulation is to efficiently and accurately solve circuits with nonlinear / time-varying components.

[0004] As an effective short-circuit current limiting device, the superconducting current limiter can quickly limit the short-circuit current to an acceptable level when a short-circuit fault occurs, thereby avoiding large DC short-circuit currents from causing serious damage to the safe and stable operation of the power grid and electrical equipment. It can greatly improve the stability of the power grid and improve the reliability and safety of power supply.

[0005] Therefore, in order to accurately reflect the electromagnetic transient characteristics of the hybrid DCCB containing a superconducting current limiter, it is necessary to study the electromagnetic transient real-time simulation technology. However, the superconducting current limiter has thermo-electric characteristics, and the nonlinear characteristics of its resistance are related to the heat it absorbs, which brings challenges to the accuracy of the above electromagnetic transient simulation. Summary of the invention

[0006] In view of the above problems, the present invention proposes a thermal-electrical combined real-time simulation method for a hybrid DCCB containing a superconducting current limiter. By establishing an electromagnetic transient simulation model of the hybrid DC circuit breaker and combining finite element analysis to calculate the heat and update the superconducting current limiter resistance value in real time, the simulation accuracy of the hybrid DC circuit breaker containing a superconducting current limiter is improved.

[0007] The technical solution of the present invention is as follows:

[0008] A thermal-electric combined real-time simulation method for a hybrid DC circuit breaker (DCCB) containing a superconducting current limiter is characterized in that the hybrid DCCB includes a main branch, a transfer branch and an energy release branch connected in parallel, wherein the main branch is composed of a fast mechanical circuit breaker, a superconducting current limiter and at least one group of power electronic switches connected in series, the transfer branch is composed of at least three groups of power electronic switches connected in series, and the energy release branch is composed of MOVs connected in parallel with the power electronic switches on the transfer branch; the thermal-electric combined real-time simulation method includes the following steps:

[0009] Step 1) establishing a hybrid DCCB electromagnetic transient simulation circuit model containing a superconducting current limiter, the model includes historical current as a state variable, injected current as an input variable, and branch voltage and branch current as output variables, and simulates the dynamic behavior of the circuit by updating the state equation and calculating the output equation;

[0010] Step 2) presetting a superconducting current limiter RQ resistance model to represent the relationship between the resistance R of the superconducting current limiter and the heat Q generated by it;

[0011] Step 3) combining the electromagnetic transient simulation circuit model of step 1) and the superconducting current limiter RQ resistance model of step 2) to perform electromagnetic transient simulation;

[0012] Step 4) When the DC current I dc When it is lower than the preset disconnection limit of the DC circuit breaker, the DC circuit breaker is triggered to disconnect and the simulation ends; otherwise, go to step 5;

[0013] Step 5) Calculate the heat Q generated by the superconducting current limiter through finite element analysis, the formula is as follows:

[0014] Q = ∑ΔQ = ∑(Δt*R*(I dc ) 2 ) (4)

[0015] Where ΔQ is the incremental heat of each calculation step, Δt is the time step, and I dc is the DC current of the superconducting current limiter;

[0016] Step 6) obtaining the heat Q of the superconducting current limiter according to the preset RQ curve and step 5), updating the resistance R value of the superconducting current limiter under the current heat Q, and returning to step 3.

[0017] Furthermore, the hybrid DCCB electromagnetic transient simulation circuit model containing a superconducting current limiter is as follows:

[0018]

[0019] In the formula, I history (t) is the historical current, Isource (t) is the injected current, U br (t) is the branch voltage, I br (t) is the branch current, P is the state matrix, Q is the input matrix, H is the output matrix, and G is the feedforward matrix, which are defined as follows:

[0020]

[0021] In the above formula, C v ,C i ,E, and F are defined as follows:

[0022]

[0023] In the above formula, C v , C i is the diagonal matrix of branch voltage and current coefficients, R nb represents the node-branch correlation matrix, G inv represents the inverse matrix of the admittance matrix, I represents the unit diagonal matrix, Y br A diagonal matrix representing the equivalent admittances.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) Traditional simulation methods only consider the electromagnetic transient behavior of the circuit, while ignoring the thermal effect of the superconducting current limiter. The present invention takes the thermal effect of the superconducting current limiter into consideration in the simulation, thereby achieving a more accurate simulation. The heat of the superconducting current limiter is calculated by real-time simulation, and the resistance value of the superconducting current limiter in the electromagnetic transient simulation is updated, thereby achieving real-time simulation of thermal-electric coupling. The thermal effect and resistance change of the superconducting current limiter in actual work can be simulated more accurately, thereby improving the accuracy of the overall simulation.

[0026] 2) The number of power electronic switches in the transfer branch is not limited to three groups, and the number of power electronic switches in the main branch is not limited to one group. This design flexibility allows the hybrid DCCB to be customized and optimized according to different application scenarios and requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the thermal-electrical combined real-time simulation technology of the hybrid DC circuit breaker containing a superconducting current limiter of the present invention.

[0028] Figure 2 It is a topological structure diagram of the hybrid DC circuit breaker containing a superconducting current limiter of the present invention.

[0029] Figure 3 It is a schematic diagram of the QR calculation of the superconducting current limiter of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with examples and drawings, but the protection scope of the present invention shall not be limited thereto.

[0031] Please refer to Figure 1 , Figure 1 It is a schematic diagram of the thermal-electric combined real-time simulation technology of the hybrid DC circuit breaker containing a superconducting current limiter of the present invention. As can be seen from the figure, firstly, an electromagnetic transient simulation circuit model of the hybrid DC circuit breaker containing a superconducting current limiter is established, and the superconducting current limiter RQ resistance model is preset. The superconducting current limiter QR value is calculated online by finite element method, and the resistance R of the superconducting current limiter is updated in real time, which reduces the fault current size, thereby protecting the electrical equipment and improving the safety of the power grid.

[0032] Figure 2 is a topological structure diagram of a hybrid DC circuit breaker containing a superconducting current limiter according to the present invention, Figure 2 It can be seen that the fast hybrid DCCB consists of a main branch, a transfer branch, and an energy release branch; the main branch mainly includes a fast mechanical circuit breaker, a superconducting current limiter, and a power electronic switch. The transfer branch mainly includes three groups of power electronic switches connected in series, and the energy release branch is a variable resistor - Metal Oxide Varistor (MOV). The transfer branch and the energy release branch are connected in parallel to form a stack, and each stack consists of a power electronic switch and a parallel MOV. The number of power electronic switches in the transfer branch is not limited to three groups, and the number of power electronic switches in the main branch is not limited to one group, which increases the flexibility of the hybrid DCCB design.

[0033] Figure 3 is a schematic diagram of the QR calculation of the superconducting current limiter of the present invention, Figure 3 It can be seen that the heat Q of the superconducting current limiter is calculated online, and the R value is updated in real time according to the QR curve, thereby improving the accuracy of the real-time simulation of electromagnetic transients of the hybrid DC circuit breaker containing a superconducting current limiter.

[0034] A thermal-electrical real-time simulation method for a hybrid DC circuit breaker containing a superconducting current limiter comprises the following steps:

[0035] Step 1) Establishing an electromagnetic transient simulation circuit model of a hybrid DC circuit breaker containing a superconducting current limiter, as shown in the following formula (1);

[0036]

[0037] Among them, I history (t) is the historical current, which is used as a state variable; I source (t) is the injected current, which is used as the input variable; U br (t) is the branch voltage, I br (t) is the branch current, U br(t), I br (t) are all used as output variables;

[0038] I history (t) Update as the state equation, U br (t), I br (t) is calculated as the output equation; the matrix P is the state matrix, Q is the input matrix, H is the output matrix, and G is the feedforward matrix, which are defined as follows:

[0039]

[0040] In the above formula, C v ,C i ,E, and F are defined as follows:

[0041]

[0042] In the above formula, C v , C i is the diagonal matrix of branch voltage and current coefficients, R nb represents the node-branch correlation matrix, G inv represents the inverse matrix of the admittance matrix, I represents the unit diagonal matrix, Y br The diagonal matrix representing the equal-valued admittance;

[0043] Step 2) presetting a superconducting current limiter RQ resistance model;

[0044] Step 3) running electromagnetic transient simulation;

[0045] Step 4) Run finite element analysis to calculate the superconducting current limiter heat Q according to the following formula:

[0046] Q = ∑ΔQ = ∑(Δt*R*(I dc ) 2 ) (4)

[0047] Where ΔQ is the incremental heat of each calculation step, Δt is the time step, and I dc is the main branch DC current;

[0048] Step 5) Calculate the R value according to the pre-set RQ curve;

[0049] Step 6) When I dc When the voltage is lower than the limit of the DC circuit breaker disconnection, the DC circuit breaker is disconnected;

[0050] Step 7) The simulation ends.

[0051] The present invention improves the accuracy of simulation by considering the thermal effect of the superconducting current limiter and its influence on the dynamic behavior of the circuit, and provides a powerful tool for the design and optimization of the hybrid DCCB. It can accurately characterize the nonlinear characteristics of the real-time simulation of the hybrid DCCB circuit, calculate the QR value of the superconducting current limiter in real time, and greatly improve the simulation accuracy.

Claims

1. A real-time simulation method for thermal-electric combined DCCB of a hybrid DC circuit breaker containing a superconducting current limiter, characterized in that: The hybrid DCCB comprises a main branch, a transfer branch and an energy release branch connected in parallel, wherein the main branch is formed by a fast mechanical circuit breaker, a superconducting current limiter and at least one group of power electronic switches in series, the transfer branch is formed by at least three groups of power electronic switches in series, and the energy release branch is composed of MOVs connected in parallel with the power electronic switches on the transfer branch; the thermal-electric combined real-time simulation method comprises the following steps: Step 1) establishing a hybrid DCCB electromagnetic transient simulation circuit model containing a superconducting current limiter, the model includes historical current as a state variable, injected current as an input variable, and branch voltage and branch current as output variables, and simulates the dynamic behavior of the circuit by updating the state equation and calculating the output equation; Step 2) presetting a superconducting current limiter RQ resistance model to represent the relationship between the resistance R of the superconducting current limiter and the heat Q generated by it; Step 3) combining the electromagnetic transient simulation circuit model of step 1) and the superconducting current limiter RQ resistance model of step 2) to perform electromagnetic transient simulation; Step 4) When the DC current I dc When it is lower than the preset disconnection limit of the DC circuit breaker, the DC circuit breaker is triggered to disconnect and the simulation ends; otherwise, go to step 5; Step 5) Calculate the heat Q generated by the superconducting current limiter through finite element analysis, the formula is as follows: Q=∑ΔQ=∑(Δt*R*(I dc ) 2 ) (4) Where ΔQ is the incremental heat of each calculation step, Δt is the time step, and I dc is the DC current of the superconducting current limiter; Step 6) obtaining the heat Q of the superconducting current limiter according to the preset RQ curve and step 5), updating the resistance R value of the superconducting current limiter under the current heat Q, and returning to step 3.

2. The method for thermal-electrical combined real-time simulation of a hybrid DC circuit breaker DCCB with a superconducting current limiter according to claim 1 is characterized in that: The hybrid DCCB electromagnetic transient simulation circuit model containing a superconducting current limiter is as follows: In the formula, I history (t) is the historical current, I source (t) is the injected current, U br (t) is the branch voltage, I br (t) is the branch current, P is the state matrix, Q is the input matrix, H is the output matrix, and G is the feedforward matrix, which are defined as follows: In the above formula, C v ,C i ,E, and F are defined as follows: In the above formula, C v , C i is the diagonal matrix of branch voltage and current coefficients, R nb represents the node-branch correlation matrix, G inv represents the inverse matrix of the admittance matrix, I represents the unit diagonal matrix, Y br A diagonal matrix representing the equivalent admittances.

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