CN115618701A - MMC (Modular multilevel converter) low-dimensional admittance electromagnetic transient modeling simulation method and device and related equipment - Google Patents
MMC (Modular multilevel converter) low-dimensional admittance electromagnetic transient modeling simulation method and device and related equipment Download PDFInfo
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Abstract
The invention provides a low-dimensional admittance electromagnetic transient modeling simulation method and device of an MMC and related equipment, wherein a discretization model of a bridge arm inductance and a discretization model of a sub-module capacitance are obtained by respectively carrying out dynamic modeling on an inductance and a capacitance in an MMC model; if the current moment is smaller than the preset time value, alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitor according to the time sequence; if the current time is not less than the preset time value, the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitance corresponding to the current time are used as simulation results, decoupling calculation of the capacitance and the inductance of the MMC is achieved, calculation time is shortened, and simulation efficiency is improved.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a low-dimensional admittance electromagnetic transient modeling simulation method and device of an MMC and related equipment.
Background
Modular Multilevel Converters (MMC) have become converters with great application prospects because of their characteristics of high rated voltage, small harmonic components, low loss, and the like. In recent years, the MMC is widely applied to long-distance high-voltage direct-current power transmission and asynchronous interconnection of power grids. In order to perform simulation analysis on a power system containing an MMC, an electromagnetic transient model of the MMC needs to be constructed and integrated into an existing electromagnetic transient simulation tool. Because each MMC is provided with thousands of sub-modules, when the MMC is connected to a power system, an electrical node in a network is increased explosively, the traditional low-dimensional admittance electromagnetic transient modeling simulation method of the MMC is used for simultaneously carrying out simulation calculation on an inductor and a capacitor, the calculation complexity is greatly increased, the calculation time of electromagnetic transient simulation of the power system is rapidly increased, and the simulation efficiency is low.
Disclosure of Invention
The invention provides a low-dimensional admittance electromagnetic transient modeling simulation method and device of an MMC and related equipment, which are used for solving the defects of long calculation time and low simulation efficiency of the traditional low-dimensional admittance electromagnetic transient modeling simulation method of the MMC.
The invention provides a low-dimensional admittance electromagnetic transient modeling simulation method of an MMC, which comprises the following steps:
respectively carrying out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor;
if the current time is less than a preset time value, alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to the time sequence;
and if the current moment is not less than the preset time value, taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitor corresponding to the current moment as simulation results.
According to the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC, provided by the invention, the step of alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to the time sequence comprises the following steps:
in calculating
Capacitor voltage of the sub-module of
Then, calculating to obtain bridge arm inductive current i at time t arm(t) Then calculate
Capacitor voltage at time
Wherein t is the current moment, and Δ t is the simulation step length.
According to the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC, provided by the invention, dynamic modeling is carried out on the inductor in the MMC model to obtain a discretization model of the bridge arm inductor, and the method comprises the following steps:
calculating a plurality of equivalent circuits of the submodule according to the on or off states of two bridge arms of the submodule;
obtaining dynamic equations of a plurality of MMC arms according to a plurality of equivalent circuits of the sub-module;
normalizing the dynamic equations of the MMC arms to obtain a unified dynamic equation of the MMC arms;
and discretizing the MMC arm unified dynamic equation to obtain a discretization model of the bridge arm inductance.
According to the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC, provided by the invention, the calculation of a plurality of equivalent circuits of the submodule according to the on or off states of two bridge arms of the submodule comprises the following steps:
obtaining a first equivalent circuit of the submodule according to the state when only one of two bridge arms of the submodule is conducted;
obtaining a second equivalent circuit of the submodule according to the state of the submodule when two bridge arms are conducted simultaneously;
and obtaining a third equivalent circuit of the submodule according to the state of the submodule when the two bridge arms are simultaneously turned off.
According to the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC, provided by the invention, the capacitor in the MMC model is dynamically modeled to obtain a discretization model of the sub-module capacitor, and the method comprises the following steps:
constructing capacitance dynamic equations of a plurality of sub-modules according to the on or off states of two bridge arms of the sub-modules;
and respectively discretizing the capacitance dynamic equation of each sub-module to obtain a discretization model of the capacitance of each sub-module.
According to the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC, provided by the invention, a capacitance dynamic equation of a plurality of sub-modules is constructed according to the on or off states of two bridge arms of the sub-modules, and the method comprises the following steps:
constructing a corresponding first capacitance dynamic equation when only one bridge arm in the sub-module is conducted;
constructing a second capacitance dynamic equation corresponding to the conduction of two bridge arms in the sub-module;
and constructing a corresponding third capacitance dynamic equation when no bridge arm is conducted in the submodule.
The invention provides a low-dimensional admittance electromagnetic transient modeling simulation method of an MMC, which further comprises the following steps:
checking whether a network switching action occurs in the network;
if so, carrying out critical damping adjustment, and modifying the discretization model of the bridge arm inductance;
solving the discretization model of the modified bridge arm inductance to obtain
Time of day and
branch current corresponding to the moment, wherein t is the current moment, and delta t is the simulation step length;
according to
Time of day and
branch current meter corresponding to timeAnd (5) operator module capacitance voltage.
The invention also provides a low-dimensional admittance electromagnetic transient modeling simulation device of the MMC, which comprises:
the modeling module is used for respectively carrying out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor;
the solving module is used for alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to the time sequence if the current moment is less than a preset time value;
and the output module is used for taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitance corresponding to the current moment as the simulation result if the current moment is not less than the preset time value.
The invention also provides an electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor executes the program to implement the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC as described in any of the above.
The present invention also provides a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements a low-dimensional admittance electromagnetic transient modeling simulation method of an MMC as described in any one of the above.
According to the low-dimensional admittance electromagnetic transient modeling simulation method, device and related equipment of the MMC, provided by the invention, the inductor and the capacitor in the MMC model are dynamically modeled respectively to obtain a discretization model of a bridge arm inductor and a discretization model of a sub-module capacitor; if the current time is less than a preset time value, alternately solving a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance according to a time sequence; if the current moment is not less than the preset time value, the discretization model solving result of the bridge arm inductor and the discretization model solving result of the sub-module capacitor corresponding to the current moment are used as simulation results, and through constructing the discretization model of the bridge arm inductor and the discretization model of the sub-module capacitor, capacitance and inductance decoupling calculation of the MMC can be realized by alternately solving the two models according to the time sequence, so that the calculation time is shortened, and the simulation efficiency is improved.
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In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is one of the flow diagrams of a low-dimensional admittance electromagnetic transient modeling simulation method of an MMC provided by the present invention;
FIG. 2 (a) is a topological structure diagram of an MMC provided by the present invention;
FIG. 2 (b) is a schematic diagram of a half-bridge sub-module according to the present invention;
FIGS. 3 (a) and 3 (b) are equivalent circuit diagrams of MMC and half-bridge sub-modules provided by the present invention;
FIG. 4 is a second flowchart of the MMC low-dimensional admittance electromagnetic transient modeling simulation method provided in the present invention;
FIG. 5 (a) is an equivalent circuit diagram of the half-bridge sub-module provided by the present invention when the upper bridge arm is conducted;
fig. 5 (b) is an equivalent circuit diagram when the lower bridge arm of the half-bridge sub-module provided by the invention is turned on;
fig. 6 (a) to (d) are equivalent circuit diagrams when the upper and lower arms of the present invention are simultaneously turned on;
fig. 7 (a) and 7 (b) are equivalent circuit diagrams of half-bridge submodules when the upper and lower bridge arms are turned off simultaneously according to the present invention;
FIG. 8 is a third schematic flow chart of a low-dimensional admittance electromagnetic transient modeling simulation method of the MMC according to the present invention;
FIG. 9 is a fourth schematic flowchart of a low-dimensional admittance electromagnetic transient modeling simulation method of the MMC according to the present invention;
FIG. 10 is a schematic structural diagram of a low-dimensional admittance electromagnetic transient modeling simulation apparatus of the MMC provided in the present invention;
fig. 11 is a schematic structural diagram of an electronic device provided in the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a flowchart of a low-dimensional admittance electromagnetic transient modeling simulation method for an MMC according to an embodiment of the present invention, and as shown in fig. 1, the low-dimensional admittance electromagnetic transient modeling simulation method for an MMC according to an embodiment of the present invention includes:
102, if the current time is less than a preset time value, alternately solving a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance according to a time sequence;
in the embodiment of the invention, the step of alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to the time sequence comprises the following steps:
in calculating
Capacitor voltage of sub-module of
Then, calculating to obtain bridge arm inductive current i at time t arm(t) Then calculate
Capacitor voltage at time
Wherein t is the current moment, and Δ t is the simulation step length.
In the simulation process, because delta t/2 delay exists between the two parts, the dynamic equation of the sub-module capacitor and the dynamic equation of the bridge arm inductor are completely decoupled in calculation. Specifically, the dynamic model of the bridge arm inductance is calculated in the main network, the sub-module capacitance dynamic model is calculated independently, and the calculations in the sub-module capacitance dynamic process are decoupled from each other.
And 103, if the current moment is not less than the preset time value, taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitance corresponding to the current moment as simulation results.
According to the traditional low-dimensional admittance electromagnetic transient modeling simulation method of the MMC, due to the fact that thousands of sub-modules are arranged in each MMC, when the MMC is connected into a power system, electrical nodes in a network are increased in an explosion mode, the calculation time of electromagnetic transient simulation of the power system is increased rapidly, and the simulation efficiency is low.
The low-dimensional admittance electromagnetic transient modeling simulation method of the MMC provided by the embodiment of the invention comprises the steps of respectively carrying out dynamic modeling on an inductor and a capacitor in an MMC model to obtain a discretization model of a bridge arm inductor and a discretization model of a sub-module capacitor; if the current time is less than a preset time value, alternately solving a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance according to a time sequence; if the current moment is not less than the preset time value, the discretization model solution result of the bridge arm inductance and the discretization model solution result of the sub-module capacitance corresponding to the current moment are used as simulation results, the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance are constructed, the dimension of a system node equation is greatly reduced, meanwhile, decoupling calculation is carried out on the capacitance and the inductance of the MMC, the calculation efficiency is improved, in addition, the inductance current is calculated firstly through the discretization model of the bridge arm inductance, the capacitance voltage is calculated according to the inductance current display, the calculation time is shortened, and the simulation efficiency is improved.
In the embodiment of the present invention, the topology of the three-phase MMC is as shown in fig. 2 (a), and each bridge arm is composed of N half-bridges connected in seriesThe structure of the half-bridge submodule is shown in fig. 2 (b), and is composed of two groups of Insulated Gate Bipolar Transistors (IGBTs)/diode switches and a capacitor. In FIG. 2 (a), L 0 Representing arm inductance, C sm Representing the sub-module capacitance; t in FIG. 2 (b) 1 And D 1 Respectively, IGBT and diode of the first IGBT/diode group (upper arm), T 2 And D 2 The IGBTs and diodes in the second IGBT/diode group (lower arm) are shown. In normal operation, the half-bridge sub-module has three states (i.e., a conducting state, a bypass state, and a latch-up state). The three states and the corresponding details of the IGBT, diode and bridge arm voltages and currents are listed in table 1, where i sm And v sm Output current and voltage, v, of half-bridge submodules respectively ci Is the capacitor voltage. It can be seen from table 1 that during normal operation only one of the four switches of the half-bridge sub-module is in a conducting state, which indicates that only one leg of the sub-module is conducting. In addition, v sm Is equal to v ci Or zero, may be determined based on the switching state of the half-bridge sub-modules.
TABLE 1 operating conditions of half-bridge submodules
In electromagnetic transient simulation, a switch can be represented by a binary resistor, and when the switch is turned on, the switch is equivalent to a small resistor, and when the switch is turned off, the switch is equivalent to a large resistor. Thus, the half-bridge converter shown in fig. 2 (a) may be equivalent in electromagnetic transient simulation to the circuit shown in fig. 3 (a), where R is T1 、R D1 、R T2 And R D2 Respectively represent switches T 1 、D 1 、T 2 、D 2 The resistance of (2). Further, suppose R 1 ＝R T1 ||R D1 And R 2 ＝R T2 ||R D2 (where | represents parallel), the half-bridge sub-modules may be further equivalent to the circuit shown in fig. 3 (b).
Based on any of the above embodiments, as shown in fig. 4, the inductance in the MMC model is dynamically modeled to obtain a discretization model of the bridge arm inductance, and the specific steps include:
402, obtaining dynamic equations of a plurality of MMC arms according to a plurality of equivalent circuits of the submodule;
in the embodiment of the present invention, calculating a plurality of equivalent circuits of the submodule according to the on or off states of two bridge arms of the submodule includes:
obtaining a first equivalent circuit of the submodule according to the state when only one of two bridge arms of the submodule is conducted;
under the normal operation condition, only one of two bridge arms of the half-bridge submodule is conducted. Therefore, if the switch has an off resistance (R) off ) Considered as ∞, the half-bridge sub-module equivalent circuit may be further equivalent to the circuits shown in fig. 5 (a), 5 (b). When T is 1 Or D 1 When conducting, the half-bridge sub-module is equivalent to the circuit shown in fig. 5 (a). When T is 2 Or D 2 When conducting, the half-bridge sub-module is equivalent to the circuit shown in fig. 5 (b), in which case the sub-module capacitance is bypassed and its voltage remains unchanged.
According to the equivalent circuit of the half-bridge sub-module, the first dynamic equation of the MMC arm can be written as:
in the formula:
K 1 ＝[1…1…1] 1×n (1.3)
v c (t)＝[v c1 (t)…v ci (t)…v cn (t)] T (1.4)
wherein N is the number of half-bridge sub-modules in the MMC arm; n is an upper bridge armThe number of the conducted half-bridge sub-modules; k 1 And the coefficient vector represents a submodule for conducting the upper bridge arm and is constructed according to the switching state of the MMC bridge arm. In the simulation, the switch states are calculated before the electrical system is solved. i.e. i arm Is bridge arm current, v arm Is the branch voltage of the bridge arm, v ci And the capacitor voltage of the half-bridge sub-module conducted for the ith upper bridge arm. R onj Is the on-resistance of the conducting switch in the jth half-bridge sub-module. If IGBT is conducted, R onj ＝R onT . Conversely, if the diode is conducting, R onj ＝R onD . Wherein R is onT Representing the on-resistance of the IGBT, R onT Representing the on-resistance of the diode. In power system transient analysis, R can be assumed onT And R onD Equal, and it can be assumed that both are R on . In this case, R is used in the electromagnetic transient simulation eq1 Will remain unchanged.
Obtaining a second equivalent circuit of the submodule according to the state of the submodule when two bridge arms are conducted simultaneously;
in the embodiment of the present invention, it is assumed that each bridge arm of the MMC has only one sub-module, and each bridge arm may be equivalent to an equivalent circuit shown in fig. 6 (a). According to kirchhoff's law, in the process of calculating the bridge arm inductance and resistance current, the sub-module capacitor can be equivalent to a voltage source with the same voltage. Thus, FIG. 6 (a) may be equivalent to the circuit shown in FIG. 6 (b), where v is c1 Is the sub-module voltage. Further, it can be equivalent to the circuit shown in fig. 6 (c) by utilizing the norton equivalent. The parallel resistance in the circuit of fig. 6 (c) may be equivalent to one resistance, resulting in an equivalent circuit as shown in fig. 6 (d).
According to the equivalent circuits of fig. 6 (a) to (d), a second dynamic equation of the bridge arm inductance can be obtained:
let R eqon ＝R on /2，v ceq1 (t)＝v c1 (t)/2, formula (1.5) can be represented as:
it can be found that formula (1.6) is in accordance with formula (1.1). According to the equations (1.1), (1.6) and the superposition theorem, the dynamic equation of the bridge arm inductance can be obtained:
in the formula,
R eq2 ＝R eq1 -n 2 R eqon (1.8)
wherein v is ceqi (t)＝v ci (t)/2 is the equivalent voltage source voltage of the submodule with the ith upper and lower bridge arms conducted simultaneously, n 2 The number of half-bridge submodules with upper and lower bridge arms conducted simultaneously. R eq1 、K 1 And v c (t) has the same meaning as in the formulae (1.2) to (1.4). It is noted that formula (1.7) encompasses formula (1.1). When n is 2 When 0, the formula (1.7) is equivalent to the formula (1.1).
And obtaining a third equivalent circuit of the submodule according to the state of the submodule when the two bridge arms are simultaneously turned off.
In the embodiment of the present invention, if the upper and lower arms of the half-bridge sub-module are turned off at the same time, the half-bridge sub-module may be equivalent to the equivalent circuit shown in fig. 7 (a), and further equivalent to the circuit shown in fig. 7 (b). It can be seen that this submodule can be seen as an open circuit.
In this case, the dynamic equation L of the bridge arm inductance 0 Can be expressed as:
let R eqoff ＝R off Formula (1.12) can be further represented as:
when a half-bridge submodule with an upper bridge arm and a lower bridge arm simultaneously turned off exists in an MMC bridge arm, a bridge arm dynamic equation can be expressed as
Wherein,
unified dynamic equation:
wherein R is eq Respectively taking R according to the switch state of the half-bridge submodule eq1 、R eq2 Or R eq3 Three values.
And step 404, discretizing the MMC arm unified dynamic equation to obtain a discretization model of the bridge arm inductance.
In order to obtain a numerical solution of the MMC bridge arm dynamic equation, a differential equation needs to be discretized first. The trapezoidal method has the properties of A-stability and the like, and is widely applied to the discretization of differential equations in modern EMTP simulation. Based on the trapezoidal method, equation (1.17) can be discretized as:
where Δ t is the integration step. Because the trapezoidal integral method and the middle rectangular integral method have similar precision [14] Thus, Δ t (K) in the formula (1.18) 1 v c (t)+K 1 v c (t-Δt))/(2L 0 ) Part can be replaced by
Δt(K 2 v ceq (t)+K 2 v ceq (t-Δt))/(2L 0 ) Can use
An approximation is made. At this point, formula (1.18) can be converted to:
to solve with an EMTP-like algorithm, equation (1.19) needs to be expressed in norton equivalent circuit form:
i arm (t)＝Gv arm (t)+i hist (t) (1.20)
wherein G is the equivalent conductance, i hist (t) is the history current. They can be represented as:
in summary, it can be seen that R is due to normal operation eq ＝R eq1 G will remain constant. G is changed only when the number of the bridge arms conducted in the half-bridge submodule changes.
In the embodiment of the present invention, the dynamic modeling of the capacitor in the MMC model to obtain the discretization model of the sub-module capacitor includes:
constructing a capacitance dynamic equation of a plurality of sub-modules according to the conducting or switching-off states of two bridge arms of the sub-modules;
and respectively discretizing the capacitance dynamic equation of each sub-module to obtain a discretization model of the capacitance of each sub-module.
Specifically, constructing a first capacitance dynamic equation corresponding to only one bridge arm in the submodule when the bridge arm is switched on includes:
according to the equivalent circuit of the half-bridge sub-modules shown in fig. 5 (a) and 5 (b), the dynamic equation of the capacitance of the half-bridge sub-module with the conducting upper bridge arm can be expressed as follows:
wherein, C smi The capacitance value of the half-bridge submodule with the ith upper bridge arm conducted, by using a trapezoidal method, the formula (1.23) can be discretized into:
for a half-bridge submodule with a conducting lower bridge arm, the submodule capacitor is bypassed. Therefore, its voltage remains unchanged:
constructing a second capacitance dynamic equation corresponding to the conduction of two bridge arms in the submodule, wherein the second capacitance dynamic equation comprises the following steps:
according to the half-bridge submodules shown in FIGS. 6 (a) - (d)The equivalent circuit is used for calculating the current i of the upper bridge arm of the submodule to obtain the capacitance voltage of the half-bridge submodule with the upper bridge arm and the lower bridge arm conducted simultaneously 1i ：
Wherein i 2i And (t) is the lower bridge arm current of the ith half-bridge submodule. In the formula (1.25), v ci (t) is difficult to calculate, so that i 1i (t) is also difficult to obtain. Fortunately, v is ci There is no abrupt change in the simulation. Rather, it remains substantially unchanged.
Thus, v ci (t) can be used
And (4) approximation. Further, i 1i (t) can be obtained by solving the formula (1.25):
then, the capacitor voltage of the sub-module with the upper and lower bridge arms conducted simultaneously can be calculated
To:
constructing a third capacitance dynamic equation corresponding to the submodule without bridge arm conduction, comprising:
the voltage of the sub-module capacitor with zero bridge arms conducting will remain constant:
in the traditional electromagnetic transient simulation based on an MMC model, due to the fact that a large number of switching devices exist in an MMC, an equivalent node conductance matrix of the MMC is time-varying, and further frequent LU decomposition of the equivalent conductance matrix is caused. However, LU decomposition of a large-scale matrix is time-consuming, and in the embodiment of the present invention, by constructing a dynamic equation, the equivalent conductance of the MMC bridge arm can be kept constant under a normal working condition. It will only change when the number of conducting branches of the half-bridge sub-modules changes. The bridge arm dynamic equation is discretized by using a hybrid integral method based on Leapfragg and a trapezoidal method, and is equivalent to a Nuton circuit with constant admittance, so that the system dimension is reduced, the branch equivalent conductance is constant, frequent LU decomposition of a high-dimensional matrix is avoided, and the simulation speed is greatly accelerated; in addition, various operation conditions of the sub-modules are considered in the model, and the precision of the sub-modules in different simulation scenes is guaranteed.
The flow of electromagnetic transient simulation based on the MMC model is shown in fig. 8. At the beginning of each time step calculation, the control system is solved first. On the basis, the state of a system switch is judged, and the state of the sub-module is further determined. Calculating the equivalent conductance of each bridge arm of the MMC according to the switching state of each half-bridge submodule, judging whether an external network has a switching action, and modifying an equivalent conductance matrix if two bridge arms of the half-bridge submodule are simultaneously switched on or off, wherein the equivalent conductance matrix comprises the following steps:
checking whether a network switching action occurs in the network;
if so, performing critical damping adjustment, and modifying the discretization model of the bridge arm inductance;
solving the discretization model of the modified bridge arm inductance to obtain
Time of day and
branch current corresponding to the moment, wherein t is the current moment, and delta t is the simulation step length;
according to
Time of day and
and calculating the sub-module capacitance voltage according to the branch current corresponding to the moment.
If no network switching action occurs, calculating historical current sources of each bridge arm of the MMC, calculating historical current sources of other elements in the network, solving a node voltage equation of the network, and calculating the historical current sources including i arm Solving the sub-module capacitor voltage t according to the sub-module switch state of each branch current inside<t max (preset time value), the simulation is finished.
In electromagnetic transient simulation, critical damping adjustment can inhibit numerical oscillation caused by network switching. In order to adapt to the critical damping adjustment process of the system, the MMC model needs to be modified. The critical damping adjustment process involves a two half step back euler method numerical integration. Assuming that a switching operation occurs at time t in the system, equation (1.17) needs to be discretized by a step size of Δ t/2. At this time, the process of the present invention,
the calculation can be performed by using equation (1.29).
Wherein,
in the formula
Capacitor voltage at time (i.e. time of day)
) Determined from the formula (1.24) or (1.27).
Then, execute
The numerical integration to t. The discretized model of the bridge arm inductance can be expressed as:
i arm (t)＝Gv arm (t)+i hist (t) (1.32)
wherein,
in summary, the flow of the critical damping adjustment process is shown in fig. 9, and includes a numerical integration calculation of two half-steps, modifying the system node admittance matrix at the time of t- Δ t/2, calculating the historical current sources of the MMC bridge arm, calculating the historical current sources of the other elements, solving the node voltage equation of the system, and calculating the current of each branch of the system; and at the same time of t + delta t/2 and t-delta t/2, after the two half-time step calculations are finished, the system is switched to a normal simulation process.
In the embodiment of the invention, when EMTP simulation calculation is carried out by simulation software for electromagnetic transient analysis of a power system, each bridge arm of the MMC is equivalent to an R-L series circuit, so that the dimension of a system node equation is greatly reduced. And meanwhile, decoupling calculation is carried out on a capacitance and inductance dynamic equation of the MMC. After obtaining the inductor current, the capacitor voltage is then explicitly calculated. In addition, the capacitance voltage calculation of the half-bridge sub-modules is mutually independent, so that the calculation efficiency is greatly improved; in the electromagnetic transient simulation, the equivalent conductance of the MMC bridge arm is kept constant under the normal working condition, and only when the number of the conducting branches of the half-bridge sub-module is changed, the conducting branches can be changed. Compared with the prior art, the method avoids frequent LU decomposition of the equivalent conductance matrix of the system in electromagnetic transient simulation, and greatly accelerates the simulation speed.
The low-dimensional admittance electromagnetic transient modeling simulation device of the MMC provided by the present invention is described below, and the low-dimensional admittance electromagnetic transient modeling simulation device of the MMC described below and the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC described above may be referred to each other.
Fig. 10 is a schematic diagram of a low-dimensional admittance electromagnetic transient modeling simulation apparatus for an MMC according to an embodiment of the present invention, and as shown in fig. 10, the low-dimensional admittance electromagnetic transient modeling simulation apparatus for an MMC according to an embodiment of the present invention includes:
the modeling module 1001 is used for respectively and dynamically modeling the inductance and the capacitance in the MMC model to obtain a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance;
the solving module 1002 is configured to alternately solve the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to a time sequence if the current time is less than a preset time value;
and the output module 1003 is configured to, if the current time is not less than the preset time value, take the discretization model solution result of the bridge arm inductance and the discretization model solution result of the sub-module capacitance corresponding to the current time as a simulation result.
The low-dimensional admittance electromagnetic transient modeling simulation device of the MMC provided by the embodiment of the invention respectively carries out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor; if the current time is less than a preset time value, alternately solving a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance according to a time sequence; if the current moment is not less than the preset time value, the discretization model solution result of the bridge arm inductance and the discretization model solution result of the sub-module capacitance corresponding to the current moment are used as simulation results, the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance are constructed, the dimension of a system node equation is greatly reduced, meanwhile, decoupling calculation is carried out on the capacitance and the inductance of the MMC, the calculation efficiency is improved, in addition, the inductance current is calculated firstly through the discretization model of the bridge arm inductance, the capacitance voltage is calculated according to the inductance current display, the calculation time is shortened, and the simulation efficiency is improved.
Fig. 11 illustrates a physical structure diagram of an electronic device, and as shown in fig. 11, the electronic device may include: a processor (processor) 1110, a communication Interface (Communications Interface) 1120, a memory (memory) 1130, and a communication bus 1140, wherein the processor 1110, the communication Interface 1120, and the memory 1130 communicate with each other via the communication bus 1140. The processor 1110 may invoke logic instructions in the memory 1130 to perform a low-dimensional admittance electromagnetic transient modeling simulation method of MMC, the method comprising: respectively carrying out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor; if the current time is less than a preset time value, alternately solving a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance according to a time sequence; and if the current moment is not less than the preset time value, taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitor corresponding to the current moment as simulation results.
In addition, the logic instructions in the memory 1130 may be implemented in the form of software functional units and stored in a computer readable storage medium when the logic instructions are sold or used as independent products. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
In another aspect, the present invention also provides a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements a low-dimensional admittance electromagnetic transient modeling simulation method for an MMC, provided by performing the above methods, the method comprising: respectively carrying out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor; if the current time is less than a preset time value, alternately solving a discretization model of the bridge arm inductance and a discretization model of the sub-module capacitance according to a time sequence; and if the current moment is not less than the preset time value, taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitor corresponding to the current moment as simulation results.
The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware. With this understanding in mind, the above-described technical solutions may be embodied in the form of a software product, which can be stored in a computer-readable storage medium such as ROM/RAM, magnetic disk, optical disk, etc., and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the methods described in the embodiments or some parts of the embodiments.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A low-dimensional admittance electromagnetic transient modeling simulation method of an MMC is characterized by comprising the following steps:
respectively carrying out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor;
if the current time is less than a preset time value, alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to the time sequence;
and if the current moment is not less than the preset time value, taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitor corresponding to the current moment as simulation results.
2. The MMC of claim 1, wherein said time-sequentially alternating solving of said discretized model of bridge arm inductance and said discretized model of sub-module capacitance comprises:
in calculating
Capacitor voltage of the sub-module of
Then, calculating to obtain bridge arm inductive current i at time t arm(t) Then calculate
Capacitor voltage at time
Wherein t is the current moment, and Δ t is the simulation step length.
3. The MMC low-dimensional admittance electromagnetic transient modeling simulation method of claim 2, wherein dynamically modeling an inductance in the MMC model to obtain a discretized model of a bridge arm inductance comprises:
calculating a plurality of equivalent circuits of the submodule according to the on or off states of two bridge arms of the submodule;
obtaining dynamic equations of a plurality of MMC arms according to a plurality of equivalent circuits of the sub-module;
normalizing the dynamic equations of the MMC arms to obtain a unified dynamic equation of the MMC arms;
and discretizing the MMC arm unified dynamic equation to obtain a discretization model of the bridge arm inductance.
4. The MMC low-dimensional admittance electromagnetic transient modeling simulation method of claim 3, wherein calculating a plurality of equivalent circuits of the submodule according to the on or off states of two legs of the submodule comprises:
obtaining a first equivalent circuit of the submodule according to the state when only one of two bridge arms of the submodule is conducted;
obtaining a second equivalent circuit of the submodule according to the state of the submodule when two bridge arms are conducted simultaneously;
and obtaining a third equivalent circuit of the submodule according to the state of the submodule when the two bridge arms are simultaneously turned off.
5. The MMC low-dimensional admittance electromagnetic transient modeling simulation method of claim 1, wherein dynamically modeling the capacitance in the MMC model to obtain a discretized model of sub-module capacitance comprises:
constructing capacitance dynamic equations of a plurality of sub-modules according to the on or off states of two bridge arms of the sub-modules;
and respectively discretizing the capacitance dynamic equation of each sub-module to obtain a discretization model of the capacitance of each sub-module.
6. The MMC of claim 5, wherein constructing a capacitance dynamic equation for a plurality of submodules according to the ON or OFF states of two legs of the submodule comprises:
constructing a corresponding first capacitance dynamic equation when only one bridge arm in the sub-modules is conducted;
constructing a second capacitance dynamic equation corresponding to the conduction of two bridge arms in the sub-module;
and constructing a corresponding third capacitance dynamic equation when no bridge arm is conducted in the submodule.
7. The MMC low-dimensional admittance electromagnetic transient modeling simulation method of claim 1, further comprising:
checking whether a network switching action occurs in the network;
if so, carrying out critical damping adjustment, and modifying the discretization model of the bridge arm inductance;
solving the discretization model of the modified bridge arm inductance to obtain
Time of day and
branch current corresponding to the moment, wherein t is the current moment, and delta t is the simulation step length;
according to
Time of day and
and calculating the sub-module capacitance voltage according to the branch current corresponding to the moment.
8. A low-dimensional admittance electromagnetic transient modeling simulation device of an MMC, comprising:
the modeling module is used for respectively carrying out dynamic modeling on the inductor and the capacitor in the MMC model to obtain a discretization model of the bridge arm inductor and a discretization model of the sub-module capacitor;
the solving module is used for alternately solving the discretization model of the bridge arm inductance and the discretization model of the sub-module capacitance according to the time sequence if the current moment is less than a preset time value;
and the output module is used for taking the discretization model solving result of the bridge arm inductance and the discretization model solving result of the sub-module capacitance corresponding to the current moment as the simulation result if the current moment is not less than the preset time value.
9. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the low-dimensional admittance electromagnetic transient modeling simulation method of the MMC according to any of claims 1 to 7 when executing the program.
10. A non-transitory computer readable storage medium having stored thereon a computer program, wherein the computer program, when executed by a processor, implements a low-dimensional admittance electromagnetic transient modeling simulation method of an MMC as claimed in any one of claims 1 to 7.
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