CN107944082A - A kind of single port submodule MMC electro-magnetic transient generalized equivalent modeling methods - Google Patents

Abstract

The invention designs a single-port sub-module MMC electromagnetic transient general equivalent modeling method. The core technical solution of the present invention is: 1. Based on the equivalent circuit of the single-port sub-module, write the node voltage equation, and use the fast nested solution algorithm to equivalently eliminate the internal nodes. Obtain the Norton equivalent expression of the equivalent circuit through equation transformation, so as to obtain its Thevenin equivalent circuit; 2. Use the sub-module Thevenin equivalent circuit to obtain the equivalent model of the entire converter, and use the electromagnetic transient The simulation program obtains the bridge arm current value of each bridge arm; 3. After the equivalent circuit is solved by one step, the node voltage value of the internal node of the single-port MMC bridge arm is obtained by obtaining the bridge arm current, and all sub-modules are updated inside information.

Description

A Universal Equivalent Modeling Method for Single-port Submodule MMC Electromagnetic Transient

technical field

The invention relates to a universal single-port sub-module MMC electromagnetic transient equivalent modeling method, which belongs to the technical field of flexible direct current transmission.

Background technique

The number of submodules (SM) in modular multilevel converters (MMC) is increasing due to engineering requirements, and submodule topologies with various advanced functions and complex structures are emerging. Although existing The MMC model can greatly improve the simulation efficiency and ensure high simulation accuracy, but most of the existing models are based on the half-bridge and full-bridge sub-modules, which have poor versatility. Aiming at MMC composed of arbitrary single-port sub-modules, the invention proposes a general electromagnetic transient equivalent modeling method based on the Thevenin equivalent model and nested fast simultaneous solving algorithm. The proposed modeling method essentially transfers the information of the internal nodes of the sub-module to the external nodes to eliminate the internal nodes, so as to obtain the reduced-order Norton or Thevenin equivalent circuit of the sub-module, and solve for one step in the equivalent circuit Afterwards, the internal information of all submodules can be quickly updated through reverse solution. This method unifies the parameter solving process of Thevenin model, and has strong versatility for MMC composed of single-port sub-modules with any structure.

Contents of the invention

The present invention provides a kind of single-port sub-module MMC electromagnetic transient general equivalent modeling method, and this modeling method comprises the following steps:

Step 1: Replace the respective IGBTs and their anti-parallel diodes of all sub-modules of the single-port MMC single bridge arm with a variable conductance G that switches between high and low resistance in the on-off state. At the same time, the trapezoidal integration method is used to discretize the sub-module capacitance into a conductance and connect a historical current source in parallel to obtain the equivalent circuit of each sub-module of a single bridge arm of a single-port MMC. The node voltage equation is written by using the equivalent circuit, and the internal nodes are eliminated based on the idea of a fast nested solution algorithm. The Norton equivalent expression of the single-port MMC sub-module is obtained through equation transformation, and the Thevenin equivalent circuit is obtained accordingly.

Step 2: Connect the single sub-modules in series to form the equivalent model of the bridge arm, then add the equivalent model of the bridge arm to the entire converter, use the electromagnetic transient simulation software to solve the entire circuit network, and obtain the bridge arm current of each bridge arm value.

Step 3: Reversely solve the internal voltage of each sub-module from the obtained bridge arm current value, and complete the update of the internal information of all sub-modules in each bridge arm of the single-port MMC.

Description of drawings

Figure 1 is a schematic diagram of the D-HBSM topology and its equivalent circuit.

Detailed ways

The present invention provides a universal single-port sub-module MMC electromagnetic transient equivalent modeling method; the following will take double half bridge sub-module MMC (double half bridge sub-module MMC, DHB-MMC) as an example, combined with the accompanying drawings The modeling steps of the invention are described in further detail.

Figure 1 is a schematic diagram of a single D-HBSM topology and its accompanying circuit. The IGBT and its anti-parallel diode of a single D-HBSM in Figure 1(a) are equivalently replaced by a variable conductance ( G 1 ~ G 8 ). In PSCAD/EMTDC, when the IGBT is turned on, the variable conductance G takes G _ON =100S; when the IGBT is turned off, the variable conductance G takes G _OFF =1e-6S. At the same time, the sub-module capacitance C of a single D-HBSM at time t is discretized into a conductance G _C and a history current source I _CEQ ( t -ΔT) in parallel. Thus, the equivalent circuit of a single D-HBSM at time t is obtained as shown in Fig. 1(b).

Step 1: In order to list the node voltage equations, first classify the dual half-bridge sub-modules. The sub-module is a dual-capacitor sub-module. Firstly, the sub-module has 6 nodes in total, nodes 1 and 2 are external nodes, k ₁ =1, k ₂ =1, and the capacitor nodes are i =1, j =3, p =4 , q = 2, the remaining nodes are 5 and 6 respectively, i , j and p , q are not equal, so there is no shared plate, no need for short-circuit contraction, and the sub-module can be determined to be 6 nodes.

For any dual half-bridge sub-module, with node 2 as the reference node, V ₂ =0 can be set, and the node voltage equation can be written as shown in formula (1):

(1)

Formula 1 is divided into blocks according to internal and external nodes, which can be rewritten as follows:

(2)

Use the idea of fast nested solution, that is, use the information of external nodes to represent the information of internal nodes, keep only external nodes and eliminate internal nodes. Expand formula (2) into the following two formulas:

(3)

(4)

V _IN can be obtained from formula (4). If V _EX can be obtained, formula (5) can be used to solve the capacitance voltage of each sub-module.

(5)

Substitute (5) into (3) to get:

(6)

In formula (6), make:

(7)

(8)

Then we can finally get an equation of the form (9):

(9)

Where Y _EX is the Norton equivalent conductance, J _EX ^Tsf is the Norton equivalent current source. Obviously, when the Norton parameters are known, the Thevenin parameters of the equivalent circuit are also known.

Step 2: Replace the six bridge arms of the single-port MMC with the equivalent model of the bridge arm obtained in step 1, and add them to the entire single-port MMC simulation circuit network, and then solve the entire circuit network by the electromagnetic transient simulation software , to get the arm current value of each arm.

Step 3: Calculate the V _EX of any sub-module according to the formula (9), and substitute it into the formula (5) to find the value of V _IN , so as to update the internal capacitor voltage information of the sub-module.

Claims (2)

1. A kind of 1. single port submodule MMC electro-magnetic transient generalized equivalent modeling methods；

   It is characterized in that, the present invention by nested rapid solving algorithm by the single bridge arms of single port MMC in whole submodule Portion node equivalent eliminates, the equivalent circuit by whole bridge arm equivalent for only surplus external node, to it is exterior equivalent while, can The various internal informations for completely retaining single bridge arm are not in the situation of loss, are a kind of accurate equivalent models；

   This method comprises the following steps：

   Step 1：Processing is numbered to all nodes, isolates internal node and external node；Row are write each submodule and are corresponded to Nodal voltage equation；To the processing of nodal voltage equation piecemeal, based on the thinking of quick nested derivation algorithm, external node is utilized Information represent internal node so that equivalent cancellation internal node；Replaced by equation, solve submodule Norton equivalent electricity The expression formula on road, and thevenin equivalent circuit is solved accordingly；

   Step 2：Single submodule is composed in series bridge arm equivalent model, then bridge arm equivalent model is added to whole transverter In, whole circuit network is solved using electromagnetic transient simulation software, obtains the bridge arm current value of each bridge arm；

   Step 3：On the basis of step 2, each node voltage inside submodule is obtained by the anti-solution of the bridge arm current tried to achieve, is completed The renewal of submodule internal information.
2. 2. a kind of general single port submodule MMC electro-magnetic transient generalized equivalent modeling methods according to claim 1, it is special Sign is, step 1 arrives step 3, and previous step is the basis that latter step performs, ring between this 3 modeling procedures Ring interlocks, order performs, and is an organic, indivisible entirety.