CN115102173A - A layered distributed control method for flexible diamond-type distribution flexible interconnected converters - Google Patents

Abstract

The invention discloses a layered distributed control method for a flexible diamond distribution flexible interconnection converter, which comprises the following steps: establishing a grid structure of a flexible interconnected power distribution network based on a power distribution interconnection converter; and constructing a layered distributed control strategy based on the grid structure and according to the structure and the principle of three-level control respectively, so as to realize the power flow control of the flexible interconnected power distribution network system. The invention realizes the multi-network coordination control and the optimized operation of the power distribution interconnection converter on the flexible interconnection power distribution network, can improve the voltage quality of a multi-region power distribution feeder line, reduce the line loss, optimize the operation level of the power distribution network, and can realize the seamless flexible switching between system-level control and local control.

Description

A layered distributed control method for flexible diamond-type distribution flexible interconnected converters

technical field

The invention relates to the technical field of power electronic technology and automatic control in power systems, in particular to a layered distributed control method for flexible diamond-type distribution flexible interconnection converters.

Background technique

With the innovation and changes in the field of energy and power, the limitations of traditional distribution networks have become increasingly prominent, and the challenges they face are becoming increasingly severe. Among them, the main problems include: large-scale integration of distributed renewable energy into the power grid, bidirectional flow of power in the distribution network, unbalanced load between feeders, and node voltage exceeding the limit; diversified load types, the structure and operation mode of traditional distribution network cannot be Meet the needs of various flexible loads; users have higher requirements for the reliability of power supply and power quality.

In the distribution network, the line voltage low-voltage over-limit often exists and occurs in the urban distribution network and other regional distribution networks, which has a serious impact on the stable operation of the power system and the power consumption of industries, commerce, and residents. . For a long time, academic circles and power companies have focused on the power quality of medium and high voltage systems, but have not considered the power quality of distribution networks. With the development of my country's economy and the continuous improvement of people's living standards, the demand for electric energy is getting higher and higher. The load of the distribution network is getting heavier and heavier, the types of loads are increasing, and the capacity is increasing. Therefore, it is difficult to guarantee the voltage quality of the distribution network.

With the development of power electronic devices, flexible DC power distribution technology has been continuously improved. The flexible DC power distribution technology based on voltage source converters has been demonstrated and applied in the medium and low voltage flexible interconnected power distribution technology, forming a flexible and interconnected power distribution network with a mix of AC and DC. There will be more and more distributed power sources and various types of loads, which will be a challenge to the stable operation of the distribution network.

SUMMARY OF THE INVENTION

The technical problem solved by the invention is that the load of the distribution network is getting heavier, the types of loads are more and more, and the capacity is larger and larger. Therefore, the voltage quality of the distribution network is difficult to guarantee, and the future distribution network will There are more and more distributed power sources and various types of loads, which will be a challenge to the stable operation of the distribution network.

In order to solve the above technical problems, the present invention provides the following technical solutions: establish a grid structure of a flexible interconnected distribution network based on distribution interconnection converters; The layered distributed control strategy realizes the power flow control of the flexible interconnected power distribution system.

Preferably, the grid structure includes arranging each multi-interconnected converter at the end of the power distribution feeder, and interconnecting the multi-interconnected converters through the DC bus.

Preferably, the three levels include converter level, local level, and system level.

Preferably, the control principle at the converter level includes defining a three-phase voltage-type PWM rectifier as an AC-DC converter, and its mathematical model after coordinate transformation is:

Among them, ed , e _q are the _dq -axis components of the AC voltage source voltage, id , i _q are the _dq -axis components of the three-phase AC current, the resistance R and the inductance L are the inductance and resistance in the main circuit of the AC side, and v _dc is the direct current side voltage, s _d , s _q are the dq-axis components of the switching function, C is the DC capacitance, and R _L is the load resistance;

The AC side inductance L and the DC side capacitance C are defined as:

为限定直流电压上升时间，R_Le为额定直流负载电阻，I_dm为额定直流电流，v_d0为直流电压稳态最低值，v_de为直流电压额定值；In the formula, _{Em is the grid phase electromotive force, T s is} the switching period, v _dc is the DC voltage, _Im is the AC fundamental phase current, Δi _max is the maximum allowable current ripple, take 20% of I _m , and T _imax is the maximum Inertia time constant, ΔP _L,max is the maximum variation of load power, Δv _dc,max is the maximum variation of DC voltage,

In order to limit the DC voltage rise time, R _Le is the rated DC load resistance, I _dm is the rated DC current, v _d0 is the minimum steady-state value of the DC voltage, and v _de is the rated value of the DC voltage;

A PI controller is introduced into the control, and the gain parameter of the PI controller is defined as:

Among them, T _s is the PWM switching period, K _PWM is the equivalent gain of the rectifier bridge, which is related to the modulation method, and K _P and K _I are the gain coefficients of the proportional link and the integral link of the PI regulator, respectively;

Simplify the closed-loop transfer function of the control loop to an inertial link:

Preferably, the control principles at the local level include primary voltage regulation control and secondary voltage regulation control.

Preferably, the primary voltage regulation control includes,

The sag equation is established, the normalized equation and the normalized sag equation are:

P _ac1 =P ₁ +P _dc1

The normalized voltage of the control AC side is equal to the normalized voltage of the DC side, namely:

......

It is defined that the DC normalized voltage of each line is equal, as:

Combining the above formulas, after a voltage regulation controlled by the local level, we can get:

Among them, N represents that there are N flexible interconnections of distribution networks, Z ₁ ,…,Z _n are the line impedances of the first,…,n distribution networks, respectively, P ₁ ,…,P _n are the first,…,n respectively. The load power of the distribution network, V _ac1 ,…,V _acn are the line end voltages of the 1st,…,n distribution networks, respectively, P _c1 ,…,P _cn are the AC and DC voltages of the 1st,…,n distribution networks, respectively The active power delivered by the converter, Q _c1 ,…,Q _cn are the reactive power delivered by the AC/DC converters of the 1st,…,n distribution network respectively, and P _dc is the power of the DC source or load.

则各线路的下垂方程变为：Preferably, the secondary voltage regulation includes, on the basis of the primary voltage regulation, defining the transmission of active power and reactive power as a given value, that is, controlling the power transmission of each feeder to a given value

Then the droop equation of each line becomes:

......

At steady state, the power and voltage equations satisfy:

The system satisfies:

After each line is flexibly interconnected, the DC normalized voltage of each line is defined to be equal, which is:

Combining the above equations, we can get:

Preferably, the control principle at the system level includes, according to the voltage information and power information of each node collected by the system, through intelligent algorithm retrieval, calculating and obtaining the optimal operating state of the system.

Preferably, it also includes establishing a mathematical model of the actual problem according to a general mathematical model, where the general mathematical model is:

minf=f(x,u)

{s.t.g(x,u)=0

h(x,u)≤0

Among them, f(x, u) is the objective function, g(x, u) and h(x, u) are equality constraints and inequality constraints, respectively, and x and u are control variables and state variables, respectively.

Beneficial effects of the invention: the invention realizes the coordinated control and optimal operation of the distribution interconnection converter for the flexible interconnected distribution network, and can improve the voltage quality of the multi-region distribution feeder, reduce the line loss, and optimize the distribution network. Operation level, and can achieve seamless and flexible switching between system-level control and local control.

Description of drawings

1 is a schematic diagram of the overall flow structure of a layered distributed control method for a flexible diamond-type power distribution flexible interconnection converter provided by an embodiment of the present invention;

2 is a schematic diagram of the system structure of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

3 is a block diagram of a current inner loop control based on feedforward decoupling of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

4 is an equivalent circuit diagram of a single distribution network line of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

5 is a block diagram of a primary voltage regulation control without communication controlled by a local level of a layered distributed control method for a flexible diamond-type power distribution flexible interconnection converter provided by an embodiment of the present invention;

6 is an equivalent circuit diagram of a flexible interconnected distribution network of a layered distributed control method for a flexible diamond-type distribution flexible interconnected converter provided by an embodiment of the present invention;

7 is a schematic diagram of the principle of primary voltage regulation without communication controlled at the local level of a layered distributed control method for a flexible diamond-type power distribution flexible interconnection converter provided by an embodiment of the present invention;

8 is a block diagram of a secondary voltage regulation control with communication controlled at a local level of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

9 is a schematic diagram of the principle of secondary voltage regulation with communication controlled at the local level of a layered distributed control method for a flexible diamond-type power distribution flexible interconnection converter provided by an embodiment of the present invention;

10 is an algorithm block diagram of a system-level control of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

11 is a circuit diagram of a simulation example of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

12 is a schematic diagram of a simulation result of the active power transfer of line 1 and line 2 of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

13 is a schematic diagram of a simulation result of the reactive power transfer of line 1 and line 2 of a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention;

FIG. 14 is a schematic diagram of a simulation result of the voltage of each node of line 1 in a layered distributed control method for a flexible diamond-type distribution flexible interconnection converter provided by an embodiment of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Example. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Many specific details are set forth in the following description to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can do so without departing from the connotation of the present invention. Similar promotion, therefore, the present invention is not limited by the specific embodiments disclosed below.

Second, reference herein to "one embodiment" or "an embodiment" refers to a particular feature, structure, or characteristic that may be included in at least one implementation of the present invention. The appearances of "in one embodiment" in various places in this specification are not all referring to the same embodiment, nor are they separate or selectively mutually exclusive from other embodiments.

Example 1

1-10, which is an embodiment of the present invention, provides a layered distributed control method for a flexible diamond-type power distribution flexible interconnection converter, including:

S1: Establish a grid structure of a flexible interconnected distribution network based on distribution interconnection converters; it should be noted that:

The grid structure includes arranging each multi-interconnected converter at the end of the distribution feeder, and interconnected by the DC bus between the multi-interconnected converters.

The three levels include converter, local and system level.

Specifically, in the grid structure of the flexible interconnected distribution network based on multiple interconnection converters (VSCs), each VSC will be configured at the end of the distribution feeder, and the DC bus interconnection between the VSCs can realize flexible interconnection between adjacent feeders , the grid structure provides a new power flow path between multi-area networks and feeders, and can realize flexible adjustment and mutual supply of power between distribution networks.

Under the grid structure of the flexible interconnected distribution network, each VSC needs to coordinate and control according to the voltage and load information of the feeder node, so as to realize the interaction and flexible adjustment of the power flow between the distribution networks. Therefore, the present invention proposes a multi-interconnection The layered distributed control strategy of the converter, the core of the layered distributed control is to control the power interacted by each feeder and each distribution network, so as to solve the problem of voltage over-limit, large line loss, and possible problems in the AC side line. Due to the lack of renewable energy absorbing capacity and many other problems, hierarchical distributed control realizes the power flow control of the flexible interconnected power distribution system and optimizes the operation level of the power distribution network through three levels of control: inverter, local, and system level.

S2: Based on the grid structure and according to the structure and principle of the three-level control, a layered distributed control strategy is constructed to realize the power flow control of the flexible interconnected power distribution system; it should be noted that:

First of all, the control purpose at the converter level is to process and transform the input current signal to output the AC/DC converter switch PWM modulation waveform, control the AC current measurement, the DC side voltage stability, realize the bidirectional power flow, and control the AC/DC side power exchange. The control principle at the converter level is as follows:

Three-phase voltage-type PWM rectifiers are widely used in distribution networks because of their low harmonic content, high power factor, and fast dynamic response. Therefore, three-phase voltage-type PWM rectifiers are selected as AC-DC converters. The mathematical model of its coordinate transformation is:

Among them, ed , e _q are the _dq -axis components of the AC voltage source voltage, id , i _q are the _dq -axis components of the three-phase AC current, the resistance R and the inductance L are the inductance and resistance in the main circuit of the AC side, and v _dc is the direct current side voltage, s _d , s _q are the dq-axis components of the switching function, C is the DC capacitance, and R _L is the load resistance;

In order to improve the operating performance of the system, it is necessary to select the appropriate AC side inductance and DC side capacitance. The AC side inductance L and the DC side capacitance C are defined as:

为限定直流电压上升时间，R_Le为额定直流负载电阻，I_dm额定直流电流，v_d0为直流电压稳态最低值，v_de为直流电压额定值；In the formula, _{Em is the grid phase electromotive force, T s is} the switching period, v _dc is the DC voltage, _Im is the AC fundamental phase current, Δi _max is the maximum allowable current ripple, take 20% of I _m , and T _imax is the maximum Inertia time constant, ΔP _L,max is the maximum variation of load power, Δv _dc,max is the maximum variation of DC voltage,

In order to limit the DC voltage rise time, R _Le is the rated DC load resistance, I _dm is the rated DC current, v _d0 is the minimum steady-state value of the DC voltage, and v _de is the rated value of the DC voltage;

According to this mathematical model, the current inner loop control based on feedforward decoupling can be established, and the control block diagram is shown in Figure 3; the PI controller is introduced into the control, and its parameter design will have an impact on the dynamic performance of the system. The gain parameter is defined as:

Among them, T _s is the PWM switching period, K _PWM is the equivalent gain of the rectifier bridge, which is related to the modulation method, and K _P and K _I are the gain coefficients of the proportional link and the integral link of the PI regulator, respectively;

Finally, the closed-loop transfer function of the control loop can be simplified to an inertial link:

Further, the control purpose at the local level is to control the power interaction between feeders only according to the local voltage information when there is no communication line, so as to improve the voltage quality problem at the end of the line, which is called primary voltage regulation; and when there is a communication line, according to the distribution network. The voltage and power information of each node is used to analyze and calculate the optimal operating state, and by controlling the power interaction, the system can operate in the optimal state, which is called secondary voltage regulation.

Specifically, the principle of control at the local level is as follows:

Assuming that there are N flexible interconnection of distribution networks, Z ₁ ,…,Z _n are the line impedances of the 1st,…,n distribution networks, respectively, P ₁ ,…,P _n are the 1st,…,n distribution networks, respectively. Load power, V _ac1 ,…,V _acn are the line end voltages of the 1st,…,n distribution networks, respectively, P _c1 ,…,P _cn are the AC/DC converter transmissions of the 1st,…,n distribution networks, respectively The active power of , Q _c1 ,…,Q _cn are the reactive power transmitted by the AC-DC converters of the 1st,…,nth distribution network respectively, P _dc is the power of the DC source/load, the equivalent of a single distribution network The circuit diagram is shown in Figure 4.

Considering that the system is in the state of no communication line, a voltage regulation is applied. After analysis, the active power transmitted by each distribution network and the voltage at the end of the line meet the natural droop characteristics. Therefore, the droop equation, the normalized equation and the normalized droop equation can be established. The sag equation is:

P _ac1 =P ₁ +P _dc1

The block diagram of the primary voltage regulation control without communication at the local level is shown in Figure 5. The normalized voltage of the control AC side is equal to the normalized voltage of the DC side, namely:

......

After each line is flexibly interconnected, the equivalent circuit diagram is shown in Figure 6. It is defined that the DC normalized voltage of each line is equal, which is:

Combining the above formulas, after a voltage regulation controlled by the local level, we can get:

Among them, the control principle is shown in Figure 7.

When there is no communication line in the system, the local level is used to control the primary voltage regulation; in the actual operation of the distribution network, when the line impedance is constant, the terminal voltage of the line is determined by the load power of the line. If the load power is higher, the voltage at the end of the line decreases. The load power is low, and the voltage at the end of the line decreases less; the result formula after one-time voltage regulation shows that after multiple feeders are flexibly interconnected, the AC side normalized voltage of each line is at the same voltage level, and the voltage of each line is at the same voltage level. The power is complementary to each other.

则各线路的下垂方程变为：Considering the state of the system with communication lines, the secondary voltage regulation is applied. On the basis of the primary voltage regulation, the transmission of active power and reactive power is defined as a given value, that is, the power transmission of each feeder is controlled to a given value.

Then the droop equation of each line becomes:

......

The block diagram of the secondary voltage regulation control with communication controlled at the local level is shown in Figure 8. At steady state, the power and voltage equations satisfy:

The system satisfies:

After each line is flexibly interconnected, the equivalent circuit diagram is shown in Figure 5. It is defined that the DC normalized voltage of each line is equal, which is:

Combining the above equations, we can get:

Among them, the control principle is shown in Figure 9.

When there is a communication line in the system, the secondary voltage regulation controlled at the local level is used to control the interaction between active power and reactive power as a given value, accurately control the power transfer of each feeder, and adjust the operation status of each line according to the demand. Layer Distributed control system layer provides interface with local layer control.

Finally, the purpose of control at the system level is to obtain the optimal operating state of the system through intelligent algorithm retrieval based on the voltage information and power information of each node collected by the system, so as to coordinate the power scheduling of each area. The voltage level does not exceed the limit, and at the same time, it meets the two problems of the minimum power loss of the overall system, optimizes the overall operation of the system, and improves the economy of the overall operation of the system. The principle of system-level control is as follows:

Essentially, the control at the system level solves an optimal power flow problem; the optimal power flow problem of a power system is a complex nonlinear programming problem with constraints. The control method used is used to achieve the optimal system stable operation state of the predetermined target; it takes into account many aspects such as safety, economy, reliability, etc. Among them, the general mathematical model can be expressed as:

minf=f(x,u)

{s.t.g(x,u)=0

h(x,u)≤0

Among them, f(x, u) is the objective function, g(x, u) and h(x, u) are equality constraints and inequality constraints, respectively, and x and u are control variables and state variables, respectively. :

From the mathematical model, the desired objective function can generally be set according to the actual needs, and the constraints of various aspects can be considered according to the variables in the objective function, and the corresponding constraints can be designed, so as to establish a mathematical model of the actual problem. .

In the control at the system level, the optimization algorithm is the core of the control; for the optimization algorithm of the flexible interconnected system involved, the problem to be solved is to control the power interaction between the distribution networks in the flexible interconnected system to achieve the overall global optimization of the system; and this The problem is a multi-variable problem, and the independence of each variable is strong, and the monotonicity of each variable is not single; therefore, when the system is optimized, many local optimal solutions will be generated, and the algorithm often falls into the local optimal interval; To this end, the simulated annealing optimization algorithm combined with the Newton-Raphson power flow algorithm is selected as the control algorithm at the system level; a major feature of this algorithm is that it can jump out of the local optimal interval with a certain probability, which is suitable for the optimization algorithm of multi-terminal flexible interconnected systems; its algorithm The block diagram is shown in Figure 10.

Based on the flexible interconnected distribution network, the present invention establishes layered distributed control to improve the operation of the flexible interconnected distribution network; on the one hand, the scheme can be considered from the overall level of the system to carry out global operation optimization control; on the other hand, it can Considering the local distribution network level, local voltage quality improvement and power balance can be performed only through local information; and it can be flexibly and seamlessly switched between system-level control and local-level control, thus realizing the distribution of power distribution. The flexible control of the system reduces the line loss, improves the voltage quality of the distribution feeder, and improves the economy and flexibility of the operation of the distribution network.

Example 2

11-14 is another embodiment of the present invention, in order to verify and explain the technical effect adopted in this method, this embodiment adopts specific examples to test the method of the present invention, and verifies the real effect of this method by means of scientific demonstration .

In order to verify the optimal effect of the flexible interconnected system-level operation optimization control on the overall operation of the distribution network system, the following example is designed for comparative analysis in this embodiment. The example consists of two independent distribution network lines, and each feeder is connected to With photovoltaic grid-connected and user load, the two lines have different line impedances and are flexibly interconnected through the DC side, as shown in Figure 11.

In the calculation example, the loads of the three nodes of line 1 are 24+j18 KVA, -50kW, 24+j18 KVA, and the loads of the three nodes of line 2 are 20+j15 KVA, -30kW, 20+j15 KVA, respectively. The rated voltage of line 1 and line 2 is 220V. When normalized, the upper and lower limits of the voltage of each distribution network are set to 110% and 90% of the rated voltage, respectively. The line impedance of line 1 is twice that of line 2.

After retrieval by the intelligent optimization algorithm, the optimal working condition is obtained, and the output results are as follows:

Line 1: P _c1 =15960W, Q _c1 =-20000Var;

Line 2: P _c2 =-15960W, Q _c2 =-20000Var;

Line loss is reduced from 14584W to 5095W.

The control effect of the present invention is verified by simulation; the simulation sequence is: when t=0s, the simulation starts, the communication secondary voltage regulation controlled by the local level is based on the power command controlled by the system level, and both line 1 and line 2 are turned on to the local level. The control is the secondary voltage regulation of communication; when t=1.5s, the analog communication line is interrupted, the control at the system level is turned off, and the control at the local level is switched to the primary voltage regulation without communication; t=2.5s, the simulation ends.

The simulation results are shown in Figure 12-14; Figure 12-14 is the active power and reactive power transfer waveforms of line 1 and line 2, the voltage levels of each node in line 1 and line 2, and the voltage levels of line 1 and line 2. dq-axis component of the inverter current.

Analyze the simulation results, as shown in Figure 12, when the system is put into secondary voltage regulation control from 0.5s to 1.5s, line 1 transmits 16kW active power to the DC side, and line 2 absorbs 16kW active power from the DC side; 1.5s When the communication between the feeders is interrupted, the system switches from the secondary voltage regulation to the primary voltage regulation; from 1.5s to 2.5s, the system no longer accepts the power command output by the system level control, but controls according to the local voltage information at the end of the line; At this time, line 1 transmits 24kW of active power to the DC side, and line 2 absorbs 24kW of active power from the DC side.

The simulation results shown in Figure 13 show that the reactive power transfer conditions of line 1 and line 2 basically coincide; during 0.5s to 1.5s, the system uses the local level to control the secondary voltage regulation without communication, and line 1 and line 2 absorb 20kVar Reactive power; at 1.5s, the system switches from secondary voltage regulation to primary voltage regulation; at 1.5s to 2.5s, the system no longer accepts the power command from the system level control output, and the reactive power of line 1 and line 2 is stable at 0Var.

In the voltage level of each node of line 1 shown in Figure 14: when the system is not controlled, the voltages of node 1, node 2 and node 3 are not over the limit, but the voltage of node 3 is at a low level, and the voltage of node 1, node 3 2. The voltage of node 3 has not reached the rated voltage level; when the system is put into the non-communication primary voltage regulation controlled by the local level, the voltage of each node has a certain rise compared with the non-controlled system, which is closer to the rated voltage level; the system When receiving the power command controlled by the system level and putting it into the communication secondary voltage regulation controlled by the local level, the voltage level of each node is greatly improved, and it is the closest to the rated voltage. In particular, the voltage at node 3, ie the voltage at the end of line 1, is significantly improved.

In the voltage level of each node of line 2: when the system is not controlled, the voltage of node 1 and node 2 does not exceed the limit, and the deviation from the rated value is large, while the voltage of node 3 is lower than 0.9p.u. The quality problem is serious; when the system is put into the one-time voltage regulation without communication controlled by the local level, the voltage of node 3 is raised by 25.6V, and is in the range of 0.9p.u.~1.1p.u.; and the voltage level of each node has been improved; the system receiving system When the level-controlled power command is put into the local level-controlled secondary voltage regulation, the voltage level of each node is similar to the primary voltage regulation control voltage level, which also solves the voltage quality problem at the end of line 2 and improves the overall voltage level.

It can be seen from the above that in the flexible interconnected distribution network, hierarchical distributed control can improve the problems of unbalanced feeder load, low voltage quality at the end of the line, and high line loss in the distribution network, and improve the reliability of the power supply of the distribution network. performance and operational flexibility.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent substitutions without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims (9)

1. A layered distributed control method for a flexible diamond-type power distribution flexible interconnection converter, comprising: Establish the grid structure of the flexible interconnected distribution network based on the distribution interconnection converter; Based on the grid structure and respectively according to the structure and principle of the three-level control, a layered distributed control strategy is constructed to realize the power flow control of the flexible interconnected power distribution system. 2. The layered distributed control method for flexible diamond-type distribution flexible interconnected converters as claimed in claim 1, characterized in that: the grid structure comprises that each multi-interconnected converter is arranged at the end of the distribution feeder, The DC bus between the multi-interconnected converters is interconnected. 3 . The layered and distributed control method for flexible diamond-type distribution flexible interconnection converters according to claim 1 , wherein the three levels include three levels of converter, local level, and system level. 4 . 4. The layered distributed control method for flexible diamond-type power distribution flexible interconnection converters as claimed in claim 3, characterized in that: the control principle at the converter level comprises: Defining a three-phase voltage-type PWM rectifier as an AC-DC converter, its mathematical model after coordinate transformation is:

Among them, ed , e _q are the _dq -axis components of the AC voltage source voltage, id , i _q are the _dq -axis components of the three-phase AC current, the resistance R and the inductance L are the inductance and resistance in the main circuit of the AC side, and v _dc is the direct current side voltage, s _d , s _q are the dq-axis components of the switching function, C is the DC capacitance, and R _L is the load resistance; The AC side inductance L and the DC side capacitance C are defined as:

In the formula, _{Em is the grid phase electromotive force, T s is} the switching period, v _dc is the DC voltage, _Im is the AC fundamental phase current, Δi _max is the maximum allowable current ripple, take 20% of I _m , and T _imax is the maximum Inertia time constant, ΔP _{L, max} is the maximum variation of load power, Δv _{dc, max} is the maximum variation of DC voltage,

In order to limit the DC voltage rise time, R _Le is the rated DC load resistance, I _dm is the rated DC current, v _d0 is the steady-state minimum value of the DC voltage, and v _de is the rated value of the DC voltage; A PI controller is introduced into the control, and the gain parameter of the PI controller is defined as:

Among them, T _s is the PWM switching period, K _PWM is the equivalent gain of the rectifier bridge, which is related to the modulation method, and K _P and K _I are the gain coefficients of the proportional link and the integral link of the PI regulator, respectively; Simplify the closed-loop transfer function of the control loop to an inertial link:

5 . The layered and distributed control method for flexible diamond-type distribution flexible interconnection converters according to claim 3 , wherein the control principles at the local level include primary voltage regulation control and secondary voltage regulation control. 6 . 6. The layered distributed control method for flexible diamond-type power distribution flexible interconnection converters according to claim 5, wherein the primary voltage regulation control comprises: The sag equation is established, the normalized equation and the normalized sag equation are:

P _ac1 =P ₁ +P _dc1 The normalized voltage of the control AC side is equal to the normalized voltage of the DC side, namely:

...

It is defined that the DC normalized voltage of each line is equal, as:

Combining the above formulas, after a voltage regulation controlled by the local level, we can get:

Among them, N represents that there are N flexible interconnections of distribution networks, Z ₁ , ..., Zn are the line impedances of the first, ..., _n distribution networks, respectively, P ₁ , ..., P _n are _{1 , . _} are the active power delivered by the AC-DC converters of the 1st, ..., n distribution networks, respectively, Q _c1 , ..., Q _cn are the AC-DC converters of the first, ..., n distribution networks, respectively Transmitted reactive power, P _dc is the power of the DC source or load. 7. The layered distributed control method for flexible diamond-type distribution flexible interconnection converters according to claim 5, wherein the secondary voltage regulation comprises: On the basis of the primary voltage regulation, the transmission of active power and reactive power is defined as a given value, that is, the power transmission of each feeder is controlled to a given value

Then the droop equation of each line becomes:

...

At steady state, the power and voltage equations satisfy:

The system satisfies:

After each line is flexibly interconnected, the DC normalized voltage of each line is defined to be equal, which is:

Combining the above equations, we can get:

8. The layered distributed control method for flexible diamond-type distribution flexible interconnection converters as claimed in claim 3, wherein the control principle at the system level comprises: According to the voltage information and power information of each node collected by the system, the optimal operating state of the system is calculated through the retrieval of the intelligent algorithm. 9. The layered distributed control method for flexible diamond-type distribution flexible interconnection converters as claimed in claim 8, characterized in that: further comprising: The mathematical model of the actual problem is established according to the general mathematical model, and the general mathematical model is: min f=f(x, u) {s.t.g(x, u) = 0 h(x, u)≤0 Among them, f(x, u) is the objective function, g(x, u) and h(x, u) are equality constraints and inequality constraints, respectively, and x and u are control variables and state variables, respectively.

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