Coordinated Control Method for DC Microgrid with Constant Power Loads Based on Consensus Algorithm

Abstract

The present invention discloses a cooperative regulation method for a DC microgrid with constant power loads based on a consensus algorithm, including: pre-establishing a bus average voltage control objective function and a power distribution control objective function; defining a system instability factor according to the stability conditions of the connected constant power loads, and using a discrete form of the dynamic consensus algorithm to estimate the system average instability factor, and constructing a system average instability factor control objective function with the goal of minimizing the system average instability factor; using PI control regulation for the three control objective functions to obtain the voltage compensation amounts corresponding to each control objective function, and dynamically adjusting the droop control voltage setpoint based on the three voltage compensation amounts, so as to achieve the stability control of the nodes accessing constant power loads.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed cooperative control of DC microgrids, and particularly to a cooperative regulation method for a DC microgrid with constant power loads based on a consensus algorithm. Background Technique

[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] With the rapid development of modern DC microgrid systems, various forms exist at both the source and load ends. Among them, constant power loads, as one of the most typical load forms, have attracted the attention of domestic and foreign scholars. Such loads draw a constant amount of power from the DC bus under strict closed-loop control, resulting in the negative impedance characteristic of constant power loads, which will greatly reduce the stability margin of the system and is not conducive to the stable operation of the system.

[0004] In response to this, existing solutions are mainly divided into three types. One is to adopt a passive damping compensation scheme, adding resistance, inductance, and capacitance elements to the system circuit to physically compensate for the lack of damping. This method is effective but brings additional losses. The second is to adopt a passive damping compensation scheme, adding virtual impedance in the system control structure to compensate for the lack of damping. This method is simple and easy to implement, but it is based on a small-signal model and is difficult to achieve stability under large disturbances. The third is to adopt non-linear control methods, including sliding mode control, model predictive control, etc., which can achieve stability under a large-signal model, but it only realizes stable operation of a single machine and does not consider the global voltage and power regulation objectives, making it difficult to be extended to the microgrid system. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a cooperative regulation method for a DC microgrid with constant power loads based on a consensus algorithm, constructs three control objectives, adopts a distributed cooperative control method, obtains the corresponding voltage compensation amounts for the three control objective functions, and dynamically adjusts the droop control voltage set point to achieve stability control of the nodes accessing constant power loads.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a cooperative regulation method for a DC microgrid with constant power loads based on a consensus algorithm, including:

[0008] Pre-construct a bus average voltage control objective function and a power distribution control objective function;

[0009] Define the system instability factor according to the stability conditions of the connected constant-power load, and use the discrete form of the dynamic consistency algorithm to estimate the average system instability factor. With the goal of minimizing the average system instability factor, construct the control objective function of the average system instability factor;

[0010] Use PI control to adjust the three control objective functions to obtain the voltage compensation amounts corresponding to the respective control objective functions. Based on the three voltage compensation amounts, dynamically adjust the droop control voltage set point to achieve the stability control of the node connected to the constant-power load.

[0011] As an alternative implementation, the system instability factor is:

[0012]

[0013] where i Li is the inductor current and V ci is the output terminal capacitor voltage.

[0014] As an alternative implementation, the stability condition of the connected constant-power load is D i (k) = 0.

[0015] As an alternative implementation, the average system instability factor estimated using the discrete form of the dynamic consistency algorithm is:

[0016]

[0017] where T com is the communication period, a ij is the adjacency coefficient, D avgi (k) and D avgj (k) are the average system instability factors of node i and node j respectively, and N i is the set of neighbor nodes of node i.

[0018] As an alternative implementation, the control objective function of the average system instability factor is D avgi (k) = 0.

[0019] As an alternative implementation, the three voltage compensation amounts are respectively:

[0020]

[0021]

[0022]

[0023] where H i (s), G i (s) and F i(s) are the equivalent transfer functions of the PI controller, v avgi , δ i and D avgi respectively represent the bus average voltage control target, the power distribution control objective function, and the system average instability factor control target. Specifically, v avgi = v ref , δ i = 0, D avgi = 0, and v ref is the preset bus voltage reference value.

[0024] As an alternative implementation, the process of dynamically adjusting the droop control voltage setpoint based on three voltage compensation amounts is expressed as:

[0025]

[0026] where i oi is the output current, and R i is a purely resistive load.

[0027] In a second aspect, the present invention provides a DC microgrid collaborative regulation system based on a consensus algorithm, including:

[0028] First and second objective function construction modules configured to pre-construct a bus average voltage control objective function and a power distribution control objective function;

[0029] A third objective function construction module configured to define a system instability factor according to the stability conditions of the connected constant power loads, and use a discrete form of the dynamic consensus algorithm to estimate the system average instability factor, and construct a system average instability factor control objective function with the goal of minimizing the system average instability factor;

[0030] A stability control module configured to use PI control to adjust the three control objective functions to obtain the voltage compensation amounts corresponding to each control objective function, and dynamically adjust the droop control voltage setpoint based on the three voltage compensation amounts to achieve stability control of the nodes connected to the constant power loads.

[0031] In a third aspect, the present invention provides an electronic device including a memory and a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the method described in the first aspect is completed.

[0032] In a fourth aspect, the present invention provides a computer-readable storage medium for storing computer instructions. When the computer instructions are executed by a processor, the method described in the first aspect is completed.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] The present invention adopts a distributed cooperative control method to design a cooperative regulation method for a DC microgrid with constant power loads based on a consensus algorithm, constructs three control objectives including a bus average voltage control objective function, a power distribution control objective function, and a system average instability factor control objective function, and uses PI control regulation for the three control objective functions to obtain their respective corresponding voltage compensation amounts, dynamically adjusts the droop control voltage setpoint, thereby realizing the stability control of the nodes accessing constant power loads. When multiple power electronic converters are connected in a cluster to form a microgrid, it can achieve precise voltage regulation of the bus voltage, accurate proportional distribution of each unit's power, and robustness to the access of large-scale constant power loads. This method fully considers the nonlinear characteristics of constant power loads and can achieve stable operation of the microgrid system under large-signal disturbances.

[0035] Advantages of additional aspects of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0037] Figure 1 It is the structure diagram of a DC microgrid with constant power loads provided for Embodiment 1 of the present invention;

[0038] Figure 2 It is the schematic diagram of Node i using a bidirectional boost converter provided for Embodiment 1 of the present invention;

[0039] Figure 3 It is the cooperative regulation block diagram of a DC microgrid with constant power loads provided for Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention will be further described below in conjunction with the drawings and embodiments.

[0041] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0043] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0044] Embodiment 1

[0045] Most of the loads in a DC microgrid are connected to the microgrid bus through power electronic converters. These loads are usually under strict closed-loop control, and the consumed power is not affected by the change of the input voltage, and can be regarded as constant power loads. To achieve the normal operation of the DC microgrid under the access of constant power loads, in the existing solutions, nonlinear control methods such as sliding mode variable structure control, model predictive control, and backstepping control are mostly adopted in the control of the power electronic converters at the bottom layer of the microgrid to achieve the stability of the system in the large-signal range except at the equilibrium point.

[0046] Most of the research objects of the existing solutions are single power electronic converters with constant power loads. Connecting multiple power electronic converters in a cluster to form a microgrid, its control objectives include three: ① precise voltage regulation of the bus voltage; ② each unit can achieve accurate proportional power distribution, and ③ the whole system is robust to the access of large-scale constant power loads.

[0047] However, most of the existing solutions only consider control objective ③ in the design process. They use nonlinear control methods to make the single power electronic converter robust to the access of constant power loads, but do not achieve the basic control objectives ① and ② from the perspective of the whole system, which restricts the popularization and application of the existing solutions in the microgrid system.

[0048] Therefore, this embodiment provides a cooperative control method for a DC microgrid with constant power loads based on the consensus algorithm, including:

[0049] Pre-construct a bus average voltage control objective function and a power distribution control objective function;

[0050] According to the stability conditions of the connected constant power loads, define a system instability factor, and use a discrete form of the dynamic consensus algorithm to estimate the average system instability factor. Taking the minimization of the average system instability factor as the goal, construct an average system instability factor control objective function;

[0051] PI control regulation is adopted for three control objective functions to obtain the voltage compensation amounts corresponding to the respective control objective functions. Based on the three voltage compensation amounts, the droop control voltage setpoint is dynamically adjusted to achieve the stability control of the node accessing the constant power load.

[0052] As Figure 1 shown in the figure, the DC microgrid for accessing constant power loads includes distributed power sources, energy storage devices, and loads. Among them, the loads include pure resistive loads and constant power loads. There are two common types of constant power loads: as Figure 1 shown in I in the figure, a dc / dc converter with a pure resistive load under strict voltage closed-loop control, and as Figure 1 shown in II in the figure, a dc / ac converter with a motor operating in a constant power mode.

[0053] In this embodiment, to meet the control objective ① of the DC microgrid system, it is necessary to control the voltages of each unit in the DC microgrid. The dynamic consistency algorithm is used to estimate the average DC bus voltage as:

[0054]

[0055] In the formula, v avgi (t) and v avgj (t) are the observed values of the average bus voltages of node i and node j respectively, j ∈ N i , N i is the set of neighbor nodes of node i, and a ij is the adjacency coefficient;

[0056] When t → ∞, and Therefore, v avgi = v ref is the control objective ① of the DC microgrid system, and v ref is the preset bus voltage reference value.

[0057] In this embodiment, to meet the control objective ② of the DC microgrid system, on the premise of controlling the voltages of each node, it is necessary to control the output currents of each unit. Specifically:

[0058]

[0059] Among them, and are the per-unit values of the output currents of node i and node j respectively, and c is a constant used to represent the coupling relationship.

[0060] When each unit is allocated according to the capacity ratio, Therefore, δ i = 0 is the control objective ② of the DC microgrid system.

[0061] Without loss of generality, in this embodiment, each unit uses a bidirectional boost converter as a constant power load and is connected to the DC bus, as Figure 2 shown. Taking the i-th unit as an example, where L i and C i respectively represent the inductor and capacitor of the boost converter, V dci represents the source voltage, i Li is the inductor current, V ci is the output capacitor voltage, i oi is the output current, and R is a purely resistive load; its mathematical model is:

[0062]

[0063] where P CPL is the power of the constant power load; u is the switch state. When u = 1, it represents that the switch tube S i1 is turned on and S i2 is turned off. When u = 0, it represents that the switch tube S i1 is turned off and S i2 is turned on. The following analyzes the two states separately.

[0064] (1) When u = 1, Equation (3) is rewritten as:

[0065]

[0066] In the orthogonal coordinate system with the abscissa i Li and the ordinate V ci , the graph of Equation (4) is a parabola.

[0067] (2) When u = 0, Equation (3) is rewritten as:

[0068]

[0069]

[0070] Equation (5) shows the unboundedness of the state variable V ci . Combining Equation (6), it can be obtained that in the same coordinate system, the graph of Equation (6) is an outward expanding spiral; from this, it can be seen that the essence of the constant power load is to cause instability during the on or off interval of the switch. For this, the stable condition of the Boost converter under the constant power load can be obtained:

[0071]

[0072] For this, the system instability factor is defined as:

[0073]

[0074] When the system is stable, Equation (7) is satisfied, and at this time, the system instability factor D i (k) = 0.

[0075] The discrete - form dynamic consensus algorithm is used to estimate the average instability factor of the system as:

[0076]

[0077] When k → ∞, and D avgi (k) = 0, where T com represents the communication period. Therefore, D avgi (k) = 0 is the control objective ③ of the DC micro - grid system.

[0078] In this embodiment, the specific expression forms of the three control objectives of the DC micro - grid system are determined above, and then the implementation of the three control objectives is completed based on the PI controller. The regulation process is as Figure 3 shown:

[0079]

[0080] Among them, H i (s), G i (s) and F i (s) are all equivalent transfer functions of the PI controller. The PI controller can achieve the non - offset regulation of the control quantity, that is, v avgi = v ref , δ i = 0 and D avgi (k) = 0; and respectively represent the voltage compensation amounts corresponding to the three control objectives;

[0081] Based on the above three voltage compensation amounts, the droop - control voltage set - point is dynamically adjusted to achieve the stability control of the node accessing the constant - power load; as shown in Equation (11):

[0082]

[0083] Embodiment 2

[0084] This embodiment provides a DC micro - grid collaborative regulation system with a constant - power load based on the consensus algorithm, including:

[0085] The first and second objective - function construction modules, configured to pre - construct the bus - average - voltage control objective function and the power - distribution control objective function;

[0086] The third objective function construction module is configured to define a system instability factor according to the stability conditions of the connected constant-power loads, and use a discrete-form dynamic consistency algorithm to estimate the average system instability factor. With the goal of minimizing the average system instability factor, a control objective function for the average system instability factor is constructed.

[0087] The stability control module is configured to use PI control regulation for the three control objective functions to obtain the voltage compensation amounts corresponding to the respective control objective functions. Based on the three voltage compensation amounts, the droop control voltage setpoint is dynamically adjusted, thereby achieving stability control for the nodes connected with constant-power loads.

[0088] It should be noted here that the above modules correspond to the steps described in Embodiment 1. The examples and application scenarios implemented by the above modules and the corresponding steps are the same, but are not limited to the content disclosed in the above Embodiment 1. It should be noted that the above modules, as part of the system, can be executed in a computer system such as a set of computer-executable instructions.

[0089] In more embodiments, there is also provided:

[0090] An electronic device includes a memory, a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the method described in Embodiment 1 is completed. For the sake of brevity, it will not be elaborated here.

[0091] It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA, or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0092] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0093] A computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by the processor, the method described in Embodiment 1 is completed.

[0094] The method in Embodiment 1 can be directly implemented by a hardware processor or by a combination of hardware and software modules in the processor. The software module can be located in a mature storage medium in the art such as random access memory, flash memory, read-only memory, programmable read-only memory, or electrically erasable programmable memory, registers, etc. This storage medium is located in the memory, and the processor reads the information in the memory and combines its hardware to complete the steps of the above method. To avoid repetition, it will not be described in detail here.

[0095] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in conjunction with this embodiment can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0096] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A coordinated control method for a DC microgrid with constant power loads based on a consensus algorithm, characterized in that Including: Pre - construct the bus average voltage control objective function and the power distribution control objective function; According to the stability conditions of the connected constant - power loads, define the system instability factor, and use the discrete - form dynamic consistency algorithm to estimate the system average instability factor. Taking the minimization of the system average instability factor as the goal, construct the system average instability factor control objective function; Adopt PI control regulation for the three control objective functions to obtain the voltage compensation amounts corresponding to each control objective function. Based on the three voltage compensation amounts, dynamically adjust the droop - control voltage setpoint, thereby realizing the stability control of the nodes accessing constant - power loads; The three voltage compensation amounts are respectively: Among them, , and are all equivalent transfer functions of the PI controller. , and respectively represent the control target of the average bus voltage, the control objective function of power distribution, and the control target of the average system instability factor. is the preset bus voltage reference value. The process of dynamically adjusting the droop - control voltage setpoint based on the three voltage compensation amounts is expressed as: Among them, is the output current, is a purely resistive load.

2. The collaborative control method for a DC microgrid with constant power loads based on a consensus algorithm according to claim 1, characterized in that The system instability factor is: Among them, is the inductor current, is the output terminal capacitor voltage.

3. The collaborative control method for a DC microgrid with constant power loads based on the consensus algorithm according to claim 2, characterized in that, The stability condition of the connected constant-power load is .

4. The collaborative control method for a DC microgrid with constant power loads based on the consensus algorithm according to claim 1, characterized in that, The system average instability factor estimated by using the discrete - form dynamic consistency algorithm is: Among them, is the communication period, is the adjacency coefficient, and are the system average instability factors of nodes and node respectively, is the set of neighbor nodes of node .

5. The collaborative control method for a DC microgrid with constant power loads based on a consensus algorithm according to claim 4, wherein, The control objective function of the system average instability factor is .

6. The coordinated control system of the DC microgrid with constant power load based on the consensus algorithm is characterized in that, Including: The first and second objective - function construction modules, configured to pre - construct the bus average voltage control objective function and the power distribution control objective function; The third objective - function construction module, configured to define the system instability factor according to the stability conditions of the connected constant - power loads, and use the discrete - form dynamic consistency algorithm to estimate the system average instability factor. Taking the minimization of the system average instability factor as the goal, construct the system average instability factor control objective function; The stability control module, configured to adopt PI control regulation for the three control objective functions to obtain the voltage compensation amounts corresponding to each control objective function. Based on the three voltage compensation amounts, dynamically adjust the droop - control voltage setpoint, thereby realizing the stability control of the nodes accessing constant - power loads; The three voltage compensation amounts are respectively: Among them, , and are all equivalent transfer functions of the PI controller. , and respectively represent the bus average voltage control target, the power distribution control objective function, and the system average instability factor control target. is the preset bus voltage reference value. The process of dynamically adjusting the droop - control voltage setpoint based on the three voltage compensation amounts is expressed as: Wherein, is the output current, is a pure resistive load.

7. An electronic device, characterized in that, Including a memory, a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the method according to any one of claims 1 - 5 is completed.

8. A computer-readable storage medium, characterized in that, For storing computer instructions, when the computer instructions are executed by the processor, the method according to any one of claims 1 - 5 is completed.

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