Delay DC micro-grid secondary control method based on active prediction compensation strategy

Abstract

The invention relates to the technical field of direct current micro-grids, in particular to a time delay direct current micro-grid secondary control method based on an active prediction compensation strategy. Comprising the following steps: calculating a voltage predicted value and a current predicted value of a current distributed power generation unit DG by using a historical control sequence cached in a secondary controller, a system kinetic equation in a continuous time domain and communication delay time; calculating a voltage auxiliary control quantity and a current auxiliary control quantity of a current distributed power generation unit DG of the DC micro-grid based on the voltage predicted value and the current predicted value, and calculating a voltage set value of primary control according to the voltage auxiliary control quantity and the current auxiliary control quantity; and generating a pulse width modulation (PWM) waveform of a DC-DC converter connected to the current distributed power generation unit DG based on the voltage set value of the primary control by using a droop control mechanism and a cascade PI controller, so as to drive the DC-DC converter to carry out voltage regulation and current distribution on the current distributed power generation unit DG based on the PWM waveform.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current microgrids, and in particular to a time-delay direct current microgrid secondary control based on an active prediction compensation strategy. Background Art

[0002] Under the background of the "dual carbon" goal, DC microgrid, as a new type of power system architecture, has been widely used in distributed energy systems in recent years due to its high efficiency, flexibility and renewable energy friendliness. DC microgrid can effectively integrate renewable energy such as photovoltaic and wind power, reduce dependence on traditional fossil energy, and meet the requirements of energy transformation and dual carbon goals. However, the control strategy of DC microgrid faces many challenges, especially at the secondary control level. The inevitable delay problem in the power communication network has a significant impact on the stability and performance of the system.

[0003] Secondary control is mainly responsible for tasks such as voltage recovery and current distribution in microgrids. Since there are inevitable delays in the communication between distributed generation units (DG) in microgrids, these delays may cause lags in control signals, leading to system oscillations, decreased stability, and even instability. Therefore, how to effectively mitigate and compensate for the impact of delays on microgrid secondary control has become a hot topic and difficulty in current research. Summary of the invention

[0004] The present invention provides a time-delay DC microgrid secondary control method based on an active prediction compensation strategy to solve the problem that the time delay introduced by a sparse communication network affects the voltage deviation correction and current distribution of the microgrid.

[0005] The first aspect of the present invention provides a method for secondary control of a delayed DC microgrid based on an active predictive compensation strategy, comprising the following steps: using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time to calculate the voltage prediction value and the current prediction value of the current distributed generation unit DG; calculating the voltage auxiliary control quantity and the current auxiliary control quantity of the current distributed generation unit DG of the DC microgrid based on the voltage prediction value and the current prediction value, and calculating the voltage setting value of the primary control according to the voltage auxiliary control quantity and the current auxiliary control quantity; using a droop control mechanism and a cascade PI controller, based on the voltage setting value of the primary control, a pulse width modulation PWM waveform of a DC-DC converter connected to the current distributed generation unit DG is generated, so as to drive the DC-DC converter based on the PWM waveform to perform voltage regulation and current distribution on the current distributed generation unit DG.

[0006] Optionally, the voltage prediction value is calculated as follows:

[0007]

[0008] The calculation formula of the current prediction value is:

[0009]

[0010] Where τ is the communication delay time, i is the distributed generation unit DG, is the voltage prediction value at time k based on the voltage information at time k-τ, v i (k-τ) is the terminal voltage of the secondary controller at time k after a delay of τ steps, t sc is the control period of the secondary control, is the voltage auxiliary control value of the ith DG at time km, m is a positive integer from 1 to τ, is the current prediction value at time k based on the current information at time k-τ, i i (k-τ) is the output current of the secondary controller at time k after a delay of τ steps, is the current auxiliary control quantity of the ith DG at time km.

[0011] Optionally, the calculating of the voltage auxiliary control amount and the current auxiliary control amount of the current distributed generation unit DG of the DC microgrid based on the voltage prediction value and the current prediction value includes: calculating the voltage auxiliary control amount using a voltage auxiliary control amount calculation formula, and calculating the current auxiliary control amount using a current auxiliary control amount calculation formula, wherein the calculation formula of the voltage auxiliary control amount is:

[0012]

[0013] The current auxiliary control amount calculation formula is:

[0014]

[0015] in, is the voltage auxiliary control quantity of the ith DG at time k based on the voltage prediction value at time k-τ, is the current auxiliary control quantity of the i-th DG at time k based on the current prediction value at time k-τ, ψ is the coupling gain of the voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i is the neighbor set of the ith DG, is the rated current of the converter connected to the i-th DG, λ is the coupling gain of the current controller, v nom is the nominal value of the terminal voltage of DG, is the rated current of the converter connected to the i-th DG, is the current prediction value of the i-th DG at time k based on time k-τ, is the voltage prediction value of the ith DG at time k based on time k-τ, is the current prediction value of the jth DG at time k based on time k-τ, is the voltage prediction value of the jth DG at time k based on time k-τ.

[0016] Optionally, calculating the voltage setting value of the primary control according to the voltage auxiliary control amount and the current auxiliary control amount includes: calculating the voltage setting value of the primary control using the primary control voltage calculation formula, wherein the primary control voltage calculation formula is:

[0017]

[0018] in, is the voltage setting value of the primary control of the i-th DG at time k, R i vir is the virtual resistance of the ith DG.

[0019] The second aspect of the present invention provides a time-delay DC microgrid secondary control device based on an active predictive compensation strategy, including: a first calculation module, used to calculate the voltage prediction value and current prediction value of the current distributed generation unit DG by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time; a second calculation module, used to calculate the voltage auxiliary control quantity and the current auxiliary control quantity of the current distributed generation unit DG of the DC microgrid based on the voltage prediction value and the current prediction value, and calculate the voltage setting value of the primary control according to the voltage auxiliary control quantity and the current auxiliary control quantity; a control module, used to generate a pulse width modulation PWM waveform of the DC-DC converter connected to the current distributed generation unit DG based on the voltage setting value of the primary control by using a droop control mechanism and a cascade PI controller, so as to drive the DC-DC converter based on the PWM waveform to perform voltage regulation and current distribution on the current distributed generation unit DG.

[0020] Optionally, the voltage prediction value is calculated as follows:

[0021]

[0022] The calculation formula of the current prediction value is:

[0023]

[0024] Where τ is the communication delay time, i is the distributed generation unit DG, is the voltage prediction value at time k based on the voltage information at time k-τ, v i (k-τ) is the terminal voltage of the secondary controller at time k after a delay of τ steps, t sc is the control period of the secondary control, is the voltage auxiliary control value of the ith DG at time km, m is a positive integer from 1 to τ, is the current prediction value at time k based on the current information at time k-τ, i i (k-τ) is the output current of the secondary controller at time k after a delay of τ steps, is the current auxiliary control quantity of the ith DG at time km.

[0025] Optionally, the second calculation module is further used to: calculate the voltage auxiliary control amount using a voltage auxiliary control amount calculation formula, and calculate the current auxiliary control amount using a current auxiliary control amount calculation formula, wherein:

[0026] The calculation formula of the voltage auxiliary control amount is:

[0027]

[0028] The calculation formula of the current auxiliary control amount is:

[0029]

[0030] in, is the voltage auxiliary control quantity of the ith DG at time k based on the voltage prediction value at time k-τ, is the current auxiliary control quantity of the i-th DG at time k based on the current prediction value at time k-τ, ψ is the coupling gain of the voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i is the neighbor set of the ith DG, is the rated current of the converter connected to the i-th DG, λ is the coupling gain of the current controller, v nom is the nominal value of the terminal voltage of DG, is the rated current of the converter connected to the i-th DG, is the current prediction value of the i-th DG at time k based on time k-τ, is the voltage prediction value of the ith DG at time k based on time k-τ, is the current prediction value of the jth DG at time k based on time k-τ, is the voltage prediction value of the jth DG at time k based on time k-τ.

[0031] Optionally, the control module is further used to: calculate the voltage setting value of the primary control by using the primary control voltage calculation formula, wherein the primary control voltage calculation formula is:

[0032]

[0033] in, is the voltage setting value of the primary control of the i-th DG at time k, is the virtual resistance of the ith DG.

[0034] A third aspect of the present invention provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the secondary control method of the DC microgrid as described in the above embodiment.

[0035] A fourth aspect of the present invention provides a computer program product having a computer program stored thereon, the program being executed by a processor to implement the secondary control method of a DC microgrid as described in the above embodiment.

[0036] In the above implementation, the voltage prediction value and current prediction value of the current distributed generation unit DG are calculated by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain, and the communication delay time, and the voltage auxiliary control quantity and current auxiliary control quantity of the current distributed generation unit DG of the DC microgrid are calculated based on the voltage prediction value and the current prediction value, and the voltage setting value of the primary control is calculated according to the voltage auxiliary control quantity and the current auxiliary control quantity, and the droop control mechanism and the cascade PI controller are used to generate a pulse width modulation PWM waveform of the DC-DC converter connected to the current distributed generation unit DG based on the voltage setting value of the primary control, so as to drive the DC-DC converter to perform voltage regulation and current distribution on the current distributed generation unit DG based on the PWM waveform. Thus, the problem of voltage deviation correction and current distribution of the microgrid affected by the delay problem introduced by the sparse communication network is solved, and the influence of the delay on the control signal is predicted in real time by introducing an active prediction mechanism, and corresponding compensation is performed, so as to effectively reduce the negative impact of the delay on the stability and performance of the system, and has higher real-time performance and adaptability, and can maintain the stable operation of the system in a complex and changeable actual environment.

[0037] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0039] Figure 1 A flowchart of a time-delay DC microgrid secondary control method based on an active prediction compensation strategy provided according to an embodiment of the present invention;

[0040] Figure 2 Schematic diagram of a hierarchical control strategy for the i-th DG in a DC microgrid according to an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a VI droop curve of a DC microgrid according to an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of secondary control using an active prediction compensation strategy according to an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of a DC microgrid experimental platform for verifying the control algorithm of the present invention according to an embodiment of the present invention;

[0044] Figure 6 It is a schematic diagram of system response of consistency-based secondary control under delay conditions in the prior art;

[0045] Figure 7 Schematic diagram of system response under 40ms delay according to a control strategy of an embodiment of the present invention;

[0046] Figure 8 Schematic diagram of a time-delay DC microgrid secondary control device based on an active prediction compensation strategy according to an embodiment of the present invention;

[0047] Fig. 9 FIG. 4 is a schematic diagram of a structure of an electronic device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0049] The following describes the time-delay DC microgrid secondary control method based on the active prediction compensation strategy of the embodiment of the present invention with reference to the accompanying drawings. In view of the problem mentioned in the above background technology that the delay problem introduced by the sparse communication network affects the voltage deviation correction and current distribution of the microgrid, the present invention provides a time-delay DC microgrid secondary control method based on the active prediction compensation strategy, in which the voltage prediction value and current prediction value of the current distributed generation unit DG are calculated using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time, and the voltage auxiliary control amount and current auxiliary control amount of the current distributed generation unit DG of the DC microgrid are calculated based on the voltage prediction value and the current prediction value, and the voltage setting value of the primary control is calculated according to the voltage auxiliary control amount and the current auxiliary control amount, and the droop control mechanism and the cascade PI controller are used to generate a pulse width modulation PWM waveform of the DC-DC converter connected to the current distributed generation unit DG based on the voltage setting value of the primary control, so as to drive the DC-DC converter based on the PWM waveform to perform voltage regulation and current distribution on the current distributed generation unit DG. In this way, the problem of voltage deviation correction and current distribution of microgrids affected by the delay introduced by the sparse communication network is solved. By introducing an active prediction mechanism, the impact of delay on control signals is predicted in real time and corresponding compensation is performed, thereby effectively mitigating the negative impact of delay on system stability and performance. It has higher real-time and adaptability, and can maintain stable operation of the system in complex and changeable actual environments.

[0050] In existing related research, there are two main solutions to the delay problem in microgrid communication networks. The first method is to design the controller under an ideal network communication environment and then perform stability analysis on it, and then design and select the control parameters based on the results of the stability analysis. Studies have shown that the delay range that the microgrid secondary control can tolerate can be calculated by Taylor expansion, linear matrix inequality, and calculation of system matrix characteristic roots. The selection of control parameters based on the results of these theoretical analyses can ensure the stability of the system under a given delay. The second method is robust control, which takes into account possible network limitations such as delay, noise, and network attacks at the beginning of controller design. Specifically, by using the Lyapunov-Krasovskii functional combined with the microgrid model, a set of linear matrix inequalities are designed to obtain the control parameters of the system under delay conditions. Compared with the first method, the second method is more effective and robust in dealing with network limitations such as delay and attack, mainly because it takes into account possible communication limitations at the beginning of controller design.

[0051] In view of the above problems, the embodiment of the present invention proposes a delayed DC microgrid secondary control method based on an active prediction compensation strategy. The method introduces an active prediction mechanism to predict the impact of delay on the control signal in real time and perform corresponding compensation, thereby effectively mitigating the negative impact of delay on system stability and performance. Compared with the existing methods, the embodiment of the present invention has higher real-time performance and adaptability, and can maintain the stable operation of the system in a complex and changeable actual environment.

[0052] Specifically, Figure 1 A schematic flow chart of a method for secondary control of a time-delay DC microgrid based on an active predictive compensation strategy provided by an embodiment of the present invention.

[0053] like Figure 1 As shown, the time-delay DC microgrid secondary control method based on active prediction compensation strategy includes the following steps:

[0054] In step S101, the voltage prediction value and the current prediction value of the current distributed generation unit DG are calculated using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain, and the communication delay time.

[0055] In step S102, the voltage auxiliary control amount and the current auxiliary control amount of the current distributed generation unit DG of the DC microgrid are calculated based on the voltage prediction value and the current prediction value, and the voltage setting value of the primary control is calculated according to the voltage auxiliary control amount and the current auxiliary control amount.

[0056] In step S103, a droop control mechanism and a cascade PI controller are used to generate a pulse width modulation (PWM) waveform of a DC-DC converter connected to the current distributed generation unit DG based on a primary controlled voltage setting value, so as to drive the DC-DC converter to perform voltage regulation and current distribution on the current distributed generation unit DG based on the PWM waveform.

[0057] Optionally, in some embodiments, the voltage prediction value is calculated as follows:

[0058]

[0059] The calculation formula for the predicted current value is:

[0060]

[0061] Where τ is the communication delay time, i is the distributed generation unit DG, is the voltage prediction value at time k based on the voltage information at time k-τ, v i (k-τ) is the terminal voltage of the secondary controller at time k after a delay of τ steps, t sc is the control period of the secondary control, is the voltage auxiliary control value of the ith DG at time km, m is a positive integer from 1 to τ, is the current prediction value at time k based on the current information at time k-τ, i i (k-τ) is the output current of the secondary controller at time k after a delay of τ steps, is the current auxiliary control quantity of the ith DG at time km.

[0062] Optionally, in some embodiments, the voltage auxiliary control amount and the current auxiliary control amount of the current distributed generation unit DG of the DC microgrid are calculated based on the voltage prediction value and the current prediction value, including: calculating the voltage auxiliary control amount using a voltage auxiliary control amount calculation formula, and calculating the current auxiliary control amount using a current auxiliary control amount calculation formula, wherein,

[0063] The calculation formula of voltage auxiliary control quantity is:

[0064]

[0065] The calculation formula of current auxiliary control quantity is:

[0066]

[0067] in, is the voltage auxiliary control quantity of the ith DG at time k based on the voltage prediction value at time k-τ, is the current auxiliary control quantity of the i-th DG at time k based on the current prediction value at time k-τ, ψ is the coupling gain of the voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i is the neighbor set of the ith DG, is the rated current of the converter connected to the i-th DG, λ is the coupling gain of the current controller, v nom is the nominal value of the terminal voltage of DG, is the rated current of the converter connected to the i-th DG, is the current prediction value of the i-th DG at time k based on time k-τ, is the voltage prediction value of the ith DG at time k based on time k-τ, is the current prediction value of the jth DG at time k based on time k-τ, is the voltage prediction value of the jth DG at time k based on time k-τ.

[0068] Optionally, in some embodiments, calculating the voltage setting value of the primary control according to the voltage auxiliary control amount and the current auxiliary control amount includes: calculating the voltage setting value of the primary control using a primary control voltage calculation formula, wherein the primary control voltage calculation formula is:

[0069]

[0070] in, is the voltage setting value of the primary control of the i-th DG at time k, is the virtual resistance of the ith DG.

[0071] In the embodiment of the present invention, step 1 is to construct a DC microgrid circuit and a primary control model: Figure 2 In the DG shown, the power source is connected to the DC bus through a DC-DC converter (a buck converter is selected as an example in the embodiment of the present invention) and supplies energy to the system through a transmission line. For the i-th DG, Indicates the power supply voltage, L i is the energy storage inductor size, C i is the filter capacitor size, Z i represents the impedance of the transmission line. It is worth noting that due to the development of energy storage technology, the volatility and intermittency of various renewable energy sources have been smoothed, so the power generation source is simplified and modeled as a constant voltage source. In addition, i i represents the output current of the ith DG, represents the output voltage of the ith converter, v i represents the terminal voltage. Since it is inconvenient to measure, the embodiment of the present invention can calculate it by Kirchhoff's voltage law (1).

[0072]

[0073] At the control level, the primary control layer of the island DC microgrid usually adopts VI droop control, which can achieve current distribution while ensuring the requirements of distributed characteristics. The primary control aims to generate a local reference voltage for each DG through the droop mechanism (2).

[0074]

[0075] In the formula, Indicates the set value of droop control at no-load. represents the virtual resistance of the i-th DG, which is inversely proportional to the generation capacity of the DG. Following the droop control, the system tracks the reference value through a cascaded “voltage-current” proportional-integral (PI) controller The specific inner loop PI controller is shown as follows:

[0076]

[0077]

[0078]

[0079]

[0080] In the formula, K P v , K I v , K P i , K I i are the proportional and integral coefficients of the voltage and current controllers respectively, is the integration variable, is the current loop reference value, is the actual duty cycle. The inner loop control (3) has a shorter local sampling period than the secondary control. Usually, hundreds or even thousands of inner loop controls can be completed during one secondary control. Therefore, it can complete real-time and accurate voltage tracking. Therefore, the dynamic response of the converter can be ignored in the subsequent secondary control layer modeling, and it is assumed that the converter terminal voltage v i (t) can track its local voltage reference value in real time

[0081] In a large number of converters in the existing power system, the droop control mechanism has been embedded in its controller. Therefore, it is necessary to design a reasonable secondary control strategy for its inherent defects of voltage deviation and inaccurate power distribution. Through the droop mechanism shown in equation (2), we can get the following: Figure 3 The droop curve shown in the figure. It can be seen from the figure that the droop curve can maintain the set value when it is unloaded. When there is current output, in order to distribute power according to the droop coefficient, the slope -R i vir The voltage drops so much that the primary control voltage setting value cannot be maintained accurately. The role of the secondary control is to compensate for the voltage deviation caused by the droop mechanism. It can be seen that while ensuring the same output current, the secondary control can adjust the voltage back to the set point v i n .

[0082] Step 2: Determine the control target and secondary control strategy of the microgrid in the presence of time delay:

[0083] In order to achieve terminal voltage recovery and accurate proportional power distribution, the secondary control constructs auxiliary control variables to re-determine the set value in formula (2) with the help of the voltage / current information of the neighboring nodes.n

[0084] v i The general method is to adjust the voltage to achieve voltage recovery by designing a voltage reference value. The common auxiliary controller based on the consistency algorithm can be designed as:

[0085]

[0086] Among them, u i v is the auxiliary control input for voltage recovery, ψ is the coupling gain of voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i Represents the neighbor set of the ith DG.

[0087] Similarly, the auxiliary controller for current proportional distribution can be designed as:

[0088]

[0089] Where u i i is the auxiliary control input for current regulation, i i rated It represents the rated current of the converter connected to the i-th DG, and also determines the power generation ratio of the DG. λ is the coupling gain of the current controller.

[0090] On this basis, the primary control set value v i n Can be done by u i v and u i i Obtained by the following formula:

[0091]

[0092] The above gives the model of the system electrical and control level. Specifically, N i represents the neighbor set of the i-th DG network layer. i When the jth DG is in the neighbor set of the i-th DG, the communication weight a ij >0. Otherwise, a ij = 0. The communication weight a between different DGs ij The adjacency matrix of the entire microgrid system can be obtained, which is recorded as A matrix. Similarly, when the containment gain g i >0 indicates that the i-th DG can obtain the information sent by the leader in the microgrid, which may be the third-party control decision maker (such as the control center). If the DG cannot obtain the leader information, then g i = 0. Based on gi The value of the microgrid system can be obtained by i}.

[0093] In actual microgrid communication networks, there is often communication delay. Assuming that there is a communication delay of τ in the secondary control network layer, no matter whether the delay is taken into account at the beginning of the design of controllers (4) and (2), the controller can only use the voltage and current values ​​after the delay. The consistency-based secondary controllers (4) and (5) given above will degenerate into the following formula:

[0094]

[0095] When the above controller uses delayed signals, the control performance may be reduced or even the microgrid may be unstable. Therefore, the embodiment of the present invention is committed to designing a secondary control strategy for active prediction and compensation of delays, so as to achieve the following two control objectives under the condition of delays:

[0096] First, the terminal voltage of each DG needs to be adjusted to the nominal value v nom , which can be expressed by the following formula:

[0097]

[0098] At the same time, in order to complete the power proportion allocation according to capacity, the power usage level of each DG also needs to be consistent, as shown in the following formula:

[0099]

[0100] Step 3, design an active voltage and current prediction mechanism: In order to achieve the control objectives of voltage recovery and power distribution in the presence of communication delay, an embodiment of the present invention proposes a microgrid secondary control strategy based on active prediction compensation.

[0101] From formula (4) and v i The dynamic equation in the continuous time domain, the discretized prediction equation of the terminal voltage can be approximately expressed as:

[0102]

[0103] Where t sc is the control period of the secondary control. From the analysis of step 2, it can be seen that the controller (7) can only obtain the voltage information v after a delay of τ steps at time k. i (k-τ),v j (k-τ),i=1,2,…,N,j∈N i To solve this problem, the embodiment of the present invention calls the following historical control sequence cached in the i-th secondary controller:

[0104]

[0105] Based on the historical control sequence and system dynamics, we attempt to perform predictive compensation. First, the voltage estimate at time k can be obtained by the following prediction:

[0106]

[0107] In the formula, the symbol represents the predicted value of time a based on the information at time b. Formula (12) shows that in order to obtain the predicted value at time k, the predicted value of the previous step must be obtained. Therefore, in order to obtain The embodiment of the present invention performs calculation in an iterative manner as shown below:

[0108]

[0109] Combining equations (12) and (13), we can get the voltage information v at time k-τ: i (k-τ) can calculate the voltage prediction value at time k As shown below:

[0110]

[0111] Where m is a positive integer from 1 to τ, which is used to indicate the number of prediction steps.

[0112] After completing the design of the voltage active predictor, the design process of the current predictor can follow a similar strategy. Considering the iterative process of equations (12)-(14), the current prediction value can be expressed as:

[0113]

[0114] This step completes the active prediction of voltage and current, providing a data basis for the next step.

[0115] Step 4: Propose a secondary control strategy based on active prediction compensation: Based on the existing voltage auxiliary controller (7), the voltage prediction value can be obtained when it is known that and In the case of i v It can be designed as follows:

[0116]

[0117] In the secondary control of DC microgrids, proportional power distribution is an equally important control objective as voltage recovery. Therefore, the current auxiliary controller u i iIt is also necessary to design a corresponding compensation strategy to reduce the negative impact of the communication delay. Different from the design process of the above voltage recovery, there is no virtual leader in the current distribution control. What is ultimately required is that the power usage level of each DG reaches an average consistency. The embodiment of the present invention designs the following current auxiliary control based on the existing current prediction value:

[0118]

[0119] Based on equations (16) and (17), the set value v of the droop control is i n The control law can be redesigned by replacing the delay value in equation (6):

[0120]

[0121] The global control block diagram of the secondary control method of the isolated DC microgrid based on the active prediction compensation strategy proposed in the embodiment of the present invention is as follows: Figure 4 As shown in FIG. 1 , it can be divided into secondary control of low-bandwidth network, primary control embedded in local controller and inner loop control for tracking given value according to time scale. From the perspective of signal flow, due to the time delay in the communication network, the i-th DG cannot obtain the real-time status and can only receive delayed information. Therefore, the embodiment of the present invention obtains the predicted voltage value by using active multi-step predictors (14) and (15). and current value The number of forward prediction steps is determined by the specific delay size τ. After completing the multi-step prediction, we can calculate the auxiliary control amount using formulas (16) and (17): and The secondary controller further generates the voltage setting value v for the primary control i n , the specific formula is shown in (18). Next, after the calculation of the droop mechanism and the cascade PI controller, the controller can generate the actual PWM waveform of each converter connected to the DG. Finally, each DG sends its real-time voltage and current values ​​to the network to form the next cycle. In summary, the control loop of a single DG in the entire microgrid forms a closed loop. By using the active voltage and current prediction mechanism and integrating the voltage and current prediction information into the secondary control strategy, the control objectives of voltage recovery and precise current distribution of the microgrid with multi-step prediction in the presence of communication delay are achieved.

[0122] The technical solution of the embodiment of the present invention is further specifically described through a hardware experiment example:

[0123] The DC microgrid hardware experimental platform used to verify the control algorithm is shown in the attached Figure 5As shown in the figure, the platform mainly includes an OPAL-RT real-time controller, model OP 5700, four DC-DC buck converters, four corresponding controlled DC sources, transmission lines (used to simulate line impedance), and fixed resistance loads. In the actual experiment, each DC-DC buck converter transmits the output current and voltage to the OPAL-RT real-time controller in analog form through current and voltage sampling. The control algorithm is deployed in the real-time simulator OP5700, which receives the electrical signals of each converter for calculation and finally generates a 20kHz frequency PWM wave to drive each DC-DC converter in digital form.

[0124] The rated voltage of the DC microgrid bus verified by the embodiment of the present invention is 48V. To simulate the actual situation, the circuit parameters of the four DGs are different. The detailed circuit and control parameters are shown in Table 1. Table 1 is a comparison table of electrical and control parameter values ​​of the isolated DC microgrid system. The power distribution ratio of the four DGs is 3:1:3:1, which will be verified in the following experimental results. At the communication network layer, in order to meet the requirements of the system's low-bandwidth communication network, the sampling time of the secondary controller is set to 10ms. The primary control is local control, so its control period is set to 0.1ms to ensure that it can quickly track the reference value. The communication network of the entire system is represented by the containment matrix and the adjacency matrix as follows:

[0125]

[0126] Table 1

[0127]

[0128]

[0129] In order to verify the effectiveness of the proposed distributed predictive secondary control strategy, a typical consistency-based secondary control strategy is selected as a comparison in the embodiment of the present invention. The current response waveforms of the system are shown in the attached figure. Figure 6 The voltage and current waveforms of the secondary control based on active prediction compensation proposed in the embodiment of the present invention are shown in the attached Figure 7 Given in.

[0130] Attached Figure 6 The system response diagrams of the traditional consistency-based quadratic control with and without delay are given. Figure 6 In (a), before time t1, due to the inherent drawbacks of the droop mechanism, each DG cannot complete the current distribution according to the preset 3:1:3:1 ratio. Therefore, the secondary control is activated at time t1, and the precise current distribution of each DG is completed at time t2. When there is a 40ms communication delay around the system, its current response is as follows: Figure 6As shown in (a), it can be seen that the system oscillation gradually diverges due to the use of delayed data, which is very dangerous and intolerable in the actual microgrid operation process.

[0131] As a comparison, Figure 7 The system response of the secondary control strategy based on active predictive compensation proposed in the embodiment of the present invention is shown. Figure 7 As shown in the voltage waveform of (a), the voltage of each DG in the microgrid is restored to the nominal value after the secondary control is activated, and the bus voltage is stabilized at 48V. Figure 7 (a) It can be seen that the output of each DG is also distributed according to the preset ratio of 3:1:3:1. It can be seen that the proposed secondary control strategy can not only complete the voltage recovery and stability of the system under delay conditions, but also realize the accurate distribution of current.

[0132] According to the time-delay DC microgrid secondary control method based on the active prediction compensation strategy proposed in an embodiment of the present invention, the voltage prediction value and the current prediction value of the current distributed generation unit DG are calculated by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time, the voltage auxiliary control quantity and the current auxiliary control quantity of the current distributed generation unit DG of the DC microgrid are calculated based on the voltage prediction value and the current prediction value, and the voltage setting value of the primary control is calculated according to the voltage auxiliary control quantity and the current auxiliary control quantity, and the droop control mechanism and the cascade PI controller are used to generate a pulse width modulation PWM waveform of the DC-DC converter connected to the current distributed generation unit DG based on the voltage setting value of the primary control, so as to drive the DC-DC converter based on the PWM waveform to perform voltage regulation and current distribution on the current distributed generation unit DG. As a result, the problem of voltage deviation correction and current distribution of the microgrid affected by the delay introduced by the sparse communication network is solved. Compared with the traditional method of passively tolerating delay, the embodiment of the present invention actively compensates for the control lag caused by the communication delay by predicting the voltage and current values ​​in real time, thereby ensuring the operating performance of the microgrid in a delay environment, thereby effectively mitigating the negative impact of the delay on the stability and performance of the system. It has higher real-time and adaptability, can maintain the stable operation of the system in a complex and changeable actual environment, and has low computational complexity and is easy to implement in practice.

[0133] Next, a time-delay DC microgrid secondary control device based on an active prediction compensation strategy proposed in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings.

[0134] Figure 8 It is a block diagram of a time-delay DC microgrid secondary control device based on an active prediction compensation strategy according to an embodiment of the present invention.

[0135] like Figure 8As shown, the time-delay DC microgrid secondary control device 10 based on active prediction compensation strategy includes: a first calculation module 100, a second calculation module 200 and a control module 300.

[0136] Among them, the first calculation module 100 is used to calculate the voltage prediction value and current prediction value of the current distributed generation unit DG by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time; the second calculation module 200 is used to calculate the voltage auxiliary control quantity and the current auxiliary control quantity of the current distributed generation unit DG of the DC microgrid based on the voltage prediction value and the current prediction value, and calculate the voltage setting value of the primary control according to the voltage auxiliary control quantity and the current auxiliary control quantity; the control module 300 is used to generate a pulse width modulation PWM waveform of the DC-DC converter connected to the current distributed generation unit DG based on the voltage setting value of the primary control by using the droop control mechanism and the cascade PI controller, so as to drive the DC-DC converter based on the PWM waveform to perform voltage regulation and current distribution on the current distributed generation unit DG.

[0137] Optionally, in some embodiments, the voltage prediction value is calculated as follows:

[0138]

[0139] The calculation formula for the predicted current value is:

[0140]

[0141] Where τ is the communication delay time, i is the distributed generation unit DG, is the voltage prediction value at time k based on the voltage information at time k-τ, v i (k-τ) is the terminal voltage of the secondary controller at time k after a delay of τ steps, t sc is the control period of the secondary control, is the voltage auxiliary control value of the ith DG at time km, m is a positive integer from 1 to τ, is the current prediction value at time k based on the current information at time k-τ, i i (k-τ) is the output current of the secondary controller at time k after a delay of τ steps, is the current auxiliary control quantity of the ith DG at time km.

[0142] Optionally, in some embodiments, the second calculation module 200 is further used to: calculate the voltage auxiliary control amount using a voltage auxiliary control amount calculation formula, and calculate the current auxiliary control amount using a current auxiliary control amount calculation formula, wherein:

[0143] The calculation formula of voltage auxiliary control quantity is:

[0144]

[0145] The calculation formula of current auxiliary control quantity is:

[0146]

[0147] in, is the voltage auxiliary control quantity of the ith DG at time k based on the voltage prediction value at time k-τ, is the current auxiliary control quantity of the i-th DG at time k based on the current prediction value at time k-τ, ψ is the coupling gain of the voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i is the neighbor set of the ith DG, is the rated current of the converter connected to the i-th DG, λ is the coupling gain of the current controller, v nom is the nominal value of the terminal voltage of DG, is the rated current of the converter connected to the i-th DG, is the current prediction value of the i-th DG at time k based on time k-τ, is the voltage prediction value of the ith DG at time k based on time k-τ, is the current prediction value of the jth DG at time k based on time k-τ, is the voltage prediction value of the jth DG at time k based on time k-τ.

[0148] Optionally, in some embodiments, the control module 300 is further used to: calculate the voltage setting value of the primary control using a primary control voltage calculation formula, wherein the primary control voltage calculation formula is:

[0149]

[0150] in, is the voltage setting value of the primary control of the i-th DG at time k, R i vir is the virtual resistance of the ith DG.

[0151] It should be noted that the aforementioned explanation of the embodiment of the secondary control method of the DC microgrid is also applicable to the secondary control device of the DC microgrid of this embodiment, and will not be repeated here.

[0152] According to the delayed DC microgrid secondary control device based on the active prediction compensation strategy proposed in the embodiment of the present invention, the voltage prediction value and current prediction value of the current distributed generation unit DG are calculated by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time, the voltage auxiliary control quantity and the current auxiliary control quantity of the current distributed generation unit DG of the DC microgrid are calculated based on the voltage prediction value and the current prediction value, and the voltage setting value of the primary control is calculated according to the voltage auxiliary control quantity and the current auxiliary control quantity, and the droop control mechanism and the cascade PI controller are used to generate a pulse width modulation PWM waveform of the DC-DC converter connected to the current distributed generation unit DG based on the voltage setting value of the primary control, so as to drive the DC-DC converter to perform voltage regulation and current distribution on the current distributed generation unit DG based on the PWM waveform. Thus, the voltage deviation correction and current distribution of the microgrid affected by the delay problem introduced by the sparse communication network are solved, and the influence of the delay on the control signal is predicted in real time by introducing the active prediction mechanism, and the corresponding compensation is performed, so as to effectively reduce the negative impact of the delay on the stability and performance of the system, and it has higher real-time performance and adaptability, and can maintain the stable operation of the system in a complex and changeable actual environment.

[0153] Fig. 9 A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. The electronic device may include:

[0154] A memory 901 , a processor 902 , and a computer program stored in the memory 901 and executable on the processor 902 .

[0155] When the processor 902 executes the program, the time-delay DC microgrid secondary control method based on the active prediction compensation strategy provided in the above embodiment is implemented.

[0156] Furthermore, the electronic device further comprises:

[0157] The communication interface 903 is used for communication between the memory 901 and the processor 902 .

[0158] The memory 901 is used to store computer programs that can be executed on the processor 902 .

[0159] The memory 901 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0160] If the memory 901, the processor 902 and the communication interface 903 are implemented independently, the communication interface 903, the memory 901 and the processor 902 can be connected to each other through a bus and communicate with each other. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus. The bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Fig. 9 Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0161] Optionally, in a specific implementation, if the memory 901, the processor 902 and the communication interface 903 are integrated on a chip, the memory 901, the processor 902 and the communication interface 903 can communicate with each other through an internal interface.

[0162] The processor 902 may be a central processing unit (CPU), or an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of the present invention.

[0163] An embodiment of the present invention further provides a computer program product having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned time-delay DC microgrid secondary control method based on an active predictive compensation strategy.

[0164] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0165] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0166] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present invention belong.

[0167] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer program product for use with an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, a "computer program product" can be any device that can contain, store, communicate, propagate or transmit a program for use with an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer program products (a non-exhaustive list) include the following: an electrical connection with one or N wirings (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). Furthermore, the computer program product may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example by optically scanning the paper or other medium and then editing, interpreting or, if necessary, processing in another suitable manner, and then storing it in a computer memory.

[0168] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiment, the N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0169] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer program product, which, when executed, includes one or a combination of the steps of the method embodiment.

[0170] In addition, each functional unit in each embodiment of the present invention may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer program product.

[0171] The computer program product mentioned above may be a read-only memory, a disk or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A secondary control method for a time-delay DC microgrid based on active prediction compensation strategy. It is characterized in that The following steps are involved: The voltage prediction value and current prediction value of the current distributed generation unit DG are calculated by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time; Calculating a voltage auxiliary control amount and a current auxiliary control amount of a current distributed generation unit DG of a DC microgrid based on the voltage prediction value and the current prediction value, and calculating a voltage setting value of a primary control according to the voltage auxiliary control amount and the current auxiliary control amount; A droop control mechanism and a cascade PI controller are used to generate a pulse width modulation (PWM) waveform of a DC-DC converter connected to a current distributed generation unit DG based on the voltage setting value of the primary control, so as to drive the DC-DC converter to perform voltage regulation and current distribution on the current distributed generation unit DG based on the PWM waveform.

2. According to claim 1, the time-delay DC microgrid secondary control method based on active prediction compensation strategy, It is characterized in that The calculation formula of the voltage prediction value is: The calculation formula of the current prediction value is: Where τ is the communication delay time, i is the distributed generation unit DG, is the voltage prediction value at time k based on the voltage information at time k-τ, v i (k-τ) is the terminal voltage of the secondary controller at time k after a delay of τ steps, t sc is the control period of the secondary control, is the voltage auxiliary control value of the ith DG at time km, m is a positive integer from 1 to τ, is the current prediction value at time k based on the current information at time k-τ, i i (k-τ) is the output current of the secondary controller at time k after a delay of τ steps, is the current auxiliary control quantity of the ith DG at time km.

3. The time-delay DC microgrid secondary control method based on active prediction compensation strategy according to claim 1, It is characterized in that The method of calculating the voltage auxiliary control amount and the current auxiliary control amount of the current distributed generation unit DG of the DC microgrid based on the voltage prediction value and the current prediction value includes: The voltage auxiliary control quantity is calculated using the voltage auxiliary control quantity calculation formula, and the current auxiliary control quantity is calculated using the current auxiliary control quantity calculation formula, where: The calculation formula of the voltage auxiliary control amount is: The current auxiliary control amount calculation formula is: in, is the voltage auxiliary control quantity of the ith DG at time k based on the voltage prediction value at time k-τ, is the current auxiliary control quantity of the i-th DG at time k based on the current prediction value at time k-τ, ψ is the coupling gain of the voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i is the neighbor set of the i-th DG, i i rated is the rated current of the converter connected to the i-th DG, λ is the coupling gain of the current controller, v nom is the nominal value of the terminal voltage of DG, is the rated current of the converter connected to the i-th DG, is the current prediction value of the i-th DG at time k based on time k-τ, is the voltage prediction value of the ith DG at time k based on time k-τ, is the current prediction value of the jth DG at time k based on time k-τ, is the voltage prediction value of the jth DG at time k based on time k-τ.

4. The time-delay DC microgrid secondary control method based on active prediction compensation strategy according to claim 1, It is characterized in that The step of calculating a voltage setting value for primary control according to the voltage auxiliary control amount and the current auxiliary control amount comprises: The voltage setting value of the primary control is calculated using the primary control voltage calculation formula, wherein the primary control voltage calculation formula is: in, is the voltage setting value of the primary control at time k, R i vir is the virtual resistance of the ith DG.

5. A time-delay DC microgrid secondary control device based on active prediction compensation strategy, It is characterized in that include: The first calculation module is used to calculate the voltage prediction value and the current prediction value of the current distributed generation unit DG by using the historical control sequence cached in the secondary controller, the system dynamics equation in the continuous time domain and the communication delay time; A second calculation module is used to calculate the voltage auxiliary control amount and the current auxiliary control amount of the current distributed generation unit DG of the DC microgrid based on the voltage prediction value and the current prediction value, and calculate the voltage setting value of the primary control according to the voltage auxiliary control amount and the current auxiliary control amount; A control module is used to generate a pulse width modulation (PWM) waveform of a DC-DC converter connected to a current distributed generation unit DG based on the voltage setting value of the primary control by using a droop control mechanism and a cascade PI controller, so as to drive the DC-DC converter to perform voltage regulation and current distribution on the current distributed generation unit DG based on the PWM waveform.

6. The time-delay DC microgrid secondary control device based on active prediction compensation strategy according to claim 5, It is characterized in that The calculation formula of the voltage prediction value is: The calculation formula of the current prediction value is: Where τ is the communication delay time, i is the distributed generation unit DG, is the voltage prediction value at time k based on the voltage information at time k-τ, v i (k-τ) is the terminal voltage of the secondary controller at time k after a delay of τ steps, t sc is the control period of the secondary control, is the voltage auxiliary control value of the ith DG at time km, m is a positive integer from 1 to τ, is the current prediction value at time k based on the current information at time k-τ, i i (k-τ) is the output current of the secondary controller at time k after a delay of τ steps, is the current auxiliary control quantity of the ith DG at time km.

7. The time-delay DC microgrid secondary control device based on active prediction compensation strategy according to claim 5, It is characterized in that The second computing module is further used for: The voltage auxiliary control quantity is calculated using the voltage auxiliary control quantity calculation formula, and the current auxiliary control quantity is calculated using the current auxiliary control quantity calculation formula, where: The calculation formula of the voltage auxiliary control amount is: The calculation formula of the current auxiliary control amount is: in, is the voltage auxiliary control quantity of the ith DG at time k based on the voltage prediction value at time k-τ, is the current auxiliary control quantity of the i-th DG at time k based on the current prediction value at time k-τ, ψ is the coupling gain of the voltage auxiliary control, a ij is the neighbor communication weight, g i is the control gain, N i is the neighbor set of the i-th DG, i i rated is the rated current of the converter connected to the i-th DG, λ is the coupling gain of the current controller, v nom is the nominal value of the terminal voltage of DG, is the rated current of the converter connected to the i-th DG, is the current prediction value of the i-th DG at time k based on time k-τ, is the voltage prediction value of the ith DG at time k based on time k-τ, is the current prediction value of the jth DG at time k based on time k-τ, is the voltage prediction value of the jth DG at time k based on time k-τ.

8. The time-delay DC microgrid secondary control device based on active prediction compensation strategy according to claim 5, It is characterized in that The control module is also used for: The voltage setting value of the primary control is calculated using the primary control voltage calculation formula, wherein the primary control voltage calculation formula is: in, is the voltage setting value of the primary control of the i-th DG at time k, R i vir is the virtual resistance of the ith DG.

9. An electronic device, It is characterized in that It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the time-delay DC microgrid secondary control method based on the active predictive compensation strategy as described in any one of claims 1 to 4.

10. A computer program product, the computer program product storing a computer program, It is characterized in that When the program is executed by a processor, a time-delay DC microgrid secondary control method based on an active prediction compensation strategy as described in any one of claims 1 to 4 is implemented.

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