A DC microgrid non-communication bus voltage recovery control method

Abstract

The present invention belongs to the field of distributed DC microgrid coordinated control research, and discloses a DC microgrid non-communication bus voltage recovery control method. The present invention samples the output voltage and current of each converter port, extracts the AC small signal voltage and current therein, calculates the reactive power generated by the AC small signal, and uses the reactive power generated by the AC small signal to adjust the input of the secondary control loop regulator, and finally realizes the synchronization of the voltage command compensation value of each converter port. The control method proposed in the present invention does not require communication, has the advantages of low cost, high reliability, low control complexity, strong flexibility and adaptability, and can be used to optimize the overall control performance of the system.

Description

Technical Field

[0001] The present invention belongs to the research field of coordinated control of distributed DC microgrids, and in particular relates to a DC microgrid non-communication bus voltage recovery control method. Background Art

[0002] As environmental problems and energy crises become more and more serious, smart microgrid technology based on renewable energy such as solar energy and wind energy has received more and more attention and application. At present, smart microgrids are mainly divided into two categories: AC microgrids and DC microgrids. Among them, DC microgrids have been favored by more and more scholars in recent years due to their advantages such as simple topology and control strategy.

[0003] One of the important goals of DC microgrid coordinated control is to achieve the output power of each distributed generation unit in proportion to its rated capacity. Among various control methods, droop control is the most widely used due to its simple structure, no need for communication, and high reliability. However, droop control has the disadvantage of mutual restraint between power sharing effect and bus voltage drop. In order to solve this problem, secondary control is widely used, and its control goal is to eliminate the bus voltage drop caused by droop control.

[0004] Some literature has proposed a method of using a central controller to send voltage compensation instructions to parallel converters synchronously. The central controller collects bus voltage information, calculates a unified voltage compensation signal, and sends it to each converter through the interconnection line to achieve synchronous compensation of voltage deviations between converters. However, the use of a central controller increases the cost and complexity of the system, and there is also a risk of single point failure.

[0005] Some literature has proposed a bus voltage compensation method that uses a distributed controller to replace a central controller. Each distributed unit communicates only with adjacent units, and uses a consensus algorithm to obtain the average value of the port voltage of each parallel converter. Then, each distributed unit uses the average value of the port voltage to compensate for the bus voltage deviation. Compared with the control method based on the central controller, the distributed control method increases the reliability of the system to a certain extent, but it has the following three shortcomings:

[0006] 1) It is a communication-based control strategy, which has the problems of high cost, high control complexity and low system reliability;

[0007] 2) The recovered quantity is the average value of the port voltage of each converter, which cannot compensate for the bus voltage drop caused by line resistance during long-distance transmission;

[0008] 3) The secondary control loop of each parallel converter utilizes an integrator. When an integration error occurs in the integrator, it will cause the port voltage command compensation value output by the converter secondary control loop to be different, thereby affecting the power sharing characteristics of the droop control;

[0009] In summary, proposing a communication-free bus voltage recovery control method for DC microgrid will have stronger engineering application value. Summary of the invention

[0010] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a DC microgrid non-communication bus voltage recovery control method, which provides a good reference value for engineering applications.

[0011] In order to achieve the above object, the present invention comprises the following steps:

[0012] S1, according to the output current i of the converter port o , bus voltage reference Droop coefficient d b and the estimated line resistance r e , generate the basic port voltage command of the converter through droop control

[0013] S2, according to the converter port output voltage v o , converter port output current i o and the estimated line resistance r e Calculate the initial estimated value of bus voltage v be ;

[0014] S3, output voltage v from the converter port o and port output current i o Extracting AC small signal voltage and AC small signal current Calculate the reactive power Q generated by a small AC signal ss ;

[0015] S4, reactive power Q generated by small AC signal ss Adjust the initial estimated value of bus voltage v be , generating an estimated value of the adjusted bus voltage

[0016] S5, using the adjusted bus voltage estimate With bus voltage reference Generate converter port voltage command compensation Δv b ;

[0017] S6, using the converter port voltage command to compensate Δv b , through droop control, generate AC small signal frequency command Then obtain the AC small signal voltage command

[0018] S7, according to the AC small signal voltage command Converter basic port voltage command Compensation Δv with converter port voltage command b Adjust the output voltage v of the converter port o .

[0019] Basic port voltage command of converter in S1 The calculation formula is as follows:

[0020]

[0021] The specific methods of S3 are as follows:

[0022] S31, sampling converter port output voltage v o , converter port output current i o , use a bandpass filter to extract the AC small signal voltage and AC small signal current

[0023] S32, AC small signal voltage and AC small signal current The coordinate transformation is converted to the two-phase rotating dq coordinate system, and the AC small signal voltage is obtained respectively The d-axis component and the q-axis component AC small signal current The d-axis component and the q-axis component

[0024] S33, according to the components of the AC small signal voltage in the two-phase rotating dq coordinate system and and the components of the AC small signal current in the two-phase rotating dq coordinate system and Calculate the reactive power Q generated by a small AC signal ss , the calculation formula is as follows:

[0025]

[0026] In S4, the reactive power Q generated by the small AC signal ss Adjust the initial estimated value of bus voltage v be , generating an estimated value of the adjusted bus voltage The calculation formula is as follows:

[0027]

[0028] in, is the coupling coefficient, and is a positive number;

[0029] In S5, the adjusted bus voltage estimate is used With bus voltage reference Generate converter port voltage command compensation Δv b The specific method is as follows:

[0030] Calculate the estimated regulated bus voltage With bus voltage reference After the secondary control regulator, the output converter port voltage command compensation Δv b .

[0031] In S6, the frequency command of the AC small signal is generated by droop control. Then obtain the voltage command of the small AC signal The specific method is as follows:

[0032] S61, compensating Δv according to the converter port voltage command b , calculate the AC small signal frequency command

[0033] S62, according to the frequency instruction of small AC signal Calculate AC small signal voltage command

[0034] In S61, AC small signal frequency command The calculation method is as follows:

[0035]

[0036] in, is the AC small signal frequency droop coefficient, and is a positive number. is the reference frequency of the small AC signal;

[0037] In S62, the voltage command of the AC small signal The calculation method is as follows:

[0038]

[0039] Among them, V ss represents the AC small signal voltage command amplitude, t represents time, and τ represents an arbitrary variable;

[0040] In S7, according to the AC small signal voltage instruction Converter basic port voltage command Compensation Δv with converter port voltage command b The specific method for adjusting the port output voltage of the converter is as follows:

[0041] S81, AC small signal voltage command Converter basic port voltage command Converter port voltage command compensation Δv b The output voltage of the converter port is v o After passing through the capacitor voltage regulator, the output converter inductor current command

[0042] S82, converter inductor current command and the converter inductor current i L After passing through the inductor current regulator, a modulation signal is output, and the modulation signal passes through the PWM module to generate a drive signal for driving the converter.

[0043] Compared with the prior art, the present invention realizes the bus voltage recovery problem under the droop control strategy of multiple parallel converters by injecting a small AC signal of a certain frequency band into each converter. The method extracts the AC small signal voltage and current by sampling the output voltage and current of each converter port, calculates the reactive power generated by the AC small signal, and uses the reactive power generated by the AC small signal to adjust the bus voltage estimation value, and finally realizes the compensation synchronization of the voltage instructions of each converter port. The control method proposed in the present invention does not require communication, has the advantages of low cost, high reliability, and low control complexity. It also has strong flexibility and adaptability. By cooperating with other control strategies, it can optimize the overall control performance of the system, providing a good reference value for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the main circuit diagram of the DC microgrid;

[0045] Figure 2 This is a structural diagram of the controller of the present invention;

[0046] Figure 3 This is the structure diagram of the traditional droop control controller;

[0047] Figure 4 The simulation waveforms under the traditional droop control are shown in Figure 1. (a) is the simulation waveform of the output current of the two converter ports; (b) is the simulation waveform of the bus voltage.

[0048] Figure 5 is a structure diagram of a bus voltage recovery controller based on line resistance estimation;

[0049] Figure 6 The simulation waveform diagram of bus voltage recovery control based on line resistance estimation value; (a) is the simulation waveform of output current of two converter ports; (b) is the simulation waveform of bus voltage;

[0050] Figure 7It is the simulation waveform of the present invention; among them (a) is the simulation waveform of the output current of the two converter ports; (b) is the simulation waveform of the bus voltage; (c) is the simulation waveform of the voltage command compensation of the two converter ports; (d) is the simulation waveform of the AC small signal reactive power of the two converters. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings.

[0052] The present invention is mainly used in the field of DC microgrid coordinated control. The main circuit diagram of the DC microgrid in the island state is as follows: Figure 1 The present invention adopts a unique control structure, including: capacitor voltage control, inductor current control, droop control, secondary control, bus voltage estimation, small signal injection, small signal regulation, such as Figure 2 shown.

[0053] The specific steps of the present invention are as follows:

[0054] 1) According to the output current i of the converter port o , bus voltage reference Droop coefficient d b and the estimated line resistance r e , generate the basic port voltage command of the converter through droop control The calculation formula is as follows:

[0055]

[0056] 2) According to the converter port output voltage v o , converter port output current i o and the estimated line resistance r e Calculate the initial estimated value of bus voltage v be , the calculation formula is as follows:

[0057] v be =v o -i o r e (1)

[0058] 3) Using the center frequency The bandpass filter processes the converter port output voltage v o and the converter port output current i o , extract the AC small signal voltage from it and AC small signal current After that, the AC small signal voltage and AC small signal current Perform coordinate transformation and convert to the two-phase rotating dq coordinate system to obtain the AC small signal voltage The component on the d-axis and the q-axis component and AC small signal current The component on the d-axis and the q-axis component Finally, the reactive power Q generated by the small AC signal is calculated using the following formula: ss :

[0059]

[0060] 4) Reactive power Q generated by small AC signal ss Adjust the initial estimated value of bus voltage v be , generating an estimated value of the adjusted bus voltage The calculation formula is as follows:

[0061]

[0062] in, is the coupling coefficient, and is a positive number;

[0063] 5) Calculate the estimated value of the adjusted bus voltage With bus voltage reference The deviation is then passed through the integral regulator to generate the converter port voltage command compensation Δv b ;

[0064] 6) Use the converter port voltage command compensation to generate AC small signal frequency command through droop control The calculation formula is as follows:

[0065]

[0066] in, is the AC small signal frequency droop coefficient, and is a positive number; is the reference frequency of the small AC signal;

[0067] After that, according to the AC small signal frequency command value Use the following formula to calculate the AC small signal voltage command value:

[0068]

[0069] Among them, V ss represents the AC small signal voltage command amplitude, t represents time, and τ represents an arbitrary variable.

[0070] 7) AC small signal voltage command Converter basic port voltage command Converter port voltage command compensation Δv b The output voltage of the converter port is vo Output converter inductor current command after capacitor voltage regulator

[0071] After that, the converter inductor current command and the converter inductor current i L After passing through the inductor current regulator, a modulation signal is output, and the modulation signal passes through the PWM module to generate a drive signal for driving the converter.

[0072] Specifically, the present invention verifies the effectiveness of the proposed control strategy based on the Matlab / Simulink simulation platform.

[0073] Based on the Matlab / Simulink simulation platform, a DC microgrid simulation model in an island state is built. The model includes two parallel buck converters with exactly the same rated power, and the load is a resistive load with a resistance of 20Ω. The main circuit parameters of the parallel buck converter are shown in Table 1.

[0074] Table 1 Circuit parameters of two parallel buck converters in the simulation model

[0075]

[0076] The controller parameters of the two parallel converters are exactly the same. All controller parameters used in the simulation experiment are shown in Table 2.

[0077] Table 2 Controller parameters of two parallel buck converters in the simulation model

[0078]

[0079] In order to verify the effectiveness of the present invention, the simulation experiment of the present invention includes two groups of comparative experiments and one group of feasibility verification experiments of the present invention. The comparative experiments include: first, the traditional droop control experiment; second, on the basis of the traditional droop control, adding secondary control to analyze the situation of directly using the line resistance estimation value with errors to directly restore the bus voltage;

[0080] 1) Experiment 1: The first set of comparative experiments

[0081] The first set of comparative experiments is a simulation experiment based on traditional droop control. The controller structure is shown in the figure below. Figure 3 The simulation results are shown in Figure 4 As shown in Figure 2. Among them, the simulated waveforms of the output currents of the two converters are shown in Figure 2. Figure 4 As shown in (a), in steady state, the output current i of converter 1 o1 =2.62A, the output current i of converter 2 o2 =1.97A, the ratio of the output current of the two converter ports is i o1 :io2 =1.3299. The bus voltage simulation waveform is as follows Figure 4 As shown in (b), in steady state, the bus voltage is 91.93V, which is consistent with the bus voltage command value In comparison, the deviation is 8.07V.

[0082] 2) Experiment 2: The second comparative experiment

[0083] The second set of comparative experiments adds secondary control to the traditional droop control and directly uses the estimated line resistance to restore the bus voltage. The controller structure is shown in the figure below: Figure 5 As shown. According to the current research on the line resistance estimation method in DC microgrid, it is difficult to accurately estimate all line resistances. Therefore, it is assumed here that the estimated value of the line resistance of converter 1 is r e1 =0.9Ω, the estimated value of the line resistance of converter 2 is r e2 =2.1Ω. The simulated waveforms of the output currents of the two converter ports are as follows: Figure 6 As shown in (a), the simulation waveforms of the output voltage of the two converter ports and the bus voltage are as follows: Figure 6 As shown in (b), it can be seen that due to the influence of the line resistance estimation error, the bus voltages estimated by the two converters using local information are different. Under the action of the secondary control integrator, the error continues to accumulate, eventually causing the system to diverge.

[0084] 3) Experiment 3: Feasibility verification experiment of the present invention

[0085] The third group of experiments is a feasibility verification experiment of the present invention. Among them, the bus voltage used for secondary control is the result calculated using the estimated value of line resistance and the converter port voltage; the simulation results are as follows Figure 7 As shown in Figure 2. Among them, the simulated waveforms of the output currents of the two converter ports are shown in Figure 2. Figure 7 As shown in (a), in steady state, the output current i of converter 1 o1 =2.62A, the output current of converter 2 is i o2 =2.38A, the ratio of the output currents of the two converters is i o1 :i o2 =1.100. The simulation waveform of bus voltage is as follows: Figure 7 As shown in (b), in steady state, the bus voltage DC bias is 100V, which is consistent with the bus voltage command Compared with the above, the complete recovery is basically achieved. The simulation waveforms of the voltage command compensation of the two converter ports are as follows: Figure 7 As shown in (c), it can be seen that under the regulation of the proposed control strategy, the outputs of the secondary control links of the two converters are exactly the same in steady state. During the regulation process, the simulation waveforms of the small signal reactive power of the two converters are as follows: Figure 7 (d) as shown.

[0086] In summary, in order to verify the feasibility of the control method, the author built a DC microgrid simulation model in an island state based on the Matlab / Simulink simulation platform, including two parallel buck converters, and the load is a pure resistance load. The simulation experiment results show that compared with the traditional control strategy, the present invention can effectively realize the non-communication bus voltage recovery while optimizing the power sharing effect of multiple parallel converters. The control strategy is correct and reliable, and provides a good reference value for engineering applications.

Claims

1. A DC microgrid non-communication bus voltage recovery control method, characterized in that: The following steps are involved: S1, according to the output current of the converter port i o , bus voltage reference , droop coefficient d b and line resistance estimate r e , generate the basic port voltage command of the converter through droop control ; S2, according to the output voltage of the converter port v o , converter port output current i o and line resistance estimates r e Calculate the initial estimate of bus voltage v be ; S3, output voltage from the converter port v o and port output current i o Extracting AC small signal voltage and AC small signal current , calculate the reactive power generated by small AC signal Q ss ; S4, reactive power generated by small AC signal Q ss Adjust the initial estimate of bus voltage v be , generating an estimated value of the adjusted bus voltage ; S5, using the adjusted bus voltage estimate With bus voltage reference Generate converter port voltage command compensation ; S6, using the converter port voltage command compensation , through droop control, generate AC small signal frequency command , and then obtain the AC small signal voltage command ; S7, according to the AC small signal voltage command , basic port voltage command of converter Compensation with converter port voltage command Adjust the output voltage of the converter port v o .

2. A DC microgrid non-communication bus voltage recovery control method according to claim 1, characterized in that: Basic port voltage command of converter in S1 The calculation formula is as follows: 。 3. A DC microgrid non-communication bus voltage recovery control method according to claim 1, characterized in that: The specific methods of S3 are as follows: S31, sampling converter port output voltage v o , converter port output current i o , use a bandpass filter to extract the AC small signal voltage and AC small signal current ; S32, the AC small signal voltage and AC small signal current The coordinate transformation is converted to the two-phase rotating dq coordinate system, and the AC small signal voltage is obtained respectively The d-axis component and the q-axis component , AC small signal current The d-axis component and the q-axis component ; S33, according to the AC small signal voltage Components in the two-phase rotating dq coordinate system and , and AC small signal current Components in the two-phase rotating dq coordinate system and , calculate the reactive power generated by small AC signal Q ss , the calculation formula is as follows: 。 4. A DC microgrid non-communication bus voltage recovery control method according to claim 1, characterized in that: In S4, the reactive power generated by the small AC signal Q ss Adjust the initial estimate of bus voltage v be , generating an estimated value of the adjusted bus voltage The calculation formula is as follows: in, is the coupling coefficient and is a positive number.

5. A DC microgrid non-communication bus voltage recovery control method according to claim 1, characterized in that: In S5, the adjusted bus voltage estimate is used With bus voltage reference Generate converter port voltage command compensation The specific method is as follows: Calculate the estimated regulated bus voltage With bus voltage reference The deviation is compensated by the output converter port voltage command after the secondary control regulator. .

6. A DC microgrid non-communication bus voltage recovery control method according to claim 1, characterized in that: In S6, the frequency command of the AC small signal is generated by droop control. , and then obtain the voltage command of the small AC signal The specific method is as follows: S61, compensation according to the converter port voltage command , calculate the AC small signal frequency command ; S62, according to the frequency instruction of small AC signal , calculate the AC small signal voltage command .

7. A DC microgrid non-communication bus voltage recovery control method according to claim 6, characterized in that: In S61, AC small signal frequency command The calculation method is as follows: in, is the AC small signal frequency droop coefficient, and is a positive number; is the reference frequency of the small AC signal; In S62, the voltage command of the AC small signal The calculation method is as follows: in, V ss Indicates the AC small signal voltage command amplitude, t Indicates time, Represents any variable.

8. A DC microgrid non-communication bus voltage recovery control method according to claim 1, characterized in that: In S7, according to the AC small signal voltage instruction , basic port voltage command of converter Compensation with converter port voltage command The specific method for adjusting the port output voltage of the converter is as follows: S71, AC small signal voltage command , basic port voltage command of converter , Converter port voltage command compensation The output voltage of the converter port v o After passing through the capacitor voltage regulator, the output converter inductor current command ; S72, converter inductor current command and the converter inductor current i L After passing through the inductor current regulator, a modulation signal is output, and the modulation signal passes through the PWM module to generate a drive signal for driving the converter.

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