Micro-grid grid-connected interface circuit design method

Abstract

The invention discloses a micro-grid grid-connected interface circuit design method, and relates to the field of power line communication. Comprising the steps of grid-connected interface circuit structure design, interface circuit parameter design and realization of energy-information integrated reliable transmission in an alternating-current micro-grid grid-connected scene. For EIT communication of the AC micro-grid, an interface circuit needs to be designed between the AC micro-grid and an AC power grid to ensure the stability of the EIT communication due to the fact that the impedance frequency characteristic of the power grid is not matched with a communication carrier wave. According to the method, a new communication strategy is provided for power line communication of the alternating-current micro-grid, and information sending, transmission and receiving are achieved through the integrated power electronic converter with the EIT function.

Description

A method for designing a microgrid grid-connected interface circuit Technical Field

[0001] This invention relates to the field of power line communication, and in particular to a design method for a microgrid grid-connected interface circuit. Background Technology

[0002] With the widespread development of distributed resources and the advancement of microgrid technology, collaboration among multiple devices in a source-storage-load cluster can improve the overall resource utilization and operational efficiency of the microgrid. Multi-device collaboration is crucial for achieving multi-objective optimal scheduling, energy management, and the balancing of interests among multiple stakeholders in the electricity market within a microgrid. To achieve collaborative control of multiple devices, droop control is typically used in microgrids to achieve power distribution among multiple devices without communication lines. However, droop control can only regulate power and voltage by detecting changes in the voltage of common nodes, making it difficult to apply to distributed optimization and other scenarios requiring the transmission of more complex collaborative information. Common communication methods in microgrid collaborative operation require establishing dedicated communication links between multiple devices, but these additional communication systems increase cost, complexity, and the risk of system failure, and fail to achieve deep integration and collaborative control of energy and information.

[0003] Both power electronics and information modulation employ carrier modulation technology. Therefore, power electronic devices can transmit information while performing power conversion, making integrated power electronic converters with simultaneous power and information transmission capabilities a promising area for research and application. Applying EIT technology in microgrids can achieve deep integration of energy and information, providing communication systems with reliability equivalent to that of power systems. Compared to traditional power line communication (PLC), this technology eliminates the need for additional communication equipment and coupling circuits, maximizing the efficient use of hardware resources and reducing costs and system complexity. Currently, EIT research and applications primarily focus on DC systems; however, practical applications remain dominated by AC systems. Therefore, designing EIT communication systems suitable for AC microgrids, especially considering AC microgrid grid connection scenarios, is of great significance. When an EIT-based microgrid connects to an AC grid, it faces the challenge of a mismatch between the grid impedance frequency characteristics and the communication channel. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a design method for a microgrid grid-connected interface circuit. The present invention designs an interface circuit between a microgrid and an AC power grid system containing an EIT communication network, and provides a design method for LCR interface circuit parameters adapted to AC system access.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] According to the present invention, a microgrid grid-connected interface circuit design method is proposed, wherein a grid-connected interface circuit is designed between the common coupling point of the AC microgrid and the power grid. The grid-connected interface circuit includes a wave-blocking inductor L. r Resonant capacitor C r and damping resistor R r .

[0007] As a further optimization of the microgrid grid-connected interface circuit design method described in this invention, the wave-blocking inductor L... r Resonant capacitor C r and damping resistor R r The parameter design range is as follows:

[0008] Step 1: The AC microgrid includes a converter, which is equivalent to a voltage source u. d With converter filter inductor L f Series, u ac_d The communication carrier voltage at the point of common coupling of the AC microgrid; in the communication frequency band, the grid equivalent is the grid harmonic voltage u. g_h and the internal resistance Z of the power grid g Series connection; when the internal resistance Z of the power grid g When the resistance is 0, the harmonic voltage generated by the grid harmonics at the point of common coupling (PCC) is at its maximum. Let the grid internal resistance Z be... g Let s be the frequency parameter of the Laplace transform, where s is zero.

[0009] PCC node communication carrier voltage u ac_d1 for:

[0010]

[0011] Among them, G d For the gain of the communication carrier in the AC microgrid, G g The gain of the AC microgrid on the harmonic voltage of the power grid;

[0012] Step 2, C r and R r The value of satisfies the following constraints:

[0013]

[0014] Among them, P loss As a limit value, The current in Rr, This refers to the AC bus voltage of the power grid.

[0015] Step 3, C r and L r The value of should satisfy:

[0016]

[0017] Among them, f cr K is the data carrier frequency. f This is the margin coefficient;

[0018] Step 4: The communication carrier voltage at the point of common coupling node of the AC microgrid is greater than the communication carrier voltage threshold F;

[0019] .

[0020] As a further optimization scheme of the microgrid grid-connected interface circuit design method described in this invention, C r one end and R r One end is connected, L r one end and C r The other end is connected.

[0021] As a further optimization scheme of the microgrid grid-connected interface circuit design method described in this invention, in step four, the communication carrier voltage at the common connection point node of the AC microgrid is greater than the communication carrier voltage threshold F; this is to consider the reliability of information transmission and ensure reliable information communication and demodulation; the value of F is determined according to the circuit parameters of the AC microgrid and the accuracy of the demodulation algorithm used.

[0022] As a further optimization of the microgrid grid-connected interface circuit design method described in this invention, K f Take a value of 1.2 to 1.5.

[0023] As a further optimization of the microgrid grid-connected interface circuit design method described in this invention,

[0024] The characteristic of an AC microgrid is that its point of common coupling is connected to the power grid;

[0025] An AC microgrid includes a converter, which includes an inverter and a rectifier. The rectifier and inverter adopt a single-phase full-bridge structure, with the single-phase inverter as the power source and the single-phase rectifier as the load. The AC side of each rectifier and inverter is connected to the common connection point of the AC microgrid.

[0026] Each rectifier and inverter is equivalent to a user in an AC microgrid;

[0027] Rectifiers and inverters generate user data using their own controllers and send information to other users via power lines.

[0028] The modulation for communication is completed in the converter. Before the power modulation of the converter, the modulated user data is added to the AC reference voltage to realize integrated energy-information communication.

[0029] As a further optimization of the microgrid grid-connected interface circuit design method described in this invention, the communication modulation adopts a power / data dual-carrier modulation method; specifically as follows: using an additional sine wave as the data carrier, the user data is first modulated onto the data carrier to obtain modulated user data, and then the modulated user data is superimposed on the power reference signal. By changing the duty cycle of PWM modulation, the signal is transmitted.

[0030] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0031] (1) The information and energy transmission technology proposed in this invention is applicable to AC microgrids. It uses power lines as communication transmission lines, and power electronic devices such as converters uniformly modulate the output voltage and data. No additional communication lines are required. It has the characteristics of low cost, high reliability and wide application range.

[0032] (2) The microgrid grid-connected interface circuit based on energy and information transmission technology proposed in this invention addresses the current limitations of integrated energy and information transmission technology, which primarily focuses on isolated AC microgrid operation and lacks analysis of the coupling between the converter and the AC grid in grid-connected microgrid systems. When a microgrid is operating in grid-connected mode, the data signal of EIT communication is affected by external factors, threatening the effectiveness of communication. The microgrid grid-connected interface circuit designed in this invention fills this gap to some extent. Attached Figure Description

[0033] Figure 1a is a circuit diagram of a single-phase full-bridge inverter;

[0034] Figure 1b is a circuit diagram of a single-phase full-bridge rectifier;

[0035] Figure 2 is a structural diagram of the AC microgrid of the present invention;

[0036] Figure 3 is a structural diagram of the interface circuit of the present invention;

[0037] Figure 4 is a structural diagram of the experimental platform of the present invention;

[0038] Figure 5a shows the system resonance without a damping resistor;

[0039] Figure 5b shows the system resonance when the damping resistance is 5Ω;

[0040] Figure 6 shows the data transmission and reception waveforms of the experimental case. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] This invention discloses a design method for a microgrid grid-connected interface circuit, relating to the field of power line communication. The main methods of this invention include grid-connected interface circuit structure design and interface circuit parameter design, achieving reliable integrated energy-information transmission in AC microgrid grid-connected scenarios. This invention addresses EIT communication in AC microgrids. Due to the mismatch between the grid impedance frequency characteristics and the communication carrier, an interface circuit needs to be designed between the AC microgrid and the AC grid to ensure the stability of EIT communication. This method provides a new communication strategy for AC microgrid power line communication, utilizing an integrated power electronic converter with EIT functionality to achieve information transmission, reception, and transmission.

[0043] This paper designs a microgrid grid-connected interface circuit based on the energy-information co-transmission technology, using an AC microgrid as the application scenario. The AC microgrid's point of common coupling (PCC) is connected to the grid. The AC microgrid includes a converter, which comprises an inverter and a rectifier. Communication modulation is performed in the converter's controller. Modulated user data is added before the converter's power modulation to achieve integrated energy-information communication. The grid-connected interface circuit is placed between the AC microgrid's PCC and the grid. The parameters of this interface circuit are designed based on the AC microgrid's own parameters.

[0044] In an AC microgrid, rectifiers and inverters employ a single-phase full-bridge structure, with single-phase inverters serving as power sources and single-phase rectifiers as loads. The AC side of each rectifier and inverter is connected to the microgrid's point of common coupling (PCC). Each rectifier and inverter is equivalent to a user within the AC microgrid. The rectifiers and inverters generate user data using their own controllers and transmit this information to other users via power lines.

[0045] The communication modulation based on the integrated energy information transmission method employs a power / data dual-carrier modulation scheme. This method uses an additional sine wave as the data carrier. First, user data is modulated onto the data carrier to obtain modulated user data. Then, the modulated user data is superimposed on the power reference signal. By changing the duty cycle of the PWM modulation, signal transmission is achieved. The grid-connected interface circuit includes a wave-blocking inductor L. r Resonant capacitor C r and damping resistor R r .

[0046] The specific steps for designing the grid-connected interface circuit parameters of a microgrid based on the information and energy transmission technology are as follows:

[0047] Step 1: Equivalently convert the converter to a voltage source u d With converter filter inductor L f Series, u ac_d The communication carrier voltage at the point of common coupling (PCC) of the AC microgrid. In the communication frequency band, the grid equivalent is the grid harmonic voltage u. g_h and the internal resistance Z of the power grid gSeries connection. When the internal resistance Z of the power grid g When the resistance is 0, the harmonic voltage generated by the grid harmonics at the PCC node is the maximum. Therefore, considering the worst-case scenario, the grid internal resistance Z can be set to 0. g It is zero. Let s be the frequency parameter of the Laplace transform. The communication carrier voltage u of the PCC node. ac_d1 for:

[0048]

[0049] Among them G d For the gain of the communication carrier in the AC microgrid, G g This refers to the gain of the AC microgrid on the harmonic voltage of the power grid.

[0050] Step 2: Consider the power loss limitations of linear components, R r The power loss should be less than the specified value P. loss C r and R r A portion of the power frequency current will flow through the series branch, which will affect R. r To avoid excessive losses, C... r and R r The value of should satisfy the following constraints:

[0051]

[0052] Step 3: Consider the resonant frequency C of the AC microgrid r Also with L r and converter filter inductor L f Resonance occurs, causing gain instability. To provide stable gain for the communication band, C r and L r The value of should satisfy:

[0053]

[0054] Among them, f cr K is the data carrier frequency. f K is the margin coefficient. f Take a value of 1.2 to 1.5.

[0055] Step 4: Consider the reliability of information transmission. The communication carrier voltage at the point of common coupling (PCC) node of the AC microgrid should be greater than a certain value F to ensure reliable information communication and demodulation. The value of F can be determined based on the circuit parameters of the AC microgrid and the accuracy of the demodulation algorithm used.

[0056]

[0057] Based on the constraint calculations in steps two through four, the wave-blocking inductance L can be obtained. r Resonant capacitor C r and damping resistor R r The design scope.

[0058] Using the single-phase bridge topology shown in Figures 1a and 1b as examples, the AC system architecture involved in this invention is analyzed. dc U represents the DC voltage of the converter. ac The common point of connection (CPCC) power supply for the AC microgrid is shown in Figure 1a, where L and C correspond to the filter inductor and capacitor, respectively, and R is the power load. Figure 1b shows a single-phase bridge inverter used as the power supply for the AC microgrid; Figure 1b shows a single-phase bridge rectifier used as the load in the AC system.

[0059] Figure 2 shows the structure of an AC microgrid. The converter topology in the figure is either the inverter shown in Figure 1a or the rectifier shown in Figure 1b. The AC sides of each converter are connected in parallel and connected to the common coupling point of the AC microgrid.

[0060] Figure 3 shows the designed AC microgrid grid-connected interface circuit based on EIT communication. The converter is represented by VSC. u1 and u2 are the primary and secondary voltages of the power frequency transformer, respectively. The interface circuit design process is as follows:

[0061] First, due to the internal resistance Z of an ideal power grid g To provide impedance to the information components and prevent information carrier injection into the power grid, a wave-blocking inductor L is added, which is zero. r L r Its main function is to pass power frequency current and block high-frequency information component current.

[0062] Secondly, in order to provide a current path for the high-frequency data carrier and achieve impedance stability, in L r Add a filter capacitor C to the AC side of the converter r As shown in Figure 3. Due to the characteristic of a capacitor to pass high frequencies and block low frequencies, the current flowing through C... r The power frequency current is much smaller than the current generated by the high-frequency information carrier, and the filter capacitor plays the role of separating the communication carrier.

[0063] Finally, due to the AC side filter inductance L of the converter f Impedance and capacitance C r Wave blocking inductor L r Together, they form a third-order LCL resonant network with damped resonance, which can lead to specific harmonic oscillations. To prevent this network from reducing system stability and causing resonance that could affect communication, capacitor C can be used. r Series resistor R r .

[0064] To verify the feasibility and reliability of the present invention, an experimental platform was built to verify the microgrid grid-connected interface circuit based on information and energy transmission technology proposed in this invention.

[0065] Implementation Case:

[0066] Figure 4 shows the AC system topology used in this invention. The AC system consists of three converters: VSC1 and VSC2 are inverters, and VSC3 is a rectifier. In the figure, U... dc1 = U dc2 = U dc3 =30V represents the DC-side voltage of the three converters, and the AC bus voltage amplitude U is also present. ac =24V, converter filter inductor L1= L2= L3=0.8mH, filter capacitor C1= C2= C3=0.66μF. T c It is a power frequency transformer with a peak primary voltage u1 of 311V and a peak secondary voltage u2 of 24V.

[0067] First, let's look at the interface circuit parameter R. r The rationality was verified. An experiment was conducted using VSC1 sending information as an example, with the communication parameters being the data carrier frequency f. cr Using a 4kHz sine wave, the symbol period of communication is 1ms, and the data modulation depth ε1=m1 / U dc =0.006, where m1 is the data carrier amplitude of VSC1. In T on During the time period, VSC1 sends data. Figure 5a shows the system resonance when there is no damping resistor; Figure 5b shows the system resonance when the damping resistor is 5Ω.

[0068] In Figures 5a and 5b, channel 1 shows the modulated data waveform of VSC1, and channel 2 shows the voltage U at the point of common coupling. ac Channel 3 shows the current i1 of VSC1, and channel F1 shows the FFT analysis of the AC bus voltage of channel 2. It can be seen that u ac The harmonic distribution. When there is no damping resistor R in the system. r Time U ac The frequency domain analysis is shown in Figure 5a. It can be seen that Z exists in the 5~6kHz range. r The network introduces resonance, and the resonance peak is relatively large. Figure 5b shows the addition of R. r The experimental waveform with a current of 5Ω, in frequency domain analysis, U ac The frequency domain is mainly concentrated between 50Hz and 4kHz. The LCL network resonance component caused by the converter circuit is low, distributed between 5 and 6kHz. This resonance point is slightly higher than the communication frequency band and will not cause interference to communication.

[0069] The experimental waveforms of the microgrid grid-connected interface circuit based on the simultaneous information and energy transmission technology designed in this case are shown in Figure 6. The data sent by user VCS1 is: "1,1,0,1,0,1,0,1,0,0,0,1,1,0,1,0,1,1,1,0,0,1". In Figure 6, channel 1 is the AC microgrid point of common coupling voltage waveform, channel 2 is the data waveform retained after filtering the point of common coupling voltage on the data receiving side, and channel 3 is the user data restored by the receiving side. High level represents "1", low level represents "0", and the data demodulation is accurate. At this time, the bus voltage harmonic THD = 4.2%, and the user communication rate is 1kbps. This experiment verifies the feasibility of the microgrid grid-connected interface circuit based on the simultaneous information and energy transmission technology.

[0070] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a microgrid grid-connected interface circuit, characterized in that, A grid-connected interface circuit is designed between the common coupling point of the AC microgrid and the power grid. The grid-connected interface circuit includes a wave-blocking inductor L. r Resonant capacitor C r and damping resistor R r。 2. The microgrid grid-connected interface circuit design method according to claim 1, characterized in that, Wave blocking inductor L r Resonant capacitor C r and damping resistor R r The parameter design range is as follows: Step 1: The AC microgrid includes a converter, which is equivalent to a voltage source u. d With converter filter inductor L f Series, u ac_d The communication carrier voltage at the point of common coupling of the AC microgrid; in the communication frequency band, the grid equivalent is the grid harmonic voltage u. g_h and the internal resistance Z of the power grid g Series connection; when the internal resistance Z of the power grid g When the resistance is 0, the harmonic voltage generated by the grid harmonics at the point of common coupling (PCC) is at its maximum. Let the grid internal resistance Z be... g Let s be the frequency parameter of the Laplace transform, and let s be zero; the communication carrier voltage u of the PCC node is... ac_d1 for: Among them, G d For the gain of the communication carrier in the AC microgrid, G g For the gain of the AC microgrid on the grid harmonic voltage; Step 2, C r and R r The value of satisfies the following constraints: Among them, P loss As a limit value, The current in Rr, The AC bus voltage of the power grid; Step 3, C r and L r The value of should satisfy: ; where f cr K is the data carrier frequency. f This is the margin factor; Step 4: The communication carrier voltage at the point of common coupling node of the AC microgrid is greater than the communication carrier voltage threshold F; 。 3. The microgrid grid-connected interface circuit design method according to claim 1, characterized in that, C r one end and R r One end is connected, L r one end and C r The other end is connected.

4. The microgrid grid-connected interface circuit design method according to claim 1, characterized in that, In step four, the communication carrier voltage at the common connection point of the AC microgrid is greater than the communication carrier voltage threshold F; this is to ensure reliable information transmission and demodulation. The value of F is determined based on the circuit parameters of the AC microgrid and the accuracy of the demodulation algorithm used.

5. The microgrid grid-connected interface circuit design method according to claim 1, characterized in that, K f Take a value of 1.2 to 1.

5.

6. The microgrid grid-connected interface circuit design method according to claim 1, characterized in that, An AC microgrid is characterized by its point of common coupling (PCC) being connected to the power grid. The AC microgrid includes converters, which consist of inverters and rectifiers. The rectifiers and inverters employ a single-phase full-bridge structure, with single-phase inverters as the power source and single-phase rectifiers as the load. The AC side of each rectifier and inverter is connected to the PCC of the AC microgrid. Each rectifier and inverter is equivalent to a user in the AC microgrid. The rectifiers and inverters generate user data using their own controllers and transmit information to other users via the power lines. Communication modulation is performed within the converters; before power modulation in the converters, the modulated user data is added to the AC reference voltage to achieve integrated energy-information communication.

7. The microgrid grid-connected interface circuit design method according to claim 6, characterized in that, The communication modulation adopts a power / data dual-carrier modulation method; specifically as follows: using an additional sine wave as the data carrier, the user data is first modulated onto the data carrier to obtain modulated user data. Then, the modulated user data is superimposed on the power reference signal. By changing the duty cycle of PWM modulation, the signal is transmitted.

Images