Single sensor control method and system applied to lcl type grid-connected inverter

Abstract

This invention relates to the field of power electronics technology and provides a single-sensor control method and system for LCL-type grid-connected inverters. The method includes: transmitting the difference between the incoming grid current and a current reference to a current regulator to obtain the regulator's output; superimposing the incoming grid current onto the regulator's output in a positive feedback manner after passing it through a second-order digital filter to obtain a modulation signal; and generating a PCC voltage estimate based on the modulation signal and the incoming grid current through the superposition of two transfer functions, followed by obtaining the current reference through a phase-locked loop structure and trigonometric function calculations. The control structure is very simple, reducing the computational complexity of the control chip in practical applications.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and particularly relates to a single-sensor control method and system for LCL-type grid-connected inverters. Background Technology

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

[0003] With the rapid development of distributed grid-connected power generation systems, grid-connected inverters, as interface devices connecting new energy sources and the power grid, have received widespread attention and research. Grid-connected inverters require sensors to measure inverter voltage and current signals and utilize feedback control technology to achieve ideal power output and high-quality power supply. Therefore, sensors are essential components in inverter devices. LCL (two inductors and one capacitor) filters are small in size and have strong harmonic suppression capabilities, currently the mainstream filter structure for grid-connected inverters. However, they suffer from resonance problems, requiring additional sensors to achieve active damping of resonant harmonics. Typically, capacitor current sensors, or inverter-side current sensors and grid-connected current sensors are used. Furthermore, grid synchronization requires additional PCC (Point of Common Coupling) voltage measurement, generating a current reference through a phase-locked loop to achieve current synchronization tracking control.

[0004] It can be seen that the normal operation of LCL-type grid-connected inverters currently requires the use of multiple current and voltage sensors. The large number of sensors and the corresponding conditioning and sampling circuits inevitably increase the size and cost of the inverter control board. The numerous sampling circuit traces also make the PCB (Printed Circuit Board) layout more complex. Engineers need to make trade-offs between the number of PCB layers and the area, which increases the workload and difficulty of PCB design. Summary of the Invention

[0005] To address the technical problems mentioned above, this invention provides a single-sensor control method and system for LCL-type grid-connected inverters. It uses only one current sensor to achieve active damping, feedback tracking, and PCC voltage estimation, ultimately realizing grid-connected inverter grid-following control. The control structure is very simple, and the PCC voltage value can be estimated using only a second-order filter, reducing the computational complexity of the control chip in practical applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a single-sensor control method for an LCL-type grid-connected inverter, comprising: Obtain the grid-connected current; The difference between the grid current and the current reference is transmitted to the current regulator to obtain the output of the current regulator. The grid current is passed through a second-order digital filter and superimposed on the output of the current regulator in the form of positive feedback to obtain the modulated wave signal. Based on the modulated wave signal and the grid current, the PCC voltage estimate is generated by superimposing two transfer functions, and then the current reference is obtained through phase-locked loop structure and trigonometric function calculation.

[0007] Furthermore, it also includes: the modulated wave signal enters pulse width modulation, intersecting with the carrier to generate the switching signals of each switch in the inverter topology, and performing DC voltage chopping inversion.

[0008] Furthermore, the current regulator adopts a proportional-integral form.

[0009] Furthermore, the current regulator adopts a proportional resonance configuration.

[0010] Furthermore, the second-order digital filter, as the active damping term of the LCL filter, raises the resonant point of the -180° phase crossing to between 0° and 90° phase.

[0011] Furthermore, the LCL filter filters the stepped wave of the inverter output, and the inverter output is obtained by converting the DC-side voltage into a stepped wave at the switching frequency through the inverter topology.

[0012] A second aspect of the present invention provides a single-sensor control system for an LCL-type grid-connected inverter, comprising: The current acquisition module is configured to acquire the grid-connected current. The current tracking module is configured to: transmit the difference between the grid current and the current reference to the current regulator to obtain the output of the current regulator; and pass the grid current through a second-order digital filter and superimpose it on the output of the current regulator in the form of positive feedback to obtain a modulated wave signal. The voltage measurement synchronization module is configured to: generate a PCC voltage estimate based on the modulated wave signal and the grid current by superimposing two transfer functions, and then obtain the current reference through a phase-locked loop structure and trigonometric function calculations.

[0013] Furthermore, it also includes an active damping module, which is configured to: enter pulse width modulation with the modulated wave signal, intersect with the carrier to generate switching signals for each switch of the inverter topology, and perform DC voltage chopping inversion.

[0014] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the single-sensor control method for an LCL-type grid-connected inverter as described above.

[0015] A fourth aspect of the present invention provides a computer device including a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, wherein the processor executes the program to implement the steps of the single-sensor control method for an LCL-type grid-connected inverter as described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention uses only a single current sensor to achieve active damping, feedback tracking, and PCC voltage estimation, ultimately realizing grid-connected inverter grid-following control. The control structure is very simple, and the PCC voltage value can be estimated using only a second-order filter, reducing the computational complexity of the control chip in practical applications.

[0017] This invention requires only one current sensor to achieve complete grid-connected control of the inverter, significantly reducing the number of sensors used in the inverter. Since the filter capacitor has a very small capacitance and the current flowing through it is small, the inverter-side current is almost the same as the grid-connected current. Therefore, current measurement can also be used for switching transistor protection. Thus, it can effectively reduce the inverter size, increase the inverter power density, and reduce inverter cost and PCB wiring complexity from the perspective of reducing the number of sensors. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 This is a flowchart of a single-sensor control method applied to an LCL-type grid-connected inverter according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the simulation test results under a strong network according to Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the simulation test results under weak network conditions in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the structure of a computer device according to Embodiment 4 of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0021] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] Example 1 This embodiment provides a single-sensor control method for LCL-type grid-connected inverters.

[0023] The single-sensor control method for LCL grid-connected inverters provided in this embodiment is an invention of a simplified single-current grid-connected control technology with a simple control structure that is easy to implement with a digital controller.

[0024] The single-sensor control method for LCL grid-connected inverters provided in this embodiment requires only one current sensor to achieve complete grid-connected control of the inverter, significantly reducing the number of inverter sensors used. Since the filter capacitor has a very small capacitance and a small current flowing through it, the inverter-side current is almost the same as the grid-connected current. Therefore, current measurement can also be used for switching transistor protection. Thus, from the perspective of reducing the number of sensors, the inverter size can be effectively reduced, the inverter power density can be increased, and the inverter cost and PCB wiring complexity can be reduced.

[0025] The single-sensor control method for LCL-type grid-connected inverters provided in this embodiment, such as Figure 1 As shown, the specific steps are as follows: Step 1: The grid-connected inverter structure includes: an inverter topology (e.g., two-level, three-level, and multi-level topologies) that converts the DC-side voltage into a stepped wave at the switching frequency to obtain the inverter output; subsequently, an LCL filter composed of two filter inductors and one filter capacitor filters the stepped wave of the inverter output to obtain a sine wave; then, the control module acquires the current signal to achieve feedback control to ensure the ideal output effect of the inverter.

[0026] Step 2: Obtain the grid-connected current i by measuring with a current sensor. G It is compared with a current reference, and the difference is transmitted to the current regulator G. c In (s), the grid current i is adjusted. G Tracking current reference.

[0027] The current regulator can be implemented using a proportional-integral (PI) form or a proportional-resonant (CR) form.

[0028] The s-domain form of the proportional integral is: (1); Where, k p k is a proportional parameter. i Let be the integration parameter, and s represent the complex variable of the Laplace.

[0029] The s-domain form of the proportional resonance is: (2); Where, kr ω is the resonance proportional parameter. r To control the resonant bandwidth, ω g This is the angular frequency of the power grid.

[0030] Step 3: Measure the grid current i G The signal passes through a second-order digital filter G ad (s) is superimposed on the current regulator G in the form of positive feedback. c The output u of (s) in On (s), the modulated wave signal u is obtained. inv .

[0031] The expression for the second-order digital filter is: (3); Where, k c and ω h These are adjustable parameters.

[0032] In this embodiment, a second-order digital filter G is introduced. ad (s) As the active damping term of the LCL filter, the inner-loop open-loop transfer function of the grid-connected inverter becomes: (4); Among them, G d (s) is the equivalent transfer function of the digital control delay, L1 represents the inverter-side inductance value of the LCL filter, L2 represents the grid-side inductance value of the LCL filter, and C f This indicates the capacitance value of the LCL filter.

[0033] It can be seen that when there is no digital filter G ad At time (s), the inverter inner loop G in-open (s) There exists a pair of conjugate poles on the imaginary axis, and the phase crosses -180°, therefore the inner loop is necessarily unstable; when a positive feedback damping term G is added... ad (s) then raises the original -180° phase crossing resonance point to between 0° and 90° phase by adjusting the amplitude sensitive parameter k. c This makes the transfer function amplitude less than 1 at the frequency point where the phase crosses -180°.

[0034] Step 4: The current reference signal needs to be generated through a phase-locked loop (PLL), and the PLL input requires a PCC voltage signal. In this step, the PCC voltage signal is estimated in real time through a disturbance observer, so PCC voltage sampling is not required, saving the voltage sensor.

[0035] The disturbance observer has two inputs: the modulated wave signal u. inv and grid current signal i GThrough two transfer functions H v (s) and H i (s) are superimposed to generate the PCC voltage estimate. The specific expression is: (5); in, , (6); Where, ω c This refers to the bandwidth parameter of the digital filter.

[0036] The voltage estimation principle of the disturbance observer in this application is briefly described as follows: The s-domain expression for the modulated wave transmitted to the grid-connected current through the inverter topology and LCL filter is: (7); Because the filter capacitor value is very small, in the low-frequency range, it includes C. f The polynomial terms can be ignored, and G in the low-frequency band d (s)=1; therefore, the PCC voltage in the low-frequency range can be approximately expressed as: (8); Through a first-order low-pass filter H v (s), and the PCC voltage can be estimated according to equation (5).

[0037] Step 5: Estimate the PCC voltage value The voltage is fed into a traditional phase-locked loop structure to obtain the real-time phase θ of the PCC voltage; to achieve unity power factor grid connection, the hysteresis phase is subtracted from the output θ. This is to eliminate the phase lag between the reference and the controlled current in current control.

[0038] in, The calculation method is as follows: , (9); Finally, for θ- Perform trigonometric function operations to obtain the expected current reference signal i. ref The specific calculation formula is as follows: (10); Among them, I m This is the reference amplitude of the current generated by DC-side voltage regulation.

[0039] Step 6: Based on the above steps, the final input is the grid current signal i. G The feedback and network control structure outputs a modulated wave u invThe pulse width modulation (PWM) module is entered, and the signal is generated by intersecting with the carrier wave to generate the switching signals of each switch in the inverter topology, thereby realizing the DC voltage chopping and inverting function.

[0040] The single-sensor control method for LCL-type grid-connected inverters provided in this embodiment uses only one current sensor to achieve active damping, feedback tracking, and PCC voltage estimation, ultimately realizing grid-connected inverter grid-following control.

[0041] The single-sensor control method for LCL grid-connected inverters provided in this embodiment has a very simple control structure. The PCC voltage value can be estimated using only a second-order filter, which reduces the computational complexity of the control chip in practical applications.

[0042] Using the proposed single-current simplified control method, simulation results of grid-connected inverter operation under both strong and weak grid environments were tested, such as... Figure 2 and Figure 3 As shown, the circuit and control parameters are set as follows: LCL filter parameters are L1=2mH, L2=1mH, C f =7uF; Current regulator G c (s) A PI controller is used, k p =7.2, k i =20000; Active damper G ad (s) in k c =10, ω h =7000; ω in the perturbation observation filter c =50000; Current reference amplitude I m =40A. It can be seen that regardless of whether it's a strong or weak network (Z... g At a current (s) = 0.5 mH·s, the output current is always synchronized with the PCC voltage and maintains good grid-connected power quality. This demonstrates that the control technology in this embodiment can achieve complete grid-connected control requirements using only a single current sensor.

[0043] Example 2 The single-sensor control system for LCL-type grid-connected inverters provided in this embodiment includes: The current acquisition module is configured to acquire the grid-connected current. The current tracking module is configured to: transmit the difference between the grid current and the current reference to the current regulator to obtain the output of the current regulator; and pass the grid current through a second-order digital filter and superimpose it on the output of the current regulator in the form of positive feedback to obtain a modulated wave signal. The voltage measurement synchronization module is configured to: generate a PCC voltage estimate based on the modulated wave signal and the grid current by superimposing two transfer functions, and then obtain the current reference through a phase-locked loop structure and trigonometric function calculations; The active damping module is configured such that the modulated wave signal enters the pulse width modulation, intersecting with the carrier to generate the switching signals of each switch in the inverter topology, and performs DC voltage chopping and inversion.

[0044] The active damping module utilizes the measured current i G Implement active damping in the LCL filter to suppress LCL resonance instability.

[0045] The voltage-free measurement synchronization module uses a disturbance observer to estimate the PCC voltage in reverse and uses the estimated PCC voltage value as the input of the phase-locked loop to obtain a current reference i synchronized with the power grid. ref .

[0046] The current tracking module utilizes the current regulator G c (s) makes the controlled current i G Track its benchmark i ref This enables the network control to achieve the desired maximum power point tracking.

[0047] It should be noted that each module in this embodiment corresponds one-to-one with each step in Embodiment 1, and their specific implementation processes are the same, so they will not be repeated here.

[0048] Example 3 This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the single-sensor control method for LCL-type grid-connected inverters as described in Embodiment 1 above.

[0049] Example 4 This embodiment provides a computer device, such as... Figure 4 As shown, the system includes a computer-readable storage medium 1003, a processor 1001, a communication interface 1002, and a computer program stored on the computer-readable storage medium 1003 and executable on the processor 1001. The processor 1001, communication interface 1002, and computer-readable storage medium 1003 can be connected via a bus or other means. The communication interface 1002 is used to receive and transmit data. When the processor 1001 executes the program, it implements the steps of the single-sensor control method for LCL-type grid-connected inverters as described in Embodiment 1 above.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A single-sensor control method applied to LCL-type grid-connected inverters, characterized in that, include: Obtain the grid-connected current; The difference between the grid current and the current reference is transmitted to the current regulator to obtain the output of the current regulator. The grid current is passed through a second-order digital filter and superimposed on the output of the current regulator in the form of positive feedback to obtain the modulated wave signal. Based on the modulated wave signal and the grid current, the PCC voltage estimate is generated by superimposing two transfer functions, and then the current reference is obtained through phase-locked loop structure and trigonometric function calculation.

2. The single-sensor control method for LCL-type grid-connected inverters as described in claim 1, characterized in that, Also includes: The modulated wave signal enters pulse width modulation and intersects with the carrier to generate the switching signals of each switch in the inverter topology, performing DC voltage chopping and inversion.

3. The single-sensor control method for LCL-type grid-connected inverters as described in claim 1, characterized in that, The current regulator uses a proportional-integral (PI) form.

4. The single-sensor control method for LCL-type grid-connected inverters as described in claim 1, characterized in that, The current regulator adopts a proportional resonance design.

5. The single-sensor control method for LCL-type grid-connected inverters as described in claim 1, characterized in that, The second-order digital filter, as the active damping term of the LCL filter, raises the resonant point of the -180° phase crossing to between 0° and 90° phase.

6. The single-sensor control method for LCL-type grid-connected inverters as described in claim 1, characterized in that, The LCL filter filters the stepped wave of the inverter output, and the inverter output is obtained by converting the DC side voltage into a stepped wave at the switching frequency through the inverter topology.

7. A single-sensor control system applied to an LCL-type grid-connected inverter, characterized in that, include: The current acquisition module is configured to acquire the grid-connected current. The current tracking module is configured to: transmit the difference between the grid current and the current reference to the current regulator to obtain the output of the current regulator; and pass the grid current through a second-order digital filter and superimpose it on the output of the current regulator in the form of positive feedback to obtain a modulated wave signal. The voltage measurement synchronization module is configured to: generate a PCC voltage estimate based on the modulated wave signal and the grid current by superimposing two transfer functions, and then obtain the current reference through a phase-locked loop structure and trigonometric function calculations.

8. The single-sensor control system for LCL-type grid-connected inverters as described in claim 7, characterized in that, It also includes an active damping module, which is configured to: enter the pulse width modulation of the modulated wave signal, intersect with the carrier to generate the switching signals of each switch of the inverter topology, and perform DC voltage chopping and inversion.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program implements the steps of the single-sensor control method for LCL grid-connected inverters as described in any one of claims 1-6.

10. A computer device comprising a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the single-sensor control method for LCL grid-connected inverters as described in any one of claims 1-6.

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