A photovoltaic DC-DC converter secondary ripple suppression method based on virtual admittance control

Abstract

The application discloses a kind of photovoltaic DC-DC converter secondary ripple suppression methods based on virtual admittance control, belong to the field of power electronics.The output rectification diode of traditional unidirectional Boost converter is replaced by the switching tube with anti-parallel diode in the application, to constitute bidirectional DC-DC converter, to provide the bidirectional power path required for secondary ripple absorption.Under weak light / no light condition, the converter is switched from maximum power tracking mode to virtual admittance control mode by MPPT-DCAPF dual-mode switching strategy;The control is closed-loop regulated to zero by ripple voltage outer ring 100Hz secondary ripple voltage of DC bus, so that the equivalent admittance of converter port tends to infinity, equivalent to "virtual short circuit", so as to actively absorb secondary ripple current;Current inner loop adopts proportional-integral resonant controller to realize zero static error tracking.The application makes full use of photovoltaic converter idle capacity to suppress secondary ripple, significantly improves the power quality of DC microgrid, reduces system cost.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control. This method is used to actively absorb the secondary ripple current of the DC bus under weak light / no light conditions, thereby reducing the secondary ripple voltage of the DC bus. Background Technology

[0002] With the rapid development of DC microgrid technology, it is gaining increasingly widespread application due to its advantages such as flexible control, high power supply reliability, and ease of integration with distributed energy sources (such as photovoltaics and energy storage). However, DC microgrids face secondary ripple problems during operation. Specifically, this problem mainly stems from two scenarios: First, when a DC microgrid is interconnected with the AC grid via a bidirectional inverter, secondary ripple is injected into the DC bus due to power imbalance fluctuations, whether under the natural operating characteristics of a single-phase grid or under unbalanced operation or fault conditions in a three-phase grid. Second, connecting AC loads, including single-phase loads and three-phase unbalanced loads, to the DC bus via a unidirectional inverter also introduces secondary ripple. Secondary ripple, due to its low frequency and wide impact range, not only interferes with the normal operation of DC-sensitive loads but also accelerates the aging of equipment such as batteries and fuel cells, and increases system switching losses, posing significant risks.

[0003] Current methods for suppressing secondary ripple are mainly divided into two categories: passive suppression and active suppression. Passive suppression typically relies on increasing the DC bus capacitance to filter ripple. While this method is simple in principle, simply increasing the capacitance significantly increases system size, weight, and cost, and it cannot be dynamically adjusted. In contrast, active suppression methods utilize power electronic converters to achieve ripple suppression, offering advantages such as fast dynamic response and strong controllability, making them more valuable in practical applications than passive suppression methods. Currently, active methods for secondary ripple suppression can be categorized by converter type into DC / AC converters and DC-DC converters. Commonly used active filtering methods for secondary ripple suppression include using energy storage systems and adding active power filters (DC-APF). However, these methods suffer from high costs, complex control, and the formation of circulating currents. Especially under low-light / no-light conditions, photovoltaic converters have lower output power, and their capacity can be reused as ripple absorption devices, but current technology has not fully utilized the regulation potential of photovoltaic converters under these conditions. If the photovoltaic converter can be reused as a ripple suppression device under this operating condition, it can not only save investment in DC-APF or energy storage filter units, but also improve equipment utilization.

[0004] Therefore, there is an urgent need for a new method for suppressing secondary ripple that is low-cost, makes full use of the idle capacity of photovoltaic converters, and has a simple and efficient control structure. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for suppressing secondary ripple in photovoltaic DC-DC converters based on virtual admittance control. Under low-light / no-light conditions, this invention switches the photovoltaic BDC to DCAPF (virtual admittance control) mode, controlling the equivalent admittance of the BDC port in the 100Hz frequency band to approach infinity. This effectively suppresses the secondary ripple voltage of the DC bus, improving system stability and economy. Furthermore, the application scenarios of this invention can be expanded. Whether it's ripple generated by AC / DC hybrid microgrids (unbalanced loads / faults in three-phase microgrids generate a large amount of secondary ripple, while single-phase microgrids naturally generate secondary ripple) or ripple generated by AC loads connected to a DC grid, this invention can utilize the idle capacity of the photovoltaic system to suppress the secondary ripple voltage of the DC bus.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control, comprising:

[0007] Under low light / no light conditions, switch the control mode of the photovoltaic converter from the maximum power point tracking (MPPT) mode to the virtual admittance control mode;

[0008] In virtual admittance control mode, the photovoltaic converter is controlled to exhibit high admittance characteristics in the 100Hz frequency band in order to actively absorb the secondary ripple current of the DC bus and suppress the secondary ripple voltage of the DC bus.

[0009] Furthermore, the photovoltaic converter is a bidirectional DC-DC converter (BDC). Based on the traditional unidirectional Boost converter, the output rectifier diode of the bidirectional DC-DC converter is replaced with a switching transistor with an anti-parallel diode, thus forming a bidirectional DC-DC converter. This allows energy to flow bidirectionally between the DC bus and the low-voltage side capacitor, so as to achieve the purpose of absorbing secondary ripple using the converter.

[0010] Furthermore, the virtual admittance control mode achieves BDC control by constructing a dual voltage outer loop + current inner loop; its implementation method includes:

[0011] A bandpass filter is used to extract the 100Hz ripple voltage signal from the DC bus.

[0012] The difference between the 100Hz ripple voltage signal and the preset ripple reference value is used to generate a secondary ripple current reference signal through the first voltage outer loop PI controller.

[0013] The low-voltage side capacitor voltage of the photovoltaic converter is collected and a DC current reference signal is generated through the second voltage outer loop.

[0014] The secondary ripple current reference signal is superimposed with the DC current reference signal to generate the total current reference signal;

[0015] The inductor current of the photovoltaic converter is collected, and the difference between it and the total current reference signal is calculated. The difference is then used to generate a modulation signal through the current inner loop controller.

[0016] A switching signal is generated based on the modulation signal to drive the photovoltaic converter to absorb secondary ripple current.

[0017] Furthermore, the preset ripple reference value is 0; the virtual admittance control mode adjusts the secondary ripple voltage of the DC bus to zero in a closed loop, so that the equivalent admittance of the photovoltaic converter at the port in the 100Hz frequency band approaches infinity, which is equivalent to a virtual short circuit.

[0018] Furthermore, the current inner loop controller is a proportional-integral resonant controller, and its transfer function is... Represented as:

[0019]

[0020] Where, ω 2f Let be the second-order ripple angular frequency, s be the Laplace operator, and K be the second-order ripple angular frequency. P K is the proportional gain coefficient. I K is the integral gain coefficient. RSC This represents the gain coefficient of the resonant controller.

[0021] Furthermore, the switching of the control mode is achieved through an MPPT-DCAPF dual-mode switching strategy, including:

[0022] Real-time detection of photovoltaic output power P PV ;

[0023] When P PV Greater than the preset high threshold P h When switching to MPPT mode;

[0024] When P PV If the value is less than the preset low threshold P1, a delay is initiated. If the value is less than the preset low threshold P1 within the delay period, a delay is initiated. PV If the value remains below P1, switch to virtual admittance control mode, i.e., DCAPF mode;

[0025] If P is within the delay period PV If the temperature rises above P1, the reset delay will be applied and the current mode will be maintained.

[0026] When P PV Between P1 and P h In between, maintain the current mode.

[0027] Furthermore, the preset high threshold P hThe preset low threshold P1 is set in the range of 20% to 25% of the photovoltaic rated power.

[0028] This invention also provides a secondary ripple suppression system for a photovoltaic DC-DC converter based on virtual admittance control, used to implement the above method, comprising:

[0029] A photovoltaic converter, whose topology is a bidirectional DC-DC converter, is used to connect photovoltaic cells to a DC bus;

[0030] The mode switching module is used to switch the control mode of the photovoltaic converter from the maximum power point tracking (MPPT) mode to the virtual admittance control mode under low light / no light conditions.

[0031] The virtual admittance control module is used to control the photovoltaic converter to exhibit high admittance characteristics in the 100Hz frequency band under virtual admittance control mode, so as to actively absorb the secondary ripple current of the DC bus and suppress the secondary ripple voltage of the DC bus.

[0032] Furthermore, the virtual admittance control module includes:

[0033] Ripple extraction unit, used to extract the 100Hz ripple voltage signal of the DC bus;

[0034] The first voltage outer loop is used to calculate the difference between the 100Hz ripple voltage signal and the preset ripple reference value, and generate a secondary ripple current reference signal through PI control.

[0035] The second voltage outer loop is used to collect the low-voltage side capacitor voltage of the photovoltaic converter and generate a DC current reference signal through PI control;

[0036] The superposition unit is used to superimpose the secondary ripple current reference signal and the DC current reference signal to generate a total current reference signal.

[0037] The inner current loop is used to calculate the difference between the collected inductor current of the photovoltaic converter and the total current reference signal, and then generate a modulation signal through a proportional-integral resonant controller.

[0038] The PWM modulation unit is used to generate a switching signal based on the modulation signal to drive the photovoltaic converter to absorb secondary ripple current.

[0039] Furthermore, the mode switching module is an MPPT-DCAPF dual-mode switching module, which is configured as follows:

[0040] Real-time detection of photovoltaic output power P PV ;

[0041] When P PV Greater than the preset high threshold P h When switching to MPPT mode;

[0042] When P PV If the value is less than the preset low threshold P1, a delay is initiated. If the value is less than the preset low threshold P1 within the delay period, a delay is initiated. PV If the value remains below P1, switch to virtual admittance control mode, i.e., DCAPF mode;

[0043] If P is within the delay period PV If the temperature rises above P1, the reset delay will be applied and the current mode will be maintained.

[0044] When P PV Between P1 and P h In between, maintain the current mode.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention is the first to propose using photovoltaic converters to suppress secondary ripple voltage in DC microgrids. Since effective suppression of secondary ripple requires the converter to have bidirectional power transmission capability, a bidirectional topology is necessary. This only requires replacing the diodes in traditional photovoltaic converters with controllable switches, resulting in a minimal increase in device cost and a reduction in power loss. On the operation side, the strategy fully utilizes the natural window of low-light / no-light conditions when photovoltaic array output sharply decreases and converter capacity is idle, ensuring that the same equipment can be fully utilized within 24 hours, significantly improving hardware utilization and avoiding the hidden waste caused by idle assets. Furthermore, without the use of additional devices, actively absorbing secondary ripple current using photovoltaic converters not only alleviates the secondary ripple voltage content of the DC bus but also reduces the installed capacity of the DC-APF, thus reducing the economic cost of the device.

[0047] From the perspective of power quality, virtual admittance control can precisely "cancel" 100Hz pulsating power, reducing the DC bus voltage ripple coefficient from about 20% to less than 3%, providing a near "battery-level" stable power supply environment for DC sensitive loads and significantly extending the service life of downstream equipment and bus capacitors.

[0048] More importantly, the method of this invention broadens the application of photovoltaic converters, enabling them to potentially undertake multiple tasks such as voltage stabilization, harmonic suppression, and power decoupling in DC microgrids in the future, providing a feasible technical path for the functional expansion of converters and new grid connection standards. Attached Figure Description

[0049] Figure 1 This is a topology diagram of the photovoltaic converter retrofit in an embodiment of the present invention;

[0050] Figure 2 This is a block diagram of the photovoltaic BDC control strategy in an embodiment of the present invention;

[0051] Figure 3This is an equivalent circuit diagram of DC power grid secondary ripple compensation in an embodiment of the present invention;

[0052] Figure 4 This is a flowchart of the dual-mode switching control in an embodiment of the present invention;

[0053] Figure 5 This is a simulation model diagram of an embodiment of the present invention;

[0054] Figure 6 These are simulation waveforms from embodiments of the present invention. Figure 1 ;

[0055] Figure 7 These are simulation waveforms from embodiments of the present invention. Figure 2 . Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. 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 application pertains.

[0058] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0059] 1. Control method design

[0060] Photovoltaic converter retrofit reference Figure 1 The control method is as follows: Figure 2 Switching strategy reference Figure 4 This invention proposes a method for suppressing secondary ripple in photovoltaic DC-DC converters based on virtual admittance control. The control principle of the entire system is as follows:

[0061] (1) Topology transformation

[0062] First, the diodes in the photovoltaic converter need to be replaced with a switching transistor—that is, it needs to become a BDC topology—to achieve a bidirectional loop and enable energy closed-loop control of the secondary ripple power. This is a prerequisite for control. (Refer to...) Figure 1By replacing the output rectifier diode of a traditional unidirectional Boost converter with a switching transistor with an anti-parallel diode, a bidirectional DC-DC converter can be constructed. This topology modification allows energy to flow bidirectionally between the DC bus and the low-voltage side capacitor, which is the necessary bidirectional power path for absorbing secondary ripple.

[0063] (2) Virtual admittance control strategy

[0064] In terms of control, refer to Figure 2 First, sample the DC bus voltage V. dc The second-order ripple component V is extracted after passing through a bandpass filter (BPF). 2f The difference between the voltage and the set voltage reference value (set to 0) is used by the PI controller to generate a secondary ripple current reference quantity I. 2f_ref This is provided to the current loop. Since the system has switched to secondary ripple absorption mode, the low-voltage side capacitor only serves as an energy buffer and is not clamped by a voltage regulator such as a photovoltaic cell. Therefore, the capacitor voltage needs to be controlled through a slow voltage outer loop (with a bandwidth much smaller than the ripple frequency) to generate a DC current reference quantity I. DCref Provided to the current loop. The two current reference values ​​are superimposed and fed into the current loop to sample the inductor current I on the BDC. L With reference quantity I 2f_ref +I DCref The difference is processed by a proportional-integral-resonant controller to generate a modulation signal, which is then used to generate a switching signal via PWM. , .

[0065] Figure 2 In this context, BPF refers to a bandpass filter, designed to accurately extract the second-order ripple in the bus voltage. Its transfer function is defined as:

[0066]

[0067] Where, ω 2f denoted as the second-order ripple frequency, Q as the quality factor, and s as the Laplace operator.

[0068] Since the BDC needs to absorb the secondary ripple current on the DC bus into its low-voltage side capacitor, its inner-loop current control must have a high bandwidth. Therefore, a proportional-integral-resonant (PIR) controller is used to achieve zero steady-state error. To this end, a resonant controller (RSC) is connected in parallel with the proportional-integral (PI) controller, and its continuous-time transfer function is:

[0069]

[0070] Where, ω 2f K is the second-order ripple angular frequency. P K is the proportional gain coefficient. I K is the integral gain coefficient. RSC This represents the gain coefficient of the resonant controller. The proportional element accelerates the system's dynamic response, the integral element eliminates steady-state errors of the DC component, and the resonant element provides theoretically infinite gain at 100Hz. This structure ensures zero steady-state error tracking of the ripple current and also zero steady-state error tracking of the DC component, achieving ripple suppression.

[0071] (3) Virtual admittance control principle

[0072] The virtual admittance control adjusts the secondary ripple voltage of the DC bus to zero through the closed-loop ripple voltage outer loop. Since the port equivalent admittance is defined as the ratio of ripple current to ripple voltage, when the ripple voltage approaches zero, the equivalent admittance approaches infinity. The converter port is equivalent to a "virtual short circuit" in the 100Hz frequency band, thereby actively absorbing the secondary ripple current.

[0073] 2. DC power grid ripple loop analysis

[0074] Figure 3 This is the equivalent circuit diagram for DC power grid ripple circuit analysis, where, It is a secondary ripple current source injected into the DC bus of a single-phase AC power grid via an interconnected inverter. and These are secondary ripple current sources injected into other distributed AC loads (such as single-phase loads or three-phase unbalanced loads); The inverter port equivalent admittance; and This is the equivalent admittance of the photovoltaic BDC port controlled in this paper; and This represents the line equivalent admittance of each DC bus section; and This represents the port equivalent admittance of other distributed converters (such as energy storage converters).

[0075] These ripple currents are shared by all branches (including the BDC, other converters, and DC loads / power supplies). The sharing ratio of each branch depends on the equivalent admittance at its port; the larger the admittance, the more ripple current is absorbed. Combined with the virtual admittance control discussed earlier, this refers to controlling the external equivalent admittance of the photovoltaic BDC. The external equivalent admittance of the BDC in the 100Hz frequency band is defined as:

[0076]

[0077] in, This is the secondary ripple voltage at the BDC port. For the secondary ripple current flowing into the BDC, This is the equivalent admittance of BDC to the outside in the 100Hz frequency band.

[0078] Since the ripple voltage reference value is set to 0 in this invention, closed-loop control is used to... Approaching 0, therefore the equivalent admittance Approaching infinity, it can be considered a virtual short-circuit state. Therefore, the ripple current will naturally flow to the photovoltaic converter, achieving the purpose of absorbing the secondary ripple of the DC bus.

[0079] 3. "MPPT-DCAPF" dual-mode switching control design

[0080] Appendix Figure 4 This is a flowchart of the "MPPT-DCAPF" dual-mode switching control. Based on the operation of a photovoltaic BDC at different times, this invention proposes an MPPT-DCAPF dual-mode switching control strategy. This switching strategy is designed to avoid interference from the proposed ripple suppression function with the normal power output of the photovoltaic system. It combines real-time power monitoring with hysteresis comparison to ensure a smooth switching between photovoltaic power generation and the secondary ripple suppression function.

[0081] The switching logic determines whether the current period is one of low light / no light based on the photovoltaic output power. If the switching conditions are met and after a delay, the MPPT mode is switched to DCAPF mode, realizing the conversion from photovoltaic power generation to active ripple absorption. The specific control logic is as follows:

[0082] Real-time monitoring of photovoltaic output power And based on preset upper and lower thresholds , Perform a hysteresis comparison.

[0083] when When this happens, the system immediately switches to MPPT mode to prioritize maximum power point tracking.

[0084] when When the power level remains below a certain threshold during the entire delay period, the delay module is activated. If the power recovers during the delay period, the system switches to DCAPF mode, clears the MPPT control signal, and enables virtual admittance control; If the above is true, then the reset delay will be applied and the original mode will be maintained.

[0085] when Between and During this period, the system maintains the current mode.

[0086] The switching threshold is set in the low-light range of 20% to 25% of the rated power to ensure that mode switching only occurs when the photovoltaic power generation revenue is significantly lower than the ripple suppression benefit. The hysteresis and delay circuit work together to effectively avoid frequent mode switching caused by instantaneous fluctuations in light intensity, thereby improving the stability and reliability of system operation.

[0087] 4. Simulation verification

[0088] Figure 5 This is a DC microgrid simulation model, and a simulation platform can be built using scientific analysis software such as MATLAB. The model includes two photovoltaic BDCs connected in parallel to the DC bus, and connected to a single-phase AC grid as a secondary ripple source. Photovoltaic BDC 1 always operates in MPPT mode; photovoltaic BDC 2 adopts the switching control strategy proposed in this invention, automatically switching the control mode according to the output power level. In the simulation, and Choose 3100W and 3000W respectively.

[0089] Simulations verified the effectiveness of virtual admittance control in DCAPF mode and the smooth transition capability of dual-mode switching. Figure 6 To verify the simulation waveform of the smooth switching of BDC from generation mode to ripple suppression mode when the light intensity decreases, the voltage oscillation amplitude before and after the switching can be used to verify that the proposed virtual admittance control has a good suppression effect on secondary ripple. During the switching process, the bus voltage quickly recovers to stability after a short adjustment. The transient voltage overshoot is controlled within a reasonable range and no obvious oscillation occurs, indicating that the proposed switching logic has a good smooth transition capability. Figure 7 To verify the simulation waveform of BDC rapidly returning from DCAPF mode to MPPT mode during illumination recovery, the waveform comparison shows that the voltage quickly recovers to the steady-state operating point of MPPT mode after switching to MPPT mode.

[0090] This embodiment also provides a photovoltaic DC-DC converter secondary ripple suppression system based on virtual admittance control to implement the above method, including a photovoltaic converter, a mode switching module and a virtual admittance control module.

[0091] The photovoltaic converter is a bidirectional DC-DC converter, used to connect the photovoltaic cells to the DC bus.

[0092] The mode switching module is used to switch the control mode of the photovoltaic converter from Maximum Power Point Tracking (MPPT) mode to Virtual Admittance Control mode under low light / no light conditions. The mode switching module is an MPPT-DCAPF dual-mode switching module, configured as follows:

[0093] Real-time detection of photovoltaic output power P PV ;

[0094] When P PV Greater than the preset high threshold P h When switching to MPPT mode;

[0095] When P PV If the value is less than the preset low threshold P1, a delay is initiated. If the value is less than the preset low threshold P1 within the delay period, a delay is initiated. PV If the value remains below P1, switch to virtual admittance control mode, i.e., DCAPF mode;

[0096] If P is within the delay period PV If the temperature rises above P1, the reset delay will be applied and the current mode will be maintained.

[0097] When P PV Between P1 and P h In between, maintain the current mode.

[0098] The virtual admittance control module is used to control the photovoltaic converter to exhibit high admittance characteristics in the 100Hz frequency band under virtual admittance control mode, so as to actively absorb the secondary ripple current of the DC bus and suppress the secondary ripple voltage of the DC bus. The virtual admittance control module includes:

[0099] Ripple extraction unit, used to extract the 100Hz ripple voltage signal of the DC bus;

[0100] The first voltage outer loop is used to calculate the difference between the 100Hz ripple voltage signal and the preset ripple reference value, and generate a secondary ripple current reference signal through PI control.

[0101] The second voltage outer loop is used to collect the low-voltage side capacitor voltage of the photovoltaic converter and generate a DC current reference signal through PI control;

[0102] The superposition unit is used to superimpose the secondary ripple current reference signal and the DC current reference signal to generate a total current reference signal.

[0103] The inner current loop is used to calculate the difference between the collected inductor current of the photovoltaic converter and the total current reference signal, and then generate a modulation signal through a proportional-integral resonant controller.

[0104] The PWM modulation unit is used to generate a switching signal based on the modulation signal to drive the photovoltaic converter to absorb secondary ripple current.

[0105] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0106] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0107] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0108] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control, characterized in that, include: Under low light / no light conditions, switch the control mode of the photovoltaic converter from the maximum power point tracking (MPPT) mode to the virtual admittance control mode; In virtual admittance control mode, the photovoltaic converter is controlled to exhibit high admittance characteristics in the 100Hz frequency band in order to actively absorb the secondary ripple current of the DC bus and suppress the secondary ripple voltage of the DC bus.

2. The method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control according to claim 1, characterized in that, The photovoltaic converter is a bidirectional DC-DC converter. Based on the traditional unidirectional Boost converter, the output rectifier diode is replaced with a switching transistor with an anti-parallel diode.

3. The method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control according to claim 1, characterized in that, The implementation method of the virtual admittance control mode includes: Extract the 100Hz ripple voltage signal from the DC bus; The difference between the 100Hz ripple voltage signal and the preset ripple reference value is used to generate a secondary ripple current reference signal through the first voltage outer loop PI controller. The low-voltage side capacitor voltage of the photovoltaic converter is collected and a DC current reference signal is generated through the second voltage outer loop. The secondary ripple current reference signal is superimposed with the DC current reference signal to generate the total current reference signal; The inductor current of the photovoltaic converter is collected, and the difference between it and the total current reference signal is calculated. The difference is then used to generate a modulation signal through the current inner loop controller. A switching signal is generated based on the modulation signal to drive the photovoltaic converter to absorb secondary ripple current.

4. The method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control according to claim 3, characterized in that, The preset ripple reference value is 0; the virtual admittance control mode adjusts the secondary ripple voltage of the DC bus to zero in a closed loop, so that the equivalent admittance of the photovoltaic converter at the port in the 100Hz frequency band approaches infinity, which is equivalent to a virtual short circuit.

5. The method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control according to claim 3, characterized in that, The current inner loop controller is a proportional-integral resonant controller, and its transfer function is... Represented as: Where, ω 2f Let be the second-order ripple angular frequency, s be the Laplace operator, and K be the second-order ripple angular frequency. P K is the proportional gain coefficient. I K is the integral gain coefficient. RSC This represents the gain coefficient of the resonant controller.

6. The method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control according to claim 1, characterized in that, The switching of the control mode is achieved through the MPPT-DCAPF dual-mode switching strategy, including: Real-time detection of photovoltaic output power P PV ; When P PV Greater than the preset high threshold P h When switching to MPPT mode; When P PV If the value is less than the preset low threshold P1, a delay is initiated. If the value is less than the preset low threshold P1 within the delay period, a delay is initiated. PV If the value remains below P1, switch to virtual admittance control mode, i.e., DCAPF mode; If P is within the delay period PV If the temperature rises above P1, the reset delay will be applied and the current mode will be maintained. When P PV Between P1 and P h In between, maintain the current mode.

7. The method for suppressing secondary ripple in a photovoltaic DC-DC converter based on virtual admittance control according to claim 6, characterized in that, The preset high threshold P h The preset low threshold P1 is set in the range of 20% to 25% of the photovoltaic rated power.

8. A secondary ripple suppression system for a photovoltaic DC-DC converter based on virtual admittance control, used to implement the method described in any one of claims 1-7, characterized in that, include: A photovoltaic converter, whose topology is a bidirectional DC-DC converter, is used to connect photovoltaic cells to a DC bus; The mode switching module is used to switch the control mode of the photovoltaic converter from the maximum power point tracking (MPPT) mode to the virtual admittance control mode under low light / no light conditions. The virtual admittance control module is used to control the photovoltaic converter to exhibit high admittance characteristics in the 100Hz frequency band under virtual admittance control mode, so as to actively absorb the secondary ripple current of the DC bus and suppress the secondary ripple voltage of the DC bus.

9. The photovoltaic DC-DC converter secondary ripple suppression system based on virtual admittance control according to claim 8, characterized in that, The virtual admittance control module includes: Ripple extraction unit, used to extract the 100Hz ripple voltage signal of the DC bus; The first voltage outer loop is used to calculate the difference between the 100Hz ripple voltage signal and the preset ripple reference value, and generate a secondary ripple current reference signal through PI control. The second voltage outer loop is used to collect the low-voltage side capacitor voltage of the photovoltaic converter and generate a DC current reference signal through PI control; The superposition unit is used to superimpose the secondary ripple current reference signal and the DC current reference signal to generate a total current reference signal. The inner current loop is used to calculate the difference between the collected inductor current of the photovoltaic converter and the total current reference signal, and then generate a modulation signal through a proportional-integral resonant controller. The PWM modulation unit is used to generate a switching signal based on the modulation signal to drive the photovoltaic converter to absorb secondary ripple current.

10. The photovoltaic DC-DC converter secondary ripple suppression system based on virtual admittance control according to claim 8, characterized in that, The mode switching module is an MPPT-DCAPF dual-mode switching module, which is configured as follows: Real-time detection of photovoltaic output power P PV ; When P PV Greater than the preset high threshold P h When switching to MPPT mode; When P PV If the value is less than the preset low threshold P1, a delay is initiated. If the value is less than the preset low threshold P1 within the delay period, a delay is initiated. PV If the value remains below P1, switch to virtual admittance control mode, i.e., DCAPF mode; If P is within the delay period PV If the temperature rises above P1, the reset delay will be applied and the current mode will be maintained. When P PV Between P1 and P h In between, maintain the current mode.

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