Two-stage photovoltaic grid-connected inverter topology and DC bus voltage fluctuation suppression method
By adopting a series compensation link and voltage-current dual closed-loop control architecture in a two-stage photovoltaic grid-connected inverter, the problem of DC bus voltage fluctuations caused by power adjustment delay or dynamic mismatch at the front and rear stages is solved, and the stability of DC bus voltage and the normal operation of the inverter grid-connected current is achieved.
Patent Information
- Application Number
- CN202510470041.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-15
- Publication Date
- 2025-06-06
AI Technical Summary
In two-stage photovoltaic grid-connected inverters, there is delay or dynamic mismatch in front and rear power adjustments, resulting in fluctuations in DC bus voltage, which may cause system instability or grid-connected current distortion.
The two-stage photovoltaic grid-connected inverter topology is adopted, including the pre-stage boost circuit and the subsequent inverter circuit, combined with the series compensation link and the voltage-current dual closed-loop control architecture, the duty cycle of the switch tube is adjusted through the PI controller, the working voltage of the photovoltaic panel is controlled, and the DC bus voltage and the dq-axis current of the inverter circuit are controlled through the outer and inner rings.
It effectively suppresses fluctuations in DC bus voltage when the light intensity changes rapidly for a short time, ensures the stability of DC bus voltage, and avoids problems such as distortion of the inverter grid connection current.
Smart Images
Figure CN120109898A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of photovoltaic power generation and power quality control, and in particular to a two-stage photovoltaic grid-connected inverter topology and a method for suppressing direct current bus voltage fluctuations. Background Art
[0002] Compared with the traditional single-stage photovoltaic grid-connected inverter, the front-stage DC-DC converter of the two-stage photovoltaic grid-connected inverter can flexibly adjust the working point of the photovoltaic panel through the Boost circuit to achieve efficient Maximum Power Point Tracking (MPPT), which is especially suitable for scenarios where the light intensity changes frequently or the output voltage of the photovoltaic array is low. However, the output power of its front-stage DC-DC converter changes rapidly with the light intensity. If there is a delay or dynamic mismatch in the power regulation of the front and rear stages, it may cause a dynamic imbalance of power between the front and rear stages, resulting in fluctuations in the DC bus voltage. In addition, sudden changes in grid voltage, load disturbances, or periodic disturbances of the MPPT algorithm itself (such as the perturbation observation method) will further aggravate the fluctuations, which may cause system instability or grid-connected current distortion.
[0003] Therefore, it is urgent to propose a suppression scheme for DC voltage fluctuation in two-stage photovoltaic grid-connected inverters. Summary of the invention
[0004] The purpose of the present invention is to provide a two-stage photovoltaic grid-connected inverter topology and a method for suppressing DC bus voltage fluctuations, which are used to solve the problem that there is a delay or dynamic mismatch in the existing front and rear stage power regulation, which may cause dynamic power imbalance between the front and rear stages, resulting in fluctuations in the DC bus voltage, and may cause system instability or grid-connected current distortion. The present invention can suppress the voltage fluctuation of the DC bus when the light intensity changes rapidly in a short time, ensure the stability of the DC bus voltage, and avoid the problems such as inverter grid-connected current distortion caused by this.
[0005] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a two-stage photovoltaic grid-connected inverter topology, including a two-stage photovoltaic grid-connected inverter and a control module; The two-stage photovoltaic grid-connected inverter includes a front-stage boost circuit and a rear-stage inverter circuit. The front-stage boost circuit connects the photovoltaic panel and the DC bus, and the rear-stage inverter circuit connects the DC bus and the grid. The control module includes a front-stage control submodule and a rear-stage control submodule; The front-stage control submodule includes a photovoltaic panel maximum power point tracking control and a series compensation link, which are respectively used to make the photovoltaic panel track the maximum power point and suppress the voltage fluctuation of the DC bus when the output of the photovoltaic panel changes; The back-end control submodule adopts a voltage-current dual closed-loop control architecture, including an outer loop and an inner loop. The outer loop is used to control the voltage of the DC bus, and the inner loop is used to control the voltage of the back-end inverter circuit. dq axis current, thereby maintaining the DC bus voltage at the voltage command value.
[0006] According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the front-stage boost circuit includes a PI controller and a switch tube. According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the control architecture of the maximum power point tracking control of the photovoltaic panel is: When the light intensity changes, the MPPT algorithm is used to calculate the operating voltage corresponding to the highest output power of the photovoltaic panel. V MPPT , the operating voltage V MPPT The actual working voltage of the photovoltaic panel V pv The deviation is input into the PI controller of the previous stage boost circuit, and the PI controller of the previous stage boost circuit adjusts the duty cycle of the switch tube to control the actual working voltage of the photovoltaic panel V pv . According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the series compensation link is located at the output side of the PI controller of the previous stage boost circuit, and the control formula is: (1) in, s is the Laplace operator, z and p The calculation formula is: (2) In the formula, ω m is the natural frequency of the system, D m ( ω m ) is the damping coefficient at the natural frequency of the equivalent mechanical link of the system before compensation, K m ( ω m ) is the elastic coefficient at the natural frequency of the equivalent mechanical link of the system before compensation; D m1 ( ω m ) is the damping coefficient at the natural frequency of the equivalent mechanical link of the compensated system. According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, a capacitor is further connected to the DC bus between the front-stage boost circuit and the rear-stage inverter circuit. C. According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the complex torque coefficient method is used to calculate ω m , D m ( ω m )and K m ( ω m ). According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the complex torque coefficient method is used to calculate ω m , D m ( ω m )and K m ( ω m ) process is: When the light intensity changes, the voltage change of the DC bus is obtained by using the small signal modeling method: (3) in, is the voltage change of the DC bus, is the change in light intensity, I pvn is the rated operating current of the photovoltaic panel, V pvn is the rated operating voltage of the photovoltaic panel, V dcn is the voltage command value, D n is the duty cycle rating; g , k mp and k G are the linearization parameters of photovoltaic panels, (4) In the formula, is the change in the working current of the photovoltaic panel, is the change in the working voltage of the photovoltaic panel, The change in operating voltage corresponding to the maximum output power of the photovoltaic panel calculated by the MPPT algorithm; G 1 It is the PI controller of the previous stage boost circuit, and the control formula is: (5) In the formula, is the proportionality coefficient, is the integration coefficient; G 2 is the PI controller of the outer loop, and the control formula is: (6) In the formula, is the proportionality coefficient, is the integration coefficient, is the voltage reference value of the DC bus, For the subsequent inverter circuit d Shaft current change; G c The expression is: (7) Will G 1 into equivalent mechanical links, and the rest into equivalent electrical links. s use jω Replace, then the expression of the equivalent mechanical link is: (8) The expression of the equivalent electrical link is: (9) The natural frequency satisfies: (10) The damping of the system at the natural frequency is: (11) Then the total damping coefficient increase of the system is obtained as: (12). According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the PI controller of the front-stage boost circuit adjusts the duty cycle of the switch tube, and the adjustment principle is: (13). According to a two-stage photovoltaic grid-connected inverter topology provided by the present invention, the light intensity changes at a rate of change greater than or equal to 0.1 pu / s.
[0007] In a second aspect, the present invention provides a method for suppressing DC bus voltage fluctuations, using the two-stage photovoltaic grid-connected inverter topology of the first aspect, the method comprising: The front-stage control submodule is used to make the photovoltaic panel track the maximum power point and suppress the voltage fluctuation of the DC bus when the output of the photovoltaic panel changes; the voltage of the DC bus is controlled by the outer loop of the rear-stage control submodule, and the voltage of the rear-stage inverter circuit is controlled by the inner loop of the rear-stage control submodule. dq axis current, thereby maintaining the DC bus voltage at the voltage command value.
[0008] The present invention has at least the following technical effects: The present invention provides a two-stage photovoltaic grid-connected inverter topology and a method for suppressing DC bus voltage fluctuations. By connecting a series compensation link, the fluctuation of the DC bus voltage can be suppressed when the light intensity changes rapidly in a short time, thereby ensuring the stability of the DC bus voltage and avoiding problems such as inverter grid-connected current distortion caused by the above. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0010] In the attached picture: Figure 1 This is a topological diagram of a two-stage photovoltaic grid-connected inverter of the present invention; Figure 2 This is a front-stage control block diagram of a two-stage photovoltaic grid-connected inverter of the present invention; Figure 3 This is a comparison diagram of the DC bus voltage changes under the condition of rapid changes in light intensity before and after the series compensation link is added to the present invention. DETAILED DESCRIPTION
[0011] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0012] Some embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.
[0013] See also Figure 1 , an embodiment of the present invention provides a two-stage photovoltaic grid-connected inverter topology, including a two-stage photovoltaic grid-connected inverter and a control module; The two-stage photovoltaic grid-connected inverter includes a front-stage boost circuit and a rear-stage inverter (DC-AC) circuit. The front-stage boost circuit connects the photovoltaic panel and the DC bus to control the working voltage of the photovoltaic panel. The rear-stage inverter circuit connects the DC bus and the power grid to stabilize the voltage of the DC bus. The control module includes a front-stage control submodule and a rear-stage control submodule; The front-end control submodule includes the maximum power point tracking control (MPPT control) of the photovoltaic panel and the series compensation link, which are used to enable the photovoltaic panel to track the maximum power point in time and suppress the voltage fluctuation of the DC bus when the output of the photovoltaic panel changes rapidly; The back-end control submodule adopts a voltage-current dual closed-loop control architecture, including an outer loop and an inner loop. The outer loop is used to control the voltage of the DC bus, and the inner loop is used to control the voltage of the back-end inverter circuit. dq axis current, thereby maintaining the DC bus voltage at the voltage command value.
[0014] Specifically, the specific control architecture of the maximum power point tracking control of the photovoltaic panel is: G When the change occurs, the MPPT algorithm is used to calculate the corresponding working voltage when the photovoltaic panel output power is the highest. V MPPT , the operating voltage V MPPT The actual working voltage of the photovoltaic panel V pv The deviation is input into the PI controller of the previous boost circuit, and the PI controller adjusts the duty cycle of the switch tube. D To control the actual working voltage of the photovoltaic panel V pv , thereby achieving fast and error-free control of the operating voltage of the photovoltaic panel.
[0015] The series compensation link is located at the output side of the PI controller of the previous Boost circuit, and the control formula is: (1) in, s is the Laplace operator, z and p The calculation formula is as follows, (2) in, ω m is the natural frequency of the entire grid-connected system, D m ( ω m ) is the damping coefficient at the natural frequency of the equivalent mechanical link of the system before compensation,K m ( ω m ) is the elastic coefficient at the natural frequency of the equivalent mechanical link of the system before compensation. The above three need to be calculated by the complex torque coefficient method; D m1 ( ω m ) is the damping coefficient at the natural frequency of the equivalent mechanical link of the compensated system, which can be adjusted according to the actual situation of the system.
[0016] Specifically, a capacitor is connected to the DC bus between the front-stage boost circuit and the rear-stage inverter circuit. C .
[0017] The following is a further discussion of the process of calculating the above parameters using the complex torque coefficient method. When the light intensity changes, the voltage change of the DC bus can be obtained using the small signal modeling method: (3) in, is the voltage change of the DC bus, is the change in light intensity, I pvn is the rated operating current of the photovoltaic panel, V pvn is the rated operating voltage of the photovoltaic panel, V dcn is the voltage command value, D n is the duty cycle rating; g , k mp and k G are the linearization parameters of the photovoltaic panel, as follows: (4) In the formula, is the change in the working current of the photovoltaic panel, is the change in the working voltage of the photovoltaic panel, The change in operating voltage corresponding to the maximum output power of the photovoltaic panel calculated by the MPPT algorithm; G 1 For the PI controller of the input Boost circuit, the control formula is: (5) In the formula, is the proportionality coefficient, is the integration coefficient; G2 It is the PI controller of the voltage outer loop of the subsequent inverter circuit, and the control formula is: (6) In the formula, is the proportionality coefficient, is the integration coefficient, is the voltage reference value of the DC bus, For the subsequent inverter circuit d Shaft current change; G c The expression is: (7) The complex torque coefficient method is used to analyze the system. G 1 Divide into equivalent mechanical links, and divide the rest into equivalent electrical links. s use jω Replace, the expression of the equivalent mechanical link is: (8) The expression of the equivalent electrical link is: (9) The natural frequency satisfies: (10) The damping of the system at the natural frequency is: (11) After adding the compensation links shown in (1) and (2), the total damping coefficient of the system is increased by: (12).
[0018] It should be noted that the light intensity G When the change occurs, the corresponding working voltage when the photovoltaic panel output power is the highest V MPPT The previous Boost circuit will also change by changing the duty cycle of the switch tube D To adjust the actual working voltage of the photovoltaic panel V pv Make it close to V MPPT , the adjustment principle is as follows: (13) In some embodiments, the light intensity changes at a rate greater than or equal to 0.1 pu / s.
[0019] It can be seen that the voltage fluctuation of the DC bus will be transmitted to the photovoltaic panel through the front-stage Boost circuit, and the output change caused by the fluctuation of the working voltage of the photovoltaic panel will affect the voltage of the DC bus in the form of breaking the power balance of capacitor charging and discharging. Therefore, there is a more obvious interaction between the front and rear stage voltage control of the two-stage photovoltaic grid-connected inverter, and this phenomenon may cause the voltage fluctuation of the DC bus during the rapid change of light intensity.
[0020] See also Figure 2 , which is a front-stage Boost circuit control architecture of a two-stage photovoltaic grid-connected inverter. The present invention increases the damping of the system by adding a series compensation link at the output end of the PI controller, thereby suppressing the DC bus voltage fluctuation.
[0021] See also Figure 3 , before and after adding the series compensation link, the DC bus voltage changes under the condition of rapid changes in light intensity (at t=1s, the light intensity increases by 10%). Figure 3 As shown. Figure 3 It can be seen that after the introduction of the series compensation link, the DC bus voltage variation amplitude is reduced from 0.018pu to 0.012pu, and the oscillation phenomenon is significantly suppressed.
[0022] Based on the same inventive concept, another embodiment of the present invention provides a method for suppressing DC bus voltage fluctuations, using the two-stage photovoltaic grid-connected inverter topology of the above embodiment, the method comprising: The front-stage control submodule is used to make the photovoltaic panel track the maximum power point and suppress the voltage fluctuation of the DC bus when the output of the photovoltaic panel changes; the voltage of the DC bus is controlled by the outer loop of the rear-stage control submodule, and the voltage of the rear-stage inverter circuit is controlled by the inner loop of the rear-stage control submodule. dq axis current, thereby maintaining the DC bus voltage at the voltage command value.
[0023] In summary, the present invention proposes a two-stage photovoltaic grid-connected inverter topology and a method for suppressing DC bus voltage fluctuations. By adding a series compensation link at the output end of the PI controller of the front-stage boost circuit and designing a reasonable parameter setting method, the DC bus voltage fluctuations of the two-stage photovoltaic grid-connected inverter under the condition of sudden changes in light intensity are effectively suppressed, the stability of the DC bus voltage is ensured, and the problems such as inverter grid-connected current distortion caused by this are avoided.
[0024] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the embodiments disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.
Claims
1. A two-stage photovoltaic grid-connected inverter topology, characterized in that: It includes a two-stage photovoltaic grid-connected inverter and a control module; The two-stage photovoltaic grid-connected inverter comprises a front-stage boost circuit and a rear-stage inverter circuit, wherein the front-stage boost circuit connects the photovoltaic panel and the DC bus, and the rear-stage inverter circuit connects the DC bus and the power grid; The control module includes a front-stage control submodule and a rear-stage control submodule; The front-stage control submodule includes a photovoltaic panel maximum power point tracking control and a series compensation link, which are respectively used to make the photovoltaic panel track the maximum power point and suppress the voltage fluctuation of the DC bus when the output of the photovoltaic panel changes; The post-stage control submodule adopts a voltage-current dual closed-loop control architecture, including an outer loop and an inner loop, wherein the outer loop is used to control the voltage of the DC bus, and the inner loop is used to control the current of the post-stage inverter circuit. dq axis current, thereby maintaining the DC bus voltage at the voltage command value.
2. The two-stage photovoltaic grid-connected inverter topology according to claim 1, characterized in that: The front-stage boost circuit includes a PI controller and a switch tube.
3. The two-stage photovoltaic grid-connected inverter topology according to claim 2, characterized in that: The control architecture of the maximum power point tracking control of the photovoltaic panel is: When the light intensity changes, the MPPT algorithm is used to calculate the operating voltage corresponding to the highest output power of the photovoltaic panel. V MPPT , the operating voltage V MPPT The actual working voltage of the photovoltaic panel V pv The deviation is input into the PI controller of the front-stage boost circuit, and the PI controller of the front-stage boost circuit adjusts the duty cycle of the switch tube to control the actual working voltage of the photovoltaic panel. V pv .
4. The two-stage photovoltaic grid-connected inverter topology according to claim 3, characterized in that: The series compensation link is located at the output side of the PI controller of the front-stage boost circuit, and the control formula is: (1) in, s is the Laplace operator, z and p The calculation formula is: (2) In the formula, ω m is the natural frequency of the system, D m ( ω m ) is the damping coefficient at the natural frequency of the equivalent mechanical link of the system before compensation, K m ( ω m ) is the elastic coefficient at the natural frequency of the equivalent mechanical link of the system before compensation; D m1 ( ω m ) is the damping coefficient at the natural frequency of the equivalent mechanical link of the compensated system.
5. The two-stage photovoltaic grid-connected inverter topology according to claim 4, characterized in that: A capacitor is also connected to the DC bus between the front-stage boost circuit and the rear-stage inverter circuit. C .
6. The two-stage photovoltaic grid-connected inverter topology according to claim 5, characterized in that: The complex torque coefficient method is used to calculate the ω m , D m ( ω m )and K m ( ω m ).
7. The two-stage photovoltaic grid-connected inverter topology according to claim 6, characterized in that: The complex torque coefficient method is used to calculate the ω m , D m ( ω m )and K m ( ω m ) process is: When the light intensity changes, the voltage change of the DC bus is obtained by using the small signal modeling method: (3) in, is the voltage change of the DC bus, is the change in light intensity, I pvn is the rated operating current of the photovoltaic panel, V pvn is the rated operating voltage of the photovoltaic panel, V dcn is the voltage command value, D n is the duty cycle rating; g , k mp and k G are the linearization parameters of photovoltaic panels, (4) In the formula, is the change in the working current of the photovoltaic panel, is the change in the working voltage of the photovoltaic panel, The change in operating voltage corresponding to the maximum output power of the photovoltaic panel calculated by the MPPT algorithm; G 1 is the PI controller of the front-stage boost circuit, and the control formula is: (5) In the formula, is the proportionality coefficient, is the integration coefficient; G 2 is the PI controller of the outer loop, and the control formula is: (6) In the formula, is the proportionality coefficient, is the integration coefficient, is the voltage reference value of the DC bus, For the subsequent inverter circuit d Shaft current change; G c The expression is: (7) Will G 1 is divided into equivalent mechanical links, and the rest is divided into equivalent electrical links. s use jω Replace, then the expression of the equivalent mechanical link is: (8) The expression of the equivalent electrical link is: (9) The natural frequency satisfies: (10) The damping of the system at the natural frequency is: (11) Then the total damping coefficient increase of the system is obtained as: (12)。 8. The two-stage photovoltaic grid-connected inverter topology according to claim 7, characterized in that: The PI controller of the front-stage boost circuit adjusts the duty cycle of the switch tube, and the adjustment principle is: (13)。 9. The two-stage photovoltaic grid-connected inverter topology according to claim 3, characterized in that: The change in light intensity is that the light intensity change rate is greater than or equal to 0.1 pu / s.
10. A method for suppressing DC bus voltage fluctuation, characterized in that: Using the two-stage photovoltaic grid-connected inverter topology as described in any one of claims 1 to 9, the method comprises: The front-stage control submodule is used to make the photovoltaic panel track the maximum power point and suppress the voltage fluctuation of the DC bus when the output of the photovoltaic panel changes; the voltage of the DC bus is controlled by the outer loop of the rear-stage control submodule, and the voltage of the rear-stage inverter circuit is controlled by the inner loop of the rear-stage control submodule. dq axis current, thereby maintaining the DC bus voltage at the voltage command value.