Flyback topology micro inverter system and active power control method

Abstract

The invention discloses an active power control method for a flyback topology micro inverter system, and the method comprises the steps: calculating the load power of a load end through a current sampling module, and carrying out the uniform power distribution of a PV primary side branch when the load power is greater than or equal to the rated power of an inverter system; when the load power is smaller than the rated power of the inverter system, the PV primary side branch is closed step by step according to the load power difference; and when the load power is smaller than the minimum set power sum, one PV primary side branch is kept to operate. When the load power is smaller than the minimum set power, all the PV primary side branches are closed, and when the load power is larger than the minimum set power of the PV primary side branch with the lowest minimum set power, the system is started. According to the invention, multi-path regulation and control can be realized, and the control stability of the system is improved. And uniform distribution control, step-by-step adjustment distribution control, minimum power control and active power control are relatively flexible and efficient, so that the service life of the system is remarkably prolonged, and the reliability of the system is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a flyback topology micro-inverter system and an active power control method, belonging to the technical field of micro-inverter systems and control methods. Background Art

[0002] In solar photovoltaic power generation systems, inverters are key devices that convert the direct current (DC) electricity generated by photovoltaic panels into alternating current (AC) for integration into the grid or loads. While traditional centralized inverters offer cost advantages, they can significantly reduce power generation efficiency under complex lighting conditions, such as partial shading or PV panels connected in series with different orientations, due to the "barrel effect." Microinverters, on the other hand, equip each photovoltaic panel with an independent inverter, enabling independent maximum power point tracking (MPPT), significantly improving system power generation efficiency and stability.

[0003] The flyback topology has been widely used in microinverters due to its advantages, such as simple circuitry, low cost, and excellent electrical isolation. However, existing flyback microinverters also have some issues. For example, their output power is generally limited, making them difficult to meet the needs of high-power applications. Efficiency decreases significantly in low-light conditions. Moreover, when multiple inputs or multiple modules are connected in parallel, power balancing between branches is difficult, which can easily cause some modules to operate inefficiently. Traditional load-sharing control can easily cause individual branches to malfunction. Furthermore, traditional flyback microinverters have certain shortcomings in responding to grid faults and implementing fast and reliable islanding protection. Summary of the Invention

[0004] The purpose of the present invention is to solve the above-mentioned deficiencies in the prior art. Aiming at the problem that the traditional load-sharing limit control causes the load power to be too small to meet the stable operation of the whole machine, a flyback topology micro-inverter system and an active power control method are proposed.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A method for controlling active power of a flyback topology micro-inverter system, the flyback topology micro-inverter system comprising a secondary inverter bridge and a DSP controller; the input end of the secondary inverter bridge being connected in parallel to a plurality of PV primary branches; any of the PV primary branches being provided with a PV photovoltaic terminal, a primary circuit sampling module, a branch switch, and a transformer output terminal; the output end of the secondary inverter bridge being connected in parallel to a power grid and a load terminal, respectively; and a current sampling module being provided in the parallel circuit of the load terminal; the DSP controller being communicatively connected to the current sampling module and any of the primary circuit sampling modules; and the DSP controller being provided with a drive control module electrically connected to any of the branch switches; the method for controlling active power comprising the following steps: S1 evenly distributes power. The current sampling module calculates the load power at the load end. When the load power is greater than or equal to the rated power of the inverter system, the PV primary branch evenly distributes power. S2 regulates and distributes power step by step. When the load power is less than the rated power of the inverter system, the PV primary branches are closed step by step according to the load power difference. The branch switches are driven by the drive control module, and the remaining PV primary branches evenly distribute power. S3 minimum power control: any PV primary branch has a minimum set power. When the load power is less than the sum of the minimum set powers of the two PV primary branches with the lowest minimum set power, one of the PV primary branches will be kept running. S4 shutdown and start trigger, when the load power is less than the minimum set power of the PV primary branch with the lowest minimum set power, all PV primary branches are closed, and the load power is detected in real time. When the load power is greater than the minimum set power of the PV primary branch with the lowest minimum set power, the system starts.

[0006] Preferably, in the steps S1 and S2, when evenly distributing the power of the PV primary branch, difference processing is performed between the set reference voltage and the detection voltage of the PV primary branch, and power regulation is performed by adjusting the duty cycle.

[0007] Preferably, in step S1 and step S2, when evenly distributing power in the PV primary branch, maximum power point tracking is performed on several PV photovoltaic terminals, and the duty cycle is adjusted according to the maximum power point voltage and current to perform power balancing control.

[0008] Preferably, in step S2, the PV primary branches are sorted according to the minimum set power, the load power difference is adapted to the minimum set power sum value, the load minimum set power sum value that is greater than the load power difference and has the smallest difference with the load power difference is selected, and the PV primary branch corresponding to the load minimum set power sum value is closed.

[0009] Preferably, in step S2, a gradient domain of the load power difference is set, and the gradient domain has several threshold spans. When the load power difference switches across the threshold spans, a step-by-step shutdown operation is triggered.

[0010] Preferably, in step S4, the power grid is monitored in real time, and when an islanding phenomenon of the inverter system is detected, all PV primary branches are closed to disconnect the micro-inverter system from the power grid.

[0011] The beneficial effects of the present invention are mainly reflected in: 1. It can realize multi-channel control and improve the control stability of the system.

[0012] 2. It has uniform distribution control, step-by-step distribution control, and minimum power control. The active power control is more flexible and efficient, which significantly improves the system service life and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Other features, objects and advantages of the present application will become more apparent upon reading the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 The present invention is a schematic flow chart of an active power control method for a flyback topology micro-inverter system.

[0014] Figure 2 It is a structural schematic diagram of a flyback topology micro inverter system of the present invention. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 making creative efforts shall fall within the scope of protection of the present invention.

[0016] The present application will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to explain the relevant inventions and are not intended to limit the inventions. It should also be noted that, for ease of description, only portions relevant to the relevant inventions are shown in the accompanying drawings. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of this application may be combined with each other.

[0017] The present invention provides an active power control method for a flyback topology micro-inverter system, such as Figure 2 As shown, the flyback topology micro-inverter system includes a secondary side inverter bridge and a DSP controller. The input end of the secondary side inverter bridge is connected in parallel with several PV primary branches. Any PV primary branch is provided with a PV photovoltaic end, a primary circuit sampling module, a branch switch and a transformer output end. The output end of the secondary side inverter bridge is connected in parallel with the power grid and the load end respectively, and a current sampling module is provided on the parallel circuit of the load end; the DSP controller is communicatively connected with the current sampling module and any primary circuit sampling module, and the DSP controller is provided with a drive control module electrically connected with any branch switch.

[0018] Reference Figure 2As shown, there are n PV primary branches, with corresponding branch switches Q1 through QN, and transformer output terminals T1 through TN. The circuit construction of the PV primary branch through the transformer and secondary inverter bridge is conventional technology and will not be elaborated on here. However, to implement the active power control method of this case, a current sampling module and a drive control module are provided to meet the requirements of data sampling and control. PV1-PVN are connected to the corresponding flyback transformers through the primary circuit sampling module, forming multiple independent power loops. The primary circuit sampling module monitors the PV voltage and current of each independent power loop in real time and feeds them into the DSP for calculation. The AC grid-side current sampling module samples the local load current in real time and feeds it into the DSP for calculation of the current real-time power state, determining whether the minimum power transfer control for a single PV branch or multiple branches is met.

[0019] Specifically, if Figure 1 As shown, the active power control method includes the following steps: Evenly distribute the power. The current sampling module calculates the load power at the load end. When the load power is greater than or equal to the rated power of the inverter system, the PV primary branch evenly distributes the power. Step-by-step adjustment and distribution: when the load power is less than the rated power of the inverter system, the PV primary branches are closed step by step according to the load power difference, the branch switches are driven by the drive control module, and the remaining PV primary branches distribute power evenly; Minimum power control: any PV primary branch has a minimum set power. When the load power is less than the sum of the minimum set powers of the two PV primary branches with the lowest minimum set power, one of the PV primary branches will be kept running.

[0020] Shutdown and start triggering: when the load power is less than the minimum set power of the PV primary branch with the lowest minimum set power, all PV primary branches are closed, and the load power is detected in real time. When the load power is greater than the minimum set power of the PV primary branch with the lowest minimum set power, the system starts.

[0021] Specific implementation process and principle description: The sampling module of the sampling device that detects the AC grid-side current calculates the power status of the local load through the inverter DSP to limit the output power of multiple flybacks in real time and set a minimum operating current reference for a single channel. If the local load is not sufficient to meet the minimum control power evenly distributed among the branches, the control output of the DSP will gradually close the PV branches, concentrating the power in fewer loops, ensuring the control current of a single channel and achieving system control stability.

[0022] When the local AC loads and electrical appliances operate at a relatively high power, each PV branch is indiscriminately controlled to output power to the secondary inverter bridge at full load through the transformer of the corresponding branch at rated power.

[0023] If the local AC load or electrical appliance operates under relatively low power conditions, the DSP determines whether the operating current value sampled by the primary circuit sampling module meets the set minimum current and turns on or off the corresponding drive circuit module to control the related Q1, Q2, Q3, QN, switch tube MOS, and turn on or off the PV branch to ensure the stability of the entire system.

[0024] Evenly distribute the power. The current sampling module calculates the load power at the load end. When the load power is greater than or equal to the rated power of the inverter system, the PV primary branch evenly distributes the power.

[0025] That is, the DSP actively controls and opens other PV branches to evenly distribute power.

[0026] Step-by-step adjustment and distribution: when the load power is less than the rated power of the inverter system, the PV primary branches are closed step by step according to the load power difference, the branch switches are driven by the drive control module, and the remaining PV primary branches distribute power evenly.

[0027] If the local AC load or electrical appliance operates at a power lower than the rated power of the inverter system, a corresponding step-by-step shutdown and evenly distributed remaining control strategy will be implemented.

[0028] Minimum power control: any PV primary branch has a minimum set power. When the load power is less than the sum of the minimum set powers of the two PV primary branches with the lowest minimum set power, one of the PV primary branches will be kept running.

[0029] If the local AC load and electrical appliances operate at relatively low power, only one of the PV branches can operate stably. The DSP will actively shut down the other branches, concentrating all power output in one PV circuit. This is better than the previous control method of evenly distributing power among all branches, which results in no branch being able to operate stably, causing system instability and ultimately inverter shutdown.

[0030] Shutdown and start triggering: when the load power is less than the minimum set power of the PV primary branch with the lowest minimum set power, all PV primary branches are closed, and the load power is detected in real time. When the load power is greater than the minimum set power of the PV primary branch with the lowest minimum set power, the system starts.

[0031] In a specific embodiment, when evenly distributing power in the PV primary branch, a difference is processed between a set reference voltage and a detection voltage of the PV primary branch, and power regulation is performed by adjusting the duty cycle.

[0032] The sampling difference and duty cycle adjustment of the distribution scheme can achieve efficient and fast response.

[0033] In a specific embodiment, when evenly distributing power in the PV primary branch, maximum power point tracking is performed on several PV photovoltaic terminals, and the duty cycle is adjusted according to the maximum power point voltage and current to perform power balancing control.

[0034] That is, MPPT control is adopted, which belongs to power balancing control.

[0035] Solutions that only need to meet the requirement of even power distribution are within the scope of protection of this case.

[0036] In a specific embodiment, the PV primary branches are sorted according to the minimum set power, the load power difference is adapted to the minimum set power sum value, the load minimum set power sum value that is greater than the load power difference and has the smallest difference with the load power difference is selected, and the PV primary branch corresponding to the load minimum set power sum value is closed.

[0037] That is, it can realize step-by-step gradient control to meet its step-by-step closing regulation needs.

[0038] In a specific embodiment, a gradient domain of load power difference is set, and the gradient domain has several threshold spans. When the load power difference switches across the threshold spans, a step-by-step shutdown operation is triggered.

[0039] Specifically, the actual power of the load has a certain degree of leapfrogging, and the step-by-step shutdown and power balancing control have a certain response timeliness. Through the specific gradient domain, adaptation to the step-by-step adjustment can be achieved to achieve rapid response, and at the same time, meet certain circuit protection requirements.

[0040] In a specific embodiment, the power grid is monitored in real time. When an islanding phenomenon of the inverter system is detected, all PV primary branches are closed to disconnect the micro-inverter system from the power grid.

[0041] That is, there is safety protection, and circuit breaker control is directly performed when islanding occurs.

[0042] From the above description, we can see that it can achieve multi-channel control and improve the control stability of the system. It has uniform distribution control, step-by-step distribution control, and minimum power control. Active power control is more flexible and efficient, which significantly improves the service life and reliability of the system.

[0043] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0044] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for controlling active power of a flyback topology micro-inverter system, the flyback topology micro-inverter system comprising a secondary inverter bridge and a DSP controller, wherein the input end of the secondary inverter bridge is connected in parallel with a plurality of PV primary branches, any of the PV primary branches being provided with a PV photovoltaic terminal, a primary circuit sampling module, a branch switch, and a transformer output terminal, the output end of the secondary inverter bridge being connected in parallel with a power grid and a load terminal, respectively, and a current sampling module being provided in the parallel circuit of the load terminal; the DSP controller being communicatively connected with the current sampling module and any of the primary circuit sampling modules, and the DSP controller being provided with a drive control module electrically connected with any of the branch switches; characterized in that The active power control method comprises the following steps: S1 evenly distributes power. The current sampling module calculates the load power at the load end. When the load power is greater than or equal to the rated power of the inverter system, the PV primary branch evenly distributes power. S2 regulates and distributes power step by step. When the load power is less than the rated power of the inverter system, the PV primary branches are closed step by step according to the load power difference. The branch switches are driven by the drive control module, and the remaining PV primary branches evenly distribute power. S3 minimum power control: any PV primary branch has a minimum set power. When the load power is less than the sum of the minimum set powers of the two PV primary branches with the lowest minimum set power, one of the PV primary branches will be kept running. S4 shutdown and start trigger, when the load power is less than the minimum set power of the PV primary branch with the lowest minimum set power, all PV primary branches are closed, and the load power is detected in real time. When the load power is greater than the minimum set power of the PV primary branch with the lowest minimum set power, the system starts.

2. The active power control method of a flyback topology micro-inverter system according to claim 1, characterized in that: In the steps S1 and S2, when evenly distributing power in the PV primary branch, difference processing is performed between the set reference voltage and the detection voltage of the PV primary branch, and power regulation is performed by adjusting the duty cycle.

3. The active power control method of a flyback topology micro-inverter system according to claim 1, characterized in that: In the steps S1 and S2, when evenly distributing power in the PV primary branch, maximum power point tracking is performed on a plurality of PV photovoltaic terminals, and the duty cycle is adjusted according to the maximum power point voltage and current to perform power balancing control.

4. The active power control method of a flyback topology micro-inverter system according to claim 1, characterized in that: In step S2, the PV primary branches are sorted according to the minimum set power, the load power difference is adapted to the minimum set power sum value, the load minimum set power sum value that is greater than the load power difference and has the smallest difference with the load power difference is selected, and the PV primary branch corresponding to the load minimum set power sum value is closed.

5. The active power control method of a flyback topology micro-inverter system according to claim 4, characterized in that: In step S2, a gradient domain of the load power difference is set, and the gradient domain has a plurality of threshold spans. When the load power difference switches across the threshold spans, a step-by-step shutdown operation is triggered.

6. The active power control method of a flyback topology micro-inverter system according to claim 5, characterized in that: In step S4, the power grid is monitored in real time. When an islanding phenomenon is detected in the inverter system, all PV primary branches are closed to disconnect the micro-inverter system from the power grid.

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