Two-stage boost converter and distributed new energy intelligent grid-connected inverter system

Abstract

The application discloses a two-stage Boost converter and a distributed new energy intelligent grid-connected inverter system, wherein the two-stage Boost converter comprises a front-stage Boost circuit, a DC-DC circuit, a positive electrode bypass switch and a negative electrode bypass switch; the front-stage Boost circuit is controlled to be connected or not connected through the bypass switch; and the two-stage Boost converter can work in different modes through the control of power switching devices, so that the photovoltaic array connected in front can be controlled. The control strategy in the distributed new energy intelligent grid-connected inverter system comprises a normal mode, a boost mode and a buck mode; different modes are switched according to power scheduling instructions and system operation data, so that flexible and accurate control of grid-connected power is realized. The system can automatically and smoothly switch among the normal mode, the boost mode and the buck mode, so that flexible and accurate control of grid-connected power is realized, the scheduling demand of the power grid is effectively responded, and the accommodation capacity and operation safety of the power grid to high proportion photovoltaic are improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation technology, and more specifically, it relates to a two-stage Boost converter and a distributed new energy intelligent grid-connected inverter system. Background Technology

[0002] As the global energy structure transitions towards a cleaner and lower-carbon model, distributed renewable energy sources such as photovoltaics and wind power have experienced rapid development and widespread application in the process of achieving the "dual carbon" goals. The integration of these distributed power sources into the distribution network helps reduce dependence on fossil fuels and lower carbon emissions. However, at the same time, the increasing proportion of renewable energy sources, coupled with their unstable and intermittent power generation characteristics, has brought new challenges to the safe and stable operation of the power grid.

[0003] Currently, traditional grid-connected photovoltaic (PV) systems often prioritize maximum power generation, with core equipment like grid-connected inverters typically employing maximum power point tracking (MPPT). This makes PV power generation dependent on environmental conditions, with output power passively fluctuating according to changes in sunlight and temperature, unable to flexibly adjust based on the actual grid conditions. When a large amount of PV capacity is installed in a local distribution network, this model can easily lead to a significant amount of excess power being fed back into the grid under conditions of strong sunlight and low electricity load. This can cause reverse overloads in distribution lines and transformers, resulting in voltage exceeding limits, threatening equipment safety and affecting the quality of power supply for users. Simultaneously, the drastic fluctuations in PV output make system dispatching more difficult, demanding higher requirements for frequency stability and reserve capacity. Therefore, the power system operation mode is shifting from the traditional source-follow-load dynamic model to a collaborative interaction between source, grid, load, and storage. Distributed power sources are no longer merely passively acting as generation units, but have become friendly regulating units capable of participating in ancillary services such as peak shaving and voltage regulation.

[0004] To improve the grid-friendliness of distributed renewable energy, the academic community mainly focuses on two directions: first, improving the power electronics hardware topology to enhance efficiency and performance; and second, developing more intelligent grid-connected control software algorithms.

[0005] In terms of hardware topology, high-gain, high-efficiency DC-DC converters are key to enabling low-voltage photovoltaic (PV) connections to higher voltage levels. Traditional Boost converters are limited by parasitic parameters, resulting in limited voltage gain improvement. Furthermore, pursuing high gain often requires operating at very high duty cycles, leading to decreased efficiency and increased electromagnetic interference. To address these issues, researchers have proposed various solutions: for example, using isolated topologies with high-frequency transformers can easily achieve high turns ratios, but this also increases size and cost; using coupled inductor technology can improve gain under non-isolation conditions, but voltage spikes caused by leakage inductance are significant, usually requiring complex circuits such as active clamping to suppress them; there are also transformerless solutions, such as switched inductor / switched capacitor, quadratic Boost, Z-source / quasi-Z-source high-gain topologies, each with its own characteristics, but trade-offs are often necessary regarding device stress, control complexity, or gain change rate. Research indicates that finding a new high-gain Boost topology that achieves a better balance between device quantity, voltage and current stress, gain capability at medium to low duty cycles, and efficiency has significant practical implications.

[0006] Research on control strategies focuses on enabling inverters to better adapt to complex grid conditions. For microgrid applications, droop control and its improved adaptive droop control are widely used for power distribution between distributed units, eliminating the need for communication interconnection. However, traditional fixed droop coefficients struggle to simultaneously guarantee voltage quality and load distribution accuracy. More importantly, grid-connected inverters need to smoothly switch between grid-connected and off-grid modes to avoid power surges and voltage oscillations during mode transitions. Existing literature employs strategies such as virtual inertia, state compensation, and active disturbance rejection control to improve the smoothness and speed of the switching process; however, these methods either have complex parameter tuning or lack room for improvement in dynamic response. Currently, most intelligent control research focuses on algorithmic improvements in downstream inverters (such as adding a power outer loop and optimizing switching logic), with less emphasis on hardware-level controllability design at the front-end power source.

[0007] Common methods for achieving active regulation of photovoltaic power include superimposing a power limiting loop on the MPPT algorithm or configuring an energy storage system on the DC side. The former may cause the system to enter the nonlinear operating region under deep power limiting, leading to stability issues; the latter will significantly increase system investment and maintenance costs and requires further improvement. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a two-stage Boost converter and a distributed new energy intelligent grid-connected inverter system. A two-stage Boost converter with bypass function is designed and used as a power regulation unit to construct a distributed new energy intelligent grid-connected inverter system. This enables the system to automatically and smoothly switch between three working states: normal mode, boost mode, and buck mode, thereby achieving flexible and precise control of grid-connected power, effectively responding to grid dispatching needs, and improving the grid's ability to absorb high proportions of photovoltaic power and its operational safety.

[0009] To achieve the above-mentioned objectives, the two-stage Boost converter of the present invention includes a front-stage Boost circuit, a DC-DC circuit, and a positive bypass switch S_P. + and negative bypass switch S_P - ,in:

[0010] The preamplifier boost circuit includes a first inductor L1, a first diode D1, a first capacitor C1, a second inductor L2, a second diode D2, a power switch Q1, a third diode D3, and a second capacitor C2, wherein:

[0011] The positive input terminal of the two-stage Boost converter is connected to the positive terminals of the first inductor L1 and the first diode D1, respectively; the negative terminal of the first diode D1 is connected to the first capacitor C1 and the second inductor L2, respectively; the other end of the first inductor L1 is connected to the other end of the first capacitor C1 and the positive terminal of the second diode D2, respectively; the other end of the second inductor L2 and the negative terminal of the second diode D2 are connected together to the positive terminals of the power switch Q1 and the third diode D3, respectively; the negative terminal of the third diode D3 is connected to the second capacitor C2; the negative input terminal of the two-stage Boost converter is connected to the other end of the power switch Q1 and the second capacitor D2, respectively; the two ends of the second capacitor C2 serve as the positive and negative output terminals of the preceding Boost circuit, respectively.

[0012] The output of the pre-amplifier boost circuit and the input of the DC-DC circuit are cascaded together, with the positive bypass switch S_P. + The negative bypass switch S_P is connected between the positive input and positive output terminals of the preceding Boost circuit. - Connected between the negative input and negative output terminals of the preceding Boost circuit, when both are simultaneously turned on, the DC input of the two-stage Boost converter is directly output to the DC-DC circuit via the bypass branch; when both are simultaneously turned off, the DC input of the two-stage Boost converter is output to the DC-DC circuit via the preceding Boost circuit.

[0013] This invention also provides a two-stage Boost converter, a three-level inverter, a filter, a data acquisition module, a control module, and a drive and isolation circuit, wherein:

[0014] A two-stage boost converter is used to perform voltage transformation on the output of the photovoltaic array;

[0015] Three-level inverters are used to convert the DC output of a two-stage Boost converter into sinusoidal AC power.

[0016] The filter is used to filter sinusoidal alternating current before connecting it to the power grid;

[0017] The data acquisition module is used to collect system operating data, including the output voltage and current of the photovoltaic array, the DC bus voltage, the grid connection point voltage and current, and the operating temperature of the power devices.

[0018] The control module is used to determine the control strategy for the two-stage Boost converter and the three-level inverter based on scheduling instructions or system operating data, and to generate the corresponding pulse width modulation signal. The specific control method is as follows:

[0019] S1: During system initialization, the control module puts the two-stage Boost converter into normal mode, with the control objective being to maximize power generation, and sets the positive bypass switch S_P... + and negative bypass switch S_P - Synchronous conduction allows the photovoltaic array output to be directly output to the DC-DC circuit via a bypass branch; the control module uses a maximum power point tracking algorithm to calculate the maximum output power of the photovoltaic array in real time. This is used as the given reference value for the active power outer loop of the three-level inverter to control the grid-connected output active power, so as to match the maximum power generation capacity of the photovoltaic array.

[0020] S2: Determine if a power scheduling command has been received. If no response is received, proceed to step S3; otherwise, proceed to step S4.

[0021] S3: Determine the effective value of the current grid connection point voltage. Does it exceed the preset threshold? Or the temperature of power devices Does it exceed the preset threshold? If none of them exceed the limit, no operation is performed and the process returns to step S2; otherwise, proceed to step S5.

[0022] S4: Determine if If yes, proceed to step S5; otherwise, proceed to step S6.

[0023] S5: The control module puts the two-stage Boost converter into boost mode and activates the positive bypass switch S_P. + and negative bypass switch S_P - Synchronous disconnection connects the preceding Boost circuit to the main power path, with the control objective being to reduce the grid-connected power to the power dispatch command level. Or the power value required to suppress overvoltage at the grid connection point; the control module sets the voltage reference value according to the power difference to be reduced. , This indicates the current maximum power point voltage. A dual closed-loop control of voltage and current is implemented on the preceding Boost circuit to ensure it operates in boost mode and stabilizes the output voltage reference value. If a power scheduling command is currently in effect. Then the control module will set the power outer loop reference value of the three-level inverter. Synchronously updated to power scheduling instructions Otherwise, the control module sets the power outer loop reference value of the three-level inverter to... , Indicate the scaling factor; then return to step S2;

[0024] S6: The control module puts the two-stage Boost converter into buck mode and activates the positive bypass switch S_P. + and negative bypass switch S_P - Synchronous disconnection connects the preceding Boost circuit to the main power path, with the control objective being to increase the grid-connected power to the level specified in the power dispatch command. The control module sets the voltage reference value according to the required increase in power difference. The voltage and current dual closed-loop control is implemented on the front-end Boost circuit to make it operate in boost mode and stabilize the output voltage reference value. Simultaneously, the control module will set the power outer loop reference value of the three-level inverter. Synchronously updated to power scheduling instructions Then return to step S2;

[0025] The drive and isolation circuit is used to receive the pulse width modulation signal generated by the control module, perform power amplification and electrical isolation, and drive the power switching devices in the two-stage Boost converter and the three-level inverter.

[0026] This invention relates to a two-stage Boost converter and a distributed renewable energy intelligent grid-connected inverter system. The two-stage Boost converter includes a front-end Boost circuit, a DC-DC circuit, a positive bypass switch, and a negative bypass switch. The bypass switches control whether the front-end Boost circuit is connected. Power switching devices control the two-stage Boost converter to operate in different modes, thereby controlling the photovoltaic array connected to the front end. The control strategy in the distributed renewable energy intelligent grid-connected inverter system includes a normal mode, a boost mode, and a buck mode. Different modes are switched according to power dispatch commands and system operating data, thereby achieving flexible and precise control of the grid-connected power.

[0027] The present invention has the following beneficial effects:

[0028] (1) At the hardware topology level, the dual-stage Boost converter of the present invention has a number of devices comparable to that of conventional circuits and has a higher voltage gain. Therefore, it is suitable for improving the low output voltage of photovoltaic arrays and can improve the efficiency of the front-end conversion.

[0029] (2) Compared with traditional photovoltaic grid-connected systems that only have maximum power point tracking, this invention uses a two-stage Boost converter as a power regulation unit, which enables the system to actively switch between normal, boost, and buck operating modes according to grid dispatch instructions or local voltage status. This fundamentally changes the uncontrollable nature of photovoltaic power generation, enabling it to actively participate in grid peak shaving and suppress voltage over-limit, effectively solving the reverse overload and voltage stability problems caused by high proportion of photovoltaic access, and significantly improving the active support capability for the grid.

[0030] (3) In terms of control strategy, the present invention realizes intelligent management of operating mode through the decision-making mechanism of prioritizing scheduling instructions and local autonomous judgment. At the same time, the present invention does not use algorithms to adjust output power, but adjusts power by applying a front-end DC-DC converter. It can also use a gradual change of reference value to ensure smooth and low-impact switching between different modes, realize flexible power regulation, and make dynamic performance and stability better than traditional algorithm control schemes.

[0031] (4) In terms of system economy and cost, compared with the method of relying on the configuration of additional energy storage system to achieve power regulation, the present invention achieves the same function by optimizing the power conversion architecture and algorithm, avoiding the high cost and maintenance problems brought about by energy storage. The system has complete protection logic and communication interface, which can respond to centralized dispatch and realize distributed autonomous operation. It has high reliability and better overall cost-effectiveness, providing an equipment-level solution for building new power systems. Attached Figure Description

[0032] Figure 1 This is a structural diagram of a specific embodiment of the two-stage Boost converter of the present invention;

[0033] Figure 2 This is a structural diagram illustrating a specific implementation of the distributed new energy intelligent grid-connected inverter system of the present invention;

[0034] Figure 3 This is a flowchart of the operating mode control of the two-stage Boost converter in this invention;

[0035] Figure 4 This is the open-loop and closed-loop Bode plot of the two-stage Boost converter under dual closed-loop control, obtained based on small-signal model analysis in this embodiment.

[0036] Figure 5This is the root locus diagram of the poles of the distributed new energy intelligent control system in this embodiment as a function of duty cycle D.

[0037] Figure 6 This is a waveform diagram of the photovoltaic array operation in boost mode of the distributed new energy intelligent control system in this embodiment;

[0038] Figure 7 This is a diagram showing the harmonic analysis of the grid-connected current of the distributed new energy intelligent control system in boost mode in this embodiment;

[0039] Figure 8 This is a waveform diagram of the photovoltaic array operation in step-down mode of the distributed new energy intelligent control system in this embodiment;

[0040] Figure 9 This is a diagram showing the harmonic analysis of the grid-connected current in step-down mode for the distributed new energy intelligent control system in this embodiment. Detailed Implementation

[0041] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0042] Example

[0043] Figure 1 This is a structural diagram of a specific embodiment of the two-stage Boost converter of the present invention. (See diagram below.) Figure 1 As shown, the two-stage Boost converter of the present invention includes a front-stage Boost circuit, a DC-DC circuit, and a positive bypass switch S_P. + and negative bypass switch S_P - ,in:

[0044] The front-end boost circuit includes a first inductor L1, a first diode D1, a first capacitor C1, a second inductor L2, a second diode D2, a power switching device Q1 (a MOSFET is used in this embodiment), a third diode D3, and a second capacitor C2, wherein:

[0045] The positive input terminal of the two-stage Boost converter is connected to the positive terminals of the first inductor L1 and the first diode D1. The negative terminal of the first diode D1 is connected to the first capacitor C1 and the second inductor L2. The other end of the first inductor L1 is connected to the other end of the first capacitor C1 and the positive terminal of the second diode D2. The other end of the second inductor L2 and the negative terminal of the second diode D2 are connected to the positive terminals of the power switch Q1 and the third diode D3. The negative terminal of the third diode D3 is connected to the second capacitor C2. The negative input terminal of the two-stage Boost converter is connected to the other end of the power switch Q1 and the second capacitor D2. The two ends of the second capacitor C2 serve as the positive and negative output terminals of the preceding Boost circuit.

[0046] The output of the pre-amplifier boost circuit and the input of the DC-DC circuit are cascaded together, with the positive bypass switch S_P. + The negative bypass switch S_P is connected between the positive input and positive output terminals of the preceding Boost circuit. - It is connected between the negative input terminal and the negative output terminal of the pre-amplifier Boost circuit. When both are turned on simultaneously, the input DC is directly output to the DC-DC circuit through the bypass branch; when both are turned off simultaneously, the input DC is output to the DC-DC circuit through the pre-amplifier Boost circuit.

[0047] In this embodiment, the DC-DC circuit includes a third inductor L3, a fourth diode D4, a power switching device Q2 (a MOSFET is used in this embodiment), a third capacitor C3, and a fourth capacitor C4, wherein:

[0048] The positive input terminal is connected to the third inductor L3. The other end of the third inductor L3 is connected to the positive terminal of the fourth diode D4 and the power switch Q2. The other end of the fourth diode D4 is connected to the series circuit of the third capacitor C3 and the fourth capacitor C4. The other ends of the power switch Q2 and the fourth capacitor C4 are connected to the negative input terminal. The two ends of the series circuit of the third capacitor C3 and the fourth capacitor C4 serve as the positive and negative output terminals, respectively. The connection point of the third capacitor C3 and the fourth capacitor C4 serves as the neutral point N.

[0049] The two-stage Boost converter designed in this invention can bypass the positive terminal bypass switch S_P + and negative bypass switch S_P - By controlling the on / off states and by controlling the power switching devices Q1 and Q2 via pulse width modulation signals, the two-stage Boost converter can operate in different modes, thereby controlling the photovoltaic array connected to the front end. This two-stage Boost converter has a number of devices comparable to that of a traditional Boost circuit and can achieve higher voltage gain at low to medium duty cycles.

[0050] Based on the two-stage Boost converter proposed in this invention, this invention also designs a distributed new energy intelligent grid-connected inverter system. Figure 2 This is a structural diagram illustrating a specific implementation of the distributed new energy intelligent grid-connected inverter system of the present invention. (See diagram below.) Figure 2 As shown, the distributed new energy intelligent grid-connected inverter system of the present invention includes a two-stage Boost converter, a three-level inverter, a filter, a data acquisition module, a control module, and a drive and isolation circuit. The following is a detailed description of each module.

[0051] A two-stage boost converter is used to perform voltage conversion on the output of a photovoltaic array.

[0052] A three-level inverter is used to convert the DC output of a two-stage Boost converter into sinusoidal AC power. In this embodiment, the three-level inverter uses a three-level NPC (neutral point clamped) inverter bridge. Its positive and negative input terminals on the DC side are connected to the positive and negative terminals of the DC bus, respectively, and the DC neutral point is connected to the midpoint of the bus capacitor. The inverter bridge consists of three identical bridge arms. Each bridge arm contains four IGBT or MOSFET power switching devices with anti-parallel diodes and two clamping diodes. By controlling the turn-on sequence of the four switches on each phase bridge arm, three phase voltage levels can be generated at its AC output terminal, thereby synthesizing a high-quality sinusoidal line voltage. Compared with traditional two-level inverters, its output waveform has lower harmonic content, and the turn-off voltage of each power switching device is only half of the DC bus voltage, which can reduce the device stress of the system and improve the system reliability.

[0053] The filter is used to filter sinusoidal alternating current before it is connected to the power grid. The filter is mainly used to remove high-order harmonics from the grid-connected current, preventing power grid fluctuations caused by these harmonics.

[0054] The data acquisition module is used to collect system operating data, including the output voltage and current of the photovoltaic array, the DC bus voltage, the grid connection point voltage and current, and the operating temperature of the power devices. In this embodiment, the data acquisition module includes a voltage and current acquisition module, a signal conditioning circuit, and a temperature detection module. The signal conditioning circuit is used to scale, filter, and level-convert the high-voltage and high-current signals acquired by the voltage and current acquisition module to adapt them to the input range of the control module. The temperature detection module includes a negative temperature coefficient thermistor or digital temperature sensor mounted on the heat sink of the main switch of the two-stage Boost converter, the IGBT module of the three-level NPC inverter bridge, or near the chip. This module monitors the case temperature of the power devices in real time and transmits the temperature signal to the control module. When the detected temperature exceeds a preset safety threshold, the control module will derated or trigger a fault shutdown to achieve overheat protection.

[0055] The control module is used to determine the control strategies for the two-stage Boost converter and the three-level inverter based on dispatch instructions or system operating data, and to generate corresponding pulse width modulation signals. In practical applications, the control module can be implemented using a host computer, and interact with the power grid dispatch master station via RS-485, Ethernet, or wireless communication modules.

[0056] Figure 3 This is a flowchart illustrating the operating mode control of the two-stage Boost converter in this invention. Figure 3 As shown, the control method of the control module for the operating mode of the two-stage Boost converter in this invention is as follows:

[0057] S301: Initialize normal mode:

[0058] During system initialization, the control module puts the two-stage Boost converter into normal mode, with the control objective being to maximize power generation, and sets the positive bypass switch S_P... + and negative bypass switch S_P - Synchronous conduction allows the photovoltaic array output to be directly output to the DC-DC circuit via a bypass branch. At this time, the front-end boost circuit does not interfere with the photovoltaic array's operating point. The control module uses a maximum power point tracking (MPPT) algorithm to calculate the current maximum output power of the photovoltaic array in real time. This value is used as the reference value for the active power outer loop of the three-level inverter to control the grid-connected active power output, in order to match the maximum power generation capacity of the photovoltaic array. At this time, the distributed new energy intelligent grid-connected inverter system is equivalent to a traditional photovoltaic grid-connected inverter.

[0059] S302: Determine if a power scheduling command has been received. If no response is received, proceed to step S303; otherwise, proceed to step S304.

[0060] S303: Determine the effective value of the current grid connection point voltage. Does it exceed the preset threshold? Or the temperature of power devices Does it exceed the preset threshold? If none of them exceed the limit, no operation is performed and the process returns to step S302; otherwise, the process proceeds to step S305.

[0061] S304: Determine if If yes, proceed to step S305; otherwise, proceed to step S306.

[0062] S305: Enter boost mode:

[0063] The control module puts the two-stage Boost converter into boost mode and activates the positive bypass switch S_P. + and negative bypass switch S_P - Synchronous disconnection connects the preceding Boost circuit to the main power path, with the control objective being to reduce the grid-connected power to the power dispatch command level. Or the power value required to suppress overvoltage at the grid connection point.

[0064] The control module sets the voltage reference value according to the power difference required for reduction. , This indicates the current maximum power point voltage. Dual closed-loop voltage and current control is implemented on the preceding boost circuit to ensure it operates in boost mode and stabilizes the output voltage reference value. In practical applications, the voltage reference value... This can be obtained through a preset power-voltage mapping table or online calculation. This voltage and current dual closed-loop control operation will increase the terminal voltage of the photovoltaic array, causing its operating point to deviate to the right from the maximum power point on the IV curve, entering the low power output region, thereby actively reducing the output power of the photovoltaic array from the source.

[0065] If a power scheduling command is currently in effect Then the control module will set the power outer loop reference value of the three-level inverter. Synchronously updated to power scheduling instructions Otherwise, the control module will set the power outer loop reference value of the three-level inverter. , This represents the proportional gain, ensuring power balance between the upstream and downstream stages and achieving precise power reduction and grid-connected operation. Since the upstream stage has already adjusted its power, the downstream MPPT algorithm will fail due to the constant input voltage; its inner loop actually operates at a stable DC bus voltage or direct tracking. This allows for fine-tuning of power and precise grid connection. Then, return to step S302.

[0066] S306: Enter buck mode:

[0067] The control module operates the two-stage Boost converter in buck mode and switches the positive bypass switch S_P to... + and negative bypass switch S_P - Synchronous disconnection connects the preceding Boost circuit to the main power path, with the control objective being to increase the grid-connected power to the level specified in the power dispatch command. .

[0068] The control module sets the voltage reference value according to the required increase in power difference. The voltage and current dual closed-loop control is implemented on the front-end Boost circuit to make it operate in boost mode and stabilize the output voltage reference value. This voltage and current dual closed-loop control operation reduces the terminal voltage of the photovoltaic array, causing its operating point to shift to the left from the maximum power point on the IV curve, entering the high power output region, thereby actively increasing the output power of the photovoltaic array from the source.

[0069] Simultaneously, the control module will input the power outer loop reference value of the three-level inverter. Synchronously updated to power scheduling instructions .

[0070] To ensure grid-friendly operation during mode switching and avoid power surges, the control module employs a gradual ramp-down mode switching strategy. Specifically, whenever a mode switch occurs, the control module gradually ramps down the voltage reference value of the two-stage Boost converter at a preset, controllable slope. Power outer loop reference value of three-level inverter Transition to the new setting value instead of using a step transition.

[0071] In this embodiment, a multimodal state machine is used in the control module to implement the control strategy, including normal mode, boost mode and buck mode. The state transition is set with two levels of trigger priority. The first priority is the power scheduling command, and the second priority is the effective value of the grid connection point voltage and the temperature of the power switching device in the system operation data. Its state transition logic is as follows: first, it is determined whether there is a valid scheduling command. Based on the power command magnitude, the boost mode or buck mode is switched. If there is no scheduling command, the boost mode or normal mode is automatically switched based on the grid connection point voltage threshold and temperature threshold.

[0072] The core of the control module control method in this invention is to transform the photovoltaic system from a passive power generator into an active regulator capable of flexibly adjusting power. It not only enables the downstream grid-connected inverter to precisely control power, but more importantly, it actively changes the operating point of the photovoltaic panels through the upstream DC-DC converter, achieving continuous power regulation from the source. Throughout the process, the system does not need to be shut down or switched to offline commissioning mode; all control loops remain online in real time, automatically coordinating the operating targets of the upstream and downstream converters based on unified scheduling instructions or local autonomous judgment.

[0073] The drive and isolation circuit is used to receive the pulse width modulation signal generated by the control module, perform power amplification and electrical isolation, and drive the power switching devices in the two-stage Boost converter and the three-level inverter.

[0074] To better illustrate the technical effects of this invention, a specific example is used to simulate and verify the distributed new energy intelligent grid-connected inverter system of this invention. In this embodiment, the control module uses a DSP, model TMS320F28335. The photovoltaic equipment in the photovoltaic array is model Zytech Solar ZT200P. The voltage and current acquisition module uses the LA25-NP / LV25-P series. The temperature detection module uses a DS18B20 sensor. The drive and isolation circuit uses an IGBT driver chip of model 1ED020I12-F2, combined with a high-speed optocoupler and transformer isolation scheme. Table 1 is the simulation parameter table of the distributed new energy intelligent control system in this embodiment.

[0075] Photovoltaic panel power 9.6kW Grid voltage 380 Grid frequency 50Hz Filter inductor 1mH Filter capacitor 50uF

[0076] Table 1

[0077] Based on the changes in external parameters, the simulation process in this embodiment can be described as follows:

[0078] (1) The simulation starts at t=0s and the system initialization is completed. The initial light intensity is set to 1000 W / m² and the ambient temperature is 25℃. The system enters normal mode by default, runs the maximum power point tracking algorithm, the photovoltaic array works stably at the maximum power point MPP1, and supplies power to the grid at the maximum power P_mppt1.

[0079] (2) At t=0.4s, the simulated midday sunlight intensity increased, with the light intensity jumping from 1000 W / m² to 1200 W / m². Under the control of the MPPT algorithm, the system automatically tracked the new maximum power point MPP2, and the photovoltaic output power increased to [missing value]. This process verifies the system's dynamic tracking performance in normal mode.

[0080] (3) At t=0.8s, the simulation receives a power reduction dispatch instruction from the power grid, requiring the active power connected to the grid to be reduced to a certain level. The system immediately switches to boost mode. The front-end high-gain converter starts up, shifting its operating point from MPP2 to the right by increasing the photovoltaic terminal voltage, thereby actively and quickly reducing the grid-connected power to the commanded value.

[0081] (4) At t=1.2s, the simulated scheduling command changes to output power reduced to The system switches to buck mode. The front-end converter adjusts its output voltage to a value lower than the current target voltage, shifting the photovoltaic operating point to the left to achieve the power command. This process verifies the system's ability to regulate power in buck mode.

[0082] (5) At t=1.6s, all external dispatch commands are cancelled, and the irradiance is maintained at 1200 W / m². The system automatically switches back to normal mode and quickly re-tracks to the maximum power point MPP2 under the current environment, resuming power generation at maximum power.

[0083] (6) At t=2.0s, a disturbance occurs in the simulated local power grid, causing the voltage at the grid connection point to rise to the over-limit threshold. Based on local monitoring, the system autonomously judges and re-enters the boost mode to provide reactive power support or reduce active power to assist in the recovery of the grid voltage.

[0084] (7) The simulation ends at t=2.5s.

[0085] Figure 4 This is the open-loop and closed-loop Bode plot of the two-stage Boost converter under dual closed-loop control, obtained based on small-signal model analysis in this embodiment. Figure 4 This indicates that the system has high gain in the mid-to-low frequency band, good low-frequency tracking and anti-interference capabilities, and a large phase margin at the crossover frequency.

[0086] Figure 5 This is the root locus diagram of the poles of the distributed new energy intelligent control system in this embodiment as a function of duty cycle D. Figure 5 The figure shows the trajectory of the system poles in the S-plane during the normal operating duty cycle range. As can be seen from the figure, all poles of the system are always located in the left half of the S-plane and far away from the imaginary axis throughout the entire duty cycle range, verifying the stability of the system under all operating conditions.

[0087] Figure 6 This is a waveform diagram of the photovoltaic array operation in boost mode of the distributed new energy intelligent control system in this embodiment. Figure 7 This is a diagram showing the harmonic analysis of the grid-connected current in boost mode for the distributed new energy intelligent control system in this embodiment. Figure 8 This is a waveform diagram of the photovoltaic array operation in step-down mode of the distributed new energy intelligent control system in this embodiment. Figure 9 This is a harmonic analysis diagram of the grid-connected current in step-down mode for the distributed new energy intelligent control system in this embodiment. (See diagram for example.) Figure 6-9 As shown, even under external interference, the system operates smoothly in both boost and buck modes, demonstrating its anti-interference capability. Furthermore, its total harmonic distortion (THD) is below the national standard limit, indicating excellent power quality. Therefore, power control and high-quality grid-connected operation can be achieved in both modes, verifying the applicability of the system in different power regulation directions.

[0088] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A two-stage Boost converter, characterized in that, Includes a pre-amplifier boost circuit, a DC-DC converter circuit, and a positive bypass switch S_P. + and negative bypass switch S_P - ,in: The preamplifier boost circuit includes a first inductor L1, a first diode D1, a first capacitor C1, a second inductor L2, a second diode D2, a power switch Q1, a third diode D3, and a second capacitor C2, wherein: The positive input terminal of the two-stage Boost converter is connected to the positive terminals of the first inductor L1 and the first diode D1, respectively; the negative terminal of the first diode D1 is connected to the first capacitor C1 and the second inductor L2, respectively; the other end of the first inductor L1 is connected to the other end of the first capacitor C1 and the positive terminal of the second diode D2, respectively; the other end of the second inductor L2 and the negative terminal of the second diode D2 are connected together to the positive terminals of the power switch Q1 and the third diode D3, respectively; the negative terminal of the third diode D3 is connected to the second capacitor C2; the negative input terminal of the two-stage Boost converter is connected to the other end of the power switch Q1 and the second capacitor D2, respectively; the two ends of the second capacitor C2 serve as the positive and negative output terminals of the preceding Boost circuit, respectively. The output of the pre-amplifier boost circuit and the input of the DC-DC circuit are cascaded together, with the positive bypass switch S_P. + The negative bypass switch S_P is connected between the positive input and positive output terminals of the preceding Boost circuit. - Connected between the negative input and negative output terminals of the preceding Boost circuit, when both are simultaneously turned on, the DC input of the two-stage Boost converter is directly output to the DC-DC circuit via the bypass branch; when both are simultaneously turned off, the DC input of the two-stage Boost converter is output to the DC-DC circuit via the preceding Boost circuit.

2. The distributed new energy intelligent grid-connected inverter system according to claim 1, characterized in that, The power switching device Q1 is a MOSFET.

3. The distributed new energy intelligent grid-connected inverter system according to claim 1, characterized in that, The DC-DC circuit includes a third inductor L3, a fourth diode D4, a power switching device Q2, a third capacitor C3, and a fourth capacitor C4, wherein: The positive input terminal is connected to the third inductor L3. The other end of the third inductor L3 is connected to the positive terminal of the fourth diode D4 and the power switch Q2. The other end of the fourth diode D4 is connected to the series circuit of the third capacitor C3 and the fourth capacitor C4. The other ends of the power switch Q2 and the fourth capacitor C4 are connected to the negative input terminal. The two ends of the series circuit of the third capacitor C3 and the fourth capacitor C4 serve as the positive and negative output terminals, respectively. The connection point of the third capacitor C3 and the fourth capacitor C4 serves as the neutral point N.

4. The distributed new energy intelligent grid-connected inverter system according to claim 3, characterized in that, The power switching device Q2 is a MOSFET.

5. A distributed new energy intelligent grid-connected inverter system, characterized in that, Includes the two-stage Boost converter, three-level inverter, filter, data acquisition module, control module, and drive and isolation circuit as described in claim 1, wherein: A two-stage boost converter is used to transform the voltage output of a photovoltaic array; Three-level inverters are used to convert the DC output of a two-stage Boost converter into sinusoidal AC power. The filter is used to filter sinusoidal alternating current before connecting it to the power grid; The data acquisition module is used to collect system operating data, including the output voltage and current of the photovoltaic array, the DC bus voltage, the grid connection point voltage and current, and the operating temperature of the power devices. The control module is used to determine the control strategy for the two-stage Boost converter and the three-level inverter based on scheduling instructions or system operating data, and to generate the corresponding pulse width modulation signal. The specific control method is as follows: S1: During system initialization, the control module puts the two-stage Boost converter into normal mode, with the control objective being to maximize power generation, and sets the positive bypass switch S_P... + and negative bypass switch S_P - Synchronous conduction allows the photovoltaic array output to be directly output to the DC-DC circuit via a bypass branch; the control module uses a maximum power point tracking algorithm to calculate the maximum output power of the photovoltaic array in real time. This is used as the given reference value for the active power outer loop of the three-level inverter to control the grid-connected output active power, so as to match the maximum power generation capacity of the photovoltaic array. S2: Determine if a power scheduling command has been received. If no response is received, proceed to step S3; otherwise, proceed to step S4. S3: Determine the effective value of the current grid connection point voltage. Does it exceed the preset threshold? Or the temperature of power devices Does it exceed the preset threshold? If none of them exceed the limit, no operation is performed and the process returns to step S2; otherwise, proceed to step S5. S4: Determine if If yes, proceed to step S5; otherwise, proceed to step S6. S5: The control module puts the two-stage Boost converter into boost mode and activates the positive bypass switch S_P. + and negative bypass switch S_P - Synchronous disconnection connects the preceding Boost circuit to the main power path, with the control objective being to reduce the grid-connected power to the power dispatch command level. Or the power value required to suppress overvoltage at the grid connection point; the control module sets the voltage reference value according to the power difference to be reduced. , This indicates the current maximum power point voltage. A dual closed-loop control of voltage and current is implemented on the preceding Boost circuit to ensure it operates in boost mode and stabilizes the output voltage reference value. If a power scheduling command is currently in effect. Then the control module will set the power outer loop reference value of the three-level inverter. Synchronously updated to power scheduling instructions Otherwise, the control module sets the power outer loop reference value of the three-level inverter to... , Indicate the scaling factor; then return to step S2; S6: The control module puts the two-stage Boost converter into buck mode and activates the positive bypass switch S_P. + and negative bypass switch S_P - Synchronous disconnection connects the front-end Boost circuit to the main power path, with the control objective being to increase the grid-connected power to the level specified in the power dispatch command. The control module sets the voltage reference value according to the required increase in power difference. The voltage and current dual closed-loop control is implemented on the front-end Boost circuit to make it operate in boost mode and stabilize the output voltage reference value. Simultaneously, the control module will set the power outer loop reference value of the three-level inverter. Synchronously updated to power scheduling instructions Then return to step S2; The drive and isolation circuit is used to receive the pulse width modulation signal generated by the control module, perform power amplification and electrical isolation, and drive the power switching devices in the two-stage Boost converter and the three-level inverter.

6. The distributed new energy intelligent grid-connected inverter system according to claim 1, characterized in that, The control module employs a ramp-gradient mode switching strategy. Specifically, whenever a mode switch occurs, the control module gradually adjusts the voltage reference value of the two-stage Boost converter at a preset, controllable ramp. Power outer loop reference value of three-level inverter Transition to the new settings.

7. The distributed new energy intelligent grid-connected inverter system according to claim 1, characterized in that, The control module employs a multimodal state machine to implement the control strategy, including normal mode, boost mode, and buck mode. The state transition is set with two levels of trigger priority. The first priority is the power scheduling command, and the second priority is the effective value of the grid connection point voltage and the temperature of the power switching device in the system operation data. Its state transition logic is as follows: first, it determines whether there is a valid scheduling command, and switches between boost mode and buck mode according to the magnitude of the power command. If there is no scheduling command, it automatically switches between boost mode and maintains normal mode according to the grid connection point voltage threshold and temperature threshold.

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