The main research focuses on the topology structure of three-phase solar grid connected inverters, maximum power point tracking of photovoltaic arrays, establishment of mathematical models, and construction of MATLAB simulation models. DSP is used as the main control chip, and space vector modulation method is used to control the three-phase output current and grid connected voltage. At the same time, classic PI regulation is used to achieve dual closed-loop control. Finally, hardware design was carried out and physical construction was carried out to further improve this design.
(1) This article introduces the development of solar power generation and the structure of inverters, the background and significance of research, the types of solar inverters, and the composition and structure of solar grid connected inverters. Finally, the main content of this design is summarized.
(2) By introducing the structure of photovoltaic cells, a mathematical model was established to verify the working characteristics of photovoltaic cells. Based on the working characteristics, perform maximum power point tracking, establish a front-end Boost boost circuit model, and establish the model in MATLAB. Use fuzzy control to achieve maximum power point tracking.
(3) Analyzed and studied the topology structure of solar inverters, derived mathematical models of solar inverters in different coordinate systems, and mainly analyzed and established models for LC type inverter circuits. Finally, the modulation method of the solar inverter was introduced, and a detailed analysis of the spatial vector was mainly conducted.
(4) This article mainly introduces the control strategy of the entire solar grid connected inverter. At the same time, based on the harmonic problem in LC filtering, we adopted a combination of classical PI regulation and repetitive control regulation to achieve dual loop control of voltage and current. A repetitive control loop is added to the current loop to suppress the disturbance of periodic repetitive signals to the system. Finally, a model was established in MATLAB to simulate the SVPWM modulation method and system control.
(5) It is an analysis and design of the hardware circuit of solar grid connected inverters. By calculating the DC side capacitance, LC filter, and parameters, DSP2812 was selected as the control chip. The sampling circuit of the signal, the driving circuit of the switching transistor, and the detection circuit were designed separately. Finally, the software CCS was introduced, and the control processes for each function were summarized. Control was achieved through programming.
(6) It is the construction of the physical hardware of the three-phase photovoltaic inverter grid connected system, as well as the detection of key circuit links, and finally the analysis of the waveform output by the oscilloscope.
Faced with the current global energy crisis, the development and utilization of renewable energy have become increasingly important. The development of power electronics technology in renewable energy generation determines the efficient utilization of energy. For solar energy resources, solar power generation has become a research focus and its application fields have become very extensive.
An analysis and design of three-phase solar grid connected inverters were conducted, including the working characteristics of photovoltaic cells, the implementation of MPPT technology through fuzzy control, the pulse width modulation method of space vectors, the main circuit topology, Clark and Park coordinate transformation, dual closed-loop control of current and voltage loops, the working principle of repetitive control, the introduction of control chip DSP, and the design of system hardware and software. The specific research results include the following aspects:
(1) The system first designed a DC/DC boost circuit to ensure a high DC voltage on the input side of the inverter. After passing through a three-phase inverter bridge, it outputs a three-phase voltage of the same frequency and amplitude as the grid voltage. Through calculation, the DC side capacitance, filtering capacitor inductance, and related hardware circuits are obtained. Finally, the hardware circuit is built and can operate stably.
(2) LC type filtering circuit was adopted, and mathematical models of three-phase solar grid connected inverters were established in different coordinate systems. SVPWM pulse width modulation technology was adopted to improve the utilization efficiency of DC power.
(3) The article provides a detailed introduction to various methods of MPPT tracking, and at the same time, we apply fuzzy control to MPPT. We explain in detail the working principle of fuzzy control and how to establish a fuzzy control module in MATLAB. Through model building and simulation, the effectiveness of fuzzy control in maximum power point tracking is verified, with good dynamic stability and improved operational efficiency
(4) We have provided a detailed introduction to the control strategy of three-phase solar grid connected inverters, and ultimately adopted a dual closed-loop control strategy of current loop and voltage loop. At the same time, we have introduced a repetitive control method, which is combined with traditional PI regulation to achieve control of the system current. By establishing a simulation model in MATLAB and analyzing and comparing the simulation waveforms after adding repetitive control, it can be clearly seen that adding repetitive control can make the entire system operate more stably, perform better, reduce harmonic interference, and improve the quality of output waveforms.
(5) Build hardware circuits for the system, calculate component parameters, introduce control chips, design LC filters, design protection and detection circuits, and write software programs. Finally, we achieved the operation of the entire system through programming, signal acquisition, and DSP control. The experimental hardware circuit was debugged by observing the output waveform, and the feasibility of the designed system was verified, which can meet the basic requirements of three-phase photovoltaic grid connection.