| The increasing penetration of distributed energy in power system has a direct influence on rotation inertia and damping of stable operation of the system,which is not conducive to maintaining instantaneous power balance to suppress frequency fluctuation.Solar photovoltaic power generation system integrates the new generation of semiconductor materials,power electronics technology,detection and control,power engineering and energy storage,and has become a research focus in the field of distributed power generation.This dissertation takes the modeling and control strategy of distributed power system as the research object.The maximum power point tracking(MPPT)control of photovoltaic cells and the operation control of photovoltaic inverters are respectively studied.The main innovative research works are as follows.Research on issues such as mathematical physical models of photovoltaic cells,output characteristics,and maximum power tracking(MPPT)control methods.The common MPPT method usually needs to detect the output voltage and current of the photovoltaic cells at the same time.In order to simplify the system structure,optimize the control performance and realize the miniaturization of the system,this dissertation presents the MPPT control mechanism of PV cell based on no voltage sensor under uniform illumination.This method only needs to detect the output current of photovoltaic cells to realize MPPT function.Comparing the proposed control method with the disturbance observation method which is widely used,the results show that the proposed method can be rapidly converged to the maximum power point with the same steady-state control precision.The global maximum power point tracking(GMPPT)strategy of photovoltaic is studied.Based on the analysis of the maximum power output characteristic of photovoltaic array,the MPPT control strategy of photovoltaic array under non-uniform illumination is studied.Traditional MPPT method cannot track the global maximum power point of the PV array under partially shaded conditions.Although artificial intelligence algorithm provides a solution to the problem at some level,but the implementation of such algorithm is generally more complicated and has certain limitations.In view of these problems,a novel PV GMPPT control method is proposed based on the virtual impedance characteristic disturbance.The global search mechanism is introduced into the conventional P&O method.When the PV array surface illumination is not uniform,the virtual impedance characteristic of photovoltaic array is used to initially locate the position area of the maximum power point on its I-U characteristic curve,then the traditional P&O method is used to accurately tracking.No additional measuring circuits are required,scheme easy to implement,which improves the applicability of the conventional MPPT algorithm under complex lighting conditions.Study on operation control stability of distributed photovoltaic(PV)inverter.Analyze the operation characteristics of distributed inverter and traditional synchronous motor.The rotational inertia and damping required for the safe and stable operation of the system are reseached.In view of the defect that traditional VSG can not give both dynamic regulation and steady-state performance,an improved virtual synchronous generator control strategy is proposed.Based on the analysis of the mathematical model of the traditional synchronous generator ontology control algorithm,the closed-loop transfer function of active power and the frequency fluctuation for the virtual synchronous generator is established.The influence mechanism of the inertia and damping on the active power response in the dynamic transition process is analyzed.The prederivative control and the inertial correction are introduced into the traditional VSG power frequency controller,a power frequency control strategy for improved virtual synchronous generator based on pre-derivative control is proposed.The closed-loop transfer function of active power and frequency fluctuation is established,and the power frequency characteristics in the off-grid and grid-connected state are analyzed.The power oscillation in the transition process can be effectively suppressed by adjusting the control parameters of the prederivative control link,and the decoupling control of VSG dynamic characteristics and steady-state performance is realized.Considering the dynamic characteristics of the DC side,the VSG control strategy of the distributed photovoltaic inverter is studied.A photovoltaic virtual synchronous generator(PVVSG)control strategy considering the power fluctuation characteristics of photovoltaic cell is proposed.The real-time output of the photovoltaic array is analyzed by using the power-voltage characteristic curve combined with the characteristic values of the power balance equation.The stable operation area of the photovoltaic array is confirmed.Based on the virtual synchronous generator,a photovoltaic virtual synchronous generator control strategy based on flexible power point tracking control method is proposed.When the output power of the photovoltaic source side fluctuates,power matching can be realized according to load or dispatching power demand,ensuring that the photovoltaic array always operates in the stable area. |
PDF Full Text Request