Research On Single-phase Current Source Grid-connected Inverter With Small Energy Storage Inductor

In photovoltaic power generation systems,voltage source inverters are traditionally used as the interface for energy conversion and utilization.However,voltage source inverters cannot be boosted in a single stage,require large electrolytic capacitors to buffer reactive energy,and require short-circuit protection.Therefore,they cannot fully meet the requirements of photovoltaic systems.The current source inverter can just solve all of the above problems: it can be boosted in a single stage,without electrolytic capacitors,without short-circuit protection,and it is suitable for small-capacity photovoltaic systems with low DC voltage levels.However,conventional current source inverters require large DC inductor to buffer the reactive energy,which increases the size and cost of the system.Therefore,it is of great theoretical and engineering significance to research current source inverters with small energy storage inductor.Of course,common-mode current suppression needs to be considered in photovoltaic systems.In addition,when a current source inverter is in the grid-connected operation mode,the stability of the system and the quality of the grid current will be affected by filter resonance problems and the background harmonics of the grid.This paper takes a new H5 current source inverter topology as the research object.Several key issues of single-phase current source grid-connected inverters such as common-mode leakage current problem,DC side current secondary ripple problem,CL filter resonance problems and grid background harmonic suppression are studied.This paper first analyzes in detail the problems existing in the application of conventional single-phase current source inverters in photovoltaic power generation systems,and then conducts research with a new H5 current-source inverter,using a modulation method suitable for this topology.It can simplify the driving method of the inverter and reduce the waveform distortion caused by the overlap-time.The analysis of common-mode voltage reveals the essential reason for the leakage current suppression capability of the new H5 current-source inverter.Aiming at the secondary ripple of the DC side current,a modulation strategy based on modulation wave reconstruction technology is proposed according to the principle of area equivalence.The amplitude of the modulated wave is adjusted in real time through the fluctuation of the DC side current,which effectively reduces the value of the energy storage inductor on the premise of ensuring good output current harmonic quality.Subsequently,the two modes of independent operation and grid-connected operation were studied separately,and closed-loop simulation verification was conducted under passive load conditions.The simulation results show that the system can resist disturbance and follow the reference.Under grid-connected operating conditions,the passive damping method of the parallel resistance of the filter inductor and the active damping method of the capacitor voltage are used to achieve resonance suppression.Aiming at the problem of grid voltage background harmonics,a combined control strategy of capacitor voltage feedback and grid voltage feedforward is proposed.Simulation results verify that the grid current quality can be guaranteed when the grid voltage contains some background harmonics.Finally,an experimental prototype was built to verify the above theory,which proved the correctness of the theoretical analysis and the feasibility of the method.