Minimizing DC capacitance requirement of cascadeded H-bridge multilevel inverters for photovoltaic systems by 3rd harmonic injection

The 2ω harmonic component on the dc link side of the H-bridge inverters has long been a thorny problem, which requires a huge dc link capacitor bank to absorb this 2ω low frequency current ripple in order to maintain the dc link voltage ripple under a tolerable value. Till now, very few papers have discussed about this topic. This paper presents a simple 3^rd harmonic injection method for the cascaded H-bridge multilevel inverters for photovoltaic systems. This approach achieves a 50% to 75% reduction of the dc link capacitance, without adding any extra components or increasing the control complexity. Theoretical analysis and simulation results are demonstrated to prove the effectiveness.