Abstract
By using a single dc voltage source to feed a 4-level switched-capacitor (SC) unit and a 3-level NPP/NPC unit simultaneously, a new 9-level inverter is developed in this work. The 4-level unit is implemented by cascading an inverting half-bridge with a double- or half-mode SC circuit. It involves four transistors, two diodes and two capacitors with self-balanced voltage. Inrush charging current variation <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> of capacitors at switching instants is successfully suppressed by inserting a small inductor into the SC unit. Compared with the existing solutions for 9-level inverters, the proposed circuit has the advantages of simpler structure and lower cost per level. These make the proposed inverter very suitable for low voltage applications such as PV and fuel cells. Circuit configuration, operation, system characteristics under POD-PWM modulation are analyzed in detail. Feasibility and dynamic performance are also demonstrated experimentally.
Highlights
With many inherent advantages, such as near-sinusoidal output voltage waveforms, reduced dv/dt stresses and operation at lower switching frequency etc., multilevel inverters (MLIs) have attracted widespread attention in both academia and industry [1], [2]
Experimental results show that the inverter is capable of generating 9 levels of ac output voltage and each level is equal to half of the dc input voltage
Compared with the existing works, the main contribution of this work is the development of a 9-level SC-MLI asymmetric double-wing structure without the use of flying capacitors
Summary
With many inherent advantages, such as near-sinusoidal output voltage waveforms, reduced dv/dt stresses and operation at lower switching frequency etc., multilevel inverters (MLIs) have attracted widespread attention in both academia and industry [1], [2]. Y. Ye et al.: Nine-Level Inverter Based on Resonant Switched-Capacitor and NPP/NPC Unit presented in [15] to [19], the numbers of components are increased to 18, 10, 13, 12 and 11, respectively. CIRCUIT CONFIGURATION The proposed inverter consists of four transistors S1∼ S4, four capacitors C1 ∼ C4, two diodes D1 and D2, one small inductor L and one 3-level NPP or NPC unit as well. When S1 and S2 operate in a complementary manner, the capacitors C3 and C4 are charged by C1 through S1 − D1 and by C2 through S2 − D2, alternately, so that their total voltage is equal to half of the source voltage, i.e., VC3 + VC4 = 2E and VC3 = VC4 = E In both structures, capacitors’ charging current spike occurred at switching instants is limited effectively by the resonant inductor L. Capacitors’ states are indicated by ‘C’, ‘D’ and ‘N’ which are indicative of charging, discharging and idle states, respectively
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