Analysis and characterization of DC Bus ripple current of two-level inverters using the equivalent centered harmonic approach

The dc bus PWM ripple current of three-phase two-level voltage source inverters is a function of the PWM method, the load current magnitude, power factor angle, and the modulation index. Thus, the ripple current characteristics are highly involved and difficult to understand. Using the double Fourier integral approach, this paper investigates the ripple current characteristics thoroughly for a wide range of operating conditions and PWM methods. Then, the equivalent harmonic approach is used to lump the ripple current carrier frequency component and its sidebands to the center as a single frequency equivalent (and the same done for the multiples of the carrier). With this approach the capacitor ESR based losses are predicted easily and the dominant frequency range can be understood better. Thus, a better inverter and dc bus capacitor design can be achieved. Analysis is supported by means of simulations and a high degree of correlation is obtained. The paper additionally evaluates and suggests PWM methods for various inverter applications with the dc bus ripple performance being the main constraint. Thus, it is beneficial for the design engineer.