Grid-connected inverters require a third-order LCL filter to meet standards such as the IEEE Std. 519-1992 while being compact and cost-effective. LCL filter introduces resonance, which needs to be damped through active or passive methods. Passive damping schemes have less control complexity and are more reliable. This study explores the splitcapacitor resistive-inductive (SC-RL) passive damping scheme. The SC-RL damped LCL filter is modelled using state space approach. Using this model, the power loss and damping are analysed. Based on the analysis, the SC-RL scheme is shown to have lower losses than other simpler passive damping methods. This makes the SC-RL scheme suitable for high power applications. A method for component selection that minimises the power loss in the damping resistors while keeping the system well damped is proposed. The design selection takes into account the influence of switching frequency, resonance frequency and the choice of inductance and capacitance values of the filter on the damping component selection. The use of normalised parameters makes it suitable for a wide range of design applications. Analytical results show the losses and quality factor to be in the range of 0.05-0.1% and 2.0-2.5, respectively, which are validated experimentally.

Semiconductor device junction temperatures are maintained within datasheet specified limits to avoid failure in power converters. Burn-in tests are used to ensure this. In inverters, thermal time constants can be large and burn-in tests are required to be performed over long durations of time. At higher power levels, besides increased production cost, the testing requires sources and loads that can handle high power. In this paper, a novel method to test a high power three-phase grid-connected inverter is proposed. The method eliminates the need for high power sources and loads. Only energy corresponding to the losses is consumed. The test is done by circulating rated current within the three legs of the inverter. All the phase legs being loaded, the method can be used to test the inverter in both cases of a common or independent cooling arrangement for the inverter phase legs. Further, the method can be used with different inverter configurations-three-wire or four-wire and for different PWM techniques. The method has been experimentally validated on a 24kVA inverter for a four-wire configuration that uses sine-triangle PWM and a three-wire configuration that uses conventional space vector PWM. Index Terms grid-connected inverter, high power inverters, inverter testing, LCL filter, thermal test NOMENCLATURE Referring to Fig. 2, v RiO , v YiO , v BiO R, Y and B phase inverter output voltages with respect to dc bus mid-point 'O' i Ri , i Yi , i Bi R, Y and B phase inverter-side inductor currents i R , i Y , i B R, Y and B phase grid-side inductor currents v cm Common mode component of voltages v RiO , v YiO , v BiO i cm Common mode current at the inverter output v RiO,dm , v YiO,dm , v BiO,dm Differential mode component of voltages v RiO , v YiO , v BiO i Ri,dm , i Yi,dm , i Bi,dm Differential mode component of currents i Ri , i Yi , i Bi Superscript 'f u' represents the fundamental component. Superscript 'ri' represents the switching ripple component.