Universal High-Frequency-Link Inverter for Renewable/Alternative Energy
thesisposted on 21.07.2015 by Siamak Mehrnami
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This Dissertation introduces new modulation schemes for single-phase differential-mode Ćuk inverter (DMCI) and differential-mode three-phase Ćuk inverter (DTCI) to improve inverter efficiency by reducing its circulating power. The DMCI is a single-stage inverter with low device count. It offers advantages over other topologies because of compactness, higher power density, and reduced cost. It is a promising topology configuration for renewable-/alternative-energy applications encompassing both isolated and non-isolated configurations. The continuous modulation scheme (CMS), which was introduced originally for DMCI, activates all of the modules of the DMCI. The new discontinuous modulation scheme (DMS) deactivates one module in each half line-cycle leading to discontinuous operation of the inverter modules. Chapter 2 outlines the DMS and a mechanism to realize it. The experimental open-loop and closed-loop results of the DMCI using CMS and DMS are provided along with comparisons of their performances. It is shown that, the DMS reduces the circulating power and mitigates the losses of the DMCI, the voltage ratings of the devices of the DMCI are also reduced with the DMS. In contrast, the CMS-based DMCI exhibits wider linearity in its normalized dc-voltage gain and yields reduced harmonic distortion of the output voltage. For DMS, to achieve comparable linearity in normalized dc-voltage gain and distortion, harmonic compensation under closed-loop control is a pathway that has been demonstrated. The DTCI is introduced in Chapter 3. The DTCI has some advantage over other differential-mode and three-phase topologies, including fewer switches, bidirectional power flow capability, and galvanic isolation. It is a promising configuration for renewable-/alternative-energy applications with isolated as well as non-isolated structures. The CMS, which was introduced originally for DTCI, activates all of the three modules of the DTCI. This modulation scheme increases the circulating power in modules and hence increases the inverter power loss. Chapter 3 introduces DMS for DTCI. DMS deactivates one module at a time resulting in a discontinuous operation of DTCI modules. It also outlines DMS and its implementation with a proper control mechanism. The proposed implementation of the DMS is straight forward. The experimental open-loop and closed-loop results of the DTCI using CMS and DMS are provided along with comparisons of their performances. It is shown that, the DMS reduces the circulating power and hence mitigates the losses. The voltage ratings of the DTCI devices also are reduced with the DMS for the same reason. DTCI exhibits a nonlinear voltage-gain with both CMS- and DMS-based modulations. It has been demonstrated that by feed-forwarding the input voltage and incorporating a static linearization method, the harmonic distortion of the DTCI output is considerably reduced.