High-Efficiency Three-Phase Current Source Rectifier Using SiC Devices and Delta-Type Topology

In this dissertation, the benefits of the three-phase current source rectifier (CSR) in high power rectifier, data center power supply and dc fast charger for electric vehicles (EV) will be evaluated, and new techniques will be proposed to increase the power efficiency of CSRs. A new topology, referred as Delta-type Current Source Rectifier (DCSR), is proposed and implemented to reduce the conduction loss by up to 20%. By connecting the three legs in a delta type on ac input side, the dc-link current in DCSR can be shared by two legs at the same time. To increase the switching speed and power density, all-SiC power modules are built and implemented for CSRs. The switching waveforms in the commutation are measured and studied based on double pulse test. Four different modulation schemes are compared for high efficiency CSR considering the switching characteristics of different device combinations. The most advantageous modulation scheme is then identified for each of the device combinations investigated. A compensation method is proposed to reduce the input current distortion caused by overlap time and slow transition in CSRs. The proposed method first minimizes the overlap time and then compensates the charge gain/loss according to the sampled voltage and current. It is verified that the proposed method can reduce the input current distortion especially when the line-to-line voltage is close to zero. The dc-link current will become discontinuous under light load in CSRs, when the traditional control algorithm may not work consistently well. To operate CSR in discontinuous current mode (DCM), the CSR is modeled in DCM and a new control algorithm with feedforward compensation is proposed and verified through experiments. A protection scheme with fast response time is proposed, analyzed and verified to protect SiC devices from overvoltage caused by current interruption in CSRs. To deal with the harmonics and voltage sag in the input ac voltage, a new control algorithm is proposed. By adding ac current feedback control and proportional-resonant (PR) control, the proposed control algorithm can reduce the input current distortion and dc output voltage ripple under input voltage disturbance

NLO Productions of ω\omega and KS0K^0_{\rm S} with a Global Extraction of the Jet Transport Parameter in Heavy Ion collisions

In this work, we pave the way to calculate the productions of $\omega$ and $K^0_{\rm S}$ mesons at large $p_T$ in p+p and A+A collisions at the RHIC and the LHC. The $\omega$ meson fragmentation functions (FFs) in vacuum at next-to-leading order (NLO) are obtained by evolving NLO DGLAP evolution equations with rescaled $\omega$ FFs at initial scale $Q_0^2=1.5$ GeV$^2$ from a broken SU(3) model, and the $K^0_{\rm S}$ FFs in vacuum are taken from AKK08 parametrization directly. Within the framework of the NLO pQCD improved parton model, we make good descriptions of the experimental data on $\omega$ and $K^0_{\rm S}$ in p+p both at the RHIC and the LHC. With the higher-twist approach to take into account the jet quenching effect by medium modified FFs, the nuclear modification factors for $\omega$ meson and $K^0_{\rm S}$ meson at the RHIC and the LHC are presented with different sets of jet transport coefficient $\hat{q}_0$. Then we make a global extraction of $\hat{q}_0$ at the RHIC and the LHC by confronting our model calculations with all available data on 6 identified mesons: $\pi^0$, $\eta$, $\rho^0$, $\phi$, $\omega$, and $K^0_{\rm S}$. The minimum value of the total $\chi^2/d.o.f$ for productions of these mesons gives the best value of $\hat{q}_0=0.5\rm GeV^2/fm$ for Au+Au collisions with $\sqrt{s_{\rm NN}}=200$ GeV at the RHIC, and $\hat{q}_0=1.2\rm GeV^2/fm$ for Pb+Pb collisions with $\sqrt{s_{\rm NN}}=2.76$ TeV at the LHC respectively, with the QGP spacetime evolution given by an event-by-event viscous hydrodynamics model IEBE-VISHNU. With these global extracted values of $\hat{q}_0$, the nuclear modification factors of $\pi^0$, $\eta$, $\rho^0$, $\phi$, $\omega$, and $K^0_{\rm S}$ in A+A collisions are presented, and predictions of yield ratios such as $\omega/\pi^0$ and $K^0_{\rm S}/\pi^0$ at large $p_T$ in heavy-ion collisions at the RHIC and the LHC are provided.Comment: 9 pages, 13 figures, 1 tabl