Research Electric Energy Conversion Lab

This video proposes a single phase commutation control method of open-end winding permanent magnet synchronous machine operated by a single DC-link dual inverter. For the control of open-end winding PMSM, a per-phase current control method which independently controls each phase is adopted. The proposed method allows the open-end winding PMSM to maintain the output torque while the only single phase of three phase windings conducts. In order to maintain the constant output torque with single phase commutation, modification of current reference is introduced. When a single phase is commutating, the other two phases do not conduct nor does the switching happen. The switching loss is significantly minimized with a small increase of conduction loss resulting in the improvement of overall drive system efficiency. The validity of the proposed control method was verified with simulation result. 

The design analysis and loss model of the four-level flying-capacitor converter in burst mode operation is introduced in this video. Detailed analysis of the proposed converter including operating mode, charge balance characteristic, and loss estimation for optimum efficiency are given. One-shot injected burst mode operation is also proposed which can reduce the voltage ripple of the flying-capacitor. The proposed scheme and analysis are verified by the simulation study. The simulation results with the input voltage range of 3-5V (for Li-Ion battery), the output voltage range of 0.6V-1.2V(typical supply voltage of digital circuits), 1mA <; load current shows the verification of the full-time active balancing scheme and the ripple minimization of the proposed technique. 

In this video, a thermal equivalent circuit (TEC) model generation method based on experimental data is proposed for estimating the stator temperature of a permanent magnet synchronous machine (PMSM). The proposed TEC model is composed of thermal resistors and capacitors, and the number of capacitors is equal to the number of temperature sensors used in the experiment. Least-square-error (LSE) method is applied to obtain optimal values of the thermal parameters that minimize temperature estimation error from the measurement data. Temperature estimation performance based on TEC model kept estimation error under 12 ° C in transient and steady states. 

This video proposes a current reference adjustment method of multiple coil magnetic manipulation system that controls a magnetized object, so-called micro-robot. This method adjusts the current references exceeding the current rating to be in the current rating by injecting a null space current vector based on the actuation matrix characteristic. This method expands the area in which a micro-robot can operate without decreasing given control command. Therefore, the proposed method maximizes micro-robot control performance in current limit situation. The current reference for each coil is calculated on PC and controlled by eight independent full bridge inverters. Advantages of the proposed method are confirmed by control area analysis and the effectiveness is verified by experimental results. 

In this video, a hybrid two-level voltage source inverter which utilizes a Si-IGBT as the high-side switch and a SiC-MOSFET as the low-side switch is suggested. Due to its uneven switch characteristics, proper discontinuous pulse width modulation (DPWM) method is applied to reduce losses generated in the inverter effectively. In addition, variable switching frequency control method is proposed to reduce the switching ripple with the cost of low increase of losses. The suggested hybrid inverter is compared to the full Si-IGBT and full SiC-MOSFET inverters in the perspective of losses and ripples. 

In this video, a highly efficient battery-balancing circuit with output voltage regulation for mobile applications is proposed and analyzed. The proposed circuit performs a cell balancing operation for series-connected multiple battery cells and voltage regulation operation simultaneously without additional power conversion stages. Therefore, it can be integrated into a battery pack with maximized power density and efficiency. These features are essential for recent low-power applications with multiple batteries, such as wireless/smart speakers, drones, and electronic point of sale that require high power density. The operational principle, electrical modeling, and trade-off relationship between system power losses and balancing characteristics are derived, and the optimal design candidates of the proposed topology are discussed in terms of Pareto optimization. The effectiveness of the proposed system was verified with a prototype board using GaN switches, and 96.05% efficiency was achieved with a 1.8 V, 0.5 A load. 

This video shows a transformer-less Series-Input-Parallel-Output Dual active Half-Bridge (SIPO-DAHB) converter. The transformer-less SIPO-DAHB converter is a high power bi-directional converter and it has a high voltage conversion ratio. Each DAHB directly transfers power from high voltage side to low voltage side (or vice-versa) with optimal efficiency. A high voltage capacitor is used for a line capacitor to block MVDC voltage or to form a resonance tank. Because the high voltage insulation transformer is replaced with a capacitor, power density could be much higher than the transformer type SIPO converter. Furthermore, the core loss and copper loss of the transformer are much higher than the capacitor ESR losses, so that high efficiency could be achieved. However, due to the transformer-less structure, in the SIPO-DAHB converter, the current of the higher module flows through the DC-link capacitors of the lower modules and causes ESR losses. To minimize ESR losses, this paper also proposes a control strategy that interleaves adjacent modules and adjusts duties. With the control strategy, the current cancelation occurs between adjacent modules and results in the minimization of the ESR losses of lower modules. The harmonic analysis of the current confirms the advantages and experimental results verifies the effectiveness of the proposed topology and control strategy.