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Broken rotor bar (BRB) fault is common in cage rotor induction motors. Motor current signature analysis (MCSA) has been a popular method to detect BRB faults. In the MCSA, the fault signature frequencies for BRB are close to the fundamental frequency. This spectral nearness leads to the requirement of larger observation windows, which inherently increases BRB fault detection time. This paper presents an alternative algorithm to detect BRB faults in induction motors from MCSA using two Taylor–Kalman (TK) filters in cascade with a subsampling scheme. The proposed BRB fault detection approach allows to use the TK filter to estimate lower frequencies with less computational burden in comparison to conventional TK analysis. Experimental analysis shows that nearly accurate estimates and competitive detection time can be achieved by the proposed BRB detection method. The performance of the proposed algorithm has been compared with classical spectral techniques using numerical simulations and records acquired from induction motors under real operating conditions.

Dual active bridge (DAB) converters have been popular in high voltage, low and medium power DC-DC applications, as well as an intermediate high frequency link in solid state transformers. In this paper, a multilevel DAB (ML-DAB) has been proposed in which two active bridges produce two-level (2L)-5L, 5L-2L and 3L-5L voltage waveforms across the high frequency transformer. The proposed ML-DAB has the advantage of being used in high step-up/down converters, which deal with higher voltages, as compared to conventional two-level DABs. A three-level neutral point diode clamped (NPC) topology has been used in the high voltage bridge, which enables the semiconductor switches to be operated within a higher voltage range without the need for cascaded bridges or multiple two-level DAB converters. A symmetric modulation scheme, based on the least number of angular parameters rather than the duty-ratio, has been proposed for a different combination of bridge voltages. This ML-DAB is also suitable for maximum power point tracking (MPPT) control in photovoltaic applications. Steady-state analysis of the converter with symmetric phase-shift modulation is presented and verified using simulation and hardware experiments.

Neutral point clamped (NPC) multilevel inverter is being used for medium and high power applications since it can synthesize more voltage levels with smaller output voltage steps compared to two level full-bridge inverters. An NPC based multi-level dual-active bridge (ML-DAB) dc-dc converter has been proposed where the low voltage side consists a full-bridge producing a two-level voltage and the high voltage side has two three-level neutral point diode clamped (NPC) switching poles which produce a five-level voltage waveform across the high frequency transformer. Capacitor voltage unbalance has been an important concern for NPC topology. A neutral-point current control scheme has been proposed to control the imbalance between the capacitor voltages in the NPC side. Experimental results for steady-state operation and the capacitor voltage balancing control have been shown in simulation.

A modular multilevel power converter configuration for grid connected photovoltaic (PV) systems is proposed. The converter configuration replaces the conventional bulky line frequency transformer with several high frequency transformers, potentially reducing the balance of systems cost of PV systems. The front-end converter for each port is a neutral-point diode clamped (NPC) multi-level dc-dc dual-active bridge (ML-DAB) which allows maximum power point tracking (MPPT). The integrated high frequency transformer provides the galvanic isolation between the PV and grid side and also steps up the low dc voltage from PV source. Following the ML-DAB stage, in each port, is a NPC inverter. N number of NPC inverters’ outputs are cascaded to attain the per-phase line-to-neutral voltage to connect directly to the distribution grid (i.e., 13.8 kV). The cascaded NPC (CNPC) inverters have the inherent advantage of using lower rated devices, smaller filters and low total harmonic distortion required for PV grid interconnection. The proposed converter system is modular, scalable, and serviceable with zero downtime with lower foot print and lower overall cost. A novel voltage balance control at each module based on power mismatch among N-ports, have been presented and verified in simulation. Analysis and simulation results are presented for the N-port converter. The converter performance has also been verified on a hardware prototype.

A novel converter configuration that allows for high frequency transformer integration and high voltage distribution is proposed for large scale grid-connected photovoltaic (PV) system. The proposed configuration has in the front-end of the solar panel, dual-active bridge dc-dc converter with three-level neutral-point clamped secondary and a high-step-up ratio high frequency transformer. The output of the dual-active bridge converter may be connected to a high voltage inverter to achieve high ac voltage to allow for direct interconnection with the utility ac grid at distribution voltage level. The proposed configuration has advantages of high frequency transformer, high efficiency and high voltage operation. Phase-shift modulation technique along with Maximum Power Point Tracking is proposed for the three-level dual-active bridge converter and the overall converter performance is verified in simulation.