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This research focuses on establishing a secure data communication system among power electronic converters connected to a common voltage bus in a dc microgrid. As a proof-of-concept, a buck and two boost dc-dc converters, sharing a 24 V dc bus, have been used for simulation in Matlab® Simulink®. Digital bits are generated at 10 kbps rate at the three converters which are modulated by frequency shift-keying (FSK) algorithm using three different frequency bands with two distinct frequencies to represent bits ‘0’ and ‘1’. Active band-pass filters are used to accurately extract useful data signal from the dc voltage waveform for the three communication channels having different frequency bands. A chaotic dynamic system is adopted for each power converter to encrypt and decrypt the data stream. The encrypted data in the communication channel is secure unless the attacker can perfectly synchronize with the chaotic dynamic system, which is very unlikely. Data in various frequency bands can be simultaneously demodulated and decrypted at the receiver with very good accuracy. The simulation result suggests that the bit-error-ratio (BER) is less than 0.01% even during system transients such as load change and/or due to transition between on-off states of other power converter(s).

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.

This paper proposes a Distributed Power Processing based Battery Energy Storage System (DPP-BESS) for improving the performance and reliability of the battery storage system. One dedicated Dual Active Bridge Converter (DABC) is connected to each cell of the battery pack, and all outputs of DABC are connected in a series-parallel combination as per the requirement for dc-link voltage, and power rating of the DPP-BESS. The main features of the system are: to determine the charging/discharging characteristics of different types of battery cells, to avoid the unnecessary discharging/charging phenomena in the battery within one cycle time, providing isolation between cells and the central inverter, and to improve the optimal power flow to/from each battery cell. Operating principle, design optimization, small signal modeling, and control scheme of the system are presented. The performance of the proposed system is validated through simulations in MATLAB®, SIMULINK®.

Cell-level power processing in battery packs can provide better efficiency, reliability and safety benefits. As part of a broader investigation of how dual-active bridges can be used for such processing, a secondary voltage control and droop control strategy have been examined for the distributed power processing based battery (DPPB) energy storage system. The control strategy is divided into primary cell-level control with high gain droop and secondary voltage control and stability analysis. The performance of proposed control strategy is validated under different loading conditions by MATLAB®, SIMULINK®. The control strategy improves the power sharing of each cell in a DPPB, and voltage regulation of DPPB output.

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.

Dual Active Bridge (DAB) dc-dc converter finds applications in the intermediate high frequency link power conversion stage of a high-power solid state transformer. In this paper, a multilevel DAB dc-dc converter is proposed. A three-level neutral point clamped (NPC) inverter topology has been used in the high voltage bridge which enables semiconductor switches to be operated in higher voltage range without using cascaded bridges and multiple DAB converters. Modulation strategy to control power flow between the active bridges with one of the bridges switching at multi-level is proposed in this paper. Steady-state analysis of the converter with the proposed modulation scheme is presented along with simulation results to augment the analysis.