Daniel Seltzer

Minimum Current Operation of Bidirectional Dual-Bridge Series Resonant DC/DC Converters

This paper discusses the steady-state operation of phase-shift modulated dual-bridge series resonant converter (DBSRC) intended for dc/dc power bidirectional control over a wide range of input and output voltages. The analysis, developed here for the most general case of three independent phase-shift control angles, demonstrates the existence of minimum current trajectories in the 3-D control space along which the DBSRC cell can deliver any admissible power level with minimum tank circulating current. At nonunity conversion ratios, minimum current operation prevents the DBSRC output bridge from experiencing severe hard-switching losses, substantially reducing the effort normally required by auxiliary zero-voltage switching assistance circuitry, and outperforming the efficiency of conventional one-angle modulation approaches especially at light load. The developed approach is validated via computer simulations and experimental tests on a 1-kW DBSRC prototype. Tests performed at a nonunity voltage conversion ratio indicate a marked light-load efficiency improvement with respect to the conventional one-angle modulation, confirming the importance of the minimum current operation when the converter is expected to operate with programmable output voltages or under wide input voltage variations.

Zero Voltage Switching Technique for Bidirectional DC/DC Converters

This paper proposes a zero voltage switching (ZVS) technique for bidirectional dc/dc converters. The dc/dc unit considered consists of two distinct bidirectional dc/dc cells paralleled at both input and output and whose two input bridges are coupled by means of passive inductive branches. A multiangle phase-shift modulation method is proposed which simultaneously achieves bidirectional power control, power sharing, and ZVS of all the electronic devices over the full power range without the need for auxiliary switches. Simulation and experimental results are reported for a 2.4 kW dc/dc unit consisting of two paralleled 1.2 kW bidirectional dual-bridge series resonant converter cells.

Gain-scheduled control of multi angle phase shift modulated dual active bridge series resonant DC/DC converters

This paper describes a feedback control approach for dual active bridge series resonant converters that makes use of gain-scheduling to improve the dynamic response of such topologies. The proposed approach uses recently developed small signal models to allow the dual active bridge series resonant converter to maintain phase margin and gain margin requirements over the entire operating range. The proposed method and its application are described, and a controller design example and experimental results are provided for a prototype 1 kW dual active bridge series resonant converter. Verification that the controller satisfies the design constraints is presented, and the gain-scheduling controller performance is compared to that of a constant gain feedback controller.

Small signal phasor modeling of dual active bridge series resonant DC/DC converters with multi-angle phase shift modulation

This paper presents an approach for generating small signal models of resonant converters focusing on the transformer-isolated dual active bridge series resonant converter (DABSRC) topology. The presented approach can be generalized to other active bridge resonant converters with one or more phase shift control inputs. Both steady state analysis and small signal modeling of the DABSRC are shown, and the resulting models are experimentally verified using a 1 kW prototype converter.

Zero voltage switching technique for bi-directional DC/DC converters

This paper proposes a zero-voltage switching (ZVS) technique for bi-directional DC/DC converters. The DC/DC unit considered consists of two distinct bi-directional DC/DC cells paralleled at both input and output and whose two input bridges are coupled by means of passive inductive branches. A multi-angle phase-shift modulation method is proposed which simultaneously achieves bi-directional power control, power sharing and ZVS of all the electronic devices over the full power range without the need for auxiliary switches. Simulation and experimental results are reported for a 2.4 kW DC/DC unit consisting of two paralleled 1.2 kW bi-directional Dual-Bridge Series Resonant Converter (DBSRC) cells.

Feedback control of phase shift modulated half bridge circuits for zero voltage switching assistance

This paper develops concepts for feedback control of phase shift modulated half-bridge (PSM-HB) circuits for zero voltage switching (ZVS) assistance. Using a novel approach to determine the amount of ZVS assistance required, feedback control is applied to the PSM-HB in order to assist ZVS in half- and full-bridge based circuit topologies that are required to operate over a wide range of conditions. Feedback control of the PSM-HB allows minimum currents to be maintained at all operating points, allowing PSM-HB circuitry to be added to existing topologies with minimal additional losses. Practical considerations such as startup sequencing, an angle modulation strategy for fast auxiliary current changes, and auxiliary device selection are presented. Experimental results are presented for a 130 V, 200 W, 100 kHz dual active bridge demonstration system with an FPGA based implementation of the proposed approach. Together with existing literature, this paper aims to improve ease of design and implementation of PSM-HB ZVS circuitry when operating over a wide range of conditions with unknown or nonlinear circuit parameters.

A high power density single-phase inverter using stacked switched capacitor energy buffer

This paper presents a high power density 2 kW single-phase inverter, with greater than 50 W/in3 power density and 90% line-cycle average efficiency. This performance is achieved through innovations in twice-line-frequency (120 Hz) energy buffering and high frequency dc-ac power conversion. The energy buffering function is performed using an advanced implementation of the recently proposed stacked switched capacitor (SSC) energy buffer architecture, and the dc-ac power conversion is performed using a soft-switching SiC-FET based converter, with a digital implementation of variable frequency constant peak current control.

Multi-mode control of series and parallel converters for bidirectional power systems

A method for smooth transitions between voltage, current, and power regulation (multi-mode control) for bidirectional power converters is proposed. This method extends existing work on multi-mode control of power converters to bidirectional systems. Additionally it is shown how inherent power sharing can be achieved in systems with parallel or series connected converters. These improvements over previous methods make this approach a good candidate for the fast bidirectional systems composed of multiple converter modules increasingly found in emerging DC power grids. Experimental results are shown for two 1 kW, 500 V, 4 A parallel output, isolated, bidirectional series resonant converters (SRCs).

Inherent volt-second balancing of magnetic devices in zero-voltage switched power converters

Small mismatches in inductor-applied volt-seconds may arise in power converters due to asymmetries in circuit parasitics or modulation waveforms. These small mismatches can have significant impact on circuit operation, including the saturation of magnetic components, loss of regulation, and decrease in converter efficiency. Various auxiliary circuits and control methods have been developed to prevent volt-second imbalances from being applied to magnetic components. In this work, an inherent feedback specific to Zero-Voltage Switched (ZVS) converters is examined which automatically compensates for volt-second mismatch. A closed-form linearized relation between volt-second mismatch and inductor current offset is derived. This relation is then verified through simulation and experimental results using two prototype circuits comprised of an inductively loaded full-bridge and a dual active bridge (DAB) converter.

Isolated bidirectional DC/AC and AC/DC three-phase power conversion using series resonant converter modules and a three-phase unfolder

This paper proposes a modular converter system to achieve high power density, high system bandwidth and scalability for isolated bidirectional DC/AC and AC/DC three-phase power conversion. The approach is based on high frequency isolated series resonant converter (SRC) modules with series output connection and a low frequency three-phase unfolder. The performance objectives are realized through elimination of traditional low frequency passive filters used in PWM inverters and instead require high control bandwidth in the SRC modules to achieve high quality AC waveforms. The system operation and performance are verified with simulation and experimental results for a 1 kW prototype.