W. L. Malan

Modeling and Control of a Resonant Dual Active Bridge With a Tuned CLLC Network

This paper proposes a linear state-space model for a phase-controlled resonant dual active bridge with a tuned capacitor-inductor-inductor-capacitor network. The proposed model is useful for fast simulation and for the estimation of state variables under large signal variation. The model is also useful for control design because the slow changing dynamics of the dq variables are relatively easy to control. Using the proposed model, a decoupled control scheme was designed which allows for the control of the high frequency link currents while also improving the soft switching range of the converter. Using steady-state relationships between state variables and the system inputs, the controller was simplified from three proportional integral (PI) controllers to a single PI controller. The controller was implemented on a low cost digital signal processor and verified experimentally. The experimental and simulation results showed the proposed models usefulness for control design and fast simulation.

A single phase AC-DC bidirectional converter with integrated ripple steering

Charging or discharging of batteries connected to the grid usually requires bulky capacitors on the battery side to filter out the large double grid frequency current ripple. This paper proposes a novel single phase ac-dc bidirectional (BD) converter that improves the utilization of the filtering capacitor by actively steering the ripple into it and thereby cycling it through a large portion of its operating voltage range. This greatly reduces the overall capacitance required to filter the double grid frequency current ripple and results in a low cost solution with high power density.

Ripple elimination for DC/AC DAB converter with phase shift and duty cycle control

Active ripple current reduction method is proposed for isolated DC/AC dual active bridge (DAB) converter to reduce the double grid frequency ripple in the DC current. Unlike those active methods that require extra switches to construct separate ripple reduction circuit, in this method, one or two branches of LC ripple steering circuits are used along with existing full bridge switches in a multiplexing manner. For the purpose of the ripple elimination, unsymmetrical phase shift modulation and duty cycle regulation methods are proposed and applied to both legs of the converter on the primary side of DAB converter. Also a current sharing (CS) scheme is presented to balance the current on both LC ripple steering circuits.

Novel modulation strategy for a CLC resonant dual active bridge

This paper proposes a novel modulation strategy for a phase controlled Capacitor-Inductor-Capacitor (CLC) Resonant Dual Active Bridge (RDAB). The proposed modulation strategy improves the soft turn-on, Zero-Current-Switching (ZCS) and Zero-Voltage-Switching (ZVS) range of the converter while only minimally increasing the required reactive currents in the ac link. A mathematical analysis of the proposed modulation scheme is presented along with a theoretical loss comparison between several modulation strategies. The proposed modulation strategy was implemented and the experimental results are presented.

Modeling and control of a CLC Resonant Dual Active Bridge

This paper proposes a linear large signal state-space model for a phase controlled CLC (Capacitor Inductor Capacitor) Resonant Dual Active Bridge (RDAB). The proposed model is useful for fast simulation and for the estimation of state variables under large signal variation. The model is also useful for control design because the slow changing dynamics of the dq variables are relatively easy to control. Simulation results of the proposed model are presented and compared to the simulated circuit model to demonstrate the proposed models accuracy. This proposed model was used for the design of a Proportional-Integral (PI) controller and it has been implemented in the circuit simulation to show the proposed models usefulness in control design.

A three port resonant solid state transformer with minimized circulating reactive currents in the high frequency link

Multi-port dc-ac and dc-dc converters are of great interest for applications where electricity is generated through a variety of energy sources and where energy storage systems are required. In this paper, a three-port, dc-dc-ac Solid State Transformer (SST) is presented that can control the magnitude and direction of power transfer between a battery, a dc bus and the ac grid. The proposed SST features a low magnetic component count, has high power density, high efficiency and provides galvanic isolation between all three ports. The presented topology is operated with a fixed switching frequency and is phase shift modulated. In this paper, a mathematical analysis of the proposed SST is presented along with its sensitivity to parameter variation. The requirements for soft switching is derived and it is demonstrated that the converter can soft switch over large input voltage variation. The modulation parameters are optimized so that the high frequency link currents are minimized while soft switching is maintained. Additionally, in the simulation results, the ac grid current is modulated so that no Power Factor Correction (PFC) circuitry is required.

On assessment of prominent heuristic methods towards selective harmonic mitigation

Low-frequency switching strategies are considered as an effective way of achieving efficient performance in multilevel inverters. Selective harmonic elimination (SHE) is a modulation technique of this category which gives a superior outcome suppressing low-order detrimental harmonics. Limited number of decision variables offered by SHE in the corresponding nonlinear equations hinders obtaining quality waveforms. Current research is targeted on two distinct objectives for CHB inverters. First objective is to obtain a quality output signal. The second one is accomplishing a realistic solution with compromised voltage quality where a broad operating range becomes mathematically challenging. These aims are achievable by deploying additional degree of freedom in the equation set. In other words, the introduction of floating voltage levels contributes to effectively doubling the number of variables. The enhancement of output waveforms is presented through several illustrations and comparisons. Subsequent laboratory implementation validates the proposal and confirms its feasibility.

Frequency modulation of a series resonant dual active bridge to minimize the circulating reactive currents in the high frequency link

A frequency modulation scheme is proposed for a Capacitor-Inductor-Inductor-Capacitor (CLLC) Resonant Dual Active Bridge (RDAB) that relies on dynamic retuning of the resonant capacitors to the switching frequency as it is modulated. The proposed modulation scheme greatly reduces the circulating reactive currents in the High Frequency Link (HFL) by operating at a range of fixed discrete switching frequencies. A Triple Phase Shift (TPS) modulation scheme is used in between the discrete steps of switching frequencies and capacitances. In this paper, a mathematical analysis is presented of the RDAB and the proposed modulation scheme is compared to all of the existing modulation schemes. The CLLC RDAB is implemented in simulation and the simulation results demonstrate the effectiveness of the proposed modulation scheme at decreasing the circulating reactive currents, and therefore, greatly decreasing the conduction losses of the converter at light load, while maintaining its soft switching capability.