This letter proposes a comprehensive zero-voltage switching analysis (ZVSA) to illustrate the commutation mechanism of full-bridge (FB) mosfets in resonant converters. Inherent contradiction between ...two conventional ZVSA techniques is discussed with specific consideration of a full-bridge LLC (FBLLC) resonant converter. An analytical approach is proposed to determine the accurate zero-voltage switching (ZVS) criterion for both zero- and finite-phase overlap operations of an FB network. Impact of the proposed ZVSA on power losses of FBLLC is explained analytically. Experimental results are presented not only to validate the proposed ZVSA, but also to validate its effect on FBLLC. Low load efficiency is improved by 6% with the proposed approach.
Optimum torque (OT)-based maximum power point tracking (MPPT) is widely used in high power turbines because of its simplicity. Several recent improvements claim better response speeds by augmenting ...the basic OT algorithm with a suitably scaled inertial torque. However, the underlying dynamic model for all these improved methods is premised on a rigid shaft, which ignores all torsional behavior. This lacuna is addressed in this paper, where a small-signal system description is developed considering a more accurate flexible shaft model. It is shown that the improvements have three possible forms, the third being proposed in this paper. Close-loop stability with each of these is analytically investigated using this accurate small-signal model. It is also proved that one of the reported approaches causes system instability while attempting even moderate improvement over the OT method. The problems in realization of the other two forms are highlighted and a realizable alternative proposed, which requires no additional sensor. Design of the proposed approach is presented in appropriate detail. It is analytically established that the proposed method ensures superior dynamic response. All analytical conclusions are validated by numerical simulations.
In this paper, two space-vector-based pulsewidth modulation (PWM) (SVPWM) strategies named equal- and proportional-duty SVPWMs are described, which are used to synthesize a four-level waveform from ...an open-end winding configuration of an induction motor. Two isolated dc-link voltages, which are in the ratio of 2 : 1, are employed to achieve this objective. Both of these PWM strategies achieve the avoidance of overcharging of the dc-link capacitor of an inverter operating with lower dc-link voltage by its counterpart with higher dc-link voltage. Implementation of these PWM strategies requires only the instantaneous three-phase reference voltages, eliminating the need of sector identification or lookup tables. The numbers of samples per cycle for individual inverters are selected in such a way that the quarter-wave, half-wave, and three-phase symmetries are achieved for the dual-inverter drive despite unequal dc-link voltages for the constituent inverters. It is also shown that one of the two PWM techniques, called the proportional-duty SVPWM, results in a better spectral performance and lower switching power loss in the overall dual-inverter system compared to the equal-duty SVPWM.
Conventionally, an AC to DC isolated converter follows a two-stage design approach, wherein the first stage is an AC to DC power factor correction (PFC) stage followed by a resonant converter stage ...for DC voltage regulation. In existing topologies, the PFC stage and the primary side resonant switch network are merged into a single switch network giving rise to 25% fewer devices. Moreover, the switches in these topologies are soft switched that facilitates high switching frequency. Hence, low volume magnetic components and capacitors can be used to achieve higher power density. However, it is an unipolar voltage-fed resonant topology and also, the power transfer is unidirectional, restricting the power flow only from AC to DC side. This paper proposes a novel isolated bidirectional bipolar voltage-fed AC to DC converter which has all the aforementioned advantages. In addition, it addresses their shortcomings by generating a bipolar voltage across the resonant tanks and realizing bidirectional power flow. A modulation and control technique is proposed for generating switching pulses for DC link voltage control and bidirectional power transfer. These are demonstrated through simulations and experiments, where 1.35 kW power is transferred at 130 kHz switching frequency, 150V (L-L) AC input voltage and 200V output DC voltage.
Conventionally, an AC to DC isolated converter follows a two-stage design approach, wherein the first stage is a hard switched power factor correction (PFC) converter followed by a soft switched ...resonant converter stage. In existing single stage two level converter topologies, the two stages are merged resulting in 25% fewer devices. All the switches in these topologies are soft switched leading to a higher switching frequency of operation. However, the voltage stress on the devices are high. Also, this two level topology is not suitable for medium voltage AC applications. Moreover, this single stage converter is an unidirectional with power flow from AC to DC side. The existing multilevel topologies for medium voltage applications have a hard switched PFC stage followed by a soft switched resonant stage. In order to overcome aforementioned shortcomings, this paper presents a novel isolated bidirectional multilevel bridge tapped resonant (MBTR) AC to DC converter. It is based on a multilevel diode clamped topology where PFC stage and resonant stage are merged into single stage with 25% reduction in device count. The switches in the proposed converter are soft switched facilitating higher switching frequency of operation. A new modulation technique is proposed for generating gating pulses for the switches. The preliminary simulation results of the proposed MBTR converter are provided.
This paper proposes a high-efficiency and high step-down isolated DC-DC converter using a saturable inductor for point-of-load (PoL) converter applications. The saturable reactor helps in reduction ...of frequency range of peak current control strategy. This method offers enhancement of light load efficiency in addition to soft switching operation throughout the load range. Circuit analysis details of frequency variation of peak current control, using saturable reactor is presented. Effectiveness of the proposed solution is verified in simulation and then validated with experimental results.
This paper proposes a detailed step-by-step design procedure and control of an LCL filter for grid connected three phase sine PWM voltage source inverter. The goal of the design is to ensure high ...quality of grid current as well as to minimize the size of filter magnetics. In order to ensure unity power factor injection into grid a current controller is designed with a constraint that only the inverter side inductor current is sensed. Good agreement between simulation and experimental results verify the effectiveness of the designed controller and the LCL filter.
Even though hill climbing search (HCS) control is the simplest MPPT algorithm that does not require any prior knowledge of the system, it has the disadvantage of being slow in its response. This ...slowness in the response is due to the number of perturbations involved in climbing the hill and the settling time of the each perturbation. This paper proposes an improved HCS control, in which the nature of the input perturbation is changed, so as to improve the control algorithm's response speed in tracking the maximum power point of a wind turbine. (6 pages)
