This paper presents the analysis, design, modeling and control of a cascaded two-stage step-down dc-dc converter with a conventional synchronous buck converter in the first stage and a new phase ...shifted switched capacitor (PSSC) buck converter in the second stage. Higher efficiency and higher power density compared to the conventional multiphase buck converter are the prominent features of the proposed architecture which make it suitable as a point of load converter, widely used in powering computing, communication and networking equipment. The first stage buck converter is operated at high switching frequency with extended duty ratio and is designed for high efficiency. The second stage PSSC converter with low input voltage attains high efficiency when operated at a fixed conversion ratio with low switching frequency and a simple constant current charging technique. A laboratory prototype converter achieved a peak efficiency of 86.8% at 30-A load current while operating at 12-V input voltage and 1.3-V output voltage. The capacitor-based output power stage drastically reduces the number of inductors compared to the multiphase buck converter. A low frequency small signal model of the converter and a state feedback controller for the output voltage are developed analytically. The closed-loop transient performance of the converter using this state feedback controller is also verified experimentally.
A high power density transformer-less quadruple active half-bridge DC-DC converter suitable for the input-stage of a two-stage 48 V VRM is proposed in this paper. The converter consists of four ...half-bridge circuits and three small AC link power transfer inductors connected strategically among them. In the absence of the transformer, the voltage matching among the half-bridge circuits is achieved by stacking all of them together in series. The converter achieves high efficiency since all of its switches undergo inherent zero-voltage switching. It also needs to handle reduced power as a significant portion of the total load power flows directly to the output. It has several other advantages like reduced switch voltage and current stresses, efficient voltage regulation ability (and hence scalability), and a wide range variable switching frequency operation. These features allow the converter to achieve a flat high-efficiency curve. Topological evolution of the converter from its isolated version is explained and the concept is generalised to obtain the transformer-less multiple active half-bridge converters. Thereafter, the circuit operation of the quadruple active half-bridge configuration is analysed and a capacitor voltage control scheme is proposed. Finally, experimental results from a 48 V-12 V, 8 A laboratory prototype show that the converter achieves a peak efficiency of 98.1% and a full load efficiency of 97.23%.
In this paper, a current fed triple active bridge (TAB) based multiport converter (MPC) for DC mircrogrid (DCMG) application is analyzed considering full range variation of the input voltage and load ...power. A generalized frequency domain modeling approach is proposed in order to reduce the design complexity. This modeling approach can be extended to higher order MPCs with `n' winding transformer coupled converters. A modified duty ratio control scheme is proposed to minimize the transformer rms current and extend zero voltage switching range. A detailed analysis is performed to identify the zero voltage switching (ZVS) region over the whole operating range of the converter. A laboratory prototype of 2kW is built to verify the proposed modulation strategy and theoretical analysis.
This paper presents a bidirectional, soft-switching, multiport DC-DC converter, using a transformer isolated Dual-Active Bridge and a PWM boost configuration to interface two energy sources with a DC ...bus. The converter is intended for integration of battery and supercapacitor with a DC micro grid, which require the battery port to be interfaced in a current source manner. The converter topology and the operating principles are introduced. Suitable control strategy to regulate the DC link voltage along with current control of the battery port is proposed. Current source property along with soft switching at constant switching frequency makes this topology well suited for energy storage applications. Experimental results are given for a Multiport converter prototype operating over an output power range of 100 W to 1000 W while supplying a constant output DC link Voltage. The converter switching frequency is above the Audible frequency band to reduce switching noise. Using Silicon MOSFETs, the prototype achieves a peak efficiency of 98.5%, and maintains greater than 90% efficiency across the wide output power range.
The multiphase interleaved synchronous buck converters with coupled phase inductors are being preferred for voltage regulator modules requiring low output voltage, high output current, and fast ...transient response since they simultaneously offer better steady-state efficiency and faster dynamic response. In this paper, a novel magnetic core structure for symmetrical coupling of multiphase buck converter phase inductors is proposed, which overcomes several limitations of asymmetrical inductor coupling proposed so far. A new analytical technique to arrive at simple dynamic equivalent circuits of the converter, as well as design guidelines for the proposed inductor structure, is presented. Experimental results from a prototype four-phase synchronous buck converter with the proposed inductor demonstrate 2% to 6% improvement in the converter efficiency compared to a similarly rated converter with uncoupled inductors while retaining the same transient performance.
Present energy need heavily relies on the conventional sources. But the limited availability and steady increase in the price of conventional sources has shifted the focus toward renewable sources of ...energy. Of the available alternative sources of energy, wind energy is considered to be one of the proven technologies. With a competitive cost for electricity generation, wind energy conversion system (WECS) is nowadays deployed for meeting both grid-connected and stand-alone load demands. However, wind flow by nature is intermittent. In order to ensure continuous supply of power suitable storage technology is used as backup. In this paper, the sustainability of a 4-kW hybrid of wind and battery system is investigated for meeting the requirements of a 3-kW stand-alone dc load representing a base telecom station. A charge controller for battery bank based on turbine maximum power point tracking and battery state of charge is developed to ensure controlled charging and discharging of battery. The mechanical safety of the WECS is assured by means of pitch control technique. Both the control schemes are integrated and the efficacy is validated by testing it with various load and wind profiles in MATLAB/SIMULNIK.
Vector control algorithms reported so far for stand alone operation of variable speed constant frequency double output induction generators propose to supply the full magnetisation current of the ...machine in addition to the torque producing component from the rotor side converter. As the rotor of a normal induction machine is not designed for this additional load this approach leads to underutilisation of the machine torque capacity. Moreover, supplying the entire magnetisation current from the rotor side is not optimal from the point of view of the machine losses. Since the load voltage is regulated by manipulating the magnetising current through a slow acting flux control loop undesirable fluctuations in the load voltage waveforms are observed during fast load transients. An improved stator flux oriented control strategy for this type of generators, proposed in this study, eliminates undesirable load voltage transients by directly regulating the stator flux through the stator side converter. The total reactive power demand of the system is dynamically distributed between the two converters according to an optimum allocation program so as to minimise the losses without disturbing the stator flux. The effectiveness of the proposed algorithms is verified experimentally on a laboratory prototype.
This paper presents the design of an onboard integrated charger using cascaded converters and cell bypass balancing circuit for lithium-ion battery packs. Lithium-ion based serially connected battery ...cells experience imbalance in operation while charging and discharging. This limits the effective capacity utilization of the battery pack. Among all the active balancing circuits, cell/module bypass reconfiguration is considered to be quite efficient and fast, but introduces surge currents and reduces the system efficiency. This may also damage the components connected and reduce the battery life. In this paper we propose a modified circuit topology to overcome this problem. Simulations are carried out for 14 series connected cells each with nominal voltage of 3.7 V and capacity of 40Ahr. The results indicate considerable scope of application of the proposed approach for on-board electric vehicle applications.
This paper presents the controller design of a wind energy conversion system built around a self-excited squirrel cage induction machine that can be operated in both standalone and grid connected ...modes. The control scheme regulates the machine terminal voltage in the standalone mode and the grid side reactive power in the grid connected mode. Both a TCR type SVC and a VSI based STATCOM are employed as flexible reactive power sources. The overall control scheme has been developed and verified in MATLAB/SIMULINK platform. The power versus terminal voltage characteristics, the terminal voltage, system frequency and reactive power versus various load levels in different modes of operation are discussed.
Improved reliability and fault tolerant operation of power converter systems are extremely important for industrial AC drives. The paper considers variable frequency variable voltage operation of a ...three-phase induction motor in single-phase mode for two common faults of a three-phase inverter, i.e., open base drive and device short-circuit. The motor performance has been extensively analyzed in single-phase mode and remedial strategies have been developed to neutralize large second and other lower order harmonic pulsating torques. In a single-phase open loop volts/Hz control made of a faulty three-phase inverter, it has been demonstrated that odd harmonic voltages at appropriate phase angles can be injected to neutralize the low frequency pulsating torques so as to permit smooth drive operation. It has been shown that the pulsating torque can be further reduced by load dependent flux programming rather than operating with constant rated flux.< >
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