A. Bhattacharya

Northeastern University, Boston, MA, United States

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Publications (5)0 Total impact

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    ABSTRACT: One way to create white light is with a RGB color mixing system, in which light from multiple monochromatic LEDs (red, green and blue) is mixed. Unfortunately, there are several variations/uncertainties between individual LEDs that can create unwanted problems, such as variations in: forward voltage drop, peak wavelength, spectral radiant intensity, and the width of the spectral power distributions (SPD) of the LEDs. This paper will explain, through experiments, behavioral models and probability theory, how the variations affect the design of LED based lighting system. We especially describe the effects such as the influence of SPD variation and Forward Voltage drop variation.
    Applied Power Electronics Conference and Exposition, 2008. APEC 2008. Twenty-Third Annual IEEE; 03/2008
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    A. Bhattacharya, B. Lehman, A. Shteynberg, H. Rodriguez
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    ABSTRACT: Often, high brightness LEDs (HB-LED) are connected in series to create strings. According to their data sheets, the HB-LEDs have a variation in their forward voltage drop. This forward voltage variation may create a non-uniform illumination if the strings are connected in parallel. This paper proposes a probabilistic approach for modeling the forward voltage drop across the HB-LEDs and determining the value of the resistance needed in each string to control the current. The results of this paper show that when the probabilistic models are used, the value of the added balancing resistance is reduced compared to when using standard worst case models.
    Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007
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    A. Bhattacharya, B. Lehman, A. Shteynberg, H. Rodriguez
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    ABSTRACT: This paper proposes a digital controller with sliding mode pulsed current averaging scheme for high-brightness (HB) light emitting diodes (LED) IC drivers. The digital controller implements a control method to adjust the 'on time' of the active switch based on the comparison of output current and a reference current. The idea is to increase or decrease the duty cycle by discrete pulses in order to control the average current being delivered to the load. A variable frequency boost converter in discontinuous conduction mode (DCM) has been used to handle the required load current. No external analog-to-digital (A/D) converter is required for the application
    Computers in Power Electronics, 2006. COMPEL '06. IEEE Workshops on; 08/2006
  • Ting Qian, B. Lehman, A. Bhattacharya, H. Ginn, M. Molen
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    ABSTRACT: For modern navy electric ship, the application of multiple shunt active power filters (SAPF) has become an attractive choice to mitigate the current distortion of the nonlinear loads. Multiple SAPF has the advantage of high power capacity and high reliability. Based on the introduction of SAPF, this paper analyzes the importance of paralleling SAPF in electric ship systems. A new paralleling approach is proposed and compared with several known paralleling/cascading methods. The proposed method separates the tasks of compensating for reactive power and harmonic currents. It has fast response and is suitable for redundancy design. Simulation results verify the analyses.
    Electric Ship Technologies Symposium, 2005 IEEE; 08/2005
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    Ting Qian, Anindita Bhattacharya, Brad Lehman, Herb Ginn, Marshall Molen
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    ABSTRACT: In any distributed power system where the impedance of the generator is non-negligible compared to the impedance of its nonlinear loads, the source voltage typically contains some distortion. Specifically, US Navy ship power generators experience a significant amount of voltage distortion. Since shunt active power filters (SAPFs) normally use the waveform of the source voltage for their reference generator, a significant voltage distortion can create undesired harmonics in the current reference, thus inject undesired harmonics into the line. This paper proposes a phase adjusting algorithm that is robust to source voltage distortion. Low pass filter (LPF) is utilized to suppress the distortion; phase shift caused by LPF or other factors is adaptively adjusted to zero by closed loop control. This approach can be implemented in either instantaneous reactive power theory based control or synchronous reference frame theory based control and no predictive estimations are needed for precise synchronization
    01/2005;