Srikanthan Sridharan

Abstract: Methods and devices for balancing voltages of capacitors in an electronic circuit are provided. The device includes a chopper circuit having a chopper inductor. Further, the chopper circuit may detect voltages across capacitors as well as an output current of the electronic circuit. In addition, the device may include a chopper control unit receiving the output current then generating a signal representing charging of the chopper inductor based on the output current. Also, the chopper control unit may receive the voltages across the capacitors and detect an imbalance between the voltages based on a polarity of the output current. Additionally, the chopper control unit may transfer of charge between the two capacitors, using the chopper inductor. Further, the chopper inductor is substantially discharged, during the transfer of charge between the capacitors.

Abstract: Applications of motor drives, ranging from automotive traction to more-electric aircraft, have widely varying speed and torque demands. With extensive use of inverter-fed drives, loss minimization techniques for such applications have evolved over the past few decades. Previous work on loss minimization has mainly focused on specific drive components. Component-level loss minimization, however, will not guarantee minimum total loss in the drive system. In this paper, a system-level loss minimization method is developed using a comprehensive loss model, to achieve true minimum total loss in the system. The total loss obtained is lower for the proposed system-based minimization than the component-based methods such as machine loss minimization, torque maximization per stator ampere, and dc-link loss minimization. Simulation and experimental results for a sample drive cycle are presented to verify the benefits of the proposed scheme for an induction motor drive. Results suggest system loss reduction of about 7%, when compared to machine-based optimization, in high-variability applications.

Abstract: The use of LC filters between inverter and motor terminals results in undesirable resonant oscillations in motor voltages and currents. Because passive damping methods employ physical resistors to suppress these oscillations, they contribute to additional losses. Lossless active damping methods with virtual resistors have been explored in the literature as a viable alternative. In a typical active damping implementation, current flow in a virtual resistor across the filter capacitor is emulated in a control loop using motor voltage feedback. Conventionally, the virtual resistance value is fixed based on empirical rules and left unchanged for all operating conditions. Choosing the resistance value is important, because high values may provide insufficient damping, whereas low values can lead to excessive damping and cause degraded dynamic response. A small-signal transfer function-based approach is developed in this paper for active damping design, based on operating conditions and dynamic tuning of the virtual resistance. With the control scheme implemented in a d-q frame, it provides the flexibility of using a differential damping approach in which the d and q axis resistance values need not be equal. Simulations and experimental results are provided for an active-damped, field-oriented-control based induction motor drive. Results confirm the effectiveness of active damping in mitigating resonance effects. This adds new degrees of freedom to the design of inverter output filters.

Abstract: Typical AC traction drive electrical components include the motor, inverter, dc link and filter elements. Drive design parameters and component values are chosen to minimize system-level drive losses. This paper presents a systematic approach for selecting rotor flux magnitude and passive component values in an induction motor drive using a comprehensive loss-minimization algorithm. The total losses obtained are lower for the proposed system-based minimization than for previously reported machine-based minimization algorithms. The effect of individual loss components on the total system loss is also studied. A standard extra-urban drive cycle is used as an example to illustrate the implementation of overall cycle-energy loss minimization. Simulation and reduced-scale experimental studies are conducted to validate the presented design scheme for a rotor-flux-oriented-control-based induction motor drive.

Abstract: Induction motor drives are conventionally operated with a fixed inverter dc-link bus voltage. However, low drive speeds will result in low modulation index and poor dc bus utilization of the inverter. Aperiodic current controllers, such as hysteresis controllers, exhibit increased switching frequencies and losses for higher dc-link voltages. These high switching frequencies can be avoided by dynamically varying the dc-link voltage according to drive operating conditions. In addition to reducing inverter switching losses, varying the dc-link voltage also reduces the switched voltage magnitude across inverter semiconductor switches, potentially increasing inverter reliability. In the proposed work, the link voltage is varied by using a front-end dc-dc buck converter. The link voltage command is derived using a loss minimization technique that uses flux and rotor speed commands to the drive. The effect of additional loss from the front-end converter on the total loss is also investigated. Simulation and experimental results indicate that a variable dc-link voltage supports substantial power electronics loss reduction in applications with highly varying speed conditions.

Abstract: In this paper,a new flux-weakening control method based on rotor flux orientation is presented to improve the current tracking capability and output characteristics of the motor torque,and the method is implemented in digital ac spindle driver system.Using Labview virtual oscilloscope to observe the real-time experimental data,the experimental results show that the method can effectively improve the dynamic response of motor as well as the output characteristics of the motor torque.

Abstract: A system for magnetic detection includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, and a controller. The optical signal is based on hyperfine states of the NV diamond material. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

Abstract: A device includes a propulsion unit configured to move the device and a steering unit configured to control the direction of the device. The device also includes a power unit configured to provide power to the propulsion unit and a charging unit configured to use an electric field to provide electrical power to the power unit. The device further includes a first magnetic sensor configured to determine a vector of one or more magnetic fields and a processor communicatively coupled to the propulsion unit, the steering unit, the power unit, and the magnetic sensor. The processor is configured to receive, from the magnetic sensor, a time-varying signal indicative of a magnetic field and determine, based on the time-varying signal, that the magnetic field is associated with an electrical power transmission line. The processor is further configured to cause the steering unit to direct the device toward the electrical power transmission line.

Abstract: A system for magnetic detection of an external magnetic field is disclosed. The system includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a magnetic field generator that generates a magnetic field, a radio frequency (RF) excitation source that provides RF excitation, an optical excitation source that provides optical excitation, an optical detector that receives an optical signal emitted by the NV diamond material, and a controller. The controller is configured to calculate a control magnetic field, control the magnetic field generator to generate the control magnetic field, receive a light detection signal from the optical detector based on the optical signal due to the sum of the generated control magnetic field and the external magnetic field, store measurement data based on the received light detection signal, and calculate a vector of the external magnetic field based on the stored measurement data.

Abstract: A method for mapping and monitoring of hydraulic fracture includes capturing, using an array of sensors, a first magnetic image of a well pay zone. A second magnetic image is captured using the array of sensors, after a well bore is padded with a fluid. A background is established based on the first and the second magnetic images. A third magnetic image is captured using the array of sensors, after a doped proppant is injected into a stage. The third image is processed to subtract the background and to obtain information regarding distribution of the fluid and the proppant in the stage.