Jeffrey H. Lang

A state observer for the permanent-magnet synchronous motor

An identity state observer for the permanent-magnet synchronous motor is derived which reconstructs the electrical and mechanical states of the motor from current and voltage measurements. The observer operates in the rotor frame and estimates direct and quadrature stator currents, rotor velocity, and rotor position. Since the rotor position is estimated, the rotor reference frame is approximated using the latest rotor position estimate. The motor dynamics and the transformation into the estimated rotor frame are nonlinear, and thus the observer and observer error dynamics are nonlinear. Therefore, stability is analyzed using a linearized error model. Simulations including realistic measurement disturbances are used to investigate the global stability and accuracy of the observer. >

State observers for variable-reluctance motors

A sequence of progressively more complex state observers, each driven by measurements of phase voltages and currents, is developed for variable-reluctance motors. For the simpler observers, the exponential stability of their error dynamics in a neighborhood of the origin is proved. For all observers, the results of numerical or physical experiments are provided to demonstrate the globally stable error dynamics. In several of the physical experiments, rotor position is estimated to better than one part in 50000 of a revolution. >

A variable-capacitance vibration-to-electric energy harvester

Past research on vibration energy harvesting has focused primarily on the use of magnets or piezoelectric materials as the basis of energy transduction, with few experimental studies implementing variable-capacitance-based scavenging. In contrast, this paper presents the design and demonstration of a variable-capacitance vibration energy harvester that combines an asynchronous diode-based charge pump with an inductive energy flyback circuit to deliver 1.8 /spl mu/W to a resistive load. A cantilever beam variable capacitor with a 650-pF dc capacitance and a 348-pF zero-to-peak ac capacitance, formed by a 43.56cm/sup 2/ spring steel top plate attached to an aluminum base, drives the charge pump at its out-of-plane resonant frequency of 1.56 kHz. The entire harvester requires only one gated MOSFET for energy flyback control, greatly simplifying the clocking scheme and avoiding synchronization issues. Furthermore, the system exhibits a startup voltage requirement below 89 mV, indicating that it can potentially be turned on using just a piezoelectric film.

Vibration-to-electric energy conversion

A system is proposed to convert ambient mechanical vibration into electrical energy for use in powering autonomous low-power electronic systems. The energy is transduced through the use of a variable capacitor, which has been designed with MEMS (microelectromechanical systems) technology. A low-power controller IC has been fabricated in a 0.6 /spl mu/m CMOS process and has been tested and measured for losses. Based on the tests, the system is expected to produce 8 /spl mu/W of usable power.

Operation of microfabricated harmonic and ordinary side-drive motors

A variable-capacitance harmonic side-drive motor is presented and the operation of this motor and ordinary variable-capacitance side-drive motors without the need for air-levitation assist is reported. Native oxide formation on motor polysilicon surfaces, resulting from the clamping of the rotor to the shield beneath it, is identified as the cause of motor operational failure. With proper release and testing directed at minimizing this oxide formation, the motors can be readily operated. Operational characteristics of the micromotors, including the role of rotor electric shielding, speed, and frictional effects, are studied. For the side-drive motors, measurements of stopping and starting voltages indicate that the drive torque required to sustain motor operation is 5-7 pN-m, while that required to initiate motor operation after a 30 second rest is nearly twice as high.<<ETX>>

Real-time observer-based (adaptive) control of a permanent-magnet synchronous motor without mechanical sensors

A theoretical and experimental analysis is presented of a closed-loop adaptive velocity control system for a 200 W permanent magnet synchronous motor. The control system utilities a mechanically sensorless full-state observer for the generation of all controller feedback information. Both the control system and its experimental performance using an implementation based on the Motorola 68020 microprocessor are presented. It is shown that the real-time observer-based adaptive velocity controller is capable of successful operation.<<ETX>>

Power MEMS and microengines

MIT is developing a MEMS-based gas turbine generator. Based on high speed rotating machinery, this 1 cm diameter by 3 mm thick SiC heat engine is designed to produce 10-20 W of electric power while consuming 10 grams/hr of H/sub 2/. Later versions may produce up to 100 W using hydrocarbon fuels. The combustor is now operating and an 80 W micro-turbine has been fabricated and is being tested. This engine can be considered the first of a new class of MEMS device, power MEMS, which are heat engines operating at power densities similar to those of the best large scale devices made today.

Micro - Heat Engines, Gas Turbines, and Rocket Engines - The MIT Microengine Project -

This is a report on work in progress on microelectrical and mechanical systems (MEMS)-based gas turbine engines, turbogenerators, and rocket engines currently under development at MIT. Fabricated in large numbers in parallel using semiconductor manufacturing techniques, these engines are based on micro-high speed rotating machinery with the same power density as that achieved in their more familiar, full-sized brethren. The micro-gas turbine is a 1 cm diameter by 3 mm thick SiC heat engine designed to produce 10-20 W of electric power or 0.050.1 Nt of thrust while consuming under 10 grams/hr of H 2 . Later versions may produce up to 100 W using hydrocarbon fuels. A liquid fuel, bi-propellant rocket motor of similar size could develop over 3 lb of thrust. The rocket motor would be complete with turbopumps and control valves on the same chip. These devices may enable new concepts in propulsion, fluid control, and por table power generation.

A simple motion estimator for variable-reluctance motors

A simple motion estimator is presented for inverter-driven variable-reluctance motors. The estimator probes unexcited phases with short voltage pulses from the inverter, and evaluates the resulting currents to measure the phase inductances. From these inductances, instantaneous motor position is estimated. Individual position estimates are optionally combined by a state observer to produce smoothed position and velocity estimates. Next, the secondary phenomena of eddy currents in the motor laminations, inverter switching noise, magnetic coupling between motor phases, and quantization introduced by digital implementation are all examined for their effects on estimator performance. Each phenomenon is addressed by a modification of the estimator. Finally, the estimator is evaluated experimentally using an inverter-driven three-phase motor having six stator poles and four rotor poles. The estimator is implemented digitally with an Intel 8031 microcomputer and little extra hardware.<<ETX>>

Design principles for highly efficient quadrupeds and implementation on the MIT Cheetah robot

In this paper, we introduce the design principles for highly efficient legged robots and the implementation of the principles on the MIT Cheetah robot. Three major energy loss modes during locomotion are heat losses through the actuators, losses through the transmission, and the interaction losses that includes all losses of the system interacting with the environment. We propose four design principles that minimize these losses: employment of high torque density motors, low impedance transmission, energy regenerative electronics and a design architecture that minimizes the leg inertia. We present the design features of the MIT cheetah robot as an embodiment of these principles. The resulting cost of transport (COT) is 0.51 during 2.3 m/s running, which rivals running animals in the same scale.