Joseph Latham

Vehicle to grid utilizing a backstepping controller for bidirectional full-bridge converter and five level active neutral point inverter

In this paper a two-stage power electronic interface is presented for Vehicle to Grid applications. A bidirectional full-bridge converter stage supplies regulated DC voltage for two parallel five-level Active Neutral Point Clamped (ANPC) inverters which generate split-phase AC voltage to power a residential load. The AC output voltage of the multilevel ANPC inverters meets the harmonic limits of IEEE 519. A backstepping controller is developed for the converter stage which meets the voltage regulation objective while adapting for variation in the battery input voltage, system disturbances, and an unknown load. Stability analysis and simulation results validate this approach.

Nonlinear current observer for backstepping control of buck-type converters

Two backstepping control schemes are developed for buck-type converters for two different types of loads. The first considers an unknown passive load, while the second considers a time-varying current source load. Both schemes utilize a novel inductor current observer which eliminates the need for a costly current sensor. For the passive load, the output voltage tracking objective is met using only parameter knowledge and the output voltage measurement. For a current source load, the output voltage tracking objective is met using parameter knowledge and measurement of output voltage and load current. A stability analysis and simulation results validate each approach.

Energy efficient DC to AC power conversion using advanced controllers and novel voltage trajectories

A typical DC:AC conversion system consists of two stages, a DC:DC converter to generate the necessary bus voltage followed by an inverter which generates the desired AC output. A modification of this system is proposed for the purpose of reducing switching losses. The proposed two-stage system consists of a buck converter which produces a mixed (DC+AC) signal which is fed to a traditional inverter. This mixed signal is designed such that it reduces the switching loss across the inverter switches while still providing the necessary voltage for the inverter input. Backstepping controllers are designed to achieve output voltage tracking objectives for both stages. Lyapunov stability analysis and simulation results validate these controller designs. Efficiency and THD comparisons are made between the typical and modified systems.

Nonlinear control of standalone inverter with unbalanced, nonlinear load

In this paper, a nonlinear backstepping controller is proposed for the control of a 3-phase 3-level diode clamped inverter with an output LC filter under different loads including balanced, unbalanced, linear and nonlinear loads. Also, the seamless transition of the inverter from standalone to grid-tie is investigated while the inverter is under the control of the proposed scheme. Lyapunov stability analysis and simulation results validate the effectiveness of the proposed control solution in terms of tracking objective and in meeting the Total Harmonic Distortion (THD) requirements of IEEE 519 and EN 50160 standards for US and European power systems, respectively.

Parameter Estimation and a Series of Nonlinear Observers for the System Dynamics of a Linear Vapor Compressor

Linear compressors are becoming more widely utilized in refrigeration for their high efficiency in comparison with traditional rotary devices. The nature of the free piston in a linear compressor requires additional control which necessitates knowledge of the mechanical dynamics of the system. Sensorless control of the system is preferred for cost effectiveness. To this end, a pair of nonlinear observers have been developed to observe signals within the system dynamics and reduce the need for costly sensors. The first utilizes a current and voltage measurements to arrive at an observed velocity. The second utilizes a velocity measurement to arrive at observations of piston acceleration as well as a lumped uncertainty term in the mechanical dynamics. A stability analysis is presented to prove boundedness and convergence for these nonlinear observers with experimental results providing further validation. As these observers rely on accurate knowledge of the model parameters, to this end, an estimator has been designed to estimate the electrical parameters of the system. Experimental results validate this method as well.

Nonlinear control for single-stage single-phase grid-connected photovoltaic systems

A nonlinear control strategy is developed for a single-stage single-phase grid-connected photovoltaic (PV) inverter in synchronous dq frame. The control scheme is proposed to achieve both maximum power point operation, regardless of the atmospheric conditions, and to control the active and reactive power. The control scheme forces the d-axis current to track a novel trajectory reference current, obtained online. The control scheme provides for energy balance from the input to the output of the system along with mitigating the PV current ripple, which is the major drawback of the single-phase PV inverter. A Lyapunov analysis is developed to prove the stability of the system and boundedness of signals. The scheme is validated through a simulation.

Simplified adaptive backstepping control of buck DC:DC converter with unknown load

In this paper a backstepping control scheme is developed for the Buck DC:DC converter topology. This control scheme achieves the output voltage tracking objective operating under the constraint of an unknown load, along with an unknown constant disturbance. This work simplifies the control scheme by utilizing a novel controller with added terms to compensate for additional missing information. This solution is more easily implemented in real-time systems, with only a small decrease in system fidelity. Lyapunov stability analysis is utilized to demonstrated closed loop system stability while meeting the voltage-tracking control objective. Simulation and experimental results validate analytical formulation.

Sensorless Resonance Tracking and Stroke Control of a Linear Vapor Compressor Via Nonlinear Observers

Linear compressors have become more common in refrigeration applications due to their high efficiency. However, in order to achieve efficient and reliable operation of the machine, the system controller must be capable of dealing with two main issues. First, the nonlinear force of gas compression acting against the mass spring piston system causes the frequency at which system efficiency is maximized, i.e., the resonant frequency, to vary with the load. Second, the unconstrained piston stroke allows for the possibility of collision with the head, which may reduce reliability. Accounting for these issues requires knowledge of the piston dynamics; however, for reliability and cost effectiveness it is preferred to operate the system without the use of internal sensors. In this work a novel system level controller is designed to simultaneously achieve resonance-tracking and stroke control objectives utilizing a pair of nonlinear observers to obtain the necessary information sensorlessly. This design is validated under experimental testing, which demonstrates both the accuracy of the observed signals and the stability and convergence of the controller.

Impact Fault Detection for Linear Vapor Compressor Using RISE Observer

In some applications, an indicator is needed for sudden system state changes, where the direct measurement of the system states is neither possible nor practical. In this brief, it is shown that the error of robust integral of the sign of the error observer can be used as an indicator of sudden system state changes. The application of this method for collision detection in a linear vapor compressor is investigated. Linear vapor compressors are becoming more widely utilized in cooling appliances, such as household refrigerators and portable coolers due to their high efficiency. The fact that the piston is free in a linear vapor compressor allows for the possibility of collisions between the compressor piston and other components of the linear vapor compressor within the compression chamber. Sensorless crash detection is preferred for purposes of reliability, ease of production, and cost effectiveness. For this purpose, a novel head crash detection scheme applying a nonlinear observer is developed. This scheme not only detects all head crashes accurately, but also provides an indicator proportional to the piston velocity at the time of impact. This indicator can be used to estimate how much the force command needs to be reduced to prevent further collision. A set of simulation and experimental test results validate the performance of the head crash detection scheme.

A filter-based controller for a buck converter

A filter-based control scheme is developed for buck-type converters. This approach relies only on a single output voltage measurement. The benefits of this approach are reducing the system cost as well as measurement noise and disturbance injected by output current and/or inductor current measurements. A Lyapunov stability analysis is utilized to demonstrate system stability. Experimental results demonstrate excellent voltage regulation and insensitivity to the load variations.