Michael L. McIntyre

Grid-connected single-phase inverters require accurate phase detection for synchronization and power control. Traditionally, phase-locked loops (PLLs) are used to estimate grid parameters. This paper proposes a novel approach that determines the grid phase angle using only current feedback, eliminating the need for grid voltage measurements or cascaded control schemes. The proposed method integrates a phase angle observer with a current controller to regulate real and reactive power. Lyapunov stability analysis and hardware experiments validate the effectiveness of the approach.

Three-phase inverters for photovoltaic grid-connected applications typically require some form of grid voltage phase-angle detection in order to properly synchronize to the grid and control real and reactive power generation. Typically, a phase-locked loop scheme is used to determine this real-time phase angle information. However, in the present work, a novel method is proposed whereby the phase angle of the grid can be accurately identified solely via the grid current feedback. This phase-angle observer is incorporated into a current controller which can manage the real and reactive power of the grid-connected PV inverter system. Moreover, the maximum power point of the photovoltaic arrays is achieved without using a DC–DC converter. The proposed method achieves the grid current and DC-link voltage control objectives without the knowledge of the grid information and without the need for a cascaded control scheme. The design of this combined observer/controller scheme is motivated and validated via a Lyapunov stability analysis. The experimental setup is prototyped utilizing a real-time Typhoon HIL 603 and National Instrument cRIO embedded controller in order to validate the proposed observer/controller scheme under different operation scenarios such as irradiation changes, frequency changes, reactive power injection, and operation with a distorted grid. The results show that the DC-link voltage and the active and reactive powers are well regulated from the proposed control scheme without the measurement of the grid phase and frequency.

In this paper, a nonlinear backstepping controller is proposed to manage the performance of a full-variable permanent magnet synchronous generator wind turbine. This nonlinear controller achieves a rotational speed objective for the generator and is validated through Lyapunov-based stability analysis. Additionally, this objective is accomplished without a measurement for wind speed that influences the wind torque. The proposed scheme is compared to a typical linear controller through simulation results. Simulation tests are performed to compare the response time and average error of each controller in both a drastic and realistic dynamic wind environment. These results demonstrate that the proposed controller is far more robust to wind turbulence than traditional control schemes. The simulation results of this study indicate a 1000% increase in response time and 3000% decrease in average controller error.

Domestic load profiles in the residential sectors are being modified with the adoption of smart home management systems and solar generation. In addition, houses with rooftop PV behave like local generators, contributing to the growth of the penetration of PV energy. Hence, the demand for power is declining day by day. However, the increasing PV penetration causes technical challenges for the power system, such as the “duck curve”. This can be addressed through home energy management (HEM) techniques including peak shaving, load shifting with smart home devices. In this regard, electric water heaters (EWH), with high thermal mass and being ubiquitous, are attractive and low-cost energy storage systems. In this article, a case study for one of the largest rural field smart energy technology demonstrators involving business, industries, and more than 5,000 residences, located in Glasgow, KY, US, is presented. Furthermore, a HEM system, which aims to minimize the total energy usage and peak demand by regulating the heating, ventilation, and air-conditioning (HVAC) systems, water heaters, and batteries, thereby benefiting both the utility and the consumer is proposed. This work also demonstrates the ability of EWH to provide ancillary services while maintaining customer comfort. The minimum participation rates for EWH and batteries are calculated and compared with respect to different peak reduction targets. Long term load prediction by considering different fractions of smart homes for the utility is also provided.

In this paper, a nonlinear controller is proposed to manage the rotational speed of a full-variable Squirrel Cage Induction Generator wind turbine. This control scheme improves upon tractional vector controllers by removing the need for a rotor flux observer. Additionally, the proposed controller manages the performance through turbulent wind conditions by accounting for unmeasurable wind torque dynamics. This model-based approach utilizes a current-based control in place of traditional voltage-mode control and is validated using a Lyapunov-based stability analysis. The proposed scheme is compared to a linear vector controller through simulation results. These results demonstrate that the proposed controller is far more robust to wind turbulence than traditional control schemes.

Three-phase inverters for grid-connected applications typically require some form of grid voltage phase detection in order to properly synchronize to the grid and control real and reactive power. This phase detection is usually based upon some type of grid voltage sensing. However, in the present work a method is proposed whereby the phase angle of the grid can be accurately identified solely via the grid current feedback. In the proposed current control scheme, the only measurement is the output inverter current and no phase locked loop (PLL) exists within the scheme. This phase observer is incorporated into a current controller which can manage the injected power to the grid. The design of this combined observer/controller system is motivated and validated via a Lyapunov stability analysis. The performance of the proposed control scheme has been compared with the conventional PI PLL-based control scheme which needs both a grid voltage and current sensor. Experimental results utilizing a Controller+ Hardware-in-the-Loop test bed have been presented in order to validate the proposed observer/controller scheme under normal operation, weak grid, distorted grid and faulty grid conditions. To summarize, this scheme archives current control for a grid connected inverter using only current feedback. In comparison, traditional methods require voltage and current feedback along with a PLL to synchronize with the grid creating a cascaded closed loop control system.

Many real-world systems are governed by the time-dependent, nonlinear differential equations. Dynamics of an electrical system are also best described using the very equations. Being one of the preferred machines when using advanced control algorithms for electric drives, DC motor has been selected for position tracking. Defining dynamic equations of the motor derived from the theory of nonlinear equations, aided our simulations by overcoming the time dependency that might not be addressed satisfactorily using regular control topologies. We incorporated integrator backstepping methodology along with a Multilevel Diode Clamped Inverter to develop full state feedback (FSFB) position tracking controller. The results thus obtained by using the integrator backstepping algorithm along with multilevel inverter were compared to the output of ideal case circuit that generated results based on integrator backstepping algorithm alone. Simulation results provide further validation with control topology being investigated for the ideal circuit and the inverter circuit.

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.

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.