1,721,028 research outputs found
Semiglobal Uniform Asymptotic Stability of an Easy-to-Implement PLL-Like Sensorless Observer for Induction Motors
No full textIn this work, stability properties of a novel and easy-to-implement sensorless observer for induction motors are investigated. The considered solution is inspired by phase-locked-loop strategies and it takes advantage from the rotor flux derivatives to define a rotating vector to align with, even if such variables are not directly measured. Input-to-State Stability properties are proven for suitably defined electrical and magneto-mechanical observation-error subsystems. Time scale separation is, then, exploited to invoke Singular Perturbation arguments and guarantee boundedness of the observation errors trajectories. Finally, the Small Gain Theorem is adopted to prove semiglobal uniform asymptotic stability of the presented scheme. Some additional interesting properties are discussed, beside the 'main stream' of the proposed analysis. Simulations indicate the observer can be profitably exploited for induction machines speed sensorless control applications
Control of Shunt Active Filters with Actuation and Current Limits
No full textIn this brief, a plug-in unit is presented to manage control voltage saturation and maximum current limit in shunt active filters (SAFs), where unconstrained control algorithms are already defined. The proposed unit extends the operating region of such devices, i.e., under large transients and overload conditions, with performance guarantees. Therefore, improved robustness, availability, and composability of SAFs are obtained. The solution is composed of two parts. An antiwindup (AW) unit is defined to deal with control input saturation by modifying the current references through a suitably designed additional dynamics. In addition, a current saturation strategy is formulated. Again the current reference is modified, accounting for the limitations of the system, augmented with the AW scheme. The approach is valid for any kind of unconstrained controller adopted to steer SAFs. Here, results are presented considering an internal-model-based current controller. Simulation and experimental tests confirm the effectiveness of the method
Increasing the operating area of shunt active filters by advanced nonlinear control
No full textThis work is aimed to rigorously manage voltage saturation and maximum current constraints in Shunt Active Filters. In this
respect, assuming “unconstrained” control algorithms have already been defined to achieve standard objectives for such devices
(i.e. current tracking for harmonic compensation and DC-bus voltage boundness), a plug-in unit, oriented to extend the system
operating region and at the same time preserving good performance under large transients and overload conditions, is presented.
This solution allows to improve availability, robustness and composability of Shunt Active Filters, which are expected to be key
features in present and next generation complex and possibly “smart” power grids. The proposed unit is composed by two parts.
First, a suitable anti-windup strategy is defined in order to deal with control input saturation. Its main purpose is to preserve the
original “unconstrained error dynamics”, in face of input saturation, while guaranteeing low computational burden and reduced
performance impairment (the latter goal, in harmonic compensation context, leads to rather non-standard problem formulation).
To this aim, the anti-windup acts on the current references through a suitably-designed additional dynamics. Then, in order to cope
with current limitations, an additional strategy has been designed; again the current references is suitably shaped to comply with
the features and bounds of the system, augmented with the above-mentioned anti-windup solution. The proposed scheme can be
simply joined to any kind of unconstrained controller adopted to steer Shunt Active Filters. In this work, an Internal-Model-based
current controller is adopted as a benchmark case. The proposed approach is validate through extensive simulation tests
Towards sensorless observers for sinusoidal electric machines with variable speed and no mechanical model: A promising approach for PMSMs
No full textOne of the major issues in developing sensorless observers for AC Sinusoidal Machines, and for all kinds of Electric Machines, is to deal with variable speed relying only on the electromagnetic model, without using any mechanical information. In this paper, the case of Permanent Magnet Synchronous Machines is considered as first benchmark. A novel and promising design strategy is presented to develop a simple sixth-order observer for estimating rotor speed/position and magnetic flux amplitude, in the context of non-zero variable speed, with unknown constant sign and bounded derivative. This framework does not cover yet any arbitrarily-varying mechanical speed, but it goes far beyond the typical simplifying assumption of “slowly-varying speed”, which is actually meant as “constant speed” in the common theoretical analysis. In the proposed method, the rotation dynamics of the machine back-electromotive force is represented by means of the Lie Groups formalism, and no open-loop integration of stator voltages and currents is adopted. Lyapunov-like and Singular Perturbations techniques are then exploited to achieve regional practical asymptotic stability, with a very wide region of attraction. The mild limitations on such stability domain are carefully analyzed and discussed. Numerical simulations are provided to show the effectiveness of the proposed observer, under heavily variable mechanical speed. Finally, taking cue from the features of the presented approach, future steps are outlined in order to further weaken the restrictions on the speed variations and to extend the results to other electric machines
An effective control solution for doubly-fed induction generator under harsh balanced and unbalanced voltage sags
No full textThis paper presents a novel control algorithm for the rotor-side converter of Doubly-Fed Induction Generators. The main goal is to endow the system with effective Low Voltage Ride Through capability, under harsh balanced and unbalanced grid voltage sags, without relying on dedicated auxiliary hardware, which is commonly adopted to sustain severe line faults. In this respect, nonlinear control theory arguments are applied to design a controller capable of mitigating oscillations (particularly on rotor currents and voltages) arising during line faults, therefore preventing the system from disconnecting for protection. The proposed solution adopts both feedforward and feedback terms. The former stems from a thoughtful analysis of the system internal dynamics, taking into account the effects of line voltage perturbations, which is exploited to design feasible state trajectories for the generator electromagnetic variables. Specifically, such references do not contain poorly-damped oscillatory modes of the machine natural dynamics, expressed in synchronously rotating frames (such components turn into slowly varying DC ones in a stationary frames). Then, a state feedback unit is designed according to modern saturated control techniques, accounting for constraints on rotor voltage, and steering real variables toward references, where priority given to rotor currents, to avoid rotor-side converter tripping due to overcurrent. In addition, a non standard line voltage reconstruction and dip detection scheme, based on adaptive state observers, is designed, to reliably cope with challenging faulty conditions. Detailed numerical simulations validate the proposed method benefits under severe symmetric and asymmetric dip scenarios
State reference design and saturated control of doubly-fed induction generators under voltage dips
No full textIn this paper, the stator/rotor currents control problem of doubly-fed induction generator under faulty line voltage is carried out. Common grid faults cause a steep decline in the line voltage profile, commonly denoted as voltage dip. This point is critical for such kind of machines, having their stator windings directly connected to the grid. In this respect, solid methodological nonlinear control theory arguments are exploited and applied to design a novel controller, whose main goal is to improve the system behaviour during voltage dips, endowing it with low voltage ride through capability, a fundamental feature required by modern Grid Codes. The proposed solution exploits both feedforward and feedback actions. The feedforward part relies on suitable reference trajectories for the system internal dynamics, which are designed to prevent large oscillations in the rotor currents and command voltages, excited by line perturbations. The feedback part uses state measurements and is designed according to Linear Matrix Inequalities (LMI) based saturated control techniques to further reduce oscillations, while explicitly accounting for the system constraints. Numerical simulations verify the benefits of the internal dynamics trajectory planning, and the saturated state feedback action, in crucially improving the Doubly-Fed Induction Machine response under severe grid faults
Energy-aware cooling for hot-water cooled supercomputers
No full textHot-water liquid cooling is a key technology in future green supercomputers as it maximizes the cooling efficiency and energy reuse. However the cooling system still is responsible for a significant percentage of modern HPC power consumption. Standard design of liquid-cooling control relies on rules based on worst-case scenarios, or on CFD simulation of portion of the entire system, which cannot account for all the real supercomputer working conditions (workload and ambient temperature). In this work we first introduce an analytical model, based on lumped parameters, which can effectively describe the cooling components and dynamics, and can be used for analysis and control purposes. We then use it to design an energy-optimal control strategy which is capable to minimize the pump and chiller power consumption while, meeting the supercomputer cooling requirements. We validate the method with simulation tests, taking data from a real HPC cooling mechanism, and comparing the results with state-of-the-art commercial cooling system control strategies
Modeling the Thermal and Power Control Subsystem in HPC Processors
No full textIn the last decade, high-performance multi-core processors have become pervasive. Processors with high cores count, multi-die SoC configuration with multiple heterogeneous units, and accelerators are commonplace today, while tailored and specific operating points are required for efficient execution of applications. In this scenario, an advanced and configurable Power Controller System (PCS) is essential to meet power and thermal constraints, as it is not effective to rely on simple reactive control policies with static conservative margins on the operating points. This paper provides a mathematical model of an HPC processor and the different control approaches implemented in state-of-the-art PCS solutions. In particular, we are comparing the performance of a custom cascade model-based control algorithm that favors cores executing more demanding workloads with the IBM Power9 control algorithm used as a reference design. The results show an average increase in the number of retired instructions of 3.46 %, with a peak of 6.45 % increase for the cores executing more demanding instructions. - Modeling, Simulation, Nonlinear system
Integrated Energy-Aware Management of Supercomputer Hybrid Cooling Systems
No full textAdvanced cooling systems and optimization strategies are critical to operate modern supercomputers and high-performance computing systems in an energy-efficient fashion. Hybrid architectures combining emerging liquid cooling with traditional air cooling are a promising solution. Standard management techniques maintain these systems at fixed operating points, typically without coordination between the diverse cooling knobs. In this paper, we propose an energy-aware optimization strategy exploiting heterogeneous cooling systems in a holistic fashion with the goal of minimizing the overall cooling system power consumption, while at the same time meeting the system thermal constraints. To this purpose, we developed a modeling approach to build a low-order analytical model, which captures the overall thermal behavior of the system. Then, this compact and computationally manageable model is exploited to set and solve a treatable optimization problem, leading to definition of an energy-optimal cooling strategy. The proposed method is presented taking Galileo as real-life case study. Galileo is a high-performance computing system with hybrid cooling architecture recently installed at CINECA (a supercomputing facility located in Italy). The cooling strategy resulting from the proposed approach is compared with common strategies in order to assess the efficiency advantages
- …
