Hernan Miranda

Predictive Torque Control of Induction Machines Based on State-Space Models

In this paper, we present a predictive control algorithm that uses a state-space model. Based on classical control theory, an exact discrete-time model of an induction machine with time-varying components is developed improving the accuracy of state prediction. A torque and stator flux magnitude control algorithm evaluates a cost function for each switching state available in a two-level inverter. The voltage vector with the lowest torque and stator flux magnitude errors is selected to be applied in the next sampling interval. A high degree of flexibility is obtained with the proposed control technique due to the online optimization algorithm, where system nonlinearities and restrictions can be included. Experimental results for a 4-kW induction machine are presented to validate the proposed state-space model and control algorithm.

Design of fast and robust current regulators for high-power drives based on complex state variables

High-power pulsewidth-modulated inverters for medium-voltage applications operate at switching frequencies below 1 kHz to keep the dynamic losses of the power devices at a permitted level. Also, the sampling rate of the digital signal processing system is then low, which introduces considerable signal delays. These have adverse effects on the dynamics of the current control system and introduce undesired cross coupling between the current components i/sub d/ and i/sub q/. To overcome this problem, complex state variables are used to derive more accurate models of the machine and the inverter. From these, a novel current controller structure employing single-complex zeros is synthesized. Experimental results demonstrate that high dynamic performance and zero cross coupling is achieved even at very low switching frequency.

Technical evaluation and practical experience of high-power grinding mill drives in mining applications

Grinding mill drives play an important role in the mining industry. Almost 60% of the electrical energy consumed by modern concentrator plants goes to grinding mill drives. Different technologies are used in grinding systems presenting special characteristics from the electrical and process points of view. This paper presents a technical evaluation and practical experience of two different technologies used in high-power grinding mill drives. The analysis is focused on the static power converter and associated control scheme required to drive the motor. Cycloconverters and load-commutated inverters are analyzed in terms of power grid interaction, motor interaction, and the required control scheme. The evaluation is supported with practical results obtained in different concentrator plant facilities.

Recent advances in mining haul trucks

Electric mining haul trucks are one of the most challenging applications of power electronics in automotive systems. This paper presents some advances in very-high-power trucks used in copper mines. The special operational and environmental requirements for this application are highlighted. It is established that the use of inverter-fed three-phase induction motors with vector control is the preferred solution to reach the required high starting torque and good dynamic performance required by these vehicles. Packaging is a key issue and special attention is dedicated to the forced-air cooling system, because the air has a high dust level including conductive and corrosive materials. The trucks high-performance electric retarding system is described along with a novel use of trolley lines in a diesel boost mode as a way to increase the power and speed of the truck and reduce fuel consumption. Advanced features like remote monitoring, the use of global positioning systems and Internet diagnostics and troubleshooting are also discussed. The paper clearly shows that modern electric haul trucks are highly sophisticated systems that make full use of advances in modern technologies to increase safety and productivity levels.

A novel direct torque control scheme for induction machines with space vector modulation

In this paper a new method for direct torque control (DTC) based on load angle control is developed. The use of simple equations to obtain the control algorithm makes it easy to understand and implement. Fixed switching frequency and low torque ripple are obtained using space vector modulation. This control strategy overcomes the most important drawbacks of classic DTC. Results show the feasibility of the proposed method, obtaining good speed control bandwidth while overcoming classic DTC drawbacks.

Model predictive current control for high-power grid-connected converters with output LCL filter

A model predictive control strategy for a highpower, grid connected 3-level neutral clamped point converter is presented. Power losses constraints set a limit on commutation losses so reduced switching frequency is required, thus producing low frequency current harmonics. To reduce these harmonics an LCL filter is used. The proposed control strategy allows control of the active and reactive power fed into the grid, reduce the switching frequency within acceptable operational margins and keep balance of the DC-link capacitor voltages while avoiding excitation of the filter resonance frequencies.

Direct Torque Control With Reduced Switching Losses for Asymmetric Multilevel Inverter Fed Induction Motor Drives

In this paper a high performance torque and flux control strategy for multilevel inverter fed induction motor drives is presented. The control method is based on direct torque control operating principles. The stator voltage vector reference is computed from the stator flux error imposed by the torque controller. This voltage reference is then generated using an asymmetric cascaded H-bridge multilevel inverter. This inverter provides nearly sinusoidal voltages with very low distortion, using less switching devices. Due to the small dv/dts, torque ripple is greatly reduced. In addition, the asymmetric multilevel inverter can generate a high and fixed switching frequency output voltages with less switching losses, since only the small power cells of the inverter operate at high switching rate. Therefore a high performance and also efficient torque and flux controller is obtained, enabling a DTC solution for multilevel inverter powered motor drives

Indirect sensorless speed control of a PMSG for wind application

In this paper, the sensorless control of a permanent magnet synchronous generator (PMSG) for wind turbine applications is presented. This kind of generator has many advantages, such as: high efficiency, high power density and low maintenance requirements. To improve these characteristics in the whole wind generator system a sensorless scheme is proposed, thereby avoiding problems of electromagnetic interferences and failures in the position sensor.

Torque Regulation by Means of Stator Flux Control for Induction Machines

The common characteristic of all direct torque control drives is the manipulation of stator flux by means of the application of an adequate stator voltage. In this work this concept is extended to the pulse width modulated of the correct stator voltage to achieve stator flux regulation and tracking of commanded torque. The strategy is based on a few simplified machine equations based on the principle that torque and load angle are related and that it is possible to control this angle in a rotor oriented coordinate system. High bandwidth control loop can be obtained using this method due to the absence of sources of uncertainty. Simulation and experimental results for a 4[kW] induction machine are presented

Smart — STATCOM control strategy implementation in wind power plants

High penetration of wind energy into the grid may introduce stability and power quality problems due to the fluctuating nature of the wind and the increasing complexity of the power system. By implementing advanced functionalities in power converters, it is possible to improve the performance of the wind farm and also to provide grid support, as it is required by the grid codes. One of the main compliance difficulties that can be found in such power plants are related to reactive power compensation and to keep the harmonics content between the allowed limits, even if the power of the WPP converters is increasing. This paper deals with an advanced control strategy design of a three-level converter performing STATCOM and Active Filter functionalities. The proposed system is called Smart-STATCOM since it has the capability of self-controlling reactive power and harmonic voltages at the same time. Therefore, deciding the amount of non-active currents (fundamental, 5th and 7th harmonics) to be injected depending on the PCC voltage quality. Experimental results of the proposed control strategy are analyzed in order to validate the performance of the entire system.