HUANUCO

No resulta novedoso, pero sí práctico, recordar que el contrato de trabajo, como los seres vivos, tiene un ciclo vital y certero: uno y otros nacen, se desarrollan, afrontan vicisitudes y finalmente mueren. La suspensión es precisamente una de sus contingencias naturales, la más frecuente y necesaria, y acaso hasta deseable.

Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line-commutated rectifiers as a source of variable dc power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2-kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations.

Current-source-inverter-based uninterruptible power supplies and V =f V =f V =f-controlled induction motor drives require sensing of two or more load voltages in addition to the dc voltage sensors used for protection purposes. This paper proposes a digital-signal-processor (DSP)-based load voltage control scheme that requires only information provided by the dc-bus voltage sensor. Load voltage estimation is based on ac line voltage reconstruction by means of a recursive least-square error algorithm that uses the information available on the dc bus and knowledge of the pulsewidth modulation gating pattern. Thus, the system minimizes the transducer count and, therefore, enhances reliability and ruggedness. Experimental results show that the load voltage can be reconstructed and its rms value controlled for a wide range of operating conditions with errors of at most 4%. Moreover, the use of the space-vector modulation technique ensures a reduced load voltage harmonic distortion, which remains within the 5% range at nominal voltage and for all load conditions. The paper presents the DSP algorithms required for the operation of the system and key experimental results obtained on a three-phase 208-V 60-Hz 2-kVA prototype unit.

This paper presents an overview analysis and a discussion of field experience with different drive configurations used in shovel applications. The analysis includes different drive topologies, shovel duty cycles for a typical truck pass loading, and energy regeneration capabilities. Special attention is given to the interaction between the high power shovel drives and the grid: harmonics injection, reactive power requirements, and voltage regulation. This paper presents operational experiences obtained in copper mine industries. The main characteristics of the newest shovels with active front end (AFE) at the line side are also included. Finally, a critical evaluation of the different topologies is presented, showing that the shovel drive operation strongly affects the behavior of the power distribution system and that the introduction of the AFE technology produces an important performance improvement.

Standard low-and medium-power induction motor drives are based on the pulsewidth modulation (PWM) voltagesource inverter fed from a diode rectifier. The dual topology, based on the current-source inverter/rectifier structure is used in medium-and high-power applications. This paper analyzes the existing motor drives based on current-source topologies and proposes a control strategy that addresses some of the drawbacks of this approach compared to the voltage-source approach. The proposed strategy features the following: 1) an on-line operated

In this paper, a phase-locked loop algorithm appropriated for digital-signal-processor-based control implementations, where the operation of a static-power converter needs to be synchronized with an ac network, is presented. The proposed algorithm includes a multiplier, a filter, a feedback closed loop, and a numerically controlled oscillator stage. As a result, a discrete sine (and cosine) signal is generated in synchronism with the fundamental component of an external-reference (ER) signal. Moreover, the sampling period of the algorithm is adjusted at each sampling instant such that an integer number of sampling periods per period of the ER signal is ensured. This is the main feature, and it is achieved by using a discrete rectangular window filter and a discrete controller. The proposed algorithm code is simple, stable, and presents high noise rejection. A comprehensive theoretical justification and various rigorous experimental tests are included.

A new modulation and control strategy for a matrix converter induction motor drive is presented in this paper. A discrete model of the converter, motor and input filter is used to predict the behaviour of torque, flux and input power of the system. The switching state that optimizes the value of a quality function is selected. The predictive control method, referred to as Predictive Torque Control for Matrix Converters is introduced in this paper, including a strategy to control the input power factor. One of the fundamental differences that the proposed approach presents is that it considers all valid voltage vectors generated by a matrix converter, including rotating vectors that are neglected by most control strategies.

A simple control scheme for hybrid active power filters connected in parallel is presented and analysed. The hybrid active power filter combines the compensation characteristics of resonant passive and active power filters. The series active power filter is implemented with a three-phase pluse-width modular (PWM) voltage-source inverter. The proposed scheme is able to compensate displacement power factor and current harmonics simultaneously. The combination of passive and active power filters allows a better performance compensation of high-power nonlinear loads. The proposed control scheme is discussed in terms of principles of operations under steady-state and transient conditions. The design and implementation of the power and control circuits are reported.

This paper presents the performance analysis of a hybrid filter composed of passive and active filters connected in series. The analysis is done by evaluating the influence of passive filter parameters variations and the effects that different active power filter's gain have in the compensation performance of the hybrid scheme. The compensation performance is quantified by evaluating the attenuation factor in a power distribution system energizing high-power nonlinear loads compensated with passive filters and then improved with the connection of a series active power filter. Finally, compensation characteristics of the hybrid topology are tested on a 10-kVA experimental setup.

Multi-cell power circuit topologies have probed to be an effective alternative to medium-voltage AC drives. Commercial units are built up based on modular units, namely cells, which are composed of a three-phase diode-based front-end rectifier, a DC link electrolytic capacitor, and a single-phase fullwave voltage-source inverter. The main advantage is the improved power quality at both AC system and motor sides. However, two drawbacks are present in these configurations. These are: (a) the single-phase operation of the inverter in each cell generates a large second current harmonic that is injected back into the DC link capacitor, thus, a large electrolytic capacitor has to be used in order to guarantee a reduced voltage ripple across it; and (b) the three-phase diode-based front-end rectifier does not provide the regenerative operating mode as required, for instance, by down-hill belt conveyors in mining applications, where this operating mode is the normal one. This paper proposes to replace the diode-based front-end rectifier by an active front-end rectifier and a novel control strategy in order to overcome the aforementioned drawbacks. In fact, the active front-end rectifier allows the topology to regenerate and the control strategy removes the large second current harmonic from the DC link capacitor, thus reducing its size. Both features are achieved without any penalties in the quality of the waveforms. Simulated results confirm the theoretical considerations.

New regulations impose more stringent limits on current harmonics injected by power converters that are achieved with pulsewidth-modulated (PWM) rectifiers. In addition, several applications demand the capability of power regeneration to the power supply. This paper presents the state of the art in the field of regenerative rectifiers with reduced input harmonics and improved power factor. Regenerative rectifiers are able to deliver energy back from the dc side to the ac power supply.

This paper presents the implementation of a predictive control scheme for an indirect matrix converter. The control scheme selects the switching state that minimizes the reactive power and the error in the output currents according to their reference values. This is accomplished by using a prediction horizon of one sample time and a very intuitive control law. Experimental results with a 6.8-kVA indirect matrix converter prototype are provided in order to validate the proposed control scheme. The converter uses standard digital signal processor operating at a sampling frequency of 20 μs. It is shown that the idea of controlling this converter topology with a predictive approach can be implemented simply and input currents with unity power factor and a total harmonic distortion lower than 5% can be obtained.

A simple control scheme for hybrid active power filters connected in parallel is presented and analyzed in this paper. The hybrid active power filter combines the compensation characteristics of resonant passive and active power filters. The series active power filter is implemented with a three-phase PWM voltage-source inverter. The proposed scheme is able to compensate displacement power factor and current harmonics simultaneously. The combination of passive and active power filters allows a better performance compensation of high power voltage nonlinear loads. The proposed control scheme is discussed in terms of principles of operations under steady state and transient conditions. The design and implementation of the power and control circuits are reported. Finally, key predicted results are verified experimentally on a 5 kVA prototype model

On-line pulsewidth modulation (PWM) pattern generators for current-source rectifiers and inverters offer a number of control advantages over off-line optimized patterns. However, when implemented using the principles which apply to voltagesource inverter PWM pattern generators, the switching frequency is equal to: 1) the carrier frequency in standard carrier-based implementations and 2) a function of the cycle frequency, sequence of space vectors, and selection of the zero space vector in space vector implementations. This paper shows that this frequency can be reduced to one-half of the respective frequencies. Two pattern generators are investigated: 1) an analog on-line carrier-based technique, namely, the modified dead-band technique and 2) a digital on-line space vector-based technique, where advantage is taken of the extra zero state available in current-source converters. It is shown that the switching frequency reduction is achieved with no penalty in the line current harmonic distortion. Moreover, a significant reduction of ac line current distortion is obtained with the modified dead-band technique for modulation indexes greater than 0.4. The principles of operation of the proposed schemes are explained. Experimental results on a 5-kVA current-source rectifier and a 5-kVA current-source inverter confirm the feasibility and features of the proposed pattern generators.

Harmonics are a very important issue in the design and operation of medium voltage inverter drives due to restrictions imposed by regulations. This paper studies the harmonics generated in a three-phase cascaded multi-cell inverter with single-phase active front end (AFE) at the input side of each cell. This study identifies accurately the origin of the harmonics present in the DC link voltage and in the input currents and discusses methods to reduce and, in some cases, eliminate them. It has been established that the low-frequency harmonics in the primary input current can be cancelled by an appropriate interconnection of the cells and of the input transformer.

This paper proposes a simple linear feedback-based control technique that ensures zero-neutral-point (NP) potential in three-level voltage-source inverters. The technique works even under dynamic load conditions and enables the decoupled control of the direct and in-quadrature load currents. The technique is based on the relative-gain-array (RGA) approach, which has been successfully used in the control of chemical-engineering processes. The resulting scheme allows the use of outer control loops to set the direct and in-quadrature load currents as required for the specific application (e.g., adjustable speed drives). Experimental results prove the theoretical considerations and show the simplicity of the proposed control scheme.

Multicell power circuit topologies have proved to be an effective alternative to medium-voltage ac drives. The main advantage is the improved power quality at both the ac system and the motor sides. However, several drawbacks are present in these configurations, such as a lack of sustained regenerative operating mode, uncontrolled input reactive power, and a large second current harmonic that is injected by the load into the dc link of each cell, which leads to a bulky electrolytic capacitor. This paper proposes to replace the input diode-based front-end rectifier with an active front-end rectifier in all cells of the topology and a novel control strategy in order to overcome the aforementioned drawbacks. In fact, the active front-end rectifier allows the topology to regenerate and the control strategy handles the reactive input power and reduces the large second current harmonic from the dc-link capacitor, thus reducing its size. These features are achieved without any penalties in the quality of both the ac input current and the motor voltage waveforms. Experimental results confirm the theoretical considerations.