Alexander Bueno

Optimum Space Vector Computation Technique for Direct Power Control

This study presents an efficient control technique for computing the optimum space-vector voltage in power converters. The presented optimized direct power control (ODPC) provides a closed-form formula for the converter space-vector voltage, which, based on Lagrange operators for the optimum trajectory, provides the commanded complex apparent power. The voltage required by the ODPC is obtained with a standard modulation that synthesizes the mean value required during the control cycle. The converters performance using the ODPC algorithm improves over existing DPC-based algorithms that use constrained optimization, such as preselected space vectors or switching tables, by providing a further harmonic in content reduction, lower computational requirements, and faster time response to changes in active and reactive power commands. The use of the ODPC results in an almost instantaneous active and reactive power reference tracking, allowing for full power inversion in less than 1.0 ms under constant switching operation. Simulation results and experimental verifications are presented to validate the advantages of the proposed control algorithm. The scope of applications of this technique is those that require low harmonic impact on the ac power supply and for power quality improvement in general.

A Simple Switch Selection State for SVM Direct Power Control

This work presents a simple scheme for vector selection in direct power control (DPC) in a three-phase rectifier without the use of switch selection tables. The method is simulated using a C language description of the system and its results are later verified on an experimental test rig. Additional states are obtained using space vector modulation (SVM) which reduce the hysteresis band of the active and reactive power controller

Harmonic and Unbalance Compensation Based on Direct Power Control for Electric Railway Systems

This paper presents a general filtering and unbalance compensation scheme for electric traction systems using a direct power control-based algorithm. For a balanced three-phase three-wire system, the proposed method is able to control the power flow exchange between the grid and the load so that the instantaneous complex power is maintained constant. As a consequence, any nonlinear unbalanced load is seen by the three-phase supply as a balanced linear load. The proposed filter is evaluated on power substations with open delta (V-V) and Scott transformer feeders, and for two-level and dual-converter in the power stage. The scheme has been simulated and experimentally validated. The results from experimental and simulation tests show the controller advantages and the applicability of the proposed method in railway systems.

Power system analysis using space-vector transformation

The space vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and analyze power sources and loads with different connections (delta and wye). this method can also be applied to analyze steady-state or transient phenomena and unbalanced sources, including harm, onics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits.

Direct Power Control of a Dual Converter Operating as a Synchronous Rectifier

This paper presents a dual converter employed as a rectifier with power factor regulation and bidirectional power flow. The active and reactive powers flowing into the converter is controlled using an optimized direct-power-control algorithm. The multilevel structure of the converter is exploited to control the voltage level in each subconverter by selecting the modulation method from one commonly found in the literature, with the option of clamping one of the subconverters. These modulation methods are used to control the power taken by each subconverter, providing limited dc-link voltage regulation. The system is first simulated in SIMULINK, and the results are experimentally validated using a digital-signal-processor-based test rig.

Harmonic and balance compensation using instantaneous active and reactive power control on electric railway systems

This work presents a general filtering and unbalance compensation scheme for electric traction systems. The proposed method uses an active filter controlled with the instantaneous active and reactive power, to reduce the harmonic current distortion and the negative sequence obtained by the system under unbalanced operation in steady state. The proposed filter is evaluated using open delta (V-V) and Scott transformers in the power substation. The scheme has been simulated and experimentally validated. Experimental and simulation results show the controller advantages and the applicability of the proposed method in railway systems.

A Flexible Hardware Platform for Applications in Power Electronics Research and Education

This work presents the design and development of a three-phase multilevel hardware platform for applications in power electronics. The emphasis of the proposed converter is in its flexibility to allow rapid set-ups of different experiments typically required in power electronics teaching and research. The proposed converter uses a cascaded H-bridge topology whereby multilevel operation with up to 9 voltage levels can be obtained. The selected power stage topology as well as the control, drivers and sensors boards designs, enable the platform to operate in multiple configurations, namely as inverter, controlled rectifier or active power filter, for one, two or three-phase systems.

Algorithm evaluation for the optimal selection of the space vector voltage using DPC in power systems

This work presents the experimental evaluation for a new scheme of optimal vector selection (OVS) in direct power control (DPC) for a three-phase rectifier without the use of switch selection tables. The OVS is physically implemented using a software configurable test rig (Platform III). Additional states were added to the standard seven space vectors obtained with a three-phase inverter bridge using space vector modulation (SVM) in order to reduce the hysteresis band of the power controller. Normal operation, model parameter fit, regenerative behavior and comparisons between two different sets of vectors are analyzed.

Advantages of the instantaneous reactive power definitions in three phase system measurement

The spatial vector concept of the instantaneous apparent power is defined. Some advantages obtained using these definitions in measuring power in a three-phase system and in vector control of electrical machines are discussed. Also, a physical interpretation of these definitions is given based on conventional electromagnetic theory.

Squirrel cage induction machine model for the analysis of sensorless speed measurement methods

In this work a squirrel cage induction machine model been developed to include the stator current effects on the MMF space harmonics, dynamic and static eccentricity harmonics, and slot harmonics. The proposed model is intended to be used on testing the behavior of different sensorless speed measurement techniques. This dynamic model has been developed using the superposition principle and a matrix description of the machine inductance. The model has been validated using experimental data, and tested using a time-frequency-distribution method for sensorless speed measurement.