Victor Cardenas

DQ transformation development for single-phase systems to compensate harmonic distortion and reactive power

An extension of the DQ transformation for single-phase systems is presented in this work, since the original approach can only be applied to three-phase systems. The theoretical principle of the proposed transformation is presented. Equations about how the fundamental component and the harmonics of the variable of concern are mapped in the dq reference frame are derived. The proposed transformation is evaluated under ideal and real conditions, and with magnitude and/or phase deviations. Besides, an adequate selection of the reference generator scheme to compensate systems with harmonic distortion and reactive power is made, obtaining an optimal selection of all parameters.

Single-Phase AC-AC Converter Operating as a Dynamic Voltage Restorer (DVR)

This paper presents a single-phase AC-AC matrix converter which is able to compensate voltage harmonics and voltage regulation at critical loads terminals. The converter is composed with the minimum number of switching devices and is controlled using a non-linear law based on passivity achieving a high reliability and robustness during transient and steady state operation condition. The proposed scheme has the advantage that energy storage devices are not required. The converter is connected between the AC mains and the load through a series transformer. A DSP and a FPGA are used to program the passivity-based controller and to determine the state of the switches respectively. In this case, the converter is able to compensate up to 25% voltage sags and 50% voltage swells and to eliminate up to the fifteenth harmonic component. The tested system presents a fast time response and the stabilization time of the load voltage is less than 1 ms. Analysis and modeling as well as simulation and experimental results of a 5 kVA, 127 V, 60 Hz experimental setup are analyzed and presented

Analysis, Design and Control of a Unified Power-Quality Conditioner Based on a Current-Source Topology

This paper presents a three-phase unified power-quality conditioner based on current source converters (CSC-UPQC), including the design guidelines of the key components, an appropriate control scheme, and a selection procedure of the dc current level. Particularly, the ride through capability criterion is used to define a minimum dc current level so that the CSC-UPQC achieves the same characteristics as a UPQC based on voltage-source converters in terms of voltage disturbance compensation in the point of common coupling (PCC) and load power factor compensation. A 1.17 MVA load fed from a 3.3 kV system is used to show the proposed design procedure, and a laboratory prototype is implemented to show the system compensating sags and swells using low switching frequency in the CSC and maintaining a unitary displacement power factor in the PCC.

A hybrid multilevel inverter for shunt active filter using space-vector control

In this paper, a current active power filter using a hybrid asymmetric multilevel inverter is presented and analyzed. The control proposed is based on a vector-control technique, generating an optimized switching pattern. The hybrid multilevel inverter increases the voltage levels number, reducing the harmonics associated to the commutation frequency. The hybrid multilevel inverter is structured by two cascaded-inverters, and the DC link voltage between the stages has the relation 1:3, generating 9 voltage levels. The signal reference is generated using a variant of the single-phase d-q Theory, allowing a fast transient response and stability. Simulated waveforms prove the viability of the control scheme and the multilevel active current filter proposed.

Voltage harmonic cancellation in single-phase systems using a series active filter with a low-order controller

This paper presents a series active filter with a low-order and simple controller, used to cancel the voltage harmonics in single-phase systems. To accomplish this objective, the series active filter is forced to inject the appropriate voltage to the line through a series connected transformer. The active filter is capable to reduce the total harmonic distortion of the AC mains from 11% to 4%, and it presents a fast response velocity. Analysis and modeling are presented as well as simulation and experimental results, which verify the viability of the proposed approach.

Detection of Sags, Swells, and Interruptions Using the Digital RMS Method and Kalman Filter with Fast Response

A fast detection algorithm for sags, swells and interruptions is developed in this paper. The proposed method is based on the combination of the digital RMS technique and the Kalman filter. The union of these methods allows using the main advantages of Kalman filter and RMS techniques and helps rejecting the extreme drawbacks of Kalman filter. The proposed approach can be applied to dynamic voltage restorers, dynamic sag correctors, uninterruptible power supplies, and other compensation topologies for power quality improvement

Decoupled and Modular Harmonic Compensation for Multilevel STATCOMs

A modular and decoupled approach to achieve harmonic cancellation in a multilevel Static Compensator (STATCOM) is presented in this paper. This work shows that it is possible to split the compensation tasks depending on the frequency components present on the line current that is intended to be compensated by using the superposition principle and the modular features of an H-bridge based multilevel STATCOM. This approach allows the implementation of the topology with dedicated modules in order to decouple and simplify the control algorithms. The H-bridge modules can be implemented with two different kinds of semiconductors: (i) slow switches for fundamental frequency compensation modules and (ii) fast switches for harmonic frequency compensation modules. As the modules meant for harmonic cancellation can self-regulate its dc voltage, they can follow the load requirements and thus operate with minimum power. The theoretical analysis is validated in a laboratory prototype.

Voltage disturbances and unbalance compensation by the use of a 3-phase series active filter

The quality of the AC mains and the power transferred from it can be improved by the use of electronic power systems such as active filters. Line perturbations (voltage changes, noise, sags, dips, flicker, harmonics, etc.) can be reduced by the action of a voltage conditioner or a series active filter. This paper is related to the study of a three-phase active filter topology that improves the voltage quality and is capable of working with two phases if any one of the 3 phases is faulted. Energy storage is achieved by a set of capacitors that compensate voltage unbalances among phases within a certain range, without the need of an additional energy source. Furthermore, the present paper presents a compensation method that is programmed in a DSP-based board. Finally, simulation and experimental results are shown.

Practical methods for tuning PI controllers in the DC-link voltage loop in Back-to-Back power converters

This paper provides two options for the design of the Proportional + Integral (PI) controller for the DC-link voltage loop, which is found in several topologies, such as AC/DC voltage source converters and Back-to-Back converters among others. The proposed methods are based in the bandwidth approach. For the design of the DC-link voltage loop, the Back-to-Back topology is used and two cases the studies are analyzed. In the first case the converter controls the power transfer between the mains and the load; in the second it controls the active and reactive power as a PWM Rectifier with active filter function (PWM-VSR-C). In both cases the dq reference frame is used for the design of the controllers. The proposed methods are practical and clearly explained. The designs are validated with simulations and experimental results.

Study of the bidirectional power flow in Back - to - Back converters by using linear and nonlinear control strategies

This paper studies the performance of the Back-to-Back (BTB) power converter based on Voltage Source Converters (VSC) for the management of the bidirectional transference of active power between two interconnected AC systems (the power supply and the load); as well as the bidirectional reactive power (for either generate and/or absorb) in both terminals of the AC interconnected systems. For power flow management two control laws are explored based on the theory of linear and nonlinear control. The nonlinear control is developed based on the feedback linearization approach. Through the two control laws is possible to obtain a decoupled model of the current components (active and reactive) in the dq synchronous reference frame. The power flow control is achieved by independently controlling the active and reactive components of the current. The control scheme includes two cascade loops (nested), for regulating DC-link voltage, as well as active and reactive power; this control scheme is typically used for VSC control, since it allows increasing the control objectives. The performance of the BTB converter for power flow control is demonstrated through simulation and experimental results using a 3kVA BTB power converter.