Reyes S. Herrera

Instantaneous Reactive Power Theory Applied to Active Power Filter Compensation: Different Approaches, Assessment, and Experimental Results

In this paper, the five main formulations of the instantaneous reactive power theory have been chosen to study nonlinear load compensation. They are p-q original theory, d-q transformation, modified or cross-product formulation, p-q-r reference frame, and vectorial theory. The obtention of the compensation current according to each formulation has been established. Next, the behavior of an active power filter (APF) that is implemented with those different control algorithms has been studied. On one hand, a simulation platform with control, APF, and load has been built to test them. Results obtained in an unbalanced and nonsinusoidal three-phase four-wire system have been compared by means of the most adequate indexes. On the other hand, the APF control strategies have been implemented in an experimental platform constituted by a 20-kVA power inverter and a 400-MHz digital signal processing controller board. The final analysis shows that, in general, the five theories present a different behavior, which depends on supply voltage, with respect to distortion. However, all of them widely decrease the waveform distortion. Moreover, a more general compensation objective is possible. It obtains balanced and sinusoidal source current in any conditions of the supply voltage.

Instantaneous Reactive Power Theory: A Comparative Evaluation of Different Formulations

This paper analyses the behavior of different active power filter (APF) control algorithms resulting from five formulations of the instantaneous power theory: p-q original theory, d-q transformation, modified or cross product formulation, p-q-r reference frame and vectorial theory are analyzed. A simulation platform with control + APF + load is built to test the different algorithms. The results obtained in an unbalanced and nonsinusoidal three-phase four-wire system are compared. The final analysis shows that from the five formulations, only the vectorial one allows balanced and sinusoidal source currents after compensation

Instantaneous Reactive Power Theory: A Reference in the Nonlinear Loads Compensation

The instantaneous reactive power theory was published 25 years ago, in an IEEE Transactions. Since then, it has been the most used in nonlinear load compensation with active power filters. Its application allows constant source power to be obtained after compensation in a simple way. Moreover, some researches have showed up some limitations of the theory, i.e., it goes optimally with source voltage balanced and sinusoidal, but not so good with source voltage unbalanced and/or nonsinusoidal, since the source current obtained is not balanced and sinusoidal. This paper presents a new compensation strategy in phase coordinates, equivalent to the original theorys one. Its simplicity, due to the nonnecessity of coordinate mathematical transformation, makes easier the modifications necessary to obtain alternative compensation objectives. In this way, this paper presents those modifications and derives compensation strategies that obtain alternative compensation objectives: unity power factor or balanced and sinusoidal source current. Finally, compensation strategies are applied to a practical power system, and the results are presented.

Distorted and unbalanced systems compensation within instantaneous reactive power framework

p-q theory has been widely used to control active power filters since its formulation in 1983. The compensation strategy used by the p-q theory has not suffered modification; so it used the constant power compensation strategy. In this way, the supply instantaneous power after compensation is constant. This kind of compensation strategy presents good results in the case of balanced and sinusoidal voltages; however, it is not appropriate in the case of unbalanced or nonsinusoidal voltages. This paper extends the p-q theory to get control strategies which allow to attack the unity power factor compensation or the balanced and sinusoidal currents compensation.

New Distortion and Unbalance Indices Based on Power Quality Analyzer Measurements

Voltage and current waveform distortion are more prevalent on power systems today related to nonlinear loads. The proliferation of loads of this kind and their interaction with the power supply system is increasing the need to use power monitoring equipment to evaluate electric power quality. Measurements show that waveform harmonics and unbalance are variable over time due to changes in load conditions and in the system configuration. Thus, the electrical engineer has a large amount of data available from each phase, acquired using commercial Analyzers. Therefore, it is necessary to find ways to characterize this group of recorded data, to allow proper evaluation of the situation. Two indices, which can be calculated with these measurements, are proposed in this work: a three-phase total demand distortion index and a total unbalance index. In addition, this paper proposes an easy way to characterize the time-varying data to simplify their representation. The exposed procedures are applied to the data registered from an electrical power system, to show the performance of the proposed methods.

Easy Handling of Sensors and Actuators over TCP/IP Networks by Open Source Hardware/Software

There are several specific solutions for accessing sensors and actuators present in any process or system through a TCP/IP network, either local or a wide area type like the Internet. The usage of sensors and actuators of different nature and diverse interfaces (SPI, I2C, analogue, etc.) makes access to them from a network in a homogeneous and secure way more complex. A framework, including both software and hardware resources, is necessary to simplify and unify networked access to these devices. In this paper, a set of open-source software tools, specifically designed to cover the different issues concerning the access to sensors and actuators, and two proposed low-cost hardware architectures to operate with the abovementioned software tools are presented. They allow integrated and easy access to local or remote sensors and actuators. The software tools, integrated in the free authoring tool Easy Java and Javascript Simulations (EJS) solve the interaction issues between the subsystem that integrates sensors and actuators into the network, called convergence subsystem in this paper, and the Human Machine Interface (HMI)—this one designed using the intuitive graphical system of EJS—located on the user’s computer. The proposed hardware architectures and software tools are described and experimental implementations with the proposed tools are presented.

Instantaneous Reactive Power Theory to N Wire Systems

The control strategy derived from the instantaneous reactive power theory is one of the most commonly used in the Active Power Filters (APFs). For the last decades other formulations have been developed in order to achieve compensation objectives different to the proposed in the original one. Nevertheless, all of them can be only applied to three-phase systems, i.e.: in those formulations frameworks, they can not be used to obtain the control strategy for a polyphase system. This paper presents a new approach which can be applied to n wire systems. The powers and currents expressions derived from the formulations presented up now can be obtain applying this new approach. In this paper, the original p-q and the modified p-q formulation expressions are obtain in the new approach framework.

A unified power quality conditioner for wide load range: Practical design and experimental results

This paper presents the obtained experimental results with a single-phase experimental prototype of a load compensation active conditioner, sLCAC. The sLCAC is composed by a series-parallel combination of active power filters, to provide a global conditioning of a load against harmonic distortion: to isolate the load voltage vL from the harmonics in the supply voltage vS, as well as to regulate it to the nominal value; and also to enhance the supply current iS, compensating the harmonic and reactive components of the load current iL. Experimental prototype results with two different types of load are presented to support the performance of the proposed design.

A New Control for a Combined System of Shunt Passive and Series Active Filters

A new control algorithm for a hybrid filter formed by a series active filter and a passive filter connected in parallel with the load is proposed. The new control strategy is based on the dual formulation of the vectorial theory of electric power, so that the signal injected by the active filter is able to compensate the reactive power and the harmonics of the load current. To verify the developed theoretical analysis, the proposed control scheme has been simulated in the platform MATLAB-Simulink and applied to a three-phase three-wire system. The simulation results to verify the effectiveness of the proposed control algorithm are presented.

Adaptive backstepping control of a DC-DC converter in photovoltaic systems

This paper presents a new nonlinear control method to regulate the voltage at the output of a DC-DC converter so as to achieve the maximum power point (MPP) of a photovoltaic (PV) system. The proposed adaptive backstepping controller of the system, based on Lyapunov functions to ensure locally stability, is applied to a buck-boost converter. A regression plane is used to initialize reference voltages and to make a modified perturb and observe method (P&O) faster, avoiding local maximum. Therefore, the maximum power extraction of the PV system is guaranteed. This system is grid-connected, thus, a DC-AC converter is connected to the buck-boost converter. The inverter supplies AC current in the point of common coupling (PCC) of the electrical network. The performance of the developed system has been analyzed by means a simulation platform in Matlab/Simulink.