R. Sebastian

Analysis of the Passive Damping Losses in LCL-Filter-Based Grid Converters

Passive damping is the most adopted method to guarantee the stability of LCL-filter-based grid converters. The method is simple and, if the switching and sampling frequencies are sufficiently high, the damping losses are negligible. This letter proposes the tuning of different passive damping methods and an analytical estimation of the damping losses allowing the choice of the minimum resistor value resulting in a stable current control and not compromising the LCL-filter effectiveness. Stability, including variations in the grid inductance, is studied through root locus analysis in the z-plane. The analysis is validated both with simulation and with experiments.

Systematic Design of the Lead-Lag Network Method for Active Damping in LCL-Filter Based Three Phase Converters

Three-phase active rectifiers guarantee sinusoidal input currents and unity power factor at the price of a high switching frequency ripple. To adopt an LCL-filter, instead of an L-filter, allows using reduced values for the inductances and so preserving dynamics. However, stability problems can arise in the current control loop if the present resonance is not properly damped. Passive damping simply adds resistors in series with the LCL-filter capacitors. This simplicity is at the expense of increased losses and encumbrances. Active damping modifies the control algorithm to attain stability without using dissipative elements but, sometimes, needing additional sensors. This solution has been addressed in many publications. The lead-lag network method is one of the first reported procedures and continues being in use. However, neither there is a direct tuning procedure (without trial and error) nor its rationale has been explained. Thus, in this paper a straightforward procedure is developed to tune the lead-lag network with the help of software tools. The rationale of this procedure, based on the capacitor current feedback, is elucidated. Stability is studied by means of the root locus analysis in z-plane. Selecting the lead-lag network for the maximum damping in the closed-loop poles uses a simple optimization algorithm. The robustness against the grid inductance variation is also analyzed. Simulations and experiments confirm the validity of the proposed design flow.

Approaching hybrid wind-diesel systems and controller area network

High wind penetration hybrid wind-diesel systems have complex control requirements. The random nature of the wind, the cubic velocity to power relationship and the fast response of wind turbines make control goals like maintain system stability, and prescribed power quality levels, not easy to achieve. This paper deals with how to implement a distributed control system based on the controller area network (CAN) in hybrid wind diesel systems with high wind penetration. Firstly some introduction to hybrid wind-diesel systems is presented. Secondly two architectures for such hybrid systems are presented and studied mainly from the control point of view. This study concludes with a need of a distributed control, and the definition of some sensor and actuator nodes in the system. The CAN bus is used to close one of the several regulation loops presented. Some considerations about real time distributed control like clock synchronization among nodes when using CAN bus are presented. Finally some advantages of using CAN with such hybrid systems are outlined.

Well-known serial buses for distributed control of backup power plants. RS-485 versus controller area network (CAN) solutions

Networking is increasingly becoming a feature of industrial products such as those for medical devices, vending machines, machine tool, and, the example analyzed here, modular power plants. As many such systems depend on cheap microcontrollers, a common approach to networking has been based on the combination of the available standard serial communication controller (UART) normally included in such devices and RS-485 drivers. However UART-based network protocols do have some potential disadvantages. Controller area network (CAN) offers an attractive alternative due to the availability and low cost of CAN based devices. This paper compares these two approaches in the design of a serial bus, devoted to internal interconnection in a commercial range of modular power backup systems, and describes the migration process from the first to the second solution.

Simulation of a high penetration wind Diesel system with a Ni-Cd battery Energy Storage

High wind penetration Wind Diesel Hybrid Systems (WDHS) have three operation modes: Diesel Only (DO), Wind Diesel (WD) and Wind Only (WO). The WDHS presented in this article consists of a Diesel Engine (DE), a Synchronous Machine (SM), a Wind Turbine Generator, the consumer Load, a Ni-Cd Battery based Energy Storage System (BESS) and a Dump Load. The DE can be engaged (DO and WD modes) or disengaged (WO mode) from the SM by means of a clutch. All the models of the previously mentioned components are presented and the performance of the WDHS has been tested through simulation using the MATLAB-Simulink environment. Simulation results with graphs for the frequency, voltage and active powers for the elements of the Isolated Power System are presented for wind speed changes in WO mode and for the transition from WO to WD mode.

Generalized distributed control system based on CAN bus for wind diesel hybrid systems

High wind penetration wind-diesel hybrid systems (WDHS) have three modes of operation: diesel only (DO), wind diesel (WD) and wind only (WO). A distributed control system (DCS) based on the CAN (controller area network) bus is proposed for diesel generators (DGs) scheduling in DO mode, for active power control in WD mode, for frequency control in WO mode and for reactive power control in the three operation modes. Also it is presented the main message for each of the DCS proposed. Finally it is specified a complete DCS solution for the control of WDHS based on two CAN buses, one high speed CAN bus with the nodes involved in the real time tasks and other low speed CAN bus which links the nodes taking part in the DGs and controllable loads scheduling task.

Decoupled droop control techniques for inverters in low-voltage AC microgrids

This paper discusses the droop control method for inverters participating in low voltage microgrids and its application as a primary control layer which can be actuated from a secondary control layer to dispatch active and reactive power. To that end, an independent and decoupled relationship between frequency and active power; and voltage and reactive power is desirable. When the classic droop control method is applied to inverters connected to the microgrid through RL type impedance, this decoupled actuation is lost. Different variants of decoupled techniques are presented and analyzed from the point of view of static and dynamic behavior. The analysis is supported on a linear dynamic phasor model of the droop controlled inverter, and verified by simulations of behavior in an isolated microgrid and in grid tied mode using a detailed SIMULINK/SimPowerSystems model of the inverter and its internal control. Among the diverse techniques, the recently proposed droop control method with dynamic decoupling is signaled as advantageous, not only in terms of decoupled actuation but also in flexibility in adjustment of static and dynamic response.

Decoupled droop control of inverters

This article first reviews the droop control method for inverters participating in low voltage microgrids, discussing static and dynamic response. Then the paper proposes a droop controller that brings independent actuation of frequency over active power and voltage over reactive power. The method is based on the application of a matrix filter that decouples dynamic actuation and reduces the multivariable system to two independent single input-single output systems. The results of static, dynamic and robustness analysis are given, with a discussion of simulation results. An advantage of this method is that the control loop can be stabilized and tuned by specifics gain parameters that are independent of the droop coefficients and of the coupling impedance of the inverter with the grid. It thus offers maximum freedom and flexibility for adjusting the static and dynamic behavior of droop control.

A systems theory perspective of electronics in engineering education

We briefly review fundamental concepts related to systems theory and systems engineering. We also review and structure a list of important properties for an electronic system and paradigms and techniques applicable to analysis and design. Then we present two specific case studies, in which the systems theory approach to electronics engineering teaching and research has been very influential.

Combining moodle and redmine as e-learning tools in Project Based Learning of Industrial Electronics

This paper reports on the application of the Project Based Learning (PBL) methodology in the teaching of Electronics Instrumentation to undergraduate students using as e-learning platforms the well-known Moodle framework and Redmine, a project management web application. In this PBL implementation each student group develops a different measurement or data acquisition project over the course of an entire academic term, maintaining customer-provider relationships with other groups. In this context, Redmine complements Moodle by providing dynamic time tracking and task management capabilities. In addition PBL is enriched by introducing the students to the use of a project management application.