Application of sliding-mode control to the design of a buck-based sinusoidal generator

This paper is devoted to the design of a sliding-mode control scheme for a buck-based inverter, with programmable amplitude, frequency, and DC offset, with no external sinusoidal reference required. A general procedure for obtaining an autonomous (time independent) switching surface from a time-dependent one is presented. For this surface, the system exhibits a zeroth-order dynamics in sliding motion. On the other hand, from the sliding-domain analysis, a set of design restrictions is established in terms of the inverter output filter Bode diagram and the output signal parameters (amplitude, frequency and DC offset), facilitating the subsequent design procedure. The control scheme is robust with respect to both power-stage parameter variations and external disturbances and can be implemented by means of conventional electronic circuitry. Simulations and experimental results for both reactive and nonlinear loads are presented.Peer ReviewedPostprint (published version

Application of Sliding Mode Control to the design of a Buck-based sinusoidal Generator

This paper is devoted to the design of a sliding-mode control scheme for a buck-based inverter, with programmable amplitude, frequency, and dc offset, with no external sinusoidal reference required. A general procedure for obtaining an autonomous (time independent) switching surface from a time-dependent one is presented. For this surface, the system exhibits a zeroth-order dynamics in sliding motion. On the other hand, from the sliding-domain analysis, a set of design restrictions is established in terms of the inverter output filter Bode diagram and the output signal parameters (amplitude, frequency and dc offset), facilitating the subsequent design procedure. The control scheme is robust with respect to both power-stage parameter variations and external disturbances and can be implemented by means of conventional electronic circuitry. Simulations and experimental results for both reactive and nonlinear loads are presented.Peer Reviewe

Sliding-Mode Control Design of a Boost-Buck Switching Converter for AC Signal Generation

This paper presents a sliding-mode control design of a boost–buck switching converter for a voltage step-up dc–ac conversion without the use of any transformer. This approach combines the step-up/step-down conversion ratio capability of the converter with the robustness properties of sliding-mode control. The proposed control strategy is based on the design of two slidingcontrol laws, one ensuring the control of a full-bridge buck converter for proper dc–ac conversion, and the other one the control a boost converter for guaranteeing a global dc-to-ac voltage step-up ratio. A set of design criteria and a complete design procedure of the sliding-control laws are derived from small-signal analysis and large-signal considerations. The experimental results presented in the paper evidence both the achievement of step-up dc–ac conversion with good accuracy and robustness in front of input voltage and load perturbations, thus validating the proposed approach.Peer Reviewe

Control of power electronic interfaces in distributed generation.

Renewable energy has gained popularity as an alternative resource for electric power generation. As such, Distributed Generation (DG) is expected to open new horizons to electric power generation. Most renewable energy sources cannot be connected to the load directly. Integration of the renewable energy sources with the load has brought new challenges in terms of the system’s stability, voltage regulation and power quality issues. For example, the output power, voltage and frequency of an example wind turbine depend on the wind speed, which fluctuate over time and cannot be forecasted accurately. At the same time, the nonlinearity of residential electrical load is steadily increasing with the growing use of devices with rectifiers at their front end. This nonlinearity of the load deviates both current and voltage waveforms in the distribution feeder from their sinusoidal shape, hence increasing the Total Harmonics Distortions (THD) and polluting the grid. Advances in Power Electronic Interfaces (PEI) have increased the viability of DG systems and enhanced controllability and power transfer capability. Power electronic converter as an interface between energy sources and the grid/load has a higher degree of controllability compared to electrical machine used as the generator. This controllability can be used to not only overcome the aforementioned shortfalls of integration of renewable energy with the grid/load but also to reduce THD and improve the power quality. As a consequence, design of a sophisticated controller that can take advantage of this controllability provided by PEIs to facilitate the integration of DG with the load and generate high quality power has become of great interest. In this study a set of nonlinear controllers and observers are proposed for the control of PEIs with different DG technologies. Lyapunov stability analysis, simulation and experimental results are used to validate the effectiveness of the proposed control solution in terms of tracking objective and meeting the THD requirements of IEEE 519 and EN 50160 standards for US and European power systems, respectively

Control por histéresis para un inversor buck-dual conectado a la red

Single-phase inverters are widely used in different renewable energy applications. Although the full-bridge inverter is typically used, dual-buck inverters provide an important advantage, since they eliminate the shoot-through problems. However, solutions proposed in the literature require additional inductors, use linear controllers designed around an operation point, or cannot be used in grid-connected applications. This paper presents a hysteresis current control of a single-phase dual-buck full-bridge inverter for grid-connected active power injection. Includes the dynamical model in state variables, as well as analytical conditions to guarantee the evolution of the error dynamics in a set with boundaries defined by the designer. Moreover, the paper provides guidelines for the design of the dead band required for the transitions between the positive and negative semi-cycles (and vice-versa) of the grid voltage. Finally, simulation results validate the main features of the controller as well as the design of the dead band.Los inversores monofásicos son ampliamente usados en diferentes aplicaciones de energías renovables. Aunque típicamente se usa el inversor de puente completo, el inversor buck-dual provee una ventaja  importante porque elimina el problema de posibles cortos-circuitos. Sin embargo, las soluciones reportadas en la literatura requieren inductores adicionales, usan controladores lineales diseñados para un punto de operación, o no se pueden usar en aplicaciones de conexión a la red. En este artículo se presenta un control por histéresis para un inversor monofásico buck-dual de puente completo con conexión a la red para inyección de corriente activa. En particular, se presenta el modelo matemático en variables de estado y se obtienen condiciones analíticas para garantizar la evolución de la dinámica de error dentro de un conjunto con límites establecido por el diseñador. Además, se discuten los elementos para diseñar la banda muerta requerida en la transición entre los semi-ciclos positivos y negativos de la tensión de la red. Finalmente, los resultados de simulación validan las principales características del controlador propuesto, así como el diseño de la banda muerta

A Fixed-Frequency Quasi-Sliding Control Algorithm: Application to Power Inverters Design by Means of FPGA Implementation

In this paper a fixed-frequency quasi-sliding control algorithm based on switching surface zero averaged dynamics (ZAD) is reported. This algorithm is applied to the design of a Buck-based inverter, and implemented in a laboratory prototype by means of a field programmable gate array (FPGA), taking into account processing speed versus computational complexity trade-off. Three control laws, namely sliding control (SC), fixed-frequency quasi-sliding ZAD and PWM-based control have been experimentally tested to highlight the features of the proposed algorithm. According to the experimental results presented in the paper, the ZAD algorithm fulfills the requirement of fixed switching frequency and exhibits similar robustness properties in the presence of perturbations to those of sliding control mode.Peer Reviewe

Power Management Strategies for a Wind Energy Source in an Isolated Microgrid and Grid Connected System

This thesis focuses on the development of power management control strategies for a direct drive permanent magnet synchronous generator (PMSG) based variable speed wind turbine (VSWT). Two modes of operation have been considered: (1) isolated/islanded mode, and (2) grid-connected mode. In the isolated/islanded mode, the system requires additional energy sources and sinks to counterbalance the intermittent nature of the wind. Thus, battery energy storage and photovoltaic (PV) systems have been integrated with the wind turbine to form a microgrid with hybrid energy sources. For the wind/battery hybrid system, several energy management and control issues have been addressed, such as DC link voltage stability, imbalanced power flow, and constraints of the battery state of charge (SOC). To ensure the integrity of the microgrid, and to increase its flexibility, dump loads and an emergency back-up AC source (can be a diesel generator set) have been used to protect the system against the excessive power production from the wind and PV systems, as well as the intermittent nature of wind source. A coordinated control strategy is proposed for the dump loads and back up AC source. An alternative control strategy is also proposed for a hybrid wind/battery system by eliminating the dedicated battery converter and the dump loads. To protect the battery against overcharging, an integrated control strategy is proposed. In addition, the dual vector voltage control (DVVC) is also developed to tackle the issues associated with unbalanced AC loads. To improve the performance of a DC microgrid consisting wind, battery, and PV, a distributed control strategy using DC link voltage (DLV) based control law is developed. This strategy provides simpler structure, less frequent mode transitions, and effective coordination among different sources without relying on real-time communication. In a grid-connected mode, this DC microgrid is connected to the grid through a single inverter at the point of common coupling (PCC). The generated wind power is only treated as a source at the DC side for the study of both unbalanced and balanced voltage sag issues at a distribution grid network. The proposed strategy consists of: (i) a vector current control with a feed-forward of the negative-sequence voltage (VCCF) to compensate for the negative sequence currents; and (ii) a power compensation factor (PCF) control for the VCCF to maintain the balanced power flow between the system and the grid. A sliding mode control strategy has also been developed to enhance the overall system performance. Appropriate grid code has been considered in this case. All the developed control strategies have been validated via extensive computer simulation with realistic system parameters. Furthermore, to valid developed control strategies in a realistic environment in real-time, a microgrid has been constructed using physical components: a wind turbine simulator (WTS), power electronic converters, simulated grid, sensors, real-time controllers and protection devices. All the control strategies developed in this system have been validated experimentally on this facility. In conclusion, several power management strategies and real-time control issues have been investigated for direct drive permanent magnet synchronous generator (PMSG) based variable speed wind turbine system in an islanded and grid-connected mode. For the islanded mode, the focuses have been on microgrid control. While for the grid-connected mode, main consideration has been on the mitigation of voltage sags at the point of common coupling (PCC)

Advances in Control of Power Electronic Converters

This book proposes a list of contributions in the field of control of power electronics converters for different topologies: DC-DC, DC-AC and AC-DC. It particularly focuses on the use of different advanced control techniques with the aim of improving the performances, flexibility and efficiency in the context of several operation conditions. Sliding mode control, fuzzy logic based control, dead time compensation and optimal linear control are among the techniques developed in the special issue. Simulation and experimental results are provided by the authors to validate the proposed control strategies

Single-Phase Bi-directional Ćuk Inverter for Battery Applications

Bidirectional inverters are widely applied in photovoltaic and wind systems that require battery power backup. They are advantageous over unidirectional inverters because of their ability to convert DC power into AC power and then AC power back into DC power to recharge for storage purposes. Generally, bidirectional inverters are designed to have multiple power stages and/or make use of transformers for isolation and voltage/current gain. This usually increases the cost of production and oftentimes reduces the efficiency of the system. At the same time, attempts at eliminating usage of transformers and reduction in the number of power stages limits the range of bidirectional inverters’ capabilities. This is because battery applications today require low voltage DC-AC inverters with AC-DC power flow capability to store energy for later use. As such, only buck-boost based topologies are majorly being proposed and used for this functionality. The buck boost converter is the most widely used in such applications because of its higher efficiency, low component count and simple structure. It has drawbacks, however, such as: pulsating input and output currents - this leads to lower high electromagnetic interference; lower power factor during AC-DC power flow rectification when the batteries are being recharged; and external filter is also required during this power flow to keep the charging voltage constant. This research proposes a bidirectional inverter that attempts to overcome the drawbacks of the widely used buck-boost converter-based topology. The bidirectional inverter proposed in this work is based on a bidirectional Ćuk converter. The Ćuk converter has both continuous input and output currents. A galvanic isolation option on a Ćuk converter is simpler than a buck boost converter - this is important for grid tied systems. The inverter is based on a pseudo DC-link architecture - it uses a front end Ćuk converter cascaded with an unfolding bridge to convert DC power into AC power. The switches in the converter stage are switched at high frequency, while the switches in the unfolding stage are switched slower at the grid frequency. This configuration is desirable over the two-stage topologies because the switching losses in the unfolding bridge are lower because of this low switching frequency used. This configuration also ensures good switch utilization at the unfolding stage by lowering the parasitic effects on the power transfer. The proposed inverter has 4 modes of operation: during modes I and II the power is positive, and it converts DC power into AC power; during modes III and IV the power is negative, and it converts AC power back into DC power. The inverter is designed such that during DC-AC power flow, the input and output inductor currents and coupling capacitor voltage are continuous for improved efficiency. During the AC-DC power flow, the coupling capacitor voltage is discontinuous to achieve a higher input power factor by improving the AC line current, thereby simultaneously increasing the efficiency. The inverter was analysed in terms of: the dead time inserted into the switches to avoid shoot through and shortcircuiting switches; the parasitic effects on the power transfer ratio. Because the Cúk inverter is a high order system, several robust control strategies, such as sliding mode and current control have been proposed. These control methods require complex theory and present practical challenges to be reviewed. As such a new nested loop control strategy was proposed based on the dynamics of the coupling capacitor as the primary energy storage in the Cúk inverter. The control strategy uses 2 loops: an inner current loop and an outer voltage loop. Lead compensators were designed for both the current and voltage loops to achieve good dynamic response at a high bandwidth. Both simulated and experimental results showed that the bidirectional inverter was able to meet the design specifications. The control strategy showed good dynamic response and disturbance rejection under several inverter variations. Although the efficiency during simulations was above 96%, the experimental efficiency dropped significantly because the inverter was built on a Vero board for easy manipulation. The AC input power factor was > 0.95 for both simulated and experimental results