1,721,164 research outputs found
Three-Phase Multilevel Inverters for LV Systems: Comparison of Modular Multilevel Converter and Flying Capacitor Structures
No full textThe rapid growth of the penetration level of renewable energy sources in low-voltage (LV) networks increases the research interest in more efficient, compact, reliable, and easily expandable energy conversion devices. Thus, multilevel converters, a promising concept for dc-ac conversion, are gaining increased interest due to their smaller size relative to the conventional two-level structure. However, several issues related to the number of components and the added complexity cannot be ignored. To enrich the literature review concerning this topic, this work reviews and provides a comparative assessment of three state-of-the-art multilevel topologies for LV applications. This review considered three structures: state-of-the-art five-level modified MMC (5L-M-MMC), five-level flying capacitor using two three-level flying capacitor converters connected in parallel (2x3L-FC), and five-level flying capacitor (5L-FC). This comparative study is supported by simulation results based on a 10 kW system
A flexible Multi-Active Half-Bridge converter for active balancing of series-connected Li-Ion cells
No full textPassive cell balancing is the most used technique to compensate the voltage mismatch in series-connected Li-Ion batteries, due to cost and simplicity. Active cell balancing is recently gaining more attention as it improves the battery capacity when the battery is ageing and, thus, lifetime when this is determined by the residual capacitance as in the electric transportation sector. This paper proposes a circuit configuration that can perform the active cell balancing using a multi-active half-bridge converter (MAHB) and a multi-winding transformer. The proposed solution has high flexibility due to different operating modes and a relatively simple circuit configuration. Depending on the State Of Charge (SOC) of each cell, the bidirectional power flows can be controlled between two arbitrary cells or between the entire string and a specific cell. A theoretical analysis is firstly carried out in order to understand the behavior of the circuit. Simulations and experimental results on a four Li-Ion cell prototype verify the validity of the proposed solution
Conclusions
No full textThis book has been conceived to give to the reader a basic and introductory knowledge of some typical power converter control problems and of their digital solutions. Although the presented material has been focused on a single converter topology, i.e., the half-bridge voltage source inverter, the control topics we have been dealing with represent, in our opinion, a significant spectrum of the more frequently encountered digital control applications in power electronics
Introduction: Digital Control Application to Power Electronic Circuits
No full textPower electronics and discrete time system theory have been closely related to each other from the very beginning. This statement may seem surprising at first, but, if one thinks of switch mode power supplies as variable structure periodic systems, whose state is determined by logic signals, the connection becomes immediately clearer. A proof of this may also be found in the first, fundamental technical papers dealing with the analysis and modeling of pulse width modulated power supplies or peak current mode controlled dc–dc converters: they often provide a mathematical representation of both the switching converters and the related control circuits, resembling or identical to that of sampled data dynamic systems
External Control Loops
No full textIn the previous chapters we have presented some examples of current control loop implementations, both for single- and for three-phase voltage source inverters. We have discussed how to design a PI current controller in the continuous time domain and how to turn it into a discrete time, or digital, controller. We also introduced the principles of dead-beat, predictive current control. In all these cases, we have seen how the presence of a current control loop actually turns the VSI into a controlled current source with predetermined speed of response and reference tracking accuracy
Digital Current Mode Control
No full textIn this chapter we begin the discussion of digital control techniques for switching power converters. In the previous chapter, we have introduced the topology and operation of the half-bridge VSI and designed an analog PI current controller for this switching converter. Referring to that discussion, the first part of this chapter is dedicated to the derivation of a digital PI current controller resembling, as closely as possible, its analog counterpart. We will see how, by using proper discretization techniques, the continuous time design can be turned into a discrete time design, preserving, as much as possible, the closed loop properties of the former. It is important to underline from the beginning that the continuous time design followed by some discretization procedure is not the only design strategy we can adopt. Discrete time design is also possible, although its application is somewhat less common: as we will explain, its typical implementations rely on the use of state feedback and pole placement techniques. The second part of the chapter will describe in detail a remarkable example of discrete time design and, in doing so, it will also show how the synthesis of regulators that have no analog counterpart whatsoever can be implemented. This is the case of the predictive or dead-beat current controller
The Test Case: a Single-Phase Voltage Source Inverter
No full textThe aim of this chapter is to introduce the test case we will be dealing with in the following sections. As mentioned in the introduction, it would be extremely difficult to describe the numerous applications of digital control to switch mode power supplies, since this is currently employed in very wide variety of cases. In order not to confuse the reader with a puzzle of several different circuit topologies and related controllers, what we intend to do is to consider just a single, simple application example, where the basics of the more commonly employed digital control strategies can be effectively explained. Of course, the concepts we are going to illustrate, referring to our test case, can find a successful application also to other converter topologies
Multi-sampling Asymmetric Dual-Edge Digital Pulse-width Modulator
No full textDigital controls are generally characterized by significant phase delays due to the analog-to-digital conversion process, sampling time, algorithm computation time, and the digital pulse-width modulator's architecture. Usually, the delay introduced by the latter has a more significant impact than previous ones, especially when approaching the switching frequency. The multi-sampling operation is largely adopted to reduce this delay. Recently proposed, double-sampling asymmetrical dual-edge (ADE) carrier-based digital pulse-width modulators (DPWM) have proven to operate with zero phase delay. Therefore, the multi-sampling architecture might provide even better results. Unfortunately, its documented operating point dependence does not allow such modulators to be used effectively. This article examines an improved multi-sampling ADE-DPWM architecture where the dependency on the operating point is significantly reduced. This manuscript also includes an accurate small-signal transfer function model. The proposed architecture and the developed small-signal model are validated in simulation and experimentally. In addition, experimental tests on a multi-loop voltage-controlled single-phase voltage-source inverter revealed the advantages of the proposed architecture over the more traditional DPWM one based on a trailing-triangle edge carrier
Li-Ion Battery-Supercapacitor Hybrid Storage System for a Long Lifetime, Photovoltaic-Based Wireless Sensor Network
No full textThis paper proposes a power management architecture that utilizes both supercapacitor cells and a lithium battery as energy storages for a photovoltaic (PV)-based wireless sensor network. The supercapacitor guarantees a longer lifetime in terms of charge cycles and has a large range of operating temperatures, but has the drawback of having low energy density and high cost. The lithium battery has higher energy density but requires an accurate charge profile to increase its lifetime, feature that cannot be easily obtained supplying the wireless node with a fluctuating source as the PV one. Combining the two storages is possible to obtain good compromise in terms of energy density. A statistic analysis is used for sizing the storages and experimental results with a 5-W PV energy source are reported
Random switching frequency in a synchronous-asynchronous digital voltage-mode control for dc-dc converters
No full textThis paper investigates the application of a random carrier-frequency pulse width modulation technique to the mixed synchronous/asynchronous digital voltage-mode controller for dc-dc converters presented in (Trzynadlowski, 1999). In the considered control architecture, the turn-on switching event is determined asynchronously by comparing the converter output voltage with a synchronously generated voltage ramp driven by the digital control using a low-resolution digital-to-analog converter (DAC). Switch turn-off is determined synchronously by the system clock. In this work, the system has been provided with a pulse width modulator which performs a limited pool random carrier-frequency modulation; this provision ensures low EMI emission and simple hardware implementation without affecting the quality of the output voltage regulation. Experimental results on a synchronous buck converter, where the digital control has been implemented in field programmable gate array (FPGA), confirm the effectiveness of the proposed solutio
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