1,721,008 research outputs found
μ-synthesis of a robust voltage controller for a buck-boost converter
No full textThis paper proposes the structured singular value (μ) approach to the problem of designing an output voltage regulator for a Buck-Boost converter with current mode control. This approach allows a quantitative description of the effects of reactive component tolerances and operating point variations, which strongly affect the converter dynamics. At first, a suitable linear converter model is derived, whose parameter variations are described in terms of perturbations of the linear fractional transformation (LFT) class. Then, μ-analysis is used to evaluate the robustness of a conventional PI voltage regulator with respect to the modeled perturbations. Finally, the approximated μ-synthesis procedure known as D-K iteration is used to design a regulator ensuring robust performance. Simulated results are presented, describing the small and large signal behaviour of a reduced-order approximation of the μ-synthesised controller
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
Line-frequency commutated rectifier complying with IEC 1000-3-2 standards
No full textConsumer and household appliances require cheap ac/dc power supplies complying with EMC standards. The commonly employed passive solutions are bulky and do not provide output voltage stabilization. Active solutions, based on PFC's with high-frequency switching, provide compactness and regulation capability, but are generally expensive due to the need for fast-recovery diodes and complex EMI filters. This paper presents a high power factor rectifier, based on a modified conventional rectifier with passive L-C filter, which improves both the harmonic content of the input current and the power factor, by means of a low frequency commutated switch and a small line-frequency transformer, and allows to comply with IEC 1000-3-2 standard with reduced overall inductive components' volume
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
Extended Analysis of The Asymmetrical Half-Bridge Flyback Converter
No full textIsolated, Zero-Voltage-Switching (ZVS) dc-dc converter topologies represent attractive solutions in the continuous run towards higher switching frequencies, allowing more compact power supplies. Among them, the Asymmetrical Half-Bridge Flyback Converter (AHBFC) represents an interesting option, featuring simple duty-cycle control at constant switching frequency, as opposed to the popular LLC converter. The majority of papers dealing with this topology consider an approximated voltage gain similar to that of an isolated Buck converter operating in CCM, i.e. proportional to the duty-cycle, and, practically, load independent. On the contrary, the true voltage gain is non monotonic at high duty-cycle values. Anytime the converter is designed for a resonant operation, as is advisable to eliminate any reverse recovery problem of the rectifier diode, the voltage gain not only increases, but becomes a function of the switching frequency. This paper investigates the converter's voltage gain in detail, deriving a theoretical framework capable of capturing its real behavior and dependencies. The proposed analytical model has been verified through simulations as well as experimental measurements taken on a 160 W prototype working at 400 kHz
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
A Flexible Energy Gateway for Hybrid Nanogrids
No full textThis paper presents the topology and control of a three-port energy gateway for hybrid ac/dc nanogrids. The simple hardware architecture allows to connect renewable energy generators, energy storage devices, like ultra-capacitors, and the utility grid through three different interface converters, which, altogether, define the three-port energy gateway of the nanogrid. The proposed energy gateway represents a trade-off between circuit complexity and control flexibility, allowing i) operation of the energy storage port over a wide voltage-range, ii) control of the local dc-bus voltage at a predefined set-point, iii) multi-directional power flow, iv) support of the local ac-bus voltage with possibility to transition into islanded operation. A hierarchical control strategy is presented that enables flexible power exchange between the ac and dc buses. At the top of the control hierarchy, a human-machine interface is dedicated to operation mode selection and parameter preset; then, a supervisory control layer is present for system-level monitoring and control functions; the lower layer of the hierarchy is constituted by converter control functions for power flow regulation, achieved leveraging on voltage and current controllers. The flexibility and effectiveness of the proposed energy gateway architecture, control, and implementation are demonstrated in the paper in a variety of operation modes by means of experimental results
Multi-Sampled Grid-Connected VSCs: A Path Toward Inherent Admittance Passivity
Full text linkThis article investigates the capability of multi-sampled pulsewidth modulator (MS-PWM) control to improve the input admittance properties of voltage source converters (VSCs). Due to delays found in digital control systems, the VSC admittance features a negative real part above a certain frequency, which may result in lowly damped or even unstable grid dynamics. To prevent the occurrence of harmonic instability, recent standards require the admittance of every grid-connected VSC to behave as a passive network. In this article, it is shown that the MS-PWM control significantly improves passivity measures by reducing the overall system delay. The passive behavior is achieved effortlessly, using a single-stage control loop. This avoids the need for passive or active damping techniques, which are associated with increased losses and number of sensors, sensitivity to noisy measurements, ambiguity of damping filter design, and overall system complexity. The experimental verification, performed on a two-level single-phase VSC, shows a very good match between admittance measurements and analytic modeling even above the switching frequency. Grid-connected operation is tested to demonstrate the improvement of resonance damping obtained with MS-PWM control
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