Predictive control is a very wide class of controllers that have found rather recent application in the control of power converters. Research on this topic has been increased in the last years due to the possibilities of today's microprocessors used for the control. This paper presents the application of different predictive control methods to power electronics and drives. A simple classification of the most important types of predictive control is introduced, and each one of them is explained including some application examples. Predictive control presents several advantages that make it suitable for the control of power converters and drives. The different control schemes and applications presented in this paper illustrate the effectiveness and flexibility of predictive control.

Predictive Control in Power Electronics and Drives

This paper presents a review of control strategies, stability analysis, and stabilization techniques for dc microgrids (MGs). Overall control is systematically classified into local and coordinated control levels according to respective functionalities in each level. As opposed to local control, which relies only on local measurements, some line of communication between units needs to be made available in order to achieve the coordinated control. Depending on the communication method, three basic coordinated control strategies can be distinguished, i.e., decentralized, centralized, and distributed control. Decentralized control can be regarded as an extension of the local control since it is also based exclusively on local measurements. In contrast, centralized and distributed control strategies rely on digital communication technologies. A number of approaches using these three coordinated control strategies to achieve various control objectives are reviewed in this paper. Moreover, properties of dc MG dynamics and stability are discussed. This paper illustrates that tightly regulated point-of-load converters tend to reduce the stability margins of the system since they introduce negative impedances, which can potentially oscillate with lightly damped power supply input filters. It is also demonstrated that how the stability of the whole system is defined by the relationship of the source and load impedances, referred to as the minor loop gain. Several prominent specifications for the minor loop gain are reviewed. Finally, a number of active stabilization techniques are presented.

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DC Microgrids—Part I: A Review of Control Strategies and Stabilization Techniques

This paper analyzes the small-signal impedance of three-phase grid-tied inverters with feedback control and phase-locked loop (PLL) in the synchronous reference ( d-q ) frame. The result unveils an interesting and important feature of three-phase grid-tied inverters – namely, that its q–q channel impedance behaves as a negative incremental resistor. Moreover, this paper shows that this behavior is a consequence of grid synchronization, where the bandwidth of the PLL determines the frequency range of the resistor behavior, and the power rating of the inverter determines the magnitude of the resistor. Advanced PLL, current, and power control strategies do not change this feature. An example shows that under weak grid conditions, a change of the PLL bandwidth could lead the inverter system to unstable conditions as a result of this behavior. Harmonic resonance and instability issues can be analyzed using the proposed impedance model. Simulation and experimental measurements verify the analysis.

Analysis of D-Q Small-Signal Impedance of Grid-Tied Inverters

A surface cleaning apparatus comprises a body including a rear compartment, a forward compartment and an intermediate compartment arranged between the rear and forward compartments. An elongate rotatable brush arrangement is positioned within and extends across the forward compartment. An electric motor is positioned in the rear compartment, and drive means extends between the rotatable brush arrangement and the electric motor.

Surface cleaning apparatus

This paper presents a review on the state-of-the-art maximum power point tracking (MPPT) techniques for PV power system applications. The main techniques that will be deliberated are the Perturb and Observe, Incremental Conductance and Hill Climbing. The coverage will also encompass their variations and adaptive forms. In addition, the more recent MPPT approaches using soft computing methods such as Fuzzy Logic Control, Artificial Neural Network and Evolutionary Algorithms are included. Whilst the paper provides as thorough treatment of MPPT at normal (uniform) insolation, its focus will be on the applications of the abovementioned techniques during partial shading conditions. It is envisaged that this review work will be a source of valuable information for PV professionals to keep abreast with the latest progress in this area, as well as for new researchers to get started on MPPT.

A review of maximum power point tracking techniques of PV system for uniform insolation and partial shading condition

This 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

Li-Ion Battery-Supercapacitor Hybrid Storage System for a Long Lifetime, Photovoltaic-Based Wireless Sensor Network

This paper describes an innovative digital control architecture for low-voltage, high-current dc-dc converters, based on a combination of current-programmed control and variable frequency operation. The key feature of the proposed architecture is the low complexity: only two digital-to-analog converters (DACs) with low resolution (7-b) are used for control. An original control algorithm is used to reduce quantization effects to negligible levels, in spite of the low resolution of the DACs. Thanks to this algorithm, both static and dynamic output voltage regulation are improved with respect to traditional digital solutions. Adaptive voltage positioning and active current sharing are inherently provided by the new architecture. A detailed description of the control strategy is given with reference to a single-phase buck converter. Extension to multiphase converters is straightforward. The digital control architecture is experimentally verified on a FPGA-based four-phase prototype buck converter operating at 350 kHz/phase. Output voltage tolerance within /spl plusmn/0.5% is experimentally demonstrated, along with negligible quantization effects and fast transient response. The features and the performance of the proposed architecture make it a valuable candidate for the control of next generation voltage regulator modules.

An innovative digital control architecture for low-Voltage, high-current DC-DC converters with tight voltage regulation

This paper proposes a simple autotuning technique for digitally controlled dc-dc converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of proportional-integral-derivative parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller parameters based on the specified phase margin and control loop bandwidth. A nice property of the proposed solution is that output voltage perturbations are introduced while maintaining the relay feedback control on the output voltage. The proposed algorithm is simple, requires small tuning times, and it is compliant with the cost/complexity constraints of integrated digital integrated circuits. Simulation and experimental results of a synchronous buck converter and of a dc-dc boost converter confirm the effectiveness of the proposed solution

Autotuning of Digitally Controlled DC–DC Converters Based on Relay Feedback

This paper presents a new class of switched tank converters (abbreviated as STCs) for high-efficiency high-density nonisolated dc–dc applications where large voltage step down (up) ratios are required Distinguished from switched capacitor converters, the STCs uniquely employ LC resonant tanks to partially replace the flying capacitors for energy transfer Full soft charging, soft switching, and minimal device voltage stresses are achieved under all operating conditions The STCs feature very high efficiency, power density, and robustness against component nonidealities over a wide range of operating conditions Furthermore, thanks to the full resonant operation, multiple STCs can operate in parallel with inherent droop current sharing, offering the best scalability and control simplicity These attributes make STC a disruptive and robust technology viable for industry's high volume adoption A novel equivalent DCX building block principle is introduced to simplify the analysis of STC A 989% efficiency STC product evaluation board (4-to-1, 650 W) has been developed and demonstrated for the next-generation of 48-V bus conversion for data center servers

Switched Tank Converters

This paper investigates the effects of control-delay minimization in the dynamic performance of the output stage of uninterruptible power supplies (UPSs) by shifting the sampling time of inductor current and output voltage toward the duty-cycle update instant. This paper shows how a small shift of the output-voltage sampling can significantly increase the UPS voltage-loop bandwidth while keeping the same stability margin. Instead, less contribution comes from the delay minimization of the inductor-current sampling, so that current-ripple cancellation techniques are not needed. A detailed model based on the modified Z-transform, which accounts for different time delays in multiloop control, is proposed. The effectiveness of the proposed analysis is demonstrated by simulation and experimental results on a typical industrial three-phase/three-phase 8-kHz 30-kVA UPS prototype. By using two control designs based on the same phase margin, the output-voltage total harmonic distortion with the normalized distorting load is reduced from 6.8% to 5.7%, using a delay of the output voltage sampling equal to 25 mus.

Stefano Saggini

Papers

Li-Ion Battery-Supercapacitor Hybrid Storage System for a Long Lifetime, Photovoltaic-Based Wireless Sensor Network

An innovative digital control architecture for low-Voltage, high-current DC-DC converters with tight voltage regulation

Autotuning of Digitally Controlled DC–DC Converters Based on Relay Feedback

Switched Tank Converters

Analysis of Control-Delay Reduction for the Improvement of UPS Voltage-Loop Bandwidth