Markus Andresen

The Smart Transformer: Impact on the Electric Grid and Technology Challenges

The increasing proliferation of renewable energy resources and new sizeable loads like electric vehicle (EV) charging stations has posed many technical and operational challenges to distribution grids [1]. Encouraged by attractive tax incentives and promotion policies, local grid end consumers are becoming not only consumers of electricity but, in many cases, also producers. The actual electric distribution system limits the use of renewable energy resources, offers poor EV infrastructure, and is based on a unidirectional information flow from sources to control centers.

Review of active thermal and lifetime control techniques for power electronic modules

Lifetime of power electronics modules can be extended with passive methods (condition monitoring) and active ones. This paper intends to give an overview in the second category, namely active thermal control or lifetime control, offering a critical comparison based on a comprehensive reference list. Mission profiles are compared to evaluate the potential of the controllers.

Power Routing in Modular Smart Transformers: Active Thermal Control Through Uneven Loading of Cells

Increasing decentralized energy production challenges the distribution grid [1], [2], and, in many countries, power generation and consumption are spatially separated, meaning that energy must be transferred over a long distance [3]. This calls for novel ways to transfer power to the loads without overloading grid feeders and to connect new intelligent loads and storage [4], which typically form the actual electric grid hybrid (ac and dc) and couple with other energy networks (multimodal) [5]. In the current configuration, transformers are passive devices that do not enable dc systems to connect or interface the electric grid with other energy grids.

Study of reliability-efficiency tradeoff of active thermal control for power electronic systems

Abstract Active thermal control for power modules can potentially extend the lifetime of the converter. This paper investigates the trade-off between the lifetime extension or de-rating and its cost due to the efficiency reduction. A short review on the existing approaches using control to reduce thermal stress of power modules is presented. Based on a given junction temperature profile, a method to evaluate the active thermal controls trade-off is presented. The concept is validated on a laboratory setup, where active thermal control is implemented by adapting the switching frequency. A discussion of the possible lifetime extension at the efficiencys expense is finally given.

Impact of active thermal management on power electronics design

Abstract Power electronic system design is typically constrained by the thermal limitation so by the overall losses and the peak current. To stay within the maximum current, reached only during transients, the system is typically overrated. Active thermal management is used to control the maximum temperature and the temperature swing to reduce failures that are mostly caused by them. In this paper it is proposed to use the active thermal management to reduce the switching losses or to move them to less stressed devices, during transients, such as a module can reach an higher current, without violating thermal constraints, and the need of overdesign can be reduced. Hence an optimal and cost effective design of power electronics system is achieved.

Active thermal control of IGBT power electronic converters

Thermal cycling is one of the main sources of aging and failures in power electronics. A possibility to reduce the stress to semiconductors is to control the amount of losses that occur in the device during operation. This work presents an active thermal controller that aims at reducing the junction temperature variations in the case of variable power profile. The switching frequency of the converter is the parameter that is affected by the active thermal control, while the operation of the converter remains unchanged. The novelty of the approach is that the switching frequency variation is exploited to prevent excessive cooling down of the semiconductor during a power reduction. A thermal model is used to estimate the losses, so the prior knowledge of the mission profile is not needed. The results of the proposed solution are validated with an experimental prototype and a wide-bandwidth temperature measurement system directly applied to the semiconductor chip. Finally, the impacts of the controller on the modules lifetime is estimated.

Power Routing for Cascaded H-Bridge Converters

Modular power converters are expected to play a major role in medium- and high-voltage/power applications. Normally, each module processes the same amount of power; however, this does not take into consideration that different modules can have a different remaining useful lifetime. This paper proposes the concept of power routing for cascaded H-bridge (CHB) converters, with the purpose of delaying the failure of the system. A third-harmonic injection into the duty cycles allows extending the imbalance capability of the structure, keeping the CHB operational even if some power paths are completely unloaded. Analytic investigation in conjunction with simulation and experimental measurements demonstrate the power routing by means of the proposed method.

Lifetime-Based Power Routing of a Quadruple Active Bridge DC/DC Converter

Medium-voltage dc/dc converters have recently acquired importance in the smart grid and dc distribution framework. However, several open issues remain with regard to the reliability of such systems. This paper proposes a modular isolated dc/dc converter with multiple quadruple active bridge building blocks. This design, in combination with a virtual resistor-based control, weights the paths depending on the components wear-out and can balance the stress of the semiconductors in the attempt of extending overall system lifetime. The effectiveness of the approach is demonstrated in simulations and supported with measurements on a small-scale demonstrator with open modules, built in order to verify in real time the capability of controlling the thermal stress of the semiconductors.

Computational light junction temperature estimator for active thermal control

The junction temperature of power semiconductors in power converters must not exceed its maximum limits and it is of major importance for several failure mechanisms. But still, the junction temperature is hard to access. Direct measurement is not practical for industrial applications, indirect measurements require substantial effort and available junction temperature models have high calculation effort. This work develops a simple junction temperature estimator, which is applied for a maximum junction temperature limitation and the capability to be applied for further algorithm relying on the junction temperature, referring to active thermal control. It is experimentally shown, that a second order estimator is sufficient to achieve high bandwidth estimation.

Variable sampling time finite control-set model predictive current control for voltage source inverters

This work introduces the control concept of variable sampling time finite control-set model predictive control (FCS-MPC). The new control concept is introduced in theory based on a review of the conventional FCS-MPC concepts performed with a constant sampling time. Based on the partitioning of the sampling instant in multiple smaller sampling instants it is possible to optimize, besides the switching states, the switching states turn-on times. Therefore, the proposed variable sampling time FCS-MPC sets both: the switching state and the related turn-on times. To utilize the available calculation power for longer sampling instants an adaptation of the control- and prediction horizon to the sampling time is proposed. The theoretical control concepts are applied to the control of a grid connected two-level voltage-source converter where a simple L-type line-filter is used to demonstrate the control performance of the variable sampling time FCS-MPC algorithms in the laboratory environment.