Prof. Frede Blaabjerg, Aalborg University, Denmark
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Power Electronics — The Key Technology For Renewable Energy System Integration
The energy paradigms in many countries (e.g., Germany and Denmark) have experienced a significant change from fossil-based resources to clean renewables (e.g., wind turbines and photovoltaics) in the past few decades. The scenario of highly penetrated renewables is going to be further enhanced– Denmark expects to be 100 percent fossil-free by 2050.
Consequently, it is required that the production, distribution , nd use of the energy should be as technologically efficient as possible and incentives to save energy at the end-user should also be strengthened. In order to realize the transition smoothly and effectively, energy conversion systems, currently based on power electronics technology, will again play an essential role in this energy paradigm shift. Using highly efficient power electronics in power generation, power transmission/distribution and end-user application, together with advanced control solutions, can pave the way for renewable energies.
In light of this, some of the most emerging renewable energies —, e.g., wind energy and photovoltaic, which by means of power electronics are changing character as a major part in the electricity generation —, are explored in this paper. Issues like technology development, implementation, power converter technologies, control of the systems, and synchronization are addressed. Special focuses are paid on the future trends in power electronics for those systems like how to lower the cost of energy and to develop emerging power devices and better reliability tool.
New Trends in Power Electronics for High-Power Applications
This talk starts with circuit configurations, controls and applications of power electronics with focus on high/medium-voltage high-power grid connections and medium-voltage high-power motor drives. The speaker presents some experimental waveforms obtained from a few downscaled systems that were designed and constructed in his laboratory.
Then, the speaker talks about a 750-V, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converter using the latest 1.2-kV 400-A SiC-MOSFET modules The maximum conversion efficiency from the dc input terminals to the dc-output terminals is as high as 99.4%. If existing Si-IGBT modules were used in the dc-dc converter, it would be impossible to attain such an extremely high efficiency. It is interesting that the SiC-MOSFET two-in-one module is the same in appearance, that is, size, shape, and terminal/pin arrangement as the latest 1.2-kV, 300-A Si-IGBT/PND two-in-one module.
Finally, this keynote ends with the following message: “Since the 1980s, power electronics scientists and engineers have been making a long voyage from a Silicon planet to a Silicon-Carbide planet. It takes five years from now to complete this challenging voyage. The success in the voyage will bring a new world to power electronics.”
Utilisation of Multiphase Electric Machines in Electric Vehicles
Although multiphase (more than three phases) machines have been known for practically half a century, it is only in recent times that they are becoming more wide-spread in industrial applications. In addition to the obvious advantage of reducing the required power-per-phase and hence required semiconductor rating, multiphase systems offer a number of other advantages that make them suitable for specific niche applications. These all stem from the fact that, regardless of the number of stator phases, independent flux and torque control of an ac machine always requires only two independently controllable currents (two degrees of freedom). The remaining degrees of freedom can then be used for other purposes. The keynote will explore the purposes that are of the highest relevance for electric vehicle applications.
Three specific issues will be covered by the presentation. These are: i) the realisation of fully integrated on-board fast (three-phase) and slow (single-phase) battery charging systems in electric vehicles, with the emphasis on topologies that require no or minimum hardware reconfiguration; ii) fault-tolerant drive operation in propulsion mode, enabling the realisation of the ‘limp-home’ mode; and, iii) use of different sub-windings in a single multiphase machine for uneven power-sharing including simultaneous motoring/generating operation of the said sub-windings. The last one is of high relevance for electric vehicles with multiple electric energy sources and it in essence can enable re-charging of the battery during high-speed driving of the vehicle. Illustrative examples, based on different stator winding phase numbers, will be used and experimental illustrations of the operation will be .provided throughout.