Power Electronics for the 22nd Century

September 07, 2015 by Jeff Shepard

During the Plenary Session of the 2015 Darnell's Energy Summit, to be hosted in Los Angeles, September 29 and 30, Dr. Slobodan Ćuk will present 'Power Electronics for the 22nd Century.' "Have you ever looked what switching converter topologies and switching methods were used 50 years ago?" asked Dr. Ćuk. "One should not be surprised that today we use the same: buck, forward, flyback and bridge-type converters based on pwm square-wave switching method," he continued.

Dr. Ćuk will present new switching methods and novel converter topologies. A closer look at the conventional converter topologies uncovers that they share the following bad traits: Excessive (3 to 4 times) device voltage and current over DC output voltage; Output diode rectifier switching (turn-on and turn-off) at full DC current; Excessive voltage and current stresses of the input active switches; Transformer flux excursions are up to ten times higher than optimally possible!; Transformer leakage inductance is the major source of losses and noise; and Transformers of flyback and LLC converters both store energy.

The root-cause of all these bad traits will be presented by Dr. Ćuk and the solution which eliminates all of them simultaneously will be provided by the new switching methods: hybrid switching and storageless switching method and novel converter topologies.

Optimal Design of Magnetics Components: PWM inductors store dc energy and become quickly useless with increased current and power leaving only one option: unchecked increase of switching frequency to MHz levels and higher. The presentation uncovers how the novel converter topologies and right ferrites result in tenfold reduction of magnetics size (both inductors and transformers!) while switching at a moderate 100 kHz instead of 1MHz!

Live Design Demonstrations via Simulation: The performance of several new converters are illustrated by salient waveforms generated on site via a state-of-the-art simulation program PLECS from PLEXIM.

And on the second day of Darnell’s Energy Summit, you will be able to hear Dr. Ćuk present 'Fast On-Board Battery Charger using Cuk Converter.' “The present day Rapid chargers for Fully Electric vehicles are so big (often half the size of the car itself!) and costly (higher than the EV cost!). They all use ac motors invented by Nikola Tesla rated at around 150kW but modified to operate at around 1.5 kHz. The increase from 50Hz frequency to 1,500Hz results in a 30-fold reduction of size and weight so that the resulting motor can fit well under a car hood and operate around 99% efficiency,” commented Dr. Ćuk.

“The problem is that the Rapid Charger to charge to 80% battery capacity in 20 minutes for even a 40kWhr batteries is so big, heavy and expensive that currently an external Standalone charger is the only available option, which does not solve the range anxiety problem. This is despite the fact that these Standalone chargers utilize switching converters operating at 150kHz switching frequencies or 100 times higher than the motor itself yet result in poor 90% efficiency. Hence a paradox: 150kW Tesla motor at 1.5kHz is 50 times smaller than the battery charger operating at 100 times higher frequency and resulting in at least 10 times higher losses!

“The reason for such a big size, cost and inefficiency are obvious. The present ac-dc chargers convert input ac power in three cascaded stages using conventional dc-dc converters, with each stage contributing its losses: bridge rectifier (four diodes and 3%), Boost converter (transistor and diode add 2% loss) and isolation stage (full-bridge with 8 switches add 5% loss) for a 90% efficiency at best and using 14 switches! Yet to drive the three-phase Tesla ac motor three such drives are needed for a total of 42 switching devices resulting in the same 90% or lower efficiency! The stored dc energy prevents scaling to high power!

“The new approach presented is a direct ac-dc charger with PFC and isolation in a single stage and with true bridgeless conversion which has only 4 switching devices. The efficiency exceeding 99% and size and weight reduction of over 20 times makes possible for the first time for a Rapid Charger to be placed on-board and sold with the Fully Electric Vehicle as its integral part. Elimination of range anxiety would pave the way for widespread use of Fully Electric Vehicles (FUV’s),” Dr. Ćuk concluded.

You will find registration information here.