Pre-Switch presents step-by-step sequence to show AI-optimized soft-switching achieving 99% operational efficiency in 200kW inverter

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Pre-Switch-Wave-gift-PR_April 2020

Screen captures illustrate active learning, analysis and adjustments that initiate and maintain optimized system timing.

April 28 2020, Campbell, Ca., USA: Pre-Switch, Inc., a Silicon Valley start-up that has developed the world’s-first AI DC/AC, AC/DC forced-resonance-based soft-switching controller delivering efficiency and performance benefits to a wide range of applications including EVs and renewables, has released a demonstration and full explanation of its CleanWave200 inverter reference. An animated sequence of 20 1µs screen captures illustrates the Pre-Switch AI actively learning from initial start-up with unknown conditions, then subsequently optimizing and adjusting the timing necessary to ensure that a PWM input generates a current ramp to simulate the first part of a sine wave output.    

Double pulse test data obtained from the 200kW inverter demonstrates that the Pre-Switch soft-switching platform – comprising the Pre-Drive™3 controller board powered by the Pre-Flex™ FPGA, and RPG gate driver board – reduces total system switching losses by 90% or more.

Upon commencement of the initial switching cycle (0), the Pre-Switch AI controller assesses multiple inputs to determine what mode the system is in, and then makes a safe but non-optimal estimate of the resonant period needed for soft switching.   During the next switching cycle (1), all AI inputs and resulting outputs from switching cycle 0 are precisely re-measured and analyzed.  A second conservative resonant timing period, similar to switching cycle 0, is issued.

In follow on switching cycle (2), the AI algorithm is now quantitatively-confident and able to predict the optimized resonant timing to ensure full soft-switching – thus minimizing losses in all aspects of the system. Then in switching cycle 3, the AI compares system inputs and results from previous switching cycles and adjusts the resonant timing to fully optimize soft-switching with the increasing load current. These inputs and outputs are stored with the previous switching cycle inputs and resulting resonant timings to improve accuracy and system optimization.  

 In subsequent cycles, soft switching accuracy continues to be optimized, stored to and compared to desired results necessary to maintain accurate forced resonance soft switching. Changes in system temperature, input voltage, output load current, and device degradation are all accounted for and optimized within the Pre-Switch AI algorithm.

Comments Pre-Switch CEO, Bruce T. Renouard: “Pre-Switch is enabling customers to build systems with switching frequencies 4X-5X faster than their hard-switched IGBT systems and 35X faster than their hard-switched SiC and GaN systems. The GIF demonstrates how our AI is working within the CleanWave200 to bi-directionally convert 800VDC to three-phase AC at power levels of up to 200kVA with a switching frequency of 100kHz at 99% efficiency levels.”

The Cleanwave200 evaluation system, reference design and design files can be ordered from Pre-Switch.

Pre-Switch: Further, Faster, Lighter, Cheaper – Cooler

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Motor Benefits

A Pre-Switch-enabled inverter reduces sine wave output distortion by 10X, enabling motors to run more efficiently. In a conventional hard switching design, the output ripple current of the half-bridge circuit switching back and forth at 10-15 switching events per fundamental frequency causes a significant level of distortion.  The distortion is effectively an induction heater in the motor coils and does no useful work. Pre-Switch technology minimizes this ripple by switching 10x faster.  The lower distortion fundamental sine wave to the motor is what we call a ‘clean wave’ and improves motor efficiency predominantly at lower RPM and lower torques which is where EV’s are driven and increases EV range.

The second benefit of the Pre-Switch soft switching architecture is that inverter dV/dt is configurable with a free lossless dV/dt filter that is part of the architecture.  Reducing dV/dt improves motor reliability and reduces motor winding insulation allowing higher power density motors. Due to the fast edge  speeds of WBG (SiC; GaN) transistors, high dV/dt is traded off for reduced switching losses.  But high dV/dt speeds of above 15-20V/ns can cause insulation damage. Inverter designers in the past accommodate these excessive dV/dt speeds by adding extra insulation in the motor. This approach has the adverse affect of reducing motor power density and increasing motor costs.  In contrast, the Pre-Switch architecture slows edge speeds but allows increased switching frequencies, eliminating the problem of high dV/dt speeds and reducing the insulation required. 

The faster switching speeds enabled with Pre-Switch can be used to spin motors faster.  In some applications a lower cost, lighter and higher RPM motor can be used.

The final benefit for motor design is that because Pre-Switch-enabled systems switch so fast, low inductance motors can be used which have the benefit of being smaller and lighter and lower cost. This is particularly suitable for applications such as electric aircraft, where designers are trying to reduce the amount of iron in the motors to keep weight to a minimum.