Pre-Switch demonstrates efficacy of AI-based soft switching using 200kVA inverter reference

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Pre-Switch demonstrates efficacy of AI-based soft switching using 200kVA inverter reference

Bruce Renouard – March 11 2020, Campbell, Ca., USA: Pre-Switch, Inc., a Silicon Valley start-up that has developed the world’s-first AI DC/AC, AC/DC soft-switching controller delivering efficiency and performance benefits to a wide range of applications including EVs and renewables, has released first data from its Cleanwave 200kW inverter reference. Double pulse test data 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.

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: this is achieved with half the transistor count.  In the case of a SiC-based EV inverter, increasing the Fsw from the ubiquitous 10kHz up to 100kHz or 300kHz creates a near perfect sine wave without any output filter.  The result is elimination of unnecessary motor iron losses and an increased motor efficiency at low torque and low RPM.  Higher switching frequencies also enable higher RPM motors that are lighter and lower cost.

Previously, soft-switching has never been successfully-implemented for DC/AC systems with varying input voltage, temperature and load conditions. However, Pre-Switch has overcome the challenges by using Artificial Intelligence (AI) to constantly-adjust the relative timing of elements within the switching system required to force a resonance to offset the current and voltage wave forms – thereby minimizing switching losses.

Comments Pre-Switch CEO, Bruce T. Renouard: “Our CleanWave200 evaluation system allows customers to assess the cycle-by-cycle adaption of Pre-Switch’s AI-based soft-switching technology and explore the benefits of higher switching frequencies in their application.  CleanWave200 is the power block of an inverter with a PWM interface.  The system bi-directionally converts 800VDC to three phase AC at power up to 200kVA with a Fsw of 100kHz and 99% efficiency.”

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.