Soft-switching gate drive solution from Pre-Switch slashes solar inverter costs

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Soft-switching gate drive solution from Pre-Switch slashes solar inverter costs

Bruce Renouard – Two-stage architecture and platform enables significant cost reduction and simplification of renewable energy systems; Grid tie filter size slashed by up to 80%

October XX 2019, Campbell, Ca., USA: Pre-Switch, Inc., a Silicon Valley start-up that emerged from stealth mode last year, has announced that its revolutionary soft-switching IGBT and silicon carbide gate driver architecture, including the Pre-Drive™3 controller board, powered by the Pre-Flex™ FPGA, and RPG gate driver board, can significantly reduce the cost of solar inverters. The two-stage architecture delivers the same switching loss performance – or better – as a five-level design, resulting in reduced cost, control complexity and BOM count. Also, Pre-Switch enables the simplification and size reduction of inverters and filters used in renewable energy systems, enabling energy to be put back into the grid easily and efficiently.

The Pre-Switch soft-switching platform enables a doubling of power output for a typical inverter, or an increase in switching speed by a factor of up to 20 times. 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. 

Explains Pre-Switch CEO, Bruce T. Renouard: “Our benefit for solar energy system designers is that our soft-switching architecture eliminates half of the system losses.  So we are able to achieve performance levels with a simple two stage design that would require five stages using conventional multi-level techniques.”`

He adds: “The architecture also allows the grid tie filter size to be reduced by up to 66.67% for IGBT systems and by up to 80% for SiC MOSFETs.  That is a huge advantage, not only in system size but also materials and shipping cost savings.”  

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.