Published September 23, 2013

SmartPower Stack™ Benefits and Opportunities

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The SmartPower Stack Consortium (comprised of five leading companies in Power Electronics) has recently released the SmartPower Stack™, which tightly integrates logic, power switching, capacitance and thermal management components into small, lightweight, interchangeable modules for use as subcomponents in commercial/utility grade PV/Solar inverters. A SmartPower Stack comprises the following components: an FPGA-based General Purpose Inverter Controller (National Instruments), Silicon based IGBT Switches (Fuji Semiconductors), programmable IGBT Drivers, ultra-low inductance Capacitors (SBE), laminated bus bars and highly efficient Heat Sinks (Methode). The product serves PV and other markets, operating from 50kW to 125kW and supporting a variety of conversion requirements (e.g. DC-AC, DC-DC, AC-DC, AC-AC).

Compared to traditional power stacks, the SmartPower Stack provides for over 35 points of advanced fault and monitoring capability. This enables continuous monitoring of the performance and health of the switching system. Data from this monitoring, augmented by predictive analytics, helps pre-empt system failure and adjusts overall system performance accordingly. Coupled with a hybrid capacitor bank that balances the benefits of electrolytic storage capability with the filtering of high frequency ripple currents of film based capacitors, the SmartPower Stack increases its lifetime by at least twice that of conventional systems.
Other benefits of the SmartPower Stack include shorter development times and lower supply chain risks and costs through multi sourcing of IGBTs.

Extend Inverter Lifetime

While most companies produce their own Power Stacks, there is a trend towards purchasing third party Power Stacks. However manufactures of third party Power Stacks have been slow to introduce new innovations to their product lines, and have limited control and fault monitoring capability. SmartPower Stack offerings use industry standard IGBT modules (providing multiple sourcing opportunities), allow for greater granularity of monitoring and control of the IGBT, provide a higher level of communication with the controller, and improve lifetime performance.

The list of fault and monitoring signals AgileSwitch Gate Drivers send to the controller are shown in the table below. Items with an * can be configured for the application:

Fault Condition/Action	Generic Sample Default Trigger Values	Action on IGBT if Active
Desat – HI (Short circuit)	>7 Volts for 6.1 µs*	Turn off HI side
Desat – LO (Short circuit)	>7 Volts 6.1 µs*	Turn off LO side
High Voltage Overshoot – HI	950 Volts*	Active Clamping occurs
High Voltage Overshoot – LO	950 Volts*	Active Clamping occurs
UVLO – HI (Undervoltage lock out)	<12 Volts	Turn off HI side
UVLO – LO (Undervoltage lock out)	<12 Volts	Turn off LO side
Cross Latch/Shoot Through	Attempt to turn on both IGBTs simultaneously	Does not allow turn on of inactive IGBT until active is off for 2 µs*
DC Link Overvoltage	900 Volts*	Shut down all IGBTs
Overcurrent	900A	Shut down all IGBTs
Temperature	>125 °C	Shut down all IGBTs

 

These fault conditions are monitored across each IGBT in a system (6 total, typical, per system) and logged and reported to the National Instruments (NI) controller. In addition, temperature, current and DC Link voltage are monitored in real time.

The fault and monitoring signals can be used to evaluate the health of the IGBT and wear leveling control techniques can be implemented to reduce the wear and tear on the most fatigued IGBTs in the system, thereby smoothing wear conditions across each of the IGBTs in a system, preventing the failure of a single IGBT, which is typically catastrophic for the inverter.

Reduce New Inverter Product Development Time

The average Non-Recurring Engineering time to complete a typical inverter embedded design is 30 engineer-months for National Instruments (NI) LabVIEW/RIO teams when compared to 144 engineer-months for the overall embedded market. Assuming skilled embedded developers at a rate of $100k/year with, the average NI embedded systems design project costs $250k compared to $1.2M for the overall embedded market- an average NRE cost savings of $950k per design, or $1,000 to $2,000 when amortized over the developed inverter. This represents a 15% reduction potential in inverter cost.

Minimize Supply Chain Risks

SmartPower Stacks help customers reduce their supply chain costs and risks. Regardless of building their own Power Stack or using a third party supplier, typical Power Stack design typically only support IGBTs from a single manufacturer. However there are often disruptions and shortages in the supply of IGBTs; this greatly increases the lead time and inventory cost of customers. SmartPower Stack’s modular design enables multi-sourcing of IGBTs from multiple manufacturers. This greatly reduces the risk of shutdowns and decrease lead times.

Summary

The SmartPower Stack Consortium has created a fully integrated sub-system solution for the power electronics industry with the highest performance for energy conversion inverters and converter systems. This effort represents the industry’s first collaboration of best-in-class technologies that are tightly integrated to deliver smart, efficient, reliable and long lasting power conversion.