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Posted on 29 June 2019

Designing for Quality

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Setting the industry standard 

The power electronics industry is conservative by nature, and this is by no means a coincidence. The consequences of failure in medium and high voltage power switching applications are simply unacceptable, and this is reflected in the cautious adoption of new technologies. Applications such as traction drives, HVDC, medium voltage industrial drives and wind turbine inverters are all alike in setting high standards of acceptance for innovative new products.

By Andy Matthews, VP Operations, Amantys Ltd

 

Amantys has a vision for the Intelligent Power Switch – a product that integrates the power transistor, gate drive and microprocessor in a tightly coupled device, delivering significant system benefits over existing techniques.

However, before introducing such a radically different approach, the first challenge the company faced was to build relationships - and revenues - by demonstrating it has the right skills, capabilities and quality processes to bring such change with products the industry already deploys.

The company has therefore introduced its first family of gate drive products – the Amantys Power Drive – implementing familiar products with enhanced performance and a greater rigour of design practice in order to win that acceptance.

Building such a reputation is founded on quality at every stage of the product development process. This begins with understanding market requirements, defining reliability lifetime targets, and flowing through design practices, to verification and test.

Amantys Power Drive

Market requirements and design targets

In developing the Amantys Power Drive, the company took a very deliberate approach to setting design criteria to meet specific performance targets, driven against clear requirements defined by a major industry OEM and IGBT module suppliers.

They highlighted particular improvements they wanted to see over an existing commercially available product, including better isolation, faster start-up and recovery times, and a gate drive with physical dimensions to fit within the footprint of the IGBT power module. In addition, there was a demand for a gate drive that could drive multiple vendors IGBT modules with a single configurable drive.

These requirements formed the targets for the product and used as the acceptance targets in EVT (Engineering Verification and Test) for form, fit and function of the eventual product.

It should be remembered that the primary function of a power transistor gate drive is to switch power safely, and in a way that protects the IGBT during abnormal system events. Testing and certification therefore becomes not only a question of performance and quality, but also of safety.

As part of this process, the team employed various design techniques. This included a rigorous component de-rating analysis, a comprehensive DFMEA study (Design Failure Modes Effect Analysis) to achieve performance and lifetime targets over the entire environmental envelope, and of course, the usual performance simulation for design envelope headroom, reliability and product lifetime.

This design methodology led directly to the adoption of surface mount MELF components in place of standard 2W resistors, to deliver better power density and longer lifetime at the extremes of the required operational specification.

DFMEA quantifies the likely severity and frequency of occurrence for each failure mode, including how well the design is able to detect each cause of failure, and how the design will perform in each instance.

As well as defining and guiding a logical design process, the process provides the design team with a traceable document for on-going design and development, and a vehicle for continuous product improvement and development.

Product verification

The next stage of development is verifying the product´s performance and quality through a combination of in-house and external third party tests.

When choosing to self-certify and in order to test worst case scenarios, companies must have adequate testing facilities to expose their products to conditions beyond their stated operation limits.

In-house testing

A series of tests are performed at Amantys including functional performance, life-time and reliability tests, and in-house certification.

Test matrix summary

As part of its investment in power electronics, the company has installed and commissioned a High Energy Test (HET) facility at its Cambridge headquarters. The Power Drive family has been tested for Reverse Bias Safe Operating Area (RBSOA), Type 1 SCSOA (Short Circuit SOA) and Pseudo Type 2 SCSOA using this facility.

In addition, the products have passed HTOL (High Temperature Operating Life) at – 95°C operational temperature and thermal cycling from -30 to +85°C.

Amantys has performed this characterisation for each of the IGBT Modules in its Powerdrive Partnership Programme and provides a graph of Safe Operating Frequency at different temperatures and gate resistor settings.

Third party testing

In addition to the Amantys in-house testing and verification, there are a series of third party tests undertaken. This includes accelerated stress testing techniques - HALT and HASS: Highly Accelerated Life Test/Stress Screen - in keeping with best practices in the automotive industry. These tests identify product failure modes in a matter of hours or days, compared to traditional test methods that may take weeks or months.

Product certification

Certification of components is a grey area, with both self-certification and industry body accredited options available to companies. But what is the driver behind certifying your products? What should we, as an industry, be striving towards at all times? Certification is not a matter of displaying a logo or stamp on your product; it is about ensuring quality processes throughout your entire design cycle, as already described - to provide customers with the highest quality product to suit their specific needs.

These needs vary according to the region into which products are sold. In the US, there is an insistence on tight regulation of certification through industry bodies and this is a legal requirement. However, throughout the EU it is currently legally permissible to have no third party certification.

A trusted and recognised EU option is the CE marking, indicating product compliance with EU legislation and enabling free movement of products within the European market. By stamping the CE mark on a product a manufacturer is declaring - on one's sole responsibility - conformity with all of the legal requirements to achieve CE marking. This mark allows the product to be sold throughout Europe, but this does not constitute a ‘quality’ marker, and is usually self-certified by the company, with supporting documentation done in-house.

Safe Operating Frequency at different temperatures and gate resistor settings

Amantys is taking a more thorough approach by seeking external accreditation of its HET facility for manufacturer type testing. Further than that, the product will also be tested and certified externally both for CE and UL standards for Europe and the US respectively, thus adding independent recognition and endorsement from an external body.

Environmental Test: operating and destruct limits for test results

When it comes to the certification of electronic products, there is the added layer of discussion surrounding whether the components themselves should be certified, or whether the final system is most important. By ensuring that our drives are certified this allows a much faster route to market, but also places quality control at the forefront of company practice and procedure.

A new player in power electronics

This cautious nature of power electronics is reflected in the relative scarcity of new entrants to the industry. Amantys is one company that has a very clear view of the credentials needed to gain credibility in this sector, and this is reflected in the company’s philosophy and approach to entering the market.

Bring something to market that the industry already knows, build it better and more rigorously than incumbent sellers, and then test and prove the product performance and reliability. The Amantys Power Drive is tested up to 14kV isolation, has faster start-up and recovery times (without a 1 sec dead-time), fits within the footprint of a 190mm x 140mm IGBT module, and drives multiple IGBT modules.

The interest we see from OEMs and IGBT module manufacturers suggests our product and design approach is gaining the reputation we’re seeking.

The next stage is to bring further step-bystep innovation to extend the capabilities of power switching systems, and this is the introduction of the Intelligent Power Switch.

Want to know more? Come and see the demonstration of our intent in Nuremberg at PCIM this year.

 

 

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