Leslie Bane, Senior Ecosystem Strategy Manager, National Semiconductor
Evaluation & Development Kits, Reference Design
Maximize PV system efficiency and safety
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Figure 1: National Semiconductor's diverse analog IC product offering for PV
To succeed in today's competitive solar market, system designers and OEMs require a system solution which may include energy-efficient analog ICs, tools, evaluation boards, and reference designs.
As the photovoltaic (PV) market has evolved over the past thirty years, system solutions providers have continued to focus their efforts on increasing efficiency of modules, quality designs, and building arrays to withstand environmental affects for the life of the array. Because arrays are expected to function reliably and safely for over 20 years, this is a huge task for the industries providers to meet such stringent demands. In the past few years, several market enablers have emerged to help system installers, designers, and owners get the best return on investment (ROI). National Semiconductor is one of these enablers.
For over 50 years, National Semiconductor has been known for its analog expertise and reliable, energy-efficient power management products. The company continues to bring this knowledge, experience, and manufacturing capability to help customers create better PV system designs. National's energy-efficient SolarMagicTM Integrated Circuit (IC) products address the critical needs of the solar PV market by combining high-performance analog and power management solutions to enable more intelligent photovoltaic systemssimplifying complex technologies, increasing reliability and safety, while reducing cost and time to market.
National has developed SolarMagic ICs for the entire PV chain from module-level electronics like DC/DC power optimizers, DC/AC microinverters, and Maximum Power Point Tracking (MPPT)-based battery charge controllers to smart combiner boxes and inverters with safety and communications solutions.
Solar PV Array Efficiency Challenges
Many mismatch factors can impact the amount of energy generated in a solar PV system. Some of these factorsshading from trees, building elements, different module tilt, orientation, and string lengthscan have an immediate and significant effect on power output. Other factors like module-to-module mismatch, module aging, and dust slowly reduce overall performance of the solar PV system over the life of the system. For example, 10% shading in the array can reduce the energy harvest of a system by as much as 50%. This significantly limits the energy output, design, and location of typical solar installations.
For years, installers designed around these mismatches or accepted the sub-optimal losses out of necessity. National's IC solutions for power optimizers and microinverters were developed to mitigate these losses.
DC/DC Power Optimizer Technology
Power optimizer technology came onto the scene in 2009 and has evolved in efficiency and form factor since then. In June 2010, National launched its SM3320 chipset to enable customers flexibility in design while bringing enhanced features such as 350W module power handling capabilities, best-in-class efficiency (99.5% peak), wide operating temperature range (-40°C to +90°C), and a tri-mode buck-boost architecture for highest system efficiency.
SolarMagic SM3320 chipset technology delivers higher PV system efficiency, lower cost per kilowatt-hour (kWh), flexible design, and lower balance of system costs. Residential and commercial rooftop installations can finally increase profit by maximizing roof utilization, recovering lost energy, and increasing energy harvest. SolarMagic technology is inverter agnostic and reduces or removes design constraints such as needing the same module layout, tilt, orientation, and string length across the array.
DC/AC Microinverter Technology
Microinverters provide DC-AC conversion at the module level and have a complementary architecture to power optimizers. They also provide some unique features such as elimination of high DC voltage levels (eliminating concerns of arcing) and complex string sizing (reducing time of installation), easily scalable array size, and reduced wiring costs. Leveraging its energy-efficient analog and power management expertise, National has expanded its SolarMagic IC product portfolio to include module-level microinverters.
Today's microinverter landscape is broken down into various architectures and offerings from the traditional topology using electrolytic capacitors with a rectified sinusoid and unfolding bridge to the advanced microinverter design offering with an intermediate high-voltage, high-efficiency DC bus using no electrolytic capacitors and ripple cancellation. Both the traditional and advanced microinverter design may include communications options like Power Line Communications (PLC) and wireless RF communications.
The SolarMagic SM72295 photovoltaic full-bridge driver is a good starting point for a microinverter design using interleaved flyback with active clamp circuitry for DC VIN of <100V. The SM72295 driver provides highly integrated functionality with four independent 3A gate drives, two current-sensing amplifiers and buffers, and built-in protection features like over-voltage and under-voltage control with a POWER GOOD indicator.
Off-Grid PV Solutions and Charge Controllers
Early PV systems were designed for small, off-grid applications, often used to charge batteries for future use in homes and buildings. However, over time systems increased in size and moved into grid-tied applications. National's MPPT digital controller and full-bridge driver ICs are designed to control highly efficient DC/DC converters commonly found in off-grid charge controller applications such as solar, automotive, marine, and street lighting applications. National's innovative charging controller products reduce system costs, improve reliability, and simplify design complexity to accelerate time to market.
The SolarMagic SM72242 enhanced MPPT controller and SM72295 full-bridge driver comprise a solid base from which to launch various PV battery-based charging designs. The charge controller reference design provides highly integrated functionality with a wide input voltage range for compatibility with most commercially available solar panels, current driving capabilities up to 100A, multi-chemistry battery support (e.g. lithium-ion, lead acid), advanced protection and battery management features, along with I2C (compliant) programming.
Safety and Arc Detection
While PV installations have increased dramatically over the past five years, so has the incidence of fires both related and unrelated to the panels themselves. The safety of firefighters working around energized solar panels has given rise to concern about PV system safety. As a result of this situation, in 2011 the U.S. National Electrical Code (NEC) was updated to include a new requirement (609.11) to specifically address rooftop PV systems. Knowing that standards often drive widespread adoption, National has developed a comprehensive safety solution to address PV module shut-off, arc detection, and theft deterrence.
The SolarMagic SM4110 PV Safety System was designed to allow for a flexible design and scalability for any size of PV array. The system is comprised of three main components: 1) a central array shut-off and control unit (SM4110-CTX), 2) a string level transmitter (SM4110-STX), and 3) receiver units (SM3010-1A1) that go inside a junction box.
In addition to providing the SolarMagic SM4110 PV Safety System to the market, National has also developed its SolarMagic SM73201-ARC-EV reference design to specifically address the presence of an electric arc within a PV system. As a result of the difficulty in detecting arcs, National has developed a unique signal processing approach (patent pending) that uses a state-of-the-art abstracted pattern recognition approach that does not require the arc signature to match a rigid pre-described absolute shape.
The arc solution operates in a temperature range of -40°C to +125°C, can detect arcs up to 100m, works with all commercially-available module technologies, and can detect all types of arcs (series, parallel, and ground). National's partners are leveraging the efficient design and small form factor of the SM73201-ARC-EV solution by integrating it within their smart combiner box or inverter.
Value of National's Solutions
To succeed in today's competitive solar market, system designers and OEMs require a total system solution which may include energy-efficient analog ICs, tools, evaluation boards, and reference designs. Efficiency and safety along with quality and reliability are key to success in PV as the demands on products and systems continue to increase. National Semiconductor is one company in the market delivering energy-efficient products and designs while at the same time diversifying its portfolio to ensure its products fit the entire value chain within the PV industry.