A Solar Solution For Every Situation

How SiC MOSFETs improve photovoltaic power systems.


Regardless of where they are used, energy conversion efficiency is paramount in solar power applications (if you are interested in their technical details, here is a blog post for you). Even small improvements reduce energy waste, decrease operating costs, lower spatial and cooling systems requirements, and much more.

The semiconductor switches used in energy conversion in photovoltaic (PV) systems play an important role. Not only do they contribute to losses themselves, but they also influence and sometimes limit the selection of other components in a system. IGBTs, for example, have low static losses but their switching losses increase at higher switching frequencies because of their slow switching behavior. Therefore, they require large and heavy magnetic and capacitive elements. Silicon MOSFETs sound like a good compromise for systems below 5 kW, but show higher static losses at high power.

A good solution is a silicon-carbide (SiC) MOSFET. These wide band-gap devices have a lower on-resistance and allow fast switching with low losses. Additionally, their thermal conductivity is about three times better than silicon.

So, SiC MOSFETs look like an excellent choice, but where can we use them in solar? 650 V and 1200 V SiC MOSFETs can be used in the DC-DC boost stage for MPPT (maximum power point tracking) and in single-phase or three-phase DC-AC inverters for PV arrays with voltages of up to 1000 V. These are mostly employed in residential or small and medium scale commercial installations. For larger commercial- or utility-type systems with 1500 V PV arrays, SiC MOSFETs classified at 1200 V can still be utilized in a DC-DC with 3-level boost arrangement. This also applies to the subsequent three-phase inverters if they are of the multilevel type. If you want to stay with a simple 2-level topology, you can use the new 2000 V SiC MOSFETs for the DC-DC boost stage.

Energy storage systems benefit as well

Renewable energy installations with a co-located energy storage system (ESS) in residential and commercial areas use bidirectional DC-DC buck-boost converters to charge a battery during the day and to make it available when the energy is needed. AC-coupled energy storage systems incorporate AC-DC and DC-AC conversion stages to charge the batteries or to feed stored energy into the grid.

In these use cases, and in all other conversion stages in solar applications, SiC MOSFETs yield lower overall losses and need smaller passive components because of their characteristics and the higher possible switching frequencies. This results in an improved conversion efficiency and in lower system costs, e.g., for the battery.

Therefore, manufacturers are striving to improve both efficiency and power density. Of high importance for them is an enhancement of partial-load efficiency to further boost the performance of the system.

Solutions are at hand

What can we as Infineon provide for solar energy systems and ESS? Our CoolSiC SiC MOSFETs are available in 650 V, 1200 V, and 2000 V classes. Discrete devices feature on-resistances as low as 7 mΩ and drain current ratings of up to 225 A. CoolSiC modules for 1200 V are at hand in various configurations, like 2-level and 3-level, having on-resistances down to 2 mΩ. Our Booster modules have dual SiC MOSFETs and SiC Schottky diodes to form a two-phase boost power stage. These modules are especially suitable for converting a PV array output voltage to the inverter DC-link input-level.

As every power conversion system needs a switch, and all switches need a driver, which in turn need a controller, we offer the EiceDRIVER family of gate drive ICs, which is tailor made for the different switch requirements, and the XMC microcontrollers. Also, each functional block needs a sensor and an auxiliary power supply. Here we provide the XENSIV TLI4971 current sensors and the CoolSET integrated power stages and 1700V CoolSiC MOSFET. Components for battery monitoring, protection, and charge/discharge control complement our portfolio. Figure 1 shows an overview of our products.

Fig. 1: A complete solution for solar power and energy storage systems.

Now, you’re probably thinking: “That’s fine, but I’d like to try this out for myself.” You can do that, as we provide a solution for that, too. Our modular reference design for 1500 V systems uses a new 3-level ANPC (active neutral-point-clamped) topology and achieves an efficiency larger than 99.0% in both directions. The effective switching frequency is up to 96 kHz. The power density is above 5 kW/kg, including heat sinks and controller.

As you have seen, SiC MOSFETs possess distinct advantages over other technologies when used in solar and energy storage applications. As a result, they enable cost-effective and energy-saving power converters.

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