Make solar inverters more reliable than the sun

In the hot summer, like most people, I usually hide in an air-conditioned room to escape the heat. Then, as the weather gets cooler and I open the windows to let in the natural breeze, I get my summer electricity bill and ask myself if the brief comfort of air conditioning is really worth it. .

Air conditioning can only achieve a Pyrrhic victory in the battle against hot weather. As an engineer, I think this is a problem that needs to be solved. My solution is simple: If you can't completely replace them, take advantage of the light and heat. So instead of consuming large amounts of expensive utility electricity, we could use solar panels on our roofs to power our air conditioners. Luckily, I'm not the first person to think of this, and with solar power almost costing the same as traditional energy, everyone can enjoy the benefits of solar power.

While much of the focus has been on photovoltaic panels, other parts of the solar power ecosystem cannot be ignored, such as power electronics. But this is only one key aspect. Photovoltaic panels generate DC voltage, but the power transmission and distribution system operates on AC, thus requiring a power inverter.

To achieve cost targets for solar power systems, the U.S. Department of Energy has proposed the following requirements as part of the Sunshot Initiative:

Conversion efficiency is greater than 98%

Service life greater than 25 years

Power density》100W/in3

System costs «$0.10/W (utility); «$0.125/W (commercial); «$0.15/w (residential) (includes the life cycle cost of power electronic equipment, including initial capital cost and operating costs over its useful life Dimension (O&M cost)

The goals of the "Sunshot Initiative" are very ambitious, and meeting them requires not only optimization of the core, but also careful consideration of each part. Careful design may lead to separation? 6? 7? 6? 7 from the border has a huge impact. The inverter's connection between low voltage DC and dangerous high voltage AC requires galvanic isolation, which can result in the power field effect transistor (FET) or insulated gate bipolar transistor (IGBT) being located opposite the controller isolation barrier that generates the gate signal side. Reinforced isolation gate drivers, such as Texas Instruments' UCC21520, are great because they combine the ability to pass signals across the isolation boundary and convert logic gate signals into actual gates from several devices to one drive. Reinforced isolated gate drivers are an ideal solution for series inverters with a maximum output power range of 500W to 10kW.

The UCC21520 improves on these integration advantages by achieving leading performance in propagation delay and delay matching between the high-side and low-side. Because it conducts faster and reduces the required dead time, which is the time during which the higher-loss body diode conducts, it reduces switching-related losses. These parameters are also less dependent on VDD, so you can relax the voltage tolerance design margin in the rest of the system, as shown in the benchmark data . Figure 1 also highlights that the UCC21520’s linear performance on VDD is much higher than that of competing products.

Microinverters are a rapidly growing architecture that converts power from a single PV module to the AC grid, typically designed for maximum output power in the 180-300W range. Through the distribution inversion process, solar arrays can be adapted to more complex roofs and smaller arrays can be installed that typically do not reach the input voltage of a string inverter. Raggie's basic isolation gate driver UCC21220 provides an alternative for solar applications where basic isolation is sufficient. It uses second-generation capacitive isolation technology to reduce costs by reducing chip size, which not only helps reduce PCB space and system costs, but also maintains leading performance in propagation delay and delay matching.

Another device that needs to cross the isolation boundary is the auxiliary power supply. Ensuring that a solar inverter can operate "smartly" and continuously regardless of the status of the AC utility/load or PV panels requires an isolated power source to provide bias power to the inverter. Since this step needs to cross isolation boundaries, it also needs to cross its components. Primary-side regulation (PSR), where the output is regulated by an auxiliary winding grounded relative to the primary-side controller rather than the optocoupler, is a great way to reduce components and cost. PSR also has the added benefit of increased service life because it eliminates difficult failure points during surge voltages. Primary-side flyback controllers, such as the UCC28700, maximize the performance and efficiency of the control scheme by implementing advanced algorithms with minimal external circuitry. The UCC28910 extends these advantages by integrating the 700V power FET and controller into a single device, further reducing the size of the bias supply.