The typical setup for generating solar energy involves a series of solar photovoltaic (PV) panels connected to a solar inverter. The PV solar panels generate a DC output and send it to the inverter. The inverter then converts the DC input into an AC output that can be fed to a utility company’s electrical grid or used by a local, off-grid electrical network. Each PV panel is typically equipped with a microcontroller, plus communication ICs that make it possible for the panel to interact with the inverter. Figure 1 gives a high-level block diagram.
Figure 1. High-level block diagram for solar PV panel
The inverter (Figure 2) is often a more complex system. Like the PV panels, it includes a microcontroller and communication ICs, but it may also include such features as an energy meter, for tracking energy use, and more complex wired and wireless connectivity, such as Ethernet or Wi-Fi, for more sophisticated interactions with the electricity grid or home network.
Figure 2. High-level block diagram for solar inverter/charger
NXP has solutions for every block shown in Figures 1 and 2. In this article, we focus on the interface products that support communications between the PV panel and the inverter, and support operation of the power meter.
Communications ICs for PV Panel and Inverter
UARTs & Protocol Bridges
Microcontrollers are usually equipped with some kind of serial interface for connecting to various peripherals. Sometimes there are enough built-in interfaces to finish the design, but sometimes the design needs more peripherals than the microcontroller can support, or the specific type of interface required isn’t there. That’s where bridges come in. NXP’s bridge ICs let you expand the microcontroller’s serial interfaces, so you can connect to more peripherals in your design. Here are two examples that might be useful in a PV panel or inverter:
- SC16IS75x/76x I2C/SPI-to-UART bridge: connects to the microcontroller’s I2C/SPI interface on one side, and offers connections to UART, IrDA, and GPIO on the other.
- SC18IS600 SPI-to-I2C bridge: connects to the microcontroller’s I2C/SPI master on one side, and offers connections to multiple I2C slaves and/or up to five GPIO on the other.
NXP also offers a wide range of single- and multi-channel UARTs. These devices can be used to transmit and receive data between the microcontroller and the communication channel, and can offload the microcontroller by checking for and managing communication errors.
Proprietary RF/IF System
Panels can be mounted some distance away from the inverter, so having wireless connectivity on board can make it easier to communicate with the inverter. NXP offers a full range of proprietary RF/IF systems, including those shown in the table. Here are two in particular:
- SA604AD/01 & SA614AD/01 low-voltage FM IF system: includes an IF amplifier, limiter amp, RSSI and quadrature detector, and has an IF bandwidth of 28 MHz.
- SA58646BD integrated wireless transceiver: a UHF 900 MHz transceiver IC with synthesizer, baseband Rx/Tx section, voltage regulator, and programmable low-battery detect time multiplexed with RSSI carrier detect.
Here are some other proprietary RF/IF systems to consider:
|LV FM IF Systems||SA604A, SA614A|
|Narrow and Wide Band FM RF/IF Receivers||SA605DK, SA615DK|
|Narrow Band FM RF/IF Receivers||SA606DK, SA616DK, SA676DK, SA58640DK, SA607DK, SA608DK|
|Wide Band FM RF/IF Receivers||SA636DK, SA58641DK, SA639DH|
|SPDT Switches||SA630D, SA58643DP|
|LNAs and Mixers with VCO||SA602A, SA612A, SA601DK, SA620DK|
|Integrated Wireless Transceiver||SA58646BD|
Power Line Modem
The TDA5051A is a low-cost ASK modem for data transmission over the power-line network. It can be used on any two-wire network for exchanging information by means of ASK carrier current technique (DC or AC network), and requires very few external components. It’s a robust solution that includes zero cross detection and a redundancy protocol, and it’s supported by NXP software. Because the TDA5051A uses a digital structure for transmission and reception, it provides an efficient solution for modulation and demodulation of low baud-rate signals. A standard quartz crystal is used to set the operating frequency: in transmission mode, the crystal defines the carrier frequency, and in reception mode it defines the detection frequency.
Power Metering ICs for Inverter
NXP offers a wide selection of small, highly accurate RTCs. In particular, our low-power RTCs (PCF8563, PCF2123, PCF8523) provide time-keeping functions and help manage standby power applications. They provide electronic tuning for temperature compensation, accuracy tuning, and aging adjustment. They also offer the industry’s lowest power consumption, with an operating current of less than 100 nA.
Our segment, character, and graphic (dot matrix) LCD drivers make it easy to add a display to the power meter. We support a wide range of formats, from 4 x 32 segments to multi-line and multi-character displays and larger displays that support full graphics.
The PCF8536 is a universal LCD driver for low multiplex rates that includes a 6-channel PWM generator. It drives signals for any multiplexed LCD containing up to eight backplanes, up to 44 segments, and up to 320 elements. The PCA8536 is an automotive-qualified version, ready to withstand harsh environments and high temperatures.
The PCF2113x is a low-power CMOS controller for dot-matrix LCD displays. It drives two lines of 12 characters or one line of 24 characters with up a 5×8 dot format. The PCF2119x drives two lines of 16 characters or one line of 32 characters with a 5×8 dot format (the “x” in the product names characterizes the built-in character set).
NXP’s portfolio provides lots of options for designers who are developing solar PV panels and inverters. This article covers just a few of the blocks in a system design. For more ideas about improving the performance of solar-energy applications, explore the rest of our website (www.nxp.com) or contact your local NXP representative.
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