Solar Micro-Inverter

Solar Micro Inverter Solutions from Texas Instruments.

Block Diagram

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Design Considerations

Solar Micro-Inverter | Solar Panel System Design

Schematic Block Diagram for Solar Micro-Inverters

Photovoltaic (PV) installations tied to the grid are usually built with arrays of modules connected in series to string inverters. A rapidly growing architecture, the microinverter, converts power from one PV module to the AC grid and is usually designed for a max output power in the range of 180-300W. Microinverter’s have advantages in terms of ease of installation, localized maximum power point tracking (MPPT) and redundancy that provides robustness to failure.

At the heart of the inverter is an MPPT algorithm which can be implemented through a microcontroller or an MPPT controller. The controller executes the very precise algorithms required to keep the panel at the maximum power extraction point while adjusting the dc-dc and dc-ac conversion to produce the output ac voltage for the grid. In addition, the controller is responsible for being locked in frequency to the grid. The controller is also programmed to perform the control loops necessary for all the power management functions. The PV maximum output power is dependent on the operating conditions and varies from moment to moment due to temperature, shading, soilage, cloud cover, and time of day so tracking and adjusting for this maximum power point is a continuous process. The controller contains advanced peripherals like high precision PWM outputs and ADCs for implementing control loops. The ADC measures variables, such as the PV output voltage and current, and then adjusts the DC/DC converter and DC/AC inverter by changing the PWM duty cycle depending on the load. Complex schemes exist to track the true maximum even in partially-shaded PV modules.

Real time processors designed to read the ADC and adjust the PWM within a single clock cycle are desirable. Communications on a simple system can be handled by a single processor, more elaborate systems with complex reporting on monitoring may require a secondary processor. Current sensing is done through through flux-gate sensors or shunt resistors. For safety reasons, isolation between the processor and the current and voltage may be required, as well as on the communications bus to the outside world. Delta-Sigma Modulators which include integrated isolation are desirable. MOSFET/IGBT drivers which can handle the higher voltages and include integrated sensing are also desired. The bias supply uses DC-DC converters to provide power to the electronics on the inverter. Sometimes, communications capability is included so users can monitor the converter, report on power and operating conditions and provide firmware updates. Typically Power Line Communication (PLC) to reduce wiring or wireless (Bluetooth, ZigBee/IEEE802.15.4, 6loWPAN) networking options are used.

The Safety MCUs offer an ARM Cortex-R4F based solution and are certified suitable for use in systems that need to achieve IEC61508 SIL-3 safety levels. These MCUs also offer integrated floating point, 12 bit ADCs, motor-control-specific PWMs and encoder inputs via its flexible HET Timer co-processor. Hercules Safety MCUs can also be used to implement scalar and vector-control techniques and support a range of performance requirements.

Application Notes (3)

Title Abstract Type Size (KB) Date Views
HTM 8 KB 23 Jul 2013 6519
HTM 8 KB 09 Jul 2012 3878
HTM 9 KB 29 May 2012 4225
    

Reference Designs

Selection and Solution Guides

Solution Guides (1)

Title Abstract Type Size (KB) Date Views
PDF 409 KB 10 Jan 2011 5489

Tools and Software

Name Part # Company Software/Tool Type
TMS320F28044 eZdsp Starter Kit (DSK) TMDSEZ28044 Texas Instruments Development Kits
TMS320F2812 eZdsp Start Kit (DSK) TMDSEZD2812 Texas Instruments Development Kits
TMS320F2812 eZdsp Starter Kit (DSK) - Socketed version TMDSEZS2812 Texas Instruments Development Kits
TMS320LF2407A eZdsp Starter Kit (DSK) TMDSEZD2407 Texas Instruments Evaluation Modules & Boards

Product Bulletin & White Papers

Product Bulletin (1)

Title Abstract Type Size (MB) Date Views
PDF 475 KB 31 Jan 2013 4904

White Papers (1)

Title Abstract Type Size (MB) Date Views
PDF 1.73 MB 03 Aug 2012 2000

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