Smart System Controller for Nano Grids

Mr. Kamaldeep Bansal, Staff Engineer, AMG Central Lab, STMicroelectronics India

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2-inch wide paper FTP-628 MCL Thermal printer is used to print the bills at customer premises. It can print at 80 mm/s (640dotlines/s) with high resolution printing of 8 dots/mm. It has been interfaced with controller using SPI protocol. L9935 is a motor driver that drives thermal printer motor. It is a two-phase stepper motor driver circuit suited to drive bipolar stepper motors. The device can be controlled by a serial interface (SPI). All protections required to design a well-protected system (short-circuit, over temperature, cross conduction etc.) are integrated in it.

System can be monitored and controlled from remote location using Ethernet interface STE100P Fast Ethernet physical layer interface for 10Base-T and 100Base-TX applications. It also provided Media Independent Interface (MII) for easy attachment to 10/100 Media Access Controllers (MAC) and a physical media interface for 100Base-TX of IEEE802.3u and 10Base-T of IEEE802.3.

GSM module can be plugged on MUC for remote connectivity using GPRS.

OTG USB Communication makes the system work both as host as well as the device. So MUC can be used to fetch images from pen drive or can be connected with PC to show different parameters on PC for further analysis.

SPIRIT1 is a very low-power and High-Performance RF transceiver, addressing RF wireless applications in the sub-1 GHz band. It can operate at 169, 315, 433, 868, and 915 MHz. SPIRIT1 module communicates with MUC using SPI protocol for wirelessly data exchange with the utility meters.

FSK, PSK multi-mode power line networking system-on-chip device ST7580 has been interfaced with MUC to monitor data coming from Energy meter using PLM Communication.

MUC System Block Diagram
Figure 7: MUC System Block Diagram

MUC Power Management

MUC can be powered by both, a +9V power adaptor as well as a 3.7V Lithium Ion battery.

MUC Power Management
Figure 8: MUC Power Management

Power adaptor along with powering the system also charges the Li-Ion battery using L6924D battery charger IC. It works in Linear Mode, and charges the battery in a constant current/constant voltage (CC/CV) profile. Various parameters, such as pre-charge current, fast-charge current, pre-charge voltage threshold, end-of-charge current threshold, and charge timer has been configured. A 22nF Capacitor is connected between T_PROG and ground to set maximum charging time. During constant current charging mode, charging current is programmed to the value around 900mA. This value is selected by connecting a 1% 13.5K resistor Rprog across I_PROG pin. When the battery voltage approaches the charge voltage (4.20V), the charger enters into a constant voltage charging mode and the charging current decreases. When the current level reaches the end-of charge level the charger enters in maintenance mode.

Adaptor supply is step down to 6.5V using L5987 switch down switching regulator with 3.5A (minimum) current limited embedded power MOSFET, so it is able to deliver up to 3 A current to the load depending on the application conditions.

Similarly Li-Ion battery supply is step up to 6.5V using STLDC08. 6.5V supply is used to drive thermal printer. Also this supply is given to different linear voltage regulators.

3.3V supply is generated using LD29150DT33 which provides 1.50 A of maximum current. This 3.3V supply drives Microcontroller section, Ethernet Section, Spirit1 Section, USB Section etc.

Fixed 5V is generated using LD29150DT50 required for TFT Display & Thermal printer.

Adjusted LD29300P2MTR voltage regulator generates 3.9V required to drive GSM module.

Multiple Use cases and Benefits

With the increasing demand of power, distribution of power really becomes a big challenge for related distribution companies. Smart controller can be the best candidate to help in handling with this. Smart controllers can help in accessing the information related to the power consumption patterns of the multiple users to manage the electricity distribution more efficiently.

With the remote connectivity, utility worker can diagnosis or troubleshoot without going to location where fault has occurred. This not only save the effort involved but also the time to troubleshoot the problem.

Dynamically changing tariff can also be integrated in the system to reduce the peak time load consumption by increasing the per unit price for the peak duration. Also end users can track the energy consumption online to view his energy consumption profiles monthly, day wise or even hour wise to help him better plan their usages. This can benefit both the end user and the utility company.

Smart Grid prototype setup
Figure 9: Smart Grid prototype setup

Conclusion

Smart system controller can help both the power generation and distribution companies in better planning and management. This can eventually help in reducing the carbon emissions associated with the generation and distribution of electricity. In future these adaptable systems can be integrated with smart devices and home so that devices can automatically respond to grid condition. This can help in making a very efficient broad ecosystem to realize the full potential of a grid system.


 

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