Intelligent Load Balancing under constrained energy availability

Standalone Webserver Running on STR9 Comstick board

Intelligent load management under constrained energy availability is a way of extending the backup and thereby reducing the installation size of of renewable energy sources like solar energy and wind energy systems in buildings. This is important in terms of reducing the cost of initial installation of such systems. Many times majority of the loads in the buildings can be categorized as critical loads and non critical loads. But some of the loads may fall in both categories depending on the comfort level and convenience of the user. So we are introducing an Ethernet based load management system which has an inbuilt intelligence which manages load as also provide some level of control over the load to the user.

Introduction

The major spot on of today’s challenges is to maintain an automation services for home and would be better if the service take care of meeting critical loads at the cost of shutting down or reducing loading of non-critical loads like Air Conditioners. This project is modeled as miniaturization of such a real time home automation involving AC, Exhaust fans along with sensor interfacing such as smoke detection, load current sensors (hall effect sensors) for taking care of security and load balancing. The processor used for this purpose is STR912 Comstick which has Ethernet interfacing support. Micro-controller runs FreeRTOS and uIP TCP/IP stack. Micro-controller stores required html pages for server in its flash. We were able to access server from anywhere inside the IISc’s local network. Page has user interface to control output pins of board or to read ADC/pin input. We have used IAR Embedded Workbench for code development and debugging.

Hardware Platform

Processor Requirements

Inbuilt Ethernet Support
Higher Operating Frequency for Faster packet processing
Large Flash memory – for storing webpages content
Enough RAM to accommodate various IP packets in buffer while processing others.

STR9 Comstick (Image taken from Hitex.com)

STR 912 Processor

For this purpose we have selected STR912FW44X processor. Main features of the processor which will be useful to our application

ARM966E-S 96Mhz
512K+32K internal Flash,
96K internal RAM
9 DMA channels (inlcuding DMA for Ethernet)
10/100Mbit Ethernet MAC
10 bit ADC

STR9 Comstick

Comstick is STR912FW44X development board by Hitex. It has a USB debugger, Ethernet and USB port and a general purpose a GPIO port which has alternate functions for CAN and ADC. It is very small size board suitable for our application where this board can be placed inside switch board to control devices. Its demos and manuals can be found at [2].

Software Library

uIP TCP/IP Stack

uIP is open source lightweight TCP/IP stack. It takes care of most of the main features of TCP/IP, it also provides ARP, UDP , ICMP ping support. Using uIP Stack, it is very easy to implement Http webserver and Client. Its documentation can be found here [3].

FreeRTOS

FreeRTOS is Real Time Operating System which we have ported on STR912. Embedding uIP Stack in FreeRTOS ensure proper timing for TCP/IP packet processing. Many demos which using different TCP/IP stacks embedded in FreeRTOS are available on [4].

Implementation of Webserver

Webserver code consist of major 3 parts.

Code for parsing URL and returning appropriate file including HTTP header.
Storing html pages,css,images in hex.
http-cgi server side scripts.

We have used FreeRTOS embeddedTCP demo for IAR [5] as reference and modified it for adding more functionality.

We will show the changes/additions required in uip http demo in order to run your own Web Page.

Select uIP TCP/IP Stack and disable all other tasks.
Change 91x_conf file according to configuration of STR9 Comstick.
Assign Physical Address MAC and IP address in uip_Task.c

To add additional functions

Add CGI Keyword in html page. Starting from %! {keyword}

for example, page to display temperature value.

<html>
<head>
</head>
<body onLoad="window.setTimeout("location.href='temperature.shtml'",7000)">
%! temperature
</body>
</html>

Callback function

HTTPD_CGI_CALL(temperature, "temperature", temperature_value);
static const struct httpd_cgi_call *calls[] = {&temperature,NULL};

static unsigned short 
generate_temperature(void *arg) {
 return snprintf((char *)uip_appdata, UIP_APPDATA_SIZE,"%u °C\n",(int)temperature_measure());
}

Data written in uip_appdata will replace ‘%! {keyword}’ in html page.

httpd_cgi function compares the name from httpd_cgi_call buffer and invokes corresponding function. The invoked function may include call to some extern functions for application, then it returns with length of string to be sent by SOCK which is put in buffer named appdata.

Demo

We had demonstrated major 3 Type of Remote Control.

Controlling 230VAC Device

User should Switch On/Off any device connected to 230V AC via Webserver interface. To demonstrate it, we controlled CFL lamp connected to AC using mechanical relay circuit. Relay was made on or off according to request received from Webpage. To isolate relay circuit to our Comstick board to prevent any type of damages due to spikes we used MCT2E opto-isolator.

Controlling 230V AC Device from STR9 Comstick

Reading Status of Sensor

This type of control is required when a user want to monitor status of a sensor. We used a Motion Sensor (PIR sensor) which gives digital output according to human presence in the room. Server webpage will display sensor status.

Reading Analog sensor value

This type of control is required when user wants to measure or log information which is analog, like if we want to monitor temperature of room or we want to see graph of power consumption in room we can use this feature. For demo we have attached potentiometer to input of ADC whose value were displayed on Server webpage.

Project Setup