Controller Development for Online UPS

CLIENT

A leading Indian company working in the field of Inverters/UPS.

OBJECTIVE

• To develop the controller for online UPS having following features:-
• Controller should regulate the output voltage (decided by the hardware configuration) with 1% accuracy.
• Synchronization action while shifting from UPS to Mains mode, to prevent the output transformer from saturation.
• Soft - Start feature.
• Bypass action when more than indicated load capacity is being driven in mains mode.
• Plug-in SNMP module to facilitate remote monitoring of UPS conditions.
• Monitoring and control of Temperature, Short circuit, Thermistor open/close conditions, Input Frequency etc. 
• LCD indications to indicate various UPS conditions like Mains mode, UPS mode, Low battery, battery under-voltage, Charging etc.

PROJECT SCOPE

Monitoring the feedback from the output voltage (Sinusoidal in nature) and implementation of Peak detection logic in software. To take corrective action using PI control technique, when output voltage falls below a certain level under loaded condition.

• To generate output Sinusoidal signal using Sine triangle PWM.
• Proper synchronization while switching from UPS to mains mode, so that the output transformer would not saturate.
• Monitoring of Analog signals like temperature, battery voltage and to provide protection.
• Development of a separate low cost SNMP plug-in module. The UPS controller would communicate to SNMP controller over SPI lines and provide health information. This information would be sent over network using SNMP and can be viewed using a standard MIB browser from any computer in the network.
• Post delivery support and release management.

KRITIKAL'S ROLE

KritiKal was solely responsible to bring the product to completion. The project required understanding of Control system techniques like PWM, PI etc along with expertise in Inverter concepts like Sine triangle PWM, drive circuits etc. Also it required understanding and proper usage of DSP engine of Microchip controllers. KritiKal has a strong background in the field of controller development for such power electronic applications development. Our command over embedded C and implementation of software filters like moving average system, glitch filters, PLL loop etc was appreciated by the client.

CHALLENGES

Control Systems knowledge: It required KSPL to have a thorough understanding of control systems because certain features like PI control of current, hysteresis etc are possible only by applying such standard techniques.

Drive Circuit and basic Inverter /Ups working principle: The project required expertise in Drive circuitry along with knowledge in the working principle of a half bridge inverter.

SNMP and TCP-IP stack: Understanding of Microchip TCP-IP stack and modify it accordingly for application as plug-in SNMP module.

Time Constraint: The timeline for this project was a major limitation. Due to heavy competition in the market of Inverters and UPS the client required a working prototype developed and deployed within six months at its site. Continuous & prompt support was provided for fixing field bugs and robustness was achieved both in terms of hardware and software.

Continuously evolving requirements: Project requirements kept evolving throughout the project life cycle as per features required by the end user.

VALUE DELIVERED

KritiKal was able to provide the working prototype with in the time limit set by the customer and the product achieved the ruggedness and robustness required by a field inverter unit by extensive testing and bug fixing by the end of support period. The product has gone under production phase now and is in process of deployment of approximately 2000 units at site.