Controller Development for Offline UPS

CLIENT

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

OBJECTIVE

To develop the controller for 1KVA Offline Inverter:-

• Provide 10% regulation of Output at Full Load.
• LED indications to indicate various operating conditions like Mains mode, Inverter mode, Low battery, battery under voltage, Charging etc.
• Synchronization action while shifting from Inverter to Mains mode.
• Soft - Start feature.
• Provide Configurable Charging profiles.
• Monitoring and control of Temperature, Short circuit, Thermistor open/close conditions, Input Frequency etc. 

PROJECT SCOPE 

• Output Voltage correction using PI. For this sinusoidal feedback is available from output.
• Sinusoidal Output (50Hz). Sine Signal was generated using PWM.
• Provide options for Mains regulated and unregulated mode.
• Monitoring of Analog signals like temperature, battery voltage and to provide protection.
• Load Current dependent Battery cut off voltage.
• Configurable Charging profile.
• Post delivery support and release management.

KRITIKAL'S ROLE 

KritiKal has a strong grasp of Inverter Operation principles and as such was valuable in offering full time consultancy in software development. Having previously worked in this domain we had a full understanding of PWM techniques, Battery characteristics, Charging profile ,Relevant led indications, Controller peripherals, software filters etc. 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: Knowledge of Control algorithms like PI and Hysteresis and software filters are vital for achieving features like Soft Start, Charging Profile development and output Voltage Regulation.

Controller: Proper understanding of Controller peripherals like Timers, Counters, Input capture, PWM, Interrupts etc are very important for Sine Triangle PWM implementation and other timing related functionalities.

Drive Circuit and basic Inverter working principle: The drive circuit had to be properly studied and basic inverter working principle had to be well understood to achieve required performance. Achieving a THD of 4% under full loaded condition was a major milestone. It required lots of Iterations of the Sine wave generation module and changes in drive circuitry.

Battery characteristics: It required KSPL to have understanding of battery charactesitics.This was useful in determining if a battery connected was in healthy condition or not and take proper actions. Two charging profiles were developed to be deployed as per field requirement.

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 within 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.