Uninterruptible power supplies (UPS) play an important role in interfacing critical loads such as computers, communication systems, medical/life support systems, and industrial controls to the utility power grid. They are designed to provide clean and continuous power to the load under essentially any normal or abnormal utility power condition. Among the various UPS topologies or configurations, on-line UPS, also known as inverter-preferred UPS, offers the best line-conditioning performance and the most protection to the load against any utility power problems. It provides regulated sinusoidal output voltage under several input line condition. When powered from the utility power lines, it draws sinusoidal input current at a high input power factor. These improved input/output characteristics make on-line UPS the ideal solution in many applications. However, because of the use of multiple power conversion stages and the associated analog controllers, on-line UPS have traditionally been the most complex and expensive type of system. In addition to the analog controllers, on-line designs require the use of a low-end microcontroller to provide easy interface to a host computer in order to establish interactive communication and to implement adequate monitoring of the system. These multiple analog and digital controller based designs result in low component integration and increased system cost. High performance microcontrollers that can be used to achieve increased integration are available today, but they do not necessarily provide a cost effective solution. Today's low-cost, high-performance DSP controllers, such as the Texas Instruments (TI) TMS320C2000, provide an improved and cost effective solution for on-line UPS design. The 'C28x has integrated peripherals specifically chosen for embedded control applications. These include: analog-to-digital converters (ADCs), PWM outputs, timers, protection circuitry, serial communications, and other functions. High CPU bandwidth and the integrated power electronic peripherals of these devices make it possible to implement a complete digital control of on-line UPS. Most instructions for the 'C28x, including multiplication and accumulation (MAC) as one instruction, are single cycle. Therefore, multiple control algorithms can be executed at high speed, making it possible to achieve the required high sampling rate for good dynamic response. This also makes it possible to implement multiple control loops of an on-line UPS in a single chip. This results in increased integration and lower system cost. Digital control also brings the advantages of programmability, immunity to noise, and eliminates redundant voltage and current sensors for each controller. With fewer components, the system requires less engineering time, and it can be made smaller and more reliable. DSP control offers another big advantage over traditional analog control -- software. The extra DSP bandwidth is available for implementing more sophisticated algorithms, as well as communications to host systems and I/O devices such as LCD displays. DSP programmability means that it is easy to update systems with enhanced algorithms for improved reliability. For all these reasons, the 'C28x provides an ideal solution for on-line UPS design.