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Issue of June 2004 
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DSPs for intelligent UPS management

Now there is a need for systems' availability and reliability 24X7 in every business, and consequently a need for better power conditioning technologies. DSPs might be a solution to your UPS problems.

Today's factory and office control systems run more mission-critical applications than ever before. Uptime demands are increasing, which means there is a need for systems' availability and reliability 24X7. Hence the need for better power conditioning technologies.

Put it in perspective

First came UPS systems with bipolar transistors. At the time of its release these transistors allowed frequencies of switching much higher than any of their predecessors. This became the founding block for Pulse-Width Modulation (PWM). The PWM was followed by UPS systems with PWM chopping. Here the electronically controlled transistors opened and closed faster to produce finer chopping required for a sinusoidal output voltage. That led to substantial regulation of output voltage under both steady and transient situations.

Then came the UPS systems that assured free frequency regulation, which is the key to adapting to non-linear loads and better discrimination. Thus, they would supply more current if a fault raised the requirement. Parallel-connected UPSs with Application Specific Integrated Circuits (ASIC), and without centralized load sharing were next to take the UPS market. The use of ASIC components made it possible to integrate a number of digital and logical functions in a single component, instead of requiring cards.

Furthermore, its Insulated Gate Bipolar Transistors (IGBTs) considerably reduced the power required, for control, from what bipolar transistors used. It also made higher switching frequencies possible. These components started the trend for simplified circuits and better reliability. The microprocessors, from this point, were used for more than just the display. They constituted the heart of the UPS control electronics. The new in-built intelligence was used to communicate with connected equipment. The result: easier operation and enhanced reliability.

Slowly but surely the UPS became an integral part of the computer environment. Now, computer users count on the devices designed specifically for them.

The latest trend is the use of Digital Signal Processors (DSPs) for Sine Wave generation for optimized real-time processing. The Sine Wave range can be expanded from 20 to 480 A. This new application contributes to Total Harmonic Management.

The Power of DSP technology

A DSP controller provides an improved and cost-effective solution for UPS design, with high performance. It replaces of bulky transformers, relays, and mechanical bypass switches with smaller, more intelligent functional equivalents. It gives increased power efficiency, and power density. Plus it is compact and light.

The DSP has integrated functions selected for sophisticated embedded controls, in UPS applications. Except for signal conditioning and actuators that provide the interface between the DSP and the power circuitry, with DSP all the control implementations are digital.

DSP implementation has fewer parts, increased reliability and a greater immunity to noise. The DSP feedback and control loops are implemented digitally so there is no need for compensation for component tolerance. In short, DSP technology provides a cost-effective alternative to control multiple power converters, and meets the demands of advanced power topologies.

The three power stages

DSP technology enables the practical implementation of non-traditional topologies that were previously very expensive. One such topology utilizes three solid-state electronic power stages to regulate and condition power. The power management and voltage to the critical load is controlled with DSP by operating these three electronic stages.

The first stage includes a front-end filter and surge protection section with a rectifier to remove spikes and surges. The DSP-controlled rectifier acts as an electronic power-factor-correcting AC-to-DC boost circuit. It provides dynamic output voltage regulation.

The second stage functions as a DC-to-AC inverter during battery operation. It acts as a balancing circuit for the DC voltage into the inverter during normal operation, and also supplies energy for recharging the batteries.

The third stage comprises the inverter that acts as an electronic DC-to-AC converter circuit that regulates the output voltage delivered to the load. This converter generates a maximum AC output voltage that is lower than the DC voltage input to the inverter. The DSP controls the rectifier, balancer, and inverter and provides a superior output voltage regulation without having to use battery power at all.

The DSP facilitates and maintains the battery charge using advanced battery charging and monitoring algorithms. Thereby increasing battery life. The DSP-controller integrated electronic bypass provides power to the load with out any expensive bypass switch.

Conclusion

DSP technology enables practical implementation of sophisticated UPS topologies and controls. It can simultaneously control multiple power converters to optimize system efficiency, advanced battery management, improved output voltage regulation, better bypass capability and communications with other equipment. The result: smaller, lighter, well designed UPS's with higher performance.

 
     
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