Broadband power demands energy efficiency

Because power requirements and their associated costs are rising, the power efficiency of each component in the system must be scrutinised by system designers.

Power usage for broadband in the US alone, is estimated to grow from $1billion to as much as $4 billion by 2020. The broadband industry is looking to equipment manufacturers to help reduce this increased demand on the power grid through improved equipment efficiency. Conservative estimates have shown that just a 5% gain in power supply efficiency, multiplied over 200 power supplies, can result in power cost savings of $50,000 per year - or $250,000 over five years.

Energy consumption

The Society of Cable Telecommunications Engineers (SCTE) has recently announced the first standards for energy management in the broadband industry to help the industry reduce energy consumption. The majority of the energy savings for SCTE’s Energy 2020 goals are expected to come from increased efficiency at the headend, which is the control centre in a broadband system where satellite signals are gathered and monitored before being pushed upstream into the broadband network.

Another point of energy savings and efficiency can be found in the power supply that pushes power from the headend through hundreds of miles of broadband network in any given community. Found roughly every four to five miles, a power supply operating in the US takes 120V AC from the power grid and reduces it to 60 or 90V AC (power needs differ internationally) before providing clean, stable power to the broadband network.

Until the late 1980s, traditional cable television content and its delivery system could easily accommodate the eight to 12ms transfer time typical of standby power systems. As combined voice, video and data services emerged as the communications content, it became clear that even milliseconds of interruption in power could have serious consequences on digital signals. For example, packet voice service is very sensitive to plant outages, since the voice packets cannot be resubmitted or recreated. Power systems were developed to meet requirements of seamless power transfer to and from system batteries that constituted the primary back-up power source.

Figure 1: Broadband backup power supply block diagram

Today, power systems with back-up power capabilities are a baseline requirement for most broadband networks. The back-up power component of these systems now incorporates enhanced thermal battery management, dual power grid switching and even integrated engine generators. Such improvements provide longer back-up runtime in the event of extended utility power outages. They also enhance battery life - both contributing to improvements in the overall reliability of the network.

The role of AC power

On the most advanced broadband power supplies, AC power entering the unit is converted into a quasi-square wave and is regulated, in most instances, by a patented ferro-resonant transformer at the required output voltage. The regulated voltage is connected to the load via the output connectors and some power is directed to the battery charger to maintain a float charge on the batteries.

When the incoming AC line voltage significantly deviates from normal, the power supply automatically switches to standby operation, activating the inverter, and maintains power to the load. During the switch to standby operation, energy from the module’s ferro-resonant transformer continues to supply power to the load. In standby mode, the power supply powers the load until the battery voltage reaches a low-battery cutoff point.

When utility power returns, the transformer module waits a short time for the utility voltage and frequency to stabilise and then initiates a smooth, in phase transfer back to AC line power. Once the transfer is complete, the battery charger recharges the batteries in preparation for the next event.

As technology advances, modern broadband power supplies offer several opportunities for increased energy savings and efficiency.

Incorporating intelligent tap switching at the input of the ferro-resonant transformer optimises the power supply’s performance, resulting in significantly reduced utility power consumption, by minimising the secondary saturation energy loss of the ferro transformer while it regulates the output voltage. The intelligent tap switching also extends the brown-out utility operation under less than full load operation. As long as the ferro transformer can keep the output in regulation it will stay in line mode which minimises the battery discharge cycle, maximising battery life. Extended line mode operation also improves the utility efficiency by preventing the charge cycle required after battery discharge cycle.

Broadband plant management

All of the broadband loads are constant power load. Higher plant voltage will reduce the current required to flow through the broadband plant. To minimise the broadband plant I²R loss, the broadband plant current has to be minimised by maximising the broadband plant voltage. Safety requirements allow a maximum voltage of 90V AC from the broadband plant, therefore the output voltage has to be maintained at the high voltage level to maximise the efficiency. The output voltage must be tightly regulated so it does not exceed the 90V AC safety limit. High and tight output voltage regulation helps to maximise the broadband plant efficiency. Capital expenditures and ongoing operating costs can also be reduced through advanced battery management. Efficiently charging batteries optimises battery health and longevity.

A multiple-stage charger provides a broadband uninterruptible power supply (UPS) optimised charge current and multiple battery voltage regulations to maximise the battery life and to optimise the charging cycle. Monitoring and managing the current flowing to each battery assures all of the batteries in the string are under the same state of charge to get the extended life benefit from the multi-stage string charger. Ending the battery discharge cycle based on individual batteries will prevent the over-discharging of a weak battery in the string, preventing damage to the weak battery.

Further optimisation of the power supply and the broadband network is achieved through Internet-enabled monitoring. The broadband UPS is connected directly to the broadband network, allowing it to transmit and receive data via a built-in modem, allowing for status monitoring, historical data analytics and direct firmware updating.

Adding intelligence

Intelligent power supplies within broadband networks provide status monitoring and valuable information before, during and after power outages. Before an outage, status monitoring identifies faulty batteries, problems with connections between the batteries and power supply and potential charging system issues. During a power outage, accurate measurement of the individual battery voltages is a requisite to creating accurate, real-time predictions of remaining runtime (autonomy), which is critical to decisions on where to dispatch service personnel.

In light of ongoing developments in the broadband industry, clean, quality power is needed with more reliability than ever before. Residential and commercial customers are spending more. Increasing revenue streams for broadband providers are based on higher-quality services, such as telephony. Where analogue technology once tolerated momentary power service interruptions, the complex digital stream is much more susceptible to power interruptions of any length. Delivering highly efficient power supplies, using battery optimisation and IP monitoring can help the broadband industry achieve the business models they are striving to attain, while keeping their customers powered.