data centres demand highly efficient ups systems: meeting ... · least in part, because cloud...

Data centres demand highly efficient UPS systems: Meeting tough performance and cost goals requires advanced techniques and technologies

Whitepaper

Copyright 2019 © TOSHIBA ELECTRONICS EUROPE GMBH, All Rights Reserved.

Data centres demand highly efficient UPS systems: Meeting tough performance and cost goals requires advanced techniques and technologies As we become ever more reliant on the technology that powers our modern lives, so the constant 24/7/365 availability of these systems becomes more important than ever. These days human knowledge, including the huge amount of data generated by the Internet of Things (IoT), is stored in a plethora of data centres that span the globe. These highly secure facilities store our data safely and allow us to access it, as we need it. However, data centre operators face a number of challenges to be able to provide the availability service levels that governments, businesses and consumers demand. Data storage is becoming a commodity and prices are falling, meaning that data centre operators must find lower cost ways of delivering a service that meets tough service standards. At the heart of delivering this capability is the Uninterruptible Power Supply (UPS) that not only cleans and conditions the power, but provides uptime capability during power outages. In this white paper, Toshiba Electronics Europe will look at some of the applications for UPS systems and consider some of the key technical improvements that are allowing modern UPS systems to deliver the efficiency, performance and size needed by the most demanding applications

Introduction Not only are we storing more and more data, we are not particularly disciplined about clearing out old data. This is, at least in part, because cloud storage is becoming ever cheaper. It is no surprise, therefore, that the data centre rack market is showing strong growth. According to a September 2017 report by leading research firm, Research and Markets (www.researchandmarkets.com), for example, the shipment of racks to data centres will grow with a CAGR of over 19.0% during the period 2016-2022. This means that a key requirement for modern data centres is the ability to scale in terms of both data storage and power supply demand. As the frequency and severity of power outages is growing rapidly on a global scale and the costs of downtime are significant, investment in UPS technology is vital. This, in turn, is leading to a strong UPS market that is predicted to reach $13.7Bn by 2022. Rapid growth in e-commerce is fuelling UPS growth in developing markets, especially Asia-Pacific where the CAGR is forecast to be around 7.2%. However, Europe is, and will remain, the largest market. In general, UPS systems are becoming smaller, lighter and more powerful as modular solutions increase in prominence while the systems they protect are becoming larger, demanding more power.

Whitepaper


Architectures of UPS systems and key requirements Given the variety of applications and user groups, including banks, data centres, smart factories, hospitals, universities and even homeowners, then it can be expected that there are a variety of UPS types available with varied advantages to serve the varied markets. The three main types of UPS in common use today include offline, line interactive and online double conversion.

Figure 1: The three main types of UPS system in common use today

In common with the different types of UPS power systems, there are several challenging requirements, some of which compete with each other. Besides the strong cost pressure the main topics that need to be addressed are efficiency, voltage conditioning and power factor correction (PFC).

Always On Efficiency

Voltage Conditioning / Power Factor

Correction Power Range Cost per VA

Stand-By No Very high Low < 5kVA Low

Line Interactive No Very high different grades* 5kV - 100kVA Medium

Online Double Conversion Yes Low-Medium High > 100kVA Medium* depends on design by supplier

Whitepaper


Today designers are looking to implement improvements within given limits dictated by the particular type of UPS system. They want to reach a better system performance that combines the highest efficiency with optimum PFC and voltage conditioning to ensure lowest Total Harmonic Distortion (THD). Modular systems that favour Line Interactive or Online Double Conversion architectures still require improvements for efficiency, voltage conditioning and power factor correction. The space pressure in almost all data centre applications means that size is important. This has fuelled the popularity of rack type approaches based around modular UPS systems. Because the total power of each module is much less than that of the overall UPS system there is more flexibility for designers to find smart solutions that address key design criteria. To be able to reduce system size further, power density must increase. This brings the challenge of being able to operate more efficiently as there is less space for thermal management; passive thermal management such as heatsinks require space and active cooling with fans has a negative impact on overall system efficiency. In order to reduce current and therefore improve I2R losses, some applications are now implementing high-voltage busses that bring further challenges for UPS designers. But high efficiency is only one element needed to ensure the best performance of systems while reducing overall energy cost. Achieving a high power factor is also crucial. Harmonics from the UPS can have an impact on the mains supply voltage, which can have a negative impact on sensitive equipment. The blade servers used in data centres, can also contribute to the problem, making excellent power factor correction methods even more important.

Improving efficiency, power factor and voltage conditioning in UPS systems The market is expected to provide new system enhancements through the use of wide band gap GaN or SiC devices. However, these technologies are still relatively new and from a supply and cost perspective not at desired levels – yet. In the meantime, designers are seeking innovative circuit designs using silicon-based components that deliver incremental increases in efficiency. It is for this reason that Toshiba has engineered a new solution that focusses on providing immediate improvements that allow designers to utilize existing components to achieve results similar to those expected from wide bandgap devices. No discussion of UPS systems and data centres would be complete without mentioning the vital need to continuously drive down cost. And there are different cost elements that need to be addressed. Total cost of ownership is driven by the basic cost of the system and the cost of energy supply. Both low system efficiency and poor power factor drive the energy bill up. That’s why we need new solutions that can increase efficiency and provide better power factor correction. Better voltage conditioning reduces the harmonics injected into the system and can be achieved, for example by increasing the switching frequency. Not only does this help to improve the approximation of an ideal sine wave, but it also has a positive impact in reducing the size and cost of passive components. However, contradicting that improvement is the fact that an increased switching frequency leads to a reduction of efficiency and requires better cooling. This demonstrates the dilemma that designers have as they struggle to create the optimum system. With conventional solutions, currently available on the market, such an optimum is hard to find. That’s why a new solution that helps to reduce switching losses at higher frequencies enables improvements in UPS efficiency, supports increased power density and improves sine wave quality. Such a solution provides a significant benefit to designers seeking optimum UPS performance. The following illustrates how switching losses are a significant source of losses with an increase of operating frequency. In a half-bridge topology as commonly used in UPS inverters, switching losses are determined by two primary mechanisms. The first is the reverse recovery charge (Qrr) stored in the freewheeling diode that causes a current peak in the lower transistor as it transitions into the conducting state. The second is the charging current peak during the reversal of the output capacitance (COSS) of the upper switching transistor.

Whitepaper


Figure 2: There are two primary power loss mechanisms in a half bridge

Figure 3: Synchronous Reverse Blocking delivers improved efficiency with standard semiconductors

A technique known as Synchronous Reverse Blocking (SRB) blocks the reverse current using an additional transistor that is controlled synchronously. The resulting reverse current is channelled through a parallel Silicon Carbide (SiC) diode that has extremely low reverse recovery charge, thereby significantly reducing the impact of Qrr. Toshiba has patented Advanced-SRB (A-SRB)[1] that significantly negates the power losses due to recharging the output capacitance (COSS) of Q1 by pre-charging before the lower transistor is turned on. Increasing VDS to around 40V using a charge pump within the driver IC, effectively reduces COSS by a factor of 100, thereby significantly reducing the losses. In a practical A-SRB realisation, the switching transistor (Q1) is a high-voltage superjunction DTMOS IV type MOSFET with a maximum blocking voltage of around 650V. The series-connected blocking transistor Q2 is a low-voltage superjunction UMOS VIII type MOSFET with a blocking voltage of 60V. The final circuit element is a SiC Schottky freewheeling diode with very low reverse recovery as shown in Figure 7 below:

I

tV

tP

t

Qrr Coss charging

Current peak caused by diode reverse recovery charge Qrr and charging of MOS output capacitance Coss.

Main current

Coss

Coss is the internal parasitic output capacitance of the superjunction MOS transistors

Whitepaper


Figure 4: Components of the A-SRB circuit topology

Toshiba’s dedicated T1HZ1F driver IC embodies the intellectual property from their A-SRB patent and generates all necessary control signals for the transistor gates from a PWM input signal as well as the charge pulse for pre-charging the output capacitance. A-SRB technology benefits the inverter in UPS applications significantly and is also suitable for solar inverters, DC/DC converters, power factor correction (PFC) and motor drive control. It is equally applicable to a half-bridge configuration as well as other power topologies as shown below.

Figure 5: Circuit topologies suitable for A-SRB

A further benefit of the A-SRB technique is that it allows for higher switching speeds to be implemented in the inverter. Compared with an IGBT approach that is frequency-limited, A-SRB’s higher frequency of operation allows for a significant size, weight and cost reduction in the output filter. The efficiency benefits of A-SRB are significant when compared to IGBT, mainly due to the frequency limitations. However, the benefits of A-SRB over a standard superjunction MOSFET approach are also substantial, and they increase with frequency.

A-SRB DriverT1HZ1F

VDD

PGND

Precharge pulse

5V out for photo coupler

Fault

EN

PWM in

High voltage DTMOS IV (e.g. 650V type) with low RDS(on)

Low voltage UMOS VIII (e.g. 60V type) with low RDS(on)

SiC Schottky diode with extremely low reverse recovery charge

Whitepaper


Figure 6: The efficiency benefits of A-SRB increase with operating frequency

As an example, at an operating frequency of 50 kHz, an A-SRB inverter would have an efficiency of 98.5%, compared to a standard superjunction solution at 95.0%. This would translate into a significant reduction in thermal management requirements that would reduce size, weight, complexity and cost – as well as significantly reducing energy costs. In fact, in a data centre, the savings are more than might be immediately apparent as the reduction in heat dissipation also leads to a reduction in the cost for air conditioning.

Toshiba A-SRB solutions Toshiba offers a variety of solutions to implement an inverter bridge with A-SRB functionality, depending upon the required power level. For modular inverters up to 300W, the T1JM4 module is a complete solution that integrates the A-SRB capable gate drivers, switching transistors and SiC Schottky diodes.

Whitepaper


Figure 7: Different options for implementing an inverter bridge with A-SRB

Alternatively, for higher power solutions a discrete design can be realised using Toshiba’s T1HZ1F gate driver ICs and discrete DT MOS, LV MOS and SiC SBD. Toshiba offer the required components as complete kits of components making ordering and inventory management easy.

Figure 8: Toshiba offer a range of kits for easy implementation of A-SRB inverters

To develop inverter solutions up to 10 kW, either kit 1 or kit 2 can be used in parallel. The scenario A-SRB scenario described above provides several options for new solutions across various types of UPS systems. However, it is particularly beneficial for line interactive and online double conversion systems that seek improvements in efficiency, power factor correction and reduction of harmonics.

Whitepaper


Conclusion As data and its availability 24/7/365 becomes more important to businesses, governments and individuals, so the companies that we trust with our data are taking steps to ensure constant availability of this information. With rising energy costs and the need for installation in small spaces where temperature control costs money, efficiency is one of the most important aspects. Providing solutions that reduce better power conditioning runs a very close second in terms of critical needs. While semiconductors continue to improve in terms of performance, designers requiring the ultimate performance are seeking out new techniques such as Toshiba’s patented A-SRB, which allows the current generation of semiconductors to offer performance comparable with forthcoming wide-bandgap devices.

Notes: [1] Toshiba Corporation Energy Systems & Solutions Company, 2016. Semiconductor switch and power conversion apparatus. Europäische Patentschrift EP 2 600 527 B1. 03.02.2016

https://apps.toshiba.de/web/ContactUs/

Whitepaper


Restrictions On Product Use

Toshiba Corporation and its subsidiaries and affiliates are collectively referred to as “TOSHIBA”. Hardware, software and systems described in this document are collectively referred to as “Product”. • TOSHIBA reserves the right to make changes to the information in this document and related Product without notice. • This document and any information herein may not be reproduced without prior written permission from TOSHIBA. Even with

TOSHIBA’s written permission, reproduction is permissible only if reproduction is without alteration/omission. • Though TOSHIBA works continually to improve Product's quality and reliability, Product can malfunction or fail. Customers are

responsible for complying with safety standards and for providing adequate designs and safeguards for their hardware, software and systems which minimize risk and avoid situations in which a malfunction or failure of Product could cause loss of human life, bodily injury or damage to property, including data loss or corruption. Before customers use the Product, create designs including the Product, or incorporate the Product into their own applications, customers must also refer to and comply with (a) the latest versions of all relevant TOSHIBA information, including without limitation, this document, the specifications, the data sheets and application notes for Product and the precautions and conditions set forth in the "TOSHIBA Semiconductor Reliability Handbook" and (b) the instructions for the application with which the Product will be used with or for. Customers are solely responsible for all aspects of their own product design or applications, including but not limited to (a) determining the appropriateness of the use of this Product in such design or applications; (b) evaluating and determining the applicability of any information contained in this document, or in charts, diagrams, programs, algorithms, sample application circuits, or any other referenced documents; and (c) validating all operating parameters for such designs and applications. TOSHIBA ASSUMES NO LIABILITY FOR CUSTOMERS' PRODUCT DESIGN OR APPLICATIONS.

• PRODUCT IS NEITHER INTENDED NOR WARRANTED FOR USE IN EQUIPMENTS OR SYSTEMS THAT REQUIRE EXTRAORDINARILY HIGH LEVELS OF QUALITY AND/OR RELIABILITY, AND/OR A MALFUNCTION OR FAILURE OF WHICH MAY CAUSE LOSS OF HUMAN LIFE, BODILY INJURY, SERIOUS PROPERTY DAMAGE AND/OR SERIOUS PUBLIC IMPACT ("UNINTENDED USE"). Except for specific applications as expressly stated in this document, Unintended Use includes, without limitation, equipment used in nuclear facilities, equipment used in the aerospace industry, lifesaving and/or life supporting medical equipment, equipment used for automobiles, trains, ships and other transportation, traffic signalling equipment, equipment used to control combustions or explosions, safety devices, elevators and escalators, and devices related to power plant. IF YOU USE PRODUCT FOR UNINTENDED USE, TOSHIBA ASSUMES NO LIABILITY FOR PRODUCT. For details, please contact your TOSHIBA sales representative or contact as via our website.

• Do not disassemble, analyze, reverse-engineer, alter, modify, translate or copy Product, whether in whole or in part. • Product shall not be used for or incorporated into any products or systems whose manufacture, use, or sale is prohibited under

any applicable laws or regulations. • The information contained herein is presented only as guidance for Product use. No responsibility is assumed by TOSHIBA for

any infringement of patents or any other intellectual property rights of third parties that may result from the use of Product. No license to any intellectual property right is granted by this document, whether express or implied, by estoppel or otherwise.

• ABSENT A WRITTEN SIGNED AGREEMENT, EXCEPT AS PROVIDED IN THE RELEVANT TERMS AND CONDITIONS OF SALE FOR PRODUCT, AND TO THE MAXIMUM EXTENT ALLOWABLE BY LAW, TOSHIBA (1) ASSUMES NO LIABILITY WHATSOEVER, INCLUDING WITHOUT LIMITATION, INDIRECT, CONSEQUENTIAL, SPECIAL, OR INCIDENTAL DAMAGES OR LOSS, INCLUDING WITHOUT LIMITATION, LOSS OF PROFITS, LOSS OF OPPORTUNITIES, BUSINESS INTERRUPTION AND LOSS OF DATA, AND (2) DISCLAIMS ANY AND ALL EXPRESS OR IMPLIED WARRANTIES AND CONDITIONS RELATED TO SALE, USE OF PRODUCT, OR INFORMATION, INCLUDING WARRANTIES OR CONDITIONS OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, ACCURACY OF INFORMATION, OR NONINFRINGEMENT.

• Do not use or otherwise make available Product or related software or technology for any military purposes, including without limitation, for the design, development, use, stockpiling or manufacturing of nuclear, chemical, or biological weapons or missile technology products (mass destruction weapons). Product and related software and technology may be controlled under the applicable export laws and regulations including, without limitation, the Japanese Foreign Exchange and Foreign Trade Law and the U.S. Export Administration Regulations. Export and re-export of Product or related software or technology are strictly prohibited except in compliance with all applicable export laws and regulations.

• Please contact your TOSHIBA sales representative for details as to environmental matters such as the RoHS compatibility of Product. Please use Product in compliance with all applicable laws and regulations that regulate the inclusion or use of controlled substances, including without limitation, the EU RoHS Directive. TOSHIBA ASSUMES NO LIABILITY FOR DAMAGES OR LOSSES OCCURRING AS A RESULT OF NONCOMPLIANCE WITH APPLICABLE LAWS AND REGULATIONS.

data centres demand highly efficient ups systems: meeting ... · least in part, because cloud...

Documents