Matrix Converter Used For UPS Application Critic Critical al loads loads such such as data data stora storage ge and comput computer er system systems, s, life suppor supportt equipment, equipment, process process equipment equipment controllers controllers,, telecommunic telecommunication ations s equipment equipment and emergency systems require continuous operation when there is a power failure. Associated problems such as poor overall power factor, heating eects, device malfunction and destruction of other equipment caused by nonlinear loads have been recorded. This trend reects in the increase use of uninterruptible power supp su pply ly (!" (!"## to prov provid ide e unint uninter erru rupt pted ed and and relia reliabl ble e powe powerr su supp pply ly with with the the provision of unity supply power factor. factor. !" systems have progressed progressed from rotary to hybrid and static type. $otating type uses motor%generator sets that are often used in high sinusoidal output applications. &ybrid type combines the use of motor%generator sets and static type. 'n this system the static !" are used to bridge bridge the gap between between the loss of the primary primary sourc source e and availab availabilit ility y of a secondary source such as a manually started diesel generator. generator. enerally static !" system are as shown in )ig.* comprising three basic elements+ a rectier-charger unit that converts input AC power into C power, an inverter unit that converts C power of a battery to AC power and a static bypass switch that transfers the critical load to the bac/%up supply and isolating from f rom the mains. A manual bypass switch is also normally added to cater for maintenance or repai repairr purpos purposes es of the !" unit. unit. The rectier rectier or charge chargerr normal normally ly uses uses a brid bridge ge%d %dio iode de in impl impleme ement ntat atio ion n witho without ut aor aordin ding g any any cont contro roll func functi tion on.. A transformer is used to step%down voltage during rectication operation, whilst during mains%failure the transformer performs as a step%up transformer. transformer. &owever due to the presence of bloc/ing switch operation there will be some distortions in the voltage and current. 'n order to minimise this distortion we now use mati0 converter instead of rectier and inverter. inverter.
The single phase matri0 converter ("!1C# requires 2 bi%directional switches as sh show own n in )ig. ig. 3+ each each capa capable ble of cond conduc ucti ting ng curr curren entt in both both dire direct ction ions, s, bloc/i bloc/ing ng forwar forward d and revers reverse e voltag voltages. es. 't requi require res s the use of bidir bidirect ection ional al switches switches capable of bloc/ing bloc/ing voltage voltage and conducting conducting current current in both directions. directions. The '4T were used due to its popularity amongst researchers that could lead le ad to high%power applications with reasonably fast switching frequency for ne control. The "!1C topology has been presented to operate as an ninterruptible !ower "upply Circuit (!"# incorporating nity !ower )actor Control. A single circuit is develo developed ped that that perfor performs ms both both the recti rectier er and invert inverter er operat operation ion may also also *
incorporate active power lter operation. The inverter transforms a C input into an AC output using the well%/nown "inusoidal !ulse 5idth 1odulation ("!51# technique, while it6s oering a reverse power ow through controlled rectier operation.
A systematic switching sequence is required that allows for the energy owing in the '4Ts to decay in order to minimise the stress on the switches. 'n conventional converters, free%wheeling diodes are used for this purpose. 'n "!1C these free%wheeling diodes do not e0ist, hence switching sequence needs to be developed to allow forced controlled free%wheeling. This is to protect the converter from being damaged as a result of voltage and current spi/es.
Proposed UPS Using SPMC7 sing "!1C the proposed system comparable to typical static !" system is as illustrated in g.2. 'n comparison only a single%circuit are required to perform both the inverter and rectier operation. "ince "!1C is characterised by pure controllable switching function, the need for the bloc/ing switch is eliminated and maybe replaced by sophisticated control algorithm that could be developed in the future. 8bserve also the use of "!1C reduces the need of having two separate circuits. 'n the proposed !", typical static !" system shown in )ig.2 is used.
'n comparison only a single circuit is required to perform both the rectier and inverter operations during normal and bac/%up modes respectively.
Inverter Operation:
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uring power failure the "!1C operates as a inverter. The battery of "!1C topology will supply for the load. 4y this approach during positive half cycle, "* and "2 will be on and "3 and "9 will be o. uring negative half cycle at "3 and "9 will be on, and "* and "2 will be o.
Rectifer Operation7 5hen there is no power failure, the main will supply for the load. The battey 'n )ig.*3 %*9 the upper switch of the rst leg which is closer to the capacitor is used to charge up the battery while the lower switches of both the rst and second leg ensure close trac/ing of the supply current to a sinusoidal reference current. 'n this, the switches of the rst leg operate in alternate sequence. This boost%charging strategy involves fast switching action of the switching devices which are piloted by !ulse 5idth 1odulation (!51# technique. All of these switching actions are carried out in the current control loop (CC:#. "ince instantaneous switching actions is required of the "!1C to ma/e the supply current follows the sinusoidal reference current closely, the current control loop time response has to be fast. 'n the simulation wor/s an operating switching frequency of 3; <&= is used.
1eanwhile the other upper switch on the second leg is used to divert the boost energy away from the battery to ensure the voltage level of the battery does not e0ceed the limit. This is achieved by actively and continuously monitoring the battery voltage level using a voltage control loop (>C:#. 'n this control loop the voltage of the battery is compared with a set reference in order to provide for the appropriate action of the switch. The switch is turned on upon detection of equality of both voltage levels. 8n the other hand, if the voltage 9
level of the battery is lower than the set reference the switch is turned o and the boost energy is directed bac/ to the battery. Therefore, this control loop is vital in ensuring the battery life is sustained.
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