W0 Will/135425
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`PCP/U820ill/iESSallli
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`attenuators, amplifiers, and filters, as required to connect the controller board 205 to the
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`power electronics in the power electronics housing 120. The Hit card (controller board
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`205) resides in the control computer housing l02 that provides a GUI for interfacing and
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`configuring the controller hoard 205. The control computer housing lti'Z also houses a
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`mass storage device, such as a hard disk (not shown) for storing data. The GUI is
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`implemented in LahViEW software (available from National instruments Corp). The
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`operator inputs various pulse parameters, which are discussed in detail below. The
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`controller hoard software computes the corresponding canacitor voltages (Va, Va) and
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`switch timing, The controller board 205 then sends the capacitor voltage commands to the
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`charger are, capacitor dischargcrs 2l5, 216, and the switch timing signals to the gate
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`drives 220, 22L The controller board 205 also samples V(:1, V52, and EL (via connections
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`27 l, 272, 274) to monitor circuit operation, and inhibits or prevents coil currents from
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`exceeding specifications.
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`[6973}
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`Typically, the controllable semiconductor switches Q1 and Q2 should be able
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`to withstand the penis coil current anti the pea}; voltages appearing across their terminals
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`at the peak pulse repetition frequency. The switches Qi and Q2 should also have turn-on
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`and turnoff times of no more than a few microseconds. The maximum voltage of the
`semiconductor switches Ql and Q2 is ideally ch-l- Vgg. However, during current
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`commutation between the two energy storage capacitors Cl and C2, the switch voltage
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`can overshoot this value due to stray inductance and the finite turn—off and turn-on times
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`of the semiconductor switches Ql and Q2, and diodes Di and D2, To address this issue.
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`semiconductor devices with fast switching times should he used,
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`[907%]
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`in one embodiment, insulated gate hipoiar transistors (lGBTs m shown in Fig.
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`33 and available from Powerex of Youngwoorl, PA) are used for the switches Ql and Q2.
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`in another embodiment, gate—turnoff thyristors (GTOS), such as integrated gate-
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`cornnnutated thyristors (iGCTs) (shown in Fig. 3C) are used for switches Ql and Q2.
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`Both of these devices can sustain pulse currents of thousands of ampercs at voltages of a
`few ltilovoits while turning on anti off in a few microseconds. Since these devices can
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`turn off while the coil current is not zero, they are used with the snuhher circuits 222, 223,
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`224, 225, 226 (discussed in detail below) which absorb the energy of the commutation
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`transients, thus inhibiting anti/or preventing voltage overshoots that exceed the voltage
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`15
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`W0 Enid/135425
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`PCP/US$21}iii/ii35aiiit
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`ratings at the semiconductor switches, and energy dissipation in the semiconductor
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`switches, which nccnrs during switching.
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`{£5075} Untike the siiicnn—contreiied rectifiers {SCRs} used in conventicnai
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`stimniators, tGBTs can he hcth turned on and off from the gate terminai. There are
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`existing 168”? modnies with peak voitagez’surge current ratings of 3300 Vein/12000
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`Amperes, 4500 vats/6000 Amperes, 4500 Voits/QOGG Ampcrcs, and 6500 Voits/tSOGO
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`Amperes, and switching times of about one micrcsecond, which can he nSed tn
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`inrpiement a cTMS system. These IGB’I‘ modules have an integrated tdtramfast reverse
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`diode between the emitter and the coiiector (e.g., Di and D2 in Fig. 3), which chimps the
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`iGBT reverse voltage, and provides a freewheeling path for the ccit current 15,4.
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`{@976}
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`iGCTs behave iike efficient SCRS when turning on and during otindtiction,
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`and behave iike iGBTs when turning oftl The tnrh~nn time for an EGCT is apprnitirnateiy
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`i its, but the turn—off time can he as long as 10 its. iGCTs with integrated reverse diodes
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`(erg, Di and D2) and gate drives (cg, gate drive 220, 221) are avaiiahie with ratings of
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`4500 Volts and 17000 Amperes surge current, providing for robustness cf the design
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`{9877}
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`in the cTMS system, the stimuiaiing cnii L. is fcrccd tn ccmmutate between
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`the twc energy stcrage capecitcrs Ci and C2 when the cnii current is at its peak.
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`Managing the forced cnmmutation transient is ti chniienging aspect of implementing the
`cTMS system. The finite turn-Off and tnrnuon times of the semiconductor switches Qi
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`and Q2, and the stray inductance in the capacitor hanks Ci and C2, the switches Qi and
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`Q2, the dicdes Di and DE, and the wiring between them, can result in vnitage cvershoots
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`that exceed the voltage ratings cf the semiconductor switches, and switching power toss
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`and treating in the semiconductor switches. The stray inductances are reduced end/or
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`minimized by installing the semiconducter switches Qi and Q2, the diedes £31 and D2,
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`and the capacitor hanks Ci and C2 as ciese tcgether as showed by the physicai
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`dimensions of the components, and interconnecting them with wires or has hars arranged
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`to minimize the area of the current inept Still, stray inductance cannot be compieteiy
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`eiitninnted. For exarnpie, a typicai capacitor bank series inductance of E50 nH with 7 RA
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`current stores magnetic energy sufficient to produce a 27 ic‘v’ spike on an HGBT switch
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`with it) nF cciiectcr capacitance, which wnnid exceed the voitage rating of a 4566 V
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`tGB’t‘ by 22500 V, resetting in potentiai damage to the 163T“ Therefore, the srinhher
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`circuits 222, 223, 224, 225, 226 are used t0 stow down the transients, emetidrate power
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`36
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`‘WO EMS/135425
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`PCTIUSZMWQSMM
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`dissipation in the semicenductor switches Q! and Q2, and previde paths for stray
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`inductances to discharge in enter to suppress the veitage oversheets.
`{@978}
`in one embodiment, as shown in Fig‘ 3A, the snuhher circuits 222, 223 each
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`inciude at capaciter 3 l2, 318 in series with a dinde 3'14, 320 and resister 316, 322, which
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`are in paraiiei with each other. Snuhher circuits 222V 223 each aise inciude capacitors
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`326, 3305 This configuration aiiews the stirnuiating ceii current tn flow through the
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`snuhher capaciter 3 12, 318 when the cerrespending semiconductor switch Qt, Q2 is
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`turning eff; thus inhibiting and/er preventing veitage cvershoets. The snubber capacitor
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`312, 318 sheuid he iarge enough to heid the peak switch veitage heiew its rated iiniit. if
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`the snuhher capacitnr 312, 318 is ten Barge, switching tosses are increased. Snuhher
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`circuit 224 inciudes capaciter 324, snuhher circuit 225 includes capacitor 328* and
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`shuhher circuit 226 includes capeciter 332 and resistor 334-.
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`[9979}
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`Snuhher circuits 22?; and 223 (see Figs. 2A9 3A) can irieiude the circuit
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`embodiments shown in Figs SD, 3E arid/er 3F. Snuhher circuits 224, 225, and 226 (see
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`Fig. 12A) can inciude the circuit embodiments shown in Figs. 3D and/er BE
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`[@8893 Appreaches fer sizing 0f snubber components wiii he readiiy understeed by
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`those of ordinary skiii in the art, and inciude, hut are net iiiriited tn, anpmaches discussed
`in manufacturer uppiicatien mates and beaks on the subject 0f power eiectrenicsi
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`{£3081}
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`The gate drives 220, 221 serve to drive (cinch) the semiconductor switches Q1
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`and Q2 te an en state or an eff state. As previousiy discussed, the gate drives 220i 221
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`receive timing Sighais from the centreiier board 205, and appiy gate veitages to the gates
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`305, 310. Some high-power switchesy such as IGCTS, are manufactured with an
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`integrated gate drive unit. {GETS typicaiiy require a separate externai gate drive. For
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`high-power iGB’i‘s‘ iii-20 uC is deiivered to the gate to raise the gate-emitter vnitage to
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`i540 Veits to turn on the device. Te switch the. gate in about 1 #3, {GET gate drives
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`need an output impedance at a few ohms, and provide peak currents of a few Amperes.
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`EGBT gate drives are avaiiahie cemmerciaiiy. in scme impiementetiehs, the gate drives
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`20, 221 incniperate shert-circuit protectinn which prevents the switch from turning on if
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`. a short circuit is detected between the coiiector and emitter terminate (in IGBTS) er the
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`suede and cathode terminate (in GTQS and iGCTs), which impreves the fauh toierance
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`and safety of the cTMS system.
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`i?
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