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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 4, JULY 2006

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Active Gate Voltage Control of Turn-on di=dt and Turn-off dv=dt in Insulated Gate Transistors Nadir Idir, Member, IEEE, Robert Bausière, Member, IEEE, and Jean Jacques Franchaud

Abstract—As the characteristics of insulted gate transistors [like metal–oxide–semiconductor field-effect transistors and insulated gate bipolar transistors (IGBTs)] have been constantly improving, their utilization in power converters operating at higher and higher frequencies has become more common. However, this, in turn, leads to fast current and voltage transitions that generate large amounts of electromagnetic interferences over wide frequency ranges. In this paper, a new active gate voltage control (AGVC) method is presented. It allows us to control the values at turn-on and at turn-off for insulated gate of power transistors, by acting directly on the input gate voltage shape. In an elementary switching cell, it enables us to strongly reduce over-current generated by the reverse recovery of the free-wheeling diode at turn-on, and oscillations of the output voltage across the transistor at turn-off. In the following sections, the AGVC in open and closed-loop for IGBT is presented, and its performance is compared with that of a more conventional method, i.e., increasing the gate resistance. Robustness of the AGVC is estimated under variations of dc-voltage supply and transistor switched current. Index Terms—Active gate voltage control (AGVC), electromagnetic interference (EMI), insulated gate bipolar transistors (IGBTs), metal–oxide–semiconductor field-effect transistor (MOSFET).

I. INTRODUCTION HE USE of high frequency switching devices in power converters induces high current and voltage variations and ) that excite oscillations in the parasitic ( elements of the power circuit, leading to conducted and radiated emissions at high frequencies. Generally, in order to control insulated gate power transistors such as insulated gate bipolar transistors (IGBTs) and metal–oxide–semiconductor field-effect transistors (MOSFETs), the gate circuit is fed by a for IGBT) between zero (or square-wave voltage source ( negative) voltage in the off-state, and up to 15 V in the on-state [1]–[3]. An active gate voltage control (AGVC) method is presented, which consists of applying a two-level voltage across the gate circuit; the height and width of the various levels are adjusted according to the type of commutation. In the first section of this paper, the operating principle of AGVC in open-loop is presented for turn-on and turn-off transition, respectively, and we compare its performance to that

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Manuscript received January 5, 2005; revised July 22, 2005. Recommended by Associate Editor E. Santi. The authors with the Laboratoire d’Electrotechnique et d’Electronique de Puissance, Université des Sciences et Technologies de Lille, Villeneuve d’Ascq F-59655, France (e-mail: [email protected]). Digital Object Identifier 10.1109/TPEL.2007.876895

Fig. 1. Experimental setup using AGVC.

of a more traditional method which consists of increasing the gate resistance. In the second section, two closed-loop control circuits are presented and implemented. The main advantage of this AGVC closed-loop is the combination of accuracy and simplicity. II. ACTIVE GATE VOLTAGE CONTROL TECHNIQUE The proposed method makes it possible to control the commutation behavior of insulated gate transistors at turn-on and turn-off, by introducing intermediate gate-voltage levels. In this study, the control technique has been applied to an IGBT (IRGPC40UD2) transistor and a free-wheeling diode (MUR3060PT) embedded into a buck-converter at 15-kHz switching frequency as shown in Fig. 1. Current measurements have been made using a current probe with 50-MHz bandwidth. All measurements have been carried out with a radiator temperature kept constant. The effect of temperature variations may be found in [6]. and The number of parameters needed to control depend on the type of commutation: two parameters are used for turn-on control and three parameters for turn-off control [4]. A. Turn-on AGVC: 2-Step Gate Control Voltage AGVC makes it possible to control the turn-on of insulated gate transistors. It consists of introducing in the square pulse voltage generator an intermediate voltage level between 0 and 15 V as shown in Fig. 2. In order to control the turn-on transition, two parameters are used: the voltage amplitude and the time duration of the intermediate voltage level . This method allows us to obtain a significant reduction of at turn-on for insulated gate transistors (like IGBTs and MOSFETs), which results in reducing the over-current due to diode reverse recovery and the electromagnetic interference (EMI) generated by power converters [5]. The influence of

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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 4, JULY 2006

Fig. 4. Variation of di=dt versus V 300 V, i = 3 A, Rg = 15 , and T

. The operating conditions are E = 360 ns.

=

Fig. 2. Drive voltage control signal and IGBT current waveforms at turn-on. The operating conditions are E = 300 V, i = 3 A, Rg = 15 , and T = 360 ns.

Fig. 5. IGBT current and voltage waveforms at turn-on for various switched = 6.8 V, V = 670 ns, current values. The operating conditions are V E = 300 V. Fig. 3. Gate control circuit (with V

= 15 V, Rp = 10 , and Rg = 15 ).

each control parameter on the transistor behavior at turn-on is discussed as follows. 1) Voltage Amplitude: The amplitude of the intermediate must be higher than the gate voltage threshold gate voltage , so that the collector current may flow through the transistor, but it must be lower than the full input voltage in order to slow down the rise of the collector current. If the value of is lower than , then the current rises with its natural slope as reaches 15 V. Experimental results soon as the drive voltage may be controlled by given in Fig. 2 show how turn-on varying only . Time duration is kept constant. The gate control signal may be realized in a very simple way with a voltage divider of ratio as indicated on Fig. 3. is that the amplitude of One consequence of reducing the diode reverse recovery current is strongly reduced. It may is relatively linear for be seen in Fig. 4 that the turn-on between 6.8 and 8.2 V. If is higher each value of at turn-on may no longer be controlled. than 11 V, 2) Time Duration: The second control parameter is the time of the intermediate gate-voltage level . It duration must be long enough to include all turn-on phases, i.e., the delay time and the current rise time. When the collector current reaches its final value, which corresponds to the end of the diode reverse recovery phase, the drive voltage reaches 15 V

(see Fig. 2). It is preferable to apply the full 15-V voltage at this precise moment since keeping a reduced drive voltage would slow down the transistor voltage fall and increase the switching losses. 3) Influence of Switched Current Variation: In order to study the influence of the switched current on the stability of AGVC at turn-on, the load current has been varied between 3 A and 6 A. The IGBT current waveforms for various load current values are shown in Fig. 5. during the turn-on transition is indeIt may be seen that pendent of the switched current value and depends only on in. A previous study [6] has shown termediate level voltage is insensitive to the variations in temperature that turn-on also. B. Turn-Off AGVC : Three-Step Gate Control Voltage AGVC also makes it possible to control at the turn-off switching of insulated gate transistors. In order to keep turn-off transition under control, it necessary to use the drive voltage control waveform given in Fig. 6, where three parameters may be identified: extraction time , amplitude of the intermediate and time duration . The role gate-voltage level of each AGVC control parameter at turn-off on the transistor switching is presented as follows. 1) Extraction Time: The first parameter of AGVC at turn-off is the zero voltage time duration , which is the time it takes for

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Fig. 7. Variation of dv=dt versus V . The operating conditions are E = 180 ns. 300 V, i = 3 A, Rg = 15 ; T o = 260 ns, and T

=

Fig. 6. Drive voltage control signal and IGBT voltage waveforms at turn-off. The operating conditions are E = 300 V, iL = 3 A, Rg = 15 ; T o = 260 ns and T = 180 ns.

the transistor output voltage to start rising. Only at this moment does the gate signal reach its intermediate value . During contains a sufficient this first phase, the input gate capacitor amount of charge to keep the transistor in the on-state. A shorter (smaller charge quantity extracted from the time duration gate) would result in an excessive delay time; on the contrary, is too long, it may result in a complete extraction of gate if charge, and in losing control of turn-off switching [1]. 2) Intermediate Drive Voltage Level: Under the assumption that the value of has been correctly set, the amplitude of interis the most decisive parameter mediate gate voltage level at turn-off. Of course, and makes it possible to control . this level must be lower than the gate threshold voltage Fig. 6 shows the transistor output voltage waveforms for var. ious values of at turn-off as a function Fig. 7 gives various values of . It may be seen of the intermediate voltage amplitude that decreases quite linearly with . of the interme3) Time Duration: The time duration diate gate-voltage level is the third parameter of turn-off AGVC. When the transistor output voltage reaches its final value, the drive voltage is brought back to zero. Any time delay between voltage rise and the end of the intermediate the end of the voltage level would result into an excess of switching losses. The turn-off gate control circuit is carried out in the same way that the turn-on gate circuit. 4) Influence of DC-Voltage Variation: In order to study the influence of the dc-supply on the stability of the AGVC at turn-off, the voltage value is varied between 100 and 300 V.

Fig. 8. IGBT current and voltage waveforms at turn-off for various dc-voltage = 5.1 V, T = 350 ns, source values. The operating conditions are V T o = 230 ns, i = 3.2 A.

Fig. 8 shows experimental collector current and emitter-collector voltage waveforms for various values of . It is clear that at turn-off does not depend on the dc-voltage value. is A previous study [6] has shown that the turn-off insensitive to the variations in temperature also. III. COMPARISON BETWEEN AGVC AND THE GATE RESISTOR VARIATION METHOD Different active gate control methods allowing to slow down commutations of an insulated gate transistor were studied [7]–[13]. The conventional solution consists of increasing the gate resistor value. The advantage of AGVC compared to this solution is highlighted by comparing the effects of these two methods upon two essential parameters of commutation: switching times and losses, for given values of dIc/dt at turn-on, and of dVce/dt at turn-off. 1) Turn-On Switching Time: The total time between the instant when the turn-on signal is applied and the beginning of the current rise can be divided into two parts. The first delay time is due mainly to the transit time of the transistor turn-on signal through the control circuit. It is generally constant since it does not depend on the operating conditions of the power transistor. Measured delay times are 240 ns for AGVC and 150 ns for the usual one-step signal. This difference results from the fact that

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Fig. 9. Measured turn-on switching waveforms of a IGBT showing drive voltage control signal, collector-to-emitter voltage and current, and gate voltage and switching losses (a) AGVC at turn-on with T = 670 ns and Rg = 15 and (b) gate resistance control. The operating conditions are E = 300 V, i = 3 A and dIc=dt = 105, 60, and 30 A/s, respectively.

using turn-on AGVC, the signal has to pass through several logic circuits (which specify the beginning and the end of the intermediate voltage level) before reaching the drivers. It is possible to reduce this delay time by employing fast logic components. takes to rise from zero to The second part is the time . It is directly proportional to the the gate threshold voltage and lengthens the commutation duration time-constant considerably when increases to slow down [1]. 2) Turn-off Switching Time: The turn-off time is composed of two parts. The first part represents the propagation time of the control signal through the logic circuits. This interval duration is conhappens indepenstant since the return to zero of voltage dently of the power circuit. The second part corresponds to the charge extraction phase reached the Miller plateau. The which ends when voltage duration of this interval is defined as the difference between the reaches 10% of its final value and the instant when tension starts to discharge. instant when capacity The measurement results show that the AGVC presents a smaller delay time compared to the gate resistor variation

IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 4, JULY 2006

Fig. 10. Measured turn-off switching waveforms of a IGBT showing drive voltage control signal, collector-to-emitter voltage and current, and gate voltage = 350 ns, and switching losses (a) AGVC at turn-off with T o = 280 ns, T and Rg = 15 and (b) gate resistance control. The operating conditions are E = 300 V, i = 3 A and dV ce=dt = 5.3, 2.5, and 1.6 kV/s, respectively.

at turn-off, but it method for the smaller values of . becomes comparable for highest values of 3) Turn-On Switching Losses: In an elementary commutation cell, whatever the gate control method employed, slowing down the turn-on current rise causes an inevitable increase in the switching losses. , the waveform of the voltage fall However, for a given is different according to whether AGVC or the usual one-step control is employed, as can be observed in Fig. 9. The more the value of the gate resistor increases, the more the turn-on switching losses increase when compared to those obtained with AGVC. 4) Turn-off Switching Losses: The current fall is more brutal with the one-step gate control signal because of the single voltage step from 15 V down to 0 V. However, for the and same switched same commutation conditions (same current and dc-voltage) the turn-off switching losses are almost the same whatever the type of control used (see Fig. 10).

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Fig. 11. Control block diagram for feedback turn-on control and idealized waveforms.

In conclusion, the obtained results show that when and are slowed down, AGVC allows us to limit switching losses. It may be noted that the amplitude of current and voltage , i.e., to parasitic oscillations are directly linked to high inductances. IV. FEEDBACK CONTROL A. Turn-On Feedback Control In the previous presentation of the AGVC at turn-on, the two adjustment parameters of the control circuit were defined: interand time interval . mediate voltage level corresponds to the gate voltage The ideal value of reaching 15 V at the moment when the current in the transistor reaches its final value (after the end of reverse recovery of the freewheel diode in the basic commutation cell). The control signal is obtained using the measurement of the evolution of the voltage across the transistor, because the use of a current sensor would make the circuit more complicated. However, as the voltage starts falling before the end of the reverse recovery of the freewheel diode (maximum current), the step that brings the drive voltage up to 15 V must be applied with a sufficient delay time to make it possible for the freewheel diode to recover its blocking properties. This avoids any risk of parasitic oscillation [4], [6]. It is thus possible to adapt the duration of the intermediate voltage interval by detecting the beginning of the decrease of the voltage across the transistor. The control block diagram and associated idealized waveforms are shown on Fig. 11. A derivator circuit is used whose exit is compared with a voltage threshold, which fixes the mobecomes equal to the input voltage . ment when voltage Two buffers D1 and D2 allow to provide the energy necessary to the IGBT switchings. Fig. 12 shows experimental waveforms of both control and power variables. The voltage V2 rises to 15 V as soon as the derivator output voltage becomes lower than the threshold which was set to 7.5 V. The turn-on feedback control then has the advantage of not having more than one adjustment parameter, the voltage level amplitude , to control at turn-on. The time length

Fig. 12. Experimental waveforms under feedback turn-on control The oper= 7.1 V, E = 300 V, i = 3 A, and Rg = 15 . ating conditions are V

of the intermediate voltage level adapts automatically to the transistor commutation conditions (switched current and dc-voltage). Fig. 13 shows the transistor emitter-collector voltage and current waveforms as well as the gate voltage and current waveforms obtained with a feedback turn-on control for three collector current values. B. Turn-Off Feedback Control The turn-off AGVC has three adjustment parameters. Only one of these parameters, the intermediate voltage amplitude , allows us to control at turn-off. and , must be However, the two other parameters, suitably adjusted so that the gate control can operate correctly. The best compromise for these values corresponds to an intermediate voltage step obtained measuring the rise in voltage across the transistor. and are set to zero at the same time as The voltages the input pulse voltage . At the end of the phase of charge starts to rise: this break extraction (Miler effect) the voltage change from 0 to of slope is detected to make the voltage 15 V as shows in Fig. 14. The height of the intermediate level fixes the positive slope of voltage . When the reached its maximum, the second break of slope is voltage back to 0 V. detected to bring the voltage The block diagram principle of the turn-off feedback control is shown in Fig. 15. The beginning and end of the intermediate drive voltage occur when the derivator output voltage is equal the voltage of the threshold detector set to 5 V and which causes . the variations of the voltage The turn-off feedback control thus requires only the adjustto give the transistor a speciment of the value of fied value, with other parameters adapting automatically to their optimal values, which is particularly advantageous when the switching conditions vary.

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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 4, JULY 2006

Fig. 15. Experimental waveforms under turn-off feedback control The oper= 5.2 V, E = 300 V, i = 3 A, and Rg = 15 . ating conditions are V

Fig. 13. Turn-on waveforms with feedback gate voltage control for various col= 7.1 V, E = 300 V lector current values. The operating conditions are V and Rg = 15 .

Fig. 16. Turn-off waveforms with feedback gate-voltage control for various = 4.3 V, E = collector current values. The operating conditions are V 300 V, and Rg = 15 . Fig. 14. Control block diagram for turn-off in closed loop and idealized waveforms.

V. CONCLUSION Fig. 16 gives the IGBT voltage and current waveforms as well as the gate voltage and current waveforms obtained with a feedback turn-off control for three collector current values. From these experimental results, it may be observed that at turn-off is slowing down as the switched current decays. This is obviously due to the longer charging time of IGBT parasitic capacitor since the switched current which must carry the gate charge out is smaller [1]. However, increase of the voltage rise time does not result in excessive switching losses in that case since the final collector current is low.

The AGVC described in this paper proves to be an effective , and the and advantageous method to limit the turn-on of insulated gate power transistors. turn-off The switching losses are increased, but less than by using a higher gate resistor to slow down the switching operation. The AGVC is not very sensitive to the values of the offstate voltage or switched current. The feedback control of the intermediate voltage level duration facilitates the development and turn-off no longer degreatly since the turn-on pend only on the magnitude of these levels. High current and high voltage IGBTs may have a different internal chip design

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and construction than the one evaluated in this paper. However, experimental measurements have been made with IGBTs up to 300-A current and 1200-V and the AGVC appears to bring the same advantages.

[13] C. Gerster and P. Hofer, “Gate-controlled dv=dt and di=dt limitation in high power IGBT converters,” Eur. Power Electron. J., vol. 5, pp. 14–22, Jan. 3–4, 1996.

REFERENCES [1] R. Hefner, “An investigation of the drive circuit requirements for the power insulated gate bipolar transistor IGBT,” IEEE Trans. Power Electron., vol. 6, no. 2, pp. 208–219, Apr. 1991. [2] N. Mohan, T. M. Undeland, and W. P. Robbins, Power Electronics: Converters, Applications and Design. New York: Wiley, 1995. [3] V. John, B.S. Suh, and T. Lipo, “High performance active gate drive for high power IGBT’s,” IEEE Trans. Ind. Appl., vol. 35, no. 5, pp. 1108–1117, Sep./Oct. 1999. [4] H. Sawezyn, N. Idir, and R. Bausiere, “Lowering the drawbacks of slowing down di=dt and dv=dt of insulated gate transistors,” in Proc. Power Electron., Machines Drives Conf., Bath, U.K., Jun. 4–7, 2002, pp. 51–556. [5] S. Igarashi, S. Takizawa, M. Tabata, and K. Kuroki, “An active control gate drive circuit for IGBT’s to realize low-noise and snubberless system,” in Proc. IEEE ISPSD’97, 1997, pp. 69–72. [6] N. Idir, R. Bausière, J.J. Franchaud, and H. Sawezyn, “Contrôle des commutations des transistors à grille isolée: Commande CATS,” in Proc. Revue Int. Génie Elect., Janvier, France, 2004, vol. 7, no. 1–2, pp. 49–74. [7] S. Musumeci, A. Raciti, A. Testa, A. Galluzzo, and M. Melito, “Switching-behavior improvement of insulated gate-controlled devices,” IEEE Trans. Power Electron., vol. 12, no. 4, pp. 645–653, Jul. 1997. [8] S. Park and T. M. Jahns, “Flexible dv=dt and di=dt control method for insulated gate power switches,” IEEE Trans. Power Electron., vol. 39, no. 3, pp. 657–664, May 2003. [9] C. Licitra, S. Musumeci, A. Raciti, A. U. Galluzzo, R. Letor, and M. Melito, “A new driving circuit for IGBT devices,” IEEE Trans. Power Electron., vol. 10, no. 3, pp. 373–378, May 1995. [10] R. Chokhawala, J. Catt, and B. Pelly, “Gate drive considerations for IGBT modules,” IEEE Trans. Ind. Appl., vol. 31, no. 3, pp. 603–610, May/Jun. 1995. [11] R. P. Palmer and H. S. Rajamani, “Active voltage control of IGBTs for high power applications,” IEEE Trans. Power Electron., vol. 19, no. 4, pp. 894–901, Jul. 2004. [12] B. Weis and M. Bruckmann, “A new gate driver circuit for improved turn-off characteristics of high current IGBT modules,” in Proc. IEEE IAS Annu. Meeting, Oct. 1998, pp. 1073–77.

Nadir Idir (M’94) received the Ph.D. degree from the Université des Sciences et Technologies de Lille, Villeneuve d’Ascq, France, in 1993. Since 1994, he has been an Associate Professor at the Laboratoire d’Electrotechnique et d’Electronique de Puissance, Université des Sciences et Technologies de Lille. His main research interests are power electronics and EMC in power converters.

Robert Bausiére (M’93) received the Ph.D. degree in physical sciences from the Université des Sciences et Technologies de Lille, Villeneuve d’Ascq, France, in 1982. He has been a Professor of power electronics at the Université des Sciences et Technologies de Lille since 1989. He is now with the Laboratoire d’Electrotechnique et d’Electronique de Puissance, Université des Sciences et Technologies de Lille. He is coauthor of three power electronic books. His main research interests are control of switching devices and multilevel power converters.

Jean Jacques Franchaud received the M.S. degree from the Laboratory of Electrical Engineering of Lille (L2EP Lille), Université des Sciences et Technologies de Lille, Villeneuve d’Ascq, France. He is a Research Engineer with the Laboratoire d’Electrotechnique et d’Electronique de Puissance, Université des Sciences et Technologies de Lille. His research interests include power electronics and EMC in power converters.