S_brehaut_ipemc_2006

Gate driving of high power IGBT by wireless transmission Stéphane Bréhaut, François Costa, member IEEE SATIE UMR8029, ENS de Cachan. 61, Avenue du Président Wilson, 94235 Cachan France [email protected]

Abstract— In high power high voltage conversion, the technology of IGBT’s drivers is a very sensitive point due to the need of a high reliability and a high degree of insulation to transmit driving information and energy to the gate driver. Many techniques exist that allow an insulated transmission of the driving signal. Some, like the levelshifter or the optocoupler are commonly used in medium voltage range but are totally unsuited to high voltage. In this last case, a classical solution leads to use, for each IGBT, a DC supply with a high insulation transformer for energy transmission and an optic fiber for the transmission of information. This solution is reliable, fast, and not sensitive to disturbances. However, in the case of numerous switches to drive, this solution becomes costly and bulky. Thus, in this paper, we propose a driving system well suited to high voltage, which can be insensitive to high-level disturbances. A wireless solution coupled to an energy supply loop is proposed, in order to reduce the cost and bulkiness of high power converters. The advantage of this solution lies in a very low propagation time, a strong immunity to noise if signal coding is well studied and a simplified supply system to drivers.

to reduce the propagation impedance of the conducted Electromagnetic Interferences (EMI). At last, the energy supply system of the drivers must exhibit a high insulation while being compact. All these specifications have led us to pay a great attention to wireless transmission. In fact, with this technology, there isn’t any contact between the control and the converter, the propagation paths of EMI are greatly reduced with the distance between the power transistor and the low power drive. So, only the energy system supply has to be highly insulated. This can be obtained more easily than for the signal transmission, because these devices are more robust to EMI, as it will be shown hereunder. In Radio Frequency Transmissions (RFT), the delay time depends of the band-pass of the transmitter/receiver. In order to avoid EMI disturbances [5], we must include a coding strategy in the driving signal [6]. This paper depicts this new high-voltage driver: firstly, we will present the diagram block of the system HVID (100 kV). Secondly, we will propose a strategy of wireless transmission. II.

I. INTRODUCTION In electrical locomotive, the use of power converters directly fed by the catenary discloses the problem of the insulation of the drivers stage [1]. Indeed, with a 25 kV catenary voltage, standard technologies are not matched with usual insulation technologies, and new structures have to be developed for the realization of High-Voltage Insulated Drivers (HVID). The data an energy paths throughout the drivers need to be insulated from the IGBT and they must be reliable with respect to data transfer and to secured energy transfer. These systems must be compact because, in architectures of high-voltage converters, the number of switches can become significant as well as the quantity of connection’s wires [2]. So, the signal transmission through a barrier of insulation is a technical challenge in a great number of applications [3]. The solutions generally adopted are the optic fiber, the opto-coupler, as well as the pulse transformer [4]. The requirements for a safe drive transmission are gathered in some points: firstly, the stage treating the driving signal must be immunized against disturbances (high dV/dt). Another significant point is that the signal transmission must be reliable and fast. Moreover, the transmitter must have low parasitic capacitances in order

1-4244-0449-5/06/$20.00 ©2006 IEEE

PRESENTATION OF THE ARCHITECTURE OF A HVID

A. General presentation Many studies develop strategies of energy transmission between two distinct parts [7][8][9][10]. The suggested structure must take into account all the constraints previously detailed. Loop wire RF Receiver_1 2.45 GHz IGBT driver_1 RF transmitter 2.45 GHz The driving energy for 6 IGBTs

Half bridge inverter

The loop wire can be carried to the ground to minimize the transmission of the common mode current’s

RF Receiver_6 2.45 GHz IGBT driver_6

Figure 1. Concept of the HVID

IPEMC 2006

Fig. 1 shows the general working principle of our structure [11] [12]. At the low-voltage side of the driver, a half-bridge inverter induces a HF current in a Litz wire loop while a 2.45 GHz RF transducer transmits the encoded driving signal to all receivers. At high-voltage side, the driving energy is absorbed on the loop while a RF receiver and a decoder restore the driving signal. A high insulation degree is achieved with this topology, while it enables to reduce the number of DC supplies and the wiring of the converter. Moreover, it offers an excellent galvanic insulation as well as an excellent immunity against EMI. In order to minimize the radiation of the HF loop, this one must be twisted. B. Globlal model of the DGIT The Double Galvanic Insulation Transformer (DGIT) is a key factor in our system due to all the constraints that it has to take into account. In order to have a better comprehension of the DGIT, we have decided to model and to compare the simulation with the measurement. The DGIT is constituted by two simple transformers connected together with a loop wire, fig. 2. Note that the turn ratio’s product is equal to 1. The magnetic material of the core is nanocrystalline

Connection to the power l

Connection to one of the IGBT driver

A 2 meters longer between the two transformers V31

V11

the stray capacitances. So, the transformer model can be represented as shown in fig. 4. If we compare the simulation with the measurement in the 10 Hz-10 MHz range, we can observe the same comportment on the full range.

Figure 4. Measurement and simulation of voltage gain of the transformer connected to power supply, in the 10 Hz-10 MHz range Lf1 +m2.lf2=50 µH R1+m2.R2=4 Ω VE

m1=1/22 LM =30 mH

VS

Figure 5. Final model of the transformer connected to power supply

V32

V12

The Theturns turns number number isis22 22for for the theprimary primarywinding windingof ofthe thefirst first transformer transformerand andfor forthe thesecondary secondaryof winding the second of thetransformer second transformer

Figure 2. Concept of the DGIT with two windings

Each simple transformer can be represented by a typical model, as shown in fig. 3, [13]; however, it can be simplified regarding the frequency range and the design, as we will show hereunder.

Then, we have applied the same approach to the second transformer. In the 4 MHz-10 MHz frequency range, we found a –40 dB slope, as shown in fig. 6. Thus, the stray capacitance effect is not longer negligible for this second transformer, so we have added it in the model as shown in fig. 7. The simulation curve matches with the measurement one in the full frequency range, fig. 6.

C12 R1+m2.R2

Lf1+m2 .lf2 m1=1/N

VE

C1

LM

C2

Rch VS

Figure 3. Simple transformer model with three spray capacitances

This one is used to describe the transformer behavior, where Lf1 is the primary leakage inductance, Lf2 is the secondary leakage inductance, LM is the mutual inductance. C1 and C2 are the primary and secondary winding capacitances. C12 represents the capacitance between primary and secondary winding. m is the winding ratio. We have measured the voltage gain in the first transformer, on the 10 Hz-10 MHz range, as shown in fig. 4. A network analyzer with high impedance ports was used. We got a typical 1st order voltage gain curve with a positive 20 dB slope from 10 Hz to 200 Hz. This is due to the mutual inductance and to the winding resistances. On the other hand, there is no influence of

Figure 6. Measurement and simulation of voltage gain of the transformer connected to the IGBT driver, in the 10 Hz-10 MHz range Lf1+m2 .lf2=0.1 µH R1+m2 .R2 =0.04 Ω VE

m1 =1/22 LM=61 µH

C2 =16 pF VS

Figure 7. Final model of the transformer connected to the IGBT driver

The next step is to connect the two transformers to the loop wire. This one has stray elements composed by a resistance, Rc, in series with an inductance, Lc. It can be added to the leakage inductances, Lf1 and Lf1’, and to the winding resistances, R1 and R1’, as shown in fig. 8. m2 .R1+R’1+RC/2 2

m .Lf1 +LC/2+L’f1 VE

m2.R1 +R’ 1+RC/2 m1=1/22

m2 =22/1

m2.Lf1 +LC/2+L’ f1 C2

Lµ2 /2

VS

Winding capacitance responsable of the resonance at 1MHz=16 pF

Figure 8. Final model of the DGIT from the power point of view

C. The power supply efficiency The converter, which generates the energy for the driver working is a half bridge inverter, as shown in fig. 12. It can deliver up to 30 Watts, the purpose being to supply up to 6 drivers with the same loop. We have used Litz wire for the loop in order to reduce the losses due to skin effect. Fig. 11 shows the measurement setup of the power transferred across the system. Because neither of the load terminals is common to the converter’s ground, differential voltage probe are used to measure voltage at the output of the half bridge and at the load terminals. The power efficiency, µ , is defined as the ratio of the output power to the input power (1). Thus we get,

The simulation and the measurement curves are superimposed, in the full 10 Hz-10 MHz range, as exhibited in fig. 9.

µ=

Pout 30 Watts ×100% = = 84 % 35 Watts Pin

(1)

The primary voltage Vp, secondary voltage Vs, primary current Ip and secondary current Is, of the transformer are shown in fig. 11. The rectified voltage at the secondary winding is conditioned by the standard specifications of drivers, typically 24 VDC. (VP)

(IP )

Figure 9. Measurement and simulation of voltage gain of the DGIT from the energy transfer point of view, in the 10 Hz-10 MHz range

(IS )

Figure 11. VP (20 V/div), IP (5 A/div), VS (50 V/div), and IS (1 A/Div), commutation frequency 22 kHz

measurement simulation

Vin

Differential voltage probe

Current probe

Iin IRF630 Vcc

Vb

Differential Vout voltage probe Current probe

H0

RT

IC1 Vs IR2153

IRF630

Iout

RLOAD

Now, we have a reliable model. Among all the stray capacitances, only the winding capacitance of the high voltage side transformer determines the –40dB slope. This is an important information in order to control the usable frequency range to transmit the energy.

(VS)

24 VDC

+12 VDC CT

Com

L0

Figure 12. Primary part of the energy supplier of the driver

Figure 10. Measurement and simulation of the parasitic capacitance in the 10kHz-10 MHz range

In order to verify the low capacitance between the primary and the secondary winding of the DGIT, we have measured its value as shown in fig. 10. The parasitic capacitance is very low, around 1 pF, which is efficient to limit the propagation of conducted EMI.

III.

TWO STRATEGIES OF RF TRANSMISSION

Two strategies can be exploited to send out the RF driving signal. On one hand, we could directly transmit the numerical value of the duty cycle on the other hand, we could emit and encode the turning on/off order of the gate driver, this last solution has been chosen due to its simplest implementation. It can be considered as an asynchronous communication.

IV.

THE ASYNCHRONOUS COMMUNICATION

A. Presentation We consider this working as an asynchronous communication because the driver doesn’t need a synchronization clock. In fact, only the electronic power switching orders are emitted, fig. 13. a0

Start bit

a1 Serial/parallel converter a2

1

Input signal

1

Transmitter

Coding of turning on IGBT_1 and turning off IGBT_2: 1 001 1

a3

Connection of the driving signal 0-5 V

a4 Stop bit

Input signal common

Figure 13. Reception of the electronic power switching orders, using 5 bits

The driving signal is connected to the input terminal of the emitter. This is coded on 5 bits serial/parallel converter and modulated by a transmitter. The choice of the coding is treated by several logic gates. As an example, table I shows how the driving of a 3 legs inverter can be operated by this method. TABLE I.

A. Choice of the band pass We are interested in the 2.45 GHz band-width. There are currently many techniques of wireless transmission in this range. “WIFI” as well as “Blue Tooth” is currently in full expansion. The main problem with “WIFI” like with “Blue tooth” is the use of complex implementation protocols. These require a consequent material and a considerable processing time. We have chosen a RF video transmitter and receiver. These transmitters have a band-width in the order of 5 MHz. Moreover, several bandwidths can be selected. As we dispose of 5 bandwidths device, we can save one bit and reduce the code on 4 bits. We have tested the RF asynchronous communication with the code presented in the previous section. The frequency of the transmitted signal is 2.5 kHz. We have selected a rate of 4 Mbytes/s. We have calculated the delay time of the transmission as expressed by (2). Number _ of _ command _ bits *2 Flow _ of _ bits 4 _ bits * 2 = 2 µs Delay _ time = 4 MHz Delay _ time =

Emission of the command by the RF transmitter

(2)

The processing time including coding and decoding on 4 bits is 2 µs

Example of a driving code for a three phases inverter

Coded value of the Address of the IGBTs IGBTs state 1 001 1 Set IGBT_1, Reset IGBT_2, arm_1 1 010 1 Set IGBT_3, Reset IGBT_4, arm_2 1 100 1 Set IGBT_5, Reset IGBT_6, arm_3 1 110 1 Reset IGBT_1, Set IGBT_2, arm_1 1 101 1 Reset IGBT_3, Set IGBT_4, arm_2 1 011 1 Reset IGBT_5, Set IGBT_6, arm_3

B. The RF reception The receiver is made up very simply with just a decoder, a serial/parallel converter and a comparator, as depicted in fig. 14. Comparator 5 bits n=5 code of turning on IGBT_1 : 1 001 1

A

n=1

Reception of the command by the RF receptor

Figure 15. Delay time created by the 4 bits code

Fig. 15 shows that the signal received at the IGBT side is quite in phase with the input signal. Also, the effective delay time is very close to the calculated one. Now, we can consider that the RF transmission concept is possible. VI.

S

APPLICATION TO A LOW-VOLTAGE FIRST

B n=1

Demodulator

Serial/parallel converter

n=5

A code of turning off IGBT_1 : 1 110 1

n=5

n=1

Comparator 5 bits

Q n=1 R

B

PROTOTYPE Isolated output signal The electronic power switching orders 0-5 V

Isolated output signal Common

In order to validate our concept, we have tested it in a MOSFET chopper with a RL load as shown in fig. 16. The gate driving of the MOSFET is transmitted by wireless communication. Ubus

Figure 14. RF receptor for each switch

The asynchronous communication is very simple to achieve. Only 5 bits make it possible to control a three phases inverter. V.

DEVELOPMENT OF A PROTOTYPE

We must have a low delay time between the input signal and the output signal received by the gate driver. Thus, the data rate must be high in order to reduce the delay time.

RF transmitter 2.45 GHz The distance between the transmitter and the driver is 2 meters RF receiver

Driver

Half bridge inverter + Double galvanic insulation

Figure 16. RF transmission on a chopper

The MOSFET has a max. reverse voltage of 200 V and a max. current of 50 A. The component’s values of the load RL are selected in order to reduce the current ripple. To validate the correct operation of the system, we have varied the commutation frequency between 100 Hz and 2.5 kHz. The information is well transmitted to the MOSFET, as fig. 17 and fig.18 show for two values of the duty cycle (50 and 20 %).

[4]

[5]

[6]

Signal which represent the order of command before the coding on 4 bits

[7] Signal which represent VDS voltage on the bounds of the MOSFET

50 Volts

[8]

Figure 17. Control of chopper with a 2.5 kHz commutation frequency [9] Signal which represent the order of command before the coding on 4 bits

[10] Signal which represent VDS voltage on the bounds of the MOSFET

50 Volts

[11]

Figure 18. Duty cycle of 80 % with a 2.5 kHz commutation frequency

But now, a second prototype is to be realized in order to check the working of the full system under high-level constraints. VII. CONCLUSION We have treated in this article the gate driving of high power IGBT by wireless transmission. We have presented how to transmit the required energy thanks to a DGIT. A 30 Watts inverter supplies the power necessary for the drivers, with an efficiency higher than 80 %. For a first validation, we have driven a lowvoltage chopper with our wireless communication system. The next step of our work will be to check it in a HV inverter leg. REFERENCES [1] [2]

[3]

A. Colasse, A. Dandoy, Ch. Delecluse, R. Maffei, Ph. Thomas, Development of a multi-voltage locomotive with 6.5 kV IGBT; Power electronics and applications, 2003, EPE 03 J.Saiz, M. Mermet, D.Frey, P.O. Jeannin, JL. Schanen, P. Muzicki. Optimisation and integration of an active clamping circuit for IGBT series association, Industry Applications Conference, 2001. Thirty-Sixth IAS Annual Meeting. Conference Record of the 2001 IEEE Volume 2, 30 Sept.-4 Oct. 2001 Page(s):1046 - 1051 vol.2 U. Schwarzer, R.W. De Doncker, Design and implementation of a driver board for a high power and high frequency IGBT

[12]

[13]

inverter, Power Electronics Specialists Conference, 2002. pesc 02. 2002 IEEE 33rd Annual Volume 4, 23-27 June 2002 Page(s):1907 – 1912 M. Munzer, W. Ademmer, B. Strzalkowski, K.T. Kaschani, Insulated signal transfer in a half bridge driver IC based on coreless transformer technology, Power Electronics and Drive Systems, 2003. PEDS 2003. The Fifth International Conference on Volume 1, 17-20 Nov. 2003 Page(s):93 - 96 Vol.1 M. Zimmermann, K. Dostert, Analysis and modeling of impulsive noise in broad-band powerline communications; Electromagnetic Compatibility, IEEE Transactions on Volume 44, Issue 1, Feb. 2002 Page(s):249 – 258 G. Roberts, P. Hadfield, M.E. Humphries, F. Bauder, J.M.G. Izquierdo, Design and evaluation of the power and data contactless transfer device; Aerospace Conference, 1997. Proceedings., IEEE Volume 3, 1-8 Feb. 1997 Page(s):523 533 vol.3 K.W. Klontz, D.M. Divan, D.W. Novotny, R.D. Lorenz, Contactless power delivery system for mining applications, Industry Applications, IEEE Transactions on Volume 31, Issue 1, Jan.-Feb. 1995 Page(s):27 – 35 J.M. Barnard, J.A. Ferreira, J.D. Van Wyk, Optimized linear contactless power transmission systems for different applications, Applied Power Electronics Conference and Exposition, 1997. APEC '97 Conference Proceedings 1997., Twelfth Annual Volume 2, 23-27 Feb. 1997 Page(s):953 - 959 vol.2 R. Mecke, C. Rathge, High frequency resonant inverter for contactless energy transmission over large air gap Power Electronics Specialists Conference, 2004. PESC 04. 2004 IEEE 35th Annual Volume 3, 20-25 June 2004 Page(s):1737 - 1743 Vol.3 T. Bieler, M. Perrottet, V. Nguyen, Y. Perriard, Contactless power and information transmission Industry Applications, IEEE Transactions on Volume 38, Issue 5, Sept.-Oct. 2002 Page(s):1266 – 1272 E. Bowles, T. Overett, T. Smith, R. Street, Advanced buck converter power supply “ABCPS” for APT.; Particle Accelerator Conference, 1999. Proceedings of the 1999 Volume 5, 27 March-2 April 1999 Page(s):3755 - 3757 vol.5 Z. Hua, Y. Wang, K.D. Mueller-Glaser, O. Simon, Channel modeling for and performance of contactless power-line data transmission; Power Line Communications and Its Applications, 2005 International Symposium on 6-8 April, 2005 Page(s):305 – 309 S. C. Tang, S. Y. Hui, H. Shu-Hung Chung, Coreless printed circuit board (PCB) transformers with multiple secondary windings for complementary gate drive circuits; Power Electronics, IEEE Transactions on Volume 14, Issue 3, May 1999 Page(s):431 – 437