Transmitter Research of Great Deep Resistivity Imaging

Transcription

1 Available online at Procedia Engineering 16 (2011 ) International Workshop on Automobile, Power and Energy Engineering Transmitter Research of Great Deep Resistivity Imaging Luan Hui a,b,yu Shengbao a,b*,fu Guoliang a,zhang Zhiwei a,a,b* a College of Instrumentation & Electrical Engineering, Jilin University, No. 938 Ximinzhu Avenue Changchun City, Jilin Province , China b Ministry of Education key Laboratory of the Earth Information Survey Instrument, No. 938 Ximinzhu Avenue Changchun City, Jilin Province , China Abstract The design of high power resistivity imaging transmitter which based on bridge cascade voltage-balance technique is proposed in this paper. The bridge cascade high voltage inverters use cascading modular structure. This approach can be multi-level series, aims to increase the output voltage. At the same time, this avoids the problems of device damage caused by voltage unbalance while the IGBT connect in series, and makes power devices work stable and reliable. In this design we use C snubber circuit to protect the IGBT. The snubber circuit is simple and has no energy consumption. Performance testing and model experiments were carried out after device development was completed. This further verified the feasibility of design for greet deep resistivity imaging transmitter Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Automobile, Power and Energy Engineering Open access under CC BY-NC-ND license. Keywords: resistivity method, bridge circuit cascade, power conversion, electrode transition 1. Introduction In recent years, rapid development has achieved in resistivity imaging method which was applied in more and more exploration areas such as engineering geological investigation, dam foundation and bridge pier site selection, gob and fissure detection, and many other engineering applications [1-6]. Existing resistivity imaging transmitter has the shortcoming that transmit voltage is small and current electrode space can't meet the detection requirements. The design of high power resistivity imaging * Corresponding author. Tel.: ; fax: address: yushengbao@jlu.edu.cn Published by Elsevier Ltd. doi: /j.proeng Open access under CC BY-NC-ND license.

2 Luan Hui et al. / Procedia Engineering 16 ( 2011 ) transmitting device based on bridge cascade voltage-balance technique is proposed to solve the problem. Because of careful consideration of the instrument application environment, the instrument has the characteristics of lightweight, low power consumption, strong anti-interference ability, and convenient operation. 2. Transmitter Resistivity imaging transmitter generate bipolar pulse which needed by measurement and transmit it to the underground through electrodes [7][8]. So the receiver can detect voltage information varied with geological mass. Different electrode combinations can achieve different current electrodes space through the electrode switching converter. The larger the current electrodes space is, the deeper the detection depth is. Transmission waveform is shown in Figure 1. Fig. 1 Transmission waveform Fig. 2 High-power transmitter module High power transmitter module is the core of transmitter design. Rational design of this circuit can guarantee the transmitter stability. The block diagram is shown in Figure 2 which including the following parts: power converter, isolation drive circuit and IGBT snubber circuit Power conversion Resistivity imaging equipment commonly uses H bridge as the main circuit of transmitter power conversion. IGBT is used as switching devices in bridge because of the quality of fast speed, small onstate voltage drop, high pressurization and bearing large current. Considering technology, distribution parameters and security, the general operating voltage is usually selected at one over third till one over two of the rating value during the output bridge design. High-power transmitter demands high performance of power devices which are very expensive. At the same time, if power devices are bearing high voltage for a long time, its stability will decreased correspondingly. So it is difficult to achieve high voltage using traditional H bridge. In order to achieve high voltage transmission, most of the power devices cascaded currently. The voltage to be launched will be distributed equally to the power devices which connect in series, reducing the voltage on each power device to achieve high voltage transmission. In this method, voltage of power

3 378 Luan Hui et al. / Procedia Engineering 16 ( 2011 ) devices are complex and difficult to guarantee the voltage balance between power devices which connect in series, then devices are easy to damage. Cascade phase-shift control technique of power devices is proposed in recent years. Through classification of the main power and power shift control at all levels, the classification access and withdrawal of the main power is achieved and the dynamic voltage balance problem of the main circuit power devices is solved. However, this control increases the complexity of the main control circuit. Because of added classification of the main power, the output waveform was influenced and the load voltage waveform was showed the rise and fall ladder at the same time. Therefore, cascade of power devices is hardly used widely [9]. The design of bridge cascade high voltage inverters uses cascading modular structure, that is, lowvoltage design at every level, multi-level series, and high voltage output. Each level bridge has a separate power supply, every level bridge separated from each other. This solves the problems of dynamic voltage balance and voltage clamping when unit cascade. Bridge cascade makes maximum voltage of each bridge at each power voltage and controls bridge output for each level synchronization. Then the output voltage is all levels of bridge voltage overlay [10][11]. In theory, this approach can be multi-level series, aims to increase the output voltage. At the same time, this avoid the problems of device damage caused by voltage unbalance while the IGBT connect in series, which can makes power devices work stable and reliable. Power conversion hardware is shown in Figure 3. Fig. 3 Power conversion hardware circuit

4 Luan Hui et al. / Procedia Engineering 16 ( 2011 ) Isolation drive circuit IGBT's drive conditions are closely related to its characteristics. While designing gate drive circuit, special attention should be paid on switching characteristics, load short-circuit capacity,false triggering caused by the duce/dt and other issues. If the positive bias voltage UCE increases, on-state voltage will drop and the conduction energy consumption Eon will decrease[12]. If +UCE is fixed, the forward voltage will drop with the increasing of drain current, and the conduction loss will increase with the rise of the junction temperature. The negative gate voltage -UCE directly affect the reliable operation of IGBT, the negative bias voltage significantly decreased when the drain surge current increased, which has no significant effect on the turn-off energy consumption. By considering the IGBT drive circuit's design requirements and the system design needs, we use fourunit high-power IGBT driver board TX-DA102D4 as the isolated driver module. Block diagram of driver board is shown in Figure 4. Drive power DC/DC Input Four channels PWM signal Fault output Optocoupler isolation KA102 User protection parameter setting Power Amplifier Four channels isolation drive output Fig. 4 Block diagram of driver board To ensure the power converting module work reliability, both the IGBT of the module's up and down bridge circuit should turn on at the same time, and that requires the drive signals generated by the control circuit should keep in good agreement with each other after the transmitting over the driver board 's tow bridge circuit Design of IGBT snubber circuit Due to the distributed inductance of the circuit and the fast IGBT turn-off speed, when the IGBT turns off, it will produce a huge surge voltage Ldi/dt threatening to the IGBT. Denoting the peak of the surge voltage is U CESP, then U CESP =U d +Ldi C /dt (1) where U d is the IGBT DC input voltage and C i is the IGBT collector current. When U CESP is beyond the IGBT's collector-emitter withstand voltage U CESP, it may damage the IGBT. In this design we use C snubber circuit to protect the IGBT, the circuit diagram is shown in Figure 5. Because the voltage across the capacitor cannot be abrupt change, the snubber capacitor C s is used to absorb the peak voltage L S di /dt generated by the stray inductance L S in the main circuit flow when the H bridge is switching the phase. The snubber capacitor places directly across the terminals of IGBT. When

5 380 Luan Hui et al. / Procedia Engineering 16 ( 2011 ) the H bridge is switching the phase, the snubber capacitor voltage begins to rise from less than V CC and has better absorption effect on the IGBT transient voltage peak U CESP. The snubber circuit is simple and has no energy consumption. Fig. 5 C snubber circuit 3. Testing 3.1. Transmission waveform Transmission waveform is bipolar pulses, we tested the transmission waveform of the maximum output voltage (500V) and the maximum output current (5A) at the frequency of 0.5Hz. The test used high-voltage probe which attenuated 100 times, the test waveforms are shown in Figure 6. Test results indicate that the developed instruments achieved the transmission of bipolar pulse waveform, and also validate the instrument met the maximum output voltage and maximum output current of the design requirements. Fig. 6 Transmission waveforms (a) output voltage at 500V (b) output current at 5A 3.2 Transmission frequency Electrical imaging transmitter not only requires the stable of the output current, but also ensures the accuracy of transmission frequency. Under the conditions of the transmission voltage at 200V and the output frequency is set at 0.5Hz, 0.25 Hz, Hz respectively, we conducted a number of tests about the output waveform using the ordinary probe attenuation 10 times, then randomly selected three test results are shown in Figure 7.

6 Luan Hui et al. / Procedia Engineering 16 ( 2011 ) We can read out the system transmission frequency from the test waveform. They are the same as the output frequency that we set Fig. 7 Transmission waveforms (a) 0.5Hz (b) 0.25Hz (c) 0.125Hz 4. Conclusion Bridge cascade voltage-balance technology is proposed to solve the problem that H bridge can't meet the high transmission power. Test results proved the feasibility of bridge cascade, achieved reliable conversion circuit of high-power bridge cascade voltage-balance, and realized the aim of using small power device to complete high transmission power. Testing results showed that transmission voltage and frequency met the design requirement. This further verified the feasibility of design for greet deep resistivity imaging transmitting devices. Testing results showed that transmission voltage and frequency met the design requirement. This further verified the feasibility of design for greet deep resistivity imaging transmitting devices. Acknowledgements The authors are grateful to Resistivity Imaging Team of Jilin University for hard working and cooperation. This work was supported by Projects in the National Science & Technology Pillar Program during the Eleventh Five-Year Plan Period and Basic Operating Expenses Project of Jilin University. References

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