Research Paper ELECTROMAGNETIC INTERFERENCE REDUCTION IN CUK CONVERTER USING MODIFIED PWM TECHNIQUES

Transcription

1 Research Paper ELECTROMAGNETIC INTERFERENCE REDUCTION IN CUK CONVERTER USING MODIFIED PWM TECHNIQUES *1 Dr. Sivaraman P and 2 Prem P Address for Correspondence Department of Electrical and Electronics Engineering, Bannari Amman Institute of Technology, Sathyamangalam, Erode, Tamil Nadu, India ABSTRACT An important increase of the electrical equipment in modern aircrafts is leading to an increase in the demand for electrical power. The usual electrical power distribution in aircraft applications is done via a three-phase 415Vac grid. A new trend of DC distribution is emerging employing a 270 Vdc grid. With the advancement in the power semiconductor devices and power transformers, DC-DC converters are designed with frequency ranging up to MHz range. Increase in the switching frequency along with the sudden change in the current di/dt or voltage dv/dt generates higher order harmonics which leads to Electro Magnetic Interference (EMI). EMI noise creates malfunctioning of the circuit and also leads to miscommunication within the system and sometimes leads to device failure. Which is an undesirable condition as far as airline is considered. Hence the reduction of EMI noise is of uttermost important. This paper focus on the reduction of EMI using passive filter along with modified PWM carrier modulation technique. A circuit model for the prediction of conducted emissions due to DC/DC converters in an aircraft black box system is proposed and corresponding attenuation method is been analyzed. The results are analyzed on simulations of CUK converters with and without filter for a switching frequency of 200 khz under similar conditions. The results so obtained are within the limit as specified by the MILSTD-461 D standard. KEYWORDS: - Electro Magnetic Interference, Electro Magnetic Compatibility, Line Impedance Stabilizer Network, Carrier Pulse Width Modulation. I. INTRODUCTION Nowadays, power supplies become inevitable part of every electronic devices. With the advancement in the technologies the size of the power device is made smaller. With the reduction in the size of the electronic devices, it is desirable to reduce the size of the power supply by increasing the power density. The power density can be reduced by having small size passive/energy storage components like inductors, capacitors, and transformer. Small sized passive components can be obtained by increasing the switching frequency. With the advancement in the power semiconductor switches and the development of PCB power transformers, it is possible to design a small sized, power efficient Dc- Dc converters in MHz range[1]-[4].the increased switching frequency range along with the change in current or change in voltage results in synthesis of harmonics in the devices which results in Electro Magnetic Interference. One of the major challenge in the development of power efficient converters primarily lay on minimization of EMI. In recent years, EMI considerations have become more important, because the EMC regulations have become more stringent. The EMI produced in the Dc-Dc converters is prolonged and it ranges from operating frequency to Several MHZ. EMI occurs by coupling between circuit element through the action of either a magnetic field or an electric field. EMI can be divided in to radiate and conducted EMI. The conducted EMI is generated due to switching action of semiconductor devices [5]. Electronic converters such as rectifiers and inverters tend to generate high frequency current harmonics at their input and voltage related interference at their output. The voltage related interference may disturb operation of communication and control system in the proximity of converter [6]. High frequency current harmonics of substantial amplitude which are injected back into voltage source can interfere with operation of nearby equipment [7]. The conducted EMI is regulated in the frequency range of 150 khz to 30 MHz. This paper addresses the filter design for high frequency PWM power converters. By analyzing the frequency spectrum of PWM converters it can be seen that most of the conducted noise energy is at fundamental frequency component. In addition to fundamental frequency component there appear higher order harmonics in frequency spectrum at multiple of switching frequency whose amplitude is lower than the amplitude of fundamental component This work mainly concentrated on the conducted EMI and its minimization technique. The conducted EMI is generated due to switching action of semiconductor devices. Converters tend to generate high frequency current harmonics at their input and voltage related interference at their output. The voltage related interference causes disturbance in the operation of communication and control system. High frequency current harmonics of high amplitude which are injected back in to voltage source can interfere with the operation of nearby equipment. Various standards that specify the limit on conducted EMI include CISPR, FCC, IEC, VDE, and military standards [8]. Some principle standards for EMI are given in [9]. The conducted EMI is regulated in the frequency range of 150 KHZ to 30 MHZ The remaining of this paper is as follows Overview of CUK converter is discussed in section-ii Simulation model for the CUK converter and Line Impedance Synchronization Network (LISN) with filter and without filter and Frequency spectrum for common mode noise is discussed in section III and section IV. II. MODELLING OF CUK CONVERTER Cuk chopper circuit, as the boost-buck series converter, can be viewed by boost and buck series application. According the doctoral thesis of Dr. Slobodan Cuk from the United States California Institute of Technology, the control of the IGBT1 in the circuit is simple and the energy between the input and output is transmitted by a capacitor, which can help to reduce the size, increase the power density and can achieve buck-boost voltage as well. The circuit structure is showed in Figure. 1.

2 Figure 1: Simulation model of CUK Converter Cuk chopper circuit, shown in Fig. 1, is different from the buck-boost chopper circuit. During the period T, the current integral of its capacitance is zero. The capacitor current I 2 of the ton multiplied by ton equals to the the capacitior current I 1 of the t off multiplied by t off, If all the devices in the circuit are in ideal conditions, the output voltage is The equation (3) and (6) are exactly the same, which means that the relationship between input and output voltages of the two circuits is the same, although the two circuits have different structures. Cuk chopper circuit has the following advantages [10]: It has the same inductance in the input and the output. Its input and output currents are continuous. The ripples of the input and output currents can be reduced as well. IV SIMULATION ANALYSIS OF CUK CONVERTER The Cuk chopper circuit model is shown in Figure. 2.The parameters are as follow: The inductance is L1=L2=2.35mH, the power E is 100V, the resistance load R is 10 Ω, the filter capacitor C is 100 μf, the inductance L1 is 0.35mH, and the switching frequency of the IGBT 1 is 200kHz. Figure 2: CUK converter simulation model Figure 3(a): output voltage waveform for 200 kkz switching frequency 1.44 Transfer Function (magnitude) db (µv) Transfer Function (phase) 150 Degrees Figure 3(b): Spectrum analyzer waveform

3 Figure 3(a) and 3(b) shows the output voltage waveform and spectrum analyzer output waveform. The output voltage waveform reveals the existence of the ripples of about 100V and spectrum analyzer infers that there exists a conducted EMI noise of the order of 1.42µv. IV.DESIGN OF FILTER Figure 4: simulation model of CUK converter with filter along with Modified PWM technique When a common mode signal passes though the inductors L1 and L2, they contribute a net non-zero flux in the shared core. The mutual inductance of both inductors attenuates the common mode signal. The leakage inductance of both inductors is used to suppress the differential mode signals. The actual size of the filter depends on the design approach. It also depends on the layout and placement of components used in the filter. Mutual couplings of passive components used affect the performance of filter. However, in general, the size of the filter is expected to decrease with increasing cutoff frequency. The filter parameters are calculated according to following expressions [12] Where A tt - is the required attenuation f C - is the cutoff frequency f SW -is switching frequency The relationship between the inductance and capacitance of the filter with filter cutoff frequency is given as follows: and constant and is given as switching frequency to the IGBT switch. The EMI compliance testing is done using a LISN. Essentially, LISN ensures that equipment under test receives the proper dc voltage and current levels and also sees controlled impedance for the ripple frequencies of interest [6]. It performs following functions [10]: Attenuates the external interference signal present on main power supply to avoid them interfering from measurements. Couples the signals from main port of the equipment under test to the measuring apparatus. The 50 μh inductors block external noise on the commercial power net from flowing through the measurement device and contaminating the test data, while the 8μF capacitors provide an alternate path for those noise currents anddivert them from the measurement device. The other 0.25μF capacitors prevent any dc from overloading the input of the test receiver.the EMI plot after the application of filter along with carrier modulation technique is shown in Figure 5(b) and corresponding output voltage waveform is shown in Figure 5(a). Gate signal for 200 khz generated using carrier modulation technique is shown in Figure 5(c). Where RL is the noise load resistor and ζ is the damping factor. The damping factor (ζ ) describes the gain at corner frequency as well as time response of the filter. Its value for many actual EMI filters is selected between and 1. It is obvious that the values of inductors and capacitors depend on cutoff frequency of the converter. Hence, the converter with higher switching frequency requires smaller EMI filter. Carrier modulation technique using sine wave as the carrier is employed in this paper. Gate pulse of 200 khz is generated by comparing the sine wave Figure 5(a): Output voltage waveform

4 x 10-3 Transfer Function (magnitude) 15 db (µv) Transfer Function (phase) Degrees Figure 5(b): spectrum analyzer output Frequency spectrum analysis of the same Cuk converter and output voltage by employing passive filter and modified carrier modulation technique infer that the Emi noise has been attenuated to zero db(µv) and the output ripples also gets reduced seldom to zero volt inspite of having a transient of few microseconds at the initial stage. It can also infer from the above analysis that by increasing the switching frequency the size of the passive elements can be made smaller hence facilitates reduction of the size of the converter as a whole. COMPARISON OF RESULTS From the Table 1 shows EMI noise allowable in standard is 80dB and its is well attenuated with the proposed modified PWM with filter combination is 10dB. Table.1 Comparison of magnitude of EMI noise Parameter EMI Without With Magnitude of EMI noise [db(µv)] standard filter filter V.CONCLUSION The consequences on implementation of a line filter along with carrier modulation technique for suppressing conducted EMI on CUK converters are investigated in this thesis. The simulation model is developed for CUK converters, with filter and without filter is included to compare the required EMI filter implementation. The conducted EMI is estimated for both models and the results for both the converts are analyzed. In DC-DC converter, the differential noise is usually reduced by decoupling capacitors, therefore, only common mode noise is measured.the frequency spectrum of Cuk converter Figure 5(c): Gate signal of 200Khz with filter and without filter is plotted and it is observed that the by using the passive filter along with the carrier modulation technique, the EMI noise is reduced from 140dB to 10dB and the ripples in the output voltage is also get reduced to zero. Measured EMI value is within the limit as specified by MILSTD-461 D standard. REFERENCES 1. A.Majid, H.B.Kotte, J.Saleem, R.Ambatipudi, S.Haller, K.Bertilsson, High Frequency Half-Bridge Converter using Multilayered Coreless Printed Circuit Board Step- Down Power Transformer, 8th Internal Conference on Power Electronics-ICPE 2011 at Jeju South Korea (May 28-June ). 2. HariBabu Kotte, High Speed (MHz) Switch Mode Power,Supplies(SMPS) using Multilayered Coreless PCB Transformer technology Passive gate drive circuit using Coreless Printed Circuit Board (PCB) Signal Transformer, Licentiate Thesis 62, Mid Sweden University, ISSN: , ISBN: RadhikaAmbatipudi, Multilayered Coreless Printed Circuit Board (PCB) Step-down Transformers for High Frequency Switch Mode Power Supplies (SMPS), Licentiate Thesis 61, Mid Sweden University, ISSN: , ISBN: HariBabu Kotte, radhikaambatipudi and kentbertilsson, High Speed Series Resonant Converter(SRC) Using Multilayered Printed Circuit Board Step-Down Power Transformer, Holland Conference. 5. Tim William, EMC for Product Designers 4th edition ISBN 13: ). 6. Electronics Handbook: Devices, Circuits, and Applications By M. H.Rashid. 7. Richard Lee Ozenbaugh, Timothy M. Pullen EMI Filter Design,Second Edition 8. N. Mohan, T. Undeland, and W. P. Robbins, Power Electronics. NewYork: Wiley, Tim William, The circuit Designer s companion, Second Edition.

5 10. Bob Mammano and Bruce carsten, Understanding and Optimizing Electromagnetic Compatibility in Switchmode Power Supplies, Texas Instruments Post Office Box Dallas, Texas Chris Likely, Achieving EMC for DC-DC Converters (last accessed February28, 2011). 12. Sivaraman, P and Nirmalkumar, A 2012, Analysis of T- Source inverter with various PWM schemes, European Journal of Scientific Research., ISSN X vol.71, no.2, pp