Design of a Power Converter Based on UC3842 for Blade Electric Vehicle

Transcription

1 Design of a Power Converter Based on UC3842 for Blade Electric Vehicle Zhenyou Wang, Qun Sun*, Hongqiang Guo School of Mechanical and Automotive Engineering, Liaocheng University Liaocheng, China *Corresonding author: sunqun@163.com Abstract In order to meet the demand of loads on a blade electric vehicle (BEV), a DC switching mode ower suly has been designed based on the current mode ulse width modulator UC3842. This device converts the 64V DC ower suly on a BEV into 12V low-voltage ower source in order to suit the usage of different loads on the vehicle. The outut ower of the converter can reach more than 100W. This aer introduces the rincile of the current mode ulse width modulator UC3842, and resents the design rinciles of the switch ower converter based on UC3842, and the related circuit design, PCB board design as well as exeriments. Keywords - switching ower suly; UC3842; the flyback tye switch ower suly. I. INTRODUCTION In recent years DC switching mode ower suly has been widely used in the area of electron device, such as SPC exchange, communication, electronic insection and many tyes of controlling device, which have greatly heled the raid develoment switching mode ower suly [1]. The costs of switching ower suly and linear ower suly both increase with the rise of the outut ower although the rates are different. Beyond some oint of the outut ower, the cost of linear ower suly is higher than the cost of switching ower suly. With the develoment and innovation in ower and electron technology, the switching ower suly has been much develoed to reduce its cost [1-2]. Recently, integrated switching ower sulies have gradually develoed towards two directions. One direction is the integration of controlling circuit of the switching ower suly, and recent PWM and PFM ICs can achieve 1MHz frequency. Another direction is the realization of single chi integration with middle and small ower consumtion. Because of the characters of the high integration, highly cost effective, simle eriheral circuit and otimal function index, single chi switching ower suly has become the first choice in the ower suly integrated circuit [3]. Generally, the switching ower suly contains PWM and MOSFET. The ower tubes of switching ower suly mostly use biolar transistors and the switching frequency can reach tens of kilohertz. While using MOSFET instead of ower tubes, the frequency can reach several hundred kilohertz [4]. In order to imrove the switching frequency, high-seed switching devices must be used. Using the resonant circuit can fit to the switching ower suly with megahertz frequency, which is called resonant switching mode. It can greatly increase the switching seed with small noise and lead to no loss in theory, which is one way to imrove the oerating frequency of the switching ower suly. Using resonant switching mode converter has been adoted in some ractical alications [5-7]. According to the actual demand of DC ower suly in blade electric vehicle (BEV), this aer reresents a DC ower suly converter. The device mainly converts the fixed 64V DC voltage of storage battery in BEV into other fixed DC voltages to meet the demand of different loads. The DC voltage can outut stabilized current with current ulse width modulator U3842, and it can rovide the rotection of over-current, over-voltage and under-voltage. The switching ower suly alication is of great significance in energy saving, resource saving and environment rotection. In the contents the following arts are included: The analysis of the oerating rincile of switching ower suly, and selection of the working mode; The main circuit selection and its arameters, The controlling chi selection and its arameters, The design and creation of high-frequency transformer, Debugging its circuit to testify its correction and feasibility. II. DESIGN OF THE SWITCHING POWER SUPPLY A. B. A. Brief Introduction to UC3842 chi UC3842 is a kind of high erformance single end outut current controlled ulse width modulator. Current mode control comares the outut induction current sensed from the inut of the ulse width comarator with the error amlifier outut signal to control the duty cycle of the outut ulse, so as to ensure the outut of the eak inductor current to follow the error voltage variations. UC3842 is a high erformance fixed frequency current DOI /IJSSST.a ISSN: x online, rint

2 mode controller using a single end outut mode, and can directly drive a biolar transistor or MOSFET tube, with advantages of fewer ins, simle eriheral circuit, convenient installation and debugging, excellent erformance and low rice. It has rotection characteristics such as under-voltage lockout and current limitation. In alication a UC3842 chi adots DIP-8 ackage and its internal modules mainly include 5.0V reference voltage source, oscillator to recisely control the duty cycle adjustment, an attenuator, an over-current detection comarator, PWM lock latch, high gain E/A error amlifier and outut circuit to drive ower MOSFET current ush-ull. B. Circuit Design of Switching Power Suly This aer resents a 100W switching ower suly develoed to meet the demand of different loads in BEV. The basic technical indices are as the following: 64±10%V inut DC voltage, 70V maximum outut voltage, 4A maximum outut current, The voltage rile is no more than 1%. B1. The Circuit Functionalities The working rocess is as following. Firstly through R2 the ower source rovides current to charge the caacitor C1, and when C1 voltage reaches the starting threshold 16V, UC3842 begins to work and rovide a driving ulse through outut in 6, roducing high and low voltage ulse. During the high voltage ulse, the field effect transistor is switched on, the current is assed through the rimary side of the transformer, and the energy is stored in the transformer. The field effect tube is cut off when high level ulse through in 6 is finished. According to Lenz's law, the transformer rimary side tries to maintain a constant current, resulting in an induced electromotive force that yields diodes conduction on the secondary side, roviding energy outward [8-10]. At the same time, the feedback coil rovides ower to UC3842 through the diode D3. In the actual design, the ower converter can be divided into three arts, namely auxiliary ower unit, PWM control unit and DC/DC conversion unit. The auxiliary ower suly consists of a small ower DC/DC isolation transformer and some other electronic comonents that rovide a stable and over 10V voltage to the PWM control circuit. The PWM control circuit adots UC3842 and uses the feedback source current to control. It also samles the outut voltage, divides voltage for comarison, and feeds the signal back to the PWM controller. The DC/DC converter is a tyical DC buck choer circuit (Choer Buck), which is comosed of a field effect transistor, a continuous current diode and an energy storage caacitor. The field effect tube grid is controlled by the PWM wave eriod of 20 khz square wave signal, and the square wave signal is rovided by the PWM controller. The more imortant arts are the auxiliary ower suly and the PWM controlling circuit which will be further exlained in the following section. B2. The auxiliary ower suly The auxiliary ower suly is a single-ended flyback switching ower suly based on UC3842, as shown in Figure 2. The DC voltage of the blade electric vehicle is connected to Pin 7 of UC3842 through R2 [11-13]. When the voltage on Pin 7 reaches 16V oen voltage of UC3842, the controller starts to work. The current consumtion is about 15 ma during normal oeration, fed by the transformer coil N2 via D3 and C10. Pin 6 oututs waves according to the RT/CT oscillation frequency and drives the switching tubes. Pin 8 oututs a 5V reference voltage that charges RT and discharges through an internal current, resulting oscillation in CT. The frequency of the oscillator is: f =1.8/(RT CT)kHz (1) The outut 12V DC shown in Figure 2 serves as the normal oerating voltage of the following control chi. Feedback outut voltage is roduced meantime using TL431 for over voltage rotection. TL431 is a three terminal rogrammable arallel voltage stabilizing diode, which has Vout= (1+/R2)*Vref. Since the reference voltage of TL431 is 2.5V, 6 and 7 are used to configure the reference rogramming voltage to 12V. Thus when the transformer winding N3 outut voltage is greater than 12V, conduction occurs in the linear otical couler PC817, the transformer N2 winding rovides feedback voltage to Pin 2 of UC3842, leading to increased voltage on Pin 2, and the internal rotection circuit starts. The outut high level ulse on Pin 6 becomes shorter or disaears, leading to shutoff of the switching tubes, so as to reduce the outut voltage. In the circuit R4, C2 and D2 constitute the absorbing circuit to eliminate the reverse eak voltage generated by the inductance leakage of the transformer, so as to rotect the switch tubes from being burned. B3. The PWM control circuit PWM controlling circuit mainly rovides the PWM signal to the field effect tube that controls the DC/DC transformation. When the forestage circuit outut voltage reaches oen threshold voltage of 16V, UC3842 begins to outut PWM ulse wave through Pin 6 to drive the MOSFET tube turn on and shut off. The outut end of the circuit uses totem ole outut, so as to achieve the effect of DC choer. In order to obtain a stable DC ower suly, the circuit is similar to the forestage circuit that uses feedback of outut voltage, through TL431 to control overload of the outut voltage. Through configuration of 6 and 9 in the circuit, the reference voltage is DOI /IJSSST.a ISSN: x online, rint

3 rogrammed to ass 13V, so that an outut voltage greater than 13V leads to conduction of the otical coulers. This means the comensation signal on Pin 1 is connected to the feedback inut Pin 2, forming loo comensation, so that a shorter time of high level ulse on Pin 6 reduces the duty cycle of the choer signal, and reduces the outut voltage. In addition, the circuit is also designed with inut over current rotection using Pin 3 of UC3842. Suly current through the current transformer (CT) becomes samled current following a certain transformation ratio, connects to Pin 3 after samling resistor R3. When the voltage on the samling resistor is greater than 1V, UC3842 stos the outut trigger ulse, shut off the switch tube, thereby rotects the switching tube to achieve over-current rotection function. C. The design of high frequency transformer The transformer is a custom designed high frequency transformer, with one rimary winding and two secondary windings, and the first secondary winding is mainly to feed the external loads and the second secondary windings are mainly to rovide normal oerating current to UC3842. The DC voltage source is ranging from 64V to 70V, and the rated outut voltage is 12V. Considering the system reliability and normal human auditory frequency range within Hz, the design of switching frequency should be above 20 khz to reduce the working noise of the charger. However enlarged switching frequency will increase the loss of the switching tube. Considering the noise and the efficiency, the switching frequency was set as 20 khz and T=50us. The rated outut is Uo1=12V and the outut of UC3842 is Uo2=25V. Assuming the time of MOSFET ranges from dead zone to turn-off is Tr=2us, then the maximum duty ratio can be reresented below, max T 2 T / T D (2) r n1v in U o1 / Dmax 13V (3) n2vin U / D 27.2V n1 n1v in n2 n2v o2 / V in inmin / V max inmin 13/ , 27.2 / Taking into account the losses of comonents, the roortion was rounded into: (4) N 1/ N 2 10 / 3, N1/ N3 10 / 5 2 /1 (5) The arameters of the transformer are shown in Table 1. Table 1. THE PARAMETERS OF THE TRANSFORMER Parameter Symbol Unit Value Duty ratio Inut voltage Vin V 70 Outut voltage 1 Vo1 V % Outut voltage 2 Vo2 V % Inut current I A 3 100% Outut current 1 Io1 A % Outut current 2 Io2 A very small Frequency f khz 20 The transformer selects a ferrite core and the valid area of magnetic core is Ae=5*5*π=79mm2. The line number of each transformer rimary side winding is N Vinmax / 4 fs Bm Ae / (6) The line number of subsidiary winding is N N / K 51/ N N / K 51/ 2 25 (7) The valid value of current and subsidiary side current are resectively I I I 3A N1 / N2 3 10/3 10A N / N A 1 By choosing current density of the line as J=3A/mm2, the cross sectional areas of rimary side winding line and secondary side winding lines are given by S S S 3 / J 2/3 0.67mm / J 10/3 3.33mm / J 1.5/3 0.5mm D. Photoelectric linear transmission of PC817 Otocouler can be used to enable signal transmission to be realized without direct link between the electrical inut and outut signals. However, to achieve linear transmission of the signal, and to get an amlified electrical signal, a drive circuit and amlifier circuit must be added, as shown in Figure 1. Rs Vs LED driver LED D Amlification circuit Rl (8) (9) Figure 1. The sketch ma of electro-otical linear transmission DOI /IJSSST.a ISSN: x online, rint

4 If the inut signal voltage is alied directly on LED without a LED drive circuit, the LED luminous intensity will become a nonlinear function of the inut voltage. This means that the electric current and the load on the electrical signal is the nonlinear function of the inut voltage. To ensure that the current flowing through the LED is roortional to the inut voltage, the driving circuit of the LED is very imortant. In order to make the outut voltage roortional to the inut voltage, it is necessary to convert the current into the voltage of the hotodiode. The drive circuit that brings negative feedback to PC817 is given below. Vs Rs Vol Vf Iol LED the circuit. The circuit structure is shown in above Figure 3, where V bias rovided by the DC ower suly is the working voltage required by hotodiode. Source idrs and rs form the low-frequency small-signal model of hotodiode [15]. Closed loo mutual blocking gain is rovided by A rf V / id 1/ F Rf (10) o E. Feedback circuit design based on TL431 TL431 is a recision adjustable reference ower suly circuit, which has a good regulation characteristics and flexible regulation value set. Its outut voltage can be arbitrarily set to any value from Vref (2.5V) into the maximum 36V with two resistors. Tyical dynamic imedance of the device is 0.2Ω, and in many alications this can be used to relace Zener diode, for examle, a digital voltmeter, o-am circuit, voltage regulator, and switching ower suly etc. The TL431 rincile diagram is shown in Figure 7. g Figure 2. Series connected negative current feedback circuit for driving PC817 Ref(R) Negative In the above figure, Vs is a voltage signal, Rs is the inut resistance, A is an integrated amlifier that can be based on LM324. LED is the lighting tube of the otocouler, Vo1 is outut voltage, Vf is a feedback voltage, and Rl is the load resistance. The voltage signal is alied to the non-inverting inut terminal of the integrated oerational amlifier, and the load resistor feedback voltage Vf is alied to the inverting inut terminal of the integrated oerational amlifier. When the voltage signal increases, Vf increases and the current flowing through Rl increases, thus according to the virtual oen rincile of integrated oerational amlifier, current Io1 is flowing through Rl and increases too. Thus the voltage on oto-couler is roortional to the current [14]. Idrs Vbias rs Rs 2.5Vref Positive(A) Figure 4. The reresentational structure diagram It can be seen from Figure 4, an internal 2.5V reference signal is connected to the inverting inut of the o am. Known from am characteristics, only when the voltage Ref terminal (inverting terminal) is very close to 2.5V, the transistor will have a stable, non-saturation current through, and along with small voltage changes on Ref terminal the transistor changes current from the 1mA to 100mA. TL431 contains the internal reference voltage of 2.5V, thus when outut feedback is alied onto the Ref end, the device can control the outut voltage through a wide range of shunt from the cathode to the anode. The shunt circuit is shown in Figure 5. V+ Vout Figure 3. Mutual resistance amlifying circuit of the outut end The circuit requires achieving current to voltage conversion, i.e., the hotodiode current changes into an outut voltage, so a mutual resistance amlifier circuit is needed. In order to reduce the load effect of amlifier inut and the outut, the amlifier inut resistance and outut resistance should be small. Therefore voltage arallel negative feedback amlifier circuit should be introduced in Figure 5. The shunt voltage regulator circuit When and R2 are secific they introduce negative R2 DOI /IJSSST.a ISSN: x online, rint

5 feedback to Vo, therefore if Vo increases, the amount of feedback increases, TL431 shunt will increase, which in turn leads to decreased Vo. Obviously, this dee negative feedback is stable when VI is equal to the reference voltage, and at this oint Vo=(1+/R2)Vref. By choosing different values of and R2, the outut voltage can be obtained from 2.5V to 36V. In articular, when = R2 it gives Vo = 5V. The combined circuit diagram of TL43 with PC817 is Figure 6. e. Outut wave at 10Ω f. Drive voltage wave at 10Ω 4 1K PC817 LM324N 2 1K 3 12K 5 1K 7 10K C7 0.01uF 6 38K 8 2K VCC TL K Figure 6. The cooerating circuit diagram of TL431 and PC817. Figure 7. g. Outut wave at 3Ω h. Drive voltage wave at 3Ω The outut voltages and waveforms under different loads III. ANALYSIS OF WXPERIMENTAL RESULTS This design adots linear otocouler to change the error amlifier voltage of the feedback circuit to construct a 64V/12V single ended flyback DC-DC switching ower suly. the outut voltage of the ower suly is stable and the load caacity is strong. Figure 7 shows the outut voltages and the driving waveforms with varying loads. In addition, Table 2 lists the corresonding load, duty cycle, and outut voltage at secific conditions. Table 2. EXPERIMENTAL DATA Load(Ω) Duty cycle(%) Outut voltage(v) 100Ω 10% Ω 15% Ω 20% Ω 35% a. Outut wave at 100Ω b. Drive voltage wave at 100Ω From the table it can be seen that when the load current increases, the duty cycle of the drive signal is also increased, but the outut voltage has been maintained at around 12.1V, and the switching ower suly load adatability is strong. IV. CONCLUSION c. Outut wave at 25Ω d. Drive voltage wave at 25Ω A DC/DC ower converter based on UC3842 chi has been develoed to convert high voltage ower source from vehicle battery to PWM controlled low oerating voltage. By utilizing good control characteristics of UC3842, effective on-off control of field effect tube is imlemented. Protection circuit has been designed to revent over current and over voltage and to ensure normal oeration of the ower converter. The exerimental results showed that the outut voltage of the converter is stable when the inut voltage range is from 64V to 70V, which meets the design requirements. The ower converter achieved oerating frequency u to 500 khz, starting current less than 1 ma, DOI /IJSSST.a ISSN: x online, rint

6 voltage adjustment rate of 0.01% / V, and the maximum duty cycle of 100%. It indicates a good rosect due to simle eriheral circuit, suerior erformance and low cost. Future work: If the ower converter is alied to the actual work, the safety of ower converter and heart dissiation of circuit modules are needed to imrove. It needs large number of exeriments, in order to texting the safety in actual work. REFERENCES [1] Q. J. Hou, L. Q. Zhang and D. G. Xu. Analysis of the basic rincile and the develoment trend of switching ower suly. Manufacturing Automation Industry, vol. 12, , Set [2] S. Hobrecht. Single IC, five outut switching ower suly system for ortable electronics. Analog Circuit Design, vol. 3, : , Feb [3] J. Q, Zhu, D. Xie, F. Wang, T. Q. Cao. Study on the Harmonics of Switching Power Suly. Procedia Engineering, vol. 29, , Feb [4] C. Si, Z. Q. Meng, Y. D. Chen. Develoment of a Soft-Switching Power Suly for Ozone Generation Based on Phase-Shifted Control. Procedia Engineering, vol. 23, , Dec [5] K.M. Tsang, W.L. Chan. A single switch DC/DC converter with galvanic isolation and inut current regulation for hotovoltaic systems. Solar Energy, vol. 119, , Set [6] A. Roshala, S. Avanesova, E. Koktsinskaya, et al. Design and analysis of Switching Network Units for the ITER coil ower suly system. Fusion Engineering and Design, vol. 86, , Oct, [7] E. Feinberg, J. Hu, E. Yuan. A stochastic search algorithm for voltage and reactive ower control with switching costs and ZIP load model. Electric Power Systems Research, vol. 133, , Ar [8] C. Maria, L. Cananà. Markov switching of the electricity suly curve and ower rices dynamics. Physica A: Statistical Mechanics and its Alications, vol. 391, , Feb [9] Y. J. Ma, Y. G. Yang, X. S. Zhou. The Alication of Power Electronic Switches in High Voltage Quick Switching Device. Procedia Engineering, vol. 29, , Feb [10] M. Uno, K. Tanaka. Pt/C catalyst degradation in roton exchange membrane fuel cells due to high-frequency otential cycling induced by switching ower converters. Journal of Power Sources, vol. 196, , Dec [11] M. Kalantar, S.M. Mousavi G. Posicast control within feedback structure for a DC DC single ended rimary inductor converter in renewable energy alications. Alied Energy, vol. 87, , Oct [12] P. Becker, E. Hymon, B. Folkmer, Y. Manoli. High Efficiency Piezoelectric Energy Harvester with Synchronized Switching Interface Circuit. Procedia Engineering, vol. 47, , Nov [13] L. Zhang, L. Yang, J. Yang, et al. Power suly design for the filament of the high-voltage electron accelerator. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Sectrometers, Detectors and Associated Equiment, vol. 804, , Dec [14] H. Wu, G. F. Shen, Y. Z. Chen. Feasibility of an electromagnetic comatibility method for MRgFUS using a wire mesh screen. Ultrasonics, vol. 72, , Dec [15] J. L. Roldanc, R. Pater, et al. Develoment of non-intrusive monitoring for reactive switching of high voltage circuit breaker. International Journal of Electrical Power & Energy Systems, vol. 61, , Oct DOI /IJSSST.a ISSN: x online, rint