Electric Bike

Transcript

TET4190 Power Electronics for Renewable Energy Mini Project: Electric Bike Fall 2010 Group members: H˚ akon Tranøy Ole Christian Nebb Torstein Stadheim Sebastian Kl¨otzer Contents 1. Abstract 3 2. History of the bicycle 3 3. Norwegian safety regulations 4 4. Configuration of the existing electric bike 5 5. Components used in the miniproject 5.1. The DC machine . . . . . . . . . 5.2. Design of the step-down converter 5.3. Generation of the PWM . . . . . 5.4. Driver circuit and MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6 7 8 10 6. Measurements on the circuit 10 7. Measurements on the test-bike 12 8. Conclusion 14 A. Appendix 16 2 1. Abstract The present report on the miniproject ’Electric Bike’ gives an overview over the work, that was carried out in the past month on the miniproject. At first, a short introduction on the development of the electric bike and the Norwegian safety regulations is given. Afterwards, a brief overview over the components of the provided test-bike is presented. A discussion of a step-down converter for the control of a DC machine with a fixed supply, including the steps during the design process, is following in the main part. The report will be concluded with an outline over the measurements on the step-down converter and on the test ride with the electric bicycle. 2. History of the bicycle The first documented cycle was introduced by Baron von Drais in 1818 in Paris. It had 2 wheels in-line, but lacked pedals and was driven by pushing the feet on the ground and steering with the front wheel. Fig. 1 shows a drawing of the aforesaid vehicle. Figure 1: Riding a Draisienne or hobbyhorse, 1819 [14] It is not known when the first electric bike was built, but there is a patented solution from 31. December 1895, by Ogden Bolton Junior, who used a hub motor on the rear wheel. [7] A patent handed in by Hosea W. Libbey in 1987 suggested a setup with a motor at the hub of the crankshaft axle. [8] There are many different names for electric bikes, e.g. pedelec, e-bike, power-assist-bike or EPAC (Electronically Power Assisted Cycles)[2] [3]. A description for the most common terms can be found at [2]: • Pedelec: the motor is only actived while pedaling, in order to support the cyclist • E-Bike: the input for the motor control is set by the turn of a handlebar throttle, which allows propulsion without the act of pedaling The biggest market for electric bicycles is in China, with an estimated amount of 120 million electric bicycles is use (Jan 2010). In many cases, the electric bike has replaced the motorcycle, traditional bicycles or cars as a mean of transportation. In Europe, one of the most important markets for eletric bikes is in the Netherlands, where in 2009, one third of the money spent on bicycles, went into electric bikes. [4] 3 3. Norwegian safety regulations According to the Norwegian regulation of vehicles (”Kjøretøyforskriften”, §4.1.5 [13]) a bike with an electric motor is to be considered as a normal bike if: 1. The bike fulfills the demands in ”Forskrift for krav om sykkel”. [12] 2. It has an electric motor whose power does not exceed 250 W. 3. When there is no pedaling activity, the power to the engine is cut. 4. The power to the engine should be decreased gradually while the driving speed increases. If the speed exceeds 25 km/h, the power should be cut. If some of these points are not fulfilled, the bike is to be considered as an electric vehicle and should be approved and classified accordingly. This also applies for the operator, who is obliged to get appropriate training in using the vehicle, i.e. a suiting drivers license. Physical laws regarding electric assisted biking As written in the title, the electric motor is only an assistance to an otherwise normally human powered bike. By assuming, that an average adult human is able to hold a constant power output of 75 W to the pedals of the bike without experiencing fatigue [11] and a minimum speed of 8 km/h for holding balance, the power output required by the electric motor can be determined by calculating the sum of the air resistance Fa , the rolling resistance Fr and the grade resistance Fg : [1] Fr = fR · m · g · cos α (1) 1 · cW · A · ρ · v 2 2 Fg = m · g · sin α (2) Fa = (3) Pres,mech = ΣF · v (4) Using m = 125 kg as the mass of the rider and the equipment, fR = 0.008 as the rolling resistance coefficient on rough asphalt, g = 9.81 m/s2 as the gravity constant, cW = 0.5 as the drag coefficient, the air density ρ = 1.225 kg/m3 , the effective frontal area A = 0.5 m2 and α as the pitch angle, the results shown in Tab. 1 were obtained. Slope [%] 0 1 2 3 4 5 6 7 8 9 10 11 12 Speed [km/h] 8 8 8 8 8 8 8 8 8 8 8 8 8 Total power need [W] 12,6 39,8 67 94,2 121,4 148,6 175,8 203,1 230,3 257,5 284,7 311,9 339,1 Need of human power [W] 0 0 0 0 0 0 0 0 0 7,5 34,7 61,9 89,1 Table 1: Power need for different slopes at minimum speed 4. Configuration of the existing electric bike The basis for the electric bike, which is used for measurements in the miniproject, is a normal citybike. After the upgrade with a wheel hub permanent magnet synchronous motor in the front wheel, a lead-acid battery pack, a suiting motor controller and a modified handle bar, a first version of the electrified bike was created. This setup was used for the measurements, which were done during last year’s miniproject on electric bikes. Before the start of the recent miniproject, the lead-acid battery pack was replaced with a lighter LiFePO4 battery pack, which offers higher power- and energy density and thereby reduces the weight of the bike by 6 kg. Additionally, a new controller, that allows regenerative braking, was installed. Fig. 2 shows the topology of the current version of the electric bike. Handle Bar = LiFePO4 Battery 3˜ 3˜ Controller M/G Hub Motor Figure 2: Topology of the drive train of the elecric bike Permanent magnet synchronous hub motor The in-wheel mounted permanent magnet synchronous hub motor, manufactured by Golden Motor Technology Co Ltd., has a rated power of 250 W at a supplying voltage of 36 V. Due to the lack of a datasheet, neither the no-load speed, nor the rated and peak torque and maximum of efficiency can be specified. Motor controller The motor controller converts the DC voltage of the battery into a 3-phase AC system and vice versa, as regenerative braking is supported. Its maximum power output is over 1 kW and therefore slightly oversized for the supplied hub motor. Nevertheless, at a weigth of 350 g, the range of the bike should not be influenced significantly. Further features of the controller include a cruise control mode, which allows riding at constant speed, over-current and under-voltage protection, as well as a sensorless operation mode, that is activated on a failure of the motor’s hall sensor. The input for the torque control of the motor controller can be set by turning the grip of the bike. The regenerative brake mode is activated by using the left brake handle. At the present state, the strength of the regenerative brake is fixed and can’t be controlled. LiFePO4 battery pack The LiFePO4 battery pack is housed in a solid metal box, which is mounted under the crossbar of the bike’s frame. It contains 40 single cells, each with an open-circuit voltage of 3.8 V and a capacity of 4 Ah. With 10 cells connected in a row and 4 in parallel, the battery pack has a rated voltage of 38 V at a capacity of 16 Ah. 5 5. Components used in the miniproject 5.1. The DC machine In order to control the three phase permanent magnet synchronous machine used in the electric bike, a three-phase converter with six switches is necessary. As the time frame for the miniproject is very limited, a functioncal design of such a converter is unlikely. Instead, a DC-motor will be used and the corresponding converter for forward operation will be designed. The main advantage of this configuration is the simplification of the circuit, as the basic operation can be achieved by controlling a single switch. As the testcircuit will only be used stationary, the disadvantages of DC machines, compared to permanent magnet synchronous machines, such as lower gravimetric and volumetric power density, lower efficiency and higher wear due to the commutator, which can be crucial in a mobile application, can be coped with. In the present miniproject, a 50 W shunt-excited DC machine, manufactured by Parvalux, is available to be powered by the converter. In order to adjust the load, it is mechanically coupled to an identical machine, which works as a generator. According to the rating plate (see. 6), the nominal voltage Va,n is 24 V and the nominal current Ia,n is 3.8 A. The resistance of the armature winding Ra amounts to 3.6 Ω, which allows the calculation of the starting current at nominal voltage to Ia,0 = Va,n = 6, 67 A. RA (5) Although the windings should be able to handle the startup current temporarily, a softstart mechanism, that delays the building-up of the terminal voltage, is still advisable for a gentle start-up. Assuming constant flux and load, the speed of a DC machine is directly proportional to the terminal voltage. By dimensioning a battery or fixed power supply according to the motor’s nominal terminal voltage, a buck converter (fig. 3) is sufficient to regulate the motor speed from start-up to nominal speed nn . L vo Vd D C Rload Figure 3: Buck converter The buck converter is able to deliver an output voltage Vo equal or smaller to the input voltage Vd , following the equation Vo = D · Vd , (6) where D is the duty cycle (0 ≤ D ≤ 1) of the switch. The voltage equation for a DC machine in steady-state, with the terminal voltage Va and 6 the back EMF Ea can be written as Va = Ia · Ra + Ea . (7) Furthermore, the relations for the torque T and the speed n are T = cT · Φ · Ia and n= (8) Ea . cn · Φ (9) In traction applications, both the load T (∼ Ia ) and the speed n (∼ Ea ) vary constantly. Therefore, according to equation (7), no linear relation between the behaviour of the machine and the duty cycle can be made out. If a linear relation between the throttle position and the motor torque is desired, a current control loop can be added to the circuit. Furthermore, in order to gain the ability of regenerative braking, an additional switch and diode has to be added and controlled. As these features are not part of the circuit, built up during the miniproject, this should not be discussed further. 5.2. Design of the step-down converter For the design of the buck converter, the basic circuit shown in fig. 3 is slightly altered. First of all, the MOSFET and the diode switch places, as a fixed source potential at the MOSFET simplifies the triggering of the gate. Secondly, due to the distributed inductance in the armature winding, which causes a small delay in the build-up of the armature current (PT1-behavior) and mostly due to the inertia of the rotor, shaft and gear box of the DC machine, which behaves as an integrator, the speed output of the machine is filtered by default. Thus, LC-filtering is not necessary and can be left out. Fig. 4 depicts the buck converter topology, that is used as the basis for the circuit. La Ra Ea D Vd PWM Figure 4: Schematic of the buck converter and DC motor As mentioned above, the duty cycle D of the switch defines the ratio between Vd and Vo . In order to control Vo , the duty cycle has to be varied manually. A possible solution to achieve this is the use of pulse-width-modulation (PWM). 7 Using unipolar PWM, the conducting and non-conducting state of the switch is gained by the comparison of a control voltage vcontrol with a high frequency sawtooth/triangular voltage vtri . Whenever vcontrol exceeds vtri , the switch will be conducting, otherwise not. As the output voltage Vo in a step-down converter is a DC-voltage, vcontrol has also to be chosen as a constant voltage. Fig. 5 shows the waveform of vcontrol and vtri and the state of the controlled switch. vtri vcontrol t on off t Figure 5: PWM waveforms To generate the PWM in the circuit, the TL494 integrated circuit (IC), with a recommended input voltage range of 7 V to 40 V, is used. It possesses an internal adjustable oscillator for the generation of the PWM signal, a dead-time control comparator, which can be used for a soft-start mechanism and over-voltage protection, a 5 V reference voltage supply and two output transistors. [6] 5.3. Generation of the PWM The frequency of the oscillator fs can be set by connecting an external timing capacitor CT and timing resistor RT , which leads to an oscillation frequency fs = 1 . RT · CT (10) To create the triangular waveform, CT is charged through RT with a constant current, resulting in a constant rise of the capacitor’s voltage. The slope of the waveform is set by the timing resistor. When the voltage over CT reaches 3 V, CT will be discharged by the internal circuit almost instantly and the charging cycle is restarted. To allow a change in the frequency while the circuit is powered up, a potentiometer is used instead of a fixed resistor. For fs to be set approximetly between 10 kHz and 20 kHz, CT = 0, 01 µF and a 5 kΩ potentiometer in series with a 4,7 kΩ resistor are chosen. Using eq. (10), this results in a range for the switching frequency between 10,3 kHz and 21,3 kHz. The control voltage vcontrol is gained by connecting the reference voltage output vref = 5 V with a 10 kΩ potentiometer, which is used as a voltage divider. This allows a smooth regulation of vcontrol between 0 V and 5 V, which, in theory, would enable the duty cycle to be varied between 0 and 1. As the TL494 possesses a minimum dead time of 3%, D = 1 can not be reached. [5] Dead-time Control (DTC) for use as soft-start and overvoltage protection 8 Although the dead-time control is usually used to avoid short circuits in applications with more than a single switch, it can also be utilized for a soft-start mechanism. The benefit of this is a reduce in the stress on the switch. In addition, when connected to a motor, a smooth start-up, independent of the chosen duty-cyle, can be guaranteed and thereby an overcurrent avoided. Concerning the TL494, the dead-time can be linearly set between 5% and 100% by applying a voltage between 0 V and 3,3 V to the according DTC pin. For the implementation of the soft-start, the DTC pin is connected with a 3.3 µF electrolytic capacitor to the 5 V reference voltage and a 180 kΩresistor to ground. On start-up, there is no charge on the capacitor, hence the voltage over the DTC pin equals the reference voltage, resulting in 100% dead time. As the capacitor is charged through the resistor, the voltage over the DTC pin decreases, and the dead-time slowly sinks to the minimum value. With the chosen parts, the time constant is τ = R · C = 180 kΩ · 3.3µF = 0, 6 s, (11) which makes sure, that a duty-cycle of 50%, which is proportional to a capacitor voltage of 3,4 V, will be reached after t = −τ · ln(1 − 3, 4 V uc (t) ) = 0, 68 s ) = −0, 6s · ln(1 − uref 5V (12) at the earliest. As the motor in the miniproject is not under load, this short period of time is enough to avoid an abrupt start-up. The dead-time control also offers an elegant way to implement an overvoltage protection. Texas Instruments’ application notes [5] suggest a solution with a TL431 shunt regulator (see fig. 6). The TL431 behaves like a zener diode with a breakdown voltage of 2,5 V, with the advantage of having an external reference pin. When the monitored voltage at this pin increases over the breakdown voltage, the TL431 goes into conduction, resulting in a forward bias of Q1. This causes the DTC to be clamped to the Reference voltage and the PWM switching to stop entirely. By these means, the supplying voltage can be monitored and the switching process entirely prohibited, when the voltage exceeds the tolerance of the motor. Unfortunately, due to a supply bottleneck, the TL431 did not arrive in time, which prevented the implementation of the protection circuit. A possible alternative way for optimizing the circuit in order to protect the motor from an overvoltage might be the simple use of a zener diode in series with a resistor. 9 ad-time control to be pulled up to the reference voltage and di Monitored Supply Rail VREF R1 Q1 Dead-Time Control R2 TL431 Figure 6: Overvoltage-protection circuit [5] Figure 31. Overvoltage-Protection Circuit 5.4. Driver circuit and MOSFET As the output current of the TL494 is limited, a half-bridge gate-driver IC (FAN73832 by urnoff Transition Fairchild) for MOSFETs and IGBTs, with a recommended supply voltage between 15 V and 20 V, is used to control the switching device. In order to allow an easy expandability, the switch is connected to the lower, inverted output of the driver IC and the bootstrap circuit is added. That means, by soldering in a second switch and diode, a half bride circuit can be built up quickly, if desired. Like the TL494, the FAN73832 also inherits a dead-time control. As this matter is already taken care of by the PWM IC, the smallest possible dead-time of 0,4 µs is set by using a dead-time resistor RDT = 22 kΩ. For the switch, an n-channel enhancement power MOSFET (IRF540A by Fairchild) with a maximum drain-source voltage of 100 V and a continuous drain current of 28 A is applicated. As these ratings exceed the ratings of DC Motor by far, safe operation, concerning transient voltage peaks during the switching process and a thermal reserve during conduction mode, is ensured. With a gate-source voltage vgs = 16 V, the on-state resistance RDS(on) is as low as 0,04 Ω, and therefore negligible compared to the resistance of the armature winding. [15] For the connection between the lower output of the driver IC and the gate of the MOSFET, a 10 Ωgate resistor has proven to be a fine solution. Since the main parts of the step-down converter circuit are discussed, the next part briefly covers the measurements on the circuit. utput pulse by the TL494 is accomplished by modulating the t tors. The turnoff transition always is concurrent with the fallin . Figure 32 shows the oscillator output as it is compared to a v ting output waveforms. If modulation of the turnoff transition is ope sawtooth waveform (see Figure 33) can be used without e of the TL494. 6. Measurements on the circuit In this short section, the main function of the buck converter, i.e. to decrease the input voltage according to the duty cycle of the switch, will be reviewed. Additionaly, a measurement of the converter’s efficiency is presented. tage Regulators With the TL494 10 The final setup for the buck converter, drawn in fig. 13, is used for the measurements. Due to the lack of an additional power supply, a measurement on the motor with varying load torque could not be done. Instead, a resistive was used. The measurement results for the output voltage Vo over duty cycle at RL = 200 Ωare displayed in fig. 7. It is shown, that the measured values for Vo follow the theoretical values very closely. It has to be noted, that the maximum duty cycle of the MOSFET is only around 0.86, which leaves room for an improvement. 25 output voltage [V] 20 15 Measurement 10 ideal output voltage 5 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 duty cycle Figure 7: Output voltage Vo over duty cycle D For the measurement of the efficiency of the converter, the power input from the signal power supply (16 V) and the load power supply (24 V) is measured and compared with the measured output on the load. The efficiency is defined as η= Pout . Psignal,in + Ppower,in (13) The results of the measurement (see Tab. 7 and 8) with a resistive load of 20 Ω and 200 Ω are illustrated in fig. 8. 100 90 80 efficiency [%] 70 60 50 RL = 200 Ohm 40 RL = 20 Ohm 30 20 10 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 duty cycle Figure 8: Efficiency η over duty cycle D The signal part of the circuit consumes power in no load. Therefore, the efficiency with a high load and low duty cycle, which results in a low power output, is especially low. With an increase of the power in the load, a steady rise in the efficiency can be made out, due to a very slow increase in the power demand of the signal circuit. 11 7. Measurements on the test-bike The electric bike, as described in section 4, is equipped with a 38 V battery pack, an electric front wheel hub motor and a three-phase inverter. The battery pack and converter are new and latter possesses additional features, in comparison to the replaced device. The main improvement ofter the old controller is the ability to handle regenerative braking, which can be activated by slightly pushing the brake handle. At the present time, a regulation of the electric braking force is not possible. Both the permanent magnet synchronous machine and the converter, which are rated at 250 W and 36 V/50 A respectively, were manufactured by Golden Motor Technology. [9] Before taking any measurements, the bicycle was set up with an amperemeter, voltmeter and data logger. The current and voltage was measured on the DC-side of the converter and the time interval between two data acquisitions was half a second. As the testparcours, a part of Singsakerbakken, spanning a length of 90 m at a height difference of approximately 6 m, which results in a slope of 6,7%, or alternatively an angle of 3,8◦ . The total weight of the bike, rider and measurement equipment was 120 kg. 10 test runs were carried out at different speed levels and the speed was held constant by regulating the throttle. At the top of the hill, the power was cut in the same place at every run and the bike was ridden back down. The measurements on the first two runs are void, because the conductor was not properly fitted in the clip-on amperemeter. The measurement data file was divided into 10 parts, one for each run. This was done by evaluating the current. When the current reached zero, bike and rider were assumed to be on top of the hill and hence a new run was beginning. Afterwards, each run was split into 3 parts; zero-, positive- and negative current. Parts with zero current were ignored, because the bike was at standstill or in no-load operation. The data with positive and negative current was averaged in their respective parts. This resulted in two averaged power measurements per run; regenerative and normal operation. A major error source, next to faulty measuring on the first two runs, turned out to be the calibration of the equipment. By evaluating the results, it became evident, that the clip-on amperemeter was not correctly zero adjusted. This is partly corrected by adding a correction current to each measurement. The correction current was found by looking at the current when it should have been zero and adding this to all the measurements. Further, the speed was hard to keep constant due to the low speed and a speed bump on the road and the only speed measurement device was a bicycle speedometer, with limited accuracy and no possibility for data logging. The results of the uphill ride using only the motor are displayed in tab. 2. 12 measurement 1 2 3 4 5 6 7 8 9 10 avg. speed [km/h] 5 5 5 8 8 8 13-14 (max) 13-14 (max) 13-14 (max) 13-14 (max) avg. current [A] 3.44 3.76 16.02 18.93 20.41 19.41 23.06 23.28 23.30 23.09 avg. voltage [A] 39.02 38.42 38.25 37.72 37.38 37.44 36.98 36.93 37.03 37.03 avg. power 131.3 140.9 612.7 713.9 763.0 726.8 852.7 859.7 862.7 854.9 Table 2: Measurements on the uphill ride The theoretically required power for riding up the test track, using eqs. (1) - (4) are shown in tab. 3. speed [km/h] 5 8 14 slope [%] 6.7 6.7 6.7 theoretical power requirement 122.2 197.6 351.4 Table 3: Theoretical power requirement at different cycling speed The efficiency η of the drive system, consisting of the controller, PMSM and wheel, can be estimated by dividing the theoretical mechanical power output Ptheo by the measured power input Pmeasured (see tab. 4). η= speed [km/h] 5 8 14 Ptheo (14) Pmeasured Ptheo [W] Pmeasured 122.2 610 197.6 740 351.4 850 η [%] 20.0 26.7 41.3 Table 4: Estimation of drive system’s efficiency It can be seen, that the system efficiency increases for a higher speed, mostly due to the rise of the efficiency of the PMSM [10]. Since there is no detailed documentation on the type and performance of the converter, no further conclusion can be drawn. 13 measurement 1 2 3 4 5 6 7 8 9 10 avg. current [A] avg. voltage [A] -0.25 41.40 -0.47 40.69 -1.81 40.51 -1.42 40.17 -2.72 40.10 -1.82 39.87 -1.7 39.81 -1.98 39.75 -1.19 39.89 -2.26 39.92 avg. power -10.2 -19.1 -73.2 -57.1 -108.9 -72.4 -67.5 -78.7 -47.3 -90.1 Table 5: Measurements on the downhill ride with regenerative braking The regenerative brake was tested with variable speed. This was accomplished by pedaling downhill while braking. The braking torque of the motor seemed to be constant and therefore, the mechanical power is proportional to the speed. Assuming a charge/discharge utilisation ratio of the battery of 0.8 and calculating the mean electric power of the regenerative brake to 74.4 W, the power gain by using recuperation is 59,5 W per testride. This increases the range of the bike on the uphill track at 5 km/h by Range increase: 59, 5 W · 100% = 9.8%, 610 W (15) respectively 8% at 8 km/h and 7% at maximum speed. It has to be noted, that this is an upper limit for the possible savings, as a normal bicycle ride contains much shorter braking phases. 8. Conclusion In the present miniproject, an electric bicycle was studied and its performance on a test track measured. As the bike was equipped with a new converter with the ability of regenerative braking, special attention was laid into the calculation of the possible saving of energy. The measurement data shows, that even with very good conditions, i.e. long braking phases, a range increase of less than 10 percent can be achieved. The major part part of the miniproject concerned the design and soldering of a converter for an electric bike. Due to the limited time frame, instead of a three phase inverter, a step down converter for powering up a stationary DC machine was built. The measurements on the converter show, that it fulfills the voltage step-down characterstic neatly, as expected from the theory. The voltage dividing potentiometer allows the adjustment of the duty cycle between 0 and 0.87; therefore, connected to a 24 V source, a voltage range of 0 V up to 20.7 V can be covered. Equipped with a soft-start mechanism, a smooth starting up of the DC machine can be ensured. Due to supply bottleneck, the desired overvoltage protection circuit could not be implemented. Possible future improvements on the converter include an investigtion on how to increase the maximum duty cycle over 0.86, the implementation of the overvoltage protection mentioned above and an implementation of a snubber circuit to improve the switching characteristic. In addition, a speed limiter, that is necessary in an electric bike according to the norwegian safety regulations presented in section 3, cannot be implemented by 14 simply controlling the voltage, as the load dependence cannot be taken into acount that way, could be implemented in an improved design. 15 A. Appendix Brand: Paravlux Motor Volts: Amps: H.P. Watt: RPM: Rating: Gear Box 24 Lbs/Ins: 3.5 3.8 A Cmkp: 4 1/15 RPM: 780 50 Ratio: 5 4000 Res.Sd: 1.s/149335/9H Cont. Table 6: Rating plate of the DC machines D Vo [V] 0 0 0.1 2.64 0.2 4.8 0.3 7.4 0.4 9.5 0.5 11.8 0.6 14.2 0.7 16.4 0.8 18.9 0.86 20.6 Isignal [mA] Iin,power [mA] η [%] 8.7 0 0 12.8 4.8 10.9 14.7 10.5 23.6 16.5 19.6 37.3 17.9 28.8 46.2 19.4 40.2 54.6 21.0 54.1 61.7 22.4 68.1 67.5 24.0 85.7 73.2 25.0 98.1 77.0 Table 7: Measurement data for RL = 200 Ω D Vo [V] 0 0 0.1 1.7 0.2 3.9 0.3 6.6 0.4 8.7 0.5 11.3 0.6 13.7 0.7 15.9 0.8 18.6 0.86 20.2 Isignal [mA] Iin,power [mA] η [%] 8.6 0 0 12.7 30 15.6 14.3 94 30.6 17.3 200 42.9 18.7 290 52.1 20.4 420 61.4 21.9 550 69.3 23.1 670 76.8 24.2 840 84.2 24.8 940 88.9 Table 8: Measurement data for RL = 20 Ω 16 duty cycle D=0.1 40 35 voltage [V] 30 25 20 drain-source voltage 15 PWM-Signal 10 5 0 0 10 20 30 40 50 60 70 80 90 100 time [µs] Figure 9: VDS and PWM-Signal for D = 0.1 duty cycle D=0.2 40 35 voltage [V] 30 25 20 drain-source voltage 15 PWM-signal 10 5 0 0 10 20 30 40 50 60 70 80 90 100 time [µs] Figure 10: VDS and PWM-Signal for D = 0.2 17 duty cycle D=0.5 40 35 voltage [V] 30 25 20 drain-source voltage 15 PWM-Signal 10 5 0 0 10 20 30 40 50 60 70 80 90 100 time [µs] Figure 11: VDS and PWM-Signal for D = 0.5 duty cycle D=0.86 40 35 voltage [V] 30 25 20 drain-source voltage 15 PWM-Signal 10 5 0 0 10 20 30 40 50 60 70 80 90 100 time [µs] Figure 12: VDS and PWM-Signal for D = 0.86 18 2 1 3 RT1 5k RT2 4.7k 3 R2 10k GND CT 0.01µ GND 3.3µ C3 47k R3 R6 180k 1 2 16 15 3 4 5 6 -I2 +I2 -I1 +I1 E1 C1 OUTC VREF VCC IC1 COMP GND E2 C2 RT CT DTC Osci. TL494BD +15V 12 14 13 8 9 R1 1k 2 4 1 7 11 C1 1µ 3 R5 22k GND 10 GND DT/(INV)SD GND IN LO VS HO VB IC2 VDD FAN73832 7 8 6 5 R4 100 D1_IN4002 C2 1µ M Figure 13: Layout of the buck converter in Eagle +24V Q1_IRF540A D2_IN4002 GND 19 2 1 References [1] Braess/Seiffert; Vieweg Handbuch Kraftfahrzeugtechnik ; 5th ed.; VIEWEG, 2007. [2] Extra Energy; Pedelec Electric Bikes ; http://www.nycewheels.com/bike-info.html, 06.10.2010. [3] Bike Europe; EPAC Standard Document for e-Bikes ; http://www.bikeeu.com/news/3376/epac-standard-document-for-e-bikes-now-available.html, 06.10.10. [4] J. David Goodman; An Electric Boost for Bicyclists ; http://www.nytimes.com/2010/02/01/business/global/01ebike.html, 31.01.2010. [5] Texas Instruments; Designing Switching Voltage Regulators With the TL494 ; http://focus.ti.com/lit/an/slva001d/slva001d.pdf; Application Report, Feb. 2005. 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