e-ISSN(Online): 2460-8122 pp 27-33
Enhancing Speed Control of BLDC Motors Using Zeta Converter for Small Electric
Vehicles
Muhammad Yusril Hafidh1, Unggul Wibawa1, Tri Nurwati1, Tamunonengi .E. Wakama2
1Electrical Engineering Department, Universitas Brawijaya, 2Raw materials research and development council.
Abuja. Nigeria,
Email : unggul@ub.ac.id, trinurti@ub.ac.id, tamunojohnson12@yahoo.com Abstract— The movement to reduce emissions can be done
by developing electric vehicles derived from renewable fuels. Small electric vehicle will use batteries and motors so that BLDC motor was chosen in this study. BLDC motors use electronic commutation so a controller is needed. The controller used is a PI controller assisted by the hysteresis current controller. The output of the hysteresis current controller needs to be converted to a DC voltage using a DC- DC converter. One of the DC-DC converters is a zeta converter which can increase or decrease the voltage so that it can be used when the load voltage varies as will be used in this study. The results showed that the BLDC motor connected to the zeta converter with the controller can be used when the load torque varies. If the applied varying load torque does not exceed the rated torque, the actual speed will return to the reference speed without exceeding a 10% error. On the other hand, the actual speed will return to the reference speed by exceeding the 10% error, if the applied varying load torque exceeds the rated torque.
Index Terms—BLDC motor, PI Controller, Hysteresis Current Controller, Zeta Converter
I. INTRODUCTION
Solar PV and electric vehicles are targeted to support the provision of 2 million four-wheeled vehicles and 13 million two-wheeled vehicles so that emissions are expected to be reduced by 314 million tons of CO2 in 2030 [1]. Electrical energy from solar PV or other renewable energy generators can be stored in batteries.
The battery has a voltage output in the form of DC voltage. The output from the battery, namely DC voltage, can be used for DC motors without going through an inverter. This DC motor is distinguished from motors that use brushes and motors that do not use brushes. Brush motors have the disadvantages of high maintenance, bulky construction and low efficiency because these DC motors have brushes and a commutator. Therefore, the electric motor used in this study is a Brushless DC (BLDC) motor.
BLDC motors were chosen because they have high reliability and efficiency, are quieter, lighter, last longer, have a wider speed range, and better speed/torque characteristics. This BLDC motor has various advantages because it does not use charcoal brushes and a commutator, but uses electronic commutation [2]. This electronic commutation is regulated by the controller with the aim of obtaining parameters with the desired values.
The PI controller has a smaller settling time and overshoot than the PID controller [3]. Therefore, the BLDC motor in this study will use a PI controller assisted by a hysteresis current controller so that the output signal from this controller can be input to the DC-DC converter.
The DC-DC converter is used so that the DC voltage can be adjusted. The DC voltage is regulated to provide the needs of the BLDC motor through the controller so that the output speed is expected to have a good speed response. This BLDC motor will be applied to motors that receive changing torque so that a step-up and step- down converter is needed. The DC-DC converter will increase or decrease the voltage depending on the controller signal based on the BLDC motor speed error.
One of the DC-DC converters to increase and decrease the voltage is the zeta converter which has the advantages that the output current is always continuous, the ripple of the output current is small because there is an inductor on the output side, the input voltage can be increased or decreased where the polarity of the output voltage is not changed and has a small ripple. In addition, the zeta converter has a fast-settling time and low switching pressure [4]. Therefore, this study will use a voltage step-down DC-DC converter, namely the zeta converter. Zeta converter with additional components and fast settling time is expected to maintain the reference speed even though the load torque varies.
This journal presents a comprehensive review of recent advancements and research efforts in optimizing BLDC motor technology for enhanced small EV performance.
II. RELATED RESEARCH
A. BLDC Motor
The BLDC motor moves like a synchronous motor where the speed of the rotating magnetic field of the stator is the same as the speed of the rotor. The similarity between the stator of a BLDC motor and an induction or synchronous motor is that it requires a three-phase AC voltage. BLDC motors get AC voltage from DC voltage which is converted to AC voltage by the inverter.
Meanwhile, the rotor section does not require a power supply because there are permanent magnets in the rotor section [5]. The permanent magnets in the rotor will attract or repel the magnetic field on the stator which comes from the AC voltage so that the magnetic field on the stator will vary depending on the polarity of the
applied AC voltage [6]. Changes in the magnetic field on the stator will be adjusted by the controller based on data from the hall sensor. This hall sensor causes BLDC motors to be different from DC motors because BLDC motors use electrical commutations, namely hall sensors, while DC motors use mechanical commutations, namely commutators. Data from the sensor will be continued to the controller which causes the motor to move continuously.
B. Hysteresis Current Controller
This controller works by comparing the actual current with a reference area in the form of a sine wave.
If the farthest limit of the hysteresis band is exceeded, the switch will be off. If the lower limit of the hysteresis band is exceeded, the modulation signal will be zero. The modulation signal will have a return value if the current is in the hysteresis band [7]. So, the actual current is forced to follow the reference current.
Fig. 1. Hysteresis Current Controller [7]
C. Speed Controller
The speed controller aims to receive a signal that represents the reference speed, then is directed to have that reference speed [8]. In this study, the speed controller used is the Proportional-Integral Controller.
The input signal from the PI controller is a speed error (E), while the output signal from this controller will be used as an input reference [9].
𝑢(𝑡) = 𝐾𝑝(𝑒(𝑡) +1
𝑇𝑖∫ 𝑒(𝑡)0𝑡 . 𝑑𝑡) (1) D. Zeta Converter
The Zeta converter is a fourth-order DC-DC converter. This is because the zeta converter has four charge storage components, namely two inductors and two capacitors [10]. Therefore, the zeta converter has two inductors (L1 & L2), two capacitors (C1 & C2), a diode and a MOSFET as a controlled switch. This converter can increase and decrease the voltage without changing the polarity [11]. In addition, the zeta converter has an output current that is always continuous, the ripple of the output current is small because there is an inductor on the output side, fast settling time and low switching pressure [4].
Fig. 2. Zeta Converter Equivalent Circuit [12]
𝐷 = |𝑉𝑂|
𝑉𝑆+|𝑉𝑂| (2) 𝐿1= 𝑉𝑆2.𝐷
𝜂𝑓𝑠𝑃𝑚𝑎𝑥 (3) 𝐿2=𝑉𝑆.𝐷.𝑉𝑂
𝜂𝑃𝑂𝑓𝑠 (4) 𝐶1= 𝐷.𝑃𝑂
𝜂(𝑉𝑂+𝑉𝑠)𝑓𝑠𝑉𝑂 (5) 𝐶2= 2𝑃𝑂𝑡ℎ𝑜𝑙𝑑
(𝑉𝑂)2−(𝑉𝑂𝑚𝑖𝑛)2 (6) III. METHODS
A. Research Flow Chart
This section will describe the steps to be taken in achieving the research objectives. The method used in this study is depicted in Figure 3.
Fig. 3. Research Flow Chart
B. Research Variable
This study used a variation of controller conditions with a load of 0 Nm, 1 Nm, 2 Nm, 3 Nm, 4 Nm, 5 Nm.
Giving variations of these conditions aims to determine the effect and comparison of the results of the given variation values when the parameters are changed.
C. Circuit Simulation Using Zeta Converter
In this study, a zeta converter is used as a DC-DC converter in a BLDC motor speed control circuit. This circuit will be simulated in Simulink MATLAB.
Fig. 4. Simulation Circuit
The test circuit uses a zeta converter, six-step inverter, BLDC motor, hall effect conversion, commutation logic and speed controller.
D. Six-Step Inverter Design
This inverter has an input in the form of a DC voltage with six MOSFETs as controlled switches that require an input signal at the gate. The output of this three-phase inverter is three-phase AC voltage.
Fig. 5. Six-Step Inverter Simulation Circuit
E. Motor BLDC Design
The three-phase trapezoidal signal type permanent magnet synchronous motor block in MATLAB SIMULINK 2020A will be used in this study as a BLDC motor block.
Fig. 6. BLDC Motor Block Simulation Circuit
The BLDC motor will be given a load that is determined every second using the "Input Step Torka"
block, namely the BLDC motor without load is given a load of 1 Nm, then another load is added to 2 Nm, then another load is added to 3 Nm, then another load is added to 4 Nm, then added the load again to 5 Nm. Furthermore, the load will be reduced to 4 Nm, then the load will be reduced again to 3 Nm, then the load will be reduced again to 2 Nm, then the load will be reduced again to 1 Nm, then the load will be reduced again to 0 Nm so that the BLDC motor is in no-load condition. Therefore, speed can be analyzed. The specifications for the BLDC motor to be used can be seen in table 1.
TABLEI
BLDCMOTORSPECIFICATIONDATA
F. PI Controller Design
Proportional-Integral controller is used to correct errors from the system. the error signal requires a system reference value and a feedback value from the BLDC motor. The reference value and the feedback value will be compared so that an error signal will be obtained. The PI controller used in this simulation is a PID controller block, then it is set to become a PI controller.
Fig. 7. PI Controller Simulation Circuit
G. Hysteresis Current Controller Design
The output signal from the PI controller will be continued on the hysteresis current controller. This hysteresis current controller is used to give the DC-DC converter a trigger signal.
_ + Vin
Va Vb Vc
Fig. 8. Hysteresis Current Controller Simulation Circuit
H. Zeta Converter Design
The zeta converter is added to the simulation of the BLDC motor system before entering the inverter section.
This Zeta converter is determined to have a power of 900 W, a maximum voltage of 100 V, a minimum voltage of 30 V and a switching frequency of 20 kHz with a ripple tolerance value of 10%.
Fig. 9. Zeta Converter Simulation Circuit
IV. RESEARCH RESULT
A. Component Calculation on Zeta Converter The simulation in this study was carried out by varying the load torque on the BLDC motor using a zeta converter. Therefore, it is necessary to calculate the value of the L1 and L2 inductors, calculation of the value of the capacitor C1 and C2. Calculation of the value of the inductor L1 and L2, and the calculation of the value of the capacitor C1 and C2 on the zeta converter is carried out to get the zeta converter voltage output.
𝐷 = |100|
48 + |100|
𝐷 = 0,675
This duty ratio (D) value will be used to calculate the inductor value.
𝐿1= (48)2𝑥0,675 0,1𝑥20000𝑥900 𝐿1= 0,864 mH
The value of 0.864 mH is rounded up to 1 mH so that the component can be found on the market.
𝐿2= 48𝑥0,675𝑥100 0,1𝑥900𝑥20000 𝐿2= 1,8 mH
A value of 1.8 mH is rounded up to 2 mH so that the component can be found on the market.
𝐶1= 0,675𝑥900
0,1𝑥(100 + 48)𝑥20000𝑥100 𝐶1= 20,52365 μF
The value of 20.52365 uF is rounded up to 22 uF so that the component can be found on the market.
𝐶2=2𝑥900𝑥16,66𝑥0,001 (100)2− (30)2 𝐶2= 3295,38462 μF
The value of 3295.38462 uF is rounded up to 3300 uF so that the component can be found on the market.
B. Test Result of BLDC Motor Connected to a Zeta Converter Without a Controller at No Load
This simulation uses the circuit in Figure 4, but does not use a controller, namely a PI controller and a hysteresis current controller.
Fig. 10. Circuit Simulation Without Controller at No Load
In this simulation, no load is used so the load used is 0 Nm. A DC voltage source of 48 V will have its voltage level changed by the zeta converter. Furthermore, the DC voltage from the zeta converter will be converted into a three-phase voltage by the inverter according to the hall effect signal so that the motor can work.
Fig. 11. Speed Response of a Zeta Converter Connected BLDC Motor Without a Controller at No Load
From Figure 11, the speed response of the BLDC motor connected to the zeta converter without the controller reaches a stable condition with a time of 5.054 seconds. However, this speed response has a speed of 3771 rpm so it has an error of 33.7234% when compared to a reference speed of 2820 rpm.
C. Test Results of a BLDC Motor Connected to a Zeta Converter Without a Controller when the Load Varies
This simulation uses the circuit in Figure 10, but the load used varies.
Fig. 12. Circuit Simulation Without a Controller when the Load Varies
From Figure 12, the BLDC motor circuit is given a voltage from a DC voltage source of 48 V, then the DC
+ +
_
voltage will be changed by the zeta converter.
Furthermore, the DC voltage from the zeta converter will be converted into a three-phase voltage by the inverter according to the hall effect signal so that the motor can work.
Figure 13. Speed Response of a BLDC Motor Connected to a Zeta Converter Without a Controller when the Load Varies
In this simulation, a load that varies every one second is 0 Nm, 1 Nm, 2 Nm, 3 Nm, 4 Nm, 5 Nm, 4 Nm, 3 Nm, 2 Nm, 1 Nm and 0 Nm. The initial torque value is the no-load torque of 0 Nm. The speed response of a BLDC motor connected to a zeta converter without a controller when the load varies has not reached a stable condition at an interval of 0-1 seconds in Figure 13 so that the speed response has not reached a stable condition when the load changes to 1 Nm, 2 Nm, 3 Nm, 4 Nm, 5 Nm, 4 Nm, 3 Nm, 2 Nm, 1 Nm and 0 Nm at one second intervals.
D. Determination of PI Controller Constants Connected to Hysteresis Current Controller
The controller in this study is used to improve the speed response. The PI controller will be connected with a hysteresis current controller. This PI controller has parameters, namely KP and KI. Meanwhile, the hysteresis current controller uses input from the BLDC motor outputs. Therefore, the parameter values of KP and KI are needed.
PI constants namely KP and KI in this study were obtained through trial and error. Testing by trial and error is determined using KP and KI values of 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, 500, 1000, 5000 with reference speed of 2820 rpm. This test aims to obtain a good speed response in this case a fast steady time and a small overshoot.
TABLEII
DETERMINATIONRESULTSOFCONSTANTPICONTROLLER CONNECTEDWITHHYSTERESISCURRENTCONTROLLER
Table II is obtained after testing each load with KP
and KI values of 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, 500, 1000, 5000. A 0 Nm load has an overshoot, while a 1 Nm to 5 Nm load has an undershoot because when testing is tested by changing the 0 Nm load to 1 Nm, 0 Nm to 2 Nm, and so on. Therefore, a load of 1 Nm to 5 Nm has an undershoot. Furthermore, the results of determining KP and KI will be used in testing BLDC motors connected to the zeta converter with the controller when no load and when the load varies.
E. Test Results of a BLDC Motor Connected to a Zeta Converter with a Controller at No Load
The BLDC motor simulation in this study used the PI controller parameters, namely KP of 0.05 and KI of 0.1 which was carried out to obtain steady time and overshoot values. This simulation uses a simulation as shown in Figure 4 with a rated speed of 2820 rpm, no- load torque of 0 Nm, KP of 0.05 and KI of 0.1.
Figure 14. Speed Response of a BLDC Motor Connected to a Zeta Converter and a Controller at No Load
From Figure 14, the speed response of the BLDC motor connected to the zeta converter reaches a stable condition with a time of 0.237 seconds. However, this speed response has an overshoot at 3022 rpm at 0.064 seconds.
F. Test Results of a BLDC Motor Connected to a Zeta Converter with a Controller when the Load Varies
The BLDC motor without load is given a load until it reaches a rated torque of 2.9588 which in this test is rounded up to 3 Nm. Furthermore, given a load exceeding the rated torque. Then, the load is reduced to around the rated torque and returns to the no-load state.
Therefore, in this test the load used was 0 Nm, 1 Nm, 2 Nm, 3 Nm, 4 Nm, 5 Nm, 4 Nm, 3 Nm, 2 Nm, 1 Nm, 0 Nm. Meanwhile, the speed used is the rated speed of 2820 rpm. The results of the KPand KI analysis in the previous discussion will be used in this test.
Figure 15. Speed Response of a BLDC Motor Connected to a Zeta Converter and a Controller when the Load Varies
From Figure 15, a load is used that varies every second, namely 0 Nm, 1 Nm, 2 Nm, 3 Nm, 4 Nm, 5 Nm, 4 Nm, 3 Nm, 2 Nm, 1 Nm and 0 Nm. The initial torque value is the no-load torque of 0 Nm. In this simulated speed response, a 0 Nm load has a settling time of 0.237 seconds and an overshoot at 3022 rpm is 0.064 seconds.
Furthermore, when given a load of 1 Nm for 1 second, the speed response has a settling time of 0.211 seconds at 1.211 seconds, undershoot at 2728 rpm at 1.008 seconds and overshoot at 2872 rpm at 1.026 seconds. Next, when given a load of 2 Nm for 2 seconds, the speed response has a settling time of 0.322 seconds at 2.322 seconds, undershoot at 2702 rpm at 2.009 seconds and overshoot at 2841 rpm at 2.026 seconds. Then when given a load of 3 Nm for 3 seconds, the speed response has a settling time of 0.372 seconds at 3.372 seconds, undershoot at 2670 rpm at 3.011 seconds and overshoot at 2826 rpm at 3.03 seconds. Then when given a load of 4 Nm for 4 seconds, the speed response has a settling time of 0.533 seconds at 4.533 seconds, undershoot at 2182 rpm at 4.041 seconds and overshoot at 2859 rpm at 4.191 seconds.
Furthermore, when given a load of 5 Nm for 5 seconds, the speed response has a settling time of 0.466 seconds at 5.466 seconds, undershoot at 2025 rpm at 5.049 seconds and overshoot at 2894 rpm at 5.217 seconds. Next, when the load is reduced to 4 Nm at 6 seconds, the speed response has a settling time of 0.416 seconds at 6.416 seconds, overshoot at 2930 rpm at 6.013 seconds and undershoot at 2160 rpm at 6.066 seconds. Then when the load is reduced to 3 Nm at 7 seconds, the speed response has a settling time of 0.374 seconds at 7.374 seconds, overshoot at 2925 rpm at 7.01 seconds and undershoot at 2656 rpm at 7.033 seconds. Then when the load is reduced to 2 Nm in 8 seconds, the speed response has a settling time of 0.363 seconds in 8.363 seconds, overshoots at 2900 rpm at 8.008 seconds and undershoots at 2708 rpm at 8.03 seconds. Furthermore, when the load is reduced to 1 Nm in 9 seconds, the speed response has a settling time of 0.272 seconds in 9.272 seconds, an overshoot of 2922 rpm in 9.011 seconds and an undershoot of 2724 rpm in 9.042 seconds. Next, when the load is reduced to 0 Nm at 10 seconds, the speed response has a settling time of 0.758 seconds at 11.758 seconds, overshoot at 2922 rpm at 10.027 seconds and undershoot at 2746 rpm at 10.222 seconds. The 0 Nm load at 0 seconds and 10 seconds has a different settling time because the 0 Nm load at 0 seconds has an initial speed of 0 rpm, while the 0 Nm load at 10 seconds has an initial speed of 2820 rpm.
So in this test, the greater the change in load will result in the speed response experiencing an undershoot first, while the smaller the change in load will result in the speed response experiencing an overshoot first. The speed response still has a good overshoot or undershoot, that is, an error of less than 10% when the load is from 0 to 3 Nm. However, the speed response becomes less good, namely an error of more than 10% when the applied load exceeds the rated torque, which is given a load of 4 and 5 Nm.
V. CONCLUSION
Based on the simulation results and analysis on Simulink, the following conclusions are obtained:
1. Designing a BLDC Motor with a zeta converter that is connected to a PI controller and a hysteresis current controller when given a varying load torque requires a DC source to supply voltage, a zeta converter to increase or decrease the DC voltage, a six-step inverter to change the voltage so that the BLDC motor can use it, BLDC motors are used to get the rotor speed with a DC starting source, hall effect conversion to convert the hall effect signal to a conducting phase signal, commutation logic to convert the conducting phase signal to a trigger signal at the gate in a three phase inverter, and speed controller namely PI controller and hysteresis current controller to correct the actual speed error value with the reference speed so that a trigger signal is generated for the gate on the zeta converter so that the switch can work according to the given signal.
2. The BLDC motor that is connected to the zeta converter with variations in load torque has a difference in speed response when not using a PI controller assisted by a hysteresis current controller and using a PI controller assisted by a hysteresis current controller. When this BLDC motor does not use a PI controller assisted by a hysteresis current controller, the speed response obtains a settling time value of more than 1 second. When this BLDC motor uses a PI controller assisted by a hysteresis current controller, the speed response obtains a settling time value of less than 1 second. Therefore, a BLDC motor is used which is connected to a zeta converter, PI controller and hysteresis current controller with load variations. The speed response of a BLDC motor connected to a zeta converter, PI controller and hysteresis current controller with variations in load torque will have an undershoot of more than 10% if a load torque exceeds the rated torque, which is around 3 Nm.
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