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Novel Boost Converter fed BLDC Motor Drive for Superior Voltage Gain
1Aritra Ghosh, 2Manoj Kumar Maharana
School of Electrical Engineering, KIIT University, Bhubaneswar, India Abstract—This paper presents a novel interleaved boost
converter with a a modified control scheme that reduces the torque ripple and optimizes the efficiency of a Brushless DC(BLDC) motor. The proposed topology presented in the paper has superior voltage gain to conventional boost converters. Furthermore, the topology reduces ripple in the voltage and current along with reduced switching stress. The control strategy proposed in the paper that helps reduce the torque ripples using Selective Harmonic Elimination(SHE) that eliminates the necessary harmonics as per the firing angles generated from the conduction modes of the BLDC motor. The validity of proposed scheme is well demonstrated through simulation results in PSIM 9.1.1 Environment.
Keywords— Brushless DC (BLDC) motor; Selective Harmonic Elimination; Boost Converter; loss minimization; Torque ripple.
I. INTRODUCTION
DC-DC converters are some of the most popular boost converter used in the market. Some advanced versions of the converters are also available like boost converter with CLD cell, quadratic boost converter and Multi Device Boost converters. The applications of these boost converters in machines and drives have expanded over the last century. Extensive use of DC-DC converters have taken place in the field of renewable energy systems and fuel cell areas. Each boost converter is advantageous over the others in different ways based on parameters like voltage gain, reliability, switching stress, torque ripples, current ripples, voltage ripples and size of parasitic components.[3,4]
Various boost converters add unnecessary ripples to the current flow which needs to be eliminated. The need for a highly reliable boost converters of a small size with high power density that can operate under extreme thermal excursions. To meet the these demands the interleaved boost converters(IBC) have come into play.
They offer low current ripple on the input side and low ripples on the output voltage. This feature of the Multi Device Boost(MDBC) converters enables improvement in the efficiency, transient response and size. This paper puts forward a novel MDBC converter with a CLD cell.
The comparative study with the conventional and advanced converters helps in justifying the necessarily
of adding the additional switches.[5,12]
The paper also puts forward a drive system where the MDBC is used and a modified control technique. The Permanent Magnet motors have long been in use because of its fast dynamic response, noiseless operation, smooth and controlled efficiency, low cost ferrites and usage of concentrated windings [1,2]. The torque waveforms generated by using the proposed drive system shows a decrease in the torque ripple[6,7]. The Control Scheme presented in this paper will be fine tuned by the use of SHE by determining the firing angles from the 1200 conduction modes of the BLDC [8,9,10]. The control loop interacts the switching gates of the inverters to optimize the efficiency of the system.
A simple 2 level 3 phase inverter is used in the drive system that is couple with the MDBC and feeds the BLDC motor.[11,13,14]
The different components of the drive system helps in determining the organization of the paper. Proposed Boost Converter with CLD cell is presented in section II followed by the comparative study with existing boost converters in section III the modeling of the BLDC motor and its conduction modes in section IV. The SHE based firing angle generation in the section V. The control scheme explaining the optimally switched inverter in section VI. The simulation results run in Power Sim 9.1.1 Environment to validate the claims made in the paper in section VII.
II. PROPOSED BOOST CONVERTER WITH CLD CELL
The proposed Boost Converter incorporates a CLD cell in it to improve the output voltage gain. Cascading multiple cells helps increase the gain but increases the power losses too. Quadratic boost converter was introduced to address this problem by incorporating a single switch. This however failed to solve all the problems. The voltage stress got incremented with this topology. In order to overcome this issue a new topology was proposed that involved the introduction q- BC with CLD cell. However, the problem of reliability, higher gain and reduction in size was not addressed satisfactorily. In order to achieve the solution to all the mentioned problems a new proposed topology of Multi-
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Device Boost Converter is mentioned in this paper as shown in Fig 1; to develop a solution to achieve a highly reliable compact model of higher voltage gain, a reduced size and reduced switching stress.
Fig 1:Proposed Dual Phase MDBC with CLD Cell The proposed converter is operated in the Continuous Conduction Mode. There are 4 modes of operation of this given topology. The equivalent circuits of all the four methods have been demonstrated in Fig 2(a), 2(b), 2(c)and 2(d). The waveform of the different components of the topology have been mentioned in Fig 3.
The different modes of operation are
Mode 1: Fig 2(a) shows the mode 1.In this mode, the switch S1 is turned ON and S2 is OFF, The diode D3 and D4 are in reversed biased condition. The inductor L1 will get charged from the supply (Vin) while the capacitor C2 and C3 will get discharged to supply the energy to the inductor L3 and load. So the inductor current iL1 and iL3 will get increased linearly as shown in Fig 3.
(a)
(b)
(c)
(d)
Fig 2: MDBC with CLD cell under (a) Mode (b) Mode2 (c) Mode 3 (d) Mode 4
Mode 2: Fig.3 (b) shows mode2. In this mode, both the switch S1 and S2 are turned OFF while the diode D3 and D4 are conducting for the time period DTS to TS/2.
The inductor L1 and L3 will get discharged to supply the energy to the capacitor C2 and C3 and load respectively. So the current iL1 and iL3 will get decreased as shown in Fig.3 .
Mode 3: In this mode, the switch S2 is turned ON and S1 is OFF and both the diode D3 and D4 are in reversed biased condition. The equivalent circuit is shown in Fig.
2(c). The inductor L1 and L3 will get charged from the input voltage source Vin and capacitor C2 and C3 respectively. Here the inductor current iL1 and iL3 will increase linearly as shown in Fig 3.
Mode 4: Mode4 is similar to mode2. In this mode, both the switch S1 and S2 are turned OFF while the diode D3 and D4 are conducting shown in Fig. 2(d). Here the inductor L1 and L3 will get discharged to supply the energy to the capacitor C2 and C3 and load respectively.
So the current iL1 and iL3 will get decreased as shown in Fig. 3.
Fig 3: Different Waveforms of MDBC with CLD cell
III. COMPARATIVE STUDY
A comparative study is presented in this section that is shown in table 1. The output voltage in Dual phase MDBC with CLD cell is higher than the other conventional boost converters and its advanced versions of boost converter. In this section, the comparative studies of the different topology of dc/dc boost converters are performed theoretically by using the designed parameters mentioned in the Table 2. This theoretical analysis has been done on resistive load with a lossless converter having 10kW, 100V input voltage, 50 kHz switching frequency (FSW), ripple current is 30% of input and output current. The Fig.4(a) Shows the performance of all the different topologies of dc/dc boost converter, during the output voltage is constant and the stress voltage is changed as per the output voltage. It is observed that the stress voltage of boost converter (BC), quadratic boost converter and multi- device boost converter (MDBC) are same as the output voltage. The stress voltages of boost converter with CLD cell and quadratic boost converter with CLD cell are same and lower than the earlier one. But MDBC with CLD cell gives the lowest stress voltage compare to all mentioned DC/DC converter topologies.
Table1: Different equations for Different boost Topologies
Fig 4(a) Stress voltage of different topologies of dc/dc
boost converter as the output voltage is constant.
Fig 4(b) Output voltage of different topologies of dc/dc boost converter change as per the change of duty ratio.
Fig.4 (a) shows the output voltage of all the different dc/dc boost converters with varying duty ratios. From this figure, it is concluded that MDBC with CLD (proposed topology) gives the highest and conventional boost converter gives the lowest output voltage gain at same input voltage.
Table2: Different parameters for Different boost Topologies
IV. BLDC MOTOR MODELLING
A three phase PMBLDC motor is operated from inverter. 120° conduction mode of the inverter are very popular to drive PMBLDC motor as shown in Fig. 5.
Fig. 5. Schematic of a three phase PMBLDC connected to inverter
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The three phase voltage equation from the equivalent circuit is
Where V is the supply voltage, Rt is the stator resistance, i is the stator current and e is the back e.m.f.
The electromagnetic torque of BLDC motor can be expressed as,
(2) The instantaneous-induced e.m.f can be written as
(3)
(4)
(5) The electromagnetic torque can be written as
(6) 120° conduction mode
The practical phase current for trapezoidal BLDC motor with different rise angle for 120° conduction mode (as shown in Fig.6) is analyzed and given below.
Fig. 6. Phase current of 120° mode with rising angle.
By using Fourier Transformation of the waveform shown in Fig.6, the practical phase current equation is derived. The current equation is mentioned below in
equation (3).
The percentage change in harmonics content with rising angle for this mode is calculated from equation (7) and is shown in Fig.7.
Fig. 7. Percentage change in harmonics content with rising angle for 120°.
Back e.m.f is proportional to the flux linkage. Fig.8 is the shape of the back e.m.f.
Fig. 8. Back e.m.f of BLDC Motor
By taking Fourier series of the back e.m.f shown above the back e.m.f equation is derived. The back e.m.f equation is mentioned below.
(8)
Fundamental torque can be found out by multiplication of equation (10) as follows where .
(9) This is the fundamental torque equation. But due to harmonics in back e.m.f as well as phase current torque ripple is generated and it affects the performance of BLDCM.
From the above discussion it is clear that harmonics content in phase current is changing depending on the rising angle. The rising angle is directly related to speed of the motor and circuit inductance. We can optimized torque ripple by eliminating dominant harmonics content from the current waveform for a speed. At higher speed, increases and 3rd harmonics increases but 7th harmonics decreases from fig.8 which makes increase in ripple torque to fundamental torque ratio.
This means at higher speed there is significant decrease in fundamental torque. By eliminating the dominant harmonics content by selective harmonics elimination process which is described in the following section we can optimize torque ripple to a lower value for entire speed range. We can decrease core and copper loss further which improves drive efficiency.
V. CONTROL SCHEME
Fig. 9 shows the entire control scheme of the drive. The f sw is estimated by look up table control. In the proposed method, the rising delay is considered. An electronic speed sensor is used to sense the speed of the motor. From the speed and armature current we can decide what should be f sw . Consequently we can eliminate dominant current harmonics that reduces loss.
With a decrease in speed and with increase in load, the switching frequency is kept at a higher value. The low switching indicates three switching per quarter cycle of the current signal. One switching is for adjusting the fundamental while the other two switching are for removal of fifth and seventh harmonics from the current.
High switching indicates seven switching for removal of fifth, seventh, eleventh, thirteenth, seventeenth and nineteenth harmonics besides adjusting the fundamental.
The modulation index reference md* for the inverter is calculated based on the sensed speed and a reference set speed as,
(10)
Fig 9: Control Scheme of the proposed drive system Where, KP and KI are the proportional and integral gains of the proportional-integral (PI) controller respectively. In the proposed switching technique, harmonic elimination based PWM scheme removes various lower order harmonics from the inverter output phase current. The switching angles are calculated and stored in a microcontroller memory as a function of modulation index
VI. SIMULATION RESULTS
The output voltage of the proposed boost converter under dynamics is shown below in fig.10. Initial transient is because of BLDCM dynamics.
Fig 10: Output voltage of dc/dc boost converter.
Torque ripple is eliminated by using newly adopted control scheme shown in fig.12.Without harmonics elimination torque ripple is more as shown in fig.11.
Fig 11:Torque ripple without harmonics elimination
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Fig 12:Torque ripple with proposed control technique and Phase current of BLDCM
Fig 13.Comparison of Proposed Drive without and with control technique
The proposed technique is effective as it minimizes torque ripple explained above as well as improves drive efficiency shown in fig.13.
VII. CONCLUSION
The paper presents a novel MDBC with CLD cell drive system that houses an optimally switched inverter by using a modified control scheme. The novel boost converter shows less ripples, low switching stress and higher voltage gain. The torque ripples are reduced and the efficiency is optimized because of reduced ripples.
The results have been verified by Psim 9.1.1 Environment. The theoretical and the simulation results are validated. From different theoretical and simulation comparison studies, it has been observed that multi- device boost converter with CLD cell has better characteristics over all the different topologies of dc-dc boost converter with respect to the high voltage gain ratio, low stress voltage and low current and voltage ripple.
REFERENCES
[1] Santra, Subhendu Bikash. Design and Implementation of UPFC based Boost Converter for Efficiency Optimization of Brushless DC Motor Drive System. Diss. JADAVPUR UNIVERSITY KOLKATA, 2012.
[2] Tashakori, A., and M. Ektesabi. "Stability analysis of sensorless BLDC motor drive using digital PWM technique for electric vehicles."
IECON 2012-38th Annual Conference on IEEE Industrial Electronics Society. IEEE, 2012.
[3] Hegazy, Omar, Joeri Van Mierlo, and Philippe Lataire. "Analysis, modeling, and implementation of a multidevice interleaved DC/DC converter for fuel cell hybrid electric vehicles." Power Electronics, IEEE Transactions on 27.11 (2012): 4445-4458.
[4] Hegazy, Omar, Joeri Van Mierlo, and Philippe Lataire. "Analysis, control and comparison of DC/DC boost converter topologies for fuel cell hybrid electric vehicle applications." Power Electronics and Applications (EPE 2011), Proceedings of the 2011-14th European Conference on. IEEE, 2011.
[5] El-Hamamsy, Sayed-Amr, Mustansir H.
Kheraluwala, and David J. Kachmarik. "Multi- resonant boost high power factor circuit." U.S.
Patent No. 5,488,269. 30 Jan. 1996.
[6] Kim, Dae-Kyong, Kwang-Woon Lee, and Byung-Il Kwon. "Commutation torque ripple reduction in a position sensorless brushless DC motor drive." Power Electronics, IEEE Transactions on 21.6 (2006): 1762-1768.
[7] Sathyan, Anand, et al. "An FPGA-based novel digital PWM control scheme for BLDC motor drives." Industrial Electronics, IEEE Transactions on 56.8 (2009): 3040-3049.
[8] Iepure, Liviu Ioan, Ion Boldea, and Frede Blaabjerg. "Hybrid If starting and observer-based sensorless control of single-phase BLDC-PM motor drives." Industrial Electronics, IEEE Transactions on 59.9 (2012): 3436-3444.
[9] Kenjo, T., Nagamori, S., “Permanent magnet and brushless dc motors”, (Oxford University Press, 1985, 1st edn.).
[10] Liao, Yuefeng, Feng Liang, and Thomas A. Lipo.
"A novel permanent magnet motor with doubly
salient structure." Industry Applications, IEEE Transactions on 31.5 (1995): 1069-1078.
[11] Krishnan, Ramu. Permanent magnet synchronous and brushless DC motor drives. CRC press, 2009.
[12] Duan, R-Y., and Jeng-Dao Lee. "High-efficiency bidirectional DC-DC converter with coupled inductor." Power Electronics, IET 5.1 (2012):
115-123.
[13] Wai, Rong-Jong, R-Y. Duan, and K-H. Jheng.
"High-efficiency bidirectional dc-dc converter with high-voltage gain." Power Electronics, IET 5.2 (2012): 173-184.
[14] Pillay, Pragasen, and Ramu Krishnan.
"Modeling, simulation, and analysis of permanent-magnet motor drives. I. The permanent-magnet synchronous motor drive."
Industry Applications, IEEE Transactions on 25.2(1989) : 265-273.
