Parasitics Assisted Soft-switching and Naturally Commutated Current-fed Bidirectional Push-pull Voltage Doubler

ABSTRACT:

A snubberless current-fed push-pull dc/dc voltage doubler is proposed with zero voltage switching (ZVS) turn-on of low voltage current-fed devices by using the parasitic resonance between the drain-source capacitance of MOSFETs and the leakage inductance of the high frequency transformer. \Secondary modulation helps reduce switching losses further by obtaining zero current switching (ZCS) turn-off of primary devices and ZVS turn-on of secondary devices. Realizing ZCS of current-fed devices introduces natural zero current commutation and eliminates the traditional requirement of active-clamp or passive snubbers in current-fed topologies. Push-pull topology has low device and driver requirement. Voltage doubler offers 2x voltage gain reducing the device count by half on secondary that simplifies the transformer and control design and efficiently reduce the low frequency dc current harmonics. The proposed topology with novel modulation is suitable for interfacing energy storage and/or fuel cell stack with dc bus in FCVs or as frontend dc/dc converter in fuel cell inverters or connecting fuel cells to dc grid. Steady-state operation and analysis of proposed topology with proposed modulation has been studied. Design of a 1kW prototype is explained. Simulation results using PSIM 9.3 and experimental results of a 1 kW prototype have been demonstrated to verify the operation, proposed mathematical analysis, design, and the proposed claims.

 KEYWORDS:

1.      Current-fed converter

2.      Push-pull

3.      Natural commutation

4.      Soft-switching

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig.1. Architecture of a dc microgrid

Fig. 2. Architecture of a fuel cell car.

EXPECTED SIMULATION RESULTS:

Fig.2. Simulation results: (a) Gating signal of switch S₁, current through switch S₁, voltage across switch S₁,(b) Gating signal of switch S₂, current through switch S₂, voltage across switch S₂, (c) Current through boost inductor L, Current through series leakage inductance, L_lk1, Current through series leakage inductance, L_lk2, (d) Current through secondary devices S₃ and S₄, (e) Voltage V_ab, output voltage V_o,Voltage across L_lk1

Fig. 3. Experimental results: (a) Gating signal of switch S₁, V_gs1, current through switch S₁, I_s1, drain-source voltage across switch S₁, V_ds1, (b) Current through boost inductor L, current through series leakage inductance, L_lk1, (c) Current through secondary device S₃, I_s3, Gating pulse of S₃, V_gs3, drain source voltage across switch S₃, V_ds3, (d) Voltage across leakage inductor V_lk1, voltage across transformer primary, V_ab,

  CONCLUSION:

A truly snubberless current-fed push-pull dc/dc converter is proposed with zero current commutation and natural device voltage clamping. Push-pull configuration and voltage doubler circuit reduces the active device and driver count. It leads to a simple control design and implementation. Voltage doubler improves the gain by 2x and reduce transformer size. Traditionally, current-fed converters are hard-switching with device voltage spike at turn-off and require snubber circuits. In this paper, an innovative modulation is proposed to utilize circuit parasitics and introduce soft-switching of all devices. Zero current commutation and device voltage clamping are obtained without additional snubber making it a truly snubberless topology. The proposed modulation solves the classical problem in current-fed converters and makes a novel contribution. Furthermore, the proposed converter topology can efficiently eliminate the low frequency current ripples on the source (fuel cell stack) side. Low frequency dc current harmonics coming from power electronics have a negative impact on the lifetime and the performance of fuel cell power generation systems. The elimination of such low frequency current ripples may also simplify the control of fuel cell system ancillaries, such as air compressor. Thus, it is suitable for low voltage high current applications requiring high voltage gain, low ripple dc current, and precise operating point control. Major applications include interfacing energy storage with dc link in FCVs due to bidirectional nature and also as a front end dc-dc converter in case of fuel cell inverters. Switching losses are reduced significantly owing to soft-switching of all the devices. Synchronous rectification may be employed to obtain high efficiency. Steady state operation, analysis and circuit design have been explained in detail. Simulation results are presented to verify the concept and experimental results are demonstrated to show the performance and the claims.

REFERENCES:

[1] F. A. Farret, M. G. Simoes, “Integration of Alternative Sources of Energy,” 1st ed. New Jersey: Wiley, 2006.

[2] A. Khaligh and Z. Li, “Battery, ultracapacitor, fuel cell, and hybrid energy storage systems for electric, hybrid electric, fuel cell, and plugin hybrid electric vehicles: State of the art,” IEEE Trans. Veh. Technol., vol. 59, no. 6, pp. 2806–2814, Oct. 2009.

[3] A. Emadi and S. S. Williamson, “Fuel cell vehicles: Opportunities and challenges,” in Proc. IEEE Power Eng. Soc., 2004, pp. 1640–1645.

[4] K. Rajashekhara, “Power conversion and control strategies for fuel cell vehicles,” in Proc. IEEE Annu. Conf. Ind. Electron. Soc., 2003, pp. 2865– 2870.

[5] A. Emadi, S. S. Williamson, and A. Khaligh, “Power electronics intensive solutions for advanced electric, hybrid electric, and fuel cell vehicular power systems,” IEEE Trans. Power Electron., vol. 21, no. 3, pp. 567– 577, May 2006.

The State of Charge Estimation of Lithium-Ion Batteries Based on a Proportional-Integral Observer

ABSTRACT:

With the development of electric drive vehicles (EDVs), the state-of-charge (SOC) estimation for lithium-ion (Li-ion) batteries has become increasingly more important. Based on the analysis of some of the most popular model-based SOC estimation methods, the proportional-integral (PI) observer is proposed to estimate the SOC of lithium-ion batteries in EDVs. The structure of the proposed PI observer is analyzed, and the convergence of the estimation method with model errors is verified. To demonstrate the superiority and compensation properties of the proposed PI observer, the simple-structure RC battery model is utilized to model the Li-ion battery. To validate the results of the proposed PI-based SOC estimation method, the experimental battery test bench is established. In the validation, the urban dynamometer driving schedule (UDDS) drive cycle is utilized, and the PI-based SOC estimation results are found to agree with the reference SOC, generally within the 2% error band for both the known and unknown initial SOC cases.

KEYWORDS:

1.      Battery

2.      Electric vehicle

3.      Lithium-ion (Li-ion) battery

4.      Proportional-integral (PI) observer

5.      Sliding-mode observer

6.      State of charge (SOC)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of different observer-based SOC estimation methods for Li-ion batteries. (a) Block diagram of the common structure. (b) Block diagram of a PI observer.

EXPECTED SIMULATION RESULTS:

Fig. 2. Identification results.

Fig. 3. UDDS current profile.

Fig. 4. SOC estimation results when the initial SOC is given.

Fig. 5. SOC estimation results when the initial SOC is unknown.

CONCLUSION:

A battery SOC estimation algorithm based on a PI observer has been proposed for Li-ion batteries. Acceptable accuracy has been verified by experiments on battery bench testing for both known and unknown initial SOC. The PI-based SOC estimation has a simple structure and is easy to implement. The compensation properties of the PI observer demonstrate that a simple RC model can be utilized to model the Li-ion battery. The estimated SOC with the PI observer converges to the reference SOC quickly, and the SOC estimation errors are maintained in a small band. Most of the errors of the PI-based SOC estimation method are confined to 2% when compared with the reference SOC that is based on Coulomb counting with known initial SOC.

REFERENCES:

[1] B. Pattipati, C. Sankavaram, and K. Pattipati, “System identification and estimation framework for pivotal automotive battery management system characteristics,” IEEE Trans. Syst., Man, Cybern. C, Appl. Rev., vol. 41, no. 6, pp. 869–884, Nov. 2011.

[2] K. Kutluay, Y. Cadirci, Y. S. Ozkazanc, and I. Cadirci, “A new online state-of-charge estimation and monitoring system for sealed lead-acid batteries in Telecommunication power supplies,” IEEE Trans. Ind. Electron., vol. 52, no. 5, pp. 1315–1327, Oct. 2005.

[3] M. Charkhgard and M. Farrokhi, “State-of-charge estimation for Lithiumion batteries using neural networks and EKF,” IEEE Trans. Ind. Electron., vol. 57, no. 12, pp. 4178–4187, Dec. 2010.

[4] L. Xu, J.Wang, and Q. Chen, “Kalman filtering state of charge estimation for battery management system based on a stochastic fuzzy neural network battery model,” Energy Convers. Manag., vol. 53, no. 1, pp. 33–39, Jan. 2012.

[5] X. Hu, F. Sun, and Y. Zou, “Estimation of state of charge of a Lithium-ion battery pack for electric vehicles using an adaptive Luenberger observer,” Energies, vol. 3, no. 9, pp. 1586–1603, 2010.

Direct Torque Control of Permanent-Magnet Synchronous Machine Drives With a Simple Duty Ratio Regulator

ABSTRACT:

The conventional switching-table-based direct torque- controlled (DTC) ac machine drive is usually afflicted by large torque ripple, as well as steady-state error of torque. The existing methods, which optimize the duty ratio of the active vector, are usually complicated and parameter dependent. Based on the analysis of instantaneous variation rates of stator flux and torque of each converter output voltage vector, a simple and effective method considering the effect of machine angular velocity is proposed to obtain the duty ratio. The experimental results carried on a dSPACE platform with a laboratory prototype of the permanent-magnet machine verify that the proposed duty-based DTC method can achieve excellent transient response, less torque ripple, and less steady-state error, without resorting to the complicated control method over a wide range of operating regions.

KEYWORDS:

1.      Direct torque control (DTC)

2.       Duty ratio

3.      Permanent-magnet synchronous machines (PMSMs)

4.       Steady-state error

5.       Torque ripple

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Control diagram of DTC of PMSM.

EXPECTED SIMULATION RESULTS:

Fig. 2. Comparison of steady-state performance of various DTC methods (rated condition: 400 r/min, 5 N · m). (a) Conventional DTC method. (b) M1. (c) M2. (d) Proposed DTC method.

Fig. 3. Dynamic performances of torque response with inner torque loop control only and without outer speed loop. Reference torque from 2 to −2 N · m. (a) Conventional DTC method. (b) M1. (c) M2. (d) Proposed DTC method.

.

Fig. 4. Dynamic and steady-state performances when reference speed changes from 200 to −200 r/min. (a) Conventional DTC. (b) Proposed DTC.

Fig. 5. Steady-state performance of the proposed DTC method with different control parameters: Ka = 0.7, Kb = 0.0005 (rated condition: 400 r/min,5 N · m).

CONCLUSION:

This paper has proposed, analyzed, and experimentally verified a simple and effective method for determining the appropriate duty ratio in DTC three-phase PMSM drives to reduce the torque ripple and the steady-state error of torque, accounting for the influence of machine angular velocity. A simple estimated method is proposed to obtain the range of the key control parameters. Compared to the existing duty-based DTC methods, the proposed method can achieve the decent performance of torque and flux at the lower price of increased average communication frequency.

The proposed duty ratio determination has the following features.

1) Simple structure: Compared to conventional DTC, just a very simple duty ratio regulator is added.

2) Parameter independent: Unlike the previous duty-based methods, where many parameters such as stator inductance and PM flux are required, in the proposed DTC method, only the torque error and speed are needed to compute the duty ratio, which makes it robust to parameter variation.

3) Outstanding steady-state performance over a wide range of operating regions, even when speed is reversed.

4) Similar excellent transient response to the conventional DTC.

Although the analysis and experiments in this paper are based on the DTC of three-phase PMSM drives, the proposed duty ratio determination can be also extended for general use and applied to the other machines of switching-table-based direct torque and power control methods, which may exhibit the same problem of ripple and/or steady-state error.

REFERENCES:

[1] I. Takahashi and T. Noguchi, “A new quick-response and high-efficiency control method of an induction-motor,” IEEE Trans. Ind. Appl., vol. IA-22, no. 5, pp. 820–827, Sep. 1986.

[2] M. Depenbrock, “Direct self-control (DSC) of inverter-fed induction machine,” IEEE Trans. Power Electron., vol. 3, no. 4, pp. 420–429, Oct. 1988.

[3] G.W. Chang, G. Espinosa-Perez, E. Mendes, and R. Ortega, “Tuning rules for the PI gains of field-oriented controllers of induction motors,” IEEE Trans. Ind. Electron., vol. 47, no. 3, pp. 592–602, Jun. 2000.

[4] A. K. Jain and V. T. Ranganathan, “Modeling and field oriented control of salient pole wound field synchronous machine in stator flux coordinates,” IEEE Trans. Ind. Electron., vol. 58, no. 3, pp. 960–970, Mar. 2011.

[5] S. Mathapati and J. Boecker, “Analytical and offline approach to select optimal hysteresis bands of DTC for PMSM,” IEEE Trans. Ind. Electron., vol. 60, no. 3, pp. 885–895, Mar. 2013.

Direct Torque Control of Permanent Magnet Synchronous Motor Based on Space Vector Modulation Control

ABSTRACT:

How to calculate the reference voltage vector is an important issue in space vector modulation direct torque control (SVM-DTC) of permanent magnet synchronous motor (PMSM). The effect of zero vector on electromagnetic torque during all speed range is analyzed on the basis of the relation between voltage vector and torque current component. And the analysis shows that in conventional DTC system of PMSM available voltage vector is only six which is the mainly cause of high ripple of torque. A robust SVM- DTC method of PMSM is designed in which the reference voltage vector is calculated with the flux position, error of torque and flux. The method is simple to implement and insensitive to motor parameters error. First order filter cascaded with high pass filter (HPF) is adopted to estimate stator flux accurately. The experimental results are carried out and show that the improved SVM-DTC has the advantage of simplicity, robustness and improved performance.

KEYWORDS:

1.      PMSM

2.      Direct torque control

3.      Space vector modulation

4.       Torque ripple

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 Block diagram of improved SVM-DTC system

EXPECTED SIMULATION RESULTS:

a)       Experimental waveforms of conventional DTC

b)       Experimental waveforms of proposed SVM-DTC

CONCLUSION:

Available voltage vector has only six which mainly causes high ripple of torque in conventional DTC. To maintain robustness and simplicity of conventional DTC system, a simple method of calculating amplitude and angle of the voltage vector is adopted in SVM-DTC. It requires only the torque and flux errors. The simulation and experimental results show that the proposed SVM-DTC scheme has excellent steady-state performance while retaining the merits of the quick dynamic responses, simplicity and robustness as in conventional DTC.

REFERENCES:

[1] Bin Wang, Yue Wang, Zhaoan Wang. Direct torque control of permanent magnet synchronous motor drives using space vector modulation [J]. Electric machines and control, 2010, 14(6):45-50.

[2] Yong-chang Zhang, Jian-guo Zhu, Wei Xu , You-guang Guo. A Simple Method to Reduce Torque Ripple in Direct Torque-Controlled Permanent-Magnet Synchronous Motor by Using Vectors With Variable Amplitude and Angle[J]. IEEE Transactions on Industrial Electronics, 2011, 58(7): 2848-2859.

[3] Gilbert Foo, M. F. Rahman. A novel speed sensorless direct torque and flux controlled interior permanent magnet synchronous motor drive [C]. Power Electronics Specialists Conference, Rhodes, Greece, 2008: 50- 56.

[4] Huaqiang Zhang, Xinsheng Wang, Pengfei Wei, etal. Study on direct torque control algorithm based on space vector modulation [J]. Electric Machines and control, 2012, 16(6):13-17.

[5] Jing Yuan; Xigeng Ma; Jiannan Liu. Simulation research of induction motor based on SVM-DTC with three-level inverter [J]. Electronics Information and Emergency Communication, China, 5th.2015, 410- 413.

Direct Torque Control of Permanent Magnet Synchronous Motor (PMSM) – an approach by using Space Vector Modulation (SVM)

ABSTRACT:

This paper proposes a method of applying the Space Vector Modulation technique for Direct Torque Control (DTC) of a permanent magnet synchronous motor (PMSM) drive. By this method it is preserved the principle of the conventional DTC regarding the decoupled torque and flux control, while providing more flexibility for the inverter voltage utilization, in order to compensate the torque and flux errors in a smoother way than conventional DTC. For this purpose, a reference voltage space vector is calculated every sample time, using a simple algorithm, based on the torque error and the stator flux angle. Numerical simulations have been made to test the proposed method and results are presented.

KEYWORDS:

1.      Direct Torque Control

2.       permanent magnet synchronous motor

3.       Space Vector Modulation

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Block diagram of the conventional DTC

EXPECTED SIMULATION RESULTS:

Fig. 2 Classic DTC, at 100 rpm

Fig. 3 Classic DTC, at 1000 rpm

Fig. 4 DTC with voltage control using the proposed method, at 100 rpm

Fig. 5 DTC with voltage control using the proposed method, at 1000 rpm

CONCLUSION:

In this paper it was presented a method of utilisation of Space Vector Modulation for the Direct Torque Control of a PMSM. For this purpose, at every control sample time a reference voltage vector is calculated and applied to the inverter using SVM. To determine the reference voltage, a simple algorithm was proposed, based on the torque error and the flux phase angle.

The results show that a smooth steady state operation was obtained when using the proposed method. Moreover, a constant inverter switching frequency is ensured by using SVM.

REFERENCES:

[1] Takahashi I., Noguchi T., A New Quick-response and High Efficiency Control Strategy of an InductionMotor, IEEE Trans. Ind. Applicat., IA, 22, 1986, pp. 820–827.

[2] Tiitinen P., Surandra M., The next generation motor control method, DTC direct torque control, Proc. Int. Conf. on Power Electron., Drives and Energy System for Ind. Growth, N. Delhi, 1996, pp. 37–43.

[3] Lascu C., Boldea I., and Blaabjerg F., Variable-Structure Direct Torque Control—A Class of Fast and Robust Controllers for Induction Machine Drives IEEE Trans. On Ind. Electronics, 51, 4, 2004.

[4] Habetler T. G., Profumo F., Pastorelli M., and Tolbert L. M., Direct Torque Control of Induction Machines Using Space Vector Modulation, IEEE Trans. Ind. Applicat., 28, 1992, pp. 1045–1053.

[5] Vas P., Sensorless Vector and Direct Torque Control. New York: Oxford University Press, 1998, pp. 223–237.