Cascade Dual Buck Inverter With Phase-Shift Control

 Cascade Dual Buck Inverter With Phase-Shift Control

ABSTRACT:

                                 

This paper presents a new type of cascade inverter based on dual buck topology and phase-shift control scheme. The proposed cascade dual buck inverter with phase-shift control inherits all the merits of dual buck type inverters and overcomes some of their drawbacks. Compared to traditional cascade inverters, it has much enhanced system reliability thanks to no shoot-through problems and lower switching loss with the help of using power MOSFETs. With phase-shift control, it theoretically eliminates the inherent current zero-crossing distortion of the single-unit dual buck type inverter. In addition, phase-shift control and cascade topology can greatly reduce the ripple current or cut down the size of passive components by increasing the equivalent switching frequency. A cascade dual buck inverter has been designed and tested to demonstrate the feasibility and advantages of the system by comparing single-unit dual buck inverter, 2-unit and 3-unit cascade dual buck inverters at the same 1 kW, 120 V ac output conditions.

KEYWORDS:

1. Cascade inverter

2. Dual buck inverter

3. Phase-shift control.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Topology of cascade dual buck half-bridge inverter.

Fig. 2. Single-unit dual buck full-bridge inverter serving as one cell for cascade dual buck full-bridge inverter. (a)Single-unit dual buck full-bridge inverter. (b) Cascade dual buck full-bridge inverter.

EXPECTED SIMULATION RESULTS:

Fig. 3. Output current i_o , ac and dc voltage waveforms for single-unit, 2-unit cascade, and 3-unit cascade inverter system at 1 kW. (a) Single-unit inverter. (b) 2-unit cascade inverter. (c) 3-unit cascade inverter.

Fig. 4. Output current i_o , ac and dc voltage waveforms for single-unit, 2-unit cascade inverter system at 300 W. (a) Single-unit inverter. (b) 2-unit cascade inverter.

Fig. 5. Output positive half-cycle current i_P , ac and dc voltage waveforms for single-unit, 2-unit cascade, and 3-unit cascade inverter system at 1 kW. (a) Single-unit inverter. (b) 2-unit cascade inverter. (c) 3-unit cascade inverter.

Fig.6. Load step-up and step-down tests for single-unit inverter and 3-unit cascade inverter system. (a) Load step up test for single-unit inverter. (b) Load step-down test for single-unit inverter. (c) Load step-up test for 3-unit cascade inverter. (d) Load step-down test for 3-unit cascade inverter.

CONCLUSION:

A new series of cascade dual buck inverters has been proposed based on single-unit dual buck inverters. The cascade dual buck inverter has all the merits of traditional cascade inverters, and improves on its reliability by eliminating shoot-through worries and dead-time concerns. With the adoption of phase-shift control, the cascade dual buck inverter solves the inherent current zero-crossing distortion problem of single-unit dual buck inverter. To prove the effectiveness of the proposed topology and control scheme, a cascade dual buck half-bridge inverter system operating at standalone mode with 1 kW, 120 V ac output capability has been designed and tested. By comparison of experimental results of single-unit dual buck inverter with 2-unit and 3-unit cascade dual buck inverters, the viability and advantages of the cascade dual buck inverter are validated

REFERENCES:

[1] J. S. Lai and F. Peng, “Multilevel converters—A new breed of power converter,” IEEE Trans. Ind. Electron., vol. 32, no. 3, pp. 509–517, May/Jun. 1996.

[2] J. Rodriguez, J. S. Lai, and F. Peng, “Multilevel inverters: A survey of topologies, controls, and applications,” IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724–738, Aug. 2002.

[3] M.Malinowski, K. Gopakumar, J. Rodriguez, andM. A. P´erez, “A survey on cascaded multilevel inverters,” IEEE Trans. Ind. Electron., vol. 57, no. 7, pp. 2196–2206, Jul. 2010.

[4] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilevel converters arrives,” IEEE Ind. Electron. Mag., vol. 2, no. 2, pp. 28–39, Jun. 2008.

[5] F. Z. Peng and J. S. Lai, “A multilevel voltage-source inverter with separate dc sources for staticVAR generation,” in Proc. Conf. Rec. IEEE-IAS Annu. Meeting, Lake Buena Vista, FL, Oct. 8–12, 1995, pp. 2541–2548.

Mitigation of Harmonics by Hysteresis Control Technique of VSI Based Statcom

Mitigation of Harmonics by Hysteresis Control

Technique of VSI Based Statcom

ABSTRACT:

Modern industrial equipments are more sensitive to these power quality problems than before and need higher quality of electrical power. Power electronic based power processing offers higher efficiency, compact size and better controllability. But on the flip side, due to switching actions, these systems behave as non-linear loads. This creates power quality problems such as voltages Sag/Swell, flickers; harmonics, asymmetric of voltage have become increasingly serious. At the same time, modern industrial equipments are more sensitive to these power quality problems than before and need higher quality of electrical power. This paper mainly deals with shunt active power filter which has been widely used for harmonic elimination. Active power filter which has been used here monitors the load current constantly and continuously adapt to the changes in load harmonics. The performance of three phase shunt active power filter using three phase two phase transformation with PI and Hysteresis current controller is explained in this paper.

KEYWORDS:

1.  Power filters (APF)

2. Composite load

3. Harmonic compensation

4. Linear and non linear load

5. Reactive power

6. Power Quality

7. Harmonics

8. Voltage Source Inverter.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:      

Figure 1. Principle of operation of an APF compensating a diode rectifier

Figure 2. Basic Compensation Technique

EXPECTED SIMULATION RESULTS:

             

                                                                                                                                                        Time(secs)

Figure 3.1. Supply voltage waveform

                                                                                                                                                       Time(secs) 

Figure 3.2.a  Load Voltage

                                                                                                                                                               Time (secs)

Figure 3.2.b   Load Current

                                                                                                                                                                                  Time (secs)

                                                      Figure 3.3. source current before and after control for each phase

                                                                                                                   Time (secs)

                           Figure 3.4 source current before and after control for all the three phases.                                                           

                                   Figure 3.5 Injected current before and after control for each phase.                        Time (secs)

      

                                                                                                                                                                   Time (secs)

                                          Figure 3.6 Injected current before and after control for all the three phases.

CONCLUSION:

An extensive review of AF’s has been presented to provide a clear perspective on various aspects of the AF to the researchers and engineers working in this field. The substantial increase in the use of solid-state power control results in harmonic pollution above the tolerable limits. The utilities in the long run will induce the consumers with nonlinear loads to use the AF’s for maintaining the power quality at acceptable levels. A large number of AF configurations are available to compensate harmonic current, reactive power, neutral current, unbalance current, and harmonics. The consumer can select the AF with the required features. Static compensation (STATCOM) gets more popular as the flexible AC transmission (FACTS) devices increase. The transformer-less STATCOM has low cost and concentrates the research interests; however, the capacitors voltage unbalance problem will deteriorate its performance with more harmonics and over current/voltage faults. A very simple hysteresis current controller based control technique with help of instantaneous power theory is proposed for STATCOM. A MATLAB/Simulink based model has been simulated. Simulation result shows the input current harmonics produce by nonlinear load is reduced after using the control strategy. FFT analysis shows the reduction in THD is remarkable.

REFERENCES:       

[1] Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems. Narain G. Hingorani, Laszlo Gyugyi. Wiley IEEE press.

[2] “A Few Aspects of Power Quality Improvement Using Shunt Active Power Filter” -C.Nalini Kiran, Subhransu Sekhar Dash, S.Prema Latha. International Journal of Scientific & Engineering Research Volume 2, Issue 5, May-2011, ISSN 2229-5518

Grid Interconnection of Renewable Energy Sources at the Distribution Level With Power-Quality Improvement Features

Grid Interconnection of Renewable Energy Sources at the Distribution Level With Power-Quality Improvement Features

ABSTRACT:

Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and validated through digital signal processor-based laboratory experimental results.

KEYWORDS:

1.      Active power filter (APF)

2.      Distributed generation (DG)

3.       Distribution system

4.       Grid interconnection

5.       Power quality (PQ)

6.       Renewable energy.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Schematic of proposed renewable based distributed generation system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results: (a) Grid voltages, (b) Grid Currents (c) Unbalancedload currents, (d) Inverter Currents.

Fig. 3. Simulation results: (a) PQ-Grid, (b) PQ-Load, (c) PQ-Inverter, (d) dc-link voltage.

CONCLUSION:

This paper has presented a novel control of an existing grid interfacing inverter to improve the quality of power at PCC for a 3-phase 4-wireDGsystem. It has been shown that the grid interfacing inverter can be effectively utilized for power conditioning without affecting its normal operation of real power transfer. The grid-interfacing inverter with the proposed approach can be utilized to:

i) Inject real power generated from RES to the grid, and/or,

ii) Operate as a shunt Active Power Filter (APF).

This approach thus eliminates the need for additional power conditioning equipment to improve the quality of power at PCC. Extensive MATLAB/Simulink simulation as well as the DSP based experimental results have validated the proposed approach and have shown that the grid-interfacing inverter can be utilized as a multi-function device. It is further demonstrated that the PQ enhancement can be achieved under three different scenarios: 1) P_RES = 0 , 2)P_RES < P_LOAD , and  3)P_RES > P_LOAD . The current unbalance, current harmonics and load reactive power, due to unbalanced and non-linear load connected to the PCC, are compensated effectively such that the grid side currents are always maintained as balanced and sinusoidal at unity power factor. Moreover, the load neutral current is prevented from flowing into the grid side by compensating it locally from the fourth leg of inverter. When the power generated from RES is more than the total load power demand, the grid-interfacing inverter with the proposed control approach not only fulfills the total load active and reactive power demand (with harmonic compensation) but also delivers the excess generated sinusoidal active power to the grid at unity power factor.

REFERENCES:

[1] J. M. Guerrero, L. G. de Vicuna, J. Matas, M. Castilla, and J. Miret, “A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1205–1213, Sep. 2004.

[2] J. H. R. Enslin and P. J. M. Heskes, “Harmonic interaction between a large number of distributed power inverters and the distribution network,” IEEE Trans. Power Electron., vol. 19, no. 6, pp. 1586–1593, Nov. 2004.

[3] U. Borup, F. Blaabjerg, and P. N. Enjeti, “Sharing of nonlinear load in parallel-connected three-phase converters,” IEEE Trans. Ind. Appl., vol. 37, no. 6, pp. 1817–1823, Nov./Dec. 2001.

[4] P. Jintakosonwit, H. Fujita, H. Akagi, and S. Ogasawara, “Implementation and performance of cooperative control of shunt active filters for harmonic damping throughout a power distribution system,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 556–564, Mar./Apr. 2003.

[5] J. P. Pinto, R. Pregitzer, L. F. C. Monteiro, and J. L. Afonso, “3-phase 4-wire shunt active power filter with renewable energy interface,” presented at the Conf. IEEE Renewable Energy & Power Quality, Seville, Spain, 2007.

Single-Stage DC-AC Converter for Photovoltaic System

Single-Stage DC-AC Converter for Photovoltaic Systems

ABSTRACT:

This paper presents a DC-AC converter that merges a DC-DC converter and an inverter in a single-stage topology to be used as an interface converter between photovoltaic systems and the electrical AC grid. This topology is based on a full bridge converter with three levels output voltage, where two diodes and one inductor have been added in order to create a Boost converter. The control system of the proposed converter is based on two hysteretic controllers: one for the grid injected current and the other for controlling the panel current. A prototype of the proposed converter including power and control circuits was developed. The MPPT algorithm is not yet implemented and, therefore, to obtain experimental results an additional power supply is used to emulate the PV panel. Theoretical analysis and design criteria are presented together with simulated results to validate the proposed concepts. Experimental results are obtained in a lab prototype to evidence the feasibility and performance of the converter.

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig.1. Power Grid connection of a PV array by means of a two stages converter.

Fig.2. Proposed converter: single-stage DC-AC converter for PV systems.

EXPECTED SIMULATION RESULTS:

 Fig.3. Experimental results: a) iLR (blue trace) with a gain of 1A/div, iLP (green trace) with a gain of 1A/div; b) grid voltage (magenta trace) with a gain of 50 V/div; c) vCF voltage (red trace) with a gain of 100V/div and iLR (blue trace) with a gain of 1A/div.

      

                                     

      

 Fig.4. Simulation results: a) iLR (blue trace) with a gain of 1A/div, iLP (green trace) with a gain of 1A/div; b) Obsetvation of iLP perturbations; c) verification of the maximum iLR switching frequency value, fSRmax.

CONCLUSION:

The new contribution of this paper consisted in the proposal of a new DC-AC converter for PV systems that includes two Boost converters and a full-bridge inverter in a single-stage topology. The unique restriction imposed by the converter is the minimum VCF voltage which must be greater than the sum of the maximum values of the panel and the grid voltage. Due to the high voltage gain given by the two input boosts, the topology is suitable to operate with low panel voltages. The theoretical concepts introduced in the paper were proved by the preliminary results obtained in the experimental tests of the converter prototype that is still in development. A converter efficiency of 90.5% was achieved. The prototype used to obtain the preliminary experimental results presented in the paper is not yet optimized in terms of layout and power density. It is expected that, in what concerns circuit layout, the reduction of the leakage inductances will result in a significant reduction of the dissipated power which will end up in efficiency increase.

REFERENCES:

[1] Johan H. R. Enslin, Mario S. Wolf, Daniel B. Snyman, and Wernher Swiegers, “Integrated Photovoltaic Maximum Power Point Tracking Converter”, in IEEE Transactions on Industrial Electronics, Vol. 44, no. 6, December 1997.

[2] Soeren B. Kjaer, John K. Pedersen and Frede Blaabjerg, ‘‘A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules’’, in IEEE Transactions on Industry Applications, Vol. 41, No. 5, 2005.

[3] Fritz Schimpf and Lars E. Norum, “Grid connected Converters for Photovoltaic, State of the Art, Ideas for Improvement of Transformerless Inverters”, Nordic Workshop on Power and Industrial Electronics, 2008.

[4] Mario Fortunato, Alessandro Giustiniani, Giovanni Petrone, Giovanni Spagnuolo, and Massimo Vitelli, “Maximum Power Point Tracking in a One-Cycle-Controlled Single-Stage Photovoltaic Inverter”, in IEEE Transactions on Industrial Electronics, vol. 55, no. 7, pp. 2684-2693, July 2008.

[5] Yeong-Chau Kuo, Tsorng-Juu Liang, and Jiann-Fuh Chen, “Novel Maximum-Power-Point-Tracking Controller for Photovoltaic Energy Conversion System”, in IEEE Transactions on Power Electronics, vol. 48, no. 3, pp. 594-601, June 2001

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Study of Induction Motor Drive with Direct Torque Control Scheme and Indirect Field Oriented Control Scheme Using Space Vector Modulation

Study of Induction Motor Drive with Direct Torque Control Scheme and Indirect Field Oriented Control Scheme Using Space Vector Modulation

ABSTRACT:

Induction motors are the starting point to design an electrical drive system which is widely used in many industrial applications. In modern control theory, different mathematical models describe induction motor according to the employed control methods. Vector control strategy can be applied to this electrical motor type in symmetrical three phase version or in unsymmetrical two phase version. The operation of the induction motor can be analyzed similar to a DC motor through this control method. With the Joint progress of the power electronics and numerical electronics it is possible today to deal with the axis control with variable speed in low power applications. With these technological projections, various command approaches have been developed by the scientific community to master in real time, the flux and the torque of the electrical machines, the direct torque control (DTC) scheme being one of the most recent steps in this direction. This scheme provides excellent properties of regulation without rotational speed feedback. In this control scheme the electromagnetic torque and stator flux magnitude are estimated with only stator voltages and currents and this estimation does not depend on motor parameters except for the stator resistance. In this dissertation report conventional DTC scheme has been described. Induction motor has been simulated in stationary d-q reference frame and its free acceleration characteristics are drawn. Conventional DTC scheme has been simulated with a 50 HP, 460V, 60 Hz induction motor. Literature review has been done to study the recent improvements in DTC scheme which somehow is able to overcome the drawbacks of conventional one. The space vector modulation technique (SVPWM) is applied to 2 level inverter control in the vector control based induction motor drive system, thereby dramatically reducing the torque ripple. Later in this project space vector PWM technique will be applied to DTC drive system to reduce the torque ripple.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 Block diagram of conventional DTC scheme for IM drives

EXPECTED SIMULATION RESULTS:

Fig.2  Electromagnetic torque

Fig.3 Rotor speed

Fig.4 Stator current

Fig.5 d-axis stator flux

Fig.6 q-axis stator flux

For TL = 2 Nm

Fig.7 Electromagnetic torque

Fig.8 Rotor speed

Fig.9 Trajectory of d axis and q axis stator flux in stationary reference frame

Fig.10 Electromagnetic torque

Fig.11 Rotor speed

Fig.12 d-axis stator flux

Fig.13 q-axis stator flux

Fig.14 d-axis stator current

Fig.15 q-axis stator current

Fig.16 Mean value of Phase voltage of inverter

Fig.17 Line voltage output of inverter

Fig.18 Electromagnetic torque

Fig.19 Rotor speed

Fig.20 q-axis stator flux

Fig.21 d-axis stator flux

CONCLUSION:

For any IM drives, Direct torque control is one of the best controllers proposed so far. It allows decoupled control of motor stator flux and electromagnetic torque. From the analysis it is proved that, this strategy of IM control is simpler to implement than other vector control methods as it does not require pulse width modulator and co-ordinate transformations. But it introduces undesired torque and current ripple. DTC scheme uses stationary d-q reference frame with d-axis aligned with the stator axis. Stator voltage space vector defined in this reference frame control the torque and flux. The main inferences from this work are:

1. In transient state, by selecting the fastest accelerating voltage vector which produces maximum slip frequency, highest torque response can be obtained.

2. In steady state, the torque can be maintained constant with small switching frequency by the torque hysteresis comparator by selecting the accelerating vector and the zero voltage vector alternately.

3. In order to get the optimum efficiency in steady state and the highest torque response in transient state at the same time, the flux level can be automatically adjusted.

4. If the switching frequency is extremely low, the control circuit makes some drift which can be compensated easily to minimize the machine parameter variation.

The estimation accuracy of stator flux is very much essential which mostly depends on stator resistance because an error in stator flux estimation will affect the behavior of both torque and flux control loops. The torque and current ripple can be minimized by employing space vector modulation technique.

REFERENCES:

[1] B. K.Bose. 1997. Power Electronics and Variable Frequency Drives. IEEE Press, New York.

[2] Kazmierkowski, R.Krishnan, Blaabjerg, Control in Power Electronics, Selected Problems.

[3] Takahashi Isao, Noguc hi Tos hihiko, „‟A New Quick-Response and High-Efficiency Control Strategy of an Induction Motor‟‟, IEEE Transactions on Industry Applications, Vol. IA-22 No-5, Sept/Oct 1986.

[4] Thomas G.Habetler, Francesco Profumo, Michele Pastorelli and Leon M. Tolbert “Direct Torque Control of IM us ing Space Vector Modulation” IEEE Transactions on Industry Applications, Vol.28, No.5, Sept/Oct 1992.

[5] E.Bassi, P. Benzi, S. Buja, “A Field Orientation Scheme for Current-Fed Induction Motor Drives Based on the Torque Angle Closed-Loop Control” IEEE Transactions on Industry Applications, Vol. 28, No. 5, Sept./ Oct. 1992.