A High-Switching-Frequency Flyback Converter in Resonant Mode

ABSTRACT

The demand of miniaturization of power systems has accelerated the research on high-switching-frequency power converters. A flyback converter in resonant mode that features low switching losses, less transformer losses, and low switching noise at high switching frequency is investigated in this paper as alternative to a conventional quasi-resonant flyback topology to increase power density. In order to find a compromise between magnet size, electromagnetic interference (EMI), and efficiency, the concept utilizes the resonant behavior between transformer leakage inductance and snubber capacitor to achieve near-zero-voltage switching at both turn-on and turn-off of the primary switch, low core loss due to a continuous transformer magnetizing current, and reduced EMI due to low di/dt and dv/dt values. Meanwhile, the concept uses the regenerative snubber to recycle the transformer leakage energy with two snubber diodes and one snubber capacitor. The proposed concept has been validated on a 340kHz 65W prototype. Compared to the conventional quasi-resonant flyback converter operating at the same switching frequency, the proposed concept has 2% efficiency improvement and better EMI performance.

 KEYWORDS:

  1. Resonant power conversion
  2. High switching frequency
  3. Flyback
  4. Switching loss
  5. Regenerative snubber.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 Proposed flyback converter, (a) schematic of the proposed concept, (b) equivalent circuit of the proposed concept.

EXPECTED SIMULATION RESULTS:

 Fig. 2. Measured waveforms of resonant-mode operation, D = 0.6. (a) Switch Si voltage and current; (b) Current of each transformer winding (c) Snubber diode current, resonant capacitor voltage and current.

Fig.3. Measured waveforms of resonant flyback at high input voltage, Ui=360V, fs=250kHz, Po=38W.

CONCLUSION

In this paper, a flyback converter in resonant mode is proposed to enable soft switching, less transformer loss and reduced EMI at high switching frequency. Experimental results show that, compared to the conventional flyback converter operating in QR/DCM and while achieving the same specifications, both the fundamental quasi-peak and the high-frequency harmonics in the measured common-mode EMI are reduced due to the resonant behavior, and the switching loss on the primary switch is minimized due to the achieved soft switching in both turn-on and turn-off of the primary switch. Furthermore, the transformer core volume is reduced by one third compared to the low-frequency conventional flyback converter. In conclusion, the resonant-mode operation of the developed flyback converter enables higher power density, high efficiency and better EMI performance at high switching frequency. Therefore, the improved flyback topology is suitable for low-power isolated DC/DC converters with limited input voltage range.

REFERENCES

  • Watson; F.C. Lee; G.C. Hua, “Utilization of an active-clamp circuit to achieve soft switching in flyback converters,” IEEE Transactions on Power Electronics, pp. 162 – 169, Jan 1996.
  • Xi; P.K. Jain; G. Joos; Y. Liu, “An improved zero voltage switching flyback converter topology,” in 29th Annual IEEE Power Electronics Specialists Conference, Fukuoka, May 1998.
  • Ching-Lung Chu; Ming-Juh Jong, “A zero-voltage-switching PWM flyback converter with an auxiliary resonant circuit,” in International Conference on Power Electronics and Drive Systems, Taipei, Nov. 2009.
  • Wei, X. Huang, J. Zhang and Z. Qian, “A Novel soft switching flyback converter with synchronous rectification,” in IEEE 6th International Power Electronics and Motion Control Conference, Wuhan, May 2009.
  • “NCP4304: Secondary Side Controller,” ON Semiconductor, 2015. [Online]. Available: http://www.onsemi.com/.

 

 

A High Efficiency Asymmetrical Half-Bridge Converter with Integrated Boost Converter in Secondary Rectifier

ABSTRACT

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-to-medium power applications because of zero-voltage switching (ZVS) of all switches and small number of components. However, when the converter is designed taking a hold-up time into consideration, it has a large DC offset current in a transformer and a small transformer turns-ratio. To solve these problems, a new AHB converter with an integrated boost converter is proposed in this letter. Because the proposed converter compensates for the hold-up time using the integrated boost converter without additional loss in the nominal state, it can achieve the optimized efficiency regardless of the hold-up time. The effectiveness and feasibility are verified with a 250-400V input and 45V/3.3A output prototype.

KEYWORDS:

  1. Hold-up time
  2. DC/DC converter
  3. Asymmetrical half-bridge converter
  4. High efficiency

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. The conventional AHB converters. (a) DCS HB converter and (b) boost-cascaded AHB converter.

Fig. 2. The proposed converter.

EXPECTED EXPERIMENTAL RESULTS:

Fig.3. Waveforms of the prototype converters with 400v input,3.3A/45v output The conventional AHB converter and (b) the proposed converter

Fig.4.Transient operation during the hold-up time

Fig.5. Measured Efficiency

CONCLUSION

In this letter, a boost-integrated AHB converter is proposed. The proposed converter integrates a boost converter in the rectifier in a new manner. Because the proposed converter can obtain an additional voltage gain during a hold-up time, it can be designed optimally in the nominal state regardless of the hold-up time requirement. Furthermore, since the proposed converter does not cause an additional loss in the nominal state, it can achieve the optimized efficiency.

REFERENCES

  • .J. K. Han, J. W. Kim, Y. Jang, B. Kang, J. Choi, and G. W. Moon, “Efficiency Optimized Asymmetric Half-Bridge Converter with Hold-Up Time Compensation,” in Proc. IEEE Power Electron. Conf., pp.2254-2261, May, 2016.
  • Wu, T. Mu, X. Gao, and Y. Xing, “A Secondary-Side Phase-Shift-Controlled LLC Resonant Converter With Reduced Conduction Loss at Normal Operation for Hold-Up Time Compensation Application,” IEEE Trans. Power Electron., vol. 30, no. 10, pp. 5352-5357, Oct. 2015.
  • S. Lai, Z. J. Su, and W. S. Chen, “New Hybrid Control Technique to Improve Light Load Efficiency While Meeting the Hold-Up Time Requirement for Two-Stage Server Power,” IEEE Trans. Power Electron., vol. 29, no. 9, pp. 4763-4775, Sep. 2014.
  • K. Kim, S. Moon, C. O. Yeon, G. W. Moon, “High-Efficiency LLC Resonant Converter With High Voltage Gain Using an Auxiliary LC Resonant Circuit,” IEEE Trans. Power Electron., vol. 31, no. 10, pp. 6901-6909, Oct. 2016
  • B. Lee, J. K. Kim, J. H. Kim, J. I. Baek, and G. W. Moon, “A High-Efficiency PFM Half-Bridge Converter Utilizing a Half-Bridge LLC Converter Under Light Load Conditions,” IEEE Trans. Power Electron., vol. 30, no. 9, pp. 4931-4942, Sep. 2015

A Frequency Adaptive Phase Shift Modulation Control Based LLC Series Resonant Converter for Wide Input Voltage Applications

ABSTRACT

This paper presents an isolated LLC series resonant DC/DC converter with novel frequency adaptive phase shift modulation control, which suitable for wide input voltage (200-400V) applications. The proposed topology integrates two half-bridge in series on the primary side to reduce the switching stress to half of the input voltage. Unlike the conventional converter, this control strategy increases the voltage gain range with ZVS to all switches under all operating voltage and load variations. Adaptive frequency control is used to secure ZVS in the primary bridge with regards to load change. To do so, the voltage gain becomes independent of the loaded quality factor. In addition, the phase shift control is used to regulate the output voltage as constant under all possible inputs. The control of these two variables also significantly minimizes the circulating current, especially from the low voltage side, which increases the efficiency as compared to a conventional converter. Experimental results of a 1Kw prototype converter with 200-400V input and 48V output are presented to verify all theoretical analysis and characteristics.

KEYWORDS:

  1. LLC
  2. Resonant converter
  3. Frequency adaptive phase shift modulation control (FAPSM)
  4. Zero-Voltage-Switching (ZVS)
  5. Wide gain range.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed LLC resonant converter.

EXPECTED SIMULATION RESULTS:

Fig. 2(a). Simulation waveforms of proposed converter under 400V input, 48V output and full load condition.

Fig. 2(b). Simulation waveforms of proposed converter under 200V input, 48V output and full load condition.

Fig. 2(c). Simulation waveforms of proposed converter under 400V input, 48V output and 20% load condition.

Fig. 2(d). Simulation waveforms of proposed converter under 200V input, 48V output and 20% load condition.

CONCLUSION

In this paper, a variable frequency phase shift modulation control for a DAB LLC resonant converter has been incorporated. This control strategy makes the converter operating at a wide gain range with ZVS over all load conditions. The combination of two half bridge connected in series on the inverter side reduces the voltage stress across each switch, which also makes the converter capable of operating at high-voltage applications. The voltage stresses remain half of the input voltage over all load variations. With the proposed control, the voltage gain becomes independent of Q and K values. Thus, the process of parameter design can be simplified. The magnetizing inductance has been calculated as high to reduce the conduction loss. It also reduced the circulating current (or, reactive power) from the secondary side even at light load condition, which increased the efficiency as compared to conventional DAB LLC resonant converter. The performance of the proposed LLC resonant converter is experimentally verified with 200-400V input and 48V output converter prototype. Therefore, the proposed converter becomes a good candidate for variable input and constant output voltage applications.

REFERENCES

  • Costinett, D. Maksimovic, and R. Zane, “Design and Control for High Efficiency in High Step-Down Dual Active Bridge Converters Operating at High Switching Frequency,” IEEE Transactions on Power Electronics, vol. 28, pp. 3931-3940, 2013.
  • P. Engel, N. Soltau, H. Stagge, and R. W. D. Doncker, “Dynamic and Balanced Control of Three-Phase High-Power Dual-Active Bridge DC-DC Converters in DC-Grid Applications,” IEEE Transactions on Power Electronics, vol. 28, pp. 1880-1889, 2013.
  • Krismer and J. W. Kolar, “Efficiency-Optimized High-Current Dual Active Bridge Converter for Automotive Applications,” IEEE Transactions on Industrial Electronics, vol. 59, pp. 2745-2760, 2012.
  • Z. Peng, L. Hui, S. Gui-Jia, and J. S. Lawler, “A new ZVS bidirectional DC-DC converter for fuel cell and battery application,” IEEE Transactions on Power Electronics, vol. 19, pp. 54-65, 2004.
  • Inoue and H. Akagi, “A Bidirectional DC-DC Converter for an Energy Storage System With Galvanic Isolation,” IEEE Transactions on Power Electronics, vol. 22, pp. 2299-2306, 2007.

 

A 2 kW, Single-Phase, 7-Level Flying Capacitor Multilevel Inverter with an Active Energy Buffer  

 ABSTRACT

High efficiency and compact single-phase inverters are desirable in many applications such as solar energy harvesting and electric vehicle chargers. This paper presents a 2 kW, 60 Hz, 450 VDC to 240 VAC power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge. The inverter features a 7-level flying capacitor multilevel converter, with low-voltage GaN switches operating at 120 kHz. The inverter also includes an active buffer for twice-line-frequency power pulsation decoupling, which reduces the required capacitance by a factor of eight compared to conventional passive decoupling capacitors, while maintaining an efficiency above 99%. The inverter prototype is a self-contained box that achieves a high power density of 216 W/in3 and a peak overall efficiency of 97.6% while meeting the constraints including input current ripple, load transient, thermal and FCC Class B EMC specifications.

KEYWORDS:

  1. Single-phase
  2. Inverter
  3. Flying-capacitor multilevel
  4. GaN

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Full system overview of the single-phase inverter.

EXPECTED EXPERIMENTAL RESULTS:

Fig. 2. Waveforms showing active energy buffer operation at 2kW. Voltage ripple on VC3 counters the ripple on VC1 so that the bus voltage is constant.

Fig. 3. Waveforms showing the output voltage, output current and the switching node voltage (VSW) of the 7-level inverter at full load.

Fig. 4. Capacitor voltages of the 7-level inverter during full load operation, obtained using National Instruments data acquisition system (PXIe-1073).

Fig. 5. Energy buffer operation during a load step-down from 100% to 75%. The input current ripple becomes within specifications after 80 ms.

Fig. 6. Inverter operation during a load step-down from 100% to 75%.

Fig. 7. Conducted EMI measurement at full power (2kW) from 150 kHz to 30 MHz, obtained using Tektronix RSA5126A real-time signal analyzer.

CONCLUSION

This paper has presented a 2 kW, 450 VDC to 240 VRMS single-phase inverter. The dc to ac conversion is accomplished through a 7-level flying-capacitor multilevel converter, with GaN transistors switching at 120 kHz, which is the highest switching frequency achieved to date for a 7-level implementation. The commutation loop in the FCML converter is identified, and a switching cell design is used to minimize loop inductance and reduce the drain-source voltage ringing. In addition, the multilevel inverter is complemented by a series stacked buffer converter for twice-line-frequency ripple compensation. The active energy buffer achieves a high efficiency of 99% while reducing the required capacitor volume by a factor of eight. The combined inverter prototype successfully demonstrated a 216 W/in3 power density with a rectangular volume of 9.26 in3. A peak overall efficiency of 97.6% is achieved, including the power losses from control and cooling fan. The prototype meets all the specifications of the Google/IEEE Little Box Challenge, such as the current ripple, the load transient, the EMC and case temperature requirement, showcasing the capability of the multilevel converter design and the series stacked active energy buffer.

REFERENCES

  • W. Kolar, U. Drofenik, J. Biela, M. L. Heldwein, H. Ertl, T. Friedli, and S. D. Round, “Pwm converter power density barriers,” in Power Conversion Conference – Nagoya, 2007. PCC ’07, pp. P–9–P–29, April 2007.
  • Meynard and H. Foch, “Multi-level conversion: high voltage choppers and voltage-source inverters,” in Power Electronics Specialists Conference, 1992. PESC ’92 Record., 23rd Annual IEEE, pp. 397–403 vol.1, Jun 1992.
  • Allebrod, R. Hamerski, and R. Marquardt, “New transformerless, scalable modular multilevel converters for hvdc-transmission,” in Power Electronics Specialists Conference, 2008. PESC 2008. IEEE, pp. 174– 179, June 2008.
  • Antonopoulos, L. A¨ ngquist, S. Norrga, K. Ilves, L. Harnefors, and H. P. Nee, “Modular multilevel converter ac motor drives with constant torque from zero to nominal speed,” IEEE Transactions on Industry Applications, vol. 50, pp. 1982–1993, May 2014.
  • Debnath, J. Qin, B. Bahrani, M. Saeedifard, and P. Barbosa, “Operation, control, and applications of the modular multilevel converter: A review,” IEEE Transactions on Power Electronics, vol. 30, pp. 37–53, Jan 2015.

.

A Sensorless Power Reserve Control Strategy for Two-Stage Grid-Connected PV Systems

ABSTRACT

Due to the still increasing penetration of grid connected Photovoltaic (PV) systems, advanced active power control functionalities have been introduced in grid regulations. A power reserve control, where namely the active power from the PV panels is reserved during operation, is required for grid support. In this paper, a cost-effective solution to realize the power reserve for two-stage grid-connected PV systems is proposed. The proposed solution routinely employs a Maximum Power Point Tracking (MPPT) control to estimate the available PV power and a Constant Power Generation (CPG) control to achieve the power reserve. In this method, the solar irradiance and temperature measurements that have been used in conventional power reserve control schemes to estimate the available PV power are not required, and thereby being a sensorless approach with reduced cost. Experimental tests have been performed on a 3-kW two-stage single-phase grid-connected PV system, where the power reserve control is achieved upon demands.

 KEYWORDS:

  1. Active power control
  2. Power reserve control
  3. Maximum power point tracking
  4. Constant power generation control
  5. PV systems
  6. Grid-connected power converters.

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Power Reserve Control Strategy

Fig.1.System configuration and control structure of a two-stage grid connected PV system with the Sensorless Power Reserve Control strategy.

EXPECTED EXPERIMENTAL RESULTS:

Fig. 2. Experimental results of the single-phase grid-connected PV system with the proposed SPRC strategy during the steady-state operation (solar irradiance level: 1000 W/m2; ambient temperature: 250C; available power estimation rate: fAPE = 0.2 Hz), where the reference power reserve ∆P are 700 W, 500 W, and 300 W: (a) PV voltage vpv, (b) PV power Ppv and ac power (Pac), (c) dc-link voltage vdc, and (d) reserved power ∆P.

 

Fig. 3. Experimental results of the single-phase grid-connected PV system with the proposed SPRC strategy at the sampling rate of fAPE = 0.05 Hz under a ramp-changing solar irradiance profile (ambient temperature: 250C), where the reference power reserve ∆P is 500 W: (a) PV voltage vpv, (b) PV power Ppv and ac power (Pac), (c) dc-link voltage vdc, and (d) reserved power ∆P.

Fig. 4. Experimental results of the single-phase grid-connected PV system with the proposed SPRC strategy at the sampling rate of fAPE = 0.2 Hz under a ramp-changing solar irradiance profile (ambient temperature: 250C), where the reference power reserve ∆P is 500 W: (a) PV voltage vpv, (b) PV power Ppv and ac power (Pac), (c) dc-link voltage vdc, and (d) reserved power ∆P.

Fig. 5. Zoomed-in view of the results in Fig. 16: (a) PV voltage vpv, (b) PV power Ppv and ac power (Pac), (c) dc-link voltage vdc, (d) reserved power P.

Fig. 6. Experimental result of the PV voltage vpv and the dc-link voltage vdc with different available power estimation sampling rates fAPE.

CONCLUSION

A cost-effective sensorless power reserve control strategy for two-stage grid-connected PV systems has been proposed in this paper. The cost-effectiveness of the proposal lies in the sensorless estimation of the available PV power, which is achieved by routinely employing a fast MPPT operation. Then, the estimated available power is used for calculating the set-point to limit the extracted PV power with the CPG operation. At the grid-side, the stored energy in the dc-link is adaptively controlled to minimize the power fluctuation during the available PV power estimation process, where the excessed energy is temporarily stored in the dc-link. With the above coordinated control strategy, the power reserve control can be achieved as it has been verified experimentally. Design considerations for a high control performance and the operational boundary have also been discussed to assist the practical implementations.

 REFERENCES

  • REN21, “Renewables 2016: Global Status Report (GRS),” 2016. [Online]. Available: http://www.ren21.net/.
  • Fraunhofer ISE, “Recent Facts about Photovoltaics in Germany,” April 22, 2016. [Online]. Available: http://www.pv-fakten.de/.
  • Solar Power Europe, “Global Market Outlook For Solar Power 2015 – 2019,” 2015. [Online]. Available: http://www.solarpowereurope.org/.
  • Reiter, K. Ardani, R. Margolis, and R. Edge, “Industry perspectives on advanced inverters for us solar photovoltaic systems: Grid benefits, deployment challenges, and emerging solutions,” National Renewable Energy Laboratory (NREL), Tech. Rep. No. NREL/TP-7A40-65063., 2015.
  • Yang, P. Enjeti, F. Blaabjerg, and H. Wang, “Wide-scale adoption of photovoltaic energy: Grid code modifications are explored in the distribution grid,” IEEE Ind. Appl. Mag., vol. 21, no. 5, pp. 21–31, Sep. 2015..

A Primary Full-Integrated Active Filter Auxiliary Power Module in Electrified Vehicles with Single-Phase On board Chargers

ABSTRACT

In single-phase ac high-voltage (HV) battery chargers, as the input current is enforced to be varying sinusoidally in phase with the input voltage, the pulsating power at two times of the line frequency will be seen on the dc-link. Bulky capacitor bank or extra active filter circuits are needed to assimilate this harmonic current, which become a major barrier in terms of power density and cost. Sinusoidal charging method can be applied, while this might affect the charging efficiency and a deep study is still needed to further investigate on the impact to the Lithium-ion battery. An active filter auxiliary power module (AFAPM) based dual-mode dual-voltage charging system for vehicle application has been proposed. The AFAPM converter has two modes: 1) the HV active filtering mode, in which the vehicle is connected to the grid and the converter assimilates the significant second-order harmonic current; 2) the low-voltage (LV) battery charging mode, in which the vehicle is running and the converter charges the LV battery from HV battery. However, a relay and inductors are still required in that converter to achieve the dual-mode operation. This paper proposes a primary full-integrated AFAPM for electrified vehicle applications with single-phase onboard chargers. The proposed AFAPM converter is composed of a two-phase bidirectional buck converter to work as an active filter (AF) and a dual-active-bridge (DAB) to operate as a LV battery charger auxiliary power module (APM). With the proposed converter, only an extra active energy storage capacitor is needed to achieve the active filtering. All the switches and inductors on the primary stage are shared between the AF and APM. Therefore, the use of a bulky capacitor bank or an additional AF circuit is avoided and thus, the cost, size and weight of the dual-voltage charging system in the electrified vehicle applications can be reduced. To confirm the effectiveness of the proposed converter, a 720 W prototype.

KEYWORDS:

  1. Active filters, auxiliary power modules
  2. Dc/Dc converters
  3. Dual-voltage charging systems
  4. Plug-in hybrid electric vehicles
  5. Single-phase chargers.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Active Filter Auxiliary Power Module

Fig. 1: The dual-voltage charging system with the proposed primary full-integrated AFAPM.

EXPECTED SIMULATION RESULTS:

Active Filter Auxiliary Power Module

Fig. 2: Simulation results of AF mode, (a) HV dc-link voltage vdc, (b) capacitor Cr voltage vcr, (c) transformer primary voltage vpri, (d) inductor Lra and Lrb current ira and irb, (e) capacitor Cr current icr.

Active Filter Auxiliary Power Module

Fig. 3: Simulation results of APM mode, (a) transformer primary voltage vpri, (b) transformer secondary voltage vsec, (c) inductor Lra and Lrb current ira and irb, (d) LV output current iLo, (e) capacitor Cr voltage vcr

CONCLUSION

In this paper, a new primary full-integrated AFAPM converter is proposed. The proposed converter is not only a LV battery charger APM, but also an AF for the HV battery charger. A full bridge and auxiliary inductors are shared between the DAB APM converter and the two phase buck AF converter. Only an active harmonic energy storage capacitor is needed to achieve active filtering. As a result, from the harmonic energy storage aspect for the 6.6 kW HV battery charger in the vehicle applications, with the proposed AFAPM method, the volume and cost can decrease to 45.8% and 44.7% of the volume and cost of the conventional extra active filter method, respectively.  A 720 W prototype has been built and experiments show promising results confirming the effectiveness of the proposed converter.

REFERENCES

  • Xue, Z. Shen, D. Boroyevich, P. Matavelli, and D. Diaz, “Dual active bridge-based battery charger for plug-in hybrid electric vehicle with charging current containing low frequency ripple,” IEEE Transactions on Power Electronics, vol. 30, no. 12, pp. 7299-7307, Dec. 2015.
  • Bilgin, P. Magne, P. Malysz, Y. Yang, V. Pantelic, M. Preindl, A. Korobkine, W. Jiang, M. Lawford, and A. Emadi, “Making the case for electrified transportation,” IEEE Transactions on Transportation Electrification, vol. 1, no. 1, pp. 4-17, Jun. 2015.
  • Jahdi, O. Alatise, C. Fisher, R. Li, and P. Mawby, “An evaluation of silicon carbide unipolar technologies for electric vehicle drive-trains,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 2, no. 3, pp. 517–528, Sep. 2014.
  • A. Mantooth, M. D. Glover, and P. Shepherd, “Wide bandgap technologies and their implications on miniaturizing power electronic systems,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 2, no. 3, pp. 374-385, Sep. 2014.

 

A PLL Based Controller for Three Phase Grid Connected Power Converters

A PLL Based Controller for Three Phase Grid Connected Power Converters

 ABSTRACT

The current control of three-phase grid-connected converters is typically carried out by using a proportional resonant controller or synchronous reference frame proportional integral regulator. The implementation of these controllers often requires knowledge of the grid voltage frequency/phase angle, which is typically provided by a synchronization unit. It implies that dynamics and possible inaccuracies of the synchronization unit have a considerable impact on the current controller performance. The aim of this letter is to design an adaptive current controller by using a conventional synchronous reference frame phase-locked loop (SRF-PLL). In this way, the current controller and synchronization part are merged into a single unit, which results in a simpler and more compact structure. The effectiveness of the proposed controller is verified using experimental results.

KEYWORDS:

  1. Current control
  2. Distributed generation (DG) systems
  3. Phase-locked loop (PLL)
  4. Power converters
  5. Synchronization
  6. Three phase grid

 SOFTWARE: MATLAB/SIMULINK

CONTROL SYSTEM CIRCUIT DIAGRAM:

Three-Phase Grid

Fig. 1. Power stage of a three-phase VSC with the proposed PLL-based controller and a harmonic/imbalance compensator.

EXPECTED EXPERIMENTAL RESULTS:

PLL Based Controller

Fig. 2. Experimental results for the test 1.

Three Phase Grid

Fig. 3. Experimental results for the test 2.

Three Phase Grid

Fig. 4. Experimental results for the test 3.

 CONCLUSION

In this letter, a PLL-based controller for grid-connected converters was proposed. This controller, which is realized by adding a positive feedback loop to the conventional SRFPLL, eliminates the need for a dedicated synchronization unit and, therefore, results in a more compact structure. To enhance the harmonic/imbalance rejection capability of the suggested controller, multiple complex integrators tuned at low-order disturbance frequencies is employed. To simplify the tuning procedure, a simple yet accurate linear model describing the frequency estimation dynamics of the proposed controller was was verified using some experimental results. The main contribution of this letter is not the proposed controller. It is actually demonstrating the possibility of making a frequency-adaptive controller from a standard PLL. The importance of this contribution will be more evident when we notice that there are a large number of advanced PLLs which can be explored for the controller design.

REFERENCES

  • M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. C. P. Guisado, M. A. M. Prats, J. I. Leon, and N. Moreno-Alfonso, “Powerelectronic systems for the grid integration of renewable energy sources: A survey,” IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1002–1016, Jun. 2006.
  • Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.
  • K. Bose, “Power electronics and motor drives recent-progress and perspective,” IEEE Trans. Ind. Electron., vol. 56, no. 2, pp. 581–588, Feb. 2009.
  • Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409, Oct. 2006.
  • Zeng and L. Chang, “An advanced SVPWM-based predictive current controller for three-phase inverters in distributed generation systems,” IEEE Trans. Ind. Electron., vol. 55, no. 3, pp. 1235–1246, Mar. 2008.

Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter

 ABSTRACT

This paper presents a nonlinear control technique for a three-phase shunt active power filter (SAPF). The method provides compensation for reactive, unbalanced, and harmonic load current components. A proportional–integral (PI) control law is derived through linearization of the inherently nonlinear SAPF system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the SAPF output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that significantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the SAPF reference currents, is proposed. The first step is to extract the SAPF reference currents from the sensed nonlinear load currents by applying the synchronous reference frame method, where a three-phase diode bridge rectifier with RL load is taken as the nonlinear load, and then, the reference currents are modified, so that the delay will be compensated. The converter, which is controlled by the described control strategy, guarantees balanced overall supply currents, unity displacement power factor, and reduced harmonic load currents in the common coupling point. Various simulation and experimental results demonstrate the high performance of the nonlinear controller. 

KEYWORDS:

  1. Active power filter
  2. Control delay compensation,
  3. Modeling
  4. Nonactive load current compensation
  5. Nonlinearc control
  6. Power quality.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Basic circuit of SAPF.

EXPECTED SIMULATION RESULTS:

Fig. 2. Steady-state response of the SAPF.

Fig. 3. Spectrum of phase 1. (a) Load current. (b) Source current after compensation.

Fig. 4. Dynamic response of SAPF under varying distorted nonlinear load conditions.

Fig. 5. Steady-state response of SAPF with nonlinear load unbalances.

Fig. 6. Spectrum of load currents and source currents after compensation for asymmetrical load conditions.

CONCLUSION

The nonlinear control algorithm of an SAPF has been implemented to enhance its response for compensation of nonactive load currents. The nonlinear control technique of the SAPF has been designed, which is based on two inner current loops and an outer dc bus voltage regulator loop. It  addition to good performance in both steady-state and transient operations. Simulation and experimental results have validated the nonlinear control approach of the SAPF. It has been shown that the system has 1.5 cycles for the outer voltage loop and 0.5 cycles for the inner current loop and is able to keep the THD of the supply current below the limits specified by the IEEE- 519 standard. The obtained results have demonstrated the high performance of the SAPF. 

REFERENCES

  • Senini and P. J. Wolfs, “Hybrid active filter for harmonically unbalanced three phase three wire railway traction loads,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 702–710, Jul. 2000.
  • Rahmani, K. Al-Haddad, H. Y. Kanaan, and B. Singh, “Implementation and simulation of a modified PWM with two current control techniques applied to a single-phase shunt hybrid power filter,” Proc. Inst. Elect. Eng.—Electr. Power Appl., vol. 153, no. 3, pp. 317–326, May 2006.
  • Singh, V. Verma, and J. Solanki, “Neural network-based selective compensation of current quality problems in distribution system,” IEEE Trans. Ind. Electron., vol. 54, no. 1, pp. 53–60, Feb. 2007.
  • R. Lin and C. H. Huang, “Implementation of a three-phase capacitor clamped active power filter under unbalanced condition,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1621–1630, Oct. 2006.
  • Grino, R. Cardoner, R. Costa-Castello, and E. Fossas, “Digital repetitive control of a three-phase four-wire shunt active filter,” IEEE Trans. Ind. Electron., vol. 54, no. 3, pp. 1495–1503, Jun. 2007.

.

An Improved Control Scheme for Grid Connected Voltage Source Inverter

ABSTRACT

In grid connected Distribution Generation systems, Voltage Source Inverters are used for interfacing the renewable energy source to the utility grid. DG has variety of problems during grid integration. The power quality problems may cause problems to the industries ranging from malfunctioning of equipment to complete plant shut down. Disturbances from the utility grid including voltage sags, harmonics and the grid impedance will affect the grid connected voltage source inverters connected to the grid. Hence the control of the grid connected inverter plays an important role in feeding a grid with high quality power. This report presents an analysis of the stability problem of a grid connected with Voltage Source Inverter and with a LC filter. The possible grid-impedance variations have a significant influence on the system stability. Whenever the grid inductive impedance increases, the low frequency gain and the bandwidth of the Proportional Integral (PI) controller have to be decreased to maintain the system stable, thereby degrading the tracking performance and disturbance rejection capability. To overcome this problem an H∞ controller is proposed with an explicit robustness in terms of grid impedance variations to incorporate the desired tracking performance and stability margin. The proposed method is simulated by using MATLAB/SIMULINK. The results of the proposed H∞ controller and the conventional PI controller are compared, which validates the performance of the proposed control scheme.

 KEYWORDS:

  1. Distributed Generation (DG)
  2. Voltage Source Inverter (VSC)
  3. LC Filter
  4. H∞ Controller
  5. Total Harmonic Distortion (THD).

SOFTWARE: MATLAB/SIMULINK

SIMULINK BLOCK DIAGRAM:

 

Figure.1.Overall Simulink Model

EXPECTED SIMULATION RESULTS:

 

Figure.2.Waveform for output voltage of PV module

Figure.3.Output current waveform of overall system

Figure.4. THD analysis with Lg=0.3 mH and rg= 0.2Ω

Figure.5. THD analysis with Lg=0.15 mH and rg=0.2Ω

CONCLUSION

In the grid connected VSI with LC filters, the possible wide range of grid impedance variations can challenge the design of the controller, particularly when the grid impedance is highly inductive. In this project, the suitability of an H∞ controller to get the desired tracking performance and stability margin is investigated. From the software results it is seen that the grid current THD of the H∞ controller are always lower than that of the PI controller, which satisfy the THD requirement of IEEE Std.1547 2003 (i.e.,5%). Further simulation work is based on demonstrating the operation of a grid in Grid connected mode and intentional islanded mode. Through this, the system is able to determine whether or not it is safe to remain connected to the grid. An islanding detection algorithm is used to act as a switch between the two controllers and this minimizes the effect of losses in the time of transition, and also to prevent the undesirable feeding of loads during fault conditions.

REFERENCES

  • Asiminoaei, L., Teodorescu,R.,Blaabjerg,F., and Borup, U., “A New Method Of On-Line Grid Impedance Estimation for PV Inverter,” in Proc. IEEE APEC, San Diego, CA, Feb. 2004, pp. 1527–1533.
  • Bierhoff, M. H., and Fuchs,F. W., “Active Damping for Three-Phase PWM Rectifiers with High-Order Line-Side Filters,” IEEE Trans. Ind. Electron., vol. 56, no. 2, pp. 371–379, Feb. 2009.
  • Bin Yu and Liuchen Chang, “Improved Predictive Current Controlled PWM for Single-Phase Grid-Connected Voltage Source Inverters,” in Proc. IEEE PESC, 2005, pp. 231 – 236.
  • Blaabjerg, F., Teodorescu, R., and Liserre, M., “Overview of Control and Grid Synchronization for Distributed Power Generation Systems,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409, Oct. 2006.

Fixed-Frequency Generalized Peak Current Control (GPCC) for Inverters

 ABSTRACT

A fast and robust fixed switching frequency peak current controller for dc-ac converters is presented. The method is specifically elaborated for single-phase grid-connected distributed generation (DG) applications. This method is called generalized peak current control (GPCC) as it can mimic any known pulse width modulation (PWM) strategy. It is shown that additional control objectives can be achieved by adaptive bands of the GPCC, which are proposed to provide active damping for inverters with LCL output filters. The proposed approach features all the advantages of peak current controllers such as simplicity, fast transient, and optimum dynamic response; with the superiority of fixed switching frequency and harmonic free output. Feasibility and performance of the controller is shown by simulations and experimental results.

 KEYWORDS:

  1. Current Control
  2. DC-AC Converters
  3. Generalized Peak Current Control (GPCC)
  4. Switching Scheme
  5. Single-Phase Grid-Connected Inverter

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the proposed controller along with the cost effective active resonant damping technique.

 

EXPECTED SIMULATION RESULTS:

Fig. 2. (a) Grid current for the LCL filter case when the active damping branch is disabled, (b) Current of inverter and grid with the proposed active damping.

Fig. 3. Dynamic performance evaluation of proposed GPCC. Peak current reference jumps from 1A to 3A at t = 0:1s.

CONCLUSION

A fixed switching frequency Generalized Peak Current Control (GPCC) method for inverters is proposed . While controlling the peak value of the inverters’ current, the proposed approach can mimic any known PWM strategy. As a result, the GPCC features all the advantages of peak current controllers, along with a fixed switching frequency and the clean output harmonic spectrum inheriting from the original PWM scheme. It is shown that the proposed technique is able to obtain additional control objectives by its adaptive bands. As an example, the GPCC is applied to a unipolar PWM scheme and the controller is elaborated for both Land LCL-type output filters. Demonstrating the advantages of resulting controller, a simple active damping strategy based on adaptive bands of the controller is proposed. Simulations and experimental results are presented to validate the method. 

REFERENCES

  • Gupta, “Generalized frequency domain formulation of the switching frequency for hysteresis current controlled vsi used for load compensation,” Power Electronics, IEEE Transactions on, vol. 27, no. 5, pp. 2526–2535, May 2012.
  • Blaabjerg, R. Teodorescu, M. Liserre, and A. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” Industrial Electronics, IEEE Transactions on, vol. 53, no. 5, pp. 1398–1409, Oct 2006.
  • Malesani and P. Tenti, “A novel hysteresis control method for currentcontrolled voltage-source pwm inverters with constant modulation frequency,” Industry Applications, IEEE Transactions on, vol. 26, no. 1, pp. 88–92, 1990.
  • Malesani, L. Rossetto, and A. Zuccato, “Digital adaptive hysteresis current control with clocked commutations and wide operating range,” Industry Applications, IEEE Transactions on, vol. 32, no. 2, pp. 316– 325, 1996.
  • Bose, “An adaptive hysteresis-band current control technique of a voltage-fed pwm inverter for machine drive system,” Industrial Electronics, IEEE Transactions on, vol. 37, no. 5, pp. 402–408, Oct 1990.