Dynamic Voltage Conditioner, a New Concept for Smart Low-Voltage Distribution System

IEEE TRANSACTION ON POWER ELECTRONICS, 2017

ABSTRACT: Power Quality (PQ) improvement in distribution level is an increasing concern in modern electrical power systems. One of the main problems in LV networks is related to load voltage stabilization close to the nominal value. Usually this problem is solved by Smart Distribution Transformers, Hybrid Transformers and Solid-state Transformers, but also Dynamic Voltage Conditioner (DVC) can be an innovative and a cost effective solution. The paper introduces a new control method of a single-phase DVC system able to compensate these long duration voltage drifts. For these events, it is mandatory to avoid active power exchanges so, the controller is designed to work with non-active power only. Operation limits for quadrature voltage injection control is formulated and reference voltage update procedure is proposed to guarantee its continuous operating. DVC performance for main voltage and load variation is examined. Proposed solution is validated with simulation study and experimental laboratory tests. Some simulation and experimental results are illustrated to show the prototype device’s performance.

 

KEYWORDS:

  1. Power Quality
  2. Power conditioning
  3. Power electronics
  4. Dynamic Voltage Conditioner DVC
  5. Dynamic Voltage Restorer DVR
  6. LV Distribution System
  7. Smart Grid

 

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1.  block diagram.

 EXPECTED SIMULATION RESULTS:

 

Fig. 2. Simulation – DVC operation limit update procedure under voltage – limits due to : Case 2.b) – (a) grid and minimum grid voltage, (b) PCC and PCC reference voltage, (c) load power factor.

Fig. 3. Experimental – DVC response to load variation, adding and removing the load – (a),(d) PCC voltage, (b),(e) DVC injected voltage, (c),(f) load current.

 

CONCLUSION:

A new device concept, which goes beyond typical DVR functionalities, is presented. The proposed device is named DVC (Dynamic Voltage Conditioner), it is an active voltage conditioner able to cover both short- and fast-events, as a typical DVR, and long-events (in the grid voltage range from 0.9-1.1 p.u.). So it can perfectly satisfy modern power system DSO requirements. In particular the paper presents only the control strategy that can be adapted during steady state condition (long-events) for a single-phase DVC. Indeed, the steady state condition is not reported in literature and the single phase configuration seems to be the best economic solution for smart grid LV distribution system. The device controller, here introduced for first time, has been designed to operate with non-active power during steady state condition. So, to guarantee DVC continuous working, the paper describes a control method to generate DVC reference voltage considering its limits. Moreover, single-phase design can decrease device initial cost and it is also more compatible with LV distribution and mostly single-phase domestic loads.

Designed control method is verified by MATLAB based simulation and laboratory experimental test bed. Results show that, the device has good performance and it can improve PQ level of the installed distribution Smart Grid network effectively (mainly in the grid voltage range from 0.9-1.1 p.u.). This is essential for nowadays modern network because the proposed DVC can give flexibility to the system operator in order to move all problematic single-phase loads on a specific phase (where the DVC is installed).

Even if the paper analyzed a single-phase system, all the theoretical analysis on device limits can be extended for three phase system and it will be addressed in future works. It should be noted that, this solution since it injects the compensation voltage in quadrature to line current, creates phase shifting on installed phase voltage so, it can impose voltage unbalance issues to the supplied three-phase loads. Therefore this device can be used effectively in LV distribution network with single phase loads only.

 

REFERENCES:

  • “IEEE recommended practice for monitoring electric power quality,” IEEE Std 1159-2009 (Revision of IEEE Std 1159-1995), pp. c1–81, June 2009.
  • Sankaran, Power quality. CRC press, 2001.
  • “IEEE application guide for IEEE std 1547(TM), IEEE standard for interconnecting distributed resources with electric power systems,” IEEE Std 1547.2-2008, pp. 1–217, April 2009.
  • Standard, “50160,” Voltage characteristics of public distribution systems, 2010.
  • Farhangi, “The path of the smart grid,” IEEE Power and Energy Magazine, vol. 8, no. 1, pp. 18–28, January 2010.

 MPPT with Single DC–DC Converter and Inverter for Grid-Connected Hybrid Wind-Driven PMSG–PV System

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, 2015

ABSTRACT: A new topology of a hybrid distributed generator based on photovoltaic and wind-driven permanent magnet synchronous generator is proposed. In this generator, the sources are connected together to the grid with the help of only a single boost converter followed by an inverter. Thus, compared to earlier schemes, the proposed scheme has fewer power converters. A model of the proposed scheme in the d − q-axis reference frame is developed. Two low-cost controllers are also proposed for the new hybrid scheme to separately trigger the dc–dc converter and the inverter for tracking the maximum power from both sources. The integrated operations of both proposed controllers for different conditions are demonstrated through simulation and experimentation. The steady-state performance of the system and the transient response of the controllers are also presented to demonstrate the successful operation of the new hybrid system. Comparisons of experimental and simulation results are given to validate the simulation model.

KEYWORDS:

  1. Grid-connected hybrid system
  2. Hybrid distributed generators (DGs)
  3. Smart grid
  4. Wind-driven PMSG–PV

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

Fig. 1. Proposed DG system based on PMSG–PV sources.

EXPECTED SIMULATION RESULTS:

(a)

(b)

Fig. 2. DC link steady-state waveforms. (a) Experimental (voltage—50 V/div, current—10 A/div, and time—500 ms/div). (b) Simulated (voltage—20 V/div, current—5 A/div, and time—500 ms/div.

(a)

(b)

Fig. 3. Steady-state grid voltage and current waveforms. (a) Experimental (voltage—50 V/div, current—10 A/div, and time—20 ms/div). (b) Simulated (voltage—50 V/div, current—5 A/div, and time— 20 ms/div).

Experimental (Voltage 50V/div, Duty-cycle 0.6/div, Time 2s/div)

Simulated (Voltage 20V/div, Duty-cycle 0.5/div, Time 2s/div)

(a) Changes in rectifier output voltage and duty cycle of the boost converter.

Experimental (Voltage 50V/div, Current 10 A/div, Time 2s/div)

Simulated (Voltage 50V/div, Current 10/div)

(b) Changes in dc-link voltage and current

Experimental (Voltage 50V/div, Current 10A/div, Time 2s/div)

Simulated (Voltage 50V/div, Current 10A/div, Time 2s/div)

Fig.4. Transient response for a step change in PMSG shaft speed.. (c) Changes in grid current.

 CONCLUSION:

A new reliable hybrid DG system based on PV and wind driven PMSG as sources, with only a boost converter followed by an inverter stage, has been successfully implemented. The mathematical model developed for the proposed DG scheme has been used to study the system performance in MATLAB. The investigations carried out in a laboratory prototype for different irradiations and PMSG shaft speeds amply confirm the utility of the proposed hybrid generator in zero-net-energy buildings. In addition, it has been established through experimentation and simulation that the two controllers, digital MPPT controller and hysteresis current controller, which are designed specifically for the proposed system, have exactly tracked the maximum powers from both sources. Maintenance-free operation, reliability, and low cost are the features required for the DG employed in secondary distribution systems. It is for this reason that the developed controllers employ very low cost microcontrollers and analog circuitry. Furthermore, the results of the experimental investigations are found to be matching closely with the simulation results, thereby validating the developed model. The steady state waveforms captured at the grid side show that the power generated by the DG system is fed to the grid at unity power factor. The voltage THD and the current THD of the generator meet the required power quality norms recommended by IEEE. The proposed scheme easily finds application for erection at domestic consumer sites in a smart grid scenario.

REFERENCES:

[1] J. Byun, S. Park, B. Kang, I. Hong, and S. Park, “Design and implementation of an intelligent energy saving system based on standby power reduction for a future zero-energy home environment,” IEEE Trans. Consum. Electron., vol. 59, no. 3, pp. 507–514, Oct. 2013.

[2] J. He, Y. W. Li, and F. Blaabjerg, “Flexible microgrid power quality enhancement using adaptive hybrid voltage and current controller,” IEEE Trans. Ind. Electron., vol. 61, no. 6, pp. 2784–2794, Jun. 2014.

[3] W. Li, X. Ruan, C. Bao, D. Pan, and X. Wang, “Grid synchronization systems of three-phase grid-connected power converters: A complexvector- filter perspective,” IEEE Trans. Ind. Electron., vol. 61, no. 4, pp. 1855–1870, Apr. 2014.

[4] C. Liu, K. T. Chau, and X. Zhang, “An efficient wind-photovoltaic hybrid generation system using doubly excited permanent-magnet brushless machine,” IEEE Trans. Ind. Electron, vol. 57, no. 3, pp. 831–839, Mar. 2010.

[5] S. A. Daniel and N. A. Gounden, “A novel hybrid isolated generating system based on PV fed inverter-assisted wind-driven induction generators,” IEEE Trans. Energy Convers., vol. 19, no. 2, pp. 416–422, Jun. 2004.

Reduction of Energy Storage Requirements in Future Smart Grid Using Electric Springs

 

ABSTRACT:

The electric spring is an emerging technology proven to be effective in i) stabilizing smart grid with substantial penetration of intermittent renewable energy sources and ii) enabling load demand to follow power generation. The subtle change from output voltage control to input voltage control of a reactive power controller offers the electric spring new features suitable for future smart grid applications. In this project, the effects of such subtle control change are highlighted, and the use of the electric springs in reducing energy storage requirements in power grid is theoretically proven and practically demonstrated in an experimental setup of a 90 kVApower grid.Unlike traditional Statcom and StaticVar Compensation technologies, the electric spring offers not only reactive power compensation but also automatic power variation in non-critical loads. Such an advantageous feature enables noncritical loads with embedded electric springs to be adaptive to future power grid. Consequently, the load demand can follow power generation, and the energy buffer and therefore energy storage requirements can be reduced.

KEYWORDS:

  1. Distributed power systems
  2. Energy storage
  3. Smart grid
  4. Stability

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

Fig. 1. Experimental setup based on the 90 kVA Smart Grid Hardware Simulation System at the Maurice Hancock Smart Energy Laboratory.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Measured rms power line voltage (vs) and non-critical load voltage (vo)

Fig. 3. Measured average powers of the wind power simulator (PG+PR), battery storage (PS) and non-critical load(P1)

Fig. 4. Measured power (Ps) and energy change (Es) of the battery storage.

Fig. 5. Measured electric spring reactive power (QES), critical load voltage (VR2) and power (P2).

 CONCLUSION:

In this paper, the differences between the output voltage control and the input voltage control of a reactive power controller are highlighted. While energy storage is an effective but expensive means to balance power supply and demand, an analysis and practical confirmation are presented to show that electric springs can reduce energy storage requirements in a power grid. Electric springs allow the non-critical load power to vary with the renewable energy profile. By reducing the instantaneous power imbalance of power supply and demand, electric springs allow the non-critical load demand profile to follow the power generation profile and reduce the energy storage requirements in power grid. This important point has been theoretically proved and practically verified in an experimental setup. Due to the advantageous features such as enabling the load demand to follow the power generation, the reduction of energy storage requirements, the reactive power compensation for voltage regulation, and the possibility of both active and reactive power control [28], electric springs open a door to distributed stability control for future smart grid with substantial penetration of intermittent renewable energy sources.

REFERENCES:

[1] D. Westermann and A. John, “Demand matching wind power generation with wide-area measurement and demand-side management,” IEEE Trans. Energy Convers., vol. 22, no. 1 , pp. 145–149, 2007.

[2] P. Palensky and D. Dietrich, “Demand side management: Demand response, intelligent energy systems, and smart loads,” IEEE Trans. Ind. Inform., vol. 7 , no. 3 , pp. 381–388, 2011.

[3] P. Varaiya, F. Wu, and J. Bialek, “Smart operation of smart grid: Risklimiting dispatch,” Proc. IEEE, vol. 99, no. 1 , pp. 40–57, 2011.

[4] I. Koutsopoulos and L. Tassiulas, “Challenges in demand load control for the smart grid,” IEEE Netw., vol. 25, no. 5 , pp. 16–21, 2011.

[5] A. Mohsenian-Rad, V. W. S. Wong, J. Jatskevich, R. Schober, and A. Leon-Garcia, “Autonomous demand-side management based on gametheoretic energy consumption scheduling for the future smart grid,” IEEE Trans. Smart Grid, vol. 1 , no. 3 , pp. 320–331, 2011.

 

 

DC Electric Springs A Technology for Stabilizing DC Power Distribution Systems

 

ABSTRACT:

There is a growing interest in using DC power systems and microgrids for our electricity transmission and distribution, particularly with the increasing penetration of photovoltaic power systems. This paper presents an electric active suspension technology known as the DC electric springs for voltage stabilization and power quality improvement. The basic operating modes and characteristic of a DC electric spring with different types of serially-connected non-critical loads will first be introduced. Then, the various power delivery issues of the DC power systems, namely bus voltage variation, voltage droop, system fault, and harmonics, are briefly described. The operating limits of a DC electric spring in a DC power grid is studied. It is demonstrated that the aforementioned issues can be mitigated using the proposed DC electric spring technology. Experiment results are provided to verify the feasibility of the proposed technology.

KEYWORDS:

  1. Smart load
  2. Distributed power systems
  3. Power electronics
  4. Electric springs
  5. DC grids
  6. Smart grid

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

Fig. 1. The basic configuration of DC electric springs.

EXPECTED SIMULATION RESULTS:

Fig. 2. Enlarged experiment waveforms based on the raw data exported from the oscilloscope corresponding

Fig. 3. Enlarged experiment waveforms based on the raw data exported from the oscilloscope corresponding

CONCLUSION:

In this paper, the concept of DC electric springs (ES) is firstly introduced to cope with several issues of DC power grids. The DC-ES is proposed as an active suspension system. Similar to their AC counterparts, the DC-ES can provide dynamic voltage regulation for the DC bus. The DC-ES connected in series with different types of non-critical loads to form a smart load have been analyzed and their operating modes have been identified and explained. Furthermore, the operating limits of the DC-ES under a given set of system parameters is studied, which provides quantitative analytical procedures to estimate the theoretical limits of ES. The paper provides a fundamental study on the DC-ES including the characteristics, the modes of operation, and the operating limits. The theoretical analysis and the performance of the DCES have been practically verified.

REFERENCES:

[1] R. Lobenstein and C. Sulzberger, “Eyewitness to DC history,” Power and Energy Magazine, IEEE, vol. 6, no. 3, pp. 84–90, May 2008.

[2] G. Neidhofer, “Early three-phase power,” Power and Energy Magazine, IEEE, vol. 5, no. 5, pp. 88–100, Sep. 2007.

[3] B. C. Beaudreau, World Trade: A Network Approach. iUniverse, 2004.

[4] H. Kakigano, Y. Miura, and T. Ise, “Distribution voltage control for DC microgrids using fuzzy control and gain-scheduling technique,” IEEE Trans. Power Electron., vol. 28, no. 5, pp. 2246–2258, May 2013.

[5] P. Loh, D. Li, Y. K. Chai, and F. Blaabjerg, “Autonomous operation of hybrid microgrid with AC and DC subgrids,” IEEE Trans. Power Electron., vol. 28, no. 5, pp. 2214–2223, May 2013.

MPPT With Single DC–DC Converter and Inverter for Grid-Connected Hybrid Wind-Driven PMSG–PV System

ABSTRACT:

A new topology of a hybrid distributed generator based on photovoltaic and wind-driven permanent magnet synchronous generator is proposed. In this generator, the sources are connected together to the grid with the help of only a single boost converter followed by an inverter. Thus, compared to earlier schemes, the proposed scheme has fewer power converters. A model of the proposed scheme in the d − q-axis reference frame is developed. Two low-cost controllers are also proposed for the new hybrid scheme to separately trigger the dc–dc converter and the inverter for tracking the maximum power from both sources. The integrated operations of both proposed controllers for different conditions are demonstrated through simulation and experimentation. The steady-state performance of the system and the transient response of the controllers are also presented to demonstrate the successful operation of the new hybrid system. Comparisons of experimental and simulation results are given to validate the simulation model.

KEYWORDS:

  1. Grid-connected hybrid system
  2. Hybrid distributed generators (DGs)
  3. Smart grid
  4. Wind-driven PMSG–PV

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 

Fig. 1. Proposed DG system based on PMSG–PV sources.

 EXPECTED SIMULATION RESULTS:


Fig. 2. DC link steady-state waveforms. (a) Experimental (voltage—50 V/div, current—10 A/div, and time—500 ms/div). (b) Simulated (voltage—20 V/div, current—5 A/div, and time—500 ms/div.

Fig. 3. Steady-state grid voltage and current waveforms. (a) Experimental (voltage—50 V/div, current—10 A/div, and time—20 ms/div). (b) Simulated (voltage—50 V/div, current—5 A/div, and time— 20 ms/div).

Fig.4. Transient response for a step change in PMSG shaft speed. (a) Changes in rectifier output voltage and duty cycle of the boost converter. (b) Changes in dc-link voltage and current. (c) Changes in grid current.

 

CONCLUSION:

A new reliable hybrid DG system based on PV and wind driven PMSG as sources, with only a boost converter followed by an inverter stage, has been successfully implemented. The mathematical model developed for the proposed DG scheme has been used to study the system performance in MATLAB. The investigations carried out in a laboratory prototype for different irradiations and PMSG shaft speeds amply confirm the utility of the proposed hybrid generator in zero-net-energy buildings. In addition, it has been established through experimentation and simulation that the two controllers, digital MPPT controller and hysteresis current controller, which are designed specifically for the proposed system, have exactly tracked the maximum powers from both sources. Maintenance-free operation, reliability, and low cost are the features required for the DG employed in secondary distribution systems. It is for this reason that the developed controllers employ very low cost microcontrollers and analog circuitry. Furthermore, the results of the experimental investigations are found to be matching closely with the simulation results, thereby validating the developed model. The steady state waveforms captured at the grid side show that the power generated by the DG system is fed to the grid at unity power factor. The voltage THD and the current THD of the generator meet the required power quality norms recommended by IEEE. The proposed scheme easily finds application for erection at domestic consumer sites in a smart grid scenario.

REFERENCES:

[1] J. Byun, S. Park, B. Kang, I. Hong, and S. Park, “Design and implementation of an intelligent energy saving system based on standby power reduction for a future zero-energy home environment,” IEEE Trans. Consum. Electron., vol. 59, no. 3, pp. 507–514, Oct. 2013.

[2] J. He, Y. W. Li, and F. Blaabjerg, “Flexible microgrid power quality enhancement using adaptive hybrid voltage and current controller,” IEEE Trans. Ind. Electron., vol. 61, no. 6, pp. 2784–2794, Jun. 2014.

[3] W. Li, X. Ruan, C. Bao, D. Pan, and X. Wang, “Grid synchronization systems of three-phase grid-connected power converters: A complexvector- filter perspective,” IEEE Trans. Ind. Electron., vol. 61, no. 4, pp. 1855–1870, Apr. 2014.

[4] C. Liu, K. T. Chau, and X. Zhang, “An efficient wind-photovoltaic hybrid generation system using doubly excited permanent-magnet brushless machine,” IEEE Trans. Ind. Electron, vol. 57, no. 3, pp. 831–839, Mar. 2010.

[5] S. A. Daniel and N. A. Gounden, “A novel hybrid isolated generating system based on PV fed inverter-assisted wind-driven induction generators,” IEEE Trans. Energy Convers., vol. 19, no. 2, pp. 416–422, Jun. 2004.