Grid-Connected Induction Motor Using a Floating DC-Link Converter Under Unbalanced Voltage sag BTech/Mtech Final Year Electrical Projects


Voltage sag This article proposes a series compensator with unbalanced voltage sag ride-through capability applied to grid connected induction motors. A conventional three-phase voltage source inverter (VSI) is intended to regulate the motor voltages. The VSI is connected in series with the grid and a three-phase machine with open-ended windings.


Voltage sag The proposed system is suitable for applications in which no frequency variation is required, like large pumps or fans. The VSI dc-link voltage operates as a floating capacitor through the energy minimized compensation (EMC) technique, in which there is no dc source or injection transformer. The motor load condition determines the minimum grid voltage positive component (sag severity) to keep EMC operation.


Voltage sag Meanwhile, a voltage unbalance may increase the dc-link voltage requirements. A 1.5-hp four-pole induction motor has been used to verify the ride-through capability of the proposed compensator under grid voltage disturbances. A total harmonic distortion (THD) analysis of grid currents demonstrates that the proposed system provides low THD even if no passive filter is used.


Voltage sag The operating principle, converter output voltage analysis, pulse width modulation technique, control strategy, and components ratings are discussed as well. Simulation and experimental results are presented to demonstrate the feasibility of the system.


  1. Floating capacitor
  2. Induction motor
  3. Series compensator
  4. Unbalanced voltage sag



Fig. 1. Block diagram of feedback small-signal model.


Fig. 2. Simulation waveforms at the steady state and half load with perphase grid (vga ) and load (vla ) voltages, as well as the converter’s line-to-line voltage (vcab ).

Fig. 3. Simulation waveforms with the proposed series compensator under balanced voltage sag at half load. (a) Rated grid voltages. (b) Three-phase voltage sag of 80%.

Fig. 4. Simulation waveforms with the proposed series compensator under unbalanced voltage sag:Fd = 15%and half load. (a) Grid voltages and currents. (b) DC-link voltage, torque, and speed.


Voltage sag The proposed system has unbalanced voltage sag ride-through capability, being suitable for grid-connected induction motors applications. Indeed, the simulation and experimental results supported the theoretical analysis. A conventional three-phase VSI using a floating dc-link capacitor has been applied as a series compensator.


Voltage sag Besides that, the proposed system does not require any additional passive filter, injection transformer, or extra power supply. A conventional three-phase H-bridge converter to compensate balanced grid voltage disturbances has recently been proposed in the literature. Compared to the conventional solution, the proposed one has a lower number of components, a single dc link, and can deal with unbalanced voltages without a complex control strategy.


Voltage sag The higher dc-link voltage requirement of the proposed series compensator was highlighted as its main drawback. Although the proposed solution provided higher THD of grid currents, its levels were acceptable. Hence, the proposed system can be easily integrated along with standard squirrel-cage induction motors when no frequency variation is required.


[1] H. G. Sarmiento and E. Estrada, “A voltage sag study in an industry with adjustable speed drives,” IEEE Ind. Appl. Mag., vol. 2, no. 1, pp. 16–19, Jan. 1996.

[2] K. Pietilainen, L. Harnefors, A. Petersson, and H. Nee, “DC-link stabilization and voltage sag ride-through of inverter drives,” IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1261–1268, Jun. 2006.

[3] A. H. Bonnett and H.M. Glatt, “Ten things you should know about electric motors: Their installation, operation, and maintenance,” IEEE Ind. Appl. Mag., vol. 24, no. 6, pp. 25–36, Nov. 2018.

[4] G.C. Jaiswal, M. S. Ballal, D. R. Tutakne, and H. M. Suryawanshi, “Impact of power quality on the performance of distribution transformers: A fuzzy logic approach to assessing power quality,” IEEE Ind. Appl.Mag., vol. 25, no. 5, pp. 8–17, Sep. 2019.

[5] “IEEE Recommended Practice for Monitoring Electric Power Quality”, IEEE Std 1159-2009 (Revision of IEEE Std 1159-1995), pp. c 1–81, Jun. 2009.

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