FEEDBACK AND COMPENSATING CONTROLLER FOR 3-PHASE UPS FOR

LOWER THDS

ByPrashanth reddy

This paper proposes a simple optimal voltage control method for three-phase uninterruptible-power supply systems. The proposed voltage controller is composed of a feedback control term and a compensating control term.

Aim Of This Project

Block diagram of the proposed optimal voltage control scheme.

Major blocks

• Optimal load current observer • Optimal voltage control• three-phase inverter• total harmonic distortion(THD)• uninterruptible power supply (UPS).

Optimal load current observer

• Feedforward control of the load current can provide excellent dynamics in three-phase PWM inverter control. However, the situation becomes more complicated and difficult in a common AC bus, feeding multiple inverter devices, in which multiple current sensors and communication channels are required.

Optimal voltage control

• A voltage controller, also called an AC voltage controller or AC regulator is an electronic module based on either thyristors, TRIACs, SCRs or IGBTs, which converts a fixed voltage, fixed frequency alternating current (AC) electrical input supply to obtain variable voltage in output delivered to a resistive load.

three-phase inverter

• The model of a three-phase inverter can be divided into two categories: one category is based on a synchronous frame system (dq-frame) that usually adopts a PI regulator; another category is built upon a stationary frame system (αβ-frame) that employs the proportional-resonant (PR) regulator

THD

• The total harmonic distortion, or THD, of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.

uninterruptible power supply (UPS).

• An uninterruptible power supply, also uninterruptible power source ,UPS or battery / flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails

Simulation and Experimental Results

• The proposed voltage control algorithm is carried out in various conditions (i.e., load step change, unbalanced load, and nonlinear load) to impeccably expose its merits. In order to instantly engage and disengage the load during a transient condition, the on–off switch is employed as shown in Fig.

Fig. Block diagram of the proposed observer-based optimal voltagecontrol system.

• The resistive load depicted in Fig. 4(a) is applied under both the load step change condition (i.e., 0%–100%) and the unbalanced load condition (i.e., phase B opened) to test the robustness of the proposed scheme when the load is suddenly disconnected.

• Fig. shows the simulation and experimental results of the proposed control method during the load step change.Moreover,

Fig. presents the comparative results obtainedby employing the conventional FLC scheme under the

same condition. Specifically, the figures display the load voltages (First waveform: VL), load currents (Second waveform: IL), and phase

Simulation and experimental results of the conventional FLC scheme under unbalanced load with −30% parameter variations in Lf and Cf (i.e., phase B opened)—First: Load output voltages (VL), Second: Load output currents (IL). (a) Simulation. (b) Experiment.

conclusion

• This paper has proposed a simple observer based optimal voltage control method of the three-phase UPS systems The proposed controller is composed of a feedback control term to stabilize the error dynamics of the system and a compensating control term to estimate the system uncertainties.

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