A Review of Control Techniques and Energy Storage for Inverter-Based Dynamic Voltage Restorer in Grid-Integrated Renewable Sources

Table 4

Description of power quality issues.

PQ issues	Characteristics	Expression	Constraints
Normal		x(t) = sin(ωt)	ω = 2πf rad/s
Voltage dip/sag	A decrease in RMS voltage	x(t) = [1 − α((t − t1) − (t − t2))] sin (ωt)	0.1 ≤ α ≤ 0.9,
			T ≤ t2 − t1 ≤ 9T
		With harmonic	0.1 ≤ α ≤ 0.9,
		x(t) = [1 − α(	T ≤ t2 − t1 ≤ 9T, 0.05 ≤ α3, α5 ≤ 0.15
		[α1sin(ωt) + α3sin(3ωt) + α5sin(5ωt)]	Σ(αi)^2 = 1
Voltage swell/rise	An increase in RMS voltage	x(t) = [1 + α()] sin (ωt)	1.1 ≤ α ≤ 0.8,
			T ≤ t2 − t1 ≤ 9T
		With harmonic	0.1 ≤ α ≤ 0.8,
		x(t) = [1 + α()]	T ≤ t2 − t1 ≤ 9T,
		[α1sin(ωt) + α3sin(3ωt) + α5sin(5ωt)]	0.05 ≤ α3, α5 ≤ 0.15, Σ(αi)^2 = 1
Transient	A sudden voltage change, current change, or both	x(t) = sin(ωt) +	0.1 ≤ α ≤ 0.8,
			0.5 T ≤ t2 − t1 ≤ 3T,
			300 Hz ≤ fn ≤ 900 Hz,
			8 ms ≤ τ ≤ 40 ms
Harmonic	The distorted voltage or current waveform is due to the existence of integral multiples in fundamental frequency	x(t) = α1sin(ωt) + α3sin(3ωt) + α5sin(5ωt) + α7 sin(7ωt)	0.05 ≤ α3,α5, α7 ≤ 0.15
			Σ(αi)^2 = 1
Voltage flicker/fluctuation	Fluctuations or a random change in the amplitude of the voltage	x(t) = [1 − α sin(2πβt)]sin (ωt)	1.1 ≤ α ≤ 0.2,
			5 Hz ≤ β ≤ 20 Hz
Voltage interruption	Reduced supply voltage or charge current to below 0.1 pu	x(t) = [1 − α()] sin (ωt)	0.9 < α ≤ 1,
			T ≤ t2 − t1 ≤ 9T