Active power decoupling with reduced converter stress for single-phase power conversion and interfacing

Abstract

Single-phase DC–AC power electronic converters suffer from pulsating power at double the line frequency. The commonest practice to handle the issue is to provide a huge electrolytic capacitor for smoothening out the ripple. However, the electrolytic capacitors having short end of lifetime limit the overall lifetime of the converter. Another way of handling the ripple power is by active power decoupling (APD) using the storage devices and a set of semiconductor switches. Here, a novel topology has been proposed in implementing APD. The topology claims the benefit of (1) reduced stress on converter switches and (2) using smaller capacitance value, thus alleviating the use of electrolytic capacitor and in turn improving the lifetime of the converter. The circuit consists of a third leg, a storage capacitor and a storage inductor. The analysis and the simulation results are shown to prove the effectiveness of the topology.

Appendices

Appendix: Steady-state instantaneous power equations derivation

Grid power derivation

Instantaneous power pumped into AC sink

$$\begin{aligned} p_g = v_g i_g \end{aligned}$$

Substituting expression of $v_g$ and $i_g$ from Eqs. (1) and (2), this equation reduces to

$$\begin{aligned}&=\dfrac{V_{gm}I_{gm}}{2}[\cos \alpha - \cos (2\omega t - \alpha )]\nonumber \\&= V_g I_g[\cos \alpha - \cos (2\omega t - \alpha )]. \end{aligned}$$

(17)

Capacitor power derivation

Power stored in capacitor C is

$$\begin{aligned} p_{C} = v_{C} i_C. \end{aligned}$$

(18)

On simplifying Eq. (18), using Eqs. (3) and (4)

$$\begin{aligned} p_C & = V_{Cm}\sin (\omega t + \theta ) I_{Cm}\sin \left( \omega t + \theta + \dfrac{\pi }{2}\right) \nonumber \\ & = - V_{C}I_C \cos \left( 2\omega t + 2\theta + \dfrac{\pi }{2}\right) \nonumber \\ & = V_{C}I_C \sin (2\omega t + 2\theta ) \nonumber \\ & = \dfrac{V_C^2}{|X_C|}(\sin 2\omega t \cos 2\theta + \cos 2\omega t \sin 2\theta )\nonumber \\ & = \dfrac{1}{|X_C|}[ \sin 2\omega t(V_C^2 - 2V_C^2 \sin ^2\theta ) + 2\cos 2\omega t( V_C \sin \theta V_C \cos \theta )]. \end{aligned}$$

(19)

Inductor power derivation

Similarly, for inductor L, power stored is

$$\begin{aligned} p_{L} = v_{L} i_L \end{aligned}.$$

(20)

Solving Eq. (20) using Eqs. (5) and (6) results in

$$\begin{aligned} p_{L} & = V_{Lm}\sin (\omega t + \phi )I_{Lm}\sin \left( \omega t + \phi - \dfrac{\pi }{2}\right) \nonumber \\ & = V_{L}I_L\left[ - \cos \left( 2\omega t + 2\phi - \dfrac{\pi }{2}\right) \right] \nonumber \\ & = -\dfrac{V_L^2}{|X_L|}\sin (2\omega t + 2\phi )\nonumber \\ & = -\dfrac{V_L^2}{|X_L|}(\sin 2\omega t \cos 2\phi + \cos 2\omega t \sin 2\phi )\nonumber \\ & = -\frac{1}{|X_L|}[\sin 2\omega t(V_L^2 - 2V_L^2 \sin ^2\phi ) + 2\cos 2\omega t( V_L \sin \phi V_L \cos \phi )]. \end{aligned}$$

(21)