Energy Storage Requirements Optimization of Full-Bridge MMC With Third-Order Harmonic Voltage Injection

Optimal Suppression Strategy for Capacitor Voltage Ripples of Hybrid MMCs Under Unbalanced Grid Voltages

“…The variables are then substituted into (20)- (22) to calculate the amplitudes of the fluctuations of the three-phase arm power. The value of the objective function P is calculated by substituting |Ppx_1|, |Ppx_2| and |Ppx_3| into equation (23), and the values are recorded as a data group (k2, φ2, k3, φ3, m, P) with the corresponding variables. Then the values of k2, φ2, k3, φ3 and m are updated and the above process is repeated to obtain the optimal injection parameters (k2min, φ2min, k2min, φ2min) and the optimal modulation index mopt by finding the data group that makes the minimum value of the objective function P.…”

“…The effect of THVI on regulating the capacitor voltage ripples has been analyzed in [23]. The study also shows that the MMC modulation index can be improved by injecting third-order harmonic voltage, which can reduce SM voltage ripples.…”

Submodule capacitance requirement reduction with capacitor voltage ripple suppression in MMC

“…Similarly, the arm current RMS of normal operation (I nor ) can be calculated with letting g = 0 in (23). Combining the mathematical relationship of (3) and (10), the expression can be derived as…”

“…However, this method is realised at a relatively low modulation ratio, otherwise arm voltage over-modulation will occur. Besides, common mode voltage injection and modulation ratio adjustment are utilised together in [22,23]. Adjusting modulation ratio to 1.414 can eliminate 1 ω st fluctuation at unity power factor and then injecting 3 ω rd common mode voltage is able to reduce the 2 ω nd capacitor voltage fluctuation.…”

Optimal Second-Harmonic Current Injection for Capacitor Voltage Fluctuation Reduction in Hybrid MMCs Under Grid-Side SLG Faults

“…However, the high volume/weight and cost of MMC-HVDC are still the concerns of manufacturers and market players. Submodule (SM) capacitors of an MMC account for about 1/2 of its volume [5], [6]. Therefore, it is necessary to reduce the capacitance of SM capacitors so as to reduce the overall volume/weight and cost of the MMC.…”