scholarly journals Circulating Current Resonant Oscillation in Modular Multilevel Converters for Variable Frequency Operation and Its Suppression Method

2018 ◽  
Author(s):  
Jianyu Pan ◽  
Ziwei Ke ◽  
Risha Na ◽  
Muneer Al Sabbagh ◽  
Julia Zhang ◽  
...  
Keyword(s):  
Variable Frequency ◽  
Resonant Oscillation ◽  
Multilevel Converters ◽  
Circulating Current ◽  
Modular Multilevel Converters ◽  
Suppression Method

scholarly journals Lifetime and reliability improvements in modular multilevel converters using controlled circulating current

2021 ◽  
Author(s):  
Nasiru B. Kadandani ◽  
Mohamed Dahidah ◽  
Salaheddine Ethni ◽  
Musbahu Muhammad
Keyword(s):  
Control Method ◽  
Semiconductor Devices ◽  
Junction Temperature ◽  
Multilevel Converters ◽  
Control Approach ◽  
Circulating Current ◽  
Inherent Feature ◽  
Modular Multilevel Converters ◽  
Current Loading ◽  
Laboratory Prototype

AbstractCirculating current has been an inherent feature of modular multilevel converters (MMC), which results in second-order harmonics on the arms currents. If not properly controlled, the circulating current can affect the lifetime and reliability of a converter by increasing the current loading, loss distribution, and junction temperature of its semiconductor devices. This paper proposes controlled circulating current injection as a means of improving the lifetime and reliability of an MMC. The proposed method involves modifying the reference modulating signals of the converter arms to include the controlled differential voltage as an offset. The junction temperature of the semiconductor devices obtained from an electro-thermal simulation is processed to deduce the lifetime and reliability of the converter. The obtained results are benchmarked against a case where the control method is not incorporated. The incorporation of the proposed control method results in a 68.25% increase in the expected lifetime of the converter and a 3.06% increase on its reliability index. Experimental results of a scaled down laboratory prototype validate the effectiveness of the proposed control approach.

scholarly journals Disturbance-Observer-Based Model Predictive Control for Battery Energy Storage System Modular Multilevel Converters

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2285 ◽  
Author(s):  
Yantao Liao ◽  
Jun You ◽  
Jun Yang ◽  
Zuo Wang ◽  
Long Jin
Keyword(s):  
Energy Storage ◽  
Model Predictive Control ◽  
Predictive Control ◽  
Current Control ◽  
Multilevel Converters ◽  
Battery Energy Storage ◽  
Circulating Current ◽  
Modular Multilevel Converters ◽  
Ac Current ◽  
Battery Energy

Although the traditional model predictive control (MPC) can theoretically provide AC current and circulating current control for modular multilevel converters (MMCs) in battery energy storage grid-connected systems, it suffers from stability problems due to the power quality of the power grid and model parameter mismatches. A two discrete-time disturbance observers (DOBs)-based MPC strategy is investigated in this paper to solve this problem. The first DOB is used to improve the AC current quality and the second enhances the stability of the circulating current control. The distortion and fluctuation of grid voltage and inductance parameter variation are considered as lump disturbances in the discrete modeling of a MMC. Based on the proposed method, the output prediction is compensated by disturbance estimation to correct the AC current and circulating current errors, which eventually achieve the expected tracking performance. Moreover, the DOBs have a quite low computational cost with minimum order and optimal performance properties. Since the designed DOBs work in parallel with the MPC, the control effect is improved greatly under harmonics, 3-phase unbalance, voltage sag, inductance parameter mismatches and power reversal conditions. Simulation results confirm the validity of the proposed scheme.

scholarly journals Circulating Current Suppression in Modular Multilevel Converters With Even-Harmonic Repetitive Control

2018 ◽  
Vol 54 (1) ◽  
pp. 298-309 ◽  
Author(s):  
Shunfeng Yang ◽  
Peng Wang ◽  
Yi Tang ◽  
Michael Zagrodnik ◽  
Xiaolei Hu ◽  
...  
Keyword(s):  
Repetitive Control ◽  
Multilevel Converters ◽  
Circulating Current ◽  
Modular Multilevel Converters

scholarly journals Local Carrier PWM for Modular Multilevel Converters with Distributed PV Cells and Circulating Current Reduction

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5585
Author(s):  
Zaid A. Aljawary ◽  
Santiago de Pablo ◽  
Luis Carlos Herrero-de Lucas ◽  
Fernando Martinez-Rodrigo
Keyword(s):  
Pulse Width Modulation ◽  
Sampling Period ◽  
External Source ◽  
Multilevel Converters ◽  
Pv Systems ◽  
Circulating Current ◽  
Modular Multilevel Converters ◽  
Power Point ◽  
Current Reduction ◽  
Circulating Currents

A new topology has been recently proposed for grid-connected photovoltaic (PV) systems, using modular multilevel converters (MMCs) and distributing PV panels throughout the MMC cells. This topology has two main advantages: it reduces the power losses related to moving the energy into the MMC capacitors from an external source, and it removes the losses and costs related to the DC to DC converters used to track the maximum power point on string converters or central converters, because that task is delegated to MMC cells. However, traditional pulse width modulation (PWM) techniques have many problems when dealing with this application: the distortion at the output increases to unacceptable values when MMC cells target different voltages. This paper proposes a new modulation technique for MMCs with different cell voltages, taking into account the measured cell voltages to generate switching sequences with more accurate timing. It also adapts the modulator sampling period to improve the transitions from level to level, an important issue to reduce the internal circulating currents. The proposed modulation has been validated using simulations that show a consistent behavior in the output distortion throughout a wide operation range, and it also reduces the circulating currents and cuts the conduction losses by half. The behavior of this new topology and this new modulation has been compared to the mainstream topology with external PV panels and also to a fixed carrier modulation.

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