New modulation scheme and voltage balancing control of modular multilevel converters for modern electric ships

Abstract

The distinctive features such as fault-tolerability, modularity, power and voltage scalability have propelled modular multilevel converters (MMCs) as one of the emerging power converter topologies for marine applications. Pulse-width modulation (PWM) schemes are widely used to control the MMCs due to their good control capability and ability to operate at higher switching frequencies. However, the required number of carriers for gating signal generation drastically increases with the submodule count per arm in an MMC. Moreover, these carriers should be accurately synchronised with each other to generate high power quality waveforms. However, it is hard to establish accurate synchronisation between these carriers due to the sampling issues, memory limitations, and computational delays. In addition, the MMC demands reconfiguration of PWM carriers and control strategy for voltage scalability and retrofit applications. To avoid these issues, a simple PWM scheme using one carrier is proposed in this study. The main advantage of the proposed scheme is an easy extension to the n-level MMC with a wide range of output voltage levels. The effectiveness of the proposed PWM scheme along with the capacitor voltage balancing control is demonstrated through detailed simulations and verified experimentally under steady-state and dynamic conditions.

Submodule power balancing control of modular multilevel converters under capacitor degradation

“…2 is implemented using the PLECS and MATLAB software platform with the parameters given in Table 3. The DC‐bus voltage selection and parameter sizing are performed as per the methodology discussed in [6, 39]. Most of the MMC studies assumed that all capacitors of SM having an equal capacitance (3.3 mF), the SM power and VB control approaches show identical performance in terms of waveform quality, power loss, and capacitor ripple.…”

“…In this study, the performance of an MMC with the proposed balancing technique is evaluated at different operating conditions and compared with the conventional VB approach [6]. Simulation studies of a single‐phase MMC using the VB control approach are carried with the aforementioned capacitor values and their results are shown in Fig.…”

“…The status of each SM is determined by comparing the inserted SM index and the SM index as follows: The SM index and status generation based on the arm current direction and number of SMs to be ON is discussed with an example for in Table 2. The required gate pulses for IGBTs are generated from previous and current switching states [ and ] of the SM by implementing a reduced switching frequency algorithm as follows: The proposed control method has reduced the number of comparisons to half in comparison with existing VB algorithms [6, 11]. Therefore, the proposed approach lessens the implementation complexity.…”

“…In recent times, modular multilevel converters (MMCs) have increased research attention due to the unique features of modularity, voltage scalability, fault‐tolerability, and potentiality to generate high power quality output waveforms [1, 2]. Owing to these pivotal characteristics, MMCs have triumphantly formed their way into commercial products in the areas of high‐voltage dc transmission, renewable energy integration, static compensator, railway traction systems, medium‐voltage motor drives, electric ship systems, and charging infrastructure for energy storage systems [2–9]. MMCs necessitate a complex control structure to effectuate the multiple control objectives such as output current control, capacitor voltage balancing (VB), inter‐arm voltage/energy balancing control, and circulating current (CC) suppression control [2, 3].…”

Lyapunov function‐based improved switching command for a boost converter with an inductor–capacitor input filter

“…Switching DC–DC converters are widely employed in many systems in various applications [1–3], e.g. renewable‐energy conversion systems [4], DC microgrids [5], and transportation applications [6]. In particular, DC–DC converters are used to supply energy from the source to the load.…”