Double-Carrier Phase-Disposition Pulse Width Modulation Method for Modular Multilevel Converters

Abstract

Modular multilevel converters (MMCs) have become one of the most attractive topologies for high-voltage and high-power applications. A double-carrier phase disposition pulse width modulation (DCPDPWM) method for MMCs is proposed in this paper. Only double triangular carriers with displacement angle are needed for DCPDPWM, one carrier for the upper arm and the other for the lower arm. Then, the theoretical analysis of DCPDPWM for MMCs is presented by using a double Fourier integral analysis method, and the Fourier series expression of phase voltage, line-to-line voltage and circulating current are deduced. Moreover, the impact of carrier displacement angle between the upper and lower arm on harmonic characteristics is revealed, and further the optimum displacement angles are specified for the circulating current harmonics cancellation scheme and output voltage harmonics minimization scheme. Finally, the proposed method and theoretical analysis are verified by simulation and experimental results.

Novel Uninterruptible Phase-Separation Passing and Power Quality Compensation Scheme Based on Modular Multilevel Converter for Double-Track Electrified Railway

“…Hence, every leg has a proportional-integral-resonance (PIR) controller, with their input being the differences between the reference and measured current. The most commonly used pulse generation scheme for the MMC topology is the nearest level modulation (NLM) [24] and the gate control signals are generated for the IGBTs in all sub-modules [25,26].…”

A Fault-Tolerant Control Strategy of Modular Multilevel Converter with Sub-Module Faults Based on Neutral Point Compound Shift

“…When the MMC system operates under PDPWM modulation, we first calculate the number of SMs that need to be input at each moment. Then, in combining the current direction of the bridge arm, the input SM is selected by means of the capacitor voltage sorting algorithm to ensure capacitor voltage equalization of each SM during system operation [19]. For the convenience of description, we take the SM open-circuit fault in the upper arm of a-phase as an example (N = 4) and discuss the fault tolerance capability of single-phase bridge arms.…”

“…Suppose we adopt the improved neutral point AC side shift control strategy and the neutral point compound shift control strategy proposed in this paper, the corresponding symmetrical output line voltage amplitudes are U fault line,ac and U fault line,acdc , respectively. To maximize the output line voltage, we can compare them according to Equation (19) and determine the modulation ratio of the phase voltage m fault j ultimately. If the modulation ratio of any phase among the three is not greater than 0, the system cannot function continuously (j = a, b, c).…”

“…This paper proposes an SM fault-tolerant control strategy based on neutral point compound shift for the MMC system under Phase Disposition PWM (PDPWM) [19] , in hope of solving the problems of complex calculation and limited fault tolerance capability of existing neutral point shift control algorithms. Compared with the current approaches, it has three main benefits: (i) The computational complexity of the fault-tolerant reconstruction adjustment parameters is reduced, and the implementation of the algorithm is simplified by optimizing AC side phase voltage vector reconstruction method; (ii) The proposed neutral point DC side shift control method further increases the number of single-arm faulty SMs that can be fault-tolerant, and improves the fault compatibility; (iii) The optimal neutral point position can be selected based on the compound shift control mechanism of the neutral point DC side and AC side so that the MMC system output line voltage is symmetrical and the amplitude is as large as possible.…”

Energy Balance Control of a Cascaded Multilevel Inverter for Standalone Solar Photovoltaic Applications

“…However, under a case of resistance-inductance (R-L) loads, high voltage spikes occur at the base of the stepped output voltage due to the lack of a path for reverse load currents, which tend to deteriorate power quality [12]. Basic modulations techniques for cascaded multilevel topologies are rooted on the fundamental frequency switching [9], sinusoidal pulse width modulation (PWM) [13,14], and space vector PWM (SV-PWM) [15]. However, in solar PV systems, DC sources of a multilevel inverter topology are supplied by PV modules, as shown in Figure 1, which brings about a series of problems:…”