Abstract
Multilevel converters have seen rising demands in the past decades, due to their increased power ratings, enhanced power quality, low switching losses and reduced electromagnetic interference. Prominent among them are the three-level (3L) neutral point clamped and the flying capacitor inverter topologies along with their derivatives. Nevertheless, the main drawback of these topologies is the requirement of a front-end boost DC–DC converter to compensate the high dc-link voltage demand, which is usually twice the grid peak voltage. This multi-stage power conversion further pulls down the overall system efficiency. A single-stage dc–ac power converter with boost capability offer an interesting alternative compared to the two stage approach. Considering this aspect, a novel three-level three-phase boost type inverter is introduced in this paper for general-purpose applications (prominently grid-connected renewable energy). The proposed inverter would reduce the DC-link voltage requirement to half using the same or even less number of active and passive components, compared to the conventional three-level neutral point clamped and flying capacitor family. The principle of operation and theoretical analysis are discussed in detail. The design methodology along with simulation and experimental waveforms for a 5 kVA inverter are presented to prove the concept of the proposed inverter topology for practical applications.
Highlights
Since the outset of photovoltaic (PV) systems in the mid 70’s, intensive research in terms of technological as well as economical aspects has witnessed remarkable developments
Providing a breakthrough for the conventional converter design was the concept of multilevel inverters (MLI) that evolved in the late 1970’s
In the European grid to switch between the positive and negative waveform for an output of 230 Vrms, at least twice the peak output is required at the DC input. This corresponds to an input voltage of 650 VDC in a voltage source inverters (VSIs), which might be even higher in real-time applications
Summary
Since the outset of photovoltaic (PV) systems in the mid 70’s, intensive research in terms of technological (power electronics and semiconductors) as well as economical (energy efficient) aspects has witnessed remarkable developments. In the European grid to switch between the positive and negative waveform for an output of 230 Vrms, at least twice the peak output is required at the DC input This corresponds to an input voltage of 650 VDC in a VSI, which might be even higher in real-time applications. The proposed topology offers an interesting alternative to the conventional two-stage power conversion with a single-stage dc–ac power converter accompanied by an in-built boost capability. This reduces the number of active and passive components as well as their voltage stress, control complexity and the required DC-link voltage significantly, impacting in the cutback of the cost and size of the system.
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