For a grid-connected inverter, a constant switching frequency hysteresis current control (HCC) technique based on targeted trajectory of current space vector (HCC-TTCSV) is proposed. The harmonic spectrum of inverter line-to-line voltage, produced by the proposed HCC-TTCSV, is ensured to exhibit similar characteristics to that of voltage-controlled conventional seven-segment space vector modulation (SVM) technique. The proposed current controller is a novel one (i.e., first of its kind) that allows the phase currents to be checked with online calculated current boundaries in stationary abc reference frame. Instead of following a current error boundary, phase current boundary check is performed. The phase current boundary values during every seven-segment switching cycle, however, are found out by observing the projections of vertices of targeted trajectory of current vector along abc axes using few trigonometric relations. The proposed controller is designed for three-phase two-level voltage-source inverter (2L-VSI), and it works well for both L filter and LCL filter. Compensation methods to overcome the current distraction effect caused by factors such as finite rate of current sampling, dead time, gate driver circuit's propagation time, and other nonidealities of the system are also discussed in detail. Theoretical background is established, and experimental verification is presented for validation.

With ever-increasing renewable power penetration, the reliable operation of grid interfaced inverter is an important criterion. The availability of a grid-connected multilevel inverter is relied upon the correctness of identifying faulty switch, if any, during operation and implementation of a fault-tolerant modulation technique to run the inverter without tripping off even under faulty conditions. Although having a large number of switches in a multilevel inverter throws challenges for the detection and localization of faults, it is a boon because power can still flow through alternative paths. In pursuit of this objective, this paper utilizes a T-type based hybrid multilevel topology where certain faulty conditions are created. The proposed fault detection scheme begins with the fast identification of faulty phase, achieved by monitoring the absolute phase error variable derived from normalized phase currents. Subsequently, the localization of faulty switch is fulfilled by intricate analysis of several current and voltage measurements. Notably, the proposed scheme does not need additional sensors to carry out all of these, where finally, a carrier-based fault tolerant scheme is devised to encounter open switch faults. The effectiveness and feasibility of the proposed scheme are evaluated by simulation studies followed by experiments on a seven-level inverter prototype.

For any grid connected system such as D-STATCOM, the conventional hysteresis current controller (HCC) for a two-level voltage source inverter (VSI) is a popular choice. It uses fixed bands in each of the three phases to contain the current errors. Although HCC is simple to implement, it has few drawbacks i.e, poor-employment of zero vectors and random switching among the available switching vectors, which may lock into limit cycles and increased switching losses of the inverter. Out of many other hysteresis techniques, a space vector modulation based technique named as SVM-HCC effectively selects a reduced set of vectors for hysteresis current control in every sector of space vector plane but its switching sequence is not optimal. Alternatively, following a different approach, the space vector hysteresis current controller (SVHCC) manifests systematic pattern in the vector switching where the sequence of inverter voltage vectors is similar to that of a voltage controlled space vector pulse width modulation (VC-SVPWM) scheme. This better way of switching in SVHCC tends to reduce the distortion of the VSI output current, which also appears as reduced ripples in the current. A comparative study on quantifying these differences among HCC, SVM-HCC and SVHCC is first time executed in this work and they are further validated using the results of simulation studies and hardware experimental investigations.

For the high and medium power level grid integration of permanent magnet synchronous generator (PMSG)-based wind energy conversion systems (WECS), the industry utilizes back-to-back multilevel converters. The three-level neutral point clamped (NPC) converter among them, is a popular choice due to its advantages, such as lower voltage stress, reduced switching losses, and improved power quality. However, practical NPC-based back-to-back converters often suffer from neutral point voltage imbalance, which results in significant ripple in the grid current and torque of PMSG-based WECS. This research paper focuses on the a zero sequence voltage (ZSV) injection method for carrier-based pulse width modulation of a three-level NPC back-to-back converter, aiming to mitigate above issues and discusses the different mode of operation based on ZSV injection on machine side converter and grid side converter. This paper also concludes that the phase current from the converter side with higher magnitude has a greater effectiveness in achieving neutral point balance when utilizing the zero sequence voltage (ZSV) method. If ZSV is injected into both side of back-to-back converter, it will give better result for neutral point balancing for low and high modulation indices. The efficacy of this method is presented using simulation study.

In this article, a novel pulsewidth modulation (PWM) technique is proposed for an existing space vector hysteresis current controller (SVHCC) scheme. A three-level neutral-point-clamped (NPC) inverter is used for dual purpose of shunt active power filtering and solar photovoltaic (PV) power integration to a distribution grid. This dual-purpose NPC inverter utilizes the proposed PWM technique for solving the neutral-point voltage-balancing issue in a unique way. Due to the inherent advantages of the SVHCC, the current control is characterized by fast action and optimal switching. A single reference current required for both filtering and maximum PV power integration is generated using instantaneous power theory, where a diode bridge rectifier load is considered to demonstrate the controller performance while compensating nonlinear current components. Thus, not only a unique space-vector-based PWM technique is adopted for fast-tracking of currents, but also a sliding current error boundary is used for the first time. This sliding technique tackles the dc-link balance issue of the NPC inverter while controlling the output currents simultaneously. The simulation and hardware results prove the aforementioned performance and demonstrate the efficacy of the proposed PWM current controller.

A non-linear hysteresis current controller (HCC) for a 2-level voltage source inverter (VSI) conventionally uses fixed-bands in individual phases for limiting the current errors. The HCC has advantages such as easy implementation, fast transient response, but it also has few disadvantages such as non-utilization of zero voltage vectors and haphazard switching of voltage vectors which may lead to limit cycles oscillations. Another type of non-linear current controller, the space vector hysteresis current controller (SVHCC), exhibits coordinated switching pattern where the inverter switching vectors tend to be similar to that of a voltage controlled space vector pulse width modulation (VC-SVPWM) scheme. This kind of optimized switching in SVHCC helps in the reduction of distortion in inverter output current injected to a grid. A comparative study of HCC and SVHCC is carried out in this work to study the distortions manifested as d-axis and q-axis current ripples. In this paper, the differences of these two PWM techniques are observed using rigorous simulation studies with respect to two operating conditions: i) distributed generation (DG) alone and ii) DG along with shunt active power filtering.

In this work, a 'smart solar inverter' based on current controlled three level NPC VSI is proposed. The proposed inverter exchanges the available solar power with the grid efficiently and also ensures quality of power at the point of common coupling (PCC). This solar inverter which also works as shunt active filter is controlled with space vector based hysteresis current controller (SVHCC). This type of configuration can fulfill requirements to maintain standard power quality for medium voltage applications. When enough solar power is available, the two-stage power converter working at maximum power point can send the excess photovoltaic power to the electric grid and also compensates the harmonic currents in loads connected at PCC. In the absence of solar power, the converter can work for the power quality improvement including power factor correction. Both Instantaneous Power (IRP) theory and Synchronous Reference Frame (SRF) theory are considered in this work for creating the reference current for the VSI. The current errors in the three phases are controlled by unified manner using space vector based approach. Through simulation studies the proposed scheme is verified under different loading conditions.