A PWM method for single-phase cascade multilevel inverters to reduce leakage ground current in transformerless PV systems

Summary This paper presents a series‐parallel photovoltaic (PV)‐storage independent microgrid (MG), where low‐voltage distributed generation units could be connected to power grid conveniently. Moreover, it provides a promising way to form medium voltage MG. For this proposed structure, a decentralized control is proposed. The PV units are controlled by a maximum power point tracking (MPPT)‐based droop control, where MPPT of the PV units is achieved. Storage units are regulated via a “droop” controller dependent its reactive power polarity and take the responsibility of keeping the power supply‐demand balance of the MG. Since all these controllers make decisions only based on their local information, the proposed control is reliable and cost‐effective. Moreover, the small‐signal stability of the system is proved. And simulation results are presented to verify the effectiveness.

Section: Introductionmentioning

confidence: 99%

A series-parallel PV-storage independent microgrid and its decentralized control

Liu

Yuan

et al. 2018

“…From the viewpoint of control in CAMI, due to a particular ratio of DC voltage sources, accordingly, some cells have been operated at high power and some carry low power . Thereby, with the suitable pulse width modulation (PWM) method, switching losses and THD can be reduced with a high number of levels . Traditionally, PWM technique operates high‐power H‐bridge or MAIN bridge at the fundamental frequency and auxiliary bridges are operated at high frequency .…”

Section: Introductionmentioning

confidence: 99%

“…22 Thereby, with the suitable pulse width modulation (PWM) method, switching losses and THD can be reduced with a high number of levels. 23,24 Traditionally, PWM technique operates high-power H-bridge or MAIN bridge at the fundamental frequency and auxiliary bridges are operated at high frequency. 25 With this scheme, CAMI suffers from many problems such as EMI, high switching losses, more complexity, and computational burden increased because many carrier waves are required to increase the number of levels.…”

Section: Introductionmentioning

confidence: 99%

Buck converter-based cascaded asymmetrical multilevel inverter with reduced components

Singh

Dahiya

Saini

2017

Summary In this paper, a new topology of the cascaded asymmetrical multilevel inverter (CAMI) has been presented. In the output voltage of the CAMI, a high number of levels are required to reduce the total harmonic distortion (THD). To increase the number of levels, more auxiliary H‐bridges are required to connect with the MAIN H‐bridge of the CAMI, which increases the number of components, cost, and space for installation. To solve this problem, a low‐rating buck converter is connected with one of the auxiliary bridge. With this modification, any number of levels can be achieved in the output voltage with lesser number of circuit components. To show the ability of the proposed variable voltage CAMI, it is compared with existing cascaded multilevel inverter topologies in terms of number of semiconductor devices, the number of DC sources, variety of DC sources, total standing voltage, the number of semiconductor devices in the current path, efficiency, and THD. In this paper, simulation of the proposed topology with nearest level control modulation has been performed using MATLAB/SIMULINK environment. The output voltage, load current, power factor, power, and THD have been obtained by simulation of 21‐level variable voltage CAMI and are validated by experiment results under a resistive and motor load. Hardware implementation has been done by compiling nearest level control modulation into dSPACE DS1104 R&D controller board.

“…Within this trend, structures of utility scale PV inverters are moving toward multilevel topologies, which provide better power quality, lighter passive filtering components, and capability to remove bulky line frequency transformers. A number of papers have recently appeared in the scientific literature dealing with multilevel inverters investigating, among many structures, cascaded H‐bridge inverters, modular multilevel converters, stacked multicell converter, packed U cells inverters, flying capacitors inverters (FCIs),, and quasi‐Z‐source multilevel converters …”

Section: Introductionmentioning

confidence: 99%

“…Considering n cells, the converter will consist of 2n switches and n-1 capacitors; this converter will give n + 1 levels (the 2 switches of the same cell must be controlled in a complementary way, which will give 2 n combinations with redundant states). Flying capacitors inverter is a competitive topology with the following features: (1) can be expanded to higher output levels (highpower applications) without DC bus extension; (2) offers extended selection of control actions and improves the filters bandwidth through the switching states redundancy; and (3) gives more ride through capabilities by the mean of storage capacitors. This results in a multilevel output voltage with reduced dv/dt ratio, and lower harmonics content.…”

mentioning

confidence: 99%

Enhanced low‐voltage ride‐through capability of flying capacitors inverter using model predictive control

Trabelsi

Ben‐Brahim

Gastli

et al. 2017

Summary This paper proposes an enhancement of the low‐voltage ride‐through (LVRT) capability of multilevel flying capacitors inverter using an improved model predictive control (MPC). The proposed solution is a multiobjective control strategy ensuring simultaneous capacitors' voltages balancing and grid current injection with reduced total harmonics distortion (THD) and unity power factor even under severe voltage sags. The proposed MPC technique makes use of a multioptimization solution for the common problem of weight dissimilarity of the control objectives. The first optimization is achieved by the inclusion of the state variables normalization within the cost function computation. This will provide to the proposed MPC technique more robustness with the ability to take into consideration external disturbances (grid voltage sag) while ensuring the meeting of the state variables constraints. The second one is achieved through accurately tuning the weighting factor based on minimizing the grid current total harmonics distortion and the maximal errors on the capacitors' voltages. Theoretical analysis and simulation results are presented to prove that the presented solution guarantees continuous and smooth power transfer to the grid even under severe voltage sags. The obtained results are validated on a 1‐kW experimental prototype.