This study investigates power injection management in photovoltaic systems integrated into microgrids with voltage unbalances. An advanced technique of modulated predictive control is implemented to address variations in voltage frequency and amplitude, incorporating new algorithms based on the study of the operational region, allowing for an expanded operational range of the system. The findings show notable improvements in the system’s availability under these adverse conditions. It’s concluded that such strategies are essential for ensuring effective integration and sustainability of renewable energies in contemporary microgrids, which are subject to network fluctuations.

The need to decarbonate the planet, due to the massive use of fossil energy, has led to turn to employ renewables energies in many applications. Among the most common energy sources are the wind, solar, and sea, being one of the most relevant the solar energy, particularly in some countries as Chile. To transport the energy, solar system must be connected to a middle voltage level lines and therefore different topologies have been proposed where some of them are based on H-Bride. This work presents the use of H-Bridge power converters connected in parallel in the dc side and connected to a transformer in the ac side to pump up to middle voltage level. Additionally, as all phases of the H-Bridge are connected in parallel in the dc side, the third harmonic, typical of this topology, is compensated and therefore the ac waveform results free of low frequency harmonics. To get the maximum power from the solar array, it is employed a maximum power point tracker which uses measuring cells, avoiding oscillations around the maximum power point. The results show the feasibility of the proposal.

Power conversion has gain relevance because of the capacity to transform the electric energy as needed in many applications such as electrical drives, electromobility, reactive power compensation, renewable energies, among others. In this context, the proper control of the power converter may lead to improve the efficiency and protect the entire power converter system. This paper presents a deadbeat control with the capability to enhance the fast dynamic response, typical of this technique, and therefore to be used for current and voltage control applications that require slower dynamic. The proposed technique is implemented in a three-phase power converter with satisfactory results; moreover, this technique is simple and light in computational cost. Finally, to corroborate the proposal, simulations are included with satisfactory results showing an improved dynamic and making the deadbeat control softer as some applications may require.

This paper proposes a hybrid control scheme based upon both a linear and a predictive control approach for a grid-tie inverter for photovoltaic applications. The proposed strategy uses the complex representation of the switching states and splits them choosing the best one without using an iterative loop. The resulting algorithm, in terms of the dynamic and static response, performs like the traditional Finite Set Model Predictive Control (FS-MPC). However, the proposed scheme is easy to implement, it does not need to tune parameters nor need a cost function and nor require iterating all the possible states to choose the best. Over the abovementioned advantages, it has the capability to operate the photovoltaic module at the maximum power point (MPP) and the ability to impose a sinusoidal current at the grid side with a unitary displacement power factor. Preliminary results are presented to validate the proposed control method.

Different maximum power point tracking methods have been developed for photovoltaics systems to extract and inject the maximum power to the grid. This paper introduces an algorithm based on the solar mathematical model and two measuring cells, one in open circuit and other in short circuit. The proposed method uses the model and adjusts the unknown PV internal system variables to specify where the maximum power point (MPP) is placed in the plane I-V or P-V. The PV array, together with a three-phase inverter, controlled by a nonlinear feedback control algorithm, are employed to inject electric power to grid, where the dc voltage of the power converter is regulated to track the MPP. Finally, the results show the feasibility of the proposal where the MPP is accurately estimated by the proposed algorithm.

This paper proposes a mixed linear control and model predictive control (MPC) scheme with extended horizon for a neutral point inverter topology (NPC) for photovoltaic applications connected to the AC network. The strategy is able to minimize the unbalance of the voltages of the capacitors in the DC link and to draw a sinusoidal current on the network with a unity displacement power factor. Unlike other MPCs, the resulting algorithm is easy to implement, the weighing factors of the cost function are not needed, and the computational cost is reduced. These advantages are added to the ability to operate the photovoltaic module at the point of maximum power (MPP).

This paper proposes an algorithm capable of estimate the global maximum power point of a large photovoltaic (PV) array system operating under partially shaded conditions. The power-voltage characteristic of a photovoltaic array is a nonlinear function that becomes more complex under partial shading conditions, in fact, the power-voltage curve may exhibit multiple local maximum power points. The proposed algorithm uses two PV reference cells, every 900 m2, one operating in open-circuit and the other one in short-circuit, to estimate the solar radiation and the ambient temperature conditions of the PV arrays. The results show an estimation error of the ambient conditions lower than 1% of the actual values. As a result, the arrays provide the maximum power possible for any distribution of irradiance and temperature conditions.

To generate medium and high voltage with low Total Harmonic Distortion (THD) are used multilevel converters, through use of low voltage semiconductors devices, for applications as AC drives, PV farms and active power filters. This converter uses between the AC supply and the power cells a multipulse transformer, which is in charge of the harmonic cancellation of the input current harmonics generated by the three - phase rectifier. This transformer is expensive, heavy, bulky and must be designed according to the power, and the number of power cells. This work uses a THD minimization strategy based on a Finite Control Set - Model Predictive Control (FCS - MPC), which propose change the multipulse transformer by a simpler transformer, achieving a low THD in the input current of multi-cell AFE rectifier. The work is centered in the solution in one disadvantage of the FCS - MPC, high switching frequency. To solve this drawback, an additional objective function is used, which reduces the states changes of the power switches. Unfortunately, because of this the FCS - MPC loses an advantage, fast dynamic response to changes. In order to improve this issue, is necessary a modified control scheme, which detects the steady state and transient state to change the objectives of the FCS-MPC. Simulation results shows the feasibility of the proposed control.

Proportional Resonant Control (PRC) is a well-known control technique applied on ac systems in order to ensure zero steady state error for sinusoidal references. However, this control technique is not suitable to operate in a variable frequency environment, which is typically found on weak micro grids and aircraft systems. Once the controller is designed, the resonant frequency is fixed, and therefore no zero steady state error can be ensured under operating frequency fluctuations. This paper extends the resonant control approach to operate in a larger frequency range in order to be applied in power inverters and achieving zero steady state error. A back-to-back topology case is studied, connected to a distorted supply (with variable frequency) feeding a critical load. The load-connected to the back-to-back topology- requires a given frequency and amplitude voltage which is easily achieved if the grid side converter successfully regulates the dc link voltage. In addition, a desired power factor at the point of common coupling can also be imposed. The approach is based in a discrete implementation of the PRC, where its resonant frequency tracks the grid frequency, independently of grid frequency variations. This issue is mathematically demonstrated and tested with accurate results.

This paper presents a deadbeat control technique applied in a voltage source rectifier to regulate both the dc voltage (active power) and reactive power injected to the grid. As the deadbeat control is based on the system model, it leads to a faster response, without overshoot and no need to tune the controller parameters. Hence, it is used to fully control the voltage source rectifier, achieving a fast dynamic response for both the dc voltage and the power factor at the point of connection. However, there are some issues related to the high amount of power required to reach the references -especially in the dc voltage- in a few control steps. The proposed technique also protects the equipment by limiting the maximum power drained to/from the source. The mathematical development is made as a function of the converter power in order to limit it, but at the same time tracking the references with high dynamics, characteristic typical of deadbeat control.

This paper proposes a control strategy for a single-stage, three-phase photovoltaic (PV) system connected to a distribution network. The control entails obtaining the maximum power point of the PV system by means of a control strategy that is based on an inner current-control loop and an outer DC-link voltage regulator. The current-control mechanism decouples the PV system dynamic from those of the network and searches for unitary power factor at the grid side. The DC-link voltage-control scheme achieves maximum active power output. The maximization of the output power is performed by operating the PV array at its maximum power point that is estimated by a proposed technique that uses two PV measuring cells, one operating in open-circuit and the other one in short-circuit.

Power quality and reliability are inherent characteristics of the cascaded multilevel converters. However, in some converters, efforts should be made to ensure the durability and reliability of the equipment. This is the case of the single-phase current source cascaded inverter (SPCS-CI) in which, due to possible differences in the DC input current to each inverter of the system, it will be necessary to limit each output voltage of each unit. This can be done through a linear control strategy. In this work, the model and the mathematics of the problems caused by unbalanced DC currents in the described cascaded system are presented. Furthermore, a control scheme based on d-q reference frame components is proposed. Along with this, a control for the DC component voltages in the individual outputs of each inverter is added, which cannot be compensated completely by the d-q scheme. The proposed control strategy is a linear scheme with an updatable decoupler that allows to control d-q and DC voltages in a set of single-phase current source inverters disposed in a cascaded arrangement. Simulated results show the effectiveness of the proposed scheme.

Multilevel converters are widely used in medium voltage applications. One of the most popular topologies in this field is the 18 pulses diode rectifier, which uses a muItipuIse transformer that realizes a current harmonics cancelation that are generated by the three phase diode rectifiers. In this work an efficiency comparison of the aforementioned topology and a Multi-Cell Active-Front-End (AFE) Rectifier operating with Finite Control Set - Model Predictive Control is performed. This efficiency comparison is focused on the rectifier losses divided into two types. The first one is the semiconductors switching and conduction losses. The second one evaluates the transformer losses, which are studied under two criteria: copper losses (Standard IEEE C57.10-1998) and the K - Factor (Standard IEEE / ANSI C57.110). The results show that the diode based rectifier topology has lower semiconductors losses, while the topology based on AFE rectifiers has lower transformers losses and a less complex design. Indeed, a reduction of a 7.2% in copper losses is achieved in the transformer secondary with respect to a multi-pulse transformer secondary.

This work compares multi-cell topologies based on Current Source Inverters (CSIs) which are connected in a Cascade H-Bridge (CHB), where the large DC inductor size needed to compensate the oscillating power drained by the inverter is the main drawback. In order to reduce the DC inductor size, two compensation methods which compensated the oscillating power are evaluated and compared with the basic topology that use a large DC inductor. The first method consists in reducing the oscillating power through active compensation, which needs to supply the oscillating power from the rectifier, and the second method consists in reducing the oscillating power through magnetic coupling. The comparison considers the operating region, the DC inductor size, the magnetic power requirements, and the cell supply voltage requirements. Because the operating region is based on the converter and load parameters but independent of the DC inductor value, the passive parameters are designed as a function of the imposed rectifier input current quality and the load voltage THD. The comparison is done for a 9.33 MVA topology, simulating in PSEVI® in order to corroborate the components design and both the input current and load voltage quality. The operating region comparison is computed with one and two cells per phase and the achieved DC inductor reduction.

Single-phase inverters have gained important acceptance last time. This is because single phase inverters have been used in renewable energy, ac drives and many other applications and controlled by name ways as linear, nonlinear predictive between others. This paper studied the control of a Single-Phase Current Source Inverter (SP-CSI) for multi-cell and three-phase applications. Cascaded H-Bridge (CHB-CSI) topology is formed by the stack of SP-CSI, with all advantages that CHB implies, as modularity and commutation noise reduction. However the control for single-phase systems cannot be achieved by Park Transformation if the current load or the current source are unbalanced. Therefore, this work proposed the Proportional Resonant Control (PRC) for the CHB based on CSIs, where the control study is formulated in continuous as well as discrete time. To complete this study a stability analysis is accomplished showing the feasibility of this control for CSI. Finally, simulation results are shown in order to corroborate the mathematical and theoretical analysis.

Multilevel inverters are the alternative for medium voltage applications. Within the inverters types there are symmetric and asymmetric topologies. The asymmetric inverters have different DC voltage values. The most common topology is when the different cells are implemented in cascade arrangement, where the DC voltage are in multiples of 3, obtaining an AC voltage with 3n= 27 levels (n = 3 cascaded inverters). This topology provides a load voltage with low harmonic content, THD <; 3%. However, this high quality voltage has a non-negligible drawback, which is the presence of regeneration in some of the inverters, independent of load type. This phenomenon is due to the modulation technique (Nearest Level Modulation) used by this inverter. In this work, the asymmetric 15 level inverter is presented. This inverter is designed to avoid the regeneration problem - power flow from the load to the inverter - in some of the power cells. This is achieved by obtaining the firing angles associated with the power cells considering a minimum load voltage THD. Finally, a power flow analysis is accomplished and simulated results show the feasibility of this approach.

A switching losses analysis is performed for an asymmetric multilevel Shunt Active Power Filter aimed to simultaneously compensate linear and nonlinear currents. The asymmetric approach consists in the inclusion of two types of modules; one meant for reactive power compensation and the other to cancel out the harmonic currents. Using the non-ideal behavior of the switching process in the power valves, the commutation losses of the presented approach are determined. Moreover, a comparison is performed with the symmetric counterpart and a power losses evaluation is made for both approaches. The analyses are carried out for a single operating point and for the entire operating region, considering the distorted power coming from the load. The presented results are supported with theoretical considerations and simulated waveforms.

Distributed and nonconventional power generation sources could lead to a wide varying grid frequency, particularly in weak systems or islanding mode operation of micro-grids. This work studies a predictive control scheme for power converters that are directly connected to the AC network featuring large frequency variations. The proposed scheme considers a fixed number of samples per period independent of the network frequency, leading to a variable sampling time under varying frequency conditions. This feature is advantageous when frequency has an important operating range because it ensures a constant resolution of the measured system variables. As discrete predictive control requires the sampling time to make accurate predictions, a synchronization system is proposed that ensures a fixed number of samples per cycle through continuous adjustment of the sampling time. Simulations show good performance of the proposed algorithms.

The main drawback of a Multi-Cell topology based on Current Source Converters is the oscillating power drained by the single-phase inverters from the DC link which requires a large DC reactor in order to avoid a significant variation of the DC current. In this work, a control scheme is proposed in order to compensate the oscillating power, avoiding to oversize the DC reactor at the expense of increasing the distortion of the input currents in each power cell and the instantaneous peak of the modulation index. However, the overall input currents present very low distortion and the instantaneous peak of the modulation index can be reduced by properly designing the multi-pulse transformer in terms of voltage ratio and phase shift. Both, the input currents distortion and the effect in the modulation index are mathematically characterized. Simulation result illustrates the effectiveness of the proposed control approach.

A comprehensive solution to simultaneously compensate both reactive power and currents harmonics is presented for a multilevel STATic COMpensator (STATCOM). The proposed approach includes asymmetric power cells that independently compensate reactive power at fundamental frequency and cancel out the current harmonics coming from a nonlinear load. The presented analysis demonstrates that, under certain conditions, the modules aimed for harmonic cancellation require lower power than the modules that compensate the fundamental power factor. Thus, each module can be implemented with specialized power valves in order to improve the overall system performance. Simulated preliminary results confirm the correctness of the proposed approach.

Due to the increasing use of distributed and non-conventional power generation sources, grid synchronization and control of static power converters under variable grid frequency is of particular interest. This work develops a discrete-time phase locked loop (PLL) based on a rotating reference frame to be used in variable frequency systems. The PLL is used in combination with a time-varying transformation based on a rotating frame for control purposes. Finally, for a back-to-back static converter topology, linear and nonlinear control strategies are proposed and evaluated under frequency variations and different operating points. The results - including stability analysis - show their particular performance under frequency variations.