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This research investigates a low-cost generator and power electronics unit for smallscale (<10kW) wind turbines, for both standalone and grid-connected applications. The proposed system uses a high-inductance permanent magnet generator together with a switched-mode rectifier (SMR) to produce a variable magnitude output current. The high inductance characteristic allows the generator to operate as a current source, which has the following advantages over conventional low-inductance generator (voltage source) systems: it offers simple control, and avoids the need for bulky / costly energy storage elements, such as capacitors and inductors. The SMR duty-cycle is controlled in an open-loop manner such that 1) maximum power is obtained for wind speeds below rated, and 2) the output power and turbine speed is limited to safe values above rated wind speed. This topology also has the ability to extract power at low wind speeds, which is well suited to small-scale wind turbines, as there is often limited flexibility in their location and these commonly see low average wind speeds. The thesis is divided into two parts; the first part examines the use of the SMR as a DC-DC converter, for use in standalone applications. The duty-cycle is essentially kept constant, and is only varied for maximum power tracking and turbine speed / power limiting purposes. The SMR operates in to a fixed voltage source load, and has the ability to allow current and hence power to be drawn from the generator even at low wind and hence turbine speeds, making it ideal for battery charging applications. Initial dynamometer testing and limited wind-tunnel testing of a commercially available wind turbine show that turbine power can be maximised and its speed can be limited by adjusting the SMR duty-cycle in an open-loop manner. The second part of the thesis examines the use of the SMR as a DC-AC converter for grid-connected applications. The duty-cycle is now modulated sinusoidally at the mains frequency such that the SMR produces an output current that resembles a fullwave rectified sinewave that is synchronised to the mains voltage. An additional H-bridge inverter circuit and low-pass filter is used to unfold, filter and feed the sinusoidal output current in to the utility grid. Simulation and initial resistive load and preliminary grid-connected tests were used to prove the inverter concept, however, the permanent magnet generator current source is identified as non-ideal and causes unwanted harmonic distortion. The generator harmonics are analysed, and the system performance is compared with the Australian Standard THD requirement. It is concluded that the harmonics are caused by 1) the low-cost single-phase output design, 2) the use of an uncontrolled rectifier, and 3) the finite back-EMF voltage. The extent of these harmonics can be predicted based on the inverter operating conditions. A feed-forward current compensation control algorithm is investigated, and shown to be effective at removing the harmonics caused by the nonideal current source. In addition, the unipolar PWM switching scheme, and its harmonic components are analysed. The low-pass filter design is discussed, with an emphasis on power factor and THD grid requirements. A normalised filter design approach is used that shows how design aspects, such as cutoff frequency and quality factor, affect the filter performance. The filter design is shown to be a trade-off between the output current THD, power loss, and quality factor. The final chapter summarises the thesis with the design and simulation of a 1kW single-phase grid-connected inverter. The inverter is designed based on the low-pass filter and feed-forward compensation analysis, and is shown to deliver an output current to the utility grid that adheres to the Australian Standards. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375316 / Thesis (Ph.D.) - University of Adelaide, School of Electrical and Electronic Engineering, 2009

[Abstract]: The disadvantages of using solar energy are its capital cost (which is about A$6/W), in comparison to that of conventional sources of energy (which is about A$1.80/W), and its conversion efficiency, which in commercially available Photovoltaic (PV) systems is less than 20%. Consequently, for utility connected PV generation to become a viable alternative energy source, its efficiency needs to be improved, its cost reduced, and the quality of power supplied by the inverters must meet stringent standards.This dissertation describes the research work carried out to optimise the conversion efficiency and to minimise the cost of a single-phase, hysteretic current controlunipolar switched inverter system, for use as an interface between solar panels and the grid network. The 1 kW (peak power) PV system being considered does not useenergy storage batteries and the inverter output is connected to the grid supply without the use of a power transformer. Improvements in the efficiency of such aninverter system often come at the expense of the quality of its output power and an increase in cost. However, in the proposed inverter system the harmonics of theoutput current has been improved without compromising its overall efficiency or its cost. An improvement in power quality has been achieved using a novel AC splitinductorfilter network that reduces electromagnetic interference, prevents unwanted operation of the inverter switches, attenuates switching frequency harmonics,minimises low frequency harmonics and provides an average value of the inverter output current necessary for the removal of DC offset currents.An improvement in inverter efficiency and a reduction in cost has been achieved by omitting the 50 Hz power transformer (transformerless) and by optimising theinverter current control strategies. In Australia, some power supply authorities permit transformerless PV inverters of less than 10 kW rating to be connected to their supply system. However, avoiding the use of transformers can lead to magnitudes of DC offset current outside the limits specified by Australian Standard 4777.2, 2005 being injected into the grid supply. In this project a new cost effective DC offset current controller that removes DC offset current from the output of the inverter has been realised. This result translates into two primary benefits; firstly, a saving of about20% in the cost of the power transformer and in the cost of providing additional solar panels to overcome transformer power losses, and secondly the DC offset controller can also be utilised in inverter applications where power transformers are used, to prevent distortion of the magnetising current.The novel design procedure proposed in this thesis for a current controller takes into account intentional and unintentional switching circuit delays, and yields higherefficiencies without sacrificing power quality or increasing the cost of the inverter system. The inclusion of the effect of circuit delays in the design procedure issignificant as it is shown that delay not only has an adverse effect on the performance of the current controller but also on the efficiency and the power quality of the inverter system.Of paramount importance for the successful completion of this project was the relationship between switching circuit delays and the level of low frequencyharmonics generated by unipolar switched inverters. Theoretical analysis is developed to show why circuit delays, inverter DC input voltage and the inductanceof the current loop, are responsible for low frequency harmonics in unipolar switched and not in bipolar switched inverters. It has also been established that unipolarswitched inverters can be designed to operate within the limits specified by the Australian Standard 4777.2, 2005 and that the low frequency harmonics can be maintained at acceptable levels.For a current controller using unipolar switching, the choice of only one of four equivalent switching combinations of the inverter switches leads to suppression of switching noise, and prevents unwanted switching without the need for additional filters. Results are presented to demonstrate the unique advantage of unipolarswitching over bipolar switching.

Conventional 2-level inverters have been quite popular in industry for drives applications. It used pulse width modulation techniques to generate a voltage waveform with high quality. For achieving this, it had to switch at high frequencies and also the switching is between 0 and Vdc. Also additional LC filters are required before feeding to a motor. 3-phase IM is the work horse of the industry. Several speed control techniques have been established namely the V/f control technique and for high performance, vector control is adopted. An electric drive system comprises of a rectifier, inverter, a motor and a load. each module is a topic by itself. This thesis work discusses the novel inverter topologies to overcome the demerits of a conventional 2-level inverter or even the basic multilevel topologies, for an electric drive. The word ‘multilevel’ itself signifies that inverter can generate more than two levels. The idea was first originated by Nabae, Takahashi and Akagi to bring an additional voltage level so that the waveform becomes a quasi square wave. This additional voltage level brought additional benefits in terms of reduced dv/dt and requirement of low switching frequency. But this was not without any cost. The inverter structure is slightly more complicated than a 2-level and also required more devices. But the advantage it gave was superior enough to such an extent that the above topology (popularly known as NPC) has become quite popular in industry. This topology was later modified to equalize the semiconductor losses among switches by replacing the clamping diodes with controllable switches and such topologies are popularly known as Active NPCs (ANPCs) because of the replacement of diodes with active switches. 3-level flying capacitors were then introduced where the additional voltage level is provided using charged capacitors. But this capacitor voltage has to be maintained at its nominal value during the inverter operation. An additional floating capacitor, which is an electrolytic capacitor is needed for this. Increasing the number of electrolytic capacitors reduces the reliability of the inverter drive since they are the weakest link in any inverters and its count has to be kept to the minimum. By using a H-bridge cell in each of the three phases, three voltage levels can be easily obtained.This is commonly known as Cascaded H-bridge (CHB) multilevel inverter. The above three topologies have been discussed with respect to generation of three pole voltage levels and these topologies are quite suited also. A higher number of voltage levels will reduce the switching frequency even lesser and also the dv/dt. On increasing the number of levels further and further, finally the inverter need not do any PWM switching and just generating the levels is sufficient enough for a good quality waveform and also low dv/dt. But when the above topologies are scaled for more than three voltage levels, all of them suffer serious drawbacks which is briefly discussed below. The diode clamped inverter (known as NPC if it is 3-level), when extended to more than three levels suffers from the neutral point balancing issue and also the count of clamping diodes increase drastically. FC inverters, when extended beyond 3-level, the number of electrolytic capacitors increases and also balancing of these capacitors to their nominal voltages becomes complicated. In the case of multilevel CHB, when extended beyond 3-level, the requirement of isolated DC sources also increases. To generate isolated supplies, phase shifting transformer and 8, 12 or 24 pulse diode rectifier is needed which increases the weight , size and cost of the drive. Therefore its application is limited. In this thesis, the aim is to develop a novel method to develop a multilevel inverter without the drawbacks faced by the basic multilevel topologies when scaled for higher number of voltage levels. This is done through stacking the basic or hybrid combination of these basic multilevel topologies through selector switches. This method is experimentally verified by stacking two 5-level inverters through a 2-level selector switch (whose switching losses can be minimized through soft cycle commutation). This will generate nine levels.Generating 9-levels through scaling the basic topologies is disadvantageous, the comparison table is provided in the thesis. This is true for any higher voltage level generation. Each of the above 5-level inverter is developed through cascading an FC with a capacitor fed H-bridge. The device count can be reduced by making the FC-CHB module common to the selector switches by shifting the selector switches between the DC link and the common FC-CHB module. Doing so, reduces the modular feature of the drive but the device count can be reduced. The FFT plot at different frequencies of operation and the switching losses of the different modules-FC, CHB and the selector switches are also plotted for different frequencies of operation. The next step is to check whether this method can be extended to any number of stackings for generation of more voltage levels. For this, a 49-level inverter is developed in laboratory by stacking three 17-level inverters. Each of the 17-level inverter is developed by cascading an FC with three CHBs. When there are 49 levels in the pole voltage waveform, there is no need to do any regular PWM since the output waveform will be very close to a sine wave even without any PWM switching. The technique used is commonly known in literature as Nearest Level Control (NLC). This method of stacking and cascading has the advantage that the FC and the CHB modules now are of very low voltages and the switching losses can be reduced. The switching losses of the different modules are calculated and plotted for different operating frequencies in the thesis. To reduce the voltages of the modules further, a 6-phase machine has been reconfigured as a 3-phase machine, the advantage being that now the DC link voltage requirement is half of that needed earlier for the same power. This further reduces voltages of the modules by half and this allows the switches to be replaced with MOSFETs, improving the efficiency of the drive. This topology is also experimentally verified for both steady state and transient conditions. So far the research focussed on a 3-phase IM fed through a stacked MLI. It can be observed that a stacked MLI needs as many DC sources as the number of stackings. A 6-phase machine apart from reduced DC link voltage requirement, has other advantages of better fault tolerant capability and better space harmonics. They are serious contenders for applications like ship propulsion, locomotive traction, electric vehicles, more electric aircraft and other high power industrial applications. Using the unique property of a 6-phase machine that its opposite windings always draw equal and opposite current, the neutral point (NP) (formed as a result of stacking two MLIs) voltage can be balanced. It was observed that the net mid point current drawn from the mid point can be made zero in a switching interval. It was later observed that with minimal changes, the mid point current drawn from the NP can be made instantaneously zero and the NP voltage deviation is completely arrested and the topology needs only very low capacity series connected capacitors energized from a single DC link. This topology is also experimentally verified using the stacked 9-level inverter topology discussed above but now for 6-phase application and experimental results are provided in the thesis. Single DC link enables direct back to back conversion and power can be fed back to the mains at any desired power factor. All the experimental verification is done on a DSP (TMS320F28335) and FPGA (Spartan 3 XCS3200) platform. An IM is run using V/f control scheme and the above inverter topologies are used to drive the motor. The IGBTs used are SKM75GB123D for the stacked 9-level inverter in the 3-phase and 6-phase experiments. For the 49-level inverter experiment, MOSFETs-IRF260N were used. Both steady state and transient results ensure that the proposed inverter topologies are suitable for high power applications.

A energia solar fotovoltaica é a forma de produção de eletricidade que mais cresce no mundo. A potência instalada mundial, até o ano de 2010, era de cerca de 40 GWP e a previsão é de que, somente em 2011, este cifra seja aumentada em mais 24 GWP. O inversor é o elemento central dos sistemas fotovoltaicos. Além de executar a conversão da energia elétrica em corrente contínua para corrente alternada, ele também é responsável pelo gerenciamento da energia entregue à rede e pelo seguimento do ponto de máxima potência. O seguimento do ponto de máxima potência (MPPT) é um processo de controle no qual o inversor procura manter o gerador fotovoltaico operando em uma região da sua curva característica na qual o produto corrente × tensão tenha o seu valor máximo, de forma a otimizar a extração de potência do gerador fotovoltaico. A eficiência de MPPT é um número que indica o grau de precisão, tanto em termos de rapidez como de magnitude, com que o seguidor do ponto de máxima potência atinge o seu objetivo. Assim podem ser definidas duas eficiências de MPPT: a eficiência estática, associada a situações em que a irradiância solar permanece constante durante o intervalo considerado, e a eficiência dinâmica de MPPT, que considera os momentos de variação na intensidade da irradiância, resultantes, por exemplo, da passagem de nuvens. As eficiências de MPPT (especialmente a dinâmica) são de difícil determinação, porém a tarefa fica muito facilitada com a utilização de um simulador de arranjos fotovoltaicos. A norma européia EN 50530:2010 Overall Efficiency of Photovoltaic Inverters propôs uma metodologia para a determinação da eficiência dinâmica de MPPT utilizando perfis variáveis de irradiância a serem programados no simulador de arranjos fotovoltaicos. O objetivo central da tese é fazer uma análise experimental da eficiência dinâmica do seguimento de máxima potência de inversores conectados à rede através da comparação dos resultados de eficiência obtidos seguindo a metodologia definida na norma citada com resultados obtidos a partir de medições em tempo real ao longo de um dia, verificando a adequação da norma às situações de campo. Para a obtenção dos dados de entrada do simulador foram medidas, por diversos dias, a irradiância e temperatura de uma célula de referência. Os inversores foram conectados à saída do simulador de arranjos fotovoltaicos e foram reproduzidas as condições de irradiância e temperatura de três dias selecionados em função do grau de nebulosidade, com comportamento dinâmico semelhante aos perfis de irradiância da norma. Os resultados foram, na maioria dos casos, discordantes. Uma análise dos resultados parciais de eficiência dinâmica indicou como causa desta discrepância a dependência que a eficiência dinâmica de MPPT tem com a taxa de variação da irradiância. Conclui-se que, embora as seqüências de irradiância propostas pela norma constituam uma eficiente ferramenta para o diagnóstico de eventuais deficiências no comportamento do seguidor de máxima potência de inversores, a média dos valores de eficiência de MPPT calculados a partir delas não pode, em princípio, ser considerada como representativa de valores diários. / Photovoltaic solar energy is the fastest growing electricity source in the world. The worldwide capacity until 2010 was about 40 GWP and, by the end of 2011, this figure will be increased by another 24 GWP. The inverter is the pivotal element of PV systems. In addition to performing the conversion of electrical energy from direct current to alternating current, the inverter is also responsible for the management of the energy delivered to the grid and for performing the maximum power point tracking. The maximum power point tracking (MPPT) is a control process by which the inverter tries to keep the PV generator operating in a region of its characteristic curve where the product current × voltage reaches its maximum value. The MPPT efficiency is a figure that indicates the degree of precision, both in terms of speed and magnitude, that the MPPT reaches its goal. Thus, two MPPT efficiencies can be defined: the static efficiency, associated to situations in which the solar irradiance does not vary during the considered interval, and also the dynamic MPPT efficiency, which considers the variation of the irradiance intensity as a result, for example, of the passage of clouds. MPPT efficiencies (especially the dynamic) are hard to determine, but the task becomes much easier with the use of a photovoltaic array simulator. The European standard EN 50530:2010 Overall Efficiency of Photovoltaic Inverters proposes a methodology for determining the dynamic efficiency of MPPT using variable irradiance profiles to be programmed into the photovoltaic array simulator. The main objective of this thesis is to make an experimental analysis of the dynamic MPPT efficiency of grid connected inverters by comparing the efficiency results obtained by following the methodology defined in the referred standard with results obtained from real time measurements in the course of a day, checking the adequacy of the standard when applied to field situations. In order to obtain the input data for the simulator, the irradiance and temperature of a reference cell were measured for several days. The inverters were connected to the output of the array simulator, which reproduced the conditions of irradiance and temperature for three days selected according to the degree of cloudiness, having a dynamic behavior similar to the standard irradiance profiles. The results, in most cases, disagree. An analysis of partial results of dynamic efficiency indicated the dependence of the dynamic MPPT efficiency to the rate of irradiance change as the cause of this discrepancy. As a conclusion, it can be stated that, although the sequences of irradiance proposed by the standard are an efficient tool for the diagnosis of deficiencies in the behavior of the MPP tracker, the average efficiency of MPPT calculated from the sequences cannot, in principle, to be considered as representative of the daily values of dynamic MPPT efficiency.

Este trabalho apresenta um método alternativo para sintonia de múltiplos controladores ressonantes aplicados aos sistemas ininterruptos de energia. A proposta do método é fornecer um conjunto de equações algébricas de simples aplicação que possibilite aos projetistas destes sistemas determinar os parâmetros dos controladores ressonantes com múltiplos modos. As equações apresentadas para determinação dos parâmetros do controlador foram obtidas diretamente com base nos parâmetros e nas características funcionais do inversor. Também nestas equações estão presentes constantes as quais garantem que todo o inversor cujo controlador for sintonizado pelo método atenda as especificações estabelecidas pela norma 60240-3. As constantes são determinadas através da formulação do problema por desigualdades matriciais lineares (LMI - Linear Matrix Inequalities) que levam em conta o equacionamento dinâmico do inversor e dos múltiplos controladores ressonantes. A solução do problema satisfaz simultaneamente a minimização do esforço de controle, onde foi empregada a formulação de custo garantido, juntamente com a localização dos polos de malha-fechada para toda a variação admissível de carga, formulada através do procedimento de D-Estabilidade. / This master thesis shows an alternative method for tuning multiple resonant controllers applied to uninterrupted power supply. The method is intended to provide a set of simple algebraic equations that enable designers of those systems to determine the parameters of the resonant controllers through multiple modes. The equations presented for determining the controller’s parameters were obtained directly based on the parameters and functional characteristics of the inverter. Additionally, constants that ensure that every inverter whose controller is attuned by the method meets the 60240-3 specifications norms can be found in these equations. The constants are determined based on the formulation of the problem through linear matrix inequalities (LMI) that take in consideration the dynamic of the inverter and of the multiple resonant controllers. The solution of the problem ensures both the needs for minimization of control efforts at guaranteed cost, along with the location of close-loop poles for every permissible load variation, formulated through the D-Stability procedure.

Este trabalho apresenta um método alternativo para sintonia de múltiplos controladores ressonantes aplicados aos sistemas ininterruptos de energia. A proposta do método é fornecer um conjunto de equações algébricas de simples aplicação que possibilite aos projetistas destes sistemas determinar os parâmetros dos controladores ressonantes com múltiplos modos. As equações apresentadas para determinação dos parâmetros do controlador foram obtidas diretamente com base nos parâmetros e nas características funcionais do inversor. Também nestas equações estão presentes constantes as quais garantem que todo o inversor cujo controlador for sintonizado pelo método atenda as especificações estabelecidas pela norma 60240-3. As constantes são determinadas através da formulação do problema por desigualdades matriciais lineares (LMI - Linear Matrix Inequalities) que levam em conta o equacionamento dinâmico do inversor e dos múltiplos controladores ressonantes. A solução do problema satisfaz simultaneamente a minimização do esforço de controle, onde foi empregada a formulação de custo garantido, juntamente com a localização dos polos de malha-fechada para toda a variação admissível de carga, formulada através do procedimento de D-Estabilidade. / This master thesis shows an alternative method for tuning multiple resonant controllers applied to uninterrupted power supply. The method is intended to provide a set of simple algebraic equations that enable designers of those systems to determine the parameters of the resonant controllers through multiple modes. The equations presented for determining the controller’s parameters were obtained directly based on the parameters and functional characteristics of the inverter. Additionally, constants that ensure that every inverter whose controller is attuned by the method meets the 60240-3 specifications norms can be found in these equations. The constants are determined based on the formulation of the problem through linear matrix inequalities (LMI) that take in consideration the dynamic of the inverter and of the multiple resonant controllers. The solution of the problem ensures both the needs for minimization of control efforts at guaranteed cost, along with the location of close-loop poles for every permissible load variation, formulated through the D-Stability procedure.

A energia solar fotovoltaica é a forma de produção de eletricidade que mais cresce no mundo. A potência instalada mundial, até o ano de 2010, era de cerca de 40 GWP e a previsão é de que, somente em 2011, este cifra seja aumentada em mais 24 GWP. O inversor é o elemento central dos sistemas fotovoltaicos. Além de executar a conversão da energia elétrica em corrente contínua para corrente alternada, ele também é responsável pelo gerenciamento da energia entregue à rede e pelo seguimento do ponto de máxima potência. O seguimento do ponto de máxima potência (MPPT) é um processo de controle no qual o inversor procura manter o gerador fotovoltaico operando em uma região da sua curva característica na qual o produto corrente × tensão tenha o seu valor máximo, de forma a otimizar a extração de potência do gerador fotovoltaico. A eficiência de MPPT é um número que indica o grau de precisão, tanto em termos de rapidez como de magnitude, com que o seguidor do ponto de máxima potência atinge o seu objetivo. Assim podem ser definidas duas eficiências de MPPT: a eficiência estática, associada a situações em que a irradiância solar permanece constante durante o intervalo considerado, e a eficiência dinâmica de MPPT, que considera os momentos de variação na intensidade da irradiância, resultantes, por exemplo, da passagem de nuvens. As eficiências de MPPT (especialmente a dinâmica) são de difícil determinação, porém a tarefa fica muito facilitada com a utilização de um simulador de arranjos fotovoltaicos. A norma européia EN 50530:2010 Overall Efficiency of Photovoltaic Inverters propôs uma metodologia para a determinação da eficiência dinâmica de MPPT utilizando perfis variáveis de irradiância a serem programados no simulador de arranjos fotovoltaicos. O objetivo central da tese é fazer uma análise experimental da eficiência dinâmica do seguimento de máxima potência de inversores conectados à rede através da comparação dos resultados de eficiência obtidos seguindo a metodologia definida na norma citada com resultados obtidos a partir de medições em tempo real ao longo de um dia, verificando a adequação da norma às situações de campo. Para a obtenção dos dados de entrada do simulador foram medidas, por diversos dias, a irradiância e temperatura de uma célula de referência. Os inversores foram conectados à saída do simulador de arranjos fotovoltaicos e foram reproduzidas as condições de irradiância e temperatura de três dias selecionados em função do grau de nebulosidade, com comportamento dinâmico semelhante aos perfis de irradiância da norma. Os resultados foram, na maioria dos casos, discordantes. Uma análise dos resultados parciais de eficiência dinâmica indicou como causa desta discrepância a dependência que a eficiência dinâmica de MPPT tem com a taxa de variação da irradiância. Conclui-se que, embora as seqüências de irradiância propostas pela norma constituam uma eficiente ferramenta para o diagnóstico de eventuais deficiências no comportamento do seguidor de máxima potência de inversores, a média dos valores de eficiência de MPPT calculados a partir delas não pode, em princípio, ser considerada como representativa de valores diários. / Photovoltaic solar energy is the fastest growing electricity source in the world. The worldwide capacity until 2010 was about 40 GWP and, by the end of 2011, this figure will be increased by another 24 GWP. The inverter is the pivotal element of PV systems. In addition to performing the conversion of electrical energy from direct current to alternating current, the inverter is also responsible for the management of the energy delivered to the grid and for performing the maximum power point tracking. The maximum power point tracking (MPPT) is a control process by which the inverter tries to keep the PV generator operating in a region of its characteristic curve where the product current × voltage reaches its maximum value. The MPPT efficiency is a figure that indicates the degree of precision, both in terms of speed and magnitude, that the MPPT reaches its goal. Thus, two MPPT efficiencies can be defined: the static efficiency, associated to situations in which the solar irradiance does not vary during the considered interval, and also the dynamic MPPT efficiency, which considers the variation of the irradiance intensity as a result, for example, of the passage of clouds. MPPT efficiencies (especially the dynamic) are hard to determine, but the task becomes much easier with the use of a photovoltaic array simulator. The European standard EN 50530:2010 Overall Efficiency of Photovoltaic Inverters proposes a methodology for determining the dynamic efficiency of MPPT using variable irradiance profiles to be programmed into the photovoltaic array simulator. The main objective of this thesis is to make an experimental analysis of the dynamic MPPT efficiency of grid connected inverters by comparing the efficiency results obtained by following the methodology defined in the referred standard with results obtained from real time measurements in the course of a day, checking the adequacy of the standard when applied to field situations. In order to obtain the input data for the simulator, the irradiance and temperature of a reference cell were measured for several days. The inverters were connected to the output of the array simulator, which reproduced the conditions of irradiance and temperature for three days selected according to the degree of cloudiness, having a dynamic behavior similar to the standard irradiance profiles. The results, in most cases, disagree. An analysis of partial results of dynamic efficiency indicated the dependence of the dynamic MPPT efficiency to the rate of irradiance change as the cause of this discrepancy. As a conclusion, it can be stated that, although the sequences of irradiance proposed by the standard are an efficient tool for the diagnosis of deficiencies in the behavior of the MPP tracker, the average efficiency of MPPT calculated from the sequences cannot, in principle, to be considered as representative of the daily values of dynamic MPPT efficiency.

A energia solar fotovoltaica é a forma de produção de eletricidade que mais cresce no mundo. A potência instalada mundial, até o ano de 2010, era de cerca de 40 GWP e a previsão é de que, somente em 2011, este cifra seja aumentada em mais 24 GWP. O inversor é o elemento central dos sistemas fotovoltaicos. Além de executar a conversão da energia elétrica em corrente contínua para corrente alternada, ele também é responsável pelo gerenciamento da energia entregue à rede e pelo seguimento do ponto de máxima potência. O seguimento do ponto de máxima potência (MPPT) é um processo de controle no qual o inversor procura manter o gerador fotovoltaico operando em uma região da sua curva característica na qual o produto corrente × tensão tenha o seu valor máximo, de forma a otimizar a extração de potência do gerador fotovoltaico. A eficiência de MPPT é um número que indica o grau de precisão, tanto em termos de rapidez como de magnitude, com que o seguidor do ponto de máxima potência atinge o seu objetivo. Assim podem ser definidas duas eficiências de MPPT: a eficiência estática, associada a situações em que a irradiância solar permanece constante durante o intervalo considerado, e a eficiência dinâmica de MPPT, que considera os momentos de variação na intensidade da irradiância, resultantes, por exemplo, da passagem de nuvens. As eficiências de MPPT (especialmente a dinâmica) são de difícil determinação, porém a tarefa fica muito facilitada com a utilização de um simulador de arranjos fotovoltaicos. A norma européia EN 50530:2010 Overall Efficiency of Photovoltaic Inverters propôs uma metodologia para a determinação da eficiência dinâmica de MPPT utilizando perfis variáveis de irradiância a serem programados no simulador de arranjos fotovoltaicos. O objetivo central da tese é fazer uma análise experimental da eficiência dinâmica do seguimento de máxima potência de inversores conectados à rede através da comparação dos resultados de eficiência obtidos seguindo a metodologia definida na norma citada com resultados obtidos a partir de medições em tempo real ao longo de um dia, verificando a adequação da norma às situações de campo. Para a obtenção dos dados de entrada do simulador foram medidas, por diversos dias, a irradiância e temperatura de uma célula de referência. Os inversores foram conectados à saída do simulador de arranjos fotovoltaicos e foram reproduzidas as condições de irradiância e temperatura de três dias selecionados em função do grau de nebulosidade, com comportamento dinâmico semelhante aos perfis de irradiância da norma. Os resultados foram, na maioria dos casos, discordantes. Uma análise dos resultados parciais de eficiência dinâmica indicou como causa desta discrepância a dependência que a eficiência dinâmica de MPPT tem com a taxa de variação da irradiância. Conclui-se que, embora as seqüências de irradiância propostas pela norma constituam uma eficiente ferramenta para o diagnóstico de eventuais deficiências no comportamento do seguidor de máxima potência de inversores, a média dos valores de eficiência de MPPT calculados a partir delas não pode, em princípio, ser considerada como representativa de valores diários. / Photovoltaic solar energy is the fastest growing electricity source in the world. The worldwide capacity until 2010 was about 40 GWP and, by the end of 2011, this figure will be increased by another 24 GWP. The inverter is the pivotal element of PV systems. In addition to performing the conversion of electrical energy from direct current to alternating current, the inverter is also responsible for the management of the energy delivered to the grid and for performing the maximum power point tracking. The maximum power point tracking (MPPT) is a control process by which the inverter tries to keep the PV generator operating in a region of its characteristic curve where the product current × voltage reaches its maximum value. The MPPT efficiency is a figure that indicates the degree of precision, both in terms of speed and magnitude, that the MPPT reaches its goal. Thus, two MPPT efficiencies can be defined: the static efficiency, associated to situations in which the solar irradiance does not vary during the considered interval, and also the dynamic MPPT efficiency, which considers the variation of the irradiance intensity as a result, for example, of the passage of clouds. MPPT efficiencies (especially the dynamic) are hard to determine, but the task becomes much easier with the use of a photovoltaic array simulator. The European standard EN 50530:2010 Overall Efficiency of Photovoltaic Inverters proposes a methodology for determining the dynamic efficiency of MPPT using variable irradiance profiles to be programmed into the photovoltaic array simulator. The main objective of this thesis is to make an experimental analysis of the dynamic MPPT efficiency of grid connected inverters by comparing the efficiency results obtained by following the methodology defined in the referred standard with results obtained from real time measurements in the course of a day, checking the adequacy of the standard when applied to field situations. In order to obtain the input data for the simulator, the irradiance and temperature of a reference cell were measured for several days. The inverters were connected to the output of the array simulator, which reproduced the conditions of irradiance and temperature for three days selected according to the degree of cloudiness, having a dynamic behavior similar to the standard irradiance profiles. The results, in most cases, disagree. An analysis of partial results of dynamic efficiency indicated the dependence of the dynamic MPPT efficiency to the rate of irradiance change as the cause of this discrepancy. As a conclusion, it can be stated that, although the sequences of irradiance proposed by the standard are an efficient tool for the diagnosis of deficiencies in the behavior of the MPP tracker, the average efficiency of MPPT calculated from the sequences cannot, in principle, to be considered as representative of the daily values of dynamic MPPT efficiency.

Este trabalho apresenta um método alternativo para sintonia de múltiplos controladores ressonantes aplicados aos sistemas ininterruptos de energia. A proposta do método é fornecer um conjunto de equações algébricas de simples aplicação que possibilite aos projetistas destes sistemas determinar os parâmetros dos controladores ressonantes com múltiplos modos. As equações apresentadas para determinação dos parâmetros do controlador foram obtidas diretamente com base nos parâmetros e nas características funcionais do inversor. Também nestas equações estão presentes constantes as quais garantem que todo o inversor cujo controlador for sintonizado pelo método atenda as especificações estabelecidas pela norma 60240-3. As constantes são determinadas através da formulação do problema por desigualdades matriciais lineares (LMI - Linear Matrix Inequalities) que levam em conta o equacionamento dinâmico do inversor e dos múltiplos controladores ressonantes. A solução do problema satisfaz simultaneamente a minimização do esforço de controle, onde foi empregada a formulação de custo garantido, juntamente com a localização dos polos de malha-fechada para toda a variação admissível de carga, formulada através do procedimento de D-Estabilidade. / This master thesis shows an alternative method for tuning multiple resonant controllers applied to uninterrupted power supply. The method is intended to provide a set of simple algebraic equations that enable designers of those systems to determine the parameters of the resonant controllers through multiple modes. The equations presented for determining the controller’s parameters were obtained directly based on the parameters and functional characteristics of the inverter. Additionally, constants that ensure that every inverter whose controller is attuned by the method meets the 60240-3 specifications norms can be found in these equations. The constants are determined based on the formulation of the problem through linear matrix inequalities (LMI) that take in consideration the dynamic of the inverter and of the multiple resonant controllers. The solution of the problem ensures both the needs for minimization of control efforts at guaranteed cost, along with the location of close-loop poles for every permissible load variation, formulated through the D-Stability procedure.