A new two-stage voltage source inverter with modulated DC-link voltage and reduced switching losses

This paper proposes a new DC/AC power converter topology that is obtained by merging a buck type DC/DC converter and a DC/AC three-phase PWM Voltage Source Inverter (VSI) without the need of the passive components (smoothing inductor and capacitance) between the two stages. The novel topology is characterized by less hard switchings needed to synthesize the desired output voltage states, mostly because the average voltage seen by the VSI is modulated in such a way that enables the elimination of its zero voltage state and allows for some zero voltage switchings, reducing the switching losses, that makes this topology more suitable for higher frequency operation, which would ultimately reduce the size of the converter in applications where a load side output filter needs to be fitted

A hybrid indirect matrix converter immune to unbalanced voltage supply, with reduced switching losses and improved voltage transfer ratio

Achieving a compact and efficient design of power electronic converters is not a straightforward procedure: minimizing the size of the filter requires a higher switching frequency that causes additional switching losses that will require a larger heatsink and therefore will increase the equipment size. A matrix converter (MC) is known to have smaller switching losses than a Voltage Source Inverter (VSI) and therefore a greater potential for size reduction but has higher conduction losses. A two-stage Indirect MC (IMC) behaves similar to a MC but its losses follow a profile similar to a VSI. The two-stage hybrid IMC which is the latest development, offers a significant improvement in the voltage transfer ratio and immunity against unbalanced voltage supply but due to the additional intermediary stage, has even higher conduction losses than indirect MCs. This paper proposes a new control strategy for a hybrid IMC that will improve both the voltage transfer ratio and the efficiency of the converter at maximum output voltage by modulating the DC-link voltage across the inverter stage in order to eliminate the zero-voltage states and their corresponding commutations

A new single-stage current source inverter for photovoltaic and fuel cell applications using reverse blocking IGBTs

Renewable energy sources such as photovoltaics (PVs) or fuel cells (FCs) are not fitted for direct power grid connection because they deliver DC voltage and current. This is why a power electronic interface is needed, consisting usually of a current-mode operated step-up DC/DC converter with/without isolation that boosts the voltage at a level that can be processed by a DC/AC inverter. This paper presents the implementation of a three-phase power electronic interface for PV/FCs that uses a single conversion stage approach based on a current source inverter (CSI) topology that would need only six reverse blocking IGBTs. In order to overcome the poor switching behavior of this device, a new way of implementing the CSI is proposed, which is proved to be more efficient. A new cost-effective CSI topology for multiple DC sources independently controlled is also proposed.The performance is assessed both in simulation and experimental

A hybrid indirect matrix converter immune to unbalanced voltage supply, with reduced switching losses and improved voltage transfer ratio

Achieving a compact and efficient design of power electronic converters is not a straightforward procedure: minimizing the size of the filter requires a higher switching frequency that causes additional switching losses that will require a larger heatsink and therefore will increase the equipment size. A matrix converter (MC) is known to have smaller switching losses than a Voltage Source Inverter (VSI) and therefore a greater potential for size reduction but has higher conduction losses. A two-stage Indirect MC (IMC) behaves similar to a MC but its losses follow a profile similar to a VSI. The two-stage hybrid IMC which is the latest development, offers a significant improvement in the voltage transfer ratio and immunity against unbalanced voltage supply but due to the additional intermediary stage, has even higher conduction losses than indirect MCs. This paper proposes a new control strategy for a hybrid IMC that will improve both the voltage transfer ratio and the efficiency of the converter at maximum output voltage by modulating the DC-link voltage across the inverter stage in order to eliminate the zero-voltage states and their corresponding commutations

Hybrid matrix converter topologies: an exploration of benefits

Matrix converters are direct AC/AC power converters that can operate with sinusoidal output/input voltage/currents without the need of passive components to store energy, which means that they are grid friendly and have a great weight/volume reduction potential. Hybrid power converters are arrangements of two different type of converters, a main one, processing the bulk of the power interconnected with an auxiliary one, more versatile, processing only a fraction of the power, with the purpose of improving the main converter performance and/or mitigate some of its drawbacks. This paper will review a few hybrid matrix converter solutions developed to address the main drawbacks of the matrix converter technology: the limited (≤0.866) voltage transfer ratio and the sensitivity to power supply disturbances

A two-stage power converter for welding applications with increased efficiency and reduced filtering

The power supply technology used in welding applications changed dramatically from manually tap-controlled 50Hz bulky transformers which had large leakage inductance to provide stable arc burn to switch-mode fast controlled highfrequency power electronics. Nowadays, the typical converter configuration consist of a diode rectifier supplying via a large electrolytic capacitor a smooth DC-link voltage to a high switching frequency H-bridge inverter that steps down the voltage and provides isolation via a high frequency transformer whilst operating with adjustable dutycycle to maintain the output current constant. This topology allows for important size reduction since the size of magnetics decreases rapidly with the increase of the frequency. This paper proposes a more complex two-stage configuration with a buck DC/DC converter operating at a reduced switching frequency to feed adjustable voltage to an H-bridge inverter, which is operating always with the required voltage at 50% dutycycle, enabling in addition the minimization of the output filter size and of the switching losses

Assessing the benefits of installing energy storage in a household equipped with photovoltaic panels

This paper evaluates the technical and financial impact of installing energy storage in a house equipped with Photovoltaic (PV) panels subject to the Feed-In Tariff (FIT). An additional benefit of installing energy storage is the possibility to purchase electricity off-peak (overnight) at a cheap rate and replace consumption during day/peak time and for this reason, the Economy7 tariff is considered. The studies carried out are using real data of PV generation and household consumption continuously recorded over a week for each of the four seasons, from a UK installation. A functional model of the battery system is implemented that includes voltage dependency versus state of charge and maximum charging and discharging currents, that account for the limitations of the amount of charge - size dependant and current that can reflect the power capability of the battery to preserve high conversion efficiencies and lifetime. As initial investigations point to a rather large battery system to maximize the synergy between PV and energy storage, the paper investigates how the performance indicators vary with the battery size. It is found that there may be a critical battery size up to which the peak rate consumption and the PV energy export decrease more rapidly. Above this critical point which in this study lies at around 25-30% of the battery size that would allow full local use of PV energy generated, the impact of increasing the battery size reduces, therefore the return of investment as a percentage decreases

Comparison of multilevel PWM versus interleaved based sinewave shaping for two-stage current source inverters used in PV applications

This paper investigates the advantages of using interleaved based direct sinusoidal current shaping techniques as alternative to 5-level Pulse Width Modulation (PWM) when used in conjunction to a two stage Current Source Inverter (CSI) in PV applications. By using simulation based modelling it is proven that; in combination with switching harmonic cancellation techniques; for a given output power, direct shaping allows for better utilization of devices and subsequently the minimization of losses without sacrificing power quality

Design and evaluation of an energy storage system for helicopters

This paper presents the design and evaluation of an energy storage system (ESS) for helicopters with the aim to recover the kinetic energy in the rotor available after landing and to be able to control the 270V dc bus voltage during load disturbances. A study is conducted in order to identify the suitable mix of commercially available energy storage devices with the aim of obtaining the minimum weight, exploring also the possibility to implement a hybrid supercapacitor-battery system. On the converter side, commercially available Silicon and Silicon-Carbide devices have been evaluated to achieve also the smallest size/weight

A cost-effective solution to power the gate drivers of multilevel inverters using the bootstrap power supply technique

Multilevel inverters are traditionally seen as a step forward in DC/AC conversion, providing more output voltage levels, better quality of the generated waveform and lower switching losses than the two-level and can process higher voltages with a given forced commutated switch technology. There are also drawbacks associated with this technology: more switching devices and associated gate driver circuitry, more complex modulation and control of the DC-link capacitor voltage sharing etc, which as of now limit its application to the high voltage/power range. This paper proposes a cost-effective solution to implement the power supply needed for powering the gate drivers based on the bootstrap supply technology, which will not need isolated DC/DC supplies for each gate driver, reducing the overall cost of a multilevel assembly and making it more appealing for lower power applications