Analysis and implementation of a novel high step-up DC–DC converter with low switch voltage stress and reduced diode voltage stress
Abstracts:A new high step-up dc-dc converter is proposed in this study. This new high step-up converter utilises the input voltage, clamped-capacitor, and the secondary side of the coupled-inductor to charge the switched-capacitor and the secondary side of the coupled inductor also charges two multiplier capacitors in parallel during the turn-on interval of the switch. The input voltage, coupled-inductor, and multiplier capacitors are in series connection to the output to accomplish the purpose of high voltage gain during the turn-off interval of the switch. By adjusting the turns ratio of the coupled inductors, the proposed circuit does not need to be operated at high duty cycle to achieve the high voltage gain. The voltage stress of the switch and diodes can be decreased to cut down the cost. Moreover, the energy of the leakage inductance can be recovered to reduce the voltage spike of the switch. Therefore, the switch with lower conduction resistance can be applied to reduce the conduction loss and increase the efficiency. Finally, simulation and experiments are conducted. A prototype circuit with input voltage of 24 V, output voltage of 400 V, and output power of 200 W is implemented to validate the property of the proposed converter.
Control algorithms based on the active and non-active currents for a UPQC without series transformers
Abstracts:This study presents control algorithms for a new unified power quality conditioner (UPQC) without the series transformers that are frequently used to make the insertion of the series converter of the UPQC between the power supply and the load. The behaviour of the proposed UPQC is evaluated in presence of voltage imbalances, as well as under non-sinusoidal voltage-and current conditions. The presented algorithms derive from the concepts involving the active and non-active currents, together with a phase-locked-loop circuit. Based on these real-time algorithms, and considering the proposed hardware topology, the UPQC is able to compensate the harmonic components of the voltages and currents, correct the power factor, and keep the load voltages regulated, all of this in a dynamic way, responding instantaneously to changes in the loads or in the electrical power system. The control algorithms were distributed in a two-DSP digital control architecture, without any communication between them. Consequently, can be increased the sampling frequency of the acquired voltages and currents and improve the UPQC performance. Furthermore, some constraints of the proposed UPQC are evidenced, particularly when the main voltages are imbalanced. Simulation and experimental results are presented to verify the UPQC performance under transient and steady state conditions.
Finite-time disturbance observer based non-singular terminal sliding-mode control for pulse width modulation based DC–DC buck converters with mismatched load disturbances
Abstracts:This study investigates a finite-time disturbance observer (FTDO) based non-singular terminal sliding-mode control (NTSMC) approach for pulse width modulation based DC-DC buck converters subject to matched/mismatched resistance load disturbances. Considering the mismatched resistance load disturbance which does not act in the same channel as the control input, a novel non-singular terminal sliding-mode manifold incorporating with a disturbance estimation technique is designed. A FTDO-based NTSMC method is introduced for DC-DC buck converter systems. A rigorous finite-time stability analysis is also presented. As compared with the nominal NTSMC and existed SMC+ extended stated observer (ESO) method, the proposed method obtains a better disturbance rejection ability no matter the disturbances satisfy the so-called matching condition or not. Simulation and experimental comparison results are implemented to verify the effectiveness of the proposed control method.
Investigation of the trade-off between switching losses and EMI generation in Gaussian S-shaping for high-power IGBT switching transients by active voltage control
Abstracts:Over three decades of development effort has brought insulated gate bipolar transistor (IGBT) technology to a high-level of maturity. IGBT converters have been widely used in industry. However, the high-speed switching transient of the IGBT-freewheel diode chopper cell causes high-level electromagnetic interference (EMI). Electromagnetic compatibility requirements are normally taken into account by utilising costly EMI filters or shielding on the load and supply side. The risk of this traditional method is to incur a delay in commercialising the converters since identification of the failure causes, modifications, and successfully re-testing are required. A promising alternative is to constrain the EMI at source by introducing active voltage control technique and shaping the IGBT switching transient into a sophisticated `S'-shape. Previously, IGBT switching waveforms have been successfully shaped into an advanced Gaussian `S'-shape with the EMI greatly reduced. In this study, the authors further investigated the trade-off between EMI generation and switching losses in such an S-shaping method. The investigation was carried out in an accurate physical IGBT/diode model that is able to accurately simulate the device switching transient. From the results, it can be seen that by using the Gaussian S-shaping method the trade-off between EMI and switching losses could be much improved.
Design of LCL and LLCL filters for single-phase grid connected converters
Abstracts:Compared with the traditional L filters, the high order LCL and LLCL filters for grid integration of voltage source converters offer better switching harmonic attenuation even with smaller passive elements. However, the inherent resonance of the high order filters complicates the control of the converter and also the design of filter parameters, especially at presence of digital delays and grid impedance variations. This study proposes a simple design procedure for the LCL and the LLCL filters of a delay-based stabilised converter that satisfies the predefined constraints on the converter current ripple, grid current harmonics and the reactive power of the capacitor and at the same time, ensures adequate stability of the simple single loop current control against the resonance. Moreover, the effect of grid impedance on the filter performance and controller stability is taken into account, thus the proposed method is robust against a wide range of grid impedance variations. Experimental results for a 3 kW test rig under steady state and transient conditions confirm the effectiveness of the proposed filter design algorithm.
Input-series and output-series connected modular single-switch flyback converter operating in the discontinuous conduction mode
Abstracts:This study proposes a modular isolated dc-dc converter, based on the input-series and output-series connection of flyback converters operating in discontinuous conduction mode, as an alternative to provide higher voltage capability for medium-voltage applications (1-10 kV), from low-voltage semiconductors and passive components. The proposed architecture allows the modular system to operate with a simplified control scheme thanks to an intrinsic voltage-balancing mechanism. The voltage-balancing mechanism is investigated by theoretical analysis, both for steady-state and dynamic operations. A small-signal ac modelling of the architecture is developed to design the total output-voltage controller. To experimentally verify the proposed technique, a laboratory prototype system with three single-switch flyback converters, with 3 kW output power, 600 V dc input and output voltages, and 40 kHz of switching frequency was built.
Wide input and wide output topology analysis for tapped-inductor converters with consideration of parasitic elements
Abstracts:In this study, a new circuit topology of tapped-inductor DC-DC converter has been introduced, considering the impacts of parasitic elements. The converter is able to provide wide input and wide output voltage range with high efficiency, including buck, boost and buck-boost modes. First, the principle and algorithm of the new converter has been investigated in detail. Then, the power conversion efficiency has been examined under different duty ratios. The voltage gain and efficiency have simultaneously been analysed with various loads. Finally, the experimental results show that the efficiencies of the new topology are high in most ranges, thus verified the correctness of theory and the effectiveness of the proposed topology.
Offset-free feedback linearisation control of a three-phase grid-connected photovoltaic system
Abstracts:In this study, a state feedback control law is combined with a disturbance observer to enhance disturbance rejection capability of a grid-connected photovoltaic (PV) inverter. The control law is based on input-output feedback linearisation technique, while the existing disturbance observer is simplified and adopted for the system under investigation. The resulting control law has a proportional-integral (PI)/almost PI-derivative-like structure, which is convenient for real-time implementation. The objective of the proposed approach is to improve the DC-bus voltage regulation, while at the same time control the power exchange between the PV system and the grid. The stability of the closed-loop system under the composite controller is guaranteed by simple design parameters. Both simulation and experimental results show that the proposed method has significant abilities to initiate fast current control and accurate adjustment of the DC-bus voltage under model uncertainty and external disturbance.
Magnetically coupled boost converter with enhanced equivalent series resistance filter capacitor for DC microgrid
Abstracts:A magnetically coupled boost (MCB) converter with the enhanced equivalent series resistance (ESR) of the filter capacitor for DC microgrid applications has been presented in this study. The proposed MCB converter with enhanced ESR filter capacitor uses only four state variables and exhibits a fourth-order minimum phase behaviour because of the complete elimination of right half plane zero. The characteristic of displaying fourth-order minimum phase behaviour of the proposed MCB converter with the enhanced ESR filter capacitor makes the design and analysis simple. Closed-loop operation of the proposed MCB converter with the enhanced ESR filter capacitor with photovoltaic input using maximum power point tracking has been carried out to verify its applicability in DC microgrid. Steady state and dynamic modelling of the MCB converter has been carried out to demonstrate its advantages. The proposed algorithm is validated on a 145 W prototype through simulation and experimentation.
Modified rectifications for improving the charge equalisation performance of series-connected battery stack
Abstracts:Two modified rectifications for improving the charge equalisation performance of series-connected battery stack are proposed in this study. Not only high reliability can be achieved because only one power switch is required, but also the control circuit is simple due to no voltage sensors. In addition, high efficiency can be achieved because of zero-voltage-switching. In this study, two modified rectifications are presented to eliminate the voltage differences between the odd and even batteries, which are not removed by the conventional methods, and reduce the number of transformer windings and diodes. Hence, the cost, size and complexity of the system can be reduced. The circuit topology and operation analysis of the proposed equaliser are described in detail. Finally, the simulations and experimental results are provided to demonstrate the performance of the proposed charge equaliser.