Leonardo Serpa

Practical Design and Implementation Procedure of an Interleaved Boost Converter Using SiC Diodes for PV Applications

The implementation of an interleaved boost converter (IBC) using SiC diodes for photovoltaic (PV) applications is presented in this paper. The converter consists of two switching cells sharing the PV panel output current. Their switching patterns are synchronized with 180° phase shift. Each switching cell has a SiC Schottky diode and a CoolMOS switching device. The SiC diodes provide zero reverse-recovery current ideally, which reduces the commutation losses of the switches. Such an advantage from the SiC diodes enables higher efficiency and higher power density of the converter system by reducing the requirement of the cooling system. This paper presents also an optimization study of the size and efficiency of the IBC. Based on 1) the steady-state characteristic of the topology; 2) the static and dynamic characteristics of the switching cells; 3) the loss model of the magnetic components; and 4) the cooling system design, the paper provides a set of design criteria, procedures, and experimental results for a 2.5 kW IBC prototype using SiC diodes.

A modified direct power control strategy allowing the connection of three-phase inverter to the grid through LCL filters

This paper proposes a novel approach to adapt a conventional direct power control (DPC) for high-power applications, where a third-order LCL filter is frequently required. The LCL filter can cause a strong resonance and requires additional effort for system control. The application of a DPC for the control of a three-phase voltage source inverter that is connected to the grid through an filter has not yet been considered. The addition of an active damping strategy, together with a harmonic rejection control loop, to the conventional DPC is proposed and analyzed in this paper. The steady-state, as well as the dynamic performance of the proposed system, is verified with simulation results and experimental measurements.

Five-level virtual-flux direct power control for the active neutral-point clamped multilevel inverter

Although multilevel inverters present numerous advantages such as high quality waveform, low switching losses, high voltage capability and low electromagnetic compatibility concerns, some drawbacks are evident. They require a higher number of semiconductors and either multiple isolated dc sources or a bank of series connected capacitors. Consequently, the control complexity increases considerably, since more switching devices normally result in a higher number of possible combinations and the balance of the capacitors has to be guaranteed. But on the other hand, multilevel inverters create an extra degree of freedom due to existing redundant voltage vectors, which produce the same output phase voltage level but with diverse effect on the dc-link and floating capacitors. Among the existing control techniques the virtual-flux direct power control (VF-DPC) has showed to be very suitable for grid connected systems since it controls the active and reactive powers directly without any internal current control loop or PWM modulator. However, in order to adapt the VF-DPC for multilevel systems, specifically for the recently proposed five-level Active Neutral-Point Clamped converter, additional features must be included and/or modified in the inner main control loop. In order to allow the controller to select a higher number of available voltage vectors, the active and reactive power hysteresis strategies are modified. Additionally, a method to balance the dc-link and floating capacitor voltages by applying available redundant states is implemented, based on the actual condition of the voltage across the lower dc-link and floating capacitors, as well output phase currents direction. The proposed five-level VF-DPC has been implemented using a 6 kW five-level prototype and has shown good static and dynamic performance.

Optimized Pulse Patterns for the 5-Level ANPC Converter for High Speed High Power Applications

This paper presents the analysis of the active neutral-point-clamped 5-level converter (ANPC5L) with regards to the total harmonic distortion (THD) for high speed, high power applications. A 5 MW machine with fundamental frequency of 500 Hz is considered. The converter can be switched up to 2 kHz, thereby making the switching frequency to fundamental frequency ratio in the range of 3-4. Different optimized pulse patterns (OPP) are studied for this case. It is shown that no extra filter is necessary to limit the THD in the considered application, when applying the proposed pulse patterns. Topology specific issues, such as the floating capacitor voltage balancing and the switching frequency of the devices, are investigated in detail for the proposed pulse patterns. The results are compared with a traditional pulse width modulation (PWM) approach

A Virtual-Flux Decoupling Hysteresis Current Controller for Mains Connected Inverter Systems

This paper proposes a new simple method of three- phase, sensorless mains voltage, power control with near constant switching frequency based on a decoupling hysteresis current controller (DHC), and the virtual-flux concept. The virtual flux method is used to extract the mains voltage from the switching state, dc voltage, and line currents. From the desired real and reactive powers the three-phase currents are generated using a DHC. The DHC avoids the switching interaction between the phases, and when a variable hysteresis band is employed a near constant switching frequency is achieved. The method is also extended for high power inverter applications that include an inductance- capacitance-inductance output filter, where some undesirable characteristic, such as filter resonance, have to be compensated. Theoretical analysis is presented and the performance of the proposed method is experimentally verified.

Virtual-Flux Decoupling Hysteresis Control for the five-level ANPC inverter connected to the grid

Interest in multilevel power converters has been increased in the last decades due to numerous advantages. Therefore, new control concepts have to be developed or existing control techniques must be extended to take advantage of these benefits.However, although multilevel inverters present numerous advantages, some drawbacks are evident. They require a higher number of semiconductors and either multiple isolated dc sources or a bank of series connected capacitors. Consequently, the control complexity increases considerably, since more switching devices normally result in a higher number of possible combinations and the balance of the capacitors has to be guaranteed. In order to fulfill these requirements, this paper extends the Virtual-Flux Decoupling Hysteresis Control (VF-DHC) scheme previously presented for the classical two-level and the industry standard three-level NPC inverters to operate with the recently introduced five-level Active Neutral-Point Clamped Inverter (ANPC).