Robert Stala

Application of Balancing Circuit for DC-Link Voltages Balance in a Single-Phase Diode-Clamped Inverter With Two Three-Level Legs

This paper presents investigations of dc-link voltages balance with the use of a passive RLC circuit in a single-phase diode-clamped inverter composed of two three-level legs. Application of the balancing circuit in the diode-clamped inverter needs proper PWM generation but the modulation method is the same for both in the balanced and unbalanced state. This method of dc-link voltages balance does not need any measurements or additional control, and this ensures fast response and low energy losses. This paper also presents mathematical analysis of the PWM modulation method and the inverter operation, and an analytical description of the natural balancing process with contribution of the load current and the balancing circuit current. Simulations and experimental results of the inverter with FPGA-based control are presented to confirm the effectiveness of the natural balancing process.

Results of Investigation of Multicell Converters With Balancing Circuit—Part II

This paper presents the results of an investigation of the multilevel multicell converters with a passive RLC balancing circuit applied for the maintenance of the voltage sharing on the capacitive sources of the converters. The topologies of DC/DC, AC/AC, DC/AC, and AC/DC multicell converters were analyzed. For the purpose of multilevel modulation, a multicell converter employs several capacitors that are connected to every cell-the flying capacitors, charged to a given level of voltage. An inadequate relation between the voltages across the flying capacitors (the unbalance state) results in the increase of the voltages above their rated values across the switches. An RLC series circuit (a balancing circuit) with the properly selected resonance frequency is connected in parallel to the load in order to eliminate the unbalance. The balancing process with the use of passive RLC depends on the configuration and parameters of the balancing circuit, the parameters of the converter, as well as on the operating conditions. This paper presents the mathematical description of both the converter and the balancing process, the balancing circuit approach in the different topologies of the multicell converters, a selection of the balancing circuit parameters, and the analysis of the improper control conditions.

A Natural DC-Link Voltage Balancing of Diode-Clamped Inverters in Parallel Systems

This paper presents a method of natural dc-link capacitor voltage balancing of three- and single-phase neutral-point-clamped (NPC) inverters working in parallel configurations. It is proven that, in such parallel systems, when the inverters are insulated, the conditions for natural balancing can be achieved, and the application of a balancing circuit can assure the dc-link voltage balance independently on load. The method enables the natural balancing of single-phase single-branch NPC converters where natural balancing conditions do not occur. The application of the method presented in the three-phase NPC converter enables achievement of neutral dc-link voltage balance by the use of only one additional passive RLC circuit. In addition, the concept of lossless balancing in such systems is introduced. In the proposed system, by the application of a balancing circuit with a transformer and by using dedicated pulse with modulation, the balancing current flows in an unbalance state only. The unnecessary components of current that can flow in the balancing circuit are not present in the proposed solution. Simulations and experimental results in a system composed of two parallel inverters are presented to verify the concepts of natural balancing.

Individual MPPT of photovoltaic arrays with use of single-phase three-level diode-clamped inverter

This paper presents the results of the investigation of the control method for realization of individual MPPT (Maximum Power Point Tracking) of photovoltaic (PV) arrays in the grid-connected PV system with a single-phase three-level diode-clamped inverter. For a system with two PV arrays the idea of control is proposed to regulate the current of each PV array independently to operate in its MPP under partial shading conditions. The method is verified using FPGA-based real-time simulations with the use of a discrete model of the power system. Such a simulation enables testing the control implemented in a dedicated hardware, such as FPGA.

Testing of the grid-connected photovoltaic systems using FPGA-based real-time model

The paper describes FPGA-based real-time simulation method of photovoltaic systems. FPGA devices are widely used for power electronic systems control, but the same chip can have implemented real-time model of controlled system. Prototyping the control circuit before application in power system increases the safeness, and can reduce time and costs of implementation. FPGA-based prototyping of power systems enables research of the system sensitivity on parameters variations, or topology conceptions. The paper presents examples of designs of the FPGA-based models of PV array, PV grid-connected transformerless systems with single phase inverter and L and LCL filters, the dc/dc converter. The conception of FPGA-based realization of spectral analysis is also presented.

High-Power Thyristor-Based DC–DC Switched-Capacitor Voltage Multipliers: Basic Concept and Novel Derived Topology With Reduced Number of Switches

This paper presents concepts and results of an investigation of power electronic thyristor-based switched-capacitor voltage multipliers (SCVMs). A concept of the SCVM power converters assumes the utilization of resonant circuits for the zero-current switching operation. The topology makes it possible to apply thyristors as active switches that create the possibility of composing the resonant switch-mode converters for high-voltage gain, high power, and low cost, and opens a huge area of applications. This paper presents an in-depth analysis of the SCVM configured as the resonant high-power thyristor-based converter. The operation with regard to the specific switching conditions of thyristors, as well as efficiency of the converter is analyzed providing the unique relationship important for the converter design, optimization, and efficiency improvement. An experimental validation confirms the feasibility and the operation concept of the SCVM and demonstrates the efficiency range. The SCVM converter can be optimized to the topology with a decreased number of switches. This paper also presents a novel topology of the resonant converter with a reduced number of switches, resonant switched capacitor voltage multiplier (RSCVM), dedicated for thyristor implementation. The RSCVM requires the specific component selection and control. The analysis of the configuration, operation, efficiency, and component selection of the RSCVM converter, as well as simulation and experimental results are presented.

Multicell DC/DC Converter with DSP/CPLD Control. Practical Results

The paper presents practical investigations of DC/DC multilevel, multicell converter with DSP/CPLD control. A flying capacitors topology, natural balancing process and method of control of three-cell DC/DC converter are presented. Practical realization of the controller with use of programmable logic, discrete regulators in signal processor, procedures of initial flying capacitors charging, protection and turn-off the converter are described

Realization of modified ripple-based mppt in a single-phase single-stage grid-connected photovoltaic system

The paper presents the results of investigation of the realization of the maximum power point tracking (MPPT) method in a single-phase, single-stage, grid-connected photovoltaic (PV) system. The algorithm is based on the analysis of harmonic components occurring in the PV array power. The paper presents analytical discussion of a modified ripple-based MPPT technique, simulation results and verification of a FPGA-based practical controller with the use of a real-time discrete model of photovoltaic (PV) system with three-level NPC inverter implemented in FPGA Cyclone II IC. The paper also demonstrates practical measurements of signals of PV arrays loaded by single-phase inverter.

Switched Capacitor-Based Power Electronic Converter—Optimization of High Frequency Resonant Circuit Components

This chapter presents issues of optimization of the resonant circuit components’ volume in a switched-capacitor voltage multiplier (SCVM). The SCVM is derived from chip-scale technology but can effectively operate as a power electronic converter in a zero current switching mode when the recharging of switched capacitors occurs in a resonant circuit supported by an inductance. Selection of the passive LC components is not strictly determined, and depends on the optimization strategy according to the volume, efficiency or cost of the converter. Optimization of the volume of LC components is limited by the energy transfer ability via switched capacitors, thus by the rated power of the converter and switching frequency. Depending on the LC values, the converter operates in some specific states that determine the efficiency of the converter and voltage stress on semiconductor switches and diodes. This chapter presents analysis of the converter parameters and operation in the cases of optimization of the resonant circuit components’ values. The analytical discussion is also supported by the simulation and experimental results. All the results are provided for the SCVM but can be useful for a variety of switched-capacitor resonant power converters.

Small-signal model and control of the interleaved two-phase coupled-inductor boost converter

Coupled-inductor boost converters are under development for high-current, high-power applications ranging from automotive fuel cells to photovoltaics. This paper presents the small-signal analysis of a coupled-inductor boost converter operating in both CCM and DCM. Due to the complexity of operation of a coupled-inductor boost converter operating in DCM, several small-signal models must be derived. Controllers for the converter are developed using the resulting small-signal models. Experimental validation of these controllers is presented from a 1 kW coupled-inductor boost converter laboratory prototype.