Three-level Flying Capacitor Converter Research Articles

Switching Control Strategy for DC–DC Converters Based on Polynomial Lyapunov Function and Sum-of-Squares Approach

The introduction of switched system theory opens new perspectives for the control design of dc/dc converters. Regarding the classical two-level converters, two switching control design methodologies have been developed based on the common quadratic Lyapunov function (CQLF) or piecewise quadratic Lyapunov function (PQLF). However, the CQLF-based design method is not applicable for the multilevel dc/dc converter (MC). As for the PQLF-based design method, it encounters the problem that the control design is very complex, involving a nonlinear optimization problem. To further advance the application of the switching system theory in power converters, a design framework based on the polynomial Lyapunov function and the sum-of-squares approach is proposed in this article. The proposed design method generalizes the CQLF-based one. Moreover, compared with the PQLF-based design method, the mathematical design procedure can be significantly simplified. Experimental validations on an MC, i.e., the three-level flying capacitor converter and a two-level Buck-Boost converter illustrate the versatility and the effectiveness of the proposed design framework. Moreover, comparative tests show the good control performance of the designed switching control strategy. The currently presented works are preliminary but could constitute an interesting direction for developing control solutions of power converters.

フライングキャパシタ変換器をベースとした非絶縁形DC-DC変換器の電流制御法比較

This paper presents a bidirectional non-isolated dc-dc converter based on three-level flying-capacitor converters. The converter uses multiple auxiliary converters, each of which is based on cascaded chopper cells and an inductor, which enables active control of the inductor current. This paper compares the following two current control methods: conventional sinusoidal-wave current control method and proposed trapezoidal-wave current control method, in terms of ac-current peak values, dc-current values, current root-mean-square (RMS) values, voltage ripples in dc-capacitor voltages, current ripples in dc currents, and converter efficiency. The validity of the comparison and trapezoidal-wave current control method is verified in a simulation using MATLAB and experimentally using a 2-kW downscaled model.

Thirteen-Level Multilevel Inverter Structure Having Single DC Source and Reduced Device Count

This article proposes a single dc source-based hybrid three-phase thirteen-level inverter suitable for medium voltage applications. The multilevel structure is composed of a three-level T-type neutral point clamped (NPC), half-bridge, and three-level Flying capacitor converter with optimal switch count and high dc bus voltage utilization as high as 0.63 times the dc-link voltage. This requires a special attention to a novel capacitor balancing method using redundant switching states in order to operate at any power factor under grid-connected mode. A unified common-mode voltage is injected in the carrier based pulse width modulation (PWM) technique to maintain the voltage balance in dc-link capacitors as well as floating capacitors. Simulation results are presented under different operating conditions that include unity power factor operation with passive load as well as grid-connected inverter mode. The performance of the proposed multilevel inverter in the grid-connected mode is also validated with experimental results using a lab prototype.

The three-level inverter topologies analysis for application by electric centrifugal pump units

In the article, the schemes for providing AC power with frequency conversion for the induction submersible electric drive of oil production units are analyzed. The electric submersible drive is widely used and has stringent efficiency requirements, so this research is relevant. The centrifugal pump units are composed of a low-voltage power source, a frequency converter, a step-up transformer, a cable line, an electric drive and a centrifugal pump. This article discusses options for replacing the step-up transformer and two-level voltage / frequency converter with a three-level flying capacitor converter (FCC) or a three-level clamping diode converter (NPC). The expected states of the power high voltage IGBT modules are described. The waveforms of the inverter output voltage and the submersible induction motor stator voltage in different circuits are shown. A voltage levels analysis for each module is done, the electric drive starting time change is estimated, the total harmonic distortions (THD) are calculated, and a 1.1% THD reduction by applying the NPC circuit is shown. The harmonic current spectrum for each circuit is presented.

Control and Experimental Verification of a Bidirectional Non-isolated DC-DC Converter Based on Three-level Flying-Capacitor Converters

Control and Experimental Verification of a Bidirectional Non-isolated DC-DC Converter Based on Three-level Flying-Capacitor Converters

Control and Experimental Verification of a Bidirectional Non-isolated DC-DC Converter Based on Three-level Flying-Capacitor Converters

Control and Experimental Verification of a Bidirectional Non-isolated DC-DC Converter Based on Three-level Flying-Capacitor Converters

Sensorless Stabilization Technique for Peak Current Mode Controlled Three-Level Flying-Capacitor Converters

This article describes a sensorless stabilization technique for peak current mode control of three-level flying-capacitor (3 ${\rm LFC}$ ) buck converters. The technique eliminates the well-known instability associated with the flying-capacitor (FC) voltage runaway, leading to stable and balanced FC voltage. In the proposed technique, the FC voltage imbalance is detected by measuring the duty cycle mismatch $D_{A}-D_{B}$ between two groups of switches of the 3 ${\rm LFC}$ topology, an information already available to the controller without any additional sensing. The resulting compensation leads to a compact solution, which can be easily embedded into an analog or digital integrated controller. Two distinct approaches are developed in this article to implement the required correction on $D_{A}-D_{B}$ , namely a sensorless peak offsetting modulation (PO-MOD) and a sensorless interleaving time modulation (IT-MOD). Operation, implementation challenges, and performances of both are investigated. The proposed solutions are verified through computer simulations and experimentally using a 16.5-to-3.3 V, 500 mA, 500 kHz 3 ${\rm LFC}$ prototype.

Common-Mode Current Suppression of Transformerless Nested Five-Level Converter With Zero Common-Mode Vectors

Three-phase transformerless multilevel converters are widely used in the high-voltage photovoltaic power generation systems because of their low total harmonic distortion, high power density, and high conversion efficiency. One three-level flying capacitor converter and dual T-type three-level circuits can be combined to derive the compact and cost-effective nested five-level converter. However, due to the lack of an isolation transformer, the common-mode current is generated to degrade the converter performance. First, the common-mode equivalent circuit model of the nested five-level converter is initially derived to further explore its common-mode current generation mechanism. Then, the zero common-mode space vector modulation (ZCM-SVM) is proposed to reduce the common-mode current, which chooses the specific zero common-mode voltage space vectors to synthesize the reference vector. Then, an advanced coordinate transformation is introduced to realize the flexible sector selection and reduce the complexity of the vector action time calculation. The proposed modulation achieves the common-mode current suppression with high dc bus voltage utilization. Finally, the effectiveness of the proposed ZCM-SVM strategy is verified by simulation and experimental results.

Model Predictive Control of Four-Leg Three-Level Flying Capacitor Converter: Influence of Model Parameter Mismatch

Abstract This paper presents a control method for a four-leg three-level flying capacitor converter (FCC) operating as a shunt active power filter (SAPF), based on model predictive control with finite number of control states (FS-MPC). Current control and capacitor voltage balancing are described. Influence of the mismatch of the inductive filter model parameters on the current control precision is analysed. Results are supported by the experimental waveforms obtained with a 10kVA set-up.

Current Controller for Multi-level Front-end Converter and Its Digital Implementation Considerations on Three-level Flying Capacitor Topology

This paper presents behaviour analysis and digital implementation of current error space phasor based hysteresis controller applied to three-phase three-level flying capacitor converter as front-end topology. The controller is self-adaptive in nature, and takes the converter from three-level to two-level mode of operation and vice versa, following various trajectories of sector change with the change in reference dc-link voltage demanded by the load. It keeps current error space phasor within the prescribed hexagonal boundary. During the contingencies, the proposed controller takes the converter in over modulation mode to meet the load demand, and once the need is satisfied, controller brings back the converter in normal operating range. Simulation results are presented to validate behaviour of controller to meet the said contingencies. Unity power factor is assured by proposed controller with low current harmonic distortion satisfying limits prescribed in IEEE 519-2014. Proposed controller is implemented using TMS320LF2407 16-bit fixed-point digital signal processor. Detailed analysis of numerical format to avoid overflow of sensed variables in processor, and per-unit model implementation in software are discussed and hardware results are presented at various stages of signal conditioning to validate the experimental setup. Control logic for the generation of reference currents is implemented in TMS320LF2407A using assembly language and experimental results are also presented for the same.

Predictive Control of Series Stacked Flying-Capacitor Active Rectifiers

This paper considers the use of back-to-back, full-bridge, three-level flying-capacitor converters in a series-input-parallel-output connected fashion for the implementation of a solid-state transformer. A finite-control-set model-based predictive control algorithm is developed for the control of the active rectifier front-ends. Pulse width modulation is used for the isolation back-ends. A solid-state transformer is constructed with two of the proposed back-to-back converters and experimental results are presented.