The conventional three-level active-neutral-point-clamped (ANPC) inverter requires high dc-link voltage at least twice the peak of ac output. To reduce the dc-link voltage, a recent topology that enhanced the voltage gain from half to unity has been presented. In this letter, an alternative ANPC topology is established by using two T-type inverters. Two floating capacitors with self-voltage balancing capability are integrated to achieve a voltage-boosting gain of 1.5. In addition, the proposed topology is capable of generating seven voltage levels. Its operation is validated through circuit analysis followed by experimental results of a prototype.

Dual-T-Type Seven-Level Boost Active-Neutral-Point-Clamped Inverter

Conventional active-neutral-point-clamped (ANPC) inverters exhibit low voltage gain that inherently leads to a high dc-link voltage requirement. An improved ANPC inverter that is capable of generating five voltage levels has recently reduced the dc-link voltage twofold to achieve unity gain. This led to the development of a single-stage dc–ac power converter with no frontend boost dc–dc converter. This article proposes novel ANPC inverters capable of unity or boosted voltage gain while generating higher voltage levels. The first topology can provide a voltage gain of 1.5 and extends the number of levels to seven by incorporating only one additional switch. The topology can also be extended by adding three switches and one floating capacitor to generate nine levels with unity voltage gain, or 11 levels with a voltage gain of 2.5. The proposed ANPC inverters and their operations are comprehensively discussed. Experimental results are provided to validate the feasibility of the proposed ANPC inverters.

Novel Active-Neutral-Point-Clamped Inverters With Improved Voltage-Boosting Capability

This paper proposes a capacitor voltage regulation method for the dual converter with a floating bridge for aerospace applications. This topology has previously been reported, but with a constrained voltage utilization factor due to the need for capacitor voltage regulations. In this paper, the effect of switching states on the voltage variation of capacitor is quantitatively modeled and an enhanced space vector modulation scheme with current feedback is proposed to achieve an active control of the floating capacitor voltages. This proposed method also allows further exploitation and utilization of converter voltage. The relationship between the allowed modulation index of dual converter and load power factor is obtained and expressed using a fitted polynomial equation. The advantages of the proposed method include boosted voltage utilization and superior performance in term of capacitor voltage balance. These advantages have been proven through simulation and experimental results on RL loads as well as with an open-end winding induction motor. The proposed modulation scheme can boost the converter voltage utilization by at least 10% while achieving full four-level operation. More importantly, the higher available voltage allows extending the constant torque region of the motor, the further beginning of field weakening operation could be postponed.

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An Active Modulation Scheme to Boost Voltage Utilization of the Dual Converter With a Floating Bridge

This paper introduces a new configuration of bidirectional multilevel converter in electric vehicle (EV) applications It has multilevel dc–dc converter with a dc link capacitor voltage balance feature The multilevel dc–dc converter operates in a bidirectional manner, which is a fundamental requirement in EVs Compared to the conventional configurations, the proposed one only implements two extra power switches and a capacitor to balance the voltage of the T-type multilevel inverter (MLI) capacitor over a complete drive cycle or at fault conditions Therefore, no extra isolated sensor, control loops, and/or special switching pattern are required Moreover, the proposed configuration due to the high-frequency cycle-by-cycle voltage balance between ${C_N}$ and ${C_P}$ , the bulky electrolytic capacitors used in T-type MLI, are replaced with more reliable longer life film capacitors This will result in a size and weight reduction of the converter by 20% This allows more real estate for the EV battery in the chassis’ space envelope to increase its capacity The proposed configuration is tested and validated using a matlab /Simulink simulation model A laboratory prototype of 1 kW is built to provide the proof of concept results as well

A Novel Bidirectional T-Type Multilevel Inverter for Electric Vehicle Applications

In this article, a computation-efficient model predictive control (MPC) is proposed to eliminate common-mode voltages (CMVs) of three-phase five-level active neutral-point-clamped (3P-5L-ANPC) converters. Originated from the CMV analysis of the 3P-5L-ANPC with all possible 125 possible voltage vectors, only 19 voltage vectors that generate zero CMV are adopted as the candidate voltage vectors for the MPC. The best voltage vector from the candidate voltage vectors is selected to track the current references. Then, appropriate switching combinations of the selected best voltage vector are determined to effectively balance the flying and dc-link capacitor voltages without any additional hardware components. Furthermore, the proposed MPC only chooses five candidate voltage vectors involving in MPC optimization according to the location of the reference voltage vector, which significantly alleviates the computational burden. Finally, the effectiveness of the proposed MPC in terms of the steady-state and dynamic performances is validated by simulated and experimental results.

Computation-Efficient Model Predictive Control With Common-Mode Voltage Elimination for Five-Level ANPC Converters

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.

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

Multilevel converters are widely employed in the 30–50 kW medium-voltage grid-connected photovoltaic (PV) generation systems due to their higher power quality and lower switching losses compared with the two-level converters. Dual T-type three-level converters and one three-level diode neutral point clamped circuit can be integrated to derive a simplified five-level modular composited converter (5L-MCC) for the medium-voltage PV grid-connected systems. However, realizing the capacitor voltage balance is a challenge to enhance its reliability. First, the model of dc capacitor voltage variation of the 5L-MCC is discussed to expose a limitation once the nearest three-vector synthesis method is employed with conventional space vector modulation (SVM). In order to extend the operational range, a hybrid space vector modulation (HSVM) strategy is proposed, which integrates the optimized SVM switching sequence for the low-modulation ( $M\, ) and a simplified vector synthesis method for the high-modulation region ( $M\geq 0.5$ ). The proposed hybrid modulation maintains the dc capacitor voltage balance over the full modulation range and power factor. Finally, the effectiveness of the proposed HSVM strategy is verified with the simulation and experimental results.

Capacitor Voltage Balance Control of Five-Level Modular Composited Converter With Hybrid Space Vector Modulation

The common-mode current casued by the parasitic parameters in the transformerless multilevel converters degrades the performance of converters and brings security issues. This paper presents a new zero common-mode voltage space vector modulation for common-mode voltage suppression in the five-level modular composited converter. Firstly, the common-mode equivalent circuit model of five-level modular composited converter is initially derived to further explore its mechanism. Then, a zero common-mode voltage space vector modulation which redistributes the zero common-mode voltage vectors through the flexible coordinate transformation is proposed, and a simpified vector synthesis method is employed to reduce the common-mode current in the five-level modular composited converter. Finally, the effectiveness of the prposed zero common-mode space vector modulation strategy is verfiied by the simulation and experimental results.

Common-mode voltage analysis and suppression in five-level modular composited converter

For improving the zero-voltage ride through the capability of a doubly fed induction generator in high proportion new energy grid in extreme faults, a coordinated control scheme of hardware and optimal control strategy is proposed. A high-temperature superconductive-fault current limiter suppresses stator fault current, adaptive virtual impedance control and active dynamic reactive power support control act on the back-to-back converter of wind turbines as optimal control strategies. Optimizing the control strategy without changing the controller structure is beneficial to engineering implementation. After mathematical derivation and simulation verification, the coordinated control strategy adopted in this paper can effectively avoid the rotor current and voltage exceeding the limit when the wind turbine is facing extreme faults, actively provide reactive power support for the busbar, realize zero voltage ride through and reduce the risk of high voltage failure at the point of failure. The control effect is obviously better than the traditional virtual impedance control.

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Jiawei Hu

Papers

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

Capacitor Voltage Balance Control of Five-Level Modular Composited Converter With Hybrid Space Vector Modulation

Common-mode voltage analysis and suppression in five-level modular composited converter

Control Strategy of Doubly-Fed Induction Generator under Zero Voltage Fault of Power Grid