Search

Cascaded H-Bridge (CHB) converters have been widely employed in various applications, providing the advantages of modularity and multilevel voltage output. However, technically the CHB converters require isolated DC-link buses, which need to be regulated individually. In this context, a control scheme for the CHB converters features the voltage balancing algorithm. The voltage balancing control is typically performed by PI controller, where its control capability is limited by linear modulation region. In this work, the modulation based voltage balancing algorithm is proposed, which extends the balancing control capability and improves the dynamic performance. The proposed method is theoretically analyzed and validated through the simulation and experimental results.

The Neutral Point Clamped (NPC) Multi-Level Inverters (MLI) have been ruling the power electronics industries for the past two decades. The Multi-Carrier Pulse Width Modulation (MCPWM) is common PWM techniques which are widely used in NPC-MLI applications. However, MCPWM is not having a good impact on the balancing of DC-link voltages, Common Mode Voltage (CMV) and limiting the Total Harmonics Distortion (THD). The Selective Harmonic Elimination (SHE) technique is introduced for reducing the THD, however all the switching angles should be maintained less than $\pi $ /2 to keep the eliminated harmonics at constant level which narrows down the modulation index range. Hence, in recent days Space Vector Modulation (SVM) technique is widely used in NPC-MLI, which gives better DC-link voltage balancing, self-neutral point balancing, near-zero CMV reduction, better-quality harmonics profile and switching loss minimization. Hence, it is a preferred solution for the majority of electrical conversion applications such as electric traction, high power industrial drives, renewable power generation, and grid-connected inverters, etc. The paper gives a comprehensive review of the SVM for NPC-MLI. First, this paper deliberates the state of art for two-level SVM and extends it to three-level (3L) SVM. Also compares the 3L SVM performance with other MCPWM techniques. Followed by the various modified MLI SVM techniques in terms of their implementations, DC-link capacitor balancing, and reduction of CMV. Further, the review of MLI SVM is widened to open-end winding Inverters and multiphase MLIs. The final part of this paper discussed the future trends and research directions on MLI SVM techniques and its applications.

This paper proposed a grid connected solar Photovoltaic (PV) Systems with a new voltage balancing converter suitable for Neutral-Point-Clamped (NPC) Multilevel Inverter (MLI). The switched-capacitors used in the proposed converter is able to balance the DC link capacitor voltage effectively by using proper switching states. The proposed balancing converter can be extended to any higher levels and it can boost the DC input voltage to a higher voltage levels without using any magnetic components. This feature allows the converter to operate with the boosting capability of the input voltage to the desired output voltage while ensuring the self-balancing. In this paper the proposed converter is used for a grid connected solar PV system with NPC multilevel inverter, which is controlled using vector control scheme. The proposed grid connected solar PV system with associated controllers and maximum power point tracking (MPPT) is implemented in Matlab/SimPowerSystem and experimentally validated using dSPACE system and designed converters. The simulation and experimental results show that the proposed topology can effectively balance the DC link voltage, extract maximum power from PV module and inject power to the grid under varying solar irradiances with very good steady state and dynamic performances.

A bipolar hybrid microgrid is a new topology which benefits from the advantages of both alternating current (AC) and direct current (DC) microgrids. Interlinking AC/DC converter is the key of this topology which has the following characteristics: being able to provide two equal pole voltages in DC side; complying with the standards of current quality at AC side; being able to control active and reactive power independently in AC side, and transmitting bidirectional power. In this paper, two categories of power converters including single-stage and two-stage converters are proposed for this topology. A new cost-effective control strategy is added to the control of general grid-connected converter for each interlinking converter, and the control of autonomous DC-link pole voltage for both candidates is achieved. Detailed simulations based on the designed control strategies are conducted to validate the function of control strategies under the operation conditions of different DC sides. The performances of two selected interlinking converters with balanced and unbalanced DC loads are analyzed. Suggested power quality of microgrid and total harmonic distortion (THD) analysis are demonstrated in grid-tied and islanded modes. Eventually, semiconductor power loss simulations based on a closed-loop thermal network simulation are conducted. Thereby, the mutual effects of power loss and initial junction temperature are investigated.

CHB is a suitable type of topology for synchronous rectifier application which has two or more independent DC loads. Focusing on the individual DC-link capacitor voltage balancing problems caused by asymmetric parameters of independent DC loads, this paper developed a new dual modulation signals based phase disposition pulse width modulation (PD-PWM) strategy using dynamic carrier bias allocation method. Its main idea is to allocate the bias of the carrier wave dynamically according to the balance situation of the system. Compared with the traditional modulation strategies, this method is more easily to be realized and has much stronger dynamic regulation ability. This modulation strategy is widely applicable to various types of CHB structures. A detailed analysis of the DC-link capacitor charge-discharge profile is performed, and an operation condition based dynamic bias allocation method is described using the cascaded H-bridge rectifier (CHBR) structure of five sub-modules as an example. A simulation model and an experiment platform are developed, and the feasibility and effectiveness of the modulation strategy are verified by simulation and experiment results.

This paper proposes a closed-loop control implementation fully-embedded into an FPGA for a permanent-magnet synchronous motor (PMSM) drive based on a four-level active-clamped converter. The proposed FPGA controller comprises a field-oriented control to drive the PMSM, a DC-link voltage balancing closed-loop control (VBC), and a virtual-vector-based modulator for a four-level active-clamped converter. The VBC and the modulator operate in consonance to preserve the DC-link capacitor voltages balanced. The FPGA design methodology is carefully described and the main aspects to achieve an optimal FPGA implementation using low resources are discussed. Experimental results under different operating conditions are presented to demonstrate the good performance and the feasibility of the proposed controller for motor-drive applications.