This paper proposes a novel T-type multilevel inverter (MLI) based on the switched-capacitor technique. The proposed inverter not only achieves that the maximum voltage stress of the switches is less than the input voltage but also has a voltage boost capability, which makes it suitable in high voltage applications. It is worth mentioning that the proposed inverter features two topology extension schemes which help it achieve a higher output level and voltage gain. With the merit of low voltage stress and reduced power devices, a seven-level inverter can be achieved using only two capacitors. Moreover, capacitor voltage self-balancing capability can simplify the complexity of the circuit and control. The topology, operating principle, modulation strategy and analysis of the capacitor of the inverter are presented. The superiorities of the proposed inverter are investigated by comparing with recently proposed hybrid MLIs and switched-capacitor MLIs. Finally, a seven-level prototype is constructed to validate the correctness of the theoretical analysis and the feasibility and effectiveness of the proposed inverter.

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A T-Type Switched-Capacitor Multilevel Inverter With Low Voltage Stress and Self-Balancing

In this paper, a new modified PWM (pulse width modulation) control method for any type of neutral point clamped (NPC) multilevel inverters is proposed. In NPC inverter topologies with more than three-level, the problem of charge balance in the split dc-link capacitors is still discussable. Hence, the most important advantage of the proposed pulse width modulation (PWM) control method is keeping the charge balance of capacitors in the neutral point (NP). To check the correct operation of the proposed PWM control method, the structure of conventional three-phase NPC five-level voltage-source inverter is also used. In this paper, different combinations of permissible switching states for five-level NPC inverter based on voltage-source is presented. Moreover, the control signals are explained for NPC five-level voltage-source inverter by using both conventional and proposed PWM control methods. In this paper, a comparison between conventional and proposed control methods is performed. The simulations performed in PSCAD software are done for both conventional and proposed PWM control methods. The good performance of the proposed control method compared to conventional control method is verified by the simulation results.

Modified PWM control method for neutral point clamped multilevel inverters

In this study, a new modified switched boost inverter (MSBI) is proposed. The proposed inverter presents higher voltage gain in comparison with conventional Z-source inverter and switched boost inverter. Moreover, the proposed inverter provides zero voltage switching turn-off of input voltage source side switches. In this study, the proposed converter is theoretically analysed in different operational modes along with design procedure and ripple analysis. The proposed MSBI is compared with similar works to evaluate its capabilities. Finally, a 50 kHz experimental prototype with input voltage of 40 V is used to verify the analysis and simulation results.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2016.0597

Modified high voltage gain switched boost inverter

In this study, a new multi-input high step-up inverter, based on isolated soft-switching DC-DC converter blocks is proposed. Each of these blocks can provide zero-voltage and zero-current switching for its semiconductors, which improve power efficiency. The interesting feature of this DC-DC converter is using bidirectional switches to generate both positive and negative output voltage levels in each DC-DC block with an appropriate control scheme. Each DC-DC converter operates by simple pulse width modulation control through fixed frequency and has two degrees of freedom, which provide the capability of output voltage regulation or maximum power point tracking. The proposed inverter consists of the cascaded connection of these DC-DC converters at their output terminal. This inverter can operate with high voltage gain, where the output voltage of each DC-DC converter is regulated. Furthermore, it can generate more output voltage levels with less number of DC-DC blocks. All these advantages make the proposed inverter suitable for photovoltaic power conditioning systems. In this study, the theoretical analysis with steady-state waveforms, design constraints, resonant tank analysis and comparison study are given. Then, experimental results of both the proposed inverter and its DC-DC blocks are presented.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-pel.2018.5801

Multi-input high step-up inverter with soft-switching capability, applicable in photovoltaic systems

An analysis of the method for ensuring the sinusoidality of the output voltage in power generation systems with self-commutated voltage inverters under the requirements of the international standard IEEE-519 is presented.
In a number of programs, especially low-power generation systems, a low-cost solution is needed to provide the sinusoidal waveform of the output voltage with the total harmonic distortion of 5 %. This solution is to use two-level voltage inverters with an output sine LC filter. However, the feature of the sine filter with the frequency converter is that the PWM frequency affects the spectrum of higher harmonics of the output voltage. In addition, there is the starting current of the filter capacitor, which can disable the power switches of the voltage inverter.
The developed method for calculating the values of the LC filter with the two-level voltage inverter in the PWM mode is presented meeting the requirements of the international standard IEEE-519, taking into account the modulation frequency and limitation of the starting current of the filter capacitor.
To confirm the required quality of the output voltage of the two-level voltage inverter with the sine filter, an appropriate simulation model was created in the Matlab/Simulink computer simulation environment. The oscillograms and harmonic analysis of the input and output voltages of the sine filter, which showed the total harmonic distortion of 1.88 %, are presented.
A physical prototype of the investigated system was created on the basis of a 5.5 kW OVEN PChV203-5K5-V frequency converter (Ukraine). Using the SIGLENT SDS1104X-E oscilloscope (China), the real waveform and the results of the harmonic analysis of the sine filter output voltage, confirming the implementation of the necessary sinusoidality criteria, were obtained

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A method for calculating the parameters of the sine filter of the frequency converter, taking into account the criterion of starting current limitation and pulse-width modulation frequency

Recently a new topology for Z-source converter entitled as Z-H converter has been presented. The Z-H converter can be used to dc/dc, dc/ac, ac/dc and ac/ac conversion without any change in it's structure. The Z-H converter compared to the traditional Z-source inverter eliminates shoot-through switching state and the front end diode of LC network. The main advantages of Z-H converter are simple structure and not needing any additional filter in circuit (because of having low ripple in waveforms). In order to check Z-H buck converter in dc/dc conversion, it's operating principle with details and related equations are explained in this paper. The performance and efficiency of Z-H buck converter are verified by the simulation results in PSCAD software.

Z-H buck converter: Analysis and simulation

First of all, in this paper, the topology and operation of the three-phase threelevel Z-source inverter based on neutral-point-clamped (Z-NPC) are studied. Moreover, different combinations of permissible switching states and control signals are explained for this inverter. In this paper, the topology of the three-phase three-level Z-NPC inverter is extended for an n-level state. Also, a combination of allowed switching states with relevant mathematical equations is presented for the proposed n-level Z-NPC inverter. In comparison with multilevel voltage-source inverters (only voltage-boost capability), the proposed multilevel Z-NPC inverter is a single-stage converter and it has a buck-boost capability of voltage. On the other hand, the control of two-stage converters compared to single-stage converters can be more difficult because of existing more active and passive components. In this paper, two new PWM control methods are also proposed for various multilevel Z-NPC inverters. One advantage of the proposed PWM control methods in comparison with conventional PWM control methods is maintaining the charge balance of the dc-link capacitors in neutral point. The correct performance of the proposed multilevel Z-NPC topology and PWM control methods are verified by the obtained results of analysis and simulations performed in the PSCAD software.

/pdf/a-new-n-level-inverter-based-on-z-npc-1kmqt0epyu.pdf

A New N-Level Inverter Based on Z-NPC

In this paper, a new extended quasi-switched Z-source inverter, using a switched-inductor cell, is proposed. The most important advantage of the proposed inverter is achieving the maximum voltage gain in the lower duty cycle with less circuit components than similar previous inverters, which causes the modulation index value increase. Furthermore, it leads to less power losses and less voltage and current ripples. The employed control method in this inverter is the pulse width modulation (PWM) simple boost control method. In this paper, theoretical analysis and comparison results of the proposed inverter with other similar ones are prepared. In addition, the experimental results reconfirm the accuracy of the proposed extended-qSZSI.

An Extended Quasi-switched Z-Source Inverter

In this paper, a new three-phase three-level neutral point clamped (NPC) inverter based on improved Quasi-Z-source (QZS) network is proposed. The proposed QZS inverter in comparison with conventional Z-source and Quasi-Z-source inverters has higher boost factor under smaller duty cycle. Moreover, smaller duty cycle, lower voltage stress, less total harmonic distortion (THD), and continuous input current are some advantages of the proposed inverter. In this paper, different combinations of allowed switching states with their control signals for proposed inverter are presented by using SPWM control method. The simulations results in PSCAD software are performed to prove the performance of the proposed topology.

Taher Ahmadzadeh

Papers

Modified PWM control method for neutral point clamped multilevel inverters

Z-H buck converter: Analysis and simulation

A New N-Level Inverter Based on Z-NPC

An Extended Quasi-switched Z-Source Inverter

Improved quasi-Z-source based three-phase three-level neutral point clamped inverter