Description:This invention relates to multilevel inverters (MLI) and, more particularly, to a single-phase MLI structure that minimizes the number of switching devices to enhance the output voltage level.
Background of the invention:
In the realm of power electronics, multilevel inverters (MLIs) have steadily evolved as a pivotal component, primarily due to their capability to operate in high-power and medium-power applications. Traditionally, the main objective of MLIs has been to produce an output voltage with multiple levels, and the preferred method to achieve this has been by increasing the number of components, specifically the switching devices. This incremental approach, however, leads to complexities in both the design and operational aspects of the inverter system. The increased number of components can also impact the overall system reliability due to potential device failures, resulting in system downtimes and maintenance challenges.
Furthermore, as the global energy landscape is undergoing a shift towards more sustainable and efficient solutions, there's a mounting pressure on researchers and manufacturers to devise methods and systems that are not just efficient, but also compact, cost-effective, and reliable. The traditional MLI configurations, with their inherent limitations, do not align well with these contemporary requirements.
To bridge this gap, the trend has been moving towards configurations that utilize a minimal number of devices. The primary motivation behind this shift is the realization that an optimized and streamlined design can result in enhanced system efficiency and reliability, while also simplifying the overall design and operational processes. Minimizing the switch count, for instance, directly reduces the conduction and switching losses, which in turn improves the efficiency of the system. Additionally, with fewer components, the system's reliability sees an uptick as there's a reduced probability of component failures.
Another important consideration has been the gating signals for these devices. Traditional modulation techniques, while effective, might not be the most optimized for newer MLI configurations. Thus, there's been a push towards exploring alternative modulation techniques that align better with the reduced switch count and can further enhance the system's output.
Additionally, while the advancements in technology have made it possible to design and incorporate intricate and highly sophisticated systems, there is an ever-present challenge in ensuring these systems remain user-friendly and maintainable. MLIs, especially those with a large number of components, often require expert intervention for maintenance, troubleshooting, and repair. By reducing the switch count, the proposed invention not only enhances the system's operational efficiency but also simplifies its structure, making it more accessible for maintenance and potential upgrades.
Another pivotal aspect that cannot be ignored in the backdrop of this invention is the evolving nature of the energy sources themselves. With a significant push towards renewable energy sources like solar and wind, the nature of input to these inverters is no longer consistent or predictable. This inconsistency makes it imperative for inverters to be more adaptable and resilient. The proposed inverter, with its minimalistic design, offers better adaptability to varying input conditions, ensuring that the output remains consistent and reliable.
Moreover, the economic implications of a reduced component count inverter design are profound. As the number of components, especially the switching devices, reduces, the overall cost of the system inherently decreases. This cost-effectiveness becomes even more pronounced when scaled up for industrial applications, where even minor savings in the component costs can translate into significant financial benefits.
The proposed inverter's design also implies a smaller footprint, making it a perfect fit for applications where space is a constraint. In urban settings, where space is often at a premium, such compact designs can be the difference between the feasibility and impracticality of certain applications.
Furthermore, a minimized switch count configuration inherently implies reduced electromagnetic interference (EMI). EMI has always been a concern with power electronic devices, as it can interfere with other electronic equipment operating nearby. With fewer switching operations and a simplified design, the proposed system can potentially offer reduced EMI, ensuring that it can seamlessly integrate into environments with sensitive electronic devices.

In conclusion, as the energy landscape continues its transformation, there's a pressing need for innovations in the MLI domain. This invention, with its focus on a streamlined design and enhanced operational efficiency, is a timely and relevant contribution to the field, offering numerous advantages that make it well-suited for the challenges of the modern world. Some patent prior art related to proposed invention mentioned below.
Patent US7034392B2: Describes a multi-level inverter configuration with a focus on reducing total harmonic distortion. Although the design emphasizes component efficiency, it still relies on a higher number of switches than the proposed design.
Patent EP2134321A1: Discusses a single-phase MLI system which uses capacitor balancing techniques. The design is distinct in its method but retains a significant switch count.
Patent WO2016032430A1: Covers an MLI with cascaded H-bridge cells. Its emphasis is on modular construction rather than minimizing switch count.
Patent US6859012B1: This patent details a method for generating gating signals for MLIs. While it discusses modulation techniques, the core design of the inverter isn't primarily focused on reducing switch numbers.
Patent JP2008253421A: This Japanese patent outlines an MLI system that has an energy storage system integrated into it. The focus is on energy conservation, not on the reduction of switching devices.
Patent CN1052835C: A Chinese patent that explains an MLI design which prioritizes fast switching and low-latency operation. Switch count doesn't appear to be a primary design constraint.
Patent DE102006033112A1: Highlights a method to improve the output voltage quality of an MLI. The method revolves around the precise timing of switch activation but doesn't inherently limit the number of switches.
Patent KR20150084756A: A Korean patent detailing an MLI design which prioritizes fault tolerance and redundancy. Although it has a robust system against failures, its design includes multiple switches.
Patent IN2784391B: An Indian patent which presents an MLI with a unique cooling mechanism to enhance system longevity. The focus here is on temperature management, and the system still uses a standard number of switches.
Summary of the proposed invention:
The proposed invention introduces a novel single-phase multilevel inverter (MLI) structure that focuses on minimizing the number of switching devices to optimize the output voltage level. By integrating three DC voltage sources and only eight switches, this advanced system can produce an output with 13 distinct voltage levels.
The ratio of the three DC sources is set in a 1:2:3 proportion, and each of the power semiconductor switches is an Insulated Gate Bipolar Transistor (IGBT) paired with a diode. The specific arrangement of the switches is crucial; certain combinations, when conducted simultaneously, can result in undesirable input voltage conditions.
Therefore, these combinations must operate in a complementary mode. The level-shifted pulse width modulation (LSPWM) technique is utilized to generate gating signals for the switches. To validate the performance and reliability of the proposed MLI, various tests and simulations have been conducted using MATLAB/Simulink under different parametric conditions. The resulting data confirms that this design effectively reduces the switch count while delivering a high-quality output voltage, making it a promising solution for various power applications.
Brief description of the proposed invention:
The invention in contemplation presents a groundbreaking approach to the design and configuration of multilevel inverters (MLIs), a critical component in the domain of power electronics. Traditionally, MLIs are favored for both high-power and medium-power applications due to their ability to produce a stepped waveform that approaches sinusoidal output without the need for transformers. Their complexity, however, often results from the multiple devices involved, particularly switching devices. These switch devices not only add to the system's intricacy but also potentially reduce the reliability and efficiency of the system.
Recognizing the challenges posed by conventional MLIs, this invention introduces an asymmetric, single-phase MLI structure specifically crafted to drastically reduce the number of switches, yet without compromising the quality of its output. A total of three DC voltage sources and just eight switches constitute the backbone of this proposed inverter system. To offer a harmonized performance, these voltage sources are methodically arranged in a ratio of 1:2:3. Each power semiconductor switch in the system is an Insulated Gate Bipolar Transistor (IGBT) which, for ensuring efficient switching and protection, is accompanied by a diode.
The design intricacy is further evident in the systematic coordination of the switches. Several switching combinations are meticulously arranged such that their simultaneous operation could compromise the integrity of the input voltage sources. To circumvent any potential pitfalls, these combinations are designated to operate in a complementary mode. That is, while one switch in the combination is turned on, its counterpart remains off, and vice versa. This subtle yet vital approach ensures the system remains stable, efficient, and free from undesirable voltage conditions that could compromise its performance or the devices connected to it.
But orchestrating such harmony among switches requires a robust technique, and this is where the level-shifted pulse width modulation (LSPWM) comes into play. The LSPWM technique is renowned for its capability to generate gating signals efficiently. In the context of this invention, it meticulously generates signals for the switches, ensuring that the desired voltage levels are achieved at the output while adhering to the complementary operational mandate.
To consolidate the theoretical foundations and practical implications of the invention, a series of tests and simulations were orchestrated using the MATLAB/Simulink platform. These simulations spanned various parametric conditions, putting the MLI through its paces. The outcomes were encouraging, validating the premise that this design can indeed minimize switch count without compromising the output voltage quality.
The broader implications of this invention are multifaceted. On one hand, it offers a more streamlined, cost-effective, and reliable solution for power applications, thanks to the reduced component count. On the other hand, by simplifying the design, it becomes more maintainable and user-friendly, reducing potential downtimes in practical applications. Furthermore, by operating under the principles of this inventive approach, the MLI can seamlessly integrate with varying input conditions, making it particularly well-suited for the dynamically changing landscape of modern power sources, especially renewables.
The modes of operation of the proposed multilevel inverter provide a holistic understanding of its functional prowess and the elegance of its intricate design. These modes essentially detail how the system functions to generate varying voltage levels from the given DC voltage sources, using the pre-defined switch configurations.
Positive Half-Cycle Operation: During the positive half-cycle, the MLI generates voltages ranging from 0Vdc to +6Vdc. Several specific switching combinations are utilized to achieve this:
• 0Vdc: The system has two configurations to produce a zero-voltage output. Either the top leg switches, specifically S1, S3, S5, and S7, are made conductive, or the bottom leg switches, namely S2, S4, S6, and S8, are activated. In both scenarios, the outcome is a null voltage across the output.
• +1Vdc: By activating switches S2, S4, S5, and S8, the first voltage source, V1, is channeled to produce an output of +1Vdc across the load.
• +2Vdc: This voltage level is realized when switches S1, S4, S5, and S7 are turned on, thereby employing the second voltage source, V2, for the desired output.
• +3Vdc: Switches S1, S3, S6, and S8 orchestrate the conduction path for the third voltage source, V3, resulting in an output of +3Vdc.
• +4Vdc: To attain a sum of V3 and V1, switches S1, S3, S5, and S8 are activated, delivering an output of +4Vdc.
• +5Vdc: An amalgamation of V3 and V2, resulting in +5Vdc, is facilitated through the conduction of switches S1, S4, S6, and S8.
• +6Vdc: The full potential of the system is realized when switches S1, S4, S5, and S8 are activated, aggregating the outputs from V1, V2, and V3 to produce a peak of +6Vdc.
Negative Half-Cycle Operation: The negative half-cycle inverts the positive half-cycle's modes, producing negative voltage levels ranging from -1Vdc to -6Vdc:
• -1Vdc: The system channels the first voltage source, V1, through switches S1, S3, S6, and S7 to produce -1Vdc.
• -2Vdc: By activating switches S2, S3, S6, and S8, the second voltage source, V2, is employed to deliver an output of -2Vdc.
• -3Vdc: The third voltage source, V3, creates an output of -3Vdc when switches S2, S4, S5, and S7 are turned on.
• -4Vdc: A combination of V1 and V3 results in -4Vdc, achieved by the activation of switches S2, S4, S6, and S7.
• -5Vdc: Switches S2, S3, S5, and S7 harness the combined power of V2 and V3, outputting -5Vdc.
• -6Vdc: Finally, the cumulative potential of all three sources, V1, V2, and V3, is tapped into by activating switches S2, S3, S6, and S7, resulting in an output of -6Vdc.
These modes encapsulate the MLI's capability to generate a stepped output waveform with precision. The precise activation and deactivation of specific switches, in accordance with the described modes, allow the inverter to function efficiently, thus validating its novel approach in minimizing the switch count while maximizing output versatility.
, Claims:1. A single-phase multilevel inverter (MLI) comprising three DC voltage sources and eight switches, wherein said voltage sources are arranged in a 1:2:3 proportion.
2. The MLI of claim 1, wherein each power semiconductor switch is an Insulated Gate Bipolar Transistor (IGBT) combined with a diode to ensure efficient switching and protection.
3. The MLI of claim 1, configured to produce 13 distinct voltage levels by employing a combination of the three DC voltage sources and the eight switches.
4. The MLI of claim 1, wherein specific switch combinations are operated in a complementary mode to avoid undesirable input voltage conditions.
5. A method for producing a positive half-cycle voltage using the MLI of claim 1, where switch combinations are activated to produce voltage levels ranging from 0Vdc to +6Vdc.
6. A method for producing a negative half-cycle voltage using the MLI of claim 1, where switch combinations are activated to produce voltage levels ranging from -1Vdc to -6Vdc.
7. The MLI of claim 1, wherein the level-shifted pulse width modulation (LSPWM) technique is employed to generate gating signals for the switches, ensuring desired voltage levels at the output.
8. A method for optimizing the MLI performance using MATLAB/Simulink simulations to validate the operation under various parametric conditions.
9. The MLI of claim 1, designed to reduce component count and increase efficiency and reliability for both high-power and medium-power applications.
10. A single-phase MLI system with a minimized switch count, configured to integrate seamlessly with varying input conditions, making it suitable for modern power sources including renewable energies.