This innovation is a regenerative Cascaded Multicell Converter (CMC), which comprises at least two power cells configured for each phase of one or more phases of the converter. Each phase includes a coupled inductor that connects a rectifier to an isolated power source, thereby delivering power to each power cell. Additionally, the regenerative CMC incorporates a controller located at the input side, which regulates the input power to each power cell based on a phase-shifted technique. This configuration aims to enhance the efficiency and performance of power conversion in regenerative applications.
Figure: Laboratory setup
Diode-bridge passive rectifiers in conventional Cascaded Multicell Converters (CMCs) introduce significant harmonic components in the input current. They also prevent CMCs from operating in regenerative modes, limiting their application in systems requiring bidirectional power flow.
PWM active rectifier-based power cells, proposed for regeneration, require inductors to filter switching frequency components due to two-level voltage operation at the input side. The harmonic components in the input current of PWM rectifier-based power cells increase the transformer's rating, leading to higher costs and inefficiencies.
These challenges necessitate a more efficient and regenerative CMC design.
- The solution introduces a coupled inductor for each phase, significantly reducing harmonic distortion and eliminating the need for overrated transformers.
- Ensures equal current sharing among power cells and supports efficient multilevel voltage operation, which enhances overall system performance.
- PWM rectifier-based power cells enable regeneration capability.
- The use of a single controller for all power cells simplifies regulation and maintenance, while the coupled inductor's ability to filter out-of-phase harmonic components optimizes the converter's efficiency.
- Multilevel voltage operation at both input and output enhances efficiency and reduces transformer overrating.
- It shows higher fault tolerance as it allows for operation with reduced capacity by bypassing faulty cells.
- The modular transformer design facilitates easy transportation, installation, and maintenance.
The experimental validation of the proposed converter has been carried out on a 400 V, 4.5 kVA prototype with three cells per phase.
- A coupled inductor of 20 mH with three limbs (similar to a conventional three-phase inductor except negligible air-gap) is used for each phase since the number of cells per phase is three. The primary side of the transformer is connected in delta.
- Two 32-bit floating point microcontroller units F28377D from Texas Instruments are used, one for the implementation of rectifier side closed loop control in d-q frame and the other for inverter side open loop V/f control.
A prototype has been developed and tested in lab environment
The experimental results indicate a reduction in harmonic content, with the regenerative CMC achieving seven-level output phase voltage at 40 Hz operation and five-level output phase voltage at 30 Hz operation with a bypassed cell. The coupled inductor configuration ensures equal current sharing among all power cells in one phase.
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This innovation offers significant societal benefits by enhancing energy efficiency and reducing harmonic pollution in power systems. By optimizing energy usage and reducing grid disturbances, the CMC contributes to a more stable and sustainable electrical infrastructure. Its ability to support bidirectional power flow facilitates applications in renewable energy integration, and industrial drives.
Its modular design and fault tolerance also improve reliability and reduce maintenance costs, making clean energy technologies more accessible and reliable for communities worldwide.
This innovation's ability to support bidirectional power flow facilitates applications in renewable energy integration, electric vehicles, and industrial drives.
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