Transformer-Based Cascaded Speed Control: Achieving Precise Motor Speed Ratios Through Transformer Turn Optimization for Multi-Motor Systems

Abstract

The study mainly analyses the relationship between precision control and speed of cascaded transformers connected to DC motors in a simulated power plant prototype. The prototype system was designed to observe specific rotational speed ratios between 3 DC motors where the second motor is operating at 50% of the first motor\'s speed, and the third motor operating at 30% of the second motor\'s speed. Controlling turn ratios of the transformer while maintaining uniform primary voltage across all transformers, the system was capable of executing with precise speed control with 0.57% error for the second motor and 4.125% error for the third motor, leading towards a high accuracy-based system prototype. By incorporating full-wave bridge rectifiers for current conversion from AC to DC and additional filtering components, the prototype ensured stable operational execution. Focusing on the advantages of the transformer-based approach for industrial applications requiring precise motor speed control, voltage-speed relationship-based graphs were plotted. This research provides valuable insights for power plant designers seeking efficient methods to implement cascaded speed control systems while maintaining power quality and operational stability.

Introduction

Industrial power plants often require precise speed control of multiple motors running at specific ratios. Traditional electronic speed controllers and variable frequency drives add complexity, maintenance, and reduce reliability. This research proposes an alternative approach by adjusting transformer turn ratios to achieve predetermined speed ratios between three DC motors in a cascaded system.

The configuration involves three transformers with equal primary voltages supplying three DC motors where:

• The second motor runs at 50% speed of the first,

• The third motor runs at 30% speed of the second.

Key challenges include determining optimal transformer turn ratios, managing AC-to-DC conversion with minimal ripple, ensuring efficient power transmission, and validating speed accuracy and stability.

The study uses Proteus simulation software to model the system, including step-down transformers, full-wave bridge rectifiers, resistors for ripple reduction, rheostats for fine-tuning motor speeds, and measurement instruments like voltmeters, ammeters, oscilloscopes, and tachometers.

The system design involves:

• Equal primary voltage input to transformers,

• Step-down voltages proportional to desired speed ratios,

• Rectification of AC to DC for motor operation,

• Real-time RPM monitoring to verify speed ratios.

Components like bridge rectifiers, transformers, rheostats, and tachometers are crucial for ensuring stable DC supply and precise motor control. Resistors filter out ripples to provide clean power, while rheostats allow resistance adjustment to fine-tune speeds without physically altering transformers.

The experimental results demonstrate that transformer turn ratio manipulation can effectively control motor speeds at defined ratios, providing a potentially simpler, cost-effective alternative to complex electronic controllers in industrial motor speed management.

Proteus software plays a critical role by enabling precise simulation of electrical parameters and circuit behavior before physical implementation, supporting the design, analysis, and validation of the transformer-based motor control system.

Conclusion

With minimal error margins (0.57% and 4.125%) and precise speed ratios (50% and 30%), the experimental setup successfully demonstrated a transformer-based solution for cascaded motor speed control. The design\'s effectiveness was verified by continuous and multiple simulation testing in Proteus, showing strong correlations between transformer turn ratios, resulting motor speeds and output voltages. Signal quality analysis revealed that appropriate filtering components significantly improved the stability of rectified DC power, ensuring reliable motor operation across all three circuits. The system\'s progressive deduction in current consumption (0.22A, 0.13A, and 0.05A), indicating efficient power distribution being proportional to each individual motor\'s speed requirements. This research provides valuable insights for power plant engineers seeking effective methods to implement multi-level and precise speed control systems while maintaining power quality and operational stability.

References

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Copyright

Copyright © 2025 Md. Nahul Rahman, Sachitra Halder. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.