Variable Speed Drive Segmentation for Compressor Efficiency
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Solution Overview
Problem
Existing variable speed drive arrangements for compressors are expensive and physically large due to the need for a variable frequency drive rated at maximum compressor power, limiting operating range and requiring constant speed operation, which is inefficient and costly.
Innovation Solution
A variable speed drive arrangement comprising a primary electrical machine, a secondary electrical machine, a gearbox, and a controller that schedules output frequency and switches phase connections to control the direction of rotation, allowing for efficient variable speed control with a smaller converter, enabling operation between maximum forward and reverse speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable frequency drive is used to drive a compressor at variable speed, then the compressor can operate at different speeds, but the variable frequency drive must be rated at maximum compressor power which makes it expensive and physically large
Solution Approach 1:
The drive system is segmented into two separate electrical machines: a primary electrical machine that operates at fixed speed and a secondary electrical machine that operates at variable speed. This segmentation allows the variable frequency drive to be sized for only the secondary machine's power requirements rather than the total compressor power, significantly reducing the drive's size and cost while maintaining variable speed capability.
Solution Approach 2:
The system dynamically switches between different operational modes using a first electrical circuit breaker. The primary electrical machine can operate independently at fixed speed, or the secondary electrical machine can be engaged via the circuit breaker to provide variable speed control when needed, allowing the system to adapt its complexity to the operational requirements.
2Ease of operation
If a small variable frequency drive is used for soft starting a constant speed motor, then the start-up is smoother, but the compressor can only be operated at constant speed and must be unloaded
Solution Approach 1:
The system separates the soft start function (handled by the primary electrical machine with small variable frequency drive) from the variable speed operation function (handled by the secondary electrical machine). The first electrical circuit breaker enables switching between these functions, allowing the compressor to achieve both smooth starting and full variable speed operation capability.
3Power
If the operating range of compressors is restricted to higher speeds, then the work done by the load is greater, but the arrangement cannot operate at lower speeds or from stationary
Solution Approach 1:
The system dynamically transitions between operational modes. The primary electrical machine provides fixed speed operation for base load, while the secondary electrical machine can be engaged through the first electrical circuit breaker to provide variable speed control across the full operating range, including acceleration from stationary and operation at lower speeds, thereby expanding the overall operating range while maintaining sufficient power output.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces the size and cost of the converter, allowing for efficient variable speed control of compressors, enabling smaller, more reliable equipment and expanded operating ranges while maintaining efficiency and cost-effectiveness.
Implementation Method 1
a primary electrical machine to supply mechanical power to the gearbox and to receive electrical power
Implementation Method 2
a secondary electrical machine mechanically coupled to the gearbox and electrically coupled to the converter; wherein the secondary electrical machine is adapted to supply or extract mechanical power from the gearbox and to receive or deliver electrical power to the converter
Implementation Method 3
a converter electrically coupled with a power grid; The controller is arranged to schedule output frequency from the converter in the range zero Hertz to maximum frequency
Data Source
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AI summary
A variable speed drive arrangement (10) comprising: a load (12); a gearbox (14) to supply mechanical drive to the load (12); a converter (28) electrically coupled with a power grid (26). Also a primary electrical machine (18) to supply mechanical power to the gearbox (14) and to receive electrical power; and a secondary electrical machine (20) mechanically coupled to the gearbox (14) and electrically coupled to the converter (28). An electrical circuit breaker (30) to selectively electrically couple the primary electrical machine (18) to the secondary electrical machine (20) or to the power grid (26); wherein the secondary electrical machine (20) is adapted to supply or extract mechanical energy from the gearbox (14) and to receive or deliver electrical energy to the converter (28). Also a control method for the arrangement comprising a starting mode and a running mode.