Reciprocating Compressor Piston Positioning for Stable BLDC Starts
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Solution Overview
Problem
Existing piston positioning processes in reciprocating compressors fail to adequately position the piston near its top dead center, leading to motor desynchronization and start failures due to high resistant torque from coolant gas pressure, resulting in inefficiencies, vibrations, and noise.
Innovation Solution
A piston positioning process for BLDC motors in reciprocating compressors that adjusts the initial and maximum current values based on piston position, reduces step sizes, and uses 150-degree electrical degree switching to stabilize torque and minimize oscillations, ensuring the piston is near top dead center before starting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piston is positioned near its top dead center before the start procedure, then the motor can overcome the resistant torque from coolant gas pressure, but the positioning process may cause mechanical oscillations and noise
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The switching frequency is adjusted dynamically based on the piston position and compression cycle phase, allowing the system to adapt to changing mechanical conditions. This dynamic adjustment reduces mechanical oscillations and noise while ensuring reliable piston positioning near top dead center.
Solution Approach 2:
The patent changes the parameter of switching frequency from a constant value to a variable parameter that depends on piston position and compression cycle phase. By modifying this key parameter dynamically, the system achieves both reliable positioning and reduced mechanical oscillations, resolving the contradiction between start success rate and harmful mechanical effects.
2Object-generated harmful factors
If the switching frequency is reduced to minimize mechanical oscillations, then noise and vibration decrease, but the positioning precision and response time may be compromised
Solution Approach 1:
The patent uses dynamic adjustment of switching frequency based on real-time piston position feedback. When the piston is in positions where low frequency causes positioning errors, the frequency is increased. When the piston is in positions where high frequency causes oscillations, the frequency is reduced. This dynamic approach maintains both positioning precision and low noise levels.
Solution Approach 2:
The patent implements feedback control by monitoring piston position and using this information to adjust the switching frequency. The controller receives position information and continuously adapts the switching frequency to maintain optimal positioning precision while minimizing mechanical oscillations and noise throughout the compression cycle.
3Manufacturing precision
If the switching frequency is increased to improve positioning accuracy, then piston positioning precision improves, but mechanical oscillations and noise increase
Solution Approach 1:
The patent dynamically adjusts switching frequency based on the piston's position in the compression cycle. High switching frequencies are used only when necessary for positioning accuracy, while lower frequencies are used during phases where oscillations would be problematic. This temporal and spatial variation in frequency resolves the contradiction between positioning accuracy and mechanical oscillations.
4Device complexity
If a fixed switching frequency is used, then the control system is simpler, but it cannot adapt to the dynamic torque requirements throughout the compression cycle
Solution Approach 1:
The patent transitions from a fixed switching frequency to a dynamic, variable frequency control system. The switching frequency is continuously adjusted according to piston position and compression phase, allowing the system to adapt to varying torque requirements. This dynamic control improves torque management effectiveness while maintaining reasonable system complexity through algorithmic rather than hardware-based adaptation.
Solution Approach 2:
The patent changes the switching frequency parameter from fixed to variable, allowing it to adapt to different operational conditions throughout the compression cycle. This parameter change enables the control system to match torque requirements dynamically, improving reliability without requiring complex additional hardware, thus balancing complexity and effectiveness.
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
The process stabilizes piston positioning, reduces power consumption, minimizes noise and vibrations, and enhances motor efficiency by matching current values to piston position, preventing desynchronization and improving start reliability.
Implementation Method 1
brushless direct current (BLDC) triphasic synchronized motor that generates trapezoidal shaped induced voltages
Implementation Method 2
resistant high torque region, due to the pressure of coolant gas over the piston
Data Source
AI summary
A positioning process of a piston of a reciprocating compressor is applied before the beginning of a start procedure of a BLDC motor. The reciprocating compressor includesthe BLDC motor having a rotor associated mechanically to the piston;a frequency inverter;a current sensor; anda processing unit having a current controller and a command unit.The switches are driven by the processing unit to control the currents applied to the phases of the motor.In each new step of the process, the value of an initial current is higher or equal to the value of the initial current of a previous step; andthe value of a maximum current is higher or equal to the value of the maximum current of the previous step. The process includes adjusting the current at each position to avoid the return of the piston and mechanical oscillation in each new step.