Motor Control Unit for Compressor Pump Efficiency
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Solution Overview
Problem
Existing motor control systems for piston compressor pumps in low-speed ranges face challenges in minimizing electrical losses, which affects the coefficient of performance in refrigeration systems.
Innovation Solution
A control unit comprising a motor speed calculation unit, speed controller unit, D/A converter, comparator unit, and PWM unit, operating in conjunction with a frequency converter to optimize motor control by reducing current levels and providing efficient PWM control signals, thereby reducing electrical losses and increasing the coefficient of performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional motor control systems are used at low rotational speeds, then the motor can drive the piston compressor pump, but electrical losses increase due to high current levels in the frequency converter and motor
Solution Approach 1:
The control system changes operating parameters by implementing peak current control that dynamically adjusts current levels based on rotational speed. At low speeds below 4000 rpm, the system reduces peak current magnitude while maintaining adequate torque production, thereby reducing electrical losses in the frequency converter and motor without compromising the coefficient of performance
2Loss of energy
If current levels are reduced to minimize electrical losses, then energy efficiency improves, but motor torque and driving capability may be compromised
Solution Approach 1:
The control system employs periodic PWM (pulse width modulation) switching to deliver current in controlled pulses rather than continuous flow. This periodic action allows the motor to produce adequate torque through high peak currents during active phases while maintaining lower average current levels, thus reducing electrical losses without compromising torque production capability
Solution Approach 2:
The system dynamically adjusts current control parameters based on operating conditions, particularly rotational speed. The peak current control algorithm modifies current magnitude and pulse width in real-time to match torque requirements, ensuring adequate motor force is delivered only when needed while minimizing energy losses during low-demand operating phases
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 solution reduces electrical losses by approximately 5-8% at low rotational speeds, enhancing the coefficient of performance of refrigeration systems by optimizing power distribution in motor and compressor pump operations.
Implementation Method 1
a motor speed calculation unit for calculating, in the digital domain, the rotational speed of the motor based on measured BEMF voltages from the motor
Implementation Method 2
a D/A converter unit for converting the calculated stator current reference from the speed controller unit to an analog stator current reference
Implementation Method 3
a comparator unit for comparing, in the analog domain, the analog stator current reference and a measured current in the intermediate DC circuit of the frequency converter
Implementation Method 4
a PWM unit for providing PWM control signals to a phase commutation unit in response to the comparator unit output
Data Source
Figure 1
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Figure 3a~3d
AI summary
The present invention relates to a control unit configured for controlling a motor driving a piston compressor pump below a selected rotational speed value. The motor is driven by a frequency converter comprising a rectifier unit being operatively connected to an inverter unit via an intermediate DC circuit. According to the present invention the control unit comprises a motor speed calculation unit for calculating, in the digital domain, the rotational speed of the motor based on measured BEMF voltages from the motor, a speed controller unit for calculating, in the digital domain, a stator current reference based on the calculated rotational speed and a rotational speed reference, a D/A converter unit for converting the calculated stator current reference from the speed controller unit to an analog stator current reference, a comparator unit for comparing, in the analog domain, the analog stator current reference and a measured current in the intermediate DC circuit of the frequency converter, and providing a comparator unit output in response to this comparison, and a PWM unit for providing PWM control signals to a phase commutation unit in response to the comparator unit output, said phase commutation unit providing a switch pattern to the inverter unit based on the measured BEMF voltages from the motor. The present invention further relates to an associated method.