Preheating apparatus and preheating method for compressor
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Solution Overview
Problem
Existing methods for preheating compressors, such as using electric heating belts or supplying power to stator windings, are inefficient, costly, and can cause mechanical wear or noise issues, particularly in high-power compressors with small stator windings.
Innovation Solution
A preheating apparatus that uses a control unit to manage the connection and disconnection of switch apparatuses, generating a superimposition of three-phase high-frequency alternating current and two-phase direct current to improve heating efficiency and reduce noise, by employing a PWM control module to synchronize the power supply with the electric motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an electric heating belt is installed on the compressor casing to heat the lubricating oil, then the lubricating oil viscosity is reduced, but the heating efficiency is poor and the heating time is long
Solution Approach 1:
The compressor motor serves dual purposes: driving the compressor and heating the lubricating oil. The stator windings generate heat through copper loss and core loss during operation, which directly heats the lubricating oil without requiring external heating devices, thus reducing heating time and improving efficiency
Solution Approach 2:
The patent replaces the mechanical electric heating belt system with an electromagnetic heating system utilizing the motor's stator windings. The electromagnetic field generated by the stator windings produces heat through resistive heating and core loss, which is more efficient than external thermal conduction heating
2Temperature
If direct current is supplied to the stator winding to generate copper loss for heating, then the lubricating oil is heated, but the heating power is limited due to small stator winding resistance in high-power compressors
Solution Approach 1:
The patent changes the electrical parameters by using alternating current instead of direct current, and specifically uses high-frequency alternating current to generate significant core loss in addition to copper loss. This parameter change enables much higher heating power in high-power compressors with small stator winding resistance
Solution Approach 2:
The patent employs periodic alternating current at high frequency to generate heating effect. The periodic nature of the alternating current creates continuous core loss and copper loss in the stator windings, providing sustained high-power heating capability
3Temperature
If alternating current with sine wave PWM modulation is supplied to generate core loss and eddy current loss for heating, then heating is achieved, but the heating effect is unsatisfactory and electric motor noise problems exist
Solution Approach 1:
The patent changes the waveform parameter from sine wave PWM modulation to square wave PWM modulation. This parameter change improves heating efficiency by generating more consistent core loss and reduces electric motor noise by eliminating the modulation artifacts associated with sine wave PWM
Solution Approach 2:
The patent uses high-frequency periodic alternating current to generate heating while the periodic nature at appropriate frequencies helps reduce noise compared to lower frequency or modulated waveforms
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 apparatus enhances preheating efficiency and reduces mechanical wear and noise issues, particularly in high-power compressors with small stator windings.
Implementation Method 1
supply a direct current to a stator winding of the electric motor, so that the current flows through a resistor of the stator winding to generate a copper loss to emit heat
Implementation Method 2
supply an alternating current to the stator winding of the electric motor, to generate a core loss and an eddy current loss on the electric motor
Implementation Method 3
generate a core loss and an eddy current loss on the electric motor, where the eddy current loss is a loss caused by an eddy current generated by the alternating magnetic field of the stator in a rotor core and a permanent magnet
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Provided is a preheating apparatus (100) for a compressor, the apparatus comprising an inverter circuit (102) and a control unit (106), wherein the inverter circuit (102) comprises a first switch apparatus (1021), a second switch apparatus (1022), and a third switch apparatus (1023), and a PWM control module (104) of the control unit (106) outputs first, second and third PWM output module control signals, a PWM output module (105) of the control unit (106) comprises a first counter (1051), a second counter (1052) and a third counter (1053), and respectively compares the first, second and third PWM output module control signals with first, second and third count vales, which have triangular waves, of the fist counter (1051), the second counter (1052) and the third counter (1053) to respectively generate first, second and third PWM control signals, which respectively control the connection and disconnection of the first switch apparatus (1021), the second switch apparatus (1022) and the third switch apparatus (1023), so as to respectively control the power of a corresponding three-phase stator winding provided by a power source (101) to an electric motor (103) of a compressor, at least two of the first, second and third PWM output module control signals being of constant numerical values. The preheating apparatus (100) superimposes a three-phase high-frequency alternating current and a two-phase direct current which are generated on the electric motor (103), such that the pre-heating effect can be improved and the noise can be reduced.