Power conversion device and air conditioner
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The instability of permanent magnet synchronous motors due to ripple components in DC voltage from commercial power sources, leading to frequent switching in weak field control, causing distortion and potential motor malfunctions such as overcurrent and rapid speed changes.
Innovation Solution
A power conversion device comprising an inverter that converts DC voltage to AC voltage for a motor with windings and permanent magnets, and a controller that adjusts the output current to manage magnetic flux, stabilizing the motor operation by controlling the saturation level of the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If weak field control is used to extend the operating range of the motor, then the motor can operate at higher speeds, but the frequent switching between normal control and weak field control causes instability and distortion in the output voltage and current
Solution Approach 1:
The patent applies preliminary action by predicting whether weak field control will be needed in advance. The prediction unit calculates a prediction value based on the rate of change of rotational speed and the current rotational speed, determining before the switching point is reached whether weak field control should be activated. This allows for smooth, pre-planned transitions between control modes, avoiding abrupt switching and the resulting instability and distortion in output voltage and current.
2Speed
If the switching threshold for weak field control is set to respond quickly to speed changes, then the control response is fast, but the DC voltage ripple causes frequent false switching between normal and weak field control
Solution Approach 1:
The patent implements feedback by using the prediction unit to continuously monitor the rotational speed and its rate of change, comparing the calculated prediction value against the saturation level. This feedback mechanism allows the system to adjust the switching decision based on actual operating conditions, preventing false switching caused by DC voltage ripple while maintaining fast response to genuine speed changes. The prediction value acts as a feedback signal that stabilizes the control state transitions.
3Speed
If the saturation level is set low to enable weak field control earlier, then the motor can achieve higher speeds sooner, but the output voltage becomes saturated more frequently causing control inaccuracies
Solution Approach 1:
The patent applies dynamics by making the saturation level adjustable rather than fixed. The control system can dynamically adjust the saturation level based on operating conditions, allowing the threshold for initiating weak field control to adapt to the current state of the motor and power supply. This dynamic adjustment enables the system to achieve higher speeds when conditions permit while maintaining control precision when DC voltage ripple is significant, resolving the contradiction between early weak field control activation and output voltage control accuracy.
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 enables stable operation of motors by reducing the frequency of weak field control switching, preventing malfunctions and ensuring consistent motor performance.
Implementation Method 1
an inverter which converts, in order to drive a motor equipped with a stator having windings and a rotor having permanent magnets, supplied DC voltage to an AC output voltage
Implementation Method 2
a controller which, when the output voltage is lower than the saturation level, increases an output current of the inverter to generate in the windings a magnetic flux in such a direction as to weaken or strengthen a magnetic flux generated by the permanent magnets
Data Source
AI summary
In order to achieve a power conversion device with which a motor can be stably driven, a power conversion device is provided with: an inverter, which converts supplied DC voltage to an AC output voltage and supplies the AC output voltage to windings, and which, in accordance with the DC voltage, changes the saturation level at which the output voltage is saturated, in order to drive a motor equipped with a stator having the windings and a rotor having permanent magnets; and a controller which, when the output voltage is lower than the saturation level, increases the output current of the inverter such that a magnetic flux that weakens or strengthens the magnetic flux generated by the permanent magnets is generated in the windings. An air conditioner including the power conversion device is also disclosed.