Bidirectional AC Switch Drive Circuit for Permanent Magnet Motor
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Solution Overview
Problem
Conventional synchronous motors have low efficiency due to a low starting point and unpredictable rotor direction, leading to inefficient operation in applications like small fans and water pumps, as the stator's alternating magnetic field struggles to consistently rotate the permanent magnetic rotor.
Innovation Solution
A drive circuit with a controllable bidirectional AC switch, AC-DC conversion circuit, and position sensor that controls the stator winding to ensure the rotor rotates in a predetermined direction by switching the AC switch based on the magnetic pole position and AC power source polarity, minimizing energy consumption by the AC-DC conversion circuit when the switch is shorted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the starting point of the motor is set to be low to ensure starting, then the motor can start reliably, but the motor cannot operate at a relatively high working point, resulting in low efficiency
Solution Approach 1:
The patent applies preliminary action by using the position sensor to detect the rotor's initial position before starting, and the switch control circuit to pre-set the switching timing of the bidirectional thyristor based on this detected position. This preliminary detection and pre-setting of switching parameters allows the motor to start reliably at a low starting point while being able to operate efficiently at higher working points, as the switching timing can be optimized for different operating conditions.
2Measurement precision
If a conventional drive circuit with constant power supply to the position sensor is used, then the magnetic pole position can be continuously detected, but the conversion circuit constantly consumes power even when not needed, resulting in high energy consumption
Solution Approach 1:
The patent applies periodic action by making the position sensor operate intermittently rather than continuously. The sensor is activated only during specific periods when needed for detection (such as during starting or when the rotor is in certain positions), and the switch control circuit supplies power to the sensor only during these intervals. This periodic operation maintains adequate position detection capability while dramatically reducing the average power consumption of the conversion circuit.
3Device complexity
If the rotor is allowed to oscillate and accelerate naturally with the alternating magnetic field, then the starting process is simple, but the rotor cannot be ensured to rotate in the same direction every time, resulting in unpredictable rotation direction
Solution Approach 1:
The patent applies feedback by using the position sensor to continuously monitor the rotor's magnetic pole position during the starting process. The switch control circuit receives this position information and uses it to adjust the switching timing and sequence of the bidirectional thyristor in real-time. This feedback mechanism ensures that the stator magnetic field is always applied in the correct phase relationship with the rotor position, guaranteeing that the rotor accelerates and rotates in the predetermined direction every time, eliminating the unpredictability of natural oscillation-based starting.
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 improves the operational efficiency of the motor by ensuring consistent rotor direction and reducing energy wastage, allowing the motor to operate at a higher working point with enhanced energy utilization.
Implementation Method 1
the stator produces an alternating magnetic field causing the permanent magnetic rotor to be oscillated
Implementation Method 2
the stator winding drives the rotor to rotate only in a predetermined direction
Implementation Method 3
a position sensor configured to detect a magnetic pole position of the permanent magnet rotor
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A drive circuit for an electric motor connected in series with an AC power source (24) between a first node A and a second node B. The drive circuit includes a controllable bidirectional AC switch (26), an AC-DC conversion circuit (28) connected in parallel with the controllable bidirectional AC switch between the first node and the second node, a position sensor (20) configured to detect a position of a rotor of the motor, and a switch control circuit (30) configured to control the controllable bidirectional AC switch (26) to be conductive or non-conductive in a predetermined way, based on the position of the rotor and a polarity of the AC power source.