SPIM Drive Circuit for Hot Switching and Low Starting Current
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Solution Overview
Problem
Existing single-phase induction motors (SPIMs) face issues with large starting currents, energy wastage due to overheating, and inefficient torque and speed fluctuations, especially during starting and operating modes, and lack optimal adjustment and control based on load situations, leading to high energy consumption.
Innovation Solution
A circuit and method involving a driver with a rectifying unit, two inverter units, and switching mechanisms to control two windings of the SPIM, allowing for variable-frequency and industrial-frequency operations, reducing starting current, and enabling hot switching between modes while minimizing energy loss and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the starting current of M winding is increased to produce sufficient starting torque, then the SPIM can start reliably, but the starting current becomes 5-10 times the rated current causing overheating and energy waste
Solution Approach 1:
The patent divides the single-phase power source into two separate winding circuits (main winding M and auxiliary winding A) with independent control. Each winding receives controlled current through separate inverter bridges, allowing independent optimization of current magnitude and phase angle. This segmentation enables the main winding to provide starting torque while the auxiliary winding provides magnetic field synthesis, avoiding the need for excessive current in a single winding.
Solution Approach 2:
The patent dynamically adjusts the current magnitude and phase angle parameters for both main and auxiliary windings through inverter control. By changing these electrical parameters based on operating conditions (starting, running, braking), the system optimizes the balance between starting torque production and energy consumption, preventing the 5-10 times rated current surge in traditional designs.
2Device complexity
If the SPIM operates at fixed industrial frequency, then the motor structure remains simple, but the motor cannot be adjusted to optimal working points based on various load situations resulting in extra energy consumption
Solution Approach 1:
The patent transforms the fixed-frequency motor into a variable-frequency drive system using two inverter bridges that can independently control the frequency and amplitude of currents supplied to main and auxiliary windings. This dynamic control capability allows the motor to adapt to varying load conditions and operate at optimal working points, significantly reducing energy consumption while maintaining relatively simple motor structure.
Solution Approach 2:
The patent makes the motor system universal by enabling it to perform multiple functions: starting with high torque, running at variable speeds, operating at different frequencies, and adapting to various load conditions. The inverter-based control system provides multi-functionality that allows a single motor design to serve diverse applications efficiently.
3Loss of energy
If power electronic devices are used to achieve variable-frequency operation and optimal control, then starting current is reduced and energy loss is minimized, but all the energy of the SPIM must come from the driver
Solution Approach 1:
The patent merges the functions of two separate inverter bridges into a unified control system that shares common DC bus and control electronics. The first inverter bridge controls the main winding while the second inverter bridge controls the auxiliary winding, but both draw power from the same rectified DC source. This merging reduces overall system complexity compared to having completely independent drive systems for each winding.
Solution Approach 2:
The patent introduces a common DC bus as an intermediary between the AC power source (through rectifier) and the two inverter bridges. This intermediary DC link decouples the two inverter systems, allowing them to operate independently while sharing the power conversion infrastructure. The DC bus mediates power distribution, reducing the complexity of direct AC-AC conversion for each winding.
4Device complexity
If the motor magnetic flux is elliptical due to non-optimal design, then the motor can operate with simple structure, but torque and speed fluctuations occur resulting in large energy consumption
Solution Approach 1:
The patent implements closed-loop control through the inverter systems that continuously monitor and adjust the currents in main and auxiliary windings. By measuring actual operating conditions and feedback-adjusting the current magnitude and phase angle, the system maintains circular magnetic flux patterns and stable torque production, eliminating the elliptical flux problems of simple designs while keeping motor structure relatively simple.
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 achieves reduced starting current, lower energy loss, stable torque and speed, extended motor life, and reliable operation with adjustable frequency control, including hot switching to grid frequency, even with inverter unit damage.
Implementation Method 1
a rectifying unit (11), a direct-current bus (12), a first inverter unit (13) and a second inverter unit (14)... The rectifying unit (11) is connected to the direct-current bus (12)
Implementation Method 2
The first inverter unit (13) is connected to a first winding (31) of the SPIM (3) through a first switch (15), and the second inverter unit (14) is connected to a second winding (32) of the SPIM (3)
Implementation Method 3
The alternating-current unit (2) comprises an input alternating-current power (21), a second switch (22) and a capacitor (23)
Implementation Method 4
there is a set of working windings on the stator, called the main winding (hereinafter, M winding), which can only produce positive and negative alternating pulse magnetic fields in the air gap of the motor
Data Source
AI summary
A circuit and a method for driving a SPIM are provide. The circuit comprises a driver and an alternating-current unit. The driver comprises a rectifying unit, a direct-current bus, a first inverter unit and a second inverter unit. The rectifying unit is connected to the direct-current bus, and the direct-current bus is respectively connected to the first inverter unit and the second inverter unit. The first inverter unit is connected to a first winding of the SPIM through a first switch, and the second inverter unit is connected to a second winding of the SPIM. The alternating-current unit comprises an input alternating-current power, a second switch and a capacitor. The input alternating-current power is connected to the first winding and the rectifying unit. The method can drive the SPIM in both variable frequency and industrial frequency, and hot switch from variable-frequency to industrial-frequency without interruption.