Electric Power Tool PWM Control for Bridge Circuit Heat
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Solution Overview
Problem
In motor control systems using complementary PWM, regenerative current flows back into the power supply when the motor is driven, leading to an increase in power supply voltage, which can cause heating and inefficiency in the bridge circuit.
Innovation Solution
A control device that selectively switches between non-complementary PWM and complementary PWM based on motor state, using a control unit to manage switching elements and diodes within the bridge circuit to either suppress regenerative current or allow it, depending on conditions such as motor rotation speed and elapsed time, thereby controlling the PWM duty ratio to prevent voltage increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If complementary PWM is used to suppress diode heating and temperature rise, then temperature control is improved, but regenerative current flows back into the power supply causing voltage increase and heat generation in the bridge circuit
Solution Approach 1:
The system dynamically switches between complementary PWM and non-complementary PWM modes based on real-time motor state detection. When the motor is stationary or rotating in the opposite direction, non-complementary PWM is used to prevent regenerative current. When the motor rotates in the forward direction, complementary PWM is used to suppress diode heating, achieving adaptive optimization of temperature control while minimizing harmful regenerative current effects.
Solution Approach 2:
The invention changes the PWM control parameter (switching mode) based on motor rotation direction and speed conditions. By detecting motor state through Hall sensors and comparing rotation direction with command direction, the system selects appropriate PWM parameters (complementary or non-complementary mode) to optimize performance and reduce harmful effects under different operating conditions.
2Object-generated harmful factors
If non-complementary PWM is used to prevent regenerative current, then power supply voltage stability is improved, but diode heating and temperature rise occur
Solution Approach 1:
The system dynamically switches between complementary PWM and non-complementary PWM modes based on real-time motor state detection. When the motor is stationary or rotating in the opposite direction, non-complementary PWM is used to prevent regenerative current. When the motor rotates in the forward direction, complementary PWM is used to suppress diode heating, achieving adaptive optimization of temperature control while minimizing harmful regenerative current effects.
Solution Approach 2:
The invention changes the PWM control parameter (switching mode) based on motor rotation direction and speed conditions. By detecting motor state through Hall sensors and comparing rotation direction with command direction, the system selects appropriate PWM parameters (complementary or non-complementary mode) to optimize performance and reduce harmful effects under different operating conditions.
3Speed
If PWM duty ratio is reduced below matching rotation speed, then motor speed control is improved, but braking current flows in reverse direction causing voltage increase
Solution Approach 1:
The system performs preliminary detection of motor rotation state using Hall sensors before PWM control is applied. By comparing the detected rotation direction with the command direction in advance, the system determines whether to enable complementary PWM mode, preventing regenerative current and voltage increase before they occur during PWM operation.
Solution Approach 2:
The system continuously monitors motor rotation direction through Hall sensors and provides feedback to the control unit. This feedback mechanism enables real-time detection of reverse rotation conditions, allowing the control unit to switch PWM modes appropriately and prevent harmful regenerative current effects during speed control operations.
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 effectively suppresses regenerative current and power supply voltage increase, reducing heat generation in the bridge circuit and improving motor control efficiency by dynamically switching between PWM modes based on motor conditions.
Implementation Method 1
The control device, when the motor is driven, selects a high-side switch and a low-side switch to be use to form a current path, depending on a rotation position of the motor, and holds one of the switches in an ON state and alternately turns on/off the other by a PWM signal having a predetermined duty ratio.
Implementation Method 2
Diodes are connected in parallel to the switching elements inside the bridge circuit. The diodes corresponding to the respective switching elements are used to flow electric current deriving from energy stored in motor winding from a negative electrode toward a positive electrode of the DC power source, when the current path to the motor is interrupted by other switching elements.
Implementation Method 3
When the motor is rotating at the time when the motor starts to be driven, and if a duty ratio of the PWM signal is smaller than a duty ratio that matches a rotation speed of the motor, electric current in the reverse direction flows to the above closed loop due to an induced voltage generated by rotation of the motor after a reflux of a driving current is ended.
Data Source
AI summary
An electric power tool in one aspect of the disclosure comprises an operation unit, a bridge circuit having a plurality of switching elements, and a control unit. The control unit is configured to select from the plurality of switching elements a pair of switching elements forming a current path of a motor. The control unit selectively executes one of non-complementary PWM in which one of the selected switching elements is turned on and the other turned on/off, and complementary PWM in which, in addition to the same control as that of the non-complementary PWM, a switching element connected to the same terminal of the motor as the other of the selected switching elements is turned on/off so that an on/off state of the switching element is reversed to that of the other of the selected switching elements.