Motor Controller Noise Cancellation Circuit
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Solution Overview
Problem
Motor controllers for electric power steering systems experience common mode noise due to stray capacitance between the electric motor and the frame ground, which contaminates the vehicle's power supply lines, affecting the reliability and efficiency of the system.
Innovation Solution
The implementation of a motor controller with dual noise cancellation circuits, each comprising an RLC circuit and a switch element, connected to the positive and negative power supply lines, which generate noise cancellation currents that counteract common mode noise currents at rising and falling voltage timings, thereby reducing noise emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PWM drive is performed on the electric motor using a three-phase inverter circuit, then the electric motor can be controlled to achieve desired current values, but common mode noise is generated due to stray capacitance between the motor and frame ground, which contaminates the power supply lines
Solution Approach 1:
The patent converts the harmful common mode noise current into a beneficial cancellation current by using the same stray capacitance path. The noise cancellation circuit generates a current that flows through the stray capacitance in the opposite direction to the noise current, thereby canceling it out. This transforms the previously harmful stray capacitance into a useful pathway for noise cancellation.
Solution Approach 2:
The noise cancellation circuit acts as an intermediary between the power supply lines and the frame ground. It introduces a controlled current path that mediates the noise current flow, providing a counteracting current that neutralizes the common mode noise before it can contaminate the power supply lines.
2Ease of operation
If the power supply lines are made long to connect the vehicle power supply to the EPS, then the EPS can be mounted on the vehicle, but the noise current is mixed into the power supply lines in the vicinity of the vehicle power supply
Solution Approach 1:
The noise cancellation circuit performs preliminary anti-action by generating counteracting currents before the common mode noise can significantly contaminate the power supply lines. The circuit is designed to detect and counteract noise currents at their source, preventing them from propagating along the long power supply lines to the vehicle power supply.
3Object-generated harmful factors
If dual noise cancellation circuits are added to reduce common mode noise, then electrical cleanliness of power supply lines is improved, but device complexity increases
Solution Approach 1:
The noise cancellation circuits are designed to perform multiple functions: they cancel common mode noise, provide electromagnetic interference filtering, and protect the power supply lines. By making the circuits multi-functional, the patent reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving comprehensive noise reduction.
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 configuration effectively minimizes common mode noise by generating opposing noise cancellation currents, improving the electrical cleanliness of the power supply lines and enhancing the overall performance and reliability of the electric power steering system.
Implementation Method 1
The first noise cancellation circuit includes a first RLC circuit being a circuit of a first resistor, a first coil, and a first capacitor... the second noise cancellation circuit includes a second RLC circuit being a circuit of a second resistor, a second coil, and a second capacitor
Implementation Method 2
at a rising timing and a falling timing of the output voltage of each phase (phase voltage) in each PWM period, a current flows via a stray capacitance that exists between the three-phase electric motor and a frame ground
Data Source
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AI summary
A motor controller includes a motor drive circuit, a noise cancellation circuit, and a control unit. The motor drive circuit supplies electric power to an electric motor. The noise cancellation circuit includes an RLC circuit, a switch element, and a pull-down resistor. One end of the RLC circuit is electrically connected to a positive terminal of a power supply via the switch element, and the other end of the RLC circuit is electrically connected to a frame ground. A connection point between the RLC circuit and the switch element is electrically connected to a negative terminal of the power supply via the pull-down resistor. The control unit turns ON the switch element for a predetermined time at falling timings of phase voltages output from the motor drive circuit.