Motor Drive Carrier Frequency Control for Ripple Current
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Solution Overview
Problem
In motor drive systems using PWM control, high ripple current leads to increased eddy currents and magnet temperature in AC electric motors, causing demagnetization and power loss, while excessive reduction of ripple current results in increased switching losses in the power converter.
Innovation Solution
A motor drive system that adjusts the carrier frequency based on a reference value for ripple current width, detected using current sampling operations, to maintain an appropriate level of ripple current, thereby preventing demagnetization and switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If carrier frequency is increased to reduce ripple current, then ripple current width is reduced, but switching loss increases
Solution Approach 1:
The patent applies dynamics by making the carrier frequency adjustable rather than fixed. The control unit dynamically changes the carrier frequency based on operating conditions (torque, speed, temperature) to optimize the balance between ripple current reduction and switching loss minimization. This resolves the contradiction by allowing the system to adapt the carrier frequency to different operational states rather than being constrained to a single fixed value.
Solution Approach 2:
The patent changes the parameter of carrier frequency based on multiple operating conditions including torque, speed, and magnet temperature. By adjusting this key parameter according to real-time system state, the patent achieves optimal ripple current suppression while preventing excessive switching losses that would occur with uniformly high carrier frequency.
2Loss of energy
If carrier frequency is decreased to reduce switching loss, then switching loss is reduced, but ripple current increases causing magnet temperature rise and demagnetization
Solution Approach 1:
The control unit dynamically adjusts carrier frequency based on magnet temperature feedback. When temperature approaches critical levels, the system increases carrier frequency to reduce ripple current and prevent demagnetization. When temperature is acceptable, it lowers carrier frequency to reduce switching losses, thus dynamically resolving the contradiction between these two opposing requirements.
Solution Approach 2:
The patent implements feedback control by monitoring magnet temperature and using this information to adjust carrier frequency. The temperature detection unit provides real-time feedback to the control unit, which then modifies the carrier frequency to maintain temperature within safe limits while optimizing efficiency, thereby resolving the contradiction between switching loss and temperature control.
3Object-affected harmful factors
If fixed high carrier frequency is used, then ripple current is suppressed, but switching loss increases and efficiency decreases
Solution Approach 1:
The patent transforms the fixed carrier frequency approach into a dynamic, condition-based adjustment system. The carrier frequency is optimized for each operating state (low torque, high torque, different speeds, temperature conditions), achieving effective ripple suppression only when necessary while maximizing efficiency in other operating conditions.
Solution Approach 2:
The system changes the carrier frequency parameter based on multiple inputs including torque commands, speed, and temperature. This parameter adaptation allows the system to achieve high efficiency in normal operation while maintaining adequate ripple suppression when operating conditions require it, thus resolving the efficiency-ripple current contradiction.
4Loss of energy
If fixed low carrier frequency is used, then switching loss is reduced, but ripple current causes excessive heat and demagnetization risk
Solution Approach 1:
The patent uses temperature feedback to ensure reliability. When magnet temperature approaches demagnetization thresholds, the control unit increases carrier frequency to suppress ripple current, regardless of the switching loss implication. This feedback mechanism guarantees reliability by preventing demagnetization while allowing efficiency optimization during normal operation.
Solution Approach 2:
The system dynamically adjusts carrier frequency to maintain reliability margins. During normal operation with acceptable temperatures, low carrier frequency reduces switching losses. When temperature indicators suggest approaching demagnetization risk, the system dynamically increases frequency to ensure reliability, thus resolving the contradiction between efficiency and reliability.
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 approach effectively maintains the ripple current width at an optimal level, reducing switching losses in the power converter and preventing demagnetization in the AC electric motor, leading to improved efficiency and extended motor performance.
Implementation Method 1
a current detector detecting motor current
Implementation Method 2
power converter performing pulse width modulation (PWM) control
Implementation Method 3
a plurality of semiconductor switching elements connected in series between the positive terminal and the negative terminal
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A ripple detection unit (310) detects a ripple current width (Irp) of a motor current controlled according to PWM control. A ripple reference setting unit (320) sets a reference value (Irp#) of the ripple current width. A frequency adjusting unit (350) sets a control signal (Vfq) indicating a carrier frequency of the PWM control according to a ripple current width deviation. A carrier generation unit (360) generates a carrier (Vcr) of the frequency based on the control signal (Vfq). Thus, it is possible to realize feedback control of the carrier frequency for maintaining the ripple current width at an appropriate level.