AC Motor Control System Torque Fluctuation Reduction
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Solution Overview
Problem
Existing AC electric motor control systems that variably control DC link voltage using a boost converter face challenges in minimizing output fluctuations without increasing electromagnetic noise, particularly in electric-powered vehicles, where torque fluctuations due to DC voltage fluctuations can lead to reduced quietness and vehicle performance issues.
Innovation Solution
A control system that includes a boost converter, an inverter, a pulse width modulation control unit, a rectangular-wave voltage control unit, and a phase restriction control unit, which manages the DC voltage and AC voltage to the motor, ensuring that the modulation degree does not exceed a reference value, and adjusts the voltage command to prevent rectangular wave voltage control when the voltage phase exceeds a limit phase, thereby minimizing torque fluctuations and electromagnetic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the carrier frequency of the boost converter is reduced to restrain DC voltage fluctuations, then torque fluctuations in the AC electric motor are reduced, but electromagnetic noise increases
Solution Approach 1:
The patent applies dynamics by making the carrier frequency variable rather than fixed. The control device dynamically adjusts the carrier frequency based on the instantaneous value of the DC voltage: when DC voltage fluctuation is detected, the carrier frequency is reduced to stabilize voltage; when DC voltage is stable, the carrier frequency is increased to reduce electromagnetic noise. This dynamic adaptation resolves the contradiction between voltage stability and noise reduction.
Solution Approach 2:
The patent changes the parameter of carrier frequency based on operating conditions. By monitoring DC voltage stability and adjusting the carrier frequency accordingly, the system optimizes performance across different operating states. This parameter change strategy allows the system to achieve both voltage stabilization and electromagnetic noise reduction at different times based on actual needs.
2Power
If rectangular wave voltage control is used to increase fundamental wave component of AC voltage, then voltage output to motor is improved, but torque fluctuations increase due to DC voltage fluctuations
Solution Approach 1:
The patent implements feedback control by continuously monitoring DC voltage and detecting fluctuations. When fluctuations are detected during rectangular wave voltage control, the system responds by adjusting the carrier frequency to reduce fluctuations, thereby preventing torque variations. This feedback mechanism ensures that power output improvement does not come at the cost of torque stability.
Solution Approach 2:
The patent applies preliminary anti-action by proactively adjusting the carrier frequency in response to detected DC voltage fluctuations before they can cause significant torque variations. The control device anticipates potential torque instability and takes corrective action by modifying the carrier frequency, thereby preventing the harmful effect rather than merely responding to it.
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 system effectively restrains output fluctuations in AC electric motors without increasing electromagnetic noise, maintaining vehicle quietness and performance by dynamically controlling the voltage and phase to prevent torque fluctuations and electromagnetic noise.
Implementation Method 1
a boost converter configured to execute bidirectional DC electric power conversion between a power storage device and an electric power line
Implementation Method 2
an inverter configured to convert the DC voltage on the electric power line into an AC voltage to be applied to the AC electric motor
Implementation Method 3
The pulse width modulation control unit is configured to control the AC voltage output from the inverter to the AC electric motor by pulse width modulation control based on a comparison between a sinusoidal voltage command signal for operating the AC electric motor
Implementation Method 4
The rectangular-wave voltage control unit controls the inverter in accordance with the torque command value such that an absolute value of a voltage phase of the rectangular wave voltage is increased when the absolute value of torque of the AC electric motor is increased
Data Source
AI summary
Fluctuations in output of an AC electric motor are restrained without increasing electromagnetic noise of a boost converter. When subjecting the AC electric motor to rectangular wave voltage control, output torque T is controlled by varying a voltage phase φv. In a region where a voltage phase is large (φv=θ2), fluctuations in torque T relative to changes in a DC voltage VH corresponding to the amplitude of a rectangular wave voltage are larger than in a region where the voltage phase is small (φv=θ1). The AC electric motor is controlled such that the rectangular wave voltage control in a region where voltage phase φv is larger than a limit-phase line PLN indicated by a set of limit phases set for each DC voltage VH is avoided.