Brushless Motor Control via Dynamic d-Current Attenuation
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Solution Overview
Problem
Electric motors with 'slender intermediate circuits' face challenges in maintaining constant torque when powered by highly pulsating DC voltage, as they require a minimum threshold voltage to operate efficiently, which is not met by standard single-phase power supplies, leading to insufficient motor current and torque fluctuations.
Innovation Solution
Implementing dynamic field attenuation by regulating the d-current with a sinusoidal profile at double the main frequency, minimizing q-current ripple, and using a control system with a function generator and extreme-value regulator to track the phase voltage based on intermediate circuit voltage, allowing operation at lower terminal voltages and increased power consumption, thereby maintaining constant torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a slender intermediate circuit with minimum or no intermediate circuit reactance is used, then the installation volume is reduced and service life is improved, but the intermediate circuit voltage pulsates strongly at twice the main frequency, causing insufficient motor current and torque fluctuations
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the d-current component based on the instantaneous value of the intermediate circuit voltage. The control system continuously monitors the voltage and modulates the d-current to compensate for voltage pulsations, transforming the static control approach into a dynamic one that adapts to changing voltage conditions, thereby maintaining stable motor operation despite voltage fluctuations
Solution Approach 2:
The patent changes the parameter of d-current from a constant or simple control signal to a dynamically varying current component that is modulated according to the intermediate circuit voltage. By varying the d-current parameter in response to voltage pulsations, the system compensates for voltage instability and maintains constant torque output
2Quantity of substance
If the intermediate circuit voltage is allowed to pulsate strongly, then smoothing capacitors can be reduced or eliminated, but the motor cannot maintain required torque constant below a certain threshold voltage
Solution Approach 1:
The patent implements feedback by continuously monitoring the intermediate circuit voltage and using this information to adjust the d-current component. The control system feeds back the voltage information to the current regulator, which then modifies the d-current to compensate for voltage drops, ensuring that motor torque remains constant even when voltage pulsates strongly
Solution Approach 2:
The d-current component acts as an intermediary that mediates between the pulsating intermediate circuit voltage and the motor torque output. By introducing this intermediate control variable, the system decouples the direct relationship between voltage and torque, allowing voltage to pulsate while maintaining constant torque through the mediating effect of the d-current regulation
3Use of energy by moving object
If d-current is regulated to zero for optimum efficiency, then field-influencing component is eliminated, but torque ripple increases and noise behavior deteriorates
Solution Approach 1:
The patent applies periodic action by introducing a d-current component that pulsates at twice the main frequency, synchronized with the intermediate circuit voltage ripple. This periodic d-current modulation counteracts the torque ripple caused by voltage pulsations, reducing noise and improving motor operation while maintaining efficiency
Solution Approach 2:
The patent introduces asymmetry by allowing the d-current to be non-zero and specifically tailored to counteract the asymmetric voltage pulsations. Rather than maintaining symmetric zero d-current for theoretical optimum efficiency, the system uses asymmetric d-current modulation to achieve practical optimum performance with reduced torque ripple and noise
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 enables the motor to maintain nearly constant torque despite pulsating intermediate circuit voltage, reduces torque ripple, and increases intermediate circuit voltage through energy feedback, ensuring stable power flux and reduced noise, even at lower voltage levels.
Implementation Method 1
a single-phase, mains AC voltage having a supply or main frequency is rectified and supplied to an inverter via a slender intermediate circuit
Implementation Method 2
the inverter being actuated for powering and commutating the electric motor
Implementation Method 3
a q-current as torque-forming component of the current-space vector is regulated perpendicularly to the permanent magnetic field
Implementation Method 4
a d-current can be regulated as field-influencing component of the current-space vector in the direction of the permanent magnet field
Data Source
AI summary
The present invention relates to a method and a system for controlling a permanent magnet excited, brushless, electronically commutated, three-phase electric motor (2) wherein a single-phase main AC voltage (UN) having a mains frequency (fN) is rectified and supplied to an inverter (8) via a slender intermediate circuit (6) containing no, or minimum, intermediate circuit reactance as intermediate circuit voltage (Uz) pulsating at double the mains frequency (2fN) which is actuated for powering and commutating the electric motor (2). Control takes place by means of a field-oriented current-space vector regulator, wherein a q-current (iq) as torque-forming component of the current-space vector (i) is regulated perpendicularly to the permanent magnetic field and a d-current (id) can be regulated as a field-influencing component of the current-space vector (i) in the direction of the permanent magnet field. In this case, dynamic field attenuation occurs, wherein the d-current (id) in the negative range is defined with a sinusoidal profile and at double the main frequency (2fN) and wherein the d-current (id) is regulated according to its phase position and its amplitude such that ripple of the q-current (iq) is minimized. Since the q-current as torque forming component is proportional to the torque, thus the torque ripple is also minimized, in spite of the strongly pulsating intermediate circuit voltage (Uz).