Multiphase Rotary Machine Control via Line-to-Line Current Zero Crossings
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Solution Overview
Problem
Conventional control systems for multiphase rotary machines face difficulties in performing sensorless control due to increased modulation factor of sinusoidal PWM voltage, which complicates the measurement of phase currents and affects the accuracy of rotational position determination.
Innovation Solution
A control system that converts direct current voltage into alternating current voltage for multiphase rotary machines, using zero crossing detectors and a command voltage determiner to modulate the voltage based on detected zero crossings of line-to-line currents and their changes, ensuring reliable rotation control independent of the modulation factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If sinusoidal PWM voltage with high modulation factor is used to control multiphase rotary machine, then torque production efficiency is improved, but phase current measurement accuracy deteriorates making sensorless control difficult
Solution Approach 1:
The patent introduces an intermediary calculation method that derives phase current information indirectly through line-to-line voltage measurements and mathematical relationships rather than direct current sensing. By using the relationship between line-to-line voltages and phase currents through PWM switching states, the system obtains current information without direct measurement, thus resolving the contradiction between high power efficiency and measurement accuracy.
Solution Approach 2:
The patent replaces the mechanical/electrical current measurement system with a computational approach. Instead of using current sensors to directly measure phase currents, the system substitutes this with voltage measurements and mathematical calculations based on PWM switching patterns, eliminating the measurement accuracy limitations while maintaining torque production efficiency.
2Use of energy by moving object
If modulation factor of sinusoidal PWM voltage is increased, then voltage utilization is improved, but difficulty of performing sensorless control increases
Solution Approach 1:
The patent implements a feedback mechanism where the control system continuously monitors line-to-line voltages and uses this information to calculate phase current states. This feedback loop allows the system to maintain accurate sensorless control even at high modulation factors by constantly updating the current state based on voltage measurements and PWM switching patterns.
Solution Approach 2:
The patent changes the measurement parameters from direct current measurement to voltage-based indirect measurement. By shifting from measuring current directly to measuring voltages and deriving current information through mathematical relationships, the system enables sensorless control to work effectively across a wider range of modulation factors including high values.
3Ease of manufacture
If conventional current measurement method is used, then implementation is simple, but measurement periods are reduced making measurement difficult at high modulation factors
Solution Approach 1:
The patent enables continuous useful action by allowing current information to be derived throughout the entire PWM cycle through voltage measurements and mathematical calculations, rather than being limited to specific measurement windows. This continuous derivation method maintains implementation simplicity while eliminating the time loss associated with restricted measurement periods.
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 controls the rotation of multiphase rotary machines without sensors, maintaining accuracy and efficiency across varying modulation factors, enabling reliable operation and maximizing torque production.
Implementation Method 1
output a sinusoidal PWM (Pulse Width Modulated) voltage to be applied to each of the three-phase windings
Implementation Method 2
an induced voltage in one phase winding of the three-phase rotary electric machine at a timing when a phase current to flow through the one phase winding becomes zero depends on the amount of change in the phase current
Data Source
AI summary
A control system aims at converting, via a switching circuit, a direct current voltage into an alternating current voltage to be applied to multiphase windings of a multiphase rotary machine to thereby control rotation of the multiphase rotary machine. In the control system, a command voltage determiner determines a command voltage value for an alternating current voltage to be applied to the multiphase windings based on a zero crossing of a line-to-line current and a zero crossing of the amount of change in the line-to-line current. A driving unit drives the switching circuit on and off based on the determined command voltage value to thereby modulate the direct current voltage to the alternating current voltage to be applied to the multiphase windings.