Polyphase Inverter Fault Control via Dynamic PWM
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Solution Overview
Problem
Existing control systems for polyphase electrical machines require overdimensioning of power switches and redundancy in the number of inverters to maintain reliability, especially in critical applications like aviation, where faults need to be mitigated without exceeding normal current amplitudes.
Innovation Solution
A method and device that utilize at least two polyphase inverters in parallel, with each inverter branch capable of handling the full phase current during faults by modifying pulse-width modulation to keep power switches conductive without switching when currents exceed 80% to 120% of the maximum amplitude, allowing sinusoidal voltage generation without overdimensioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power switches are designed to switch currents twice the normal amplitude to handle inverter faults, then reliability is improved, but device complexity and overdimensioning increase
Solution Approach 1:
The patent applies dynamics by making the power switch conduction state adjustable based on operating conditions. During fault conditions, the PWM control is modified to keep power switches conductive without switching when current exceeds a threshold (80%-120% of Imax/n), transitioning from normal switching operation to continuous conduction mode. This dynamic adaptation allows the system to handle fault currents without requiring power switches to be permanently overdimensioned, resolving the contradiction between reliability and device complexity.
2Reliability
If additional inverters are added to the system to maintain reliability during faults, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies parameter changes by modifying the PWM control parameters in response to detected faults. When a fault is detected in one inverter, the control system changes the operating parameters of the remaining healthy inverters by adjusting their duty cycles and switching patterns. This allows the healthy inverters to compensate for the faulty one and maintain balanced three-phase currents without requiring additional inverters, thus resolving the contradiction between reliability and device complexity.
3Loss of energy
If power switches remain conductive without switching during high current periods, then energy loss is reduced, but control precision becomes more difficult
Solution Approach 1:
The patent applies feedback by continuously monitoring the phase current amplitude and using this information to dynamically adjust the PWM control strategy. The control system detects when the absolute value of phase current exceeds the threshold (80%-120% of Imax/n) and responds by modifying the power switch conduction pattern to eliminate switching during these high-current periods. This feedback mechanism enables the system to automatically optimize energy efficiency while maintaining proper control, resolving the contradiction between energy loss and control precision.
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 reliable control of polyphase electrical machines by isolating faulty branches and redistributing current without overloading power switches or requiring additional inverters, reducing dissipation and maintaining operational safety margins.
Implementation Method 1
controlling the inverters by pulse-width modulation so as to control the switching of the power switches
Implementation Method 2
the faulty branch is isolated, the phase of the electrical machine corresponding to the faulty branch being powered by the or each other corresponding inverter branch
Implementation Method 3
the power switches of the or each other corresponding inverter branch conductive in succession and without switching while the absolute value of the phase current concerned is greater than or equal to a threshold... reducing dissipation
Data Source
AI summary
A polyphase electrical machine controlled by at least two parallel inverters, each including a number of branches equal to a number of phases of the machine and controlled by PWM. When detecting an inverter branch is faulty, the faulty branch is isolated and the phase in question is powered by each corresponding other inverter branch. The PWM is modified to make power switches of each other branch conductive in succession, without switching while absolute value of the current of the phase in question is greater than or equal to a threshold of 80% to 120% of (n−1)Imax/n, n is number of inverters and Imax is maximum magnitude of the phase current. It is thus possible to continue generating substantially sinusoidal voltages on each of the phases, while avoiding overdimensioning the power switches to ensure in event of a fault they can deliver currents of amplitude higher than in normal operation.