Inverter Switch Load Redistribution via Phase Angle Adjustment
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Solution Overview
Problem
Existing inverter control methods using space vector modulation lead to thermal overloading of power semiconductor switches, especially at low rotational speeds, due to uneven loading of switches, resulting in increased technical complexity and reduced lifespan.
Innovation Solution
The method involves adjusting the phase angle of the current space vector to redistribute the load across switches, allowing one overloaded switch to be relieved while loading another more heavily, thereby achieving a more even distribution of load and reducing thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If space vector modulation is used to control the inverter, then the electrical machine can be supplied with multi-phase electric current, but individual power semiconductor switches are switched very frequently or for very long time at low speeds, causing thermal stress and requiring complex inverter design
Solution Approach 1:
The patent applies dynamics by making the switching states of power semiconductor switches adjustable and adaptable based on operating conditions. The control device dynamically selects from multiple possible switching states to achieve more even load distribution across switches, particularly at low speeds where thermal stress is problematic. This dynamic adaptation allows the inverter to maintain reliability without requiring switches to be over-designed for worst-case scenarios.
Solution Approach 2:
The patent changes the switching parameters (switching states) of the power semiconductor switches based on the operating point of the electrical machine. By modifying which switches are activated and for how long, the control device redistributes the thermal load more evenly across all switches, preventing any single switch from being subjected to excessive thermal stress that would require complex cooling or oversized component design.
2Loss of energy
If certain zero vectors are used in certain angular ranges to reduce switching losses, then switching losses are reduced, but some power semiconductor switches are permanently loaded and overloading cannot be avoided
Solution Approach 1:
The patent makes the selection of zero vectors dynamic rather than static. Instead of using certain zero vectors in certain angular ranges as fixed rules, the control device continuously evaluates the thermal state and load distribution across switches, selecting zero vectors that will maintain even loading while minimizing switching losses. This dynamic approach prevents permanent overloading of specific switches.
Solution Approach 2:
The control device uses feedback about the thermal load and switching states to make intelligent decisions about which zero vectors to apply. By monitoring the operating conditions and adjusting the switching strategy accordingly, the system can reduce switching losses while preventing any single switch from becoming permanently overloaded, thus maintaining reliability.
3Reliability
If power semiconductor switches are designed for very long switch-on times and very high currents, then thermal overloading is prevented, but the inverter becomes technically complex
Solution Approach 1:
The patent changes the switching parameters dynamically to prevent any single switch from being subjected to very long switch-on times and very high currents continuously. By redistributing the switching workload across multiple switches through intelligent selection of switching states, the system maintains switch reliability without requiring each switch to be designed for worst-case continuous operation, thereby reducing inverter complexity.
Data Source
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AI summary
The invention relates to a method for controlling an inverter (10) using space-vector pulse width modulation, in particular to control an electric machine (14), the inverter (10) being equipped with a plurality of controllable switches (S) and being designed to provide a polyphase electric current (IU, IV, IW), in particular to supply polyphase electric current (IU, IV, IW) to the electric machine (14). In said method, a desired current space vector (I1*) having a desired phase angle (alpha1) and a desired amplitude (I1) is predefined, and the inverter (10) is controlled in such a way that a plurality of different successive switching states (V0-V7) is established for the switches (S) in order to provide the electric current (IU, IV, IW) in the form of a current space vector (I*), the inverter (10) being controlled in such a way that the current space vector (I2*) is provided at a phase angle (alpha2) which differs from the desired phase angle (alpha1) in order to load the switches (S) according to a desired load value (m) for the switches (S).