IGBT Junction Temperature Control via High-Frequency Injection PWM
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
At low speeds, multiphase inverters face thermal stress issues due to increasing IGBT switching losses, leading to potential derating or oversizing of switches to prevent thermal overload, which is not practically addressed by reducing switching frequency or using conventional DPWM techniques.
Innovation Solution
Implementing high-frequency injection and discontinuous pulse width modulation (DPWM) in multiphase inverter control to mitigate thermal stress by computing phase duty ratios based on desired output parameters and common mode frequency, reducing switching losses without altering the inverter switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional PWM or SVPWM techniques are used at low speeds, then the inverter can operate at rated power, but IGBT switching losses increase causing thermal stress and potential overload
Solution Approach 1:
The patent applies discontinuous pulse width modulation (DPWM) which periodically zeros out certain phase legs during each switching cycle. This periodic action reduces the number of switching events for IGBTs while maintaining the fundamental output frequency, thereby reducing switching losses and thermal stress during low-speed operation at rated power
Solution Approach 2:
The patent changes the modulation index parameter to be less than unity during low-speed operation. This parameter change allows the inverter to operate at rated power while reducing the duty cycle of switching devices, which directly reduces switching losses and prevents thermal overload
2Loss of energy
If switching frequency is reduced to lower IGBT losses, then switching losses decrease, but the inverter cannot deliver rated power at low speeds
Solution Approach 1:
By implementing DPWM with periodic zero-vector insertion, the patent maintains the fundamental output frequency required for rated power delivery while reducing the effective switching frequency of IGBTs. This allows the inverter to deliver rated power at low speeds without incurring excessive switching losses
Solution Approach 2:
The patent dynamically adjusts the modulation strategy based on operating conditions. During low-speed operation, it switches to DPWM with reduced modulation index, while maintaining conventional PWM at higher speeds. This dynamic adaptation enables rated power delivery across the full speed range without thermal constraints
3Temperature
If derating is applied to prevent thermal overload, then IGBT thermal stress is reduced, but the inverter operates below rated power capability
Solution Approach 1:
The patent uses DPWM to periodically reduce switching activity in certain phase legs, which directly reduces IGBT junction temperature during low-speed operation. This allows the inverter to operate at rated power without thermal derating by maintaining temperature within safe limits through reduced switching frequency
Data Source
AI summary
Methods, apparatus and computer readable mediums are presented for controlling a multiphase inverter in which third harmonic injection pulse width modulation (THIPWM) is used for generating inverter switching control signals at or above a non-zero threshold inverter output frequency, and high frequency injection discontinuous pulse width modulation (HFIDPWM) is used for inverter output frequencies below the threshold, where the threshold frequency corresponds to a threshold period less than or equal to the thermal impedance time constant of the inverter switching devices, and the injected high frequency component for HFIDPWM corresponds to a common mode period less than the thermal impedance time constant to mitigate thermal stress on the inverter switches and low speed inverter output derating.