Parallel Inverter Arms with Mixed Switching Elements
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Solution Overview
Problem
Existing power conversion devices with mixed switching elements, such as IGBTs and MOSFETs, face inefficiencies and increased noise due to differing switching frequencies and characteristics, particularly when considering the losses associated with freewheeling diodes during high-frequency switching.
Innovation Solution
The power conversion device employs a configuration where each arm is structured with switch sections in parallel, utilizing a higher switching response element and a shorter reverse recovery time freewheeling diode, allowing current to flow through the freewheeling diode during specific phases, thereby reducing losses and noise by optimizing the combination of switching elements and freewheeling diodes for different switching frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency of the inverter circuit is increased to improve efficiency and reduce noise, then the switching loss of the MOSFET decreases, but the loss of the freewheeling diode increases significantly
Solution Approach 1:
The patent applies local quality by assigning different characteristics to different parts of the circuit. Specifically, the upper-stage IGBT is paired with a first freewheeling diode having longer reverse recovery time, while the lower-stage MOSFET is paired with a second freewheeling diode having shorter reverse recovery time. This localized differentiation allows each stage to operate optimally at its designated switching frequency without the second diode's losses affecting the first stage.
Solution Approach 2:
The patent segments the freewheeling diodes into two distinct types with different reverse recovery time characteristics. The first freewheeling diode is associated with the IGBT upper stage, and the second freewheeling diode is associated with the MOSFET lower stage. This segmentation allows independent optimization of each stage's switching performance and loss characteristics.
2Adaptability or versatility
If different types of switching elements (IGBT and MOSFET) are mixed in the inverter circuit to achieve wide application range, then the efficiency is improved across different operating ranges, but the noise and loss increase due to different switching characteristics
Solution Approach 1:
The patent applies local quality by pairing each switching element type with a specifically optimized freewheeling diode. The IGBT upper stage uses a first freewheeling diode with longer reverse recovery time suitable for lower frequency operation, while the MOSFET lower stage uses a second freewheeling diode with shorter reverse recovery time optimized for higher frequency operation. This localized optimization reduces noise and losses generated by mismatched characteristics.
3Productivity
If the duty factor of the lower-stage MOSFET is increased for two-phase modulation control at low load, then the efficiency is improved, but the loss of the freewheeling diode connected to the MOSFET increases
Solution Approach 1:
The patent applies parameter changes by selecting a second freewheeling diode with specifically optimized reverse recovery time parameter for the MOSFET lower stage. This parameter optimization allows the MOSFET to operate with high duty factor at low loads, improving efficiency while the optimized diode parameter minimizes the associated freewheeling losses during these high-duty-factor operations.
Data Source
AI summary
A power conversion device that includes an inverter circuit in which arms are connected in parallel to each other between a DC positive terminal and a DC negative terminal in accordance with a number of phases of alternating currents of a plurality of phases, the arms for the respective phases each including two switch sections that are connected in series and to be brought into conduction in an on state and out of conduction in an off state, the power conversion device being configured to convert electric power between DC power and AC power of the plurality of phases while a connection point between the two switch sections of each of the arms is set as an AC input or output point of each phase.