Power Bridge Control for Loss Balancing in Rotating Machines
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Solution Overview
Problem
Existing power bridge control methods fail to minimize instantaneous losses in semiconductor switches at low electrical frequencies, leading to inefficiencies in rotating electrical machines, particularly during startup or blocked rotor conditions.
Innovation Solution
A method for controlling a power bridge by adjusting the duty cycle and common mode voltage to balance switching and conduction losses between upper and lower semiconductor switches, with specific balancing implemented when the electrical frequency is below a threshold, and prioritizing switching loss minimization at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional PWM control is used with fixed switching frequency, then the control is simple and reliable, but instantaneous losses are not minimized at low electrical frequencies leading to reduced current capacity
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The control device adapts the switching frequency dynamically based on the electrical frequency of the rotating electrical machine. At low electrical frequencies, the switching frequency is increased to minimize instantaneous losses, while at higher frequencies, the switching frequency returns to nominal levels. This dynamic adaptation resolves the contradiction between minimizing losses and maintaining current capacity.
Solution Approach 2:
The patent changes the parameter of switching frequency based on operating conditions. By monitoring the electrical frequency and adjusting the switching frequency accordingly, the system optimizes instantaneous loss minimization at low frequencies without compromising overall performance. This parameter change allows the system to adapt to varying operational demands and resolve the trade-off between loss reduction and current capacity.
2Loss of energy
If switching frequency is increased to minimize instantaneous losses at low frequencies, then losses are reduced, but thermal management becomes more challenging due to reduced thermal filtering
Solution Approach 1:
The patent uses dynamic adjustment of switching frequency to address the thermal management challenge. By increasing switching frequency only when electrical frequency is low (where instantaneous losses are most problematic), the system minimizes losses without subjecting the semiconductor switches to continuously high switching frequencies that would cause excessive thermal stress. The thermal capacities of the chip-package-substrate assembly can effectively filter the temperature variations under this dynamic control strategy.
Solution Approach 2:
The system changes the switching frequency parameter adaptively based on the electrical frequency condition. At low electrical frequencies, the switching frequency is temporarily increased to reduce instantaneous losses, but returns to nominal levels at higher frequencies, preventing cumulative thermal stress. This conditional parameter change resolves the contradiction between loss minimization and thermal management.
Data Source
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AI summary
The invention relates to a method performed in a power bridge (3) comprising multiple arms (B1, B2, Bi, Bn). Each arm comprises upper and lower semiconductor switches arranged in series and connected in parallel to first and second terminals (B+, B-) of a common voltage source (2). The mid-point of the arm is connected to a phase of an electrical load (1). The aforementioned switches are controlled complementarily by pulses having a duty factor set value (RC1, RC2, RCi, RCn) determined as a function of a first phase voltage set value (V1, V2, Vi, Vn) in relation to a reference terminal of the electrical load (1) and of a common-mode voltage (V0) in relation to one of the first or second terminals, such as to control the switching losses of the switches. According to the invention, the common-mode voltage (V0) is determined such as to balance switching losses and conduction losses between the switches.