Adaptive Dead Time Control for Half-Bridge Power Converters
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Solution Overview
Problem
The dead time in power converters limits the maximum modulation depth and efficiency of PWM-controlled power converters, leading to reduced output voltage and distorted current waveforms, which cannot be fully utilized due to nonlinearity and inefficiencies.
Innovation Solution
A controller and method that modify the dead time interval between switching power semiconductor switches, allowing for variable dead time based on the requested duty cycle, and utilize a diode to conduct current during non-active states of the switches, thereby removing unnecessary dead time and improving duty cycle efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is added to prevent both transistors conducting at the same time, then safety and reliability are improved, but modulation depth and efficiency deteriorate
Solution Approach 1:
The patent implements adaptive dead time adjustment where the dead time duration is dynamically modified based on the PWM duty cycle. When the duty cycle exceeds a predetermined threshold, the controller automatically adjusts the dead time to extend the active state duration, thereby recovering modulation depth and efficiency while maintaining safety during normal operation.
Solution Approach 2:
The controller changes the dead time parameter adaptively based on operating conditions. By monitoring the duty cycle and adjusting the dead time duration accordingly, the system optimizes the trade-off between safety (preventing shoot-through) and efficiency (maximizing active state time), particularly recovering performance at high duty cycles where traditional fixed dead time causes significant losses.
2Reliability
If dead time is increased to ensure no simultaneous conduction, then short circuit prevention is improved, but output voltage and current waveform quality deteriorate
Solution Approach 1:
The system dynamically adjusts dead time based on the PWM command characteristics. For high duty cycle commands where dead time causes significant voltage deviation, the controller compensates by extending the effective active time, thereby maintaining output voltage accuracy while preserving the protective function during critical switching transitions.
3Device complexity
If fixed dead time is used to simplify control, then device complexity is reduced, but modulation depth and duty cycle range are limited
Solution Approach 1:
The controller implements a duty-cycle-dependent dead time adjustment mechanism that automatically adapts the dead time duration based on the PWM command magnitude. This dynamic approach recovers up to 6% modulation depth that would be lost with fixed dead time, while maintaining relatively simple control logic that can be implemented in existing PWM controllers.
4Power
If DC bus voltage is increased to compensate for dead time losses, then output voltage capability is improved, but system cost increases
Solution Approach 1:
Instead of increasing the DC bus voltage to compensate for dead time losses, the patent changes the control parameter (dead time duration) adaptively. This software-based compensation approach recovers the lost modulation depth and output voltage capability without requiring hardware modifications or higher voltage ratings, thereby avoiding increased system cost.
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 enhances the duty cycle and efficiency of power converters by mitigating dead time delays, allowing for a higher modulation depth and smoother output waveforms, reducing losses and costs associated with compensating for dead time limitations.
Implementation Method 1
A controller and method that modify the dead time interval between switching power semiconductor switches, allowing for variable dead time based on the requested duty cycle, and utilize a diode to conduct current during non-active states of the switches
Data Source
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AI summary
The present disclosure relates to a controller, a circuit and method for controlling a power converter using pulse width modulation (PWM). At least one logic block (13, 15, 16) of the controller is configured to re¬ move a command (4) which is configured to control the other power semiconductor switch (2) in a half-bridge (1,2) so that the other power semiconductor switch (2) remains in a non-conductive state while an antiparallel diode (6) allows an electric current (5) to pass in one direction, called the diode's forward direction, while blocking current in the opposite direction. In case the diode (6) is conducting instead of the other power semiconductor switch during the duration of the state of the command, the switching command (4) for the latter is omitted. The controller is further configured to modify the dead time interval (Tdead) between switching from the power semiconductor switch (3) to another power semiconductor switch (4) or vice versa in order to avoid a discontinuity in the transfer function (25).