Coupled-Inductor ZVS Control Through PWM Phase Shift
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Solution Overview
Problem
Existing power systems face challenges in reducing switching losses during state transitions in switching circuits due to non-zero voltage across switches, leading to inefficiencies in power conversion.
Innovation Solution
A switching circuit with a coupled inductor and a controller that adjusts the phase difference between PWM signals for two switch legs to ensure zero voltage switching (ZVS) by controlling the equivalent inductance of the coupled inductor, allowing the inductor ripple current to discharge the switch capacitor and reduce voltage to zero.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional switching circuits are used without ZVS control, then the circuit structure is simple, but switching losses increase due to non-zero voltage across switches during state transitions
Solution Approach 1:
The patent applies preliminary action by pre-charging the switch capacitor through the coupled inductor before the switch transitions to the on-state. The controller activates the anti-parallel diode of the other switch in the bridge leg during the dead-time interval, allowing current to flow through the coupled inductor and charge the capacitor in advance. This ensures that when the switch turns on, the voltage across it is already reduced to zero, eliminating switching losses without requiring complex additional circuitry.
Solution Approach 2:
The coupled inductor serves as an intermediary element that transfers energy between the two switch legs of the bridge circuit. By introducing this magnetic coupling element, the patent enables the switching node voltage to be controlled and reduced to zero before switching occurs. The coupled inductor mediates the energy transfer process, allowing one switch leg to assist the other in achieving ZVS conditions while maintaining a relatively simple overall circuit structure.
2Loss of energy
If ZVS is implemented without phase difference control, then the switching losses are reduced, but the voltage rise time at the switching node increases leading to timing errors
Solution Approach 1:
The patent implements feedback control by continuously monitoring the voltage at the switching node and using this information to adjust the phase difference between the PWM signals of the two bridge legs. The controller measures the actual voltage rise time and compares it with the desired timing, then dynamically adjusts the phase shift to compensate for variations in voltage rise time. This feedback mechanism ensures that ZVS conditions are maintained while minimizing timing errors and maintaining precise switching control.
Solution Approach 2:
The patent applies dynamics by making the phase difference between the PWM signals a variable parameter that can be dynamically adjusted based on operating conditions. Rather than using a fixed phase shift, the controller continuously adapts the phase difference to optimize ZVS performance under varying load and voltage conditions. This dynamic adjustment allows the system to maintain optimal switching timing and minimize voltage rise time variations while preserving the energy-saving benefits of ZVS.
3Loss of energy
If the coupled inductor current is not sufficiently controlled, then the circuit operation is simple, but the ripple current is insufficient to discharge the switch capacitor for ZVS
Solution Approach 1:
The patent employs feedback control to monitor the current through the coupled inductor and adjust the PWM duty cycles of the two bridge legs to maintain the required current level. The controller measures the actual coupled inductor current and compares it with the desired current waveform needed for ZVS, then adjusts the switching signals to correct any deviations. This feedback mechanism ensures sufficient ripple current is generated to discharge the switch capacitor while avoiding excessive current that would increase conduction losses.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the duty cycle and frequency of the PWM signals to optimize the coupled inductor current waveform. By varying these control parameters, the system can generate the appropriate ripple current amplitude and shape needed for ZVS under different operating conditions. This parameter adjustment allows the circuit to maintain sufficient discharge current for the switch capacitor while keeping the control system relatively simple and avoiding excessive current that would increase conduction losses.
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 effectively reduces conduction losses by ensuring the ripple current is sufficient for ZVS, enhancing the efficiency of power conversion in power circuits like inverters and converters.
Implementation Method 1
a coupled inductor comprising: a first winding; and a second winding
Implementation Method 2
the first switch leg and the second switch leg to control currents flowing through the coupled inductor such that ZVS may be applied
Data Source
Figure 1A~1B
Figure 2
Figure 3A
AI summary
Systems and methods are described for performing zero voltage switching (ZVS). A switching circuit may comprise a first switch leg, a second switch leg; a controller, and a coupled inductor. The controller may be configured to operate the first and second switch legs to control a current flowing through the coupled inductor such that ZVS may be applied to the first and second switch legs. The system may recognize a switching event time (e.g., where a pulse width modulation (PWM) signal controls a switch should transition from an off-state to an on-state) of a switch in the first switch leg, and recognize a switching node voltage rise event time of the first switch leg based on a measurement of a voltage at a switching node of the first switch leg. The controller may be configured to drive one or more switches using PWM signals. For example, the controller may drive one or more switches based on determining, for a switching instance, a phase difference between a first PWM signal and a second PWM signal for generating a ripple current for ZVS.