Magnetron Power Supply Current Overshoot Control
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Solution Overview
Problem
The existing high frequency heating devices, such as microwave ovens, face challenges in suppressing the overshoot of input current generated during the unstable state immediately after the magnetron begins oscillating, leading to potential overload and shut-down issues due to over-voltage detection.
Innovation Solution
The solution involves adjusting the PWM setting values for the control signal of the input current in both the non-oscillation (start mode) and oscillation (steady mode) of the magnetron, allowing for a smooth transition from the start state to the steady state, thereby suppressing the overshoot of the input current and preventing overloads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the magnetron starts oscillating from a non-oscillating state, then the high frequency heating operation begins, but an overshoot of input current is generated causing overload and shut-down issues
Solution Approach 1:
The control system performs preliminary actions by detecting the oscillation state of the magnetron and adjusting the PWM duty cycle before the full power operation begins. The controller gradually increases the duty cycle from an initial value during the startup phase, preventing current overshoot before it occurs. This preliminary control adjustment ensures a smooth transition from non-oscillating to oscillating state without generating harmful current spikes.
2Loss of energy
If a dead time is provided to delay turning off the semiconductor switching element, then the generation of unnecessary loss and noise is prevented, but the response time of the control system increases
Solution Approach 1:
The control system dynamically adjusts the dead time parameter based on the operating conditions. During startup when the magnetron is transitioning from non-oscillating to oscillating state, the dead time is optimized to prevent current overshoot. During steady-state operation, the dead time is adjusted to minimize switching losses. This dynamic adjustment of the dead time parameter allows the system to optimize both energy efficiency and response time according to the specific operating phase.
3Power
If the PWM setting value is set to maximum output, then the heating power is maximized, but the overshoot of input current during unstable state causes overload
Solution Approach 1:
The control system implements periodic monitoring of the magnetron oscillation state and adjusts the PWM duty cycle accordingly. During the startup phase, the system uses a lower initial duty cycle that is gradually increased in periodic steps as the magnetron stabilizes. This periodic adjustment strategy allows the system to eventually reach maximum power output while preventing current overshoot during the unstable transition period. The controller continuously adapts the duty cycle based on real-time oscillation detection.
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 the overshoot of the input current during unstable states, preventing overloads and ensuring stable operation of the magnetron, even when the PWM setting value is set to maximum output, thus avoiding shut-downs caused by over-voltage.
Implementation Method 1
a semiconductor switching element carries out a high frequency switching operation
Implementation Method 2
immediately after the oscillation of a magnetron
Data Source
AI summary
A power supply for a high frequency heating is provided. When processes from a non-oscillation to an oscillation of a magnetron are finely classified, the non-oscillation (a start mode), the oscillation (a start mode), and the oscillation (a steady mode) are obtained. A problem resides in an unstable state immediately after the oscillation. When a PWM setting value at this time is set to a value lower than a PWM setting value in the steady mode, even if the PWM setting value during the steady mode is set to a maximum output value, the input current is not controlled to a large current including the over-shoot immediately after the oscillation. After the magnetron shifts to a stable state, the PWM setting value shifts to a PWM setting value of an actual steady mode, so that the over-shoot of the input current can be suppressed as much as possible.