Voltage Step-Down Circuit for Power Converter Imbalance
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Solution Overview
Problem
Conventional power converters experience increased ripple current and temperature in smoothing capacitors due to voltage imbalances in three-phase AC power supplies, leading to reduced lifespan and efficiency, especially at low motor rotation speeds.
Innovation Solution
A power converter with a voltage step-down circuit and imbalance determining unit that switches the voltage step-down switching element when voltage imbalance occurs, reducing ripple current and stabilizing the DC bus voltage, thereby preventing excessive heat and prolonging capacitor lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a step-up converter circuit is used to correct voltage imbalance, then the DC bus voltage can be maintained, but the ripple current in the smoothing capacitor increases and temperature rises
Solution Approach 1:
The patent introduces a voltage step-down circuit as an intermediary component between the rectifier and inverter. This circuit includes a step-down switching element, reactor, and smoothing capacitor that work together to reduce voltage fluctuations caused by imbalance, thereby reducing ripple current and temperature rise in the main smoothing capacitor while maintaining stable DC bus voltage.
Solution Approach 2:
The patent changes the operating parameters by introducing a voltage step-down switching element that can dynamically adjust the voltage level. By controlling the ON/OFF state of this switching element based on detected voltage imbalance, the system optimizes the DC bus voltage and reduces harmful ripple effects without requiring continuous step-up conversion.
2Stability of the object's composition
If the step-up converter continuously operates to correct voltage imbalance, then the DC bus voltage is maintained, but loss increases
Solution Approach 1:
The patent employs periodic switching action of the voltage step-down switching element based on detected voltage imbalance conditions. The control unit periodically activates the step-down circuit only when voltage imbalance is detected, rather than continuous operation, thereby reducing energy loss while maintaining voltage stability when needed.
3Loss of energy
If PWM control is used to reduce voltage at low rotation speeds, then motor efficiency improves, but the peak value of output voltage increases causing increased iron loss
Solution Approach 1:
The patent applies preliminary voltage regulation by the step-down circuit before the voltage is applied to the motor. By pre-reducing voltage fluctuations and peak values at the DC bus level, the system prevents excessive peak voltages from reaching the motor during PWM operation at low speeds, thereby reducing iron loss without compromising motor efficiency.
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
The solution stabilizes the operation of the power converter, reduces loss, and extends the lifespan of the smoothing capacitor by minimizing ripple current and temperature increases, while maintaining efficient motor operation across varying rotation speeds.
Implementation Method 1
a rectifier rectifying a three-phase AC voltage supplied from a three-phase AC power supply
Implementation Method 2
a voltage step-down circuit including a voltage step-down switching element, a reactor, a backflow prevention element, and a smoothing capacitor and stepping down a DC voltage supplied from the rectifier
Implementation Method 3
a smoothing capacitor smooths the DC voltage
Implementation Method 4
an inverter circuit converting the DC voltage smoothed by the smoothing capacitor into an AC voltage
Data Source
AI summary
A power converter that includes a rectifier rectifying a voltage supplied from a three-phase AC power supply, a voltage step-down circuit including a voltage step-down switching element, a reactor, a backflow prevention element, and a smoothing capacitor and stepping down a DC voltage supplied from the rectifier, and an inverter circuit converting the DC voltage smoothed by the smoothing capacitor into an AC voltage. The power converter includes an imbalance determining unit determining, based on states of the voltage step-down circuit and the smoothing capacitor, whether or not voltage imbalance has occurred in the three-phase AC power supply and a voltage step-down control unit performing switching of the voltage step-down switching element in a case where the imbalance determining unit determines that the voltage imbalance has occurred.