Noise reduction circuit, load system, power conversion device, and refrigeration device
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Solution Overview
Problem
When the voltage of the power source of the noise canceller is lower than the DC link voltage of the power converter, there is a disadvantage regarding the insufficient flow of compensation current.
Innovation Solution
The noise reduction circuitry sets the voltage Vcc to be equal to or more than the maximum value of the absolute value of V(t) and includes a noise detection unit that detects common mode noise, amplifies the detected noise current, and uses high-speed transistors with low voltage resistance to compensate for the noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the voltage of the power source of the noise canceller is set lower than the DC link voltage of the power converter, then elements with low voltage resistance can be used in the noise canceller, but the compensation current flow becomes insufficient
Solution Approach 1:
The patent changes the voltage parameter Vcc of the power source in the noise canceller to be equal to or greater than the maximum absolute value of V(t). This parameter change ensures that the compensation current can flow sufficiently while still allowing the use of elements with low voltage resistance, thereby resolving the contradiction between ease of manufacture and reliability
Solution Approach 2:
The patent employs high-speed transistors that can dynamically adjust and supply sufficient compensation current even with low voltage resistance. The dynamic current supply capability of these transistors ensures reliable noise cancellation performance while maintaining ease of manufacture with low-voltage elements
2Reliability
If high-speed transistors with low voltage resistance are used in the noise canceller, then the voltage resistance is reduced and compensation current can flow better, but the device complexity increases
Solution Approach 1:
By optimizing the voltage parameter Vcc to be equal to or greater than the maximum absolute value of V(t), the patent enables the use of simple low-voltage transistors rather than requiring complex high-voltage transistor configurations. This parameter change reduces device complexity while maintaining reliable compensation current flow
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 suppresses the insufficient flow of compensation current and reduces impedance, allowing for reliable noise cancellation even when the power source voltage is lower than the DC link voltage.
Implementation Method 1
an operational amplifier 35h that outputs a compensation current Io(t) obtained by amplifying the detected common mode noise current Ic(t)
Implementation Method 2
a first transistor Tr1 that supplies a compensation current Io(t) to a power line 1 based on an output of the operational amplifier 35h, and a second transistor Tr2 that supplies the compensation current Io(t) to the power line 1 based on an output of the operational amplifier 35h
Implementation Method 3
a coupling capacitor Cc and an output capacitor Co that form a current path between the power line 1 and the earth 2
Data Source
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AI summary
[Problem] To suppress the disadvantage that occurs with regard to the flow of a compensation current when a voltage of a power source of a noise canceller is lower than a DC link voltage of a power converter. [Solving means] A noise reduction circuitry includes a noise canceller that injects a compensation current into a power line or an earth to reduce a common mode noise current flowing to an alternating-current power source from a power converter including a switching element connected to the alternating-current power source through the power line and the earth, and a direct-current power source that supplies power to the noise canceller, and a voltage Vcc of the direct-current power source is less than 2/3 of a peak value of a DC link voltage of the power converter, and when a connection point between the power line and a path connecting the power line and the earth via the noise canceller is a first connection point, and a connection point between the path and the earth is a second connection point, when the compensated common mode noise current whose positive direction is a direction of flow from the alternating-current power source side to the first connection point and flowing through the power line on a side closer to the alternating-current power source than the first connection point is Ig(t), when the compensation current whose positive direction is a direction of flow from the alternating-current power source side to the first connection point and flowing through the path is Io(t), when an impedance of the path is Z 1, when an impedance on a side closer to the alternating-current power source than the first connection point and the second connection point is Z2, and when V(t) = 2 * (Z1 * Io(t) - Z2 * Ig(t)), the voltage Vcc is set to be a maximum value of a quasi-peak value of V(t) or √2 times or more an effective value of V(t).