Power Conversion Device Voltage Change Detection
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Solution Overview
Problem
Existing power conversion devices face instability and increased costs due to the need for high-precision three-phase source voltage sensors and multiple A/D converters, making it difficult to detect source voltage changes and control motor speed effectively, especially when dealing with abrupt changes in power supply.
Innovation Solution
A power conversion device that detects voltage changes based on output DC voltage and current changes, eliminating the need for three-phase voltage detection, and switches to partial boost operation to suppress sudden changes, reducing the number of parts and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three-phase source voltage sensors and multiple A/D converters are used to detect source voltage changes, then detection precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts only the necessary detection function from the complex three-phase voltage detection system. By using a single DC bus voltage sensor to detect output voltage changes and combining this with current change detection, the system achieves source voltage change detection without requiring three-phase voltage sensors and multiple A/D converters, thus reducing device complexity while maintaining detection capability
Solution Approach 2:
The invention introduces an intermediary detection approach by monitoring the relationship between output DC voltage and input current changes. Instead of directly detecting source voltage changes through complex sensors, the system uses the correlated changes in output voltage and input current as intermediary indicators to infer source voltage fluctuations, thereby simplifying the detection system
2Reliability
If semiconductor switching elements are stopped to protect against overcurrent, then device reliability is improved, but output DC voltage drops and causes load instability
Solution Approach 1:
The invention performs preliminary detection of source voltage changes by monitoring output DC voltage and input current changes before overcurrent occurs. By identifying the impending voltage drop and switching to diode rectification operation in advance, the system prevents the severe output voltage collapse that would occur if protection were only activated after overcurrent, thus maintaining better output stability while still protecting the device
Solution Approach 2:
The invention allows the converter to skip the protective shutdown state by transitioning to diode rectification operation. This alternative path enables the system to bypass the complete stopping of semiconductor switching elements, maintaining continuous power flow through the diodes while still protecting against damage, thereby avoiding the output voltage collapse associated with full shutdown
3Reliability
If diode rectification operation is used to protect against overcurrent, then device protection is improved, but output DC voltage drops and excessive surge current occurs at power restoration
Solution Approach 1:
The invention performs preliminary detection of source voltage changes and anticipates the power restoration event. By monitoring the duration and characteristics of the voltage drop, the system prepares for power restoration by gradually transitioning back to converter operation rather than immediately restarting, thus preventing excessive surge currents while maintaining the protective benefits of diode rectification during the disturbance
Data Source
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AI summary
A power conversion device includes: a plurality of reactors (L1, L2, L3) each having one end thereof connected to each phase of an AC power supply (1); a converter circuit (4) connected to the other ends of the plurality of the reactors to convert AC power to DC power; a smoothing capacitor (5) connected between the DC terminals on the output side of the converter circuit; a current detection circuit (7, 32) for detecting a DC bus current Ish constituting the sum of the load current and the current flowing in the smoothing capacitor; a voltage detection circuit (8) for detecting the output DC voltage of the converter circuit; and a control unit (6) for controlling the converter circuit using the current value detected by the current detection circuit and the voltage detection value detected by the voltage detection circuit. The occurrence of a change in the source voltage of the power supply is determined based on the change amount of the voltage detection value and the change amount of the current value.