Inverter Motor Insulation Inspection via Switching Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Inverter systems face challenges in accurately measuring motor insulation resistance due to leak currents from semiconductor elements and other components, especially when multiple inverters are connected to a single DC bus, leading to errors in insulation resistance measurement.
Innovation Solution
The inverter system incorporates a controller that performs specific switching operations and voltage detection processes to isolate the measurement target motor, using a resistor connected to the DC bus and voltage detection circuits to calculate insulation resistance by accounting for error factors such as discharge resistors and reactor insulation resistance, allowing for accurate measurement without disconnection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the motor is disconnected from the inverter for insulation resistance measurement, then the measurement accuracy is improved, but the productivity deteriorates due to increased inspection time and workload
Solution Approach 1:
The patent extracts the measurement function from the traditional offline inspection process and integrates it into the inverter system itself. The inverter's controller performs insulation resistance measurements by utilizing its internal circuitry and switching elements, eliminating the need to disconnect the motor and use external measurement equipment. This extraction of the measurement function to the inverter enables online monitoring without affecting productivity.
Solution Approach 2:
The inverter system performs self-diagnosis by using its own controller and circuitry to measure the insulation resistance of the connected motor. The controller automatically executes measurement routines, processes the measured values, and determines insulation status without requiring external measurement devices or manual disconnection of the motor. This self-service capability maintains productivity while enabling accurate measurement.
2Productivity
If the inverter function is used to measure insulation resistance without disconnection, then the productivity is improved, but the measurement accuracy deteriorates due to leak currents from semiconductor elements and other components
Solution Approach 1:
The patent segments the measurement process into distinct phases: a first measurement phase where specific switching elements are turned off to isolate certain current paths, and a second measurement phase where different switching elements are controlled. By dividing the measurement into multiple stages with different circuit configurations, the system can eliminate the influence of leak currents from semiconductor elements and other components through comparative analysis of the measured values.
Solution Approach 2:
The controller performs multiple measurements and uses feedback from the first measured value to determine the second measured value. The insulation resistance is calculated by comparing the two measured values, where the difference between them represents the insulation resistance of the motor. This feedback mechanism allows the system to cancel out the influence of constant leak currents from the inverter components.
3Adaptability or versatility
If multiple inverters are connected to a single DC bus, then the system versatility is improved, but the measurement accuracy deteriorates due to interference from other motors' insulation resistance and leak currents
Solution Approach 1:
The patent segments the circuit paths by selectively controlling the switching elements of each inverter. During measurement of a specific motor, the controller turns off the switching elements of other inverters connected to the same DC bus, isolating the measurement circuit path to only the target motor. This segmentation of circuit paths eliminates interference from other motors' insulation resistance and leak currents, enabling accurate measurement in multi-inverter systems.
Solution Approach 2:
The system dynamically controls the switching elements during the measurement process. The controller temporarily changes the operational state of switching elements in the inverter system - turning them off during measurement phases - to isolate the measurement path. This dynamic control allows the system to maintain versatility with multiple inverters while achieving accurate measurement by temporarily reconfiguring the circuit topology.
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 enables precise measurement of motor insulation resistance, eliminating the need for periodic motor disconnection and reducing maintenance workload, thereby improving productivity in complex machine tool environments.
Implementation Method 1
a capacitor (5) that smooths the DC power on the DC bus (4)
Implementation Method 2
a first voltage detection circuit (9) that detects an across voltage across the resistor (Rr)
Implementation Method 3
a resistor (Rr) connected from one of a positive voltage side or a negative voltage side of the DC bus (4) to ground
Data Source
AI summary
An inverter system includes a converter, an inverter, a first switch SW1 that connects between the converter and an AC power source, a capacitor that smooths a DC power in a DC bus, a resistor Rr connected from a positive voltage side of the DC bus to ground, a second switch SW2 that connects between the resistor Rr and ground, and a controller that controls drive of the inverter system. The controller is configured to: after charging the capacitor, while the first switch SW1 is in an OFF state, turn on the second switch SW2 and obtain a first across voltage ER1 of the resistor Rx; turn on an element, among semiconductor elements of the inverter, that is connected to the negative voltage side of the DC bus, and then obtain a second across voltage ER2 of the resistor Rx; and inspect insulation resistance of a motor based on the across voltages ER1, ER2.