Frequency Converter Synchronization via Resistive Voltage Division
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Solution Overview
Problem
Existing methods for synchronizing converters with alternating voltage sources, such as those from rotating electrical machines or mains voltage, require complex current measurements and test pulses, which can lead to high currents and are limited by the need for direct phase current measurement, making them inefficient and impractical for all scenarios.
Innovation Solution
The method determines the properties of the alternating voltage source using resistors already present in the circuitry, allowing for synchronization without separate input or output phase current measurements, by comparing voltages across resistive circuits to a defined voltage limit and calculating key time instants to determine phase sequence and frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current measurement methods are used for synchronization, then accurate phase information can be obtained, but the device complexity and cost increase due to requiring separate current measurement elements
Solution Approach 1:
The patent makes the existing resistive voltage division circuits serve a dual function: their primary function of providing switch state information is maintained, and they are additionally used for determining alternating voltage properties (phase sequence, frequency, magnitude) during synchronization. This eliminates the need for separate current measurement elements while maintaining measurement accuracy.
Solution Approach 2:
The patent enables the frequency converter's own internal resistive circuits to provide the measurement data needed for synchronization without requiring external or additional measurement devices. The system uses its existing infrastructure to solve the synchronization problem.
2Measurement precision
If test pulses are applied for synchronization, then voltage properties can be determined, but high currents may be generated that can damage the machine
Solution Approach 1:
The patent determines the properties of the alternating voltage (phase sequence, frequency, magnitude) before applying any switching operations or test pulses that could generate harmful currents. By using the resistive circuits to gather voltage information in advance, the system can synchronize safely without subjecting the machine to damaging current peaks.
3Measurement precision
If direct phase current measurement is required for synchronization, then accurate synchronization can be achieved, but the method becomes impractical for all scenarios including machines without measurement elements
Solution Approach 1:
The patent creates a universal synchronization method that works across different machine configurations by making the resistive voltage division circuits serve multiple purposes. This approach is applicable whether or not separate current measurement elements are present, as it uses the infrastructure that already exists in all frequency converters.
Solution Approach 2:
The frequency converter uses its own internal resistive circuits to provide all necessary measurement data for synchronization, making the system self-sufficient and adaptable to various machine configurations without requiring external measurement devices or specialized setups.
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 simplifies the synchronization process, allowing for fast and minimal additional element-based determination of alternating voltage properties, enabling effective synchronization with reduced current peaks and minimal additional hardware requirements.
Implementation Method 1
These resistor circuits in the example of FIG. 1 comprise two resistors in series and produce thus resistive voltage division of the voltage over the lower branch switches.
Data Source
AI summary
A method of determining a rotational state of a three-phase alternating voltage supply which is connected to a converter and rotating in an uncontrolled manner, wherein the converter is connected to an intermediate voltage circuit and comprises phase-specific upper and lower controllable switches, which are connected in series between the intermediate voltage circuit, free-wheeling diodes connected in parallel with each of the controllable switches, and resistive circuits connected in parallel with the lower controllable switches. The method comprises the steps of selecting a voltage limit, comparing the voltages of the alternating voltage supply in the resistive circuits with the voltage limit, determining a first time instant when any of the voltages of the resistive circuits crosses the voltage limit, determining a second time instant when any of the voltages of the resistive circuits subsequently crosses the voltage limit, determining the phase sequence of the converter output phases from the phases that crossed the voltage limit at the first and second time instants, determining the frequency of the alternating voltage source from the determined time instants, the method being applicable when the voltage of the intermediate circuit is equal to or higher than the voltage of the alternating voltage source.