Converter Current Space Vector Determination Using Shunt Resistors
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Solution Overview
Problem
Existing converters used in pulse width modulation for electric motors face challenges in accurately determining the current space vector due to current ripple and require costly potential-isolating current sensors, leading to inefficiencies and increased production costs.
Innovation Solution
A method and converter design that uses current sensors in the lower or upper branches of the half-bridges, employing a symmetrical pulse width modulation method to determine the current space vector without external sample-hold circuits and with only one analog/digital converter, allowing for offset-free detection and reduced component costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If potential-isolating current sensors are arranged in the feed lines to the motor, then continuous current signals freed from current ripple can be obtained, but the cost increases significantly
Solution Approach 1:
The patent replaces expensive potential-isolating current sensors with inexpensive shunt resistors that are placed in the lower branches of the half-bridges. These simple resistive elements provide sufficient measurement capability without requiring costly isolation technology, thereby resolving the contradiction between measurement precision and manufacturing cost.
Solution Approach 2:
The patent introduces shunt resistors as intermediary elements in the lower branches of the half-bridges to enable current measurement. These resistors serve as a mediator that converts current into measurable voltage signals without requiring direct potential isolation between the sensor and control electronics.
2Device complexity
If shunt resistors are arranged in all lower branches of the half-bridges, then current measurement is simplified, but in the shaded areas of the hexagon no or only imprecise determination of the current space vector is possible
Solution Approach 1:
The patent dynamically selects which shunt resistors to use for current measurement based on the instantaneous switching state of the converter. The control system adapts the measurement configuration in real-time, switching between different combinations of shunt resistors depending on which ones are currently connected to the lower branches, thereby maintaining accurate current space vector determination across all operating conditions.
Solution Approach 2:
The patent divides the current measurement function into segments, using different shunt resistors for different switching states. Instead of relying on all three shunt resistors simultaneously, the system segments the measurement task across time, using only the relevant shunt resistors for each specific switching state to determine the current space vector accurately.
3Ease of manufacture
If current sensors are arranged in the lower or upper branches of the half-bridges, then costly potential-isolating sensors are eliminated, but current ripple affects the determination of the current space vector
Solution Approach 1:
The patent employs periodic sampling of current values at specifically timed intervals within the pulse width modulation period. By sampling at the optimal moment when current ripple is minimized, the system achieves accurate current space vector determination using simple shunt resistors without potential isolation, thereby resolving the contradiction between manufacturing cost and measurement precision.
Solution Approach 2:
The patent uses feedback control to compensate for current ripple effects in the measurements. The control system continuously monitors the current signals and adjusts the determination of the current space vector based on feedback information, eliminating the need for expensive potential-isolating sensors while maintaining measurement accuracy.
Data Source
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AI summary
The invention relates to a converter and to a method for determining a current space vector for a converter that can be operated with pulse-width modulation, comprising signaling electronics and a power output stage that comprises circuit breakers disposed in three half bridges, each of which comprises a lower and an upper branch. Means for detecting the respective currents are disposed either in all three lower or in all three upper branches of the half bridges. At least one associated current sampled value is determined within a time segment by using two of the three means provided for detecting the currents. A current space vector is formed from the current sampled values determined by said pair of means, or the current values are formed in the output branches, in particular for use in a control and/or regulating method. Said pair of means is selected differently according to the output voltage space vector.