Soft Starter Synchronization for Permanent-Magnet Machines
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Solution Overview
Problem
Current solutions for starting and operating permanent-magnet synchronous machines on a stiff grid face challenges such as high starting currents, cost and availability issues due to encoder requirements, and lack of market-ready soft starter solutions for high-efficiency motors, particularly in the lower power range.
Innovation Solution
A method for grid synchronization of permanent-magnet three-phase machines using a soft starter with thyristors and mechanical bypass contacts, where control signals initiate bypass contact switching and firing pulses for thyristors based on phase current measurements, allowing operation without encoders and preventing overcurrents and oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a damper cage is provided in the rotor to enable reliable runup on a stiff grid, then the machine can operate reliably on grid, but the feeding grid is subjected to very high starting currents
Solution Approach 1:
A soft starter with thyristors is introduced as an intermediary device between the grid and the permanent-magnet synchronous machine. The soft starter controls the voltage applied to the machine during starting, enabling gradual acceleration without subjecting the grid to high starting currents, while still achieving reliable runup on stiff grid
2Ease of operation
If an encoder system is used for vectorial closed-loop control during soft starting, then speed and position control is achieved, but the costs and availability of the system decrease
Solution Approach 1:
The encoder system is extracted/removed from the solution. The patent achieves soft starting with speed and position control using only the existing rotor windings and control algorithms, eliminating the need for encoders and their associated costs and availability issues
3Object-generated harmful factors
If a soft starter is used to reduce voltage during switch-on, then starting current is limited, but the solution is only possible in off-load state or on low load
Solution Approach 1:
The control system uses feedback from current sensors and control algorithms to dynamically adjust the thyristor firing angles during soft starting. This enables the soft starter to handle a wide range of loads by continuously adapting the voltage application based on actual machine response, rather than being limited to off-load or low-load conditions
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
Enables efficient grid synchronization of permanent-magnet three-phase machines without overcurrents or drive train oscillations, allowing for targeted acceleration and connection to a power supply grid, reducing costs and improving availability by eliminating encoder needs.
Implementation Method 1
a soft starter (also referred to as soft-starting device) represents a cost-friendly solution for runup of a permanent-magnet synchronous machine on a stiff grid. Such a soft starter reduces the voltage during switch-on (for example by way of phase gating)
Implementation Method 2
The method comprises the step of generating a first control signal, by which the switching-on of the mechanical bypass contacts is initiated
Implementation Method 3
A method for grid synchronization of permanent-magnet three-phase machines using a soft starter with thyristors and mechanical bypass contacts, where control signals initiate bypass contact switching and firing pulses for thyristors based on phase current measurements, allowing operation without encoders and preventing overcurrents and oscillations
Data Source
AI summary
A method is for a network synchronization of a permanently excited three-phase machine including a soft starter, including thyristors, and mechanical bypass contacts for bridging the thyristors in the network operation. The method includes generating a first control signal, to initiate switching the mechanical bypass contacts to become conductive, after a criterion is reached while running up the three-phase machine on the soft starter, a time at which the first control signal is generated representing actuation time of the bypass contacts; generating ignition pulses for the thyristors within a time period, running from the actuation time to a contact time of the bypass contacts, using a second control signal; and operating the three-phase machine in the network operation via the bypass contacts. Each ignition pulse for a thyristor is generated when a phase current measurement indicates that the current strength in the assigned phase has fallen below a threshold value.