Abstract: Soft starters have been widely used in industry, and many soft starter products have appeared on the market. This article introduces a new series of Sirius soft starters with special features, which can be used as a reference for readers. Keywords : Semiconductor soft starter 1 Introduction In soft starter devices, semiconductors must withstand large temperature fluctuations, which is why good load cycling capability is essential. Using thyristor modules specially developed by Semikron, cost-effective, ultra-compact soft starters that meet these requirements can be developed. Siemens Automation and Drives (A&D) selected semiconductor manufacturer Semikron to develop suitable thyristor modules for its new generation of Sirius soft starters. The result is the anti-parallel thyristor module SEMiSTART: Due to double-sided chip cooling, this module has only half the thermal resistance of conventional modules and a very compact structure. Excellent cooling performance means the module can withstand greater overload current in a short time. Furthermore, the new module employs press-fit technology, ensuring high reliability. 2. Semiconductor-Based Soft Starter The soft starter is used to regulate the motor's supply voltage during the starting phase of an asynchronous motor. Two anti-parallel thyristors are connected in series between the motor windings and the power supply. During acceleration to normal speed (ramp start), the motor winding voltage is controlled via phase control. The starting torque and starting current of the motor are controlled by adjusting the thyristor conduction angle. The starting time can also be controlled via the soft starter. The current flowing through the semiconductor causes it to dissipate power, which raises the semiconductor temperature, thus requiring cooling. To prevent the semiconductor from continuing to consume power after the acceleration process, a mechanical switch is used for bypassing. Since there is no need to switch large loads, the bypass switch can be relatively small. 3. Requirements for Semiconductors When used in soft starters, the semiconductor must be able to withstand considerable chip temperature variations and must exhibit excellent load cycling capability. If these conditions are met, the lifespan of a soft starter will be very long. Furthermore, the compactness and cost-effectiveness of the soft starter are also crucial. However, even with a soft starter, the starting current during startup is still several times (3-5 times) the rated current. In high-power systems, the peak starting current often reaches several thousand amperes. Therefore, the semiconductor must be able to withstand such a large starting current during startup. At the same time, the soft starter must optimize cost and be as compact as possible. For this reason, the size of the semiconductor used (including the heatsink) must be as small as possible. Therefore, for cost reasons, the rated current of the thyristor devices actually used is much smaller than the large current during startup. This is why the thyristor chip will heat up significantly during startup, such a short period, such as from TStart=40℃ to TRamp-up=130℃, resulting in a 90℃ temperature difference in the chip. If a system switches 3 times per hour, 8 hours per day, 365 days a year, then the total number of load changes over 10 years will reach 87,600. Even under conditions of numerous load changes, these thyristors must be able to repeatedly withstand overload currents during startup for up to 10 years. 4. Reliable Soft-Start Control The SEMiSTART module consists of two anti-parallel thyristors connected between a heatsink. The size of the SEMiSTART module heatsink is optimized for chip size and compact soft-starters for specific applications, as shown in Figure 1. Figure 1. Thyristor Module Based on Press-Connect Technology Ensures High Reliability The heatsink also serves as an electrical connector. The chip connection method used is based on press-connect technology. In the SEMiSTART module, two anti-parallel thyristor chips are pressed between two heatsinks. This assembly and connection method does not include solder layers, which is why the SEMiSTART module has excellent load cycling capability and a long service life. The total thermal resistance between the thyristor chips and the heatsinks is much lower than that of other conventional devices. Because the chips are pressed between two heatsinks and cooled on both sides, the thermal resistance is very low. For this reason, the module size can be smaller compared to conventional modules. Another advantage of the SEMiSTART module is its ease of installation. In fact, this module requires no mounting clamps or thermal grease. The attached table provides an overview of the SEMiSTART module series. Appendix: SEMiSTART Module Series Overview 5. New Generation Modular Control Equipment Two new compact soft starters from the renowned Sirius product line provide load and power protection during the starting phase of three-phase induction motors, as shown in Figure 2. Figure 2: New Generation Compact Sirius Soft Starters The new Sirius 3RW40 soft starter is designed for standard applications with simple or more demanding requirements, replacing the star-delta starters used in these applications. This two-phase controlled soft starter is used to switch motors with output power ranging from 75 kW to 250 kW (400V). It features two-phase control and a specially designed thyristor module, SEMiSTART. The result is an ultra-compact soft starter at a very attractive price. The Sirius soft starter is only one-third the width of a star-delta starter. This means that if a Sirius soft starter is used, there will be more space in the control cabinet. The new Sirius 3RW44 soft starter also offers additional unique features for starting motors with output power up to 710 kW (400V, standard connection) under very demanding conditions. It is also suitable for motors with output power up to 1200 kW (40V). The Sirius 3RW44 features the SEMiSTART module with three-phase control. These two new soft starters from the modular Sirius series feature advanced power semiconductor technology based on the SEMiSTART SCR module, making them the optimal solution for any soft starting application. The new Sirius series soft starters were designed through close collaboration and coordination between Semikron module development engineers and Siemens Automation & Drives (A&D) device development engineers, resulting in a cost-effective and highly robust series of soft starters. The new SEMiSTART modules used in these soft starters all have excellent overload capacity. 6 Advantages of SEMiSTART Modules (1) Compact design, saving space; (2) Due to extremely low thermal resistance, there are better heat transfer characteristics between the semiconductor chip and the heat sink; (3) Thanks to the use of press-fit technology (no solder layer), the reliability is very high; (4) No size requirements for the heat sink; (5) Easy installation: no special clamps or thermal grease required. 7 Conclusion Soft starters have been widely used in industry, and many soft starter products have appeared on the market. The new Sirius series soft starters introduced in this article were designed under the close cooperation and coordination of SEMiSTART module development engineers and Siemens Automation and Drives (A&D) device development engineers, resulting in a cost-effective and highly powerful soft starter series.