*Article* **Improving Reliability and Energy Efficiency of Three Parallel Pumps by Selecting Trade-Off Operating Points**

**Safarbek Oshurbekov, Vadim Kazakbaev, Vladimir Prakht \* and Vladimir Dmitrievskii**

> Department of Electrical Engineering, Ural Federal University, 620002 Yekaterinburg, Russia; safarbek.oshurbekov@urfu.ru (S.O.); vadim.kazakbaev@urfu.ru (V.K.); vladimir.dmitrievsky@urfu.ru (V.D.) **\*** Correspondence: va.prakht@urfu.ru; Tel.: +7-343-375-45-07

**Abstract:** Reliability, along with energy efficiency, is an important characteristic of pump units in various applications. In practical pump applications, it is important to strike a balance between reliability and energy efficiency. These indicators strongly depend on the applied control method of the pump unit. This study analyzes a trade-off method for regulating a system with three parallel pumps equipped with only one frequency converter (multi-pump single-drive system). A typical operating cycle of a pumping system with variable flow rate requirements is considered. The proposed trade-off method is compared with the traditional regulation, when a change in the operating point of the pump is achieved only by changing the rotation speed, and with the method for maximum reliability. It is shown that the proposed trade-off method makes it possible to ensure sufficient reliability of the multi-pump system operation without a significant increase in energy consumption.

**Keywords:** centrifugal pump; energy efficiency; induction motor; parallel pumps; throttling; variable speed pump
