The phrase "are controlled by several" is correct and usable in written English.
It can be used when discussing entities or systems that are managed or regulated by multiple parties or factors.
Example: "The resources in the ecosystem are controlled by several governing bodies to ensure sustainability."
Alternatives: "are managed by multiple" or "are regulated by various".
They are controlled by several base station controllers and a few mobile service centres to which they are connected via a radio or fixed network.
The shape and size of a volcano are controlled by several factors.
It has been shown that, like much of parental behaviour in the higher vertebrates, brood patches and "broodiness" are controlled by several hormones, combined with visual and tactile stimuli.
Most agriculturally important traits in crops, such as yield and quality, are controlled by several genes known as quantitative trait loci (QTLs) (Collard et al. 2005).
The results obtained show that the ensuing surface profiles are controlled by several factors: applied boundary conditions, Taylor factor and shear tendency of the individual grains and the spatial distribution of grain neighborhood orientations.
Winds at MLO are controlled by several factors including the strength of synoptic scale or trade winds, the height and strength of the trade wind inversion, the flow of the synoptic winds around the island mountain topography, and the daily heating and cooling cycle on the island.
The village is controlled by several groups including al-Nusra Front.
Northern Mali is controlled by several violent Islamist and separatist groups, including Al Qaeda in the Islamic Maghreb.
Far Further is controlled by several veteran music executives, including John Styll, a leading figure in the gospel music business.
The road to Gudara is controlled by several sets of gunmen with varying loyalties, and no one travels it at night.
The automatic cycle of the typesetter is controlled by several large cams mounted on a single shaft driven by an electric motor.
