Danfoss VLT Series Operating Instructions Manual page 6

1 Extended and Advanced Cascade Controller
Option
NB!
If MCO 102 is installed, the relay option MCB 105 can extend the number of relays to 13.
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Application
Cascade control is a common control system used to control parallel pumps or fans in an energy efficient way.
The Cascade Controller option provides the capability to control multiple pumps configured in parallel in a way that makes them appear as a single larger
pump.
When using Cascade Controllers, the individual pumps are automatically turned on (staged) and turned off (de-staged) as needed in order to satisfy the
required system output for flow or pressure. The speed of pumps connected to VLT AQUA Drives is also controlled to provide a continuous range of
system output.
Illustration 1.1: Cascade control of multiple pumps
The Cascade Controllers are optional hardware and software components that can be added to the VLT AQUA Drive. It consists of an option board
containing 3 relays that is installed in the B option location on the Drive. Once options are installed the parameters needed to support the Cascade
Controller functions will be available through the control panel in the 27-** parameter group. The Extended Cascade Controller offers more functionality
than the Basic Cascade Controller. It can be used to extend the Basic Cascade with 3 relays and even to 8 relays with the Advanced Cascade Control card
installed.
While the Cascade controller is designed for pumping applications and this document describes the cascade controller for this application, it is also possible
to use the Cascade Controllers for any application requiring multiple motors configured in parallel.
Master/Follower Operation
The Cascade Controller software runs from a single VLT AQUA Drive with the Cascade Controller option card installed. This frequency converter is referred
to as the Master Drive. It controls a set of pumps each controlled by a frequency converter or connected directly to mains through a contactor or through
a soft starter.
Each additional frequency converter in the system is referred to as a Follower Drive. These frequency converters do not need the Cascade Controller
option card installed. They are operated in open loop mode and receive their speed reference from the Master Drive. The pumps connected to these
frequency converters are referred to as Variable Speed Pumps.
Each additional pump connected to mains through a contactor or through a soft starter is referred to as a Fixed Speed Pump.
Each pump, variable speed or fixed speed, is controlled by a relay in the Master Drive. The frequency converter with the Cascade Controller option card
installed has five relays available for controlling pumps. Two (2) relays are standard in the FC and additional 3 relays are found on the option card MCO
101 or 8 relays and 7 digital inputs on option card MCO 102.
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MI.38.C3.02 - VLT is a registered Danfoss trademark
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VLT Operating Instructions