Maestro Universal MCM Option Centrifugal Controller (From the July 2018 Turbo-Air Chronicle By Ingersoll Rand)

Do you know what MCM Stands for? No, put down the urban dictionary, it’s not that. MCM is something the Maestro Universal does rather well. What is it? It’s Multiple Compressor Management.

In a typical Plant Air system with multiple machines, each has its own controller. Each compressor is doing its job to adjust inlet and discharge valves in order to keep the compressor at the required System Pressure in the main header.

With the Maestro Universal, each unit will maintain itself to the setpoints, throttling back or loading up as needed based on the System Pressure. All machines running, all the time. But will they run smoothly, all together, with each making changes that will affect the other? Maybe, let’s consider a few things.

Let’s assume we have multiple compressors that are all the same capacity (or close to the same), and all are being used to run a process.

  • Each machine will most likely have the same assigned System Pressure setpoint (1) and, as demand decreases and it moves close to surge, the Inlet Valves will increase pressure to the System Pressure offset (2) to keep it out of surge.
  • When this happens, the increase in pressure will result in the other compressors “INHERITING” the need to throttle back and decrease their output.
  • The machines run together and adjust based on the impact each “INHERITS” from the actions of the others.

This is known as Inherent Load Coordination. With multiple machines, it’s not a bad idea to coordinate the responses to low demand in order to minimize multiple machines from blowing off at the same time. Staggering the System Pressure Offset is a usefully way to control the sequence in which the compressors open their anti-surge valve and eventually unload.

So it can be done, but is there a better way? Yes, this is where the MCM option shines. MCM was designed for 3 to 32 machines. That’s right, up to 32 machines all running together can be managed by one Maestro Universal controller.

The MCM system assigns unit numbers to each compressor and priority numbers to determine which machines load or unload first. It groups machines together to operate at a Network Setpoint (System Pressure), and monitors each unit to determine if individual machines are doing their job or need an adjustment to improve their contribution to the network.

When an adjustment is needed, the software will increase or decrease an individual machine’s setpoints to bring it in line with the network’s needs. Each machine’s output is coordinated to make all machines work together as if they were one large variable output compressor.

This makes the MCM a Distributed load control method. Each controller continues to operate independently, controlling to its own Individual System Pressure Set Point, responding to its own system pressure transmitter.

The MCM network has a lead compressor that makes decisions and the others are followers. In the event that the lead machine fails, another unit will automatically pick up the lead role and keep the network adjusted. By simply changing the Individual System Pressure Set Point of each unit, MCM can achieve proper loading of the machines to match the plant demand as closely as possible without blowing off.

Example of screen from Compressor #1 on three compressor system.

For more information see AAEDR-K-0123, Maestro Universal MCM Operating Instructions or this brochure.