Hitachi X200 Series instruction manual PID Loop Configuration, Other PID-related topics

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PID Loop Configuration

The inverter’s PID loop algorithm is configurable for various applications.

PID Output Limit - The PID loop controller has a built-in output limit function. This function monitors the difference between the PID setpoint and the loop output (inverter output frequency), measured as a percentage of the full scale range of each. The limit is specified by parameter A078.

•When the difference (Setpoint – loop output) is smaller than or equal to the A078 limit value, the loop controller operates in its normal linear range.

•When the difference (Setpoint – loop output) is larger than the A078 limit value, the loop controller changes the output frequency as needed so that the difference does not exceed the limit.

The diagram below shows PID setpoint changes and the related output frequency behavior when a limit value in A078 exists.

		Limit imposed
%		on output
Output limit
	A078
PID Setpoint
Output freq.	A078
Output limit		Limit imposed
		on output
		t

Inverter Mounting and installation

Error Inversion - In typical heating loops or ventilation loops, an increase in energy into the process results in an increasing PV. In this case, the Loop Error = (SP – PV). For cooling loops, an increase in energy into the process results in a decreasing PV. In this case, the Loop Error = –(SP – PV). Use A077 to configure the error term.

			A077				=00
SP	+					Error			Freq.
				Σ				PID
								calculation
					- PV
		PV						from process with
							positive correlation

			A077				=01
SP	-					Error			Freq.
				Σ				PID
								calculation
					+ PV
		PV						from process with
							negative correlation

Other PID-related topics:

•“PID Control” on page 3–22

•“PID ON/OFF and PID Clear” on page 4–26

•“Output Deviation for PID Control” on page 4–41

•“PID Second Stage Output” on page 4–45