JPH0316517B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for controlling the capacity of a turbo compressor, and more particularly to a control method for suppressing surge generation by controlling a blow-off valve provided on the output side of a turbo compressor. .

Prior Art The one shown in FIG. 6 is conventionally known as one of the flow control systems for a turbo compressor. In FIG. 6, a suction throttle valve 2 is provided on the input side of the turbo compressor 1, and a pressure detector 3 is provided on the output side, and the opening of the suction throttle valve 2 is determined according to the output of the pressure detector 3. A pressure regulator 4 is provided to configure a pressure control loop.

Furthermore, a blowoff valve 5 for discharging excess air is provided on the output side of the turbo compressor 1, and a flow rate controller 7 for controlling the opening degree of the blowoff valve 5 based on a flow rate detector 6 and a signal from the flow rate detector 6. is provided to form a flow rate control loop. In the above control system,
The capacity of the turbo compressor 1 is controlled by controlling the suction throttle valve 2 (or suction guide vane) to keep the discharge pressure (or flow rate in some cases) constant. In this case, the air discharge valve 5 (or bypass valve) is controlled by the flow rate control loop so that the suction or discharge flow rate does not fall below a specified value in order to prevent surges in the compressor.

However, in such conventional control methods, the pressure control loop and the flow rate control loop are designed to operate independently of each other, so when the two control loops are in the controlled state, the mutual control loop is affected. Interference is likely to occur, so that the loop gain that is possible with each individual loop cannot be obtained, and it becomes necessary to reduce the loop gain of one or both loops. For this reason, when a load fluctuation occurs, a large overshoot occurs in the control amount, which is particularly problematic for flow rate control aimed at preventing surges. In order to solve this problem, increasing the surge margin has the disadvantage of increasing the amount of air discharged.

Purpose of the Invention It is an object of the present invention to provide a turbo compressor control method that eliminates the above-mentioned drawbacks, prevents the occurrence of surges, performs stable flow control and pressure control operations, and reduces the amount of air discharged. do.

Structure of the Invention The turbo compressor control method of the present invention includes a flow rate detector that detects the suction flow rate or discharge flow rate of the compressor, and a blowoff valve provided on the discharge side of the compressor based on a signal from the detector. Or, a flow control loop consisting of a flow rate controller that controls the opening degree of a bypass valve installed in a bypass line from the discharge side to the suction side of the compressor, and detects the suction pressure and/or discharge pressure of the compressor. In a capacity system equipped with a pressure control loop consisting of a pressure detector that controls a pressure detector and a pressure regulator that controls a suction capacity adjustment device of a compressor based on a signal from the detector, the discharge detected by the pressure detector is The pressure is differentiated, and from the differentiation result, when the discharge pressure is increasing, a signal corresponding to the differential output is outputted to operate the above-mentioned air blow valve or bypass valve to the open side, while the discharge pressure is decreased. When the airflow valve or the bypass valve is closed, a signal of 0 is output to operate the airflow valve or the bypass valve to the closed side, and the airflow is controlled based on the signal obtained by adding this signal and the detection signal from the flow rate controller. It is characterized by controlling the opening degree of the valve or bypass valve.

Embodiment In FIG. 1, parts equivalent to those in FIG. 6 are given the same reference numerals.

The output signal of the pressure regulator 4 is applied to a differentiation circuit 11, and its differential output is supplied to a limiter 12.

The differential circuit 11 detects whether the discharge pressure of the compressor 1 is increasing or decreasing from the change in the output of the pressure regulator 4, and the limiter 12 controls the discharge pressure when the discharge pressure is increasing. In order to operate the valve 5 to the open side, a signal of a magnitude below a certain predetermined upper limit is outputted, and on the other hand, when the discharge pressure is in a downward trend, a signal of 0 is outputted to operate the discharge valve 5 to the closed side. Output.

The output signal of the limiter 12 is applied to an adding circuit 13, and the sum of the output signal and the output signal of the flow rate controller 7 is calculated by the adding circuit 13, and the opening degree of the blow-off valve 5 is adjusted according to the calculation.

In the above configuration, for example, when the load decreases, the discharge pressure from the compressor 1 increases, and the output of the pressure regulator 4 decreases, the suction throttle valve 2 is throttled. on the other hand,
The output of the differentiating circuit 11 outputs a signal to operate the blow-off valve 5 to the open side, and this signal is applied to the adding circuit 13 via the limiter 12, and added to the output of the flow rate controller 7 to obtain the added value. Then the blowoff valve 5 is opened.

That is, the blowoff valve 5 is controlled based on a pressure control loop (output of the limiter 12) and a flow rate control loop (output of the flow rate regulator 7). Note that even if the discharge pressure increases significantly and the output of the differentiating circuit 11 becomes greater than a predetermined value, there is an upper limit to the signal output from the limiter 12, so the pressure control loop that contributes to the opening degree of the blow-off valve 5 The amount of control is suppressed within a certain limit.

On the other hand, when the discharge pressure of the compressor 1 decreases, the limiter 12 outputs a signal of 0, so the opening degree of the blow-off valve 5 is controlled only by the flow rate control loop.

As mentioned above, the output of the differentiating circuit 11 is applied to the air discharge valve 5 as a feed forward signal, so
By adjusting the amount of feed forward, it is possible to reduce the phase difference between the flow rate control loop and the pressure control loop, reduce mutual interference between the two loops, and stabilize the system. The operation of the above-described embodiment is shown in the flowchart of FIG.

The above operation causes the system to operate along line ADB in FIG. Note that the curve ACD is an operating curve of a conventional control system. Therefore, the distance from the surge limit line S can be increased, and the surge prevention characteristics against load fluctuations can be improved.

In other words, since the surge prevention line (FIC line) can be brought closer to the surge line S, it becomes possible to widen the capacity adjustment range in which the turbo compressor does not release air, and energy-saving operation becomes possible.

FIG. 3 shows another embodiment of the present invention, and shows a blow-off valve 5.
Instead, a bypass valve 20 is provided in the direction from the discharge side to the suction side of the compressor 1.

Then, the signals obtained by the differentiating circuit 11 and limiter 12 similar to those in the embodiment shown in FIG. It controls the degree of

In FIG. 4, a pressure detector 3 and a pressure regulator 4 are provided on the suction side of the compressor 1, and the opening degree of the bypass valve 20 is controlled by the signal from the addition circuit 13, as in the embodiment shown in FIG. This is how it was done.

In FIG. 5, two pressure regulators 4a and 4b are provided on the suction side and the discharge side of the compressor 1, and the output of each pressure regulator 4a and 4b is selected by an autoselector 21. . When the suction pressure falls below a set value, the auto selector 21 selects the output signal of the suction side pressure regulator 4a and sends it to the differentiating circuit 11.
It is differentiated and then sent to the adder circuit 1 via the limiter 12.
Send to 3.

On the other hand, when the discharge pressure exceeds the set value, the auto selector 21 selects the output signal of the pressure regulator 4b on the discharge side and adds the signal to the adding circuit 1 in the same manner as above.
Send to 3.

With this configuration, the opening degree of the bypass valve 20 is controlled according to a signal from either the suction side pressure regulator 4a or the discharge side pressure regulator 4b, and the discharge side and suction pressures of the compressor 1 are set to the specified values. Keep it so that it does not exceed. Note that instead of the bypass valve, a blowoff valve may be provided that releases part of the output air to the atmosphere.

Effects of the Invention As detailed above, according to the present invention, mutual interference between the flow rate control loop and the pressure control loop can be reduced in the turbo compressor control system, surge generation can be prevented, and the system can be easily stabilized. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of this invention, FIG. 2 is a flowchart showing the operation of the embodiment of FIG. 1, and FIGS. 3 to 5 are block diagrams showing other embodiments of this invention. 6 is a block diagram of a conventional system, and FIG. 7 is an operating curve of flow rate versus discharge pressure for the system of FIG. 1 and the system of FIG. 5. 1... Turbo compressor, 2... Suction throttle valve, 3...
...Pressure detector, 4...Pressure regulator, 5...Air discharge valve, 6...Flow rate detector, 7...Flow rate controller, 11
...Differentiating circuit, 12...Limiter, 13...Addition circuit.

Claims (1)

[Claims] 1. A capacity control method for a turbo compressor, which includes a flow rate detector that detects the suction flow rate or discharge flow rate of the compressor, and a blow-off valve provided on the discharge side of the compressor based on a signal from the detector; A flow rate control loop consisting of a flow rate controller that controls the opening degree of a bypass valve installed in a bypass line from the discharge side to the suction side of the compressor, and a pressure that detects the suction pressure and/or discharge pressure of the compressor. In a capacity system equipped with a pressure control loop consisting of a detector and a pressure regulator that controls a suction capacity adjustment device of a compressor based on a signal from the detector, the discharge pressure detected by the pressure detector is Differentiate, and from the differential result,
When the discharge pressure is rising, a signal corresponding to the differential output is outputted to open the blowoff valve or the bypass valve, while when the discharge pressure is falling, the blowoff valve or the bypass valve is opened. A signal of 0 is output in order to operate the bypass valve to the closing side, and the opening degree of the air discharge valve or the bypass valve is controlled based on the signal obtained by adding the signal and the detection signal from the flow rate controller. A method for controlling a turbo compressor, characterized in that: