JPH0546797B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electric compressor.

(Prior Art) In general, so-called capacity control is performed in a compressor (compressor) in which the amount of discharged air is controlled by detecting the discharge pressure that changes due to fluctuations in the amount of air consumed. In particular, conventional capacity controls for electric compressors powered by electric motors such as induction motors include (1) intake blockage control (2) inverter control (3) unloader ON-OFF control, etc. .

Here, intake blockage control is a method that controls the amount of discharged air by operating the motor at a nearly constant rotation rate using a commercial power source and opening and closing the intake blockage valve provided in the intake path of the compressor according to changes in discharge pressure. be. Although this control has the advantage of being able to finely adjust the discharge pressure, since the compressor always rotates at the rated speed, the motor is not able to operate under light or medium loads with low air consumption (low load factor). It has the disadvantage of high power consumption.

On the other hand, inverter control converts the commercial power supply into AC voltage of another frequency using an inverter, and uses the fact that the motor rotation speed is determined by the power supply frequency to change the oscillation frequency of the inverter according to changes in discharge pressure. Capacity control is performed by controlling the rotational speed of the motor. However,
This inverter control allows for finer adjustment of the discharge pressure, that is, more precise control, and has the advantage of being highly energy-saving as it consumes less power during light and intermediate loads, but when the load is heavy near the rated load factor, There is a drawback that power consumption increases due to internal loss of the inverter and deterioration of motor efficiency due to inverter drive.

In addition, unloader ON-OFF control means that when the compressor discharge pressure exceeds a predetermined pressure, the intake blockage valve is fully opened, the pressure in the compressor discharge chamber is removed by the pump, and then the discharge pressure is adjusted to a certain width. When a pressure drop occurs, the intake blockage valve is fully opened to return to full load, and the discharge chamber pressure is removed by the pump when the intake blockage valve is fully closed, resulting in a large energy-saving effect over the entire load range. Yes, but
Excessive repetition of fully opening and fully closing the intake blockage valve will shorten the life of the machine, so in order to reduce the frequency of repetition, the fluctuation range of the discharge pressure from fully closed to fully open of the intake blockage valve must be widened. However, it has the disadvantage that it cannot be applied to loads where fluctuations in discharge pressure would be a problem.

Figure 1 shows the motor input for the load factor (ratio of consumed air amount to rated discharge air amount) for the above three controls, where A is intake blockage control, B is inverter control, and C is unloader ON-OFF. Each corresponds to the control. Note that since motor input is considered to be power consumption, the higher the point on the graph is, the lower the efficiency is, at the same load factor. Therefore, the point Q where curves A and B intersect
On the light/medium load factor side to the left, inverter control B and unloader ON- are used as compared to intake blockage control A.
OFF control C has overwhelmingly high efficiency, but at heavy loads beyond point Q, the relationship is reversed and intake blockage control A becomes advantageous.

As described above, conventional capacity control has its advantages and disadvantages, and it has been impossible to maintain high efficiency over the entire load range.

(Objective of the Invention) The present invention was proposed in view of the above points, and its purpose is to enable precise control of discharge pressure, maintain high efficiency over the entire load range, and save energy. Our objective is to provide a highly effective electric compressor.

That is, in the present invention, an electric motor is provided with an intake blocker 7 that operates to open and close an intake blocker valve according to the discharge pressure to control the amount of intake air, and a compressor 5 connected to and driven by a motor 4. In the compressor, the power supply terminal of the motor 4 is connected to the power supply switching unit 3, and the power supply switching unit 3 is configured to switch the power between the inverter 2 and the commercial power supply according to a signal from the inverter 2, An air consumption amount detection circuit 16 that detects the amount of air consumption from the frequency and input current of the AC power source or by a flow meter installed in the discharge air flow path; A control switching command generation circuit 17 that provides a control switching signal to the inverter 2 and the intake blocker 7, and a pressure sensor 1 provided in the compressed air discharge path.
A signal processing circuit 14 outputs a frequency setting signal according to the discharge pressure to the inverter 2 based on the pressure signal from the inverter 2; It is equipped with a phase adjuster 18 that matches the frequency with the commercial power supply, and when the load factor is light or medium load below a certain value, the control switching command generation circuit 17 is activated by the output signal from the consumed air amount detection circuit 16. A switching signal to inverter control is issued to the inverter 2 and the intake blocker 7, and the inverter 2 sends a signal to the power supply switching unit 3 to switch the power source to the inverter 2, and
The intake blockage valve is fully opened, and the signal processing circuit 14 outputs a frequency setting signal based on the pressure signal of the pressure sensor 12 to control the rotation speed of the inverter 2. When the load is applied, the control switching command generation circuit 17 issues a switching signal to the intake blockage control to the inverter 2 and the intake blockage section 7 based on the output signal from the consumed air amount detection circuit 16, and the inverter 2 switches to the power supply switching section 3. A signal is given to switch the power supply to the commercial power supply, the intake blockage section 7 starts operating and switches to intake blockage control that controls the amount of intake air, and when switching between inverter control and intake blockage control according to the load factor, The above object is achieved by providing a parallel operation period in which the output of the inverter 2 and the commercial power source are matched in phase and frequency, and switching is performed without disconnecting the power source of the motor 4.

(Structure of the Invention) The present invention will be described in detail below with reference to the drawings showing examples.

FIG. 2 is a block diagram showing one embodiment of the present invention. To explain the configuration in the figure, a commercial power source (usually three-phase AC, but it is omitted in the illustration) is connected to terminal 1, and the commercial power applied to terminal 1 passes through the breaker MCB. It is divided into two paths, one of which is connected to one end of the contact MC ₁ of the power supply switching section 3 via the inverter 2, and the other is connected to one end of the contact MC ₂ of the power supply switching section 3 immediately afterward.
Note that the contacts MC ₁ and MC ₂ of the power supply switching section 3 are controlled by a signal from the inverter 2, as will be described later. Next, the contacts of the power switching section 3
The other ends of MC ₁ and MC ₂ are connected to each other, and the motor 4
connected to the power terminal of the Note that, as mentioned above, since the line of the AC power supply is usually three-phase, the contacts MC ₁ and MC ₂ are actually each made up of three contacts, which are individually connected. Furthermore, it goes without saying that the contacts MC ₁ and MC ₂ are not limited to mechanical contacts such as relays and collectors, but semiconductor switches and the like can also be used.

Next, the main shaft of the motor 4 is connected to the input shaft of the compressor 5, and the compressor 5 receives the power from the motor 4 and moves from the intake port 6 to the intake blocker 7 to the compressor 5 to the receiver tank 8 to the service valve 9 to the discharge port. Air is sent out through 10 routes. Further, a part of the compressed air is taken out to the intake blockage part 7 as a control pressure through the side passage 11,
The intake blockage section 7 operates to open and close the intake blockage valve using this control pressure, and to control the amount of intake air according to the discharge pressure.

In addition, a pressure sensor 12 is installed in the compressed air discharge path.
The pressure signal converted into an electric signal is input to the error amplification circuit 13, and the error amplification circuit 13 extracts the difference between the set value given by the pressure setting device 15 and the pressure signal, and outputs the result. The signal is sent to a signal processing circuit 14. Next, the signal processing circuit 14 provides a frequency setting signal to the inverter 2 based on the output signal of the error amplification circuit 13.

On the other hand, an air consumption detection circuit 16 is connected to the power input terminal of the motor 4, detects the frequency of the AC power supply applied to the motor 4 and the motor input current, and measures the air consumption from these detected values. It's becoming like that. That is, in the case of inverter control, the rotation speed of the compressor 5 (same as the rotation speed of the motor 4) and the amount of air consumption have a nearly linear relationship, and in the case of intake blockage control, the load current of the motor 4 has a nearly linear relationship. Since it has a certain relationship with the degree of load applied to the motor 4, that is, the amount of air consumed,
The amount of air consumed can be estimated using these values. Note that it is also possible to provide a flow meter in the flow path of the discharged air and directly detect the amount of consumed air; in this case, connection to the power supply line of the motor 4 is not necessary.

Next, the output signal of the consumed air amount detection circuit 16 is given to the control switching command generation circuit 17, and this control switching command generation circuit 17 sends a switching signal for switching the control when the consumed air amount reaches a certain value to the inverter. 2 and the intake blockage part 7. Further, a phase adjuster 18 is provided between the input and output terminals of the inverter 2, and operates to match the phase and frequency of the inverter 2 with the commercial power source during the control switching period, as will be described later.

FIG. 3 shows the operating state of the embodiment shown in FIG. 2, with the load factor plotted on the vertical axis and the rotational speed of the compressor 5 (same as the rotational speed of the motor 4) on the horizontal axis.

The operation will be described below with reference to FIGS. 2 and 3.

Assuming that starting has already been carried out and the state is at a light/medium load rate with a small amount of air consumption, the output signal of the air consumption amount detection circuit 16 will not reach a predetermined value, so a control switching command will be generated. The circuit 17 gives an operation signal to the inverter 2 and gives an operation stop signal to the intake blockage section 7, so that the intake blockage valve is fully opened. Note that the above predetermined value is determined depending on the load condition where the efficiency of inverter control and intake blockage control is reversed.
For example, this corresponds to the load factor indicated by point Q in FIG.

Therefore, in the above inverter control state, if a difference occurs between the discharge pressure detected by the pressure sensor 12 and the set value of the pressure setting device 15, the error amount is detected by the error amplification circuit 13, The signal processing circuit 14 changes the frequency setting signal, and the inverter 2 changes the oscillation frequency to increase or decrease the rotation speed of the motor 4 so that it approaches the set pressure. That is, the inverter 2 receives a frequency setting signal from the signal processing circuit 14 so as to lower the frequency when the discharge pressure is high, and to raise the frequency when the discharge pressure is low. Since these operations are performed quickly, the discharge pressure of the compressor 5 is maintained at a substantially constant value. Note that during this inverter control period, the contact _MC2 of the power supply switching section 3 is in an off state.

Next, when the amount of consumed air increases from the above-mentioned light/medium load factor state (point a in Figure 3), pressure changes occur due to the imbalance with the discharged air amount, so the feedback operation described above is performed. The oscillation frequency of the inverter 2 increases almost linearly as the load factor increases, and the rotation speed of the motor 4 is increased to continue delivering compressed air at a constant pressure.

When the amount of consumed air increases further and reaches a load factor at which the efficiency of inverter control and intake blockage control is reversed (point Q in Figure 1, point b in Figure 3), the increase in the load factor is due to the detection of the amount of consumed air. detected by the circuit 16;
A control switching signal is issued from the control switching command generation circuit 17 to the inverter 2 and the intake blocker 7, and a control switching period begins. To explain the operation in this state in detail, point b in FIG.
When the intake blocker 7 receives an operation signal from the control switching command generating circuit 17, it starts operating, operates the intake blocker valve that had been in the open state, and switches the side passage 1.
The intake block valve is controlled in accordance with the discharge pressure taken out from the compressed air discharge path through the compressor 1, and the intake air amount of the compressor is controlled in accordance with the discharge pressure.

Meanwhile, in parallel with this operation, the inverter 2 receives a signal from the control switching command generation circuit 17 and rapidly increases the oscillation frequency to a point c at which the compressor 5 reaches the rated rotational speed _N0 . When the rotational speed of the motor 4 reaches the value at point c, the phase adjuster 18 is operated to completely synchronize the output of the inverter 2 with the phase and frequency of the commercial power supply.
When synchronization is achieved, contact MC ₂ of power supply switching section 3 is turned on in response to a signal from inverter 2, and parallel operation is performed using the output of inverter 2 and the commercial power supply. After that, after a predetermined period of time in which it is expected that the contacts etc. are completely operated, the contacts of the power supply switching unit 3
Turn off MC ₁ and switch to running only on commercial power. The reason for providing a period of parallel operation using the inverter output and the commercial power supply during switching is to reduce the rush current at the time of switching, and the power supply to the motor 4 is continuously switched without being in an open state. Therefore, the shock at the time of switching is greatly reduced. Therefore, it is possible to set the capacity of the commercial power supply to a small value.

As a result of the above operation, the capacity control of the compressor 5 is completely switched from inverter control to intake blockage control, and the compressor 5 remains at almost the rated rotation speed until the heavy load region where the load factor is 100% (point d). The pressure is adjusted by the operation of the intake blocker 7. If the above operations are shown in sequence in FIG. 3, the sequence becomes a→→b→→c→→d.

Next, a case where the air consumption decreases from a heavy load state to a light/intermediate load state will be described. In FIG. 3, when the load factor decreases from the point d side, the rotational speed of the compressor 5 remains almost at the rated rotational speed. Then, when reaching point c, where the efficiency of inverter control and intake blockage control is reversed,
This fact is detected by the operations of the consumed air amount detection circuit 16 and the control switching command generation circuit 17, and the control switching command generation circuit 17 provides a switching signal to the inverter 2 and the intake blocker 7. In response to the operation signal from the control switching command generation circuit 17, the inverter 2 resumes the oscillation operation that had been stopped until then, and by the operation of the phase adjuster 18, the inverter 2 outputs an output whose phase and frequency completely match those of the commercial power supply. Send out. Then, when the inverter 2 goes into standby, contact MC ₁ of the power switching section 3 is turned on in response to a signal from the inverter 2, and the motor 4 enters the parallel operation state, and after a predetermined period of time, the power switching section 3
Contact MC ₂ is turned off and switched to inverter control. Therefore, from now on, inverter 2
The motor 4 is controlled to a rotation speed according to the load factor by the output. At the same time, the intake blocker 7 receives an operation stop command from the control switching command generation circuit 17 and fully opens the intake block valve. Furthermore, during the above switching, there is also a period of parallel operation using the inverter output and the commercial power supply, and the power supply to the motor 4 is switched continuously without being left in an open state, making it possible to reduce inrush current. Become. However, if the above operations are shown step by step in Figure 3, d
→→c→b→→a.

Further, FIG. 4 shows another embodiment, in which a filter 19 is inserted into the connection path between contact MC ₂ of power supply switching unit 3 and motor 4, and contact MC ₁ of power supply switching unit 3 and reverse operation are inserted. Both ends of the filter 19 are short-circuited by the contact MC' ₁ , which prevents harmonic components contained in the output of the inverter 2 from leaking into the line during the period of parallel operation between the inverter output and the commercial power supply. . Note that the other configurations are similar to those shown in FIG. 2.

Next, FIG. 5 is a flowchart showing a process for preventing unnecessary control switching when applying the present invention. In other words, if you respond too faithfully to changes in the amount of air consumed, the control will be switched even in response to temporary fluctuations, for example, and such frequent switching operations will not improve efficiency, but will instead reduce the efficiency of the equipment. This is because it leads to deterioration.

In FIG. 5, when the operation is started in step 100, the current control is confirmed in step 101, and if it is inverter control, the process moves to step 102, and if it is intake occlusion control, the process moves to step 105. Then, step 102,
In step 105, it is checked based on the amount of air consumption whether the current control is in a region where it is necessary to change it, and if there is no need to change, step 1 is performed.
The process returns to step 01, and if switching becomes necessary, the process proceeds to steps 103 and 106, respectively. Next, in steps 103 and 106, it is checked whether a certain period of time has elapsed since a change in the load factor occurred and it became necessary to switch control, and if the change is not in the area requiring switching for more than a certain period of time due to a temporary change. Then, the process returns to step 101, and if the current condition is constant for a certain period of time or longer, the process proceeds to steps 104 and 107, respectively, to switch the control currently being performed.

Therefore, the above function can be applied by including it in the control switching command generation circuit 17 shown in FIGS. 2 and 4.

(Effects of the Invention) As described above, in the present invention, in the device that controls the discharge air amount of an electric compressor, the intake air amount is controlled by the inverter control that controls the rotation speed of the electric compressor and the intake blockage valve. The intake blockage control is switched so that the motor input is small relative to the load factor of the electric compressor, and at the time of switching, a parallel operation period is provided in which the phase and frequency of the inverter output and commercial power supply are completely synchronized. To provide an electric compressor with high energy-saving effect, which enables precise control of discharge pressure by switching without disconnecting the power to the motor, and maintains high efficiency over the entire load range. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the conventional control load factor and motor input, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is an explanation of the operation of the embodiment of Fig. 2. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a flowchart showing processing for stabilizing control. 1...Terminal, 2...Inverter, 3...Power switching section, 4...Motor, 5...Compressor, 6...
...Intake port, 7...Intake blockage part, 8...Receiver tank, 9...Service valve, 10...Discharge port,
11... Side path, 12... Pressure sensor, 13... Error amplifier circuit, 14... Signal processing circuit, 15... Pressure setting device, 16... Air consumption amount detection circuit, 17...
...Control switching command generation circuit, 18...Phase adjuster,
19... Filter, MC ₁ , MC ₂ , MC' ₁ ... Contact,
MCB... Breaker.

Claims (1)

[Claims] 1. An electric compressor comprising an intake blocker 7 that opens and closes an intake blocker valve according to discharge pressure to control the amount of intake air, and a compressor 5 connected to and driven by a motor 4, comprising: The power supply terminal of the motor 4 is connected to the power supply switching section 3, and the power supply switching section 3 is configured to switch the power supply between the inverter 2 and the commercial power supply according to a signal from the inverter 2, and the frequency and input of the AC power applied to the motor 4 are connected. A consumption air amount detection circuit 16 detects the amount of air consumption from the current or by a flow meter provided in the discharge air flow path, and an inverter 2 receives an output signal from this air consumption amount detection circuit 16 and sends a control switching signal to the inverter 2. and a control switching command generation circuit 17 that provides the control switching command to the air intake blocker 7, and a pressure sensor 1 provided in the compressed air discharge path.
A signal processing circuit 14 outputs a frequency setting signal according to the discharge pressure to the inverter 2 based on the pressure signal from the inverter 2; It is equipped with a phase adjuster 18 that matches the frequency with the commercial power supply, and when the load factor is light or medium load below a certain value, the control switching command generation circuit 17 is activated by the output signal from the consumed air amount detection circuit 16. A switching signal to inverter control is issued to the inverter 2 and the intake blocker 7, and the inverter 2 sends a signal to the power supply switching unit 3 to switch the power source to the inverter 2, and
The intake blockage valve is fully opened, and the signal processing circuit 14 outputs a frequency setting signal based on the pressure signal of the pressure sensor 12 to control the rotation speed of the inverter 2. When the load is applied, the control switching command generation circuit 17 issues a switching signal to the intake blockage control to the inverter 2 and the intake blockage section 7 based on the output signal from the consumed air amount detection circuit 16, and the inverter 2 switches to the power supply switching section 3. A signal is given to switch the power supply to the commercial power supply, the intake blockage section 7 starts operating and switches to intake blockage control that controls the amount of intake air, and when switching between inverter control and intake blockage control according to the load factor, An electric compressor characterized in that a parallel operation period is provided in a state where the output of an inverter 2 and the phase and frequency of a commercial power source are matched, and switching is performed without disconnecting the power source of a motor 4. 2. The electric compressor according to claim 1, wherein a filter is inserted in the connection path between the commercial power source and the motor 4 during the parallel operation period between the inverter 2 and the commercial power source.