JPH0241761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention performs voltage control of a relatively light load connected to an AC power source, and is mainly suitable for controlling the speed of an induction motor of an air conditioner.

Configuration of the conventional example and its problems The conventional example will be explained using FIGS. 1 to 3.

FIG. 1 shows a generally widely known variable output voltage autotransformer (hereinafter referred to as a slider). 1
is an AC power source, 2 is a slider, 3 is an output tap of slider 2, and 4 is a load. The power supply voltage V _I of the AC power supply 1 now applied to the input of the slider 2 is relatively reduced depending on the position of the output tap 3, and is applied to the load 4 as a load voltage V _L.
The states of the power supply voltage V _I and the load voltage V _L are shown in FIG. 3 using solid lines and broken lines, respectively.

The method of varying the AC output voltage using a slider has a simple structure and is relatively inexpensive, so it is widely used, but its disadvantages are that it is heavy and has a mechanical structure, making it unsuitable for control as a system. It can be said that there is. Furthermore, since the factor that determines the output voltage is mechanical contact, there is also the problem that long-term reliability and environmental reliability are low.

Next, FIG. 2 shows an example of an electronic alternating voltage variable system.

5 and 6 are diodes, 7 is an NPN transistor,
8 is a PNP transistor, 9 is a fixed resistor, 10
is a variable resistor. 1 and 4 are the same as in FIG.

NPN with fixed resistor 9 and variable resistor 10
The base voltages of transistor 7 and PNP transistor 8 are determined, the emitter potential is determined, and therefore the voltage applied to load 4 is determined. Transistors 7 and 8 correspond to the positive and negative phases of AC power supply 1, and the difference between the voltage applied to AC power supply 1 and load 4, that is, the voltage drop, is consumed as V _CE of transistors 7 and 8. be done. Diodes 5 and 6 are necessary to block base-to-collector current when the respective transistors 7 and 8 are reverse biased.

Even with the circuit shown in FIG. 2, the voltage waveforms of the power supply voltage V _I and the load voltage V _L are as shown in FIG. 3.

According to FIG. 2, the load voltage V _L can be varied by varying the variable resistor 10.
There are limits to miniaturization and cost reduction due to the fact that the transistors 7 and 8, which mainly consume power, are two elements and that their collectors must be insulated from each other. In addition, a load voltage V _L is always applied to both ends of the variable resistor 10 connected to the bases of the transistors 7 and 8, and as a result, the variable resistor 10 must have a withstand voltage equivalent to the voltage V _I of the AC power supply 1. In addition, insulation is also required to safely vary the output. Therefore, in order to systemize this circuit using a microcomputer or the like, an insulated, high-voltage control element is required, making it unsuitable for compact systems.

Purpose of the invention Therefore, the present invention overcomes the problems of the above-mentioned conventional example,
It has a simple circuit configuration, can be systemized, and is aimed at power control for relatively light loads.

Structure of the Invention In order to achieve the above object, the present invention connects one end of the AC input of a diode bridge to a load and the other end directly to a single-phase AC power supply, and connects the DC output of the diode bridge to a single-phase AC power source. A drain and a source of the power MOS FET are connected to the drain and source, a series circuit of a fixed resistor and a variable resistor is connected in parallel to the drain and source, and a series circuit of a fixed resistor and a variable resistor is connected to the connection point of the fixed resistor and variable resistor. By connecting the gate of the power MOS FET and varying the resistance value of the variable resistor, the voltage applied to the load can be varied. are attached to the same heat radiator, and the heat radiator is configured to be ventilated by an air blower that stops in response to the stop of the semiconductor power control element.

Explanation of the embodiment In Fig. 4, the voltage between the drain and source of the N-channel FET 12 is from the power supply voltage V _I to the load voltage.
A voltage obtained by subtracting V _L is applied (hereinafter abbreviated as drain voltage V _DS ), and a voltage obtained by dividing the drain voltage by fixed resistor 9 and variable resistor 10 is applied to gate −
The gate voltage is applied between the source (hereinafter referred to as the gate voltage V _GS
). 6 and 7 are characteristic diagrams of the FET 12. Figure 6 shows the I _DS -V _GS characteristics. usually,
The FET has a threshold voltage _VTH , and when the gate voltage _VGS exceeds the threshold voltage _VTH , it enters the ON region and a drain current _IDS flows.

FIG. 7 shows the I _DS -V _DS characteristics. gate voltage
Using V _GS as a parameter, the relationship between drain current I _DS and drain voltage V _DS is determined. The dash-dotted line in FIG. 7 indicates the operating point of the circuit shown in FIG. I _DP indicates the peak current value of the drain current I _DS when V _L =V _I. V _DP indicates the peak voltage value of the drain voltage V _DS when V _L =O, that is, V _DS ≈V _I. When increasing the value of gate voltage V _GS , drain current I _DS
The operating point moves in the increasing direction and the drain voltage V _DS in the decreasing direction.

Furthermore, since the power supply voltage V _I is an AC voltage, the operating point line shown by the dashed line is at the 7th point due to the voltage phase.
Move in the direction of the arrow in the diagram.

Therefore, when the value of the variable resistor 10 shown in FIG. 4 is set to a certain value, the operating point A is found at one point on the operating point line connecting I _DP -V _DP . Power supply voltage V _I
Due to the phase of , the operating point is the above operating point A, I _DS and V _DS
It will move almost on a straight line connecting the origin of.

FIG. 5 shows the relationship between power supply voltage V _I and load voltage V _L. Threshold voltage of the gate mentioned above
Due to the influence of V _TH , in the phase where the voltage value of the power supply voltage V _I decreases, the drain current I _DS decreases extremely, so the load voltage V _L decreases.

However, since the gate threshold voltage V _TH decreases relatively slowly with respect to the drain current, there are few harmonic components.

Furthermore, if the FET 12 is selected to have a gate threshold voltage of approximately O, the load voltage V _L can be made almost similar to the power supply voltage V _I.

Generally, primary voltage control is often used as a means of variable speed for induction motors. As a means for achieving this, "tuck switching control" is widely used, in which the ratio of the main coil and auxiliary coil of the induction motor is changed stepwise to achieve variable speed. There is also a phase control method using thyristors, but for air conditioners,
It is not used outside of certain fields because of noise and the generation of electrical sounds that resonate with the wind tunnel of air conditioners.

Since the primary voltage control according to the present invention is a method of varying the voltage applied to the induction motor, the power corresponding to the voltage drop becomes heat loss of the power FET, so a heat radiation design using a radiator is required.

Regarding the primary voltage control of the induction motor, the efficiency seen from the power source is approximately the same when using "tack switching control" and when using a variable voltage method such as the present invention.

In other words, the input sum of the induction motor with the switching tap and the input of the electronic AC voltage variable device of the present invention and the induction motor without the switching tap are approximately equal in each speed range.

In other words, in the low speed range of an induction motor,
Compared to the tap switching method, the loss of the induction motor itself is reduced, and the power FET takes care of that loss.

On the other hand, in the case of tap switching control, the number of taps is normally limited to 3 to 4 due to volume constraints of the induction motor, but according to the present invention, an infinite number of stages can be set. In addition, the switching means for tap switching control normally uses switching using relay contacts, but there are restrictions on the switching timing and number of switching due to the life of the contacts and the generation of switching noise. Therefore, it is possible to change gears without any restrictions.

On the other hand, recently, compressor capacity control using inverters has begun to be widely adopted as a capacity control method for air conditioners, but in order to take advantage of the characteristics of compressor capacity control, air conditioning feeling, blowout temperature, energy saving, etc. From this point of view, there is a strong demand for fine-grained speed control of induction motors, especially those used in air blowers. This embodiment meets this requirement, and focuses on the heat sink of the power control element (usually a power transistor, GTO, etc.) of the inverter device, and the heat sink of both the electronic AC voltage variable device of the present invention and the inverter device. It brings together the
It is particularly effective when used in integrated air conditioners such as window-mounted types.

Next, one embodiment of the present invention will be described using FIGS. 8 and 9.

FIG. 8 is a system circuit diagram of an air conditioner according to an embodiment of the present invention. 13 is an electronic AC voltage variable device, 14 is an indoor blower using an induction motor, 15 is a power control element, 16 is an inverter device, 17 is a compressor, 18 is an outdoor blower, and 19 is an input of the indoor blower 14. The disconnection point 20 is an on/off contact of the inverter device 16 and the outdoor fan 18. The electronic AC voltage variable device 13 and the inverter device 16 each have a speed change function, and are controlled by a control device using a microcomputer. Here, the FET 12 and the power control element 15 are assembled into the same radiator, and forced ventilation is performed by the outdoor fan 18, which is shown in the mounting diagram of FIG. 9.

Reference numeral 21 denotes a heat sink, which is thermally designed in advance in anticipation of the maximum loss of the FET 12 and power control element 15 during ventilation. In addition, since the outdoor fan 18 is basically synchronized with the ON/OFF of the inverter device, basically the heat radiator 21 should be designed to dissipate heat by considering only the heat generated by the FET 12 when there is no ventilation. good.

However, for example, there is a condition where the indoor and outdoor blowers 14 and 18 are stopped and only the inverter device 16 is turned on, such as during defrosting during heating of an air conditioner. In this case, normally the inverter device 16
is often installed outside the room and the outside temperature is low, so the ambient temperature of the radiator 21 is low and the air conditioning load is light during defrosting, so the heat loss of the power control element 15 of the inverter device 16 is also small. , Furthermore, since the indoor fan 14 is stopped, the FET 12 is
It is set to OFF.

The heat dissipation design of the radiator 21 is performed under the above conditions, but in a normal air conditioner, the maximum loss of the power control element 15 of the inverter device 16 is the maximum loss of the FET 12 that controls the indoor fan 14. ,
As a result, the heat radiator 21 can be designed with almost the same size as the heat radiator formed by the power control element 15 of the inverter device 16.

Effects of the Invention According to the present invention, power control for relatively light loads can be provided compactly and inexpensively, and systemization can be easily implemented.

The first feature is that the power control element in the electronic AC voltage variable device can be realized with one element.

The part that controls the second output (i.e. the fourth
The voltage applied to the variable resistor 10) in the figure is low. Since this voltage is the gate voltage _VGS , it can normally be controlled with an upper limit of about 10V. Therefore, the control voltage is extremely low for controlling an AC power source of 100 V or 200 V, and it can be easily systemized by combining a microcomputer or the like using a photocoupler or the like.

Furthermore, the circuit configuration is extremely simple and can be constructed at low cost, and even in the event of an abnormality such as a short or open circuit of each component, the load is placed on the power supply side of the circuit, so it has the advantage of high safety. are doing.

In addition, when controlling the induction motor for the blower of an air conditioner, the air volume can be controlled almost steplessly, making it silent and
Since it is a non-contact type, there are no restrictions on switching operations, and the efficiency of the induction motor will not be reduced.In addition, the heat sink can be omitted for models that also use an inverter, which improves feeling, saves energy, It has many advantages such as comprehensive cost reduction.

As described above, it has various excellent effects, and is the most suitable means for systematically controlling the voltage of relatively light loads.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example using a slider, Fig. 2 is a circuit diagram showing a conventional example using a transistor, Fig. 3 is a voltage control waveform diagram of Figs. 1 and 2, and Fig. 4 is a circuit diagram of an electronic AC voltage variable device according to an embodiment of the present invention, FIG. 5 is a voltage control waveform diagram, FIG. 6 is an FFT I _DS -V _GS characteristic diagram, and FIG.
_{FIG. 8} is a system circuit diagram of an air conditioner according to an embodiment of the present invention, and FIG. 9 is a perspective view thereof. 1... AC power supply, 4... Load, 9... Fixed resistor, 10... Variable resistor, 11... Diode bridge, 12... Power MOS FET, 13...
Electronic AC voltage variable device, 14... Indoor blower, 15... Power control element, 16... Inverter device, 17... Compressor, 18... Outdoor blower,
19...On/off contact, 21...Radiator.

Claims (1)

[Claims] 1. Connect one end of the AC input of the diode bridge to a load and the other end directly to a single-phase AC power supply, and connect the drain and source of the power MOS FET to the DC output of the diode bridge. , a series circuit of a fixed resistor and a variable resistor is connected in parallel to the drain and source, further, the gate of the power MOS FET is connected to the connection point of the fixed resistor and the variable resistor, and the gate of the power MOS FET is connected to the connection point of the fixed resistor and the variable resistor. The voltage applied to the load is varied by varying the resistance value of the device, and the power MOS FET and other semiconductor power control elements are attached to the same heat sink, and this heat sink has the An electronic alternating current voltage variable device configured to provide ventilation using a blower that stops in response to the stoppage of a semiconductor power control element.