KR20000020055A - Device for improving power factor of motor - Google Patents

Abstract

PURPOSE: A device for improving a power factor of a motor is provided to suppress a harmonic current by improving the power factor and to maintain stably a direct current link voltage even when a load varies. CONSTITUTION: A device for improving a power factor includes a motor driving device, an inductor(L1,L2), a diode(D5,D6), a switching unit(31), a zero potential detector(32) and a controller(33). The motor driving device includes a bridge diode(22) and a smoothing capacitor(C). The bridge diode rectifies with full wave an AC voltage input from a power supply and outputs the rectified voltage. The smoothing capacitor smoothers the DC voltage output from the bridge diode and outputs to a load. The inductor and the diode are serially connected between the bridge diode and the smoothing capacitor. The switching unit are parallel connected between the inductor and the diode. The zero potential detector detects a zero potential of the AC voltage and outputs an interrupt signal. The controller switches on the switching unit for a predetermined time when the interrupt signal input from the zero potential detector.

Description

Power factor improvement device of motor

The present invention relates to a power factor improving apparatus for an electric motor, and more particularly, to a power factor improving apparatus for an electric motor that improves the power factor of the electric motor.

FIG. 1 is a circuit diagram of a general motor driving apparatus. The general motor driving apparatus includes a power input unit 1 for inputting AC power and an AC power input from the power input unit 1 for full-wave rectification. A bridge diode 2 for outputting a direct current power (DC) and a smoothing capacitor (C) for smoothing and outputting the direct current power (DC) input by full-wave rectification through the bridge diode (2) to the load (3) It is composed.

However, a general electric motor drive device configured as described above uses a relatively large capacity smoothing capacitor (C) to obtain a direct current power supply (DC) having a small ripple, which is influenced by the smoothing capacitor (C). The waveform of the current is distorted, so the power factor is lowered.

That is, as shown in FIG. 2, when the power supply voltage Vs is applied from the power supply input unit 1, the waveform of the power supply current Is has a narrow pulse width form under the influence of the smoothing capacitor C. FIG. The power factor is lowered to about 0.5 to 0.7.

As such, when the power factor decreases, the high frequency current component increases, and as the harmonic current component increases, power supply noise and electromagnetic waves are generated.

In addition, as the harmonic current component increases as described above, reactive power increases to supply a large amount of current to the device, and as the amount of current supply increases, a component having a large rated current value must be used when designing the device.

Therefore, a power factor improving device for improving the power factor of the electric motor is used, and such a power factor improving device can be largely divided into an active type power factor improving device and a passive type power factor improving device.

The active power factor improving device is a method of improving power factor by connecting a buck converter or boost converter between a bridge diode and a smoothing capacitor to make a current waveform into a power voltage and an in-phase waveform. The passive power factor correction device is a method of improving the power factor by controlling the impedance by connecting the inductor and the capacitor to the rear end of the bridge diode or the power input terminal.

However, such an active power factor improving apparatus has a disadvantage in that reliability is degraded due to a complicated control circuit and a high switching frequency, and the switching operation itself may cause noise.

In addition, the power factor improvement apparatus of the manual type as described above has a disadvantage that the power factor improvement effect is not very large as well as the DC link voltage is changed according to the load.

3 is a circuit diagram of a motor driving apparatus including a manual power factor improving apparatus according to the prior art, wherein the motor driving apparatus includes a power input unit 11 for inputting AC power (AC) and a power input unit (11). A bridge diode 12 for full-wave rectifying the input AC power AC and outputting a DC power DC, and smoothing the DC power DC input by full-wave rectification through the bridge diode 12 to load 13. And a power factor improving device 14 connected between the bridge diode 12 and the smoothing capacitor C1, and the power factor improving device 14 includes an inductor connected in parallel to each other. L1) and condenser C2.

In the passive power factor improvement apparatus configured as described above, the impedance Z viewed from the bridge diode 12 is obtained by the following equation (1).

Where s = jω.

Therefore, by appropriately adjusting the value of the inductor L1 and the capacitor C2 of the power factor improving device 14 to have a small impedance for the first harmonic current of the power supply current and a high impedance for other harmonic currents. Therefore, the power factor can be improved by improving the waveform of the power supply current.

At this time, the power factor improving device 14 is ideally to have an impedance of '0' for the first harmonic current of the power supply current, and to have an infinite impedance for other harmonic currents. Since there is no ideal inductor L1 and capacitor C2, it has a relatively small impedance for the first harmonic current and a relatively large impedance for the third and fifth harmonic currents that have the greatest influence on distortion. Improve power factor.

However, the conventional power factor improvement device according to the prior art should ideally have a power factor of '1', but in practice it shows a relatively low power factor of about 0.8 to 0.9. There was a problem that the link voltage is changed according to the load variation.

Accordingly, the present invention has been made to solve the above-mentioned problems, and improves the power factor to suppress the harmonic current components and to maintain the DC link voltage stably even under load fluctuations. The purpose is to provide a device.

In order to achieve the above object, an apparatus for improving power factor of a motor includes a bridge diode for full-wave rectifying and outputting AC power inputted from a power input unit, and a direct-current power supplied through full-wave rectification through the bridge diode to load the load. An electric motor drive device including a smoothing capacitor, comprising: an inductor and a diode connected in series between the bridge diode and the smoothing capacitor; a switching element connected in parallel between the inductor and the diode; And a control unit for detecting a zero potential point and outputting an interrupt signal, and a controller for turning on the switching element for a predetermined time when an interrupt signal is input from the zero potential detection unit.

1 is a circuit diagram of a general electric motor drive device,

2 is a waveform diagram of a power supply voltage Vs and a power supply current Is in the motor driving apparatus shown in FIG. 1;

3 is a circuit diagram of a motor driving apparatus equipped with a manual power factor improving apparatus according to the prior art;

4 is a circuit diagram of a motor driving apparatus provided with a power factor improving apparatus according to an embodiment of the present invention;

5 is a circuit diagram of a motor driving apparatus provided with a power factor improving apparatus according to an embodiment of the present invention;

6 is a circuit diagram of a motor driving apparatus equipped with a power factor improving apparatus according to an embodiment of the present invention;

7 is a waveform diagram of a power supply voltage Vs and a power supply current Is for explaining the properties of the inductor provided in the power factor improving apparatus according to the first to third embodiments of the present invention;

8 is a waveform diagram of a power supply voltage Vs and a power supply current Is for explaining the operation of the power factor improving device according to the first to third embodiments of the present invention.

<Explanation of symbols for the main parts of the drawings>

21: power input unit 22: bridge diode

23 load 24 power factor improvement device

31: switching element 32: zero potential detection unit

33: control unit C: smoothing capacitor

D5, D6: Diodes L1, L2: Inductors

Z1: Transistor

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

4 is a circuit diagram of a motor driving apparatus including a power factor improving apparatus according to an embodiment of the present invention, wherein the motor driving apparatus includes a power input unit 21 for inputting AC power and an AC power input unit 21. Bridge diode 22 for full-wave rectification of AC power AC input from the output DC power DC, and smoothing the DC power DC input through full-wave rectification through the bridge diode 22 to load 23. ) And a power factor improving device 24 connected between the bridge diode 22 and the smoothing capacitor C.

The power factor improving device 24 includes an inductor L1 and a diode D5 connected in series between the bridge diode 22 and the smoothing capacitor C, and the inductor L1 and the diode D5. A switching element 31 connected in parallel between the output terminal of the inductor L1 and a shorting or opening of the negative terminal of the DC link, and a zero potential point of the AC power source AC to detect an interrupt signal. And a control unit 33 for outputting a zero potential detection unit 32 and an ON signal when the interrupt signal is input from the zero potential detection unit 32.

The switching element 31 includes a transistor Z1 for switching operation under the control of the controller 33 and a stabilizing diode D6 connected in parallel to both ends of the transistor Z1.

The controller 33 is configured to include a ROM table (not shown) and a timer register (not shown) in which the on / off start time of the switching element 31 suitable for the load 23 is stored. When the interrupt signal is input from the zero potential detection unit 32, the 'on / off' start time of the switching element 31 stored in the ROM table is stored in the timer register, and the 'on / off' start is started from the timer register. When the interrupt signal is reached, the switching element 31 is controlled to be 'on / off'.

FIG. 5 is a circuit diagram of a motor driving apparatus including a power factor improving apparatus according to a second embodiment of the present invention, and the same reference numerals are used for the same configuration as the motor driving apparatus shown in FIG. 4.

The power factor improving device according to the second embodiment of the present invention shown in FIG. 5 has the same configuration as the power factor improving device according to the first embodiment of the present invention shown in FIG. 4, and is directly connected to an input terminal of the diode D5. Inductor L2 is further provided.

FIG. 6 is a circuit diagram of a motor driving apparatus including a power factor improving apparatus according to a third embodiment of the present invention, and the same reference numerals are used for the same configuration as the motor driving apparatus shown in FIG. 4.

The power factor improving device according to the third embodiment of the present invention shown in FIG. 6 has the same configuration as the power factor improving device according to the first embodiment of the present invention shown in FIG. 4, and is directly connected to an input terminal of the switching element 31. A connected inductor L2 is further provided.

The operation and effects of the power factor improving apparatus according to the first to third embodiments of the present invention configured as described above will be described in detail with reference to FIGS. 4 to 8.

In the power factor improvement apparatus according to the first to third embodiments of the present invention, the inductor L1 is provided at the output terminal of the bridge diode 22, and the bridge diode 22 is inputted from the power input unit 21. As the full-wave rectification of the power supply AC outputs the DC power supply DC to the inductor L1, a current flows in the inductor L1, and thus the power supply current Is is determined by the current flowing in the inductor L1. Accordingly, the power supply current Is can be controlled by adjusting the voltage VL across the inductor L1.

At this time, when a positive voltage is applied to the inductor L1 (when the input terminal voltage of the inductor L1 is higher than the output terminal voltage of the inductor L1), the current flows to the inductor L1, and the current flows to the inductor L1. ), The current continues to flow in the same direction by the accumulated amount even if the negative voltage is applied to the inductor L1 (even if the input terminal voltage of the inductor L1 is lower than the output terminal voltage of the inductor L1). do.

Therefore, if the value of the inductor L1 has a relatively large value due to the property of the inductor L1 as shown in FIG. 7, the power supply current Is is greatly delayed (compared to the power supply voltage Vs). delayed by θ1).

In this case, the power factor PF is determined by the magnitude of the phase difference θ of the power supply voltage Vs and the fundamental wave current Is1 and the magnitude of the fundamental wave current Is1, as shown in Equation 2 below. power factor can be improved by controlling?) and fundamental wave current Is1.

Where P is the average power, S is the apparent power, Is1 is the fundamental wave current of the supply current Is, and θ is the phase difference between the supply voltage Vs and the fundamental wave current Is. .

Therefore, as shown in FIG. 7, when the phase delay portion of the power supply current Is is applied to the inductor L1 with a positive voltage in synchronization with the zero potential point of the power supply voltage Vs, the inductor L1 is applied. As a current flows through the power supply, the power supply voltage Vs and the power supply current phase are coincident with each other, and the waveform of the power supply current Is also becomes a sine wave, thereby improving the power factor.

As shown in FIG. 4, the both ends of the switching element 31 are connected to the output terminal of the inductor L1 and the negative terminal of the DC link in order to force a current to flow through the inductor L1. By switching the switching element 31 in the state, a current can flow in the inductor L1 in a desired section.

In addition, when the current is forced to flow through the inductor L1 by switching the switching element 31 as described above, the DC link voltage rises as if it is a boost converter, so that the DC link voltage is stabilized even when the load fluctuates. I can keep it.

That is, integrating the voltage VL across the inductor L1 for one period becomes '0', so assuming that current flows in the inductor L1 continuously, the inductor L1 is turned on when the switching element 31 is turned on. The voltage across both ends of VL becomes the input voltage Vd of the inductor L1, and the voltage Vd across the inductor L1 becomes the input voltage of the inductor L1 when the switching element 31 is 'off'. It becomes Vd-Vo minus the output voltage Vo from (Vd).

Therefore, the following equation (3) holds.

Where Vo is the output voltage of the inductor, Vd is the input voltage of the inductor, ton is the 'on' time of the switching element, and toff is the 'off' time of the switching element.

When Equation 3 is divided by the switching period Ts, Equation 4 below is established.

Where D is ton / Ts: the 'on' duty of the switching element.

Accordingly, it can be seen from Equation 4 that the output voltage Vo of the inductor L1 increases as the 'on' duty of the switching element 31 increases.

In conclusion, the power factor improving device according to the first to third embodiments of the present invention forcibly flows current through the inductor L1 using the switching element 31, and thus forcibly applies current to the inductor L1. By adjusting the flow section (the 'on' duty of the switching element), the power factor can be improved and the DC link voltage can be kept stable.

According to one embodiment of the present invention embodied by the above principle, as shown in FIG. 4, the zero potential detection unit 32 receives the power supply voltage Vs supplied from the power input unit 21. The controller detects a weak point and outputs an interrupt signal to the control unit 33. The control unit 33 controls the switching element 31 'on / off' according to the interrupt signal input from the zero potential detection unit 32.

That is, when AC power is applied from the power input unit 21, the load 23 of an inverter, a motor, etc. starts to operate. At this time, a frequency corresponding to twice the frequency of the power voltage from the zero potential detection unit 32 is started. The interrupt signal is input to the controller 33.

When the interrupt signal is input from the zero potential detection unit 32, the controller 33 stops the operation and jumps the program pointer to the interrupt service routine to execute the command according to the interrupt signal.

The interrupt service routine reads the 'on / off' start time of the switching element 31 corresponding to the load 23 previously stored in the ROM table, stores it in the timer register, and returns to the original program routine.

When the timer register reaches the stored 'on / off' start time, the timer register outputs an interrupt signal, and the control unit 33 causes the switching element 31 to be 'on / off'.

At this time, the time when the switching element 31 is 'on' immediately after the zero potential point of the power supply voltage (Vs), the voltage VL of both ends of the inductor (L1) is negative (-) to the inductor (L1) Although no current flows, when the switching element 31 is 'on', both ends of the inductor L1 are short-circuited with the output terminal of the bridge diode 22 and the negative end of the DC link, so that the switching element 31 is connected to the inductor L1. On and at the same time a positive voltage is applied and current flows.

That is, as shown in FIG. 8, when the switching element 31 is 'on' immediately after the zero potential point of the power supply voltage Vs, a current flows through the inductor L1 forcibly, as shown by a dotted line in FIG. 8. The current Is rises.

Thereafter, when the switching element 31 is 'off' after a predetermined time, the current accumulated in the inductor L1 flows through the diode D5. At this time, the current flowing through the diode D5 decreases slightly. .

After a while, the DC link voltage becomes smaller than the voltage at the input terminal of the inductor L1, and the inductor L1 takes a positive voltage to increase the current flowing through the inductor L1. As the voltage of is lower than the DC link voltage, the negative voltage is applied to the inductor L1. At this time, no current flows from the bridge diode 22, and the current accumulated in the inductor L1 flows while decreasing.

Therefore, as shown in FIG. 8, the forced current and the original current are combined to compensate for the phase of the current and have a sinusoidal waveform.

Meanwhile, as shown in FIG. 5, the power factor improving device according to the second embodiment of the present invention has the same configuration as the power factor improving device according to the first embodiment of the present invention, and is only connected in series to the input terminal of the diode D5. As the inductor L2 is further provided, the current flowing through the switching element 31 is increased when the switching element 31 is 'on'.

The power factor improving device according to the third embodiment of the present invention has the same configuration as the power factor improving device according to the first embodiment of the present invention, as shown in FIG. 6, and is connected in series to the input terminal of the switching element 31. As the inductor L2 is further provided, the impedance toward the switching element 31 becomes large, thereby delaying the current flowing toward the switching element 31, thereby causing the 'on' time of the switching element 31 under a large load. Can be increased.

As described above, according to the present invention, by forcibly flowing a current through the inductor near the zero potential point of the power supply voltage, the power factor is improved to suppress the harmonic current components, and the DC link voltage can be stably maintained even when the load changes. It has an effect.

Claims (5)

In a motor drive device having a bridge diode for full-wave rectifying and outputting AC power input from the power input unit, and a smoothing capacitor for smoothing and outputting the DC power input by full-wave rectification through the bridge diode to the load, An inductor and a diode connected in series between the bridge diode and the smoothing capacitor; A switching element connected in parallel between the inductor and the diode; A zero potential detection unit for detecting an zero potential point of the AC power supply and outputting an interrupt signal; And a control unit configured to 'on' the switching element for a predetermined time when an interrupt signal is input from the zero potential detection unit. The method of claim 1, The control unit may include a ROM table (not shown) in which an on / off start time of a switching element suitable for a load is stored, and when an interrupt signal is input from the zero potential detection unit, the switching element stored in the ROM table. The power factor improvement device of the motor, characterized in that to control the 'on / off' switching element according to the 'on / off' start time. The method according to claim 1 or 2, The power factor improvement device of the motor, characterized in that the 'on' period of the switching element is smaller than the half period of the power supply voltage. The method according to claim 1 or 2, A power factor improvement apparatus for an electric motor, characterized in that the inductor further connected in series to the input terminal of the diode. The method according to claim 1 or 2, And an inductor connected in series to an input terminal of the switching element.