KR100311652B1 - Breaking control method in an electric washing machine - Google Patents

Abstract

The braking control method in the washing machine according to the present invention is performed by repeatedly performing the charging and discharging, which charges back electromotive force generated from the motor during braking of the washing machine to the capacitor of the DC link stage and discharges the charged voltage back to the motor. Controlling counter electromotive force; And controlling the counter electromotive force by variably adjusting a switching duty ratio of a voltage (current) pulse entering and exiting a motor driving unit according to a voltage value of a DC link terminal corresponding to a variation in a magnitude of a power voltage supplied to the motor.

According to the present invention, the counter electromotive force generated from the motor during braking of the washing machine is used to repeatedly perform charging and discharging by varying the switching duty ratio of voltage (current) pulses entering and exiting the motor driving unit (inverter) instead of the braking resistor. By solving the problem, it is possible to fundamentally solve the problem of securing the space and dissipation of heat generated from the resistor, and minimizing the adverse effect on the circuit element by reducing the voltage variation of the DC link stage. Promote reliability and prolong life.

Description

Braking control method in an electric washing machine

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking control method in a washing machine, and more particularly, to a braking control method in a washing machine capable of effectively controlling a motor in response to back electromotive force generated in a motor during braking of a washing machine without using a braking resistor.

In general, a washing machine is largely composed of a washing tank for washing and dehydrating laundry, a motor for providing rotation driving force to the washing tank, and a control unit for controlling the motor. In such a washing machine, an inverter is generally used to more precisely control the motor (rotational speed) and to cope with various operating conditions. Thus, such a washing machine may be referred to as an inverter washing machine.

1 is a block diagram schematically illustrating a motor control system of a conventional inverter washing machine.

Referring to FIG. 1, a conventional motor control system of an inverter washing machine includes a rectifying unit 101 which receives an AC power source from the outside and converts the DC power into a direct current, and converts a DC voltage passed through the rectifying unit 101 into a three-phase alternating current. Motor driving unit (inverter) 102 to supply to the motor 110 and the braking for consuming the voltage (reverse electromotive force) flowing back from the motor 110 to the power supply terminal side when braking the motor 110 as thermal energy by the resistance. A voltage comparator comparing the resistance 103, the voltage sensing unit 104 for sensing the voltage at the link terminal of the rectifier 101, and the voltage sensed by the voltage sensing unit 104 and the reference voltage Vref ( 105, the switching unit 106 for turning on / off the braking resistor 103 circuit stage according to the comparison result by the voltage comparing unit 105, the rotational speed of the motor 110 and A sensor 107 for detecting the position of the rotor and a transmission signal from the sensor 107 Control the operation of the motor based thereon, and correspondingly according to the control commands from the microcomputer 108, which controls all logic related to the overvoltage release of the system upon braking of the motor. And a signal output section 109 for outputting a control signal to the motor driving section (inverter) 102. As shown in FIG. 2, the motor driving unit (inverter) 102 includes six switches each configured by parallel connection of one transistor Q1 to Q6 and a diode D1 to D6. It consists of a series / parallel combination circuit of the elements S1 to S6. In FIG. 1, reference numeral C denotes a capacitor for removing an AC component mixed in a DC voltage output through the rectifying unit 101.

Then, the operation of the control system of the conventional inverter washing machine having the above configuration will be described.

First, when AC power from outside (eg, AC 220V, 60Hz) is supplied to the system, the rectifier 101 converts the input AC voltage into DC voltage and outputs the DC voltage. Then, the motor driving unit (inverter) 102 converts the DC voltage back into a three-phase (U, V, W) AC voltage and supplies it to the motor 110. Here, the operation of the motor driving unit 102 (inverter) is made according to the control command of the microcomputer 108 as well. That is, the microcomputer 108 has previously programmed and stored a predetermined control algorithm related to the on / off control of the six switching elements S1 to S6 of the motor driving unit 102 (inverter). By the control algorithm, the switching elements S1 to S6 operate on / off to supply the three-phase AC voltage to the motor 110.

As described above, when the three-phase AC voltage is supplied from the motor driving unit 110 to the motor 110, the motor 110 rotates, thereby performing washing or dehydration.

On the other hand, if the vibration of the washing machine is opened due to the opening of the lid of the washing machine or unbalanced (unbalanced state) of the washing tank during the normal operation as described above, there is a case where the operating state is to be suddenly stopped. That is, a case in which the motor 110 must be stopped suddenly occurs. Here, the braking mechanism at this time will be described.

In the normal operation of the washing machine, the motor 110 can be seen as a load (power consumption source) from the system point of view, so that current flows from the power supply side to the motor 110 side. As such, when the motor 110 is normally operated and brake is applied to the motor 110 (cutting off the power supplied to the motor 110), the motor 110 is stopped while the rotation speed is decreased. That is, the motor 110 is not immediately stopped when power is cut off, but is rotated for a predetermined time by the rotational inertia force and then stopped. At this time, that is, while the motor 110 is rotated by the rotational inertia force after the power is cut off, the motor 110 acts as a generator, not a load, and thus is caused by the back EMF generated by the motor 110 Current flows from the motor 110 side to the power supply terminal (DC link end) side. As such, when the current generated from the motor 110 flows to the power supply terminal side, the voltage detector 104 senses a voltage between the rectifier 101 and the motor driver 102 and transmits the voltage to the voltage comparator 105. Then, the voltage comparator 105 compares the voltage sensed by the voltage detector 104 with the preset reference voltage Vref, and switches when the detected voltage exceeds the reference voltage (more precisely, the predetermined voltage tolerance range). A control signal for turning on the unit 106 is output. As a result, the switching unit 106 is turned on, i.e., the circuit stage composed of the braking resistor 103 and the switching unit 106 is turned on, and as a result, it flows from the motor 110 side to the power supply terminal side, that is, to the rectifier 101. The electric current no longer flows toward the rectifying part 101, but is consumed as thermal energy (Joule heat) through the braking resistor 103. Therefore, adverse effects that may be caused on the system circuit due to the increase in the voltage level of the DC link stage by the counter electromotive force generated from the motor 110 is prevented. That is, the deterioration or damage of the circuit element in the rectifying part 101 or the capacitor | condenser C located between the rectifying part 101 and the motor drive part 102 is prevented.

However, the control system of the conventional inverter washing machine as described above has a mechanism for consuming a current flowing back from the motor 110 to the DC link end side when braking the motor 110 as heat energy by the braking resistor 103. As a result, a resistor that can withstand a relatively large voltage is required. Such resistors are generally large in size, and thus, space installation problems arise in installation. In addition, there is another problem of effectively dissipating heat generated from the resistor.

The present invention has been made in view of the above problems, and an object thereof is to provide a braking control method in a washing machine that can effectively control a motor without using a braking resistor during braking of a washing machine.

1 is a block diagram schematically showing a motor control system of a conventional inverter washing machine.

FIG. 2 is a circuit configuration diagram of a motor driving unit (inverter) of the motor control system of the inverter washing machine of FIG. 1.

Figure 3 is a block diagram schematically showing a control system of the washing machine employed for the implementation of the braking control method in the washing machine according to the present invention.

Figure 4 is an ideal waveform diagram of the three-phase AC voltage applied to the motor from the motor drive unit (inverter) of a typical inverter washing machine.

5A is an actual waveform diagram of a three-phase AC voltage applied to a motor from a motor driving unit (inverter) of an inverter washing machine in which a braking control method in the washing machine according to the present invention is employed.

5B is an enlarged fragmentary view of a portion 'A' of the voltage waveform graph of FIG. 5A.

FIG. 5C is a time chart showing 'ON' and 'OFF' sections on the graph of FIG. 5B. FIG.

<Explanation of symbols for main parts of the drawings>

101,301 Rectifier 102,302 Motor drive (inverter)

103 ... Brake resistance 104,303 ... Voltage detection part

105 ... Voltage comparison section 106 ... Switching section

107,304 ... Sensor 108,305 ... Microcomputer

109 ... signal output 110,306 ... motor

In order to achieve the above object, a braking control method in a washing machine according to the present invention includes charging a back electromotive force generated from a motor during braking of a washing machine to a capacitor at a DC link stage, and discharging the charged voltage back to the motor. Controlling the counter electromotive force by repeatedly performing discharge; And

Controlling the counter electromotive force by variably adjusting a switching duty ratio of a voltage (current) pulse entering and exiting a motor driving unit according to a voltage value of a DC link terminal corresponding to a deviation of a magnitude of a power voltage supplied to the motor. It has its features.

Here, preferably, when the voltage value of the DC link stage is an intermediate value within the voltage value range of the DC link stage corresponding to the distribution range of the power supply voltage, the switching duty ratio is made small. The counter electromotive force is controlled, and when the voltage value of the DC link terminal is between the intermediate value and the maximum value, the switching duty ratio is increased to control the counter electromotive force energy.

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

3 is a block diagram schematically illustrating a control system of a washing machine employed for implementing a braking control method in the washing machine according to the present invention.

Referring to Figure 3, the control system of the washing machine employed for the implementation of the braking control method in the washing machine according to the present invention is not significantly different from the control system of the conventional inverter washing machine. That is, the control system of the washing machine employed in the method of the present invention includes a rectifying unit 301 that receives an AC power from the outside and converts it into direct current, and converts the DC voltage passed through the rectifying unit 301 into three-phase alternating current again. Motor driving unit (inverter) 302 to supply to the motor 306, the voltage sensing unit 303 for detecting the voltage of the rectifier 301 link terminal, the rotational speed of the motor 306 and the position of the rotor Is compared to the sensor 304 and the voltage sensed by the voltage sensing unit 104 and the reference voltage (Vref) and applied to the motor 306 by the motor driver (inverter) 302 according to the result Control the voltage being received, and control the operation of the motor 306 based on the transmission signal from the sensor 304, while controlling all the logic related to the overvoltage release of the system during braking of the motor. A microcomputer 305 is provided. Reference numeral C denotes a capacitor for removing the AC component mixed in the DC voltage output through the rectifier 301.

Here, in particular, the microcomputer 305 charges the capacitor 301 with the current flowing back toward the rectifier 301 by the counter electromotive force generated from the motor 306 when the washing machine is braked, and is charged in the capacitor 301. A control algorithm for turning on / off the switching elements S1 to S6 in the motor driving unit (inverter) 302 by a predetermined rule so that such charging and discharging are repeatedly performed, which discharges the voltage back to the motor 306. It is preprogrammed and stored.

The biggest difference between the control system of the washing machine employed in the method of the present invention as described above and the control system of the conventional inverter washing machine described in FIG. 1 is that the conventional control system suppresses the back EMF generated from the motor 110 during braking. While the motor 110 is braked by consuming heat energy by 103, the control system employed in the method of the present invention does not process the counter electromotive force by such a braking resistor 103, but rather a DC link. It charges the counter electromotive force to the capacitor C on the single side, senses the voltage on the DC link terminal side at every moment, compares it with the set reference voltage, and discharges it from the capacitor C to the motor 306 according to the result. The charging and discharging are repeatedly performed to process the counter electromotive force to brake the motor 306.

Then, the braking control method in the washing machine according to the present invention will be described with respect to the control system of the washing machine employed in the method of the present invention having the above configuration.

While the washing machine is normally operated by a process such as washing or dehydration, when the lid of the washing machine is opened or the vibration is severe due to the unbalanced state of the washing tank, the user suddenly stops the driving state. When the power supplied to the motor 306 is cut off by the user's stop operation, the motor 306 subsequently functions as a generator, not a load, as described above, and thus the counter electromotive force generated by the motor 306. Electric current flows from the motor 306 side to the power supply terminal (DC link end) side. As such, when the current generated from the motor 306 flows to the power supply terminal side, the voltage detector 304 senses a voltage between the rectifier 301 and the motor driver 302 and transmits the voltage to the microcomputer 105. Then, the microcomputer 305 compares the voltage sensed by the voltage detector 303 with the preset reference voltage Vref and controls the counter electromotive force energy according to the result. That is, according to the feature of the method according to the present invention by varying the switching duty ratio of the voltage (current) pulse entering and exiting the motor drive unit 302 according to the voltage magnitude of the DC link terminal corresponding to the variation in the magnitude of the power supply voltage to the motor ( The back EMF energy flowing back toward the DC link end is controlled. This will be described in more detail by way of example.

Currently, homes are usually supplied with single-phase AC 220V, 60 Hz commercial power. However, at this time, AC 220V does not mean that AC 220V is always always supplied, but AC 220V ± 15% of power (187V to 253V) is supplied. Therefore, when the power supply voltage supplied to the washing machine is AC 187V, which is AC 220V-15%, the voltage of the DC link terminal passing through the rectifying unit 301 is about 265V (187V × ) This means that the back EMF generated from the motor 306 may be sent to the DC link stage when the washing machine is braked. That is, in the inverter washing machine, a circuit is designed to withstand a certain range of voltage (for example, up to 400 V) in response to the counter electromotive force during braking flowing back to the DC link stage and the voltage level of the DC link stage increases. When the voltage of the DC link stage is 265V, there is a relatively large margin until reaching the set maximum allowable value of 400V, so that the back EMF generated from the motor 306 during braking can be sent to the DC link stage. Therefore, at this time, the switching duty ratio is reduced (by reducing the discharge amount from the capacitor to the motor) to control while increasing the counter electromotive force (regenerative energy: in the present invention to be used as such a concept for convenience). Here, the explanation regarding the switching duty ratio will be added.

The three-phase AC voltages U, V, and W supplied from the motor driving unit (inverter) 302 to the motor 306 may be represented as shown in FIG. However, the case of FIG. 4 shows the voltage waveform under the most ideal state without voltage fluctuation, perfect equilibrium between three phases, and no external factors involved, and in fact, the voltage waveform applied to the motor 306 is not. . That is, as shown in FIG. 5A, the voltage actually applied to the motor 306 (selecting the U phase for convenience) generally has one sinusoidal waveform, but has a waveform having a very fluctuation in instantaneous value. . FIG. 5B is an enlarged view of a portion 'A' of the voltage waveform graph of FIG. 5A. In the method according to the present invention, the section of the voltage value rising portion from the lower left to the upper right of the graph is 'ON', and the upper left to the right. Set the section of the voltage drop to the bottom to 'OFF'. Here, 'ON' means that the voltage is applied to the motor 306, 'OFF' means that the voltage applied to the motor 306 is cut off. FIG. 5C is a time chart illustrating such 'ON' and 'OFF' sections, where the switching duty ratio is a ratio between a load period (ON period) and {load period (ON period) + idle period (OFF period)}. Say. If this is expressed as an expression, it is as follows.

In Equation 1, D _r represents a switching duty ratio, T _on represents a time of 'ON' section, and T _off represents a time of 'OFF' section.

With the above concept of switching duty ratio in mind, the switching duty ratio is ultimately the denominator value (T _on + T _off ) in Equation 1 under a given condition (eg, one cycle of the ON + OFF interval is 16 kHz). Since it is constant, it can be said that it depends _on T _{on which} is a molecular value. Thus, the smaller switching duty ratio described above means that the value of T _on is eventually reduced, which reduces the amount of voltage discharge from the capacitor C at the DC link stage to the motor 306, that is, the motor 306. This means that the voltage application (discharge) time to the side is shortened. Inversely, this means that the charging time from the motor 306 to the condenser C is increased, which can increase the amount of back electromotive force (regenerative energy) from the motor 306 to the condenser C. It will mean.

On the other hand, when the power supply voltage supplied to the washing machine is AC 253V, which is AC 220V + 15%, the voltage of the DC link terminal passing through the rectifying unit 301 is about 357V (253V × ) This means that the back EMF generated from the motor 306 during braking of the washing machine should not be sent to the DC link stage much. Because, as described above, since the highest breakdown voltage of the DC link stage is 400V, when a large amount of back electromotive force flows into the DC link stage, the voltage level can easily be exceeded beyond the breakdown voltage tolerance. Therefore, at this time, the switching duty ratio is increased (by increasing the discharge amount from the capacitor to the motor) to control while reducing the counter electromotive force (regeneration energy). In the above series of procedures, the variable adjustment of the switching duty ratio is of course performed by a control algorithm stored in advance in the microcomputer 305, and in this regard, the switching element in the motor drive unit (inverter) 302 is actually connected. The S1 to S6 are selectively turned on / off according to the control algorithm, and the duration ratio of the on / off is controlled so that the variation in the duty ratio is realized.

On the other hand, the above description has been taken as the example of the DC link terminal voltage (265V, 357V) corresponding to the minimum value (187V) and the maximum value (253V) of the power supply voltage for the sake of understanding, but the DC link terminal voltage as shown above, If the values are not distinguished, the question arises, on what basis, the switching duty ratio is controlled to increase or decrease the counter electromotive force. Accordingly, as one preferred embodiment, the voltage value Vdc of the DC link terminal corresponding to the applied power supply voltage is based on an intermediate value within the voltage range of the DC link terminal corresponding to the distribution range of the power supply voltage. Below the median (Vmd) (Vdc Vmd) controls the back EMF energy by reducing the switching duty ratio. By controlling the back EMF energy by increasing the ratio, the problem of large and small application of the switching duty ratio can be solved. For example, as described above, when a power source (187V to 253V) of AC 220V ± 15% is supplied to a general household, when such a power supply voltage is supplied to a washing machine, the corresponding DC link voltage is 265V to It will have a range of 357V. Therefore, the intermediate value within this voltage range is 311V (this is the voltage of the DC link stage when AC 220V is supplied), and the DC link stage corresponding to the power supply voltage at any moment based on the 311V When the voltage is less than 311V, the switching duty ratio is reduced to control the back EMF energy. When the voltage of the DC link terminal is between 311V and 357V, the switching duty ratio is increased to control the back EMF energy. As a result, the counter electromotive force generated from the motor during braking of the washing machine can be effectively controlled without using a braking resistor.

As described above, the braking control method in the washing machine according to the present invention is not a conventional method of consuming heat energy by the braking resistor in the process of processing the back EMF generated from the motor during braking, but entering and exiting the motor driving unit (inverter). Since the counter electromotive force is processed by repeating the charging and discharging by the variable adjustment of the switching duty ratio of the voltage (current) pulse, the problem of securing the space due to the installation of the resistor and the problem of dissipation of heat generated from the resistor are fundamental. I can solve it. In addition, it is possible to increase the reliability and extend the life of the circuit element by minimizing the adverse effect that may be caused to the circuit element by reducing the voltage variation of the DC link stage. In addition, by not using a resistor, the circuit design can be simplified, and the cost of the product can be reduced.

Claims (2)

Controlling the counter electromotive force by recharging and discharging the back electromotive force generated from the motor during braking of the washing machine to the capacitor of the DC link stage and discharging the charged voltage back to the motor; And And controlling the counter electromotive force by variably adjusting a switching duty ratio of a voltage (current) pulse entering and exiting a motor driving unit according to a voltage value of a DC link terminal corresponding to a deviation of a magnitude of a power voltage supplied to the motor. Braking control method in a washing machine. The method of claim 1, When the voltage value Vdc of the DC link stage is less than or equal to the intermediate value Vmd based on the intermediate value Vmd within the voltage value range of the DC link stage corresponding to the distribution range of the power supply voltage (Vdc). Vmd) controls the back EMF energy by reducing the switching duty ratio. A braking control method in a washing machine characterized by controlling the back EMF energy by increasing the ratio.