KR101224161B1 - method of controlling inverter for restarting induction motor and inverter therefor - Google Patents

Abstract

The present invention relates to a control method of an inverter for minimizing damage to an electric motor or an inverter without a speed sensor when the induction motor is controlled by a V / F control inverter and restarting the motor according to the power recovery. For example, when the disconnection control signal is applied, operating the voltage / frequency reference value according to the last command frequency f_last immediately before the disconnection control signal is applied, and the next N times (N is an integer of 1 or more). S), the deceleration sequence including the step of operating with a voltage / frequency reference value according to the command frequency f_set of the predetermined variable speed signal with respect to the current operating frequency is repeatedly performed during the power cut section.

Description

Method of controlling inverter for restarting motor and inverter for same

The present invention is a voltage / frequency control method (Voltage / Frequency control, V / F control) when the induction motor controlled by an inverter short circuit occurs, the control method of the inverter to minimize the damage to the motor or inverter when the motor restarts due to the power failure And it relates to an inverter equal to this.

A load such as a fan tends to rotate continuously for a predetermined time due to an inertia force even when the inverter stops operating due to power failure. In particular, when instantaneous power failure occurs in the AC input power, the motor is free-run by inertia, and the inverter loses the rotation information of the motor.

When restarting by power recovery, if a voltage not proportional to the actual speed of the motor is applied in V / F operation of the induction motor, the inverter stops due to overcurrent or excessive regenerative voltage generated across the DC link, or in the worst case, both the motor and the inverter It may be damaged. Therefore, it is important to accurately grasp the rotational information of the motor when restarting.

When the motor is free-run due to a power failure, a V / F control method for controlling the motor's rotation information in real time using a speed sensor and then applying the appropriate voltage corresponding to the rotation information at the time of restarting is proposed. There is a bar.

However, the use of the speed sensor has the advantage that can accurately grasp the rotation information, while the manufacturing cost of the control system increases. In general, since the DC link stage is equipped with a capacitor having a predetermined capacity, it is not necessary to require precise rotation information so as to use a speed sensor, and a control method capable of minimizing damage to the system at an appropriate level is sufficient.

In addition, a plurality of cooling fans are mounted in the main power supply of the high-speed railway, etc., and a separate driving inverter is generally adopted for each fan. At this time, since the speed sensor must be installed for each fan, the unit cost of the inverter system is further increased.

The problem to be solved by the present invention is to propose an inverter control method for driving and restarting the induction motor that can minimize the damage of the system due to power recovery without using a relatively expensive device such as a speed sensor.

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In order to solve the above problems, the present invention, the step of operating the voltage / frequency reference value according to the last command frequency (f_last) immediately before the application of the power failure control signal when the power failure control signal is applied; And operating with a voltage / frequency reference value according to the command frequency f_set of the variable speed signal predetermined for the current operating frequency in the next N unit time (s), where N is an integer of 1 or more. In one embodiment, an inverter control method characterized in that is repeatedly performed during a power cut section.

In addition, the present invention to solve the above problems, the input unit for receiving at least one fixed speed signal for the driving section and one variable speed signal for the power cut section; A first switch for selecting one of the input signals of the input unit, a first feedback circuit for delaying the command frequency Wcom ** of the selected applied signal, and a second for selecting one of the selected applied signal and ground A frequency delay unit including a switch; A first proportional calculation circuit for calculating a voltage V * corresponding to the delayed frequency W *, a second feedback circuit for delaying the calculated voltage V *, and the proportionally calculated voltage V * A voltage delay unit including a voltage switch for selecting one of a ground and a ground; And a second proportional calculation circuit for calculating a frequency W ** corresponding to the delayed voltage V **, and selecting one of the calculated frequency W ** and the delayed frequency W *. A third switch and a pulse width modulation controller configured to receive the delayed voltage V ** and an output of the third switch as a control signal, wherein the first switch, the second switch, the voltage switch, and the first switch; According to another embodiment, an inverter of a voltage / frequency control method is characterized in that the three switches are controlled by a sequence of predetermined patterns according to disconnection or recovery.

Here, the first switch and the voltage switch is synchronized with the operation control signal of the driving section or the recovery section, and the disconnection control signal of the disconnection section to perform switching, and the second switch and the third switch after applying the disconnection control signal. The switching operation of the predetermined pattern is performed during the first unit time.

In addition, the first switch is connected to the variable speed signal of the connection portion while the power cut control signal is applied in the power cut section, the voltage switch is connected to ground if there is no power cut control signal in the power cut section, and the first switch if the power cut control signal is present. It is connected to the proportional calculation circuit.

In addition, the second switch maintains the current connection state for the first unit time after applying the power cutoff control signal, and the third switch is first applied after applying the power cutoff control signal through the first pattern connected to the ground for the first unit time after applying the power cutoff control signal. During the unit time, it operates as a voltage / frequency reference value according to the last command frequency f_last immediately before the power cut control signal is applied.

In this case, the second switch changes the current connection state to another connection state at the next N unit time (s) after application of the power cutoff control signal, and the third switch includes the first switch. Command frequency f_set of the variable speed signal predetermined for the current operating frequency at the next N unit time (s) after application of the power cut control signal through the second pattern connected to the frequency W ** of the two proportional calculation circuit. Operate with a voltage / frequency reference according to

The deceleration sequence including the first pattern and the second pattern is repeatedly performed in the power cut section.

In the above two embodiments, the command frequency f_set of the variable speed signal may be a predetermined value according to the turn of the deceleration sequence.

According to the present invention, when the motor is restarted by power recovery, by applying an appropriate driving voltage according to the actual rotational speed of the motor it is possible to minimize the electrical damage caused to the inverter or the motor. In addition, as the number of motors to be started in a large-capacity system increases, manufacturing costs of the inverter system may be increased by expensive devices such as speed sensors. In addition, even if the actual rotational speed of the motor falls below a certain level, the minimum driving voltage is controlled so that the load such as a cooling fan connected to the motor can be continuously operated.

1 is a block diagram conceptually illustrating a configuration and a control signal flow of an inverter according to an embodiment of the present invention.
2 illustrates an external input control signal and a switching sequence for explaining an inverter control method according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Also, the singular forms as used below include plural forms unless the phrases expressly have the opposite meaning.

Throughout the specification, when a part is said to "include" a certain component, it means that it may further include other components, except to exclude other components unless specifically stated otherwise.

1 is a block diagram conceptually illustrating a configuration and a control signal flow of an inverter according to an embodiment of the present invention.

First, the connection relationship of each element constituting the inverter is as follows.

The input unit receives at least one fixed speed signal for the driving section and one variable speed signal for the power cut section.

In the example of FIG. 1, input stages of SP1 to SP3 are provided to provide three kinds of fixed speed signals. By selectively switching any one of SP1 to SP3, the induction motor connected to the inverter can be controlled at three speeds.

In comparison, the variable speed signal is provided to one input of SP4. Since the variable speed signal is defined as a speed signal corresponding to an operating frequency immediately before power failure, the maximum value of the variable speed is preferably set not to exceed the maximum fixed speed signal. For example, when SP1, SP2, and SP3 are fixed speed signals input at command frequencies of 20 Hz, 44 Hz, and 55 Hz, respectively, the command frequency range of the variable speed signal may be set to 20 Hz to 55 Hz.

The frequency delay unit includes a first switch SW1 for selecting one of the input signals from the input unit, and a first feedback circuit including a frequency filter Kw / S for delaying the command frequency Wcom ** of the selected applied signal. And a second switch SW2 for selecting one of the selected applied signal and ground. For convenience of description, the contact point to the first feedback circuit among the contacts switched by the second switch SW2 is referred to as W1, and the ground contact point is referred to as W2.

The voltage delay unit includes a first proportional calculation circuit 11 for calculating a voltage V * corresponding to the frequency W * delayed by the first feedback circuit, and a voltage filter for delaying the calculated voltage V *. And a second feedback circuit including Kv / S, and a voltage switch Sv for selecting one of the proportionally calculated voltage V * and ground. For convenience of explanation, the output contact of the first proportional calculation circuit 11 is referred to as V1 and the ground contact is referred to as V2 among the contacts switched by the voltage switch Sv.

The pulse width modulation controller includes a second proportional calculation circuit 12 that calculates a frequency W ** corresponding to the voltage V ** delayed by the second feedback circuit, and the calculated frequency W ** and And a third switch SW3 for selecting one of the delayed frequencies W *, and receives one of the contact outputs of the third switch SW3 and the delayed voltage V ** as a control signal. For convenience of explanation, the output contact of the second proportional calculation circuit 12 is called W3 among the contacts switched by the third switch SW3, and the output contact of the first feedback circuit is called W4.

Switching operations of the first switch SW1, the second switch SW2, the voltage switch Sv, and the third switch SW3 are controlled by a sequence of predetermined patterns as the inverter power is cut off or restored. Thus, an appropriate level of start control value is applied to the motor connected to the inverter. Although not shown in FIG. 1, an external input control signal for controlling switching operations of the first switch SW1, the second switch SW2, the voltage switch Sv, and the third switch SW3 may be applied to the inverter. The external input control signal may be divided into an operation control signal for when the operation power is supplied (or a power recovery) and an interruption control signal for when the operation power is disconnected.

Hereinafter, an operation process when a power failure occurs in an inverter having the above connection configuration will be described in detail with reference to each switch SW1 to SW3 and Sv and a sequence of an external input control signal.

2 illustrates an external input control signal and a switching sequence for explaining an inverter control method according to an embodiment of the present invention.

For the sake of understanding, an operation process of an inverter connected to an electric motor for driving a fan for cooling a railway system will be described as an example. However, the inverter of FIG. 1 will be described. Therefore, it is assumed that three fixed speed signals SP1 to SP3 and one variable speed signal SP4 are input to the inverter, and that SP1 / SP2 / SP3 are input at a command frequency of 20 Hz / 44 Hz / 55 Hz, respectively. do.

In FIG. 2, the term “gap section” refers to a section in which an operation power is supplied to a inverter or a recovery is performed, and thus normal operation is performed, and is used in the same meaning as the driving section or the recovery section in the entire specification.

In addition, the "four-section" refers to a section in which the inverter is not normally operated because the supply of the driving power is interrupted for some reason, and is used in the same meaning as the power cut section throughout the specification.

In FIG. 2, a ground speed indicator (GSI) is a control signal indicating the ground speed of a railway, in which an operation control signal for instructing the drive of the inverter for driving a cooling fan in a live wire section and an inverter for power recovery in a power cut section are provided. The term also refers to the disconnection control signal for controlling the emergency drive. The GSI may be used in the same sense as the external input control signal in the description of FIG. 1.

In addition, Ttt is a timer included in an inverter or a control system including an inverter, and counts a predetermined time every time the application of the GSI is started, such as when the inverter is initially driven or power-off after power failure. Provides criteria for performing switching operations. In the example of FIG. 2, it is assumed that Ttt is designed to count 15 seconds, and that the inverter of FIG. 2 is operated by a predetermined oscillator (not shown) with 15 seconds as one unit time. However, the count time and the unit time are not necessarily limited to 15 seconds and may be set as various times.

In FIG. 1, the first switch SW1 and the voltage switch Sv are switches that operate in synchronization with only the GSI regardless of the timer Ttt, and the second switch SW2 and the third switch SW3 are timers Ttt. These switches operate under the influence of.

The operation process of the inverter will be described in earnest as follows.

In the live section, the speed of the motor can be arbitrarily adjusted by entering SP1 to SP3. 2 shows an example of adjusting the speed by inputting fixed speed signals of SP1, SP1, SP2, SP3, SP2, SP1, SP2, and SP3 in the live section.

At this time, the operation control signal is constantly applied to the inverter by GSI, and the first switch SW1 is switched to the input terminals SP1 to SP3 corresponding to the speed to be set at that time, and the second switch SW2 and the voltage switch are different. Sv and the third switch SW3 are fixedly connected to the contacts of W1, V1, and W3, respectively.

When a power failure occurs and enters a four-segment section, during the first unit time t1 after the entry, the first switch SW1 maintains a connection with the input terminal (SP3 in FIG. 2) connected immediately before, and the third switch ( SW3 maintains the connection of W3 while the second switch SW2 and the voltage switch Sv are both switched to ground contacts.

Subsequently, from the second unit time t2, the power cut control signal is applied to the GSI, and the first switch SW1 is connected to the variable speed signal SP4 and the voltage switch Sv returns to V1. At this time, while the counter Ttt counts 15 seconds in the second unit time t2, the second switch SW2 maintains the current state (here, the ground state W2) and the third switch SW3 is switched to W4. The pulse width modulation control unit receives a voltage (V **) / frequency (W *) control signal at a command frequency immediately before disconnection (that is, a command frequency for SP3). In other words, when a power failure occurs, the command frequency immediately before the power failure is memorized.

When the counter ends, the second switch SW2 changes the switching from the current state to the other state, and the third switch SW3 returns to the W3 contact point again. In this case, since the current state of the second switch SW2 is the ground state W2, the switch is switched to the W1 contact point. Therefore, in the third unit time t3 after the end of the counter, the variable speed signal SP4 having a speed corresponding to the pre-stored command frequency is applied, and a voltage / frequency control signal is generated accordingly.

The first power cut control signal can be applied for two unit times, thereby completing the first power cut control sequence.

Next, in the case where the power failure section is continued, after the unit time t4 elapses, the power failure control signal GSI is applied again and the counter Ttt is operated.

First, at the unit time t4, the first switch SW1 is connected to the input terminal SP3 connected immediately before the disconnection, and the voltage switch Sv is switched to the ground contact, while the second switch SW2 and the third switch are connected. The switch SW3 maintains the current connection state.

Subsequently, during the unit time t5 at which the counter operates, the second switch SW2 maintains the current connection state (here, W1) while the third switch SW3 is switched to W4 so that the disconnection control signal is returned to the pulse width modulation controller. The voltage (V **) / frequency (W *) control signal by the command frequency immediately before being applied (that is, the command frequency for the immediately preceding SP4) is input. In other words, each time the disconnection control signal is reapplied, the command frequency immediately before reappliation can be obtained.

When the counter ends, the second switch SW2 changes the switching from the current state to the other state, and the third switch SW3 returns to the W3 contact point again. Here, since the current state of the second switch SW2 is the W1 state, the second switch SW2 is switched to the ground contact W2. Therefore, in the sixth unit time t6 after the end of the counter, a new variable speed signal SP4 'with a speed corresponding to the pre-stored command frequency is applied before reapplying the power cut control signal, and a voltage / frequency control signal is generated accordingly. . SP4 'applied at the sixth unit time t6 is a variable speed signal decelerated to a predetermined magnitude compared to SP4 applied at the third unit time t3.

The second applied power control signal may be applied for three unit times, thereby completing the second power control control sequence.

Subsequently, when the power failure section continues, the power failure control sequence differs only in that the power failure control signals are applied for M unit times (M is an integer of 4 or more), and the power failure control sequence may be repeatedly executed with the same switching principle.

As described above, whenever the power failure section is continued and the power failure control sequence is repeated, the voltage / frequency control signal for the variable speed signal decelerated to a predetermined magnitude is applied to the pulse width modulation control unit, which is decelerated by the free run of the motor. Proportional to rotation speed.

On the other hand, if the power cut control sequence is repeated repeatedly, the target speed of the variable speed signal converges to 0. However, there is a problem that it is difficult to restart the motor which is stopped even in a subsequent time even if the power is restored later. Therefore, when the power cut control sequence is performed a predetermined number of times or the variable speed (or command frequency) of the SP4 reaches a predetermined value, it can be controlled to maintain the value without further reducing.

Lastly, when power recovery is made and the gas line section is entered again, the GSI of the operation control signal is applied to the inverter, and the counter Ttt starts, and the motor is gradually restarted for the unit time by the finally stored command frequency.

In the above, a process of starting and restarting one motor by one inverter has been described. However, if the same principle is extended, a plurality of motors may be started and restarted by one inverter. In this case, since it is not necessary to include a speed sensor for each motor, the construction cost of the inverter can be reduced accordingly.

In addition, the embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Wcom **: Reference frequency reference value of input signal
W *: Frequency reference value delayed by frequency filter (Kw / S)
V *: Voltage reference value calculated in proportion to the delay frequency (W *)
V **: Voltage reference value delayed by voltage filter (Kv / S)
W **: Frequency reference value calculated in proportion to the delay voltage (V **)

Claims (11)

delete delete delete In the inverter of the voltage / frequency control method,
An input unit receiving at least one fixed speed signal for a driving section and one variable speed signal for a power cut section;
A first switch for selecting one of the input signals of the input unit, a first feedback circuit for delaying the command frequency Wcom ** of the selected applied signal, and a second for selecting one of the selected applied signal and ground A frequency delay unit including a switch;
A first proportional calculation circuit for calculating a voltage V * corresponding to the delayed frequency W *, a second feedback circuit for delaying the proportional calculated voltage V *, and the proportional calculated voltage V * A voltage delay unit including a voltage switch for selecting one of a ground and a ground; And
A second proportional calculation circuit for calculating a frequency W ** corresponding to the delayed voltage V **, and a third for selecting one of the calculated frequency W ** and the delayed frequency W * And a pulse width modulation control unit configured to receive a switch and a delayed voltage V ** and an output of the third switch as a control signal.
And the first switch, the second switch, the voltage switch, and the third switch are controlled in a sequence of a predetermined pattern according to disconnection or recovery. 5. The method of claim 4,
The first switch and the voltage switch performs a switching in synchronization with the operation control signal of the driving section or the recovery section and the disconnection control signal of the disconnection section,
And the second switch and the third switch perform a switching pattern of a predetermined pattern for the first unit time after applying the power cutoff control signal. The method of claim 5,
The first switch is connected to the variable speed signal of the connecting portion while the power cut control signal is applied in the power cut section,
The voltage switch is connected to the ground if there is no power cut control signal in the power cut section, and if the power cut control signal is connected to the first proportional calculation circuit. The method according to claim 6,
The second switch maintains the current connection state for the first unit time after applying the power cutoff control signal, and the third switch is the first unit after applying the power cutoff control signal through a first pattern connected to ground for the first unit time after applying the power cutoff control signal. And a voltage / frequency reference value according to the last command frequency (f_last) immediately before application of the disconnection control signal during the time period. The method of claim 7, wherein
The second switch changes the current connection state to another connection state at the next N unit time (s) after application of the power cutoff control signal, and the third switch is the second switch state. After applying the power control signal through the second pattern connected to the frequency W ** of the proportional calculation circuit, the next N unit time (s) is applied to the command frequency f_set of the variable speed signal predetermined for the current operating frequency. Inverter according to the operating voltage / frequency reference value. 9. The method of claim 8,
The deceleration sequence including the first pattern and the second pattern is repeatedly performed in the power cut section. 10. The method of claim 9,
And the command frequency f_set of the variable speed signal is predetermined according to the turn of the deceleration sequence. 10. The method of claim 9,
And the command frequency (f_set) of the variable speed signal is no longer changed after a deceleration sequence of a predetermined time is performed.

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