Method for compensating instantaneous power failure in high voltage inverter and high voltage inverter system using the same

The present invention relates to an instantaneous power failure compensation method for a high-voltage inverter and a high-voltage inverter system using the method.

In general, the inverter cuts off the Pulse Width Modulation (PWM) output within a few ms in the event of a power failure in the input power supply. At this time, if the inertia of the load is large, it takes a long time to accelerate the load when the power supply is restored. Since such an operation leads to a large loss at the industrial site, the instantaneous power failure compensation technology of the inverter is applied in a place where enormous damage is expected due to a process failure when the inverter is stopped.

1A and 1B are examples for explaining the operation of the instantaneous power failure compensation device of the conventional inverter, FIG. 1A is a drawing showing a normal state, and FIG. 1B is a drawing showing a case where a power cutoff occurs.

In general, the electrolytic capacitor 210 incorporated in the inverter 200 (shown outside the inverter 200 for convenience of explanation) charges power from the inverter 200 under normal conditions (FIG. 1A), and the power supply 100 is cut off due to a power failure. Then, the load 300 is driven by using the electric power charged in the electrolytic capacitor 210 (Fig. 1B). At this time, since the capacity of the general electrolytic capacitor 210 is designed so that it operates normally when the instantaneous power failure time is 16 msec, the inverter 200 does not stop if the instantaneous power failure time is within 16 msec. It can drive a load of 300.

However, a power outage in an area where the power supply condition is not good may be 16 msec or more, and in this case, there is a problem that the inverter 200 is stopped, which causes a problem of causing great damage at the industrial site.

On the other hand, the demand for high-voltage inverters is increasing at the same time as the demand for energy saving is increasing. As such a high-voltage inverter, a series-connected H-bridge (Cascaede H-Bridge, hereinafter referred to as "CHB") system is mainly used. Since CHB high-voltage inverters are installed in important equipment at industrial sites, reliability is important.

However, the conventional instantaneous power failure compensation device of the inverter shown in FIG. 1A has a problem that the instantaneous power failure cannot be overcome when applied to a CHB type high voltage inverter. The reason is as follows.

First, conventional instantaneous power outage compensation devices cannot control the DC links of multiple unit power cells of a high voltage inverter.

Second, the conventional instantaneous power failure compensation device uses the fed-back reference voltage as the DC link voltage command, but when actually applied in a high-voltage inverter, the DC link voltage of each power cell depends on the parasitic component of the capacitor. Since they are different from each other, it is impossible to drive with one voltage command at the time of actual driving.

Thirdly, the conventional instantaneous power failure compensation device has not been presented with a solution considering the external environment of a large-capacity load to which a CHB type high-voltage inverter is attached.

<p> An object of the present invention is that when a momentary power failure occurs in a high-voltage inverter, the high-voltage inverter operates without stopping by converting the mechanical kinetic energy stored in the load into electrical energy to correspond to the power failure section. It is to provide an instantaneous power failure compensation method to be continued and a high voltage inverter system using the method.</p>

<p> In order to solve the above-mentioned technical problems, in a high-voltage inverter including a plurality of power cells connected in series to form one phase voltage supplied to an electric motor, the instantaneous power failure compensation method of the present invention comprises a plurality of power cells. When the input voltage is less than the reference value, the output frequency of multiple power cells is reduced by a predetermined value at that time, the output frequency is reduced with a predetermined deceleration gradient, and when the input voltage is restored, the output at the time of restoration Including the step of maintaining the frequency for a predetermined time.</p><p> In one embodiment of the present invention, a step of increasing the output frequency with a predetermined acceleration gradient may be further included.</p><p> In one embodiment of the present invention, the step of increasing the output frequency may increase the output frequency to the output frequency before the instantaneous power failure.</p><p> In one embodiment of the present invention, when the voltage of the direct current (DC) links of a plurality of power cells rises, the step of increasing the output frequency by the amount of the voltage increase may be further included.</p><p> In one embodiment of the present invention, the step of reducing the output frequencies of the plurality of power cells by a predetermined value may reduce the output frequencies so as to be smaller than the speed of the electric motor.</p><p> In one embodiment of the present invention, the reduction width of the output frequency may be larger than the slip frequency.</p><p> In one embodiment of the present invention, the output frequency may be maintained so that the speed of the electric motor becomes smaller than the output frequency at the stage of maintaining the output frequency at the time of recovery for a predetermined time.</p><p> Further, in order to solve the above-mentioned technical problems, in a high-voltage inverter including a plurality of power cells which are connected in series and constitute one phase voltage supplied to an electric motor, the instantaneous power failure compensation method of the present invention provides a plurality of electric powers. When the power is restored after the input voltage of the cell becomes equal to or lower than the reference value, the output frequency at the time of restoration can be maintained for a predetermined time.</p><p> Further, in order to solve the above-mentioned technical problems, the high-voltage inverter system of the present invention is connected in series to form one phase voltage supplied to an electric motor, via a plurality of power cells, and a plurality of power cells and a network. When the input voltage of a plurality of power cells is equal to or less than the reference value, the output frequencies of the plurality of power cells are reduced by a predetermined value at that time, the output frequency is reduced by a predetermined deceleration gradient, and the input voltage becomes When recovering, it includes a control unit that maintains the output frequency at the time of recovery for a predetermined time.</p><p> In one embodiment of the present invention, the control unit may increase the output frequency with a predetermined acceleration gradient after maintaining the output frequency for a predetermined time.</p><p> In one embodiment of the present invention, the control unit may increase the output frequency to the output frequency before the instantaneous power failure.</p><p> In one embodiment of the present invention, when the voltage of the DC link of a plurality of power cells rises while the output frequency is reduced by a predetermined deceleration gradient, the control unit increases the output frequency by the increase in voltage. May be good.</p><p> In one embodiment of the present invention, the control unit may reduce the output frequencies of the plurality of power cells so as to be smaller than the speed of the electric motor.</p>

<p> According to the present invention, when a momentary power failure occurs in a high-voltage inverter, the mechanical kinetic energy stored in the load is converted into electrical energy to correspond to the power failure section so that the high-voltage inverter continues to operate without stopping. Therefore, it is possible to cope with an instantaneous power failure of 16 ms or more, which was not possible with a conventional CHB type high-voltage inverter. Thereby, the present invention can prevent the damage caused by the momentary stop of the inverter, thereby ensuring the reliability of the product process and improving the quality of the product.</p>

<figref num="1A">It is an example diagram for demonstrating the operation of the instantaneous power failure compensation device of a conventional inverter.</figref><figref num="1B">It is an example diagram for demonstrating the operation of the instantaneous power failure compensation device of a conventional inverter.</figref><figref num="2">It is a block diagram of one Embodiment of the CHB type high voltage inverter to which this invention is applied.</figref><figref num="3">It is a detailed block diagram of one Embodiment of the power cell of FIG.</figref><figref num="4">It is a flowchart of one Embodiment for explaining the instantaneous power failure compensation method which concerns on this invention.</figref><figref num="5">It is an embodiment graph for demonstrating the instantaneous power failure compensation method which concerns on this invention.</figref><figref num="6">It is a graph which showed the motor output current with respect to the input voltage at the time of the momentary power failure of the conventional inverter.</figref><figref num="7A">It is an example diagram for demonstrating that the output current of a high voltage inverter was compensated by the instantaneous power failure compensation method which concerns on this invention.</figref><figref num="7B">It is an example diagram for demonstrating that the output current of a high voltage inverter was compensated by the instantaneous power failure compensation method which concerns on this invention.</figref><figref num="8A">It is an example diagram for demonstrating that the output current of a high voltage inverter was compensated by the instantaneous power failure compensation method which concerns on this invention.</figref><figref num="8B">It is an example diagram for demonstrating that the output current of a high voltage inverter was compensated by the instantaneous power failure compensation method which concerns on this invention.</figref>

The present invention can have various embodiments by making various modifications, and the specific embodiments will be described in detail by exemplifying the drawings. However, it should be understood that this does not limit the invention to any particular embodiment, but includes all modifications, equivalents or alternatives contained within the ideas and technical scope of the invention.

The present invention makes it possible to continuously operate a high-voltage inverter without stopping even when a momentary power failure occurs. That is, in the present invention, when a momentary power failure occurs, the high-voltage inverter is not stopped, the power failure is recognized, and the mechanical kinetic energy of the load is regenerated by the inverter for continuous operation. At this time, since the DC link voltage of the power cell changes according to the amount of regeneration, it is possible to avoid a power failure section through inverter control that maintains an appropriate voltage.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a configuration diagram of an embodiment of a CHB type high voltage inverter to which the present invention is applied.

As shown in the figure, the high voltage inverter to which the present invention is applied is of the CHB type and includes a phase shift transformer 10, a power cell 20, a control unit 30, and an electric motor 40.

The phase shift transformer 10 replaces the phase of the input power supply and supplies it to the plurality of power cells 20. Since this is widely known in the technical field of the present invention, detailed description thereof will be omitted.

The control unit 30 is connected to a plurality of power cells 20 via a network, and at this time, the type of network is, for example, a measurement control network (Controller Area Network, CAN), but is not limited thereto. Absent. The control unit 30 controls the power cell 20 via communication with the power cell 20 to compensate for the instantaneous power failure of the present invention. This will be described below with reference to the drawings.

The power cell 20 is a single-phase inverter, which is connected in series to form one phase voltage to be supplied to the motor 40, and is a three-phase inverter capable of obtaining a high-voltage output as a whole. In order to explain one embodiment of the present invention, a single-phase inverter equipped with 18 power cells 20 (corresponding to 6 each) will be described, but the present invention is not limited to this. It is self-evident to those who have ordinary knowledge in the technical field to which they belong. The larger the number of power cells 20, the larger the power that can be output to the motor 40.

Further, the power cell 20 communicates with the control unit 30 via the network, and performs instantaneous power compensation under the control of the control unit 30. For this purpose, it includes a power cell control unit that communicates with the control unit 30. The detailed configuration of the power cell will be described below.

FIG. 3 is a detailed configuration diagram of an embodiment of the cell of FIG. 2, and it is obvious that the configurations of the plurality of power cells 20 are the same as each other.

As shown in the figure, the power cell 20 according to the present invention includes a rectifying unit 21, a DC link unit 22, an inverter unit 23, and a power cell control unit 24.

The rectifying unit 21 converts the three-phase AC input voltage to direct current, and the DC link unit 22 stores the voltage converted to direct current by the rectifying unit 21. The DC link unit 22 can also convert the rectified waveform into a stable direct current via a smoothing capacitor.

The inverter unit 23 switches the rectified direct current to generate an alternating current and applies it to the electric motor 40. The inverter unit 23 switches according to the output frequency of the power cell control unit 24, and the transistor of the inverter unit 23 may be, for example, an insulated gate bipolar transistor (IGBT), but is limited to this. It's not something.

Since the operations of the rectifying unit 21, the DC link unit 22, and the inverter 23 are widely known to those who have ordinary knowledge in the technical field to which the present invention belongs, detailed description thereof will be omitted.

The power cell control unit 24 transmits the voltage of the DC link unit 22 to the control unit 30, and transmits the output frequency of the inverter unit 23 under the control of the control unit 30. The output frequency and voltage of the inverter unit 23 can be adjusted by the switching control of the control unit 30. That is, the power cell control unit 24 transmits a control signal under the control of the control unit 30.

In a high-voltage inverter including a plurality of power cells as shown in FIG. 2, it was impossible to make the DC link portions 22 of the plurality of power cells 20 the same with the conventional instantaneous power failure compensation device, but it is possible according to the present invention. become. Hereinafter, the compensation method of the present invention will be described with reference to the drawings.

FIG. 4 is a flowchart of an embodiment for explaining the instantaneous power failure compensation method according to the present invention, and it has already been explained that it is performed by the control unit 30 of FIG.

As shown in the figure, the power cell control unit 24 checks the input voltage input to the power cell 20, and when an input voltage equal to or lower than the reference value is input to the power cell 20 (S41), it determines that this is a power failure. Then, this is notified to the control unit 30.

In the conventional high-voltage inverter, the inverter stops immediately when such a situation occurs. This is because the capacity of the electric motor 40, which is a load, is larger than the capacity of the capacitor of the DC link portion 22 of the power cell 20, so that a low voltage trip occurs before the control loop is activated.

In order to prevent such a low voltage trip, the control unit 30 of the present invention starts the regeneration procedure at the same time when a power supply below the reference value is input (S41), that is, when a momentary power failure occurs. As a result, the output frequency of the inverter unit 23 is reduced (S42). By reducing the output frequency in this way, it is possible to obtain regenerative energy that can control the power failure section at the initial stage of the power failure. At this time, preferably, the output frequency is reduced so as to be smaller than the actual speed of the motor 40.

After that, the output frequency of the inverter unit 23 is reduced by a predetermined deceleration gradient suitable for the load amount of the load (motor 40) (S43). Since the speed of the electric motor 40 is smaller than the output frequency output from the inverter unit 23 by the slip frequency, the speed of the electric motor 40 is also reduced in proportion to the deceleration gradient of the output frequency of the inverter unit 23.

At this time, the power cell control unit 24 continuously confirms the voltage of the DC link unit 22 and transmits this to the control unit 30. This is to prevent overvoltage trips from occurring.

That is, when the amount of regeneration is large and the voltage of the DC link unit 22 rises (S44), the control unit 30 increases the reduced output frequency by the increase in the voltage to consume energy (S45). ).

After that, when the input voltage rises and the power is restored so as to pass through the power failure section (S46), the output frequency is raised so as to return to the existing speed command in the conventional inverter, but the control unit 30 of the present invention is an electric motor. The output frequency at the time of power recovery is maintained to prevent the slip from spreading excessively at the time of power recovery and causing an overcurrent trip due to the large inertia of 40 (S47).

That is, the control unit 30 of the present invention maintains the output frequency at the time of power recovery for a predetermined time so as not to exceed the overcurrent limit value of the inverter in the power recovery mode (S47). The time for maintaining the output frequency is preferably determined in advance according to the load amount of the motor 40.

After that, the control unit 30 increases the output frequency with the set acceleration gradient so that the electric motor 40 returns to the speed before the instantaneous power failure (S48). The acceleration gradient at this time is preset by the user. As a result, the speed of the motor 40 can be increased by the same gradient as the acceleration gradient of the output frequency, and can be restored to the speed before the instantaneous power failure (S49). The instantaneous power failure compensation sequence of the control unit 30 of the present invention will be clarified by explaining with reference to the following graph.

FIG. 5 is an embodiment graph for explaining the instantaneous power failure compensation method according to the present invention, and is an exemplary diagram showing the relationship between the output frequency, the motor speed, the input voltage, and the power of the motor when a power failure occurs. .. The graph of FIG. 5 will be described in comparison with each stage of FIG.

As shown, the input voltage is input up to t1 while maintaining a constant value. Generally, the input voltage is alternating current, but Fig. 5 shows the effective value (rms). In the normal state, the difference between the output frequency of the inverter unit 23 and the actual speed of the electric motor 40 is called the "slip frequency".

When the input voltage falls below the reference value at t1 (S41), the control unit 30 determines that there is a power failure and reduces the output frequency by a predetermined value (S42) (part A).

After that, the control unit 30 reduces the output frequency with a preset deceleration gradient until t2 at the time of power recovery (S43). Such a decrease in output frequency is repeated until t2 at the time of power recovery.

When the input voltage is restored at t2 (S46) and the power is restored, the output frequency at the time of restoration is maintained for a predetermined time (from t2 to t4) (S47). At t4 when the predetermined time has passed, the output frequency is increased at the set acceleration gradient (S48), and at t5, the state before the power failure is restored (S49). After that, it can be seen that the output frequency is maintained constant.

At this time, the time t3 is the time when the output frequency of the inverter unit 23 and the actual speed of the electric motor 40 are the same. That is, the time for maintaining the output frequency may be set after the time when the output frequency of the inverter unit 23 and the actual speed of the electric motor 40 become the same.

This will be explained from the aspect of energy. When a momentary power failure starts at t1, the energy of the motor 40 is regenerated to the inverter side, so the energy decreases. At this time, if the recovery energy is large, an overvoltage trip may occur, so the voltage-to-frequency (Voltage to Frequency, hereinafter referred to as V / F) ratio must be reduced.

When the power is restored at t2, the input voltage and recovery energy are supplied to the inverter unit 23 at the same time up to t3, so the energy is suppressed up to t3.

FIG. 6 is a graph showing the motor output current with respect to the input voltage of the conventional inverter at the time of instantaneous power failure.

As shown in the figure, when the input voltage input to the power cell is cut off for 16 msec or more, the output current of the high-voltage inverter becomes 0 and the motor stops.

7A and 7B are illustrations for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention, and when the electric motor 40 has a load of 4000 V, the electric motor 40 Shows the case of operating at frequencies of 54 Hz and 56 Hz, respectively.

As shown in FIG. 7A, even when the power failure time is 177 ms, that is, even when the input voltage is not applied to the power cell 20 for 177 ms, the output current of the high-voltage inverter is stably driven without stopping. , It can be seen that the electric motor 40 outputs the current.

Further, as shown in FIG. 7B, the output current of the high-voltage inverter does not stop stably even when the power failure time is 173 ms, that is, even when the input voltage is not applied to the power cell 20 for 173 ms. It can be seen that it is driven and the electric motor 40 outputs the current.

8A and 8B are illustrations for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention, and when the electric motor 40 has a load amount of 3000 V, the electric motor 40 Shows the case where is operating at frequencies of 49 Hz and 51 Hz, respectively.

As shown in FIGS. 8A and 8B, the output current of the high-voltage inverter does not stop stably even when the power failure time is 130 ms, that is, even when the input voltage is not applied to the power cell 20 for 130 ms. It can be seen that it is driven and the electric motor 40 outputs the current.

The compensation method of the present invention can control a plurality of power cells at the same time to cope with an instantaneous power failure of 16 ms or more, which is impossible with a conventional CHB type high-voltage inverter.

The above-mentioned compensation method of the present invention aims to prevent damage caused by a momentary stop of the inverter, thereby ensuring the reliability of the product process and improving the quality of the product.

The present invention has been described in detail with reference to the above embodiments, but a person having ordinary knowledge in the technical field to which the present invention belongs is within the limit of not departing from the scope of the present invention with respect to the above-described embodiments. You will understand that various transformations can be made with. Therefore, the scope of rights of the present invention should not be determined only by the described embodiments, and must be determined not only by the scope of claims described later but also by the scope of claims and equivalents thereof.

10 phase shift transformer 20 power cell 21 Rectifier 22 DC link section 23 Inverter section 24 Power cell control unit 30 Control unit 40 electric motor 100 power supply 200 inverter 210 electrolytic capacitors 300 load