Patent Description:
In general, a compressor of an air conditioner uses an electric motor (or motor) as a driving source. A motor generally has a structure in which a rotating shaft located inside a stator is supported by a bearing in a physical contact manner. Recently, in response to the need to develop a high-speed rotation motor in which a rotating shaft is supported by a magnetic bearing even without a physical contact. Such a motor employing a magnetic bearing receives power through a power transforming apparatus.

It is generally known that the power transforming apparatus includes a rectifier, a power factor controller, and an inverter type power transforming unit. Specifically, an AC commercial voltage output from a commercial power supply is rectified by the rectifier. The voltage rectified by the rectifier is supplied to the power transforming unit such as an inverter. In this case, the power transforming unit generates AC power for driving the motor by using the voltage output from the rectifier. Also, in some cases, a DC-DC converter for improving a power factor may be provided between the rectifier and the inverter.

On the other hand, in the power transforming apparatus and an air conditioner, power supply is essential to maintain a role of a magnetic bearing even in the event of a power failure. In general, an uninterruptible power supply (UPS) is used in a power transforming apparatus to maintain the role of the magnetic bearing even in the event of the power failure.

An uninterruptible power supply (UPS) refers to a device that instantly supplies alternative power when power supply becomes impossible due to a power outage or the like. Such an UPS is expensive and requires maintenance because it has a built-in battery. Also, the UPS has a disadvantage that an operating temperature is limited.

In addition, the power transforming apparatus and the air conditioner require a backup bearing to protect a magnetic bearing coil in the event of a failure or unstable control of the magnetic bearing. The backup bearing is designed to withstand friction and speed in an instantaneous transient state. The backup bearing may be damaged or its lifespan may be reduced if a power outage or failure occurs during high-speed rotation, and in severe cases, even product damage may be caused. In general, the lifespan of the backup bearing is less than about <NUM> to <NUM> cycles. When a fault occurs in the backup bearing, the operation of the product is stopped, and maintenance costs due to replacement are required.

On the other hand, the prior art patent document <CIT> (hereinafter, Patent Document <NUM>) discloses performing a regeneration by performing a hysteresis voltage control when a power failure occurs.

However, according to Patent Document <NUM>, when a converter fails during a normal operation, the regenerative voltage control cannot be performed. That is, there is a problem that an operation in response to the power failure cannot be performed. In addition, an accurate voltage control is difficult during the regenerative voltage control.

Another prior art patent document <CIT> (hereinafter, Patent Document <NUM>) discloses supplying power to an inverter and a magnetic bearing controller by using a separate regenerative circuit upon a power failure. However, even in Patent Document <NUM>, it is impossible to deal with a case where a converter fails during a normal operation and an accurate voltage control is difficult during the regenerative voltage control, similar to Patent Document <NUM>. In order to solve these problems, separate additional circuits, such as a power failure and speed detection circuit, a regenerative circuit, and the like, should be configured.

<FIG> shows an example of a power transforming apparatus using a UPS device <NUM> according to the related art.

Explaining operations according to the related art with reference to <FIG>, during a normal operation, an AC input voltage that is input to an MCCB <NUM> is output to an AMB controller <NUM> and an inverter controller <NUM> sequentially via a step-down transformer <NUM> and a static bypass of a UPS device <NUM>. Thereafter, power is supplied to a three-phase motor <NUM> to which a magnetic bearing is applied. On the other hand, upon a power failure, a DC voltage charged in a battery embedded in the UPS device <NUM> is converted into AC power through an AC/DC rectifier and a DC/AC inverter, and then power is supplied to the AMB controller <NUM>.

Accordingly, as described above, in addition to the problem of an increase in product price due to an increase in material costs, maintenance costs are additionally needed depending on the lifespan of the battery. Even a limited operating temperature makes an exterior application of the power transforming apparatus difficult.

<CIT> discloses a resonant conversion apparatus with extended hold-up time and method of operating the same.

<CIT> discloses a converter, in particular an emergency converter for driving a load such as LEDs from either mains supply or a battery and a method for switching between either mains supply or battery-driven operation in an emergency converter.

<NPL> on Average power balance method for power failure compensation control of high-speed turbo molecular pump with AMB system.

<CIT> disclose a power supply circuit for a magnetic bearing system.

Additional background art can be found in <CIT> and <CIT>.

Therefore, an aspect of the present disclosure is to provide a power transforming apparatus that is capable of stably supplying power even upon a power failure and does not cause maintenance costs due to an addition of a battery, and an air conditioner having the same.

Another aspect of the present disclosure is to provide a power transforming apparatus that is capable of stably supplying power to a magnetic bearing controller even upon a power failure, and is allowed for outdoor installation without a limit in an operating temperature so as to be applicable to an air-cooled air conditioner, and an air conditioner including the same.

The present invention is defined in independent claim <NUM>; the dependent claims define embodiments of the present invention.

In order to achieve these and other advantages and in accordance with the present invention, as embodied and broadly described herein, there is provided a power transforming apparatus that supplies power to a magnetic bearing-applied motor and includes an inverter and a converter. Upon an initial operation, the converter receives an AC voltage as first power and an auxiliary circuit performs initial charging using the first power. The auxiliary circuit supplies rectified second power to an inverter controller and a magnetic bearing controller connected to the converter. Accordingly, the inverter controller outputs a driving signal to the inverter using the second power so as to perform an initial charging operation. Thereafter, the inverter controller controls the inverter to supply rectified DC voltage to the converter. After the initial charging, the converter cuts off the supply of the second power by the auxiliary circuit and supplies the DC voltage supplied in response to the operation of the inverter to the inverter controller and the magnetic bearing controller. Meanwhile, since the power supply through the converter is not allowed during a fault in the converter, the second power of the auxiliary circuit is supplied to the inverter controller and the magnetic bearing controller again such that a magnetic bearing gap control can be stably performed.

The power transforming apparatus further includes a step-down transformer to step down a three-phase input voltage to supply to the converter and the auxiliary circuit.

The power transforming apparatus further includes a relay located between the converter and the auxiliary circuit so as to be turned on or off by the converter.

The converter turns off the relay to cut off the supply of the second power during the normal operation, and outputs a control signal for turning on the relay to supply the second power again upon the power failure.

In an implementation, the step-down transformer may be respectively connected to the converter and the auxiliary circuit through power lines as a separated branched Tap.

The step-down transformer supplies a stepped-down AC voltage to the converter through a first branch line and supplies the stepped-down AC voltage to the auxiliary circuit through a second branch line upon an initial operation.

In an implementation, the step-down transformer may include a circuit structure in which an output voltage ratio of 380V:220V satisfies at least <NUM>:<NUM>.

In an implementation, the converter may detect the power failure and transmit a power failure detection signal to the inverter controller and the magnetic bearing controller.

In an implementation, when the power failure detection signal is received, the inverter controller may block a thyristor (SCR) of a rectifier connected to the inverter.

In an implementation, the inverter controller may switch a control mode of the inverter from a speed control mode into a voltage control mode when a reverse rotation of the motor is started after receiving the power failure detection signal.

In an implementation, the rectifier may control initial charging and a power factor of an AC input voltage of the inverter during the normal operation.

In an implementation, the rectifier may be operated to suppress a regenerative reverse voltage, in response to the inverter controller blocking the thyristor (SCR).

In an implementation, the magnetic bearing controller may perform a magnetic bearing gap control by receiving the second power from the auxiliary circuit and applying a current to the magnetic bearing applied to the motor, upon the power failure.

In an implementation, the magnetic bearing controller may perform the magnetic bearing gap control using the rectified DC voltage supplied from the converter during the normal operation.

In an implementation, the converter may change an output thereof into an OFF state and the inverter and the magnetic bearing controller may generate control power by receiving the second power from the auxiliary circuit when a converter fault signal is detected.

Each of those implementations may also be applicable to an air conditioner including the power transforming apparatus.

Hereinafter, effects of a power transforming apparatus according to the present invention will be described.

In a power transforming apparatus including a magnetic bearing-applied motor and an air conditioner including the same according to at least one of implementations of the present disclosure, an effective response to a power failure can be allowed by applying regenerative stepping-up and a DC/DC converter without an additional UPS device.

In addition, the present disclosure may have an advantage in that it is unnecessary to implement a separate power failure detection circuit for regenerative control or an additional circuit for regeneration without adding a UPS device. Furthermore, an accurate regenerative constant voltage control can be performed even without an additional circuit for regeneration.

In addition, the present disclosure can improve reactive power due to a lowered power factor of an AC control power of a magnetic bearing. Specifically, by supplying power in a DC form through a DC/DC converter, only active power can be supplied.

Also, in the power transforming apparatus including the magnetic bearing-applied motor and the air conditioner including the same according to the present disclosure, since the UPS device can be excluded, battery replacement costs cannot be required and even an external application can be allowed.

Description will now be given in detail according to exemplary implementations disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same or similar reference numbers, and description thereof will not be repeated. In general, a suffix such as "module" and "unit" may be used to refer to elements or components. Use of such a suffix herein is merely intended to facilitate description of the specification, and the suffix itself is not intended to give any special meaning or function. In describing the present disclosure, if a detailed explanation for a related known function or construction is considered to unnecessarily divert the gist of the present disclosure, such explanation has been omitted but would be understood by those skilled in the art.

<FIG> is a representative circuit diagram of a power transforming apparatus employing a magnetic bearing without a UPS device according to the present disclosure.

A power transforming apparatus <NUM> according to the present disclosure includes a three-phase rectifier <NUM>, a DC link capacitor <NUM>, a three-phase inverter <NUM>, a step-down transformer <NUM>, an auxiliary circuit <NUM>, and a DC/DC converter <NUM>, a magnetic bearing controller <NUM>, and an inverter controller <NUM>, and is connected to an MCCB <NUM> for supplying an AC voltage and a three-phase motor <NUM> to which a magnetic bearing is applied.

In the power transforming apparatus <NUM> according to the present disclosure, upon an initial operation, a three-phase AC voltage input to the MCCB <NUM> is supplied to the DC/DC converter <NUM> via the step-down transformer <NUM>.

In the present disclosure, the step-down transformer <NUM> may be implemented to have a structure in which an output voltage ratio of 380V: 220V satisfies <NUM>:<NUM>. Specifically, the step-down transformer <NUM> may supply an AC voltage for an inverter/magnetic bearing control with an upper controller (cycle control) by stepping down a line voltage (R, T phase) of three-phase power to 220V.

The step-down transformer <NUM> may supply control power to the DC/DC converter <NUM> through a separated branched Tap for an initial operation. This may be distinguished from a structure in which the step-down transformer <NUM> (<FIG>) of the related art power transforming apparatus is connected to the UPS device <NUM> through a single output structure (about 500VA to 3000VA).

The step-down transformer <NUM> may thus require a very small (low) output ratio (e.g., <NUM>:<NUM>) for initial control power of the DC/DC converter <NUM> by virtue of the structure of the separated branched Tap.

Therefore, during the initial control of the DC/DC converter <NUM>, AC power (220V) input from the step-down transformer <NUM> is used. After the initial charging operation of the three-phase inverter <NUM> is completed, power is changed to a DC voltage of the DC capacitor <NUM> of an inverter side according to a potential difference between voltages of the DC/DC converter <NUM> and the three-phase inverter <NUM>.

Although not shown, in another example, the step-down transformer <NUM> may have a structure in which a separate external step-down transformer is further applied together with the step-down transformer <NUM> of <FIG>.

The three-phase rectifier <NUM> may receive three-phase AC power passed through the reactor <NUM>, convert the three-phase AC power into DC power, and supply the DC power to the three-phase inverter <NUM>.

The three-phase rectifier <NUM> may have a structure of a half-wave phase-controlled rectifier including a thyristor (SCR, silicon-controlled rectifier) at an upper end thereof.

During a normal operation, the three-phase rectifier <NUM> may serve to control the initial charging and an AC input power factor of the three-phase inverter <NUM>. In addition, in case of a power failure (power outage, power interruption), the three-phase rectifier <NUM> may serve as a breaker for blocking a three-phase AC power input from a motor regenerative voltage control, in order to prevent a regenerative reverse voltage.

The three-phase inverter <NUM> may include six power switching elements (IGBTs) and a gate drive circuit for driving the IGBTs.

The IGBT is a switching element having a structure of a power MOSFET (metal oxide semi-conductor field effect transistor) and a bipolar transistor, and has advantages of low driving power, high-speed switching, high voltage characteristics, and high current density.

The three-phase inverter <NUM> may rotate the three-phase motor <NUM> of a compressor by changing a DC voltage to an AC voltage through a voltage-type inverter during a normal operation. In addition, in the event of a power failure, the three-phase inverter <NUM> may operate as a three-phase PWM step-up converter in order to step up a generation voltage of the three-phase motor <NUM> which rotates in reverse by a pressure difference of the compressor. At this time, a voltage controlled by the three-phase inverter <NUM> should be greater than a counter electromotive voltage of the three-phase motor <NUM>.

The DC/DC converter <NUM> supplies DC power to the inverter controller <NUM> and the magnetic bearing controller <NUM> through power lines <NUM> during a normal operation.

The DC/DC converter <NUM> may perform a power failure detection function. When a power failure is detected, the DC/DC converter <NUM> may provide a power failure detection signal to the inverter controller <NUM> and the magnetic bearing controller <NUM> through communication lines <NUM>.

The DC/DC converter <NUM> may also constantly control a ratio of an output DC voltage to an input DC voltage. The DC/DC converter <NUM> may include a converter controller (not shown).

The auxiliary circuit <NUM> initially supplies power to the magnetic bearing controller <NUM> and the inverter controller <NUM> by performing AC/DC rectification.

The auxiliary circuit <NUM> may increase an output voltage during a normal operation after initial charging, and cut off a power supply in response to a turn-off of a DC relay <NUM>.

The auxiliary circuit <NUM> supplies power to the magnetic bearing controller <NUM> and the inverter controller <NUM>, in response to a turn-on of the DC relay <NUM> when a fault (breakdown, failure) of the DC/DC converter <NUM> is detected. That is, mode switching may be allowed upon the fault of the DC/DC converter <NUM>.

The ON/OFF control of the DC relay <NUM> is performed by a converter controller of the DC/DC converter <NUM>.

The auxiliary circuit <NUM> may include an NTC or a fixed resistor for limiting (or removing) an inrush current that is generated due to a difference between output voltages during the initial charging and the mode switching. Accordingly, a stable power supply to the magnetic bearing controller <NUM> and the inverter controller <NUM> can be achieved without a transient state. This will be described in more detail later with reference to <FIG>.

The magnetic bearing controller <NUM> may serve to lift a shaft of the three-phase motor <NUM> by applying a current to a magnetic bearing applied to the three-phase motor <NUM>.

Although not shown in detail, the magnetic bearing (AMB) controller <NUM> may include a control board, a current amplifier, and a power supply (SMPS).

The inverter controller <NUM> may output a PWM for driving the thyristor (SCR) of the three-phase rectifier <NUM> and the IGBT of the inverter <NUM> during a normal operation. Accordingly, a speed control for variably controlling the three-phase motor <NUM> at a desired speed may be performed.

Also, the inverter controller <NUM> may control an initial charging circuit <NUM> for the initial charging of the three-phase motor <NUM>. In addition, the inverter controller <NUM> may control the inverter <NUM> to operate as a step-up converter, in response to a power failure detection signal being input from the DC/DC converter <NUM> upon a power failure.

Hereinafter, <FIG> is a flowchart illustrating operations responsive to a power failure in a power transforming apparatus employing a magnetic bearing without a UPS device according to the present disclosure.

As illustrated in <FIG> and <FIG>, a method of operating a power transforming apparatus according to the present disclosure may start with an operation of supplying control power based on an initial driving signal (S10).

In detail, operations of the power transforming apparatus <NUM> will be described with reference to <FIG>. A three-phase AC voltage that is input to the MCCB <NUM> is supplied to the DC/DC converter <NUM> via the step-down transformer <NUM>. Then, in response to an AC relay ON signal, an AC/DC rectification is executed for the three-phase AC voltage input to the auxiliary circuit <NUM>, such that power can be supplied to the magnetic bearing controller <NUM> and the inverter controller <NUM>.

When power is supplied to the inverter controller <NUM>, an initial charging operation is performed by the three-phase inverter supplied with the three-phase power (S20).

Specifically, in <FIG>, a relay for an initial charging of three-phase power may be driven by the inverter controller <NUM>. The inverter controller <NUM> may output a trigger signal to the thyristor (SCR) of the three-phase rectifier <NUM>. Then, the three-phase rectifier <NUM> may supply DC power to the DC link capacitor <NUM>. Thereafter, power charged in the DC link capacitor <NUM> may be supplied to the DC/DC converter <NUM> as input power and control power (Normal operation).

Next, a power failure detection signal may be detected during a normal operation (S30). The detection of the power failure detection signal may be performed by the DC/DC converter <NUM> (more specifically, the converter controller (not shown)) without a separate detection circuit.

When the power failure detection signal is detected, the DC/DC converter <NUM> may transmit the power failure detection signal to the magnetic bearing controller <NUM> and the inverter controller <NUM>, and controls a relay of the inverter controller <NUM> to be turned off (S40). In addition, the inverter controller <NUM> may block the thyristor (SCR) of the three-phase rectifier <NUM>.

Thereafter, when the reverse rotation of the motor starts after the compressor stops, the inverter may be operated by switching a control mode of the inverter from a speed control mode to a voltage control mode (S50).

Specifically, when the compressor stops, a direction of pressure may be changed and the motor may rotate in a reverse direction. The control mode of the three-phase inverter <NUM> may be switched immediately when the motor rotates in the reverse direction. Specifically, the three-phase inverter <NUM> may be switched from the speed control mode to the voltage control mode.

When switched to the voltage control mode, the three-phase inverter <NUM> may perform a regenerative constant voltage control using the IGBT of the three-phase inverter <NUM> and position estimation information of a sensorless algorithm of the inverter controller <NUM>.

Specifically, when the reverse rotation of the motor <NUM> is caused due to the pressure difference of the compressor after an occurrence of the power failure, the three-phase inverter <NUM> may perform the regenerative constant voltage control by using phase angle information obtained through a sensorless control logic of the three-phase converter <NUM>.

During the regenerative constant voltage control, the magnetic bearing controller <NUM> and the inverter controller <NUM> use a relatively very small quantity of power compared to a large-capacity inverter. Accordingly, upon the regenerative constant voltage control, a stepping-up operation may be performed by using a phase inductance of the motor <NUM>, the IGBT of the inverter <NUM>, and the DC link capacitor <NUM> located between the three-phase rectifier <NUM> and the inverter <NUM>, without a separate auxiliary circuit.

In this regenerative constant voltage control, the stepping-up operation should be performed with a voltage greater than a counter electromotive force of the motor <NUM>. That is, the motor <NUM> should be able to supply power to the magnetic bearing controller <NUM> by stably performing the step-up control in a range of <NUM> to <NUM>. Here, the range of <NUM> to <NUM> may mean the minimum speed level for protecting a backup bearing.

As described above, a stable power supply suitable for the input spec of the DC/DC converter <NUM> can be achieved, even during the power failure, through the power failure detection by the converter <NUM>, the operation of the inverter controller <NUM>, and the regenerative constant voltage control.

On the other hand, while the power failure detection signal is not detected according to the determination in step S30, namely, during the normal operation, input power is supplied from the DC/DC converter <NUM> (more specifically, the converter controller) to the magnetic bearing controller <NUM> and the inverter controller <NUM>.

<FIG> is a flowchart illustrating operations carried out when a fault of a converter and/or a power failure occurs in a power transforming apparatus according to the present disclosure.

The power transforming apparatus according to the present disclosure mainly includes four operations. Specifically, the power transforming apparatus performs those operations including <NUM>) an initial operation, <NUM>) a normal operation when power is normally supplied, <NUM>) a response operation when a fault of the DC/DC converter occurs (steps S407 to S409), and <NUM>) a response operation when a power failure of the DC/DC converter occurs (step S410 to S414).

First, a description will be given of <NUM>) an initial operation (steps S401 and S402).

An AC relay may be turned on to supply control power to a motor to which a magnetic bearing is applied (S401).

Specifically, in <FIG>, initial charging of the auxiliary circuit <NUM> is performed with an AC voltage that is transferred to the auxiliary circuit <NUM> through a first branch line of the step-down transformer <NUM> (i.e., two power lines connected from the step-down transformer <NUM> to the auxiliary circuit <NUM>). Accordingly, control power is supplied to the DC/DC converter <NUM>. In addition, power is supplied to the DC/DC converter <NUM> through a second branch line of the step-down transformer <NUM> (i.e., two power lines connected from the step-down transformer <NUM> to the DC/DC converter <NUM>).

Next, a relay for three-phase initial charging may be turned on (driven) by the inverter controller <NUM> (S402). Specifically, the relay in the initial charging circuit <NUM> may be turned on by the inverter controller <NUM>, to perform initial charging for charging a DC voltage to the DC link capacitor <NUM> of the inverter. In addition, the inverter controller <NUM> may output a trigger signal (ON signal) to the thyristor of the three-phase rectifier <NUM>.

Hereinafter, a description will be given of <NUM>) a normal operation (steps S404 to S406, and S415).

As a result of the determination in step S403, when no converter fault (fault signal) is detected in the DC/DC converter <NUM>, that is, during a normal operation, the converter <NUM> is turned on (S404) and the relay <NUM> is turned off, such that the output by the auxiliary circuit <NUM> can be turned off (S405). That is, the DC/DC converter <NUM> supplies power to the magnetic bearing controller <NUM> and the inverter controller <NUM>. The magnetic bearing controller <NUM> may perform a magnetic bearing gap control (S406).

Hereinafter, a description will be given of <NUM>) a response operation (steps S407 to S409) in case of a fault of the converter.

As a result of the determination in step S403, when a converter fault (fault signal) is detected in the DC/DC converter <NUM>, the converter controller may change the output of the DC/DC converter <NUM> to an OFF state (S407).

Then, the converter controller changes the relay <NUM> from the OFF state to the ON state, such that power can be supplied through the auxiliary circuit <NUM> (S408). That is, power is supplied through the auxiliary circuit <NUM> instead of the DC/DC converter <NUM>.

At this time, the auxiliary circuit <NUM> may be switched to an AC/DC circuit using a thyristor switching element for power, and an inrush current may be suppressed by an NTC circuit. This will be described in more detail later with reference to <FIG>.

The converter controller may notify the fault of the DC/DC converter <NUM> by outputting a fault signal to the magnetic bearing controller <NUM> (S409). Since the power supply is continued by the auxiliary circuit <NUM>, the magnetic bearing controller <NUM> may perform a magnetic bearing gap control even at this time (S406).

Hereinafter, a description will be given of <NUM>) a response operation (steps S410 to S414) in case of a power failure of the converter.

As a result of the determination in step S410, when an occurrence of a power failure is detected in the DC/DC converter <NUM>, the DC/DC converter <NUM> may output a power failure detection signal to the magnetic bearing controller <NUM> and the inverter controller <NUM> (S411).

Then, the inverter controller <NUM> may output a control signal for blocking the thyristor SCR of the three-phase rectifier <NUM> in order to turn off the control of the inverter <NUM> (S412).

Then, the inverter controller <NUM> performs a regenerative constant voltage control mode (S413). When the compressor is stopped as the inverter control is OFF, a direction that pressure is applied may change and thus the motor starts to rotate in reverse.

As soon as the motor starts to rotate in the reverse direction, the control mode of the inverter <NUM> may be switched from a speed control into a voltage control. The regenerative constant voltage control may be performed using the six switching elements (IGBTs) of the inverter <NUM> and position estimation information obtained through the sensorless algorithm of the inverter controller <NUM>. Accordingly, a stable power supply that meets the input spec of the DC/DC converter <NUM> can be achieved even during the power failure.

As described above, in the power transforming apparatus to which the magnetic bearing is applied according to the present disclosure, the stable power supply can be achieved by the regenerative step-up control and the control of the converter, even without a UPS device, upon the occurrence of the fault or power failure of the converter.

<FIG> is a circuit diagram illustrating an output structure of a step-down transformer <NUM> for an initial operation in a power transforming apparatus according to the present disclosure.

As illustrated in <FIG>, one end of the step-down transformer <NUM> may be connected to branch lines between the MCCB <NUM> and the reactor <NUM>, and another end may be branched into two taps again. Specifically, the another end of the step-down transformer <NUM> may have a structure in which a first connection line is connected to the DC/DC converter <NUM> and a second connection line is connected to the auxiliary circuit <NUM>.

In the present disclosure, the step-down transformer <NUM> may supply an AC voltage for controlling the inverter and the magnetic bearing by stepping down a line voltage (R, T phase) of the three-phase power supply to 220V. The AC voltage may have a very small (low) output ratio for initial control power (<NUM>:<NUM>) of the DC/DC converter <NUM>.

Initially, AC power input from the step-down transformer <NUM> is be used as control power for the DC/DC converter <NUM>. This may be about 220V. The initial control power of the DC/DC converter <NUM> may be supplied to the auxiliary circuit <NUM> through a third connection line <NUM>, to be initially charged in the auxiliary circuit <NUM>. To this end, the DC/DC converter <NUM> may be implemented as an insulation structure.

Afterwards, when the initial charging of the three-phase inverter <NUM> of about 380V is completed, the control power of the DC/DC converter <NUM> may be changed to a voltage (DC) of the DC link capacitor <NUM> of the three-phase inverter <NUM>.

<FIG> is an exemplary circuit diagram illustrating of a circuit structure for initial charging and switching of the auxiliary circuit connected with the step-down transformer <NUM>, in the power transforming apparatus according to the present disclosure.

The power transforming apparatus according to the present disclosure includes the auxiliary circuit (AC/DC circuit) <NUM> for performing a response operation to the initial operation of the inverter <NUM> and the fault of the DC/DC converter <NUM>.

The auxiliary circuit <NUM> performs an initial charging operation using control power of the DC/DC converter <NUM> applied through the third connection line <NUM> (<FIG>).

When the auxiliary circuit <NUM> is initially charged, power is supplied to the inverter controller <NUM> such that the inverter controller <NUM> can supply the control power (SMPS) for operating the inverter. Then, the inverter <NUM> performs the initial charging operation by receiving three-phase power through the inverter controller <NUM>, so as to charge the voltage to the DC link capacitor <NUM> and perform a preparation operation for driving the motor <NUM>.

In addition, the auxiliary circuit <NUM> may perform a function for stably supplying power to the magnetic bearing controller <NUM> when the fault of the DC/DC converter <NUM> occurs.

Specifically, when a converter fault signal is detected, the converter controller may turn off the output of the DC/DC converter <NUM> and controls a transfer switch (SCR or Relay) of the auxiliary circuit <NUM>. Accordingly, a stable DC power supply to the magnetic bearing controller <NUM> can be continued.

The auxiliary circuit <NUM> according to the present disclosure may have an NTC (or resistor) or SCR structure to suppress an inrush current, which is generated due to a difference between an AC input voltage and a DC output voltage, when switching to an alternative operation due to a fault of the converter.

As illustrated in <FIG>, the auxiliary circuit <NUM> may be mainly divided into a series structure (a) and parallel structures (b and c).

For example, the auxiliary circuit <NUM> may include a relay (DC Relay) instead of a thyristor (SCR). In addition, when implemented in the parallel structures (b and c), a fixed resistor may be applied instead of the NTC.

As illustrated in (a) of <FIG>, when the auxiliary circuit <NUM> is implemented in the series structure, the NTC may be commonly used to limit (remove) an inrush current generated upon the initial charging and the operation mode switching. The thyristor (SCR) may also be used as a common switch for the initial charging and the operation mode switching.

When the auxiliary circuit <NUM> has the parallel structure as illustrated in (b) of <FIG>, the NTC may be commonly used to limit (remove) an inrush current upon the initial charging and the operation mode switching. An AC relay <NUM> may also be used as a common switch for the initial charging and the operation mode switching. The thyristor SCR may be used for changing a current path to eliminate an occurrence of NTC loss.

When the auxiliary circuit <NUM> has the parallel structure as illustrated in (c) of <FIG>, an initial charging resistor <NUM>, an initial charging relay <NUM>, and an AC power relay <NUM> may be applied to an input terminal upon the initial charging. In this structure, the NTC may be used only for limiting an inrush current upon the operation mode switching and the SCR may be used for changing a current path to eliminate NTC loss.

The NTC applied to the circuits of <FIG> may be difficult to be applied to a system having a high operating temperature. This is because an inrush current suppression performance is greatly reduced, which results from a great change in resistance value according to temperature. Therefore, the resistance value of the NTC should be set to an appropriate fixed resistance value that does not limit a maximum load current.

<FIG> are various exemplary circuit diagrams illustrating an output structure of the DC/DC converter <NUM> in the power transforming apparatus according to the present disclosure.

In the present disclosure, the DC/DC converter <NUM> may have an insulation structure. The DC/DC converter <NUM> may supply power to the inverter controller <NUM> and the magnetic bearing controller <NUM> in an on-line manner during a normal operation. The DC/DC converter <NUM> is used for supplying a regenerative voltage during a power failure.

The detection of the power failure may be performed by the DC/DC converter <NUM> without a separate additional circuit. Specifically, a generation of a power failure signal may be detected based on a DC voltage input to the converter <NUM> and an input voltage sensed by the auxiliary circuit <NUM>.

<FIG> illustrates a case in which the DC/DC converter <NUM> has a single output structure, <FIG> and <FIG> illustrate a case in which the DC/DC converter <NUM> has a multi-output structure, and <FIG> illustrates a case in which the DC/DC converter <NUM> has a topology form.

First, the DC/DC converter <NUM> of <FIG> may supply the same DC voltage (about 300V) in parallel to the magnetic bearing controller <NUM> and the inverter controller <NUM> through two connection lines <NUM> and <NUM>. For example, the DC/DC converter <NUM> may include one full-bridge circuit <NUM> and one FRD (fast recovery diode) circuit <NUM>.

The DC/DC converter <NUM> may additionally include a plurality of separate SMPSs (combination AC/DC and DC/DC) to generate control power for each of the magnetic bearing controller <NUM> and the inverter controller <NUM>. The plurality of SMPSs having an insulation structure may supply control power to the magnetic bearing controller <NUM> and the inverter controller <NUM> through power lines <NUM> and <NUM> branched in parallel.

The DC/DC converter <NUM> of <FIG> may include one full-bridge circuit <NUM> and two FRD circuits 720a and 720b, and the FRD circuits 720a and 720b may be connected in parallel with each other. The first FRD circuit 720a may be connected to the magnetic bearing controller <NUM> and the second FRD circuit 720b may be connected to the inverter controller <NUM>.

The DC/DC converter <NUM> of <FIG> may supply a high DC voltage (about 300V) to the magnetic bearing controller <NUM>, and supply an additionally-insulated low DC voltage (+ 24V) to the inverter controller <NUM>. At this time, the magnetic bearing controller <NUM> may need an SMPS for generating control power. Since the inverter controller <NUM> already has the insulation structure, the control power can be generated only by a regulator circuit.

The DC/DC converter <NUM> of <FIG> may have a structure in which the second FRD circuit 720b is connected to both the magnetic bearing controller <NUM> and the inverter controller <NUM> through power lines <NUM> and <NUM> of the second FRD circuit 720b that are additionally provided in the circuit structure of <FIG>. Other parts in the circuit structure of <FIG> may be the same as those in the circuit structure of the DC/DC converter <NUM> of <FIG>.

The DC/DC converter <NUM> of <FIG> may supply a high DC voltage (about 300V) only to a 'power circuit (or power line)' of the magnetic bearing controller <NUM>. The DC/DC converter <NUM> of <FIG> may supply an additional-insulated low DC voltage (+24V) to control circuits (control lines) of the magnetic bearing controller <NUM> and the inverter controller <NUM>.

Although the DC/DC converter <NUM> of <FIG> may be more complex than the circuit structures of <FIG>, an insulation power structure for separating the control circuit (line) and the power circuit (line) from each other can be designed, and control power can be generated only by a regulator circuit design even without a plurality of SMPSs.

The DC/DC converter <NUM>, for example, the topologies in the structures of (a) and (b) of <FIG> have been configured as insulation topologies for responding to inputs in a wide range, in order to flexibly deal with an input voltage variation and regenerative voltage control of a large-capacity inverter in a magnetic bearing system without a UPS device. As an example, (a) of <FIG> illustrates an LLC resonant full-bridge DC/DC converter, and (b) of <FIG> illustrates a PSFB (phase-shift full-bridge) DC/DC converter.

Hereinafter, an overall operation of a magnetic bearing system of the magnetic transforming apparatus according to the present disclosure will be described again with reference to <FIG>.

In <FIG>, a first control flow <NUM> corresponds to a control flow of an operation executed upon an initial operation and a fault of a converter.

Upon the initial operation, a three-phase AC voltage is supplied as control power to the DC/DC converter <NUM> through the step-down transformer <NUM>. The initial control power supplied to the DC/DC converter <NUM> is then supplied to the auxiliary circuit <NUM>. Such power is supplied to the magnetic bearing controller <NUM> and the inverter controller <NUM>. When power is supplied to the inverter controller <NUM>, an initial charging operation of the inverter is started.

Also, even when a fault of the converter occurs, power is supplied to the magnetic bearing controller <NUM> and the inverter controller <NUM> through the auxiliary circuit <NUM>, instead of the DC/DC converter <NUM>, along the first control flow <NUM>. To this end, the DC relay <NUM> is switched from an OFF state back to an ON state.

In <FIG>, a second control flow <NUM> indicates a control flow during a normal operation.

During the normal operation, a DC voltage charged in the DC link capacitor of the inverter is supplied to the magnetic bearing controller <NUM> and the inverter controller <NUM> through the DC/DC converter <NUM> due to a difference between a voltage (about 220V) of the DC/DC converter <NUM> and a voltage (about 380V) of the inverter <NUM>.

In <FIG>, a third control flow <NUM> indicates a control flow upon a power failure. When a power failure signal is detected in the DC/DC converter <NUM>, the DC/DC converter <NUM> may transmit the power failure detection signal to the magnetic bearing controller <NUM> and the inverter controller <NUM>, and controls the relay of the inverter controller <NUM> to be turned off.

In addition, the inverter controller <NUM> may block the thyristor (SCR) of the three-phase rectifier <NUM>. When a reverse rotation of the motor starts after the compressor stops due to cutting off a power output to the inverter, the inverter may be operated by switching a control mode of the inverter from a speed control mode to a voltage control mode.

The switching of the control mode of the three-phase inverter <NUM> may be carried out at the moment when the motor rotates in reverse. When the control mode of the inverter is switched to the voltage control mode, a regenerative constant voltage control is performed so as to enable a stable power supply that meets the input spec of the DC/DC converter <NUM>.

As described above, in a power transforming apparatus including a magnetic bearing-applied motor and an air conditioner including the same according to at least one of implementations of the present disclosure, an effective response to a power failure can be allowed by applying regenerative stepping up and a DC/DC converter without an additional UPS device.

The present disclosure may have an advantage in that it is unnecessary to implement a separate power failure detection circuit for regenerative control or an additional circuit for regeneration without adding a UPS device. Furthermore, an accurate regenerative constant voltage control can be performed even without an additional circuit for regeneration.

The present disclosure can improve reactive power due to a lowered power factor of a magnetic bearing AC control power supply. Specifically, by supplying power in a DC form through a DC/DC converter, only active power can be supplied.

Claim 1:
A power transforming apparatus (<NUM>) for supplying power to a magnetic bearing-applied motor (<NUM>), the apparatus (<NUM>) comprising:
an inverter (<NUM>);
an inverter controller (<NUM>) connected to the inverter (<NUM>) and configured to control an operation of the inverter (<NUM>);
a converter (<NUM>);
a magnetic bearing controller (<NUM>) connected to the converter (<NUM>);
a step-down transformer (<NUM>) to step down a three-phase alternating-current, AC, input voltage to supply an alternating-current, AC, stepped-down first power to the converter (<NUM>) through a first branch line and to supply the AC stepped down first power to an auxiliary circuit (<NUM>) through a second branch line upon an initial operation,
an auxiliary circuit (<NUM>) configured to perform charging of the auxiliary circuit (<NUM>) using the first power and to supply rectified second power to the inverter controller (<NUM>) and the magnetic bearing controller (<NUM>) through a relay (<NUM>) located between the converter (<NUM>) and the auxiliary circuit (<NUM>), said relay (<NUM>) being turned on or off by the converter (<NUM>),
wherein the converter (<NUM>) is adapted to receive the first power through the step-down transformer (<NUM>) upon the initial operation,
wherein the inverter controller (<NUM>) is configured to output a driving signal to the inverter (<NUM>) using the second power, and to control the inverter (<NUM>) to supply a rectified direct-current, DC, voltage to the converter (<NUM>) upon the initial operation,
wherein the converter (<NUM>) is configured to cut off the supply of the second power by turning off the relay (<NUM>) and to control the rectified DC voltage to be supplied to the inverter controller (<NUM>) and the magnetic bearing controller (<NUM>) during a normal operation,
wherein the converter (<NUM>) is configured to supply a regenerative voltage during a power failure, and
wherein the converter (<NUM>) is configured to output a control signal by turning on the relay (<NUM>) so that the second power of the auxiliary circuit (<NUM>) is supplied to the inverter controller (<NUM>) and the magnetic bearing controller (<NUM>) upon a fault of the converter (<NUM>).