Patent Description:
Three-phase motors are widely used in industrial equipment such as fans, pumps, and FA equipment. A motor drive system for driving such a three-phase motor generally includes an AC-AC converter consisting of a rectifier circuit that rectifies a three-phase AC voltage so as to generate a DC voltage (rectified voltage), a subsequent DC link, and an inverter circuit that generates a three-phase AC voltage from a DC link voltage.

In a motor drive system, it is required that the entire system can be miniaturized and made denser for the purpose of allowing for the use of low voltage resistant elements, the reduction in design man-hours, and the commonization of components. As one of the technologies that realize this, the motor is configured to include a modular motor that is independent for each segment of a three-phase winding, and in order to drive each segment for each modular, "modular motor drive (MMD) system" has been proposed in which an inverter circuit is modularized (see, for example, Non-patent Literature <NUM>). However, in this type of MMD, although the inverter circuit is modularized, the rectifier circuit is not modularized. In this case, since a high voltage resistant semiconductor element is required for the rectifier circuit, miniaturization and densification of the entire motor drive system are difficult. Further, in this MMD, the fault tolerance of the rectifier circuit is not taken into consideration, and there is a problem that the motor cannot be driven in the case of failure of the rectifier circuit.

As described, conventional rectifier circuits have a problem that fault tolerance in the case of failure of a rectifier circuit cannot be realized in addition to a problem that miniaturization and densification of a motor drive system cannot be sufficiently achieved. In this background, a purpose of the present invention is to achieve a fault tolerant motor drive system.

The invention is defined by the features of claim <NUM>. The dependent claims recite advantageous embodiments of the invention.

An AC-AC converter according to the present invention includes: n single-phase rectifier circuit modules, where n is a multiple of three, that convert an AC voltage of each phase of a three-phase AC input voltage supplied from a three-phase AC power supply into a DC voltage, the n single-phase rectifier circuit modules being connected to one another using a delta connection or a star connection; the same number of inverter circuit modules as the single-phase rectifier circuit modules that convert the DC voltage into a three phase AC output voltage; and controllers that control switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules such that when any one of the n single-phase rectifier circuit modules fails, the inverter circuit modules connected to the remaining single-phase rectifier circuit modules and the one of the single-phase rectifier circuit modules evenly output three-phase AC output voltage.

The AC-AC converter according to the invention includes a switching unit that switches between the delta connection and the star connection of the single-phase rectifier circuit modules, in accordance with a magnitude of the AC input voltage.

The ratio between a power supply voltage of the three-phase AC power supply and the maximum DC link voltage is denoted by R. At this time, the switching unit switches the single-phase rectifier circuit modules to the delta connection when R is smaller than a predetermined value and switches the single-phase rectifier circuit modules to the star connection when R is equal to or more than the predetermined value.

The value of R may be in the range of <NUM>/√<NUM> ± <NUM>%.

The controllers may control the switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules such that the phase of a three-phase input current that is input from the three-phase AC power supply and the phase of the three-phase AC input voltage match while keeping the DC voltage constant.

The controllers calculate target capacitor power based on the difference between a DC link voltage of a DC link provided on the downstream side of the single-phase rectifier circuit modules and a target link voltage, calculate target motor power for outputting power to an external motor by subtracting the target capacitor power from target DC power, and control the switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules such that the pulsation of three-phase AC power related to the three-phase AC input voltage and the pulsation of DC power related to the DC voltage are absorbed by using a load of the external motor based on the target capacitor power and the target motor power.

The DC link may include a capacitor. At this time, the capacitor may absorb the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage.

The controllers may control the switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules such that input power from the three-phase AC power supply is evenly distributed to all the single-phase rectifier circuit modules.

The controllers may control the switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules such that input power from the three-phase AC power supply is distributed to the single-phase rectifier circuit modules at different ratios.

The controllers may calculate the power voltage of each phase of the three-phase AC power supply and control the switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules such that the amount of power distributed to the single-phase rectifier circuit modules that correspond to a phase with a high power supply voltage is larger than the amount of power distributed to the single-phase rectifier circuit modules that correspond to a phase with a low power supply voltage.

Optional combinations of the aforementioned constituting elements, and implementations of the invention in the form of methods, apparatuses, programs, transitory or non-transitory storage media, systems, and the like may also be practiced as additional modes of the present invention.

According to the present invention, it is possible to achieve a miniaturized and densified fault tolerant motor drive system.

Embodiments will now be described by way of examples only, with reference to the accompanying drawings which are meant to be exemplary, not limiting and wherein like elements are numbered alike in several Figures in which:.

Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The embodiments do not intend to limit the scope of the invention but exemplify the invention. Not all of the features and the combinations thereof described in the embodiments are necessarily essential to the invention. The same or equivalent constituting elements, members, and processes illustrated in each drawing shall be denoted by the same reference numerals, and duplicative explanations will be omitted appropriately. The scales and shapes shown in the figures are defined for convenience's sake to make the explanation easy and shall not be interpreted limitatively unless otherwise specified. Terms like "first", "second", etc., used in the specification and claims do not indicate an order or importance by any means unless specified otherwise and are used to distinguish a certain feature from the others. Some of the components in each figure may be omitted if they are not important for explanation.

<FIG> and <FIG> are functional block diagrams of an AC-AC converter <NUM> according to the first embodiment. The AC-AC converter <NUM> includes single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, inverter circuit modules <NUM>, <NUM>, and <NUM>, and controllers <NUM>, <NUM>, and <NUM>. That is, the rectifier circuit of the AC-AC converter <NUM> is modularized by the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>. The inverter circuit of the AC-AC converter <NUM> is modularized by the inverter circuit modules <NUM>, <NUM>, and <NUM>. Each of the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> is, for example, a single-phase bridge circuit configured by using a switching element and includes two input terminals and two output terminals. Each of the inverter circuit modules <NUM>, <NUM>, and <NUM> is, for example, a three-phase bridge circuit configured by using a switching element and includes two input terminals and three output terminals. As described above, in the AC-AC converter <NUM>, since both the rectifier circuit and the inverter circuit are modularized, the entire motor drive system can be configured in a small size and with high density.

The single-phase rectifier circuit module <NUM> is connected to a U-phase output terminal ACU of a three-phase AC power supply such as a commercial power supply and converts a U-phase single-phase AC voltage vU supplied from the output terminal ACU into a DC voltage. The single-phase rectifier circuit module <NUM> is connected to a V-phase output terminal ACV of the above-mentioned three-phase AC power supply and converts a V-phase single-phase AC voltage vV supplied from the output terminal ACV into a DC voltage. The single-phase rectifier circuit module <NUM> is connected to a W-phase output terminal ACW of the above-mentioned three-phase AC power supply and converts a W-phase single-phase AC voltage vW supplied from the output terminal ACW into a DC voltage. The single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> are connected to each other using a delta connection (<FIG>) or a star connection (<FIG>). A delta connection (also called Δ connection) and a star connection (also called Y connection) are well-known connection methods in three-phase AC circuits. That is, a delta connection is a connection in which each phase of a U phase, a V phase, and a W phase is connected in the direction in which a phase voltage is applied so as to form a closed circuit. In a delta connection, the line voltage is equal to the phase voltage, and the line current is equal to √<NUM> times the phase current. A star connection is a connection that connects each phase of the U phase, the V phase, and the W phase at a neutral point N at one end thereof. In a star connection, the line voltage is equal to √<NUM> times the phase voltage, and the line current is equal to the phase current.

DC links vdc1, vdc2, and vdc3 are provided on the downstream side of the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, respectively (see <FIG> and <FIG>).

The inverter circuit module <NUM> converts a DC voltage vdc1 converted by the single-phase rectifier circuit module <NUM> into three-phase AC output voltages v11a, v11b, and v11c. The inverter circuit module <NUM> converts a DC voltage vdc2 converted by the single-phase rectifier circuit module <NUM> into three-phase AC output voltages v12a, v12b, and v12c. The inverter circuit module <NUM> converts a DC voltage vde3 converted by the single-phase rectifier circuit module <NUM> into three-phase AC output voltages v13a, v13b, and v13c. The three-phase AC output voltages v11a, v11b, and v11c are supplied to a first winding WS<NUM> of a three-phase motor. The three-phase AC output voltages v12a, v12b, and v12c are supplied to a second winding WS<NUM> of the three-phase motor. The three-phase AC output voltages v13a, v13b, and v13c are supplied to a first winding WS<NUM> of the three-phase motor. In this way, the three-phase motor is driven by three-phase output supplied to the first, second, and third windings WS<NUM>, WS<NUM>, and WS<NUM>.

The controllers <NUM>, <NUM>, and <NUM> control respective switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> such that when any one of the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> fails, the remaining single-phase rectifier circuit modules and the inverter circuit modules evenly output three-phase AC output power.

<FIG> is a diagram showing a state when one of the single-phase rectifier circuit modules, that is the single-phase rectifier circuit module <NUM>, fails in the AC-AC converter of <FIG>. Before the failure of the single-phase rectifier circuit module <NUM>, it is assumed that the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> each evenly output one-third of the three-phase AC output power. When the single-phase rectifier circuit module <NUM> fails, the controllers <NUM>, <NUM>, and <NUM> control the switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> such that the remaining single-phase rectifier circuit modules <NUM> and <NUM> and the inverter circuit modules <NUM> and <NUM> each evenly output <NUM>/<NUM> of three-phase AC output power. At this time, although the third winding WS<NUM> of the motor does not operate, the output to the remaining windings WS<NUM> and WS<NUM> increases from <NUM>/<NUM> to <NUM>/<NUM>, and the total output of the motor therefore does not change. As shown in <FIG>, since the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> are connected to one another by using a delta connection, even when the single-phase rectifier circuit module <NUM> fails, the three-phase AC output power is output without the influence of this failure affecting the remaining single-phase rectifier circuit modules <NUM> and <NUM>, and the motor can continue to be driven in a fault tolerant manner.

<FIG> is a diagram showing a state when one of the single-phase rectifier circuit modules, that is the single-phase rectifier circuit module <NUM>, fails in the AC-AC converter of <FIG>. Before the failure of the single-phase rectifier circuit module <NUM>, it is assumed that the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> each evenly output one-third of the three-phase AC output power. When the single-phase rectifier circuit module <NUM> fails, the controllers <NUM>, <NUM>, and <NUM> control the switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> such that the remaining single-phase rectifier circuit modules <NUM> and <NUM> and the inverter circuit modules <NUM> and <NUM> each evenly output <NUM>/<NUM> of three-phase AC output power. At this time, although the third winding WS<NUM> of the motor does not operate, the output to the remaining windings WS<NUM> and WS<NUM> increases from <NUM>/<NUM> to <NUM>/<NUM>, and the total output of the motor therefore does not change. As shown in <FIG>, since the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> are connected to one another by using a star connection, even when the single-phase rectifier circuit module <NUM> fails, the three-phase AC output power is output without the influence of this failure affecting the remaining single-phase rectifier circuit modules <NUM> and <NUM>, and the motor can continue to be driven in a fault tolerant manner.

As explained above, it is possible to achieve a miniaturized and densified fault tolerant motor drive system.

In the above-described embodiment, the number of single-phase rectifier circuit modules and the number of inverter circuit modules are both three. However, the numbers are not limited to this, and the number of the rectifier circuit modules and the number of the inverter circuit modules may be any multiple of three as long as the numbers are the same. For example, when there are six (<NUM> × <NUM>) rectifier circuit modules and inverter circuit modules, two sets of delta connections or star connections can be formed, and when there are nine (<NUM> × <NUM>) rectifier circuit modules and inverter circuit modules, three sets of delta connections or star connections can be formed.

In the above embodiment, three controllers <NUM>, <NUM>, and <NUM> are provided, and these controllers individually control the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, respectively, and the inverter circuit modules <NUM>, <NUM>, and <NUM>, respectively. However, the present invention is not limited to this, and for example, one controller may collectively control the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM>.

<FIG> and <FIG> are functional block diagrams of an AC-AC converter <NUM> according to the second embodiment. The AC-AC converter <NUM> includes a switching unit <NUM> in addition to the features of the AC-AC converter <NUM> shown in <FIG> and <FIG>. Since the other features of the AC-AC converter <NUM> are the same as those of the AC-AC converter <NUM>, duplicate explanations will be omitted.

The switching unit <NUM> switches between the delta connection and the star connection of the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>. The switching unit <NUM> may be, for example, an automatic switch or a manual switch. <FIG> shows the AC-AC converter <NUM> when the connection is switched to the delta connection by the switching unit <NUM>. <FIG> shows the AC-AC converter <NUM> when the connection is switched to the star connection by the switching unit <NUM>.

According to the present embodiment, the connection of the single-phase rectifier circuit modules can be freely switched between the delta connection and the star connection in accordance with the magnitude of the input voltage and the application.

The top graph in <FIG> is a graph of a rectifier input voltage vR with respect to a power supply voltage vG at the time of the delta connection and at the time of the star connection. However, the power supply voltage on the horizontal axis is expressed using a ratio VG/Vde,max to the maximum value vdc,max of the DC link voltage (the same applies hereinafter). The middle graph in <FIG> is a graph of a modulation factor MR with respect to the power supply voltage vG at the time of the delta connection and at the time of the star connection. The modulation factor MR is defined as the ratio between a rectifier input peak voltage vR and a DC link voltage vdc as follows: <MAT> The bottom graph in <FIG> is a graph of a rectifier input current iR with respect to the power supply voltage vG at the time of the delta connection and at the time of the star connection.

In the case of the delta connection, the rectifier input voltage is equal to the line voltage. Therefore, a rectifier input voltages vR,D is √<NUM> times the power supply voltage vG (hereinafter, D on the right side of the subscript represents a delta connection and Y represents a star connection) as follows: <MAT> Therefore, a modulation factor MR,D at the time of the delta connection is as follows: <MAT>.

In the case of the star connection, the rectifier input voltage is equal to the line voltage. Therefore, the following is established: <MAT> A modulation factor MR,Y is as follows: <MAT>.

As shown in <FIG>, when the power supply voltage is small, it is more advantageous to use the delta connection than to use the star connection in that a high rectifier input voltage can be obtained. On the other hand, when the power supply voltage is high, since the rectifier input voltage becomes too high, it is more advantageous to use the star connection than to use the delta connection. In particular, if the delta connection is used when the power supply voltage vG is <NUM>/√<NUM> or more (vG/vdc,max ≧ <NUM>/√<NUM>) of the maximum DC link voltage vdc,max, it is necessary to design the maximum DC link voltage vdc,max to be √<NUM> times the maximum power supply voltage or more, and it is thus necessary to use parts with high voltage resistance.

From the above, in the third embodiment, when the ratio between the power supply voltage vG and the maximum DC link voltage vdc,max of the DC link provided on the downstream side of the single-phase rectifier circuit module is denoted by R, the switching unit <NUM> switches the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> to the delta connection when R is smaller than a predetermined value and switches the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> to the star connection when R is equal to or more than the predetermined value.

According to the present embodiment, the connection of the single-phase rectifier circuit modules can be accurately switched between the delta connection and the star connection in accordance with the size of the power supply voltage.

In particular, the value of R may be in the range of <NUM>/√<NUM> ± <NUM>%. This allows for the selection of an accurate R while having a margin of ± <NUM>%.

In particular, the value of R may be <NUM>/√<NUM>. Thereby, the optimum R can be selected.

In the fourth embodiment, the controllers <NUM>, <NUM>, and <NUM> control switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> such that the phase of a three-phase input current that is input from the three-phase AC power supply and the phase of the three-phase AC voltage match while keeping the DC voltage constant.

The control of the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> performed by the controllers <NUM>, <NUM>, and <NUM> as described allows for the absorption of the pulsation of power produced by the DC voltages generated by the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>. That is, according to the present embodiment, since the rectifier circuit <NUM> can be used as a PFC rectifier circuit, control with a power factor of <NUM> can be realized.

In the fifth embodiment, the controllers <NUM>, <NUM>, and <NUM> calculate target capacitor power based on the difference between the DC link voltage and a target link voltage, calculate target motor power by subtracting the target capacitor power from target DC power, and control the switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> such that the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage are absorbed based on the target capacitor power and the target motor power. According to this embodiment, the power pulsation can be absorbed without using a large-capacity DC link capacitor.

Hereinafter, the configuration and operation of the controllers <NUM>, <NUM>, and <NUM> in the fifth embodiment will be described in detail with reference to <FIG> is a detailed functional block diagram of the controller <NUM> (although <FIG> shows the controller <NUM> as a representative of the controllers <NUM>, <NUM>, and <NUM>, the same applies to the controllers <NUM> and <NUM>). The controller <NUM> includes a DC link voltage controller <NUM>, a rectifier circuit controller <NUM>, a speed controller <NUM>, and an inverter controller <NUM>. The controller <NUM> controls the switching elements constituting the single-phase rectifier circuit module <NUM> and the inverter circuit module <NUM> so as to adjust the generated DC voltage and the three-phase AC voltage.

The DC link voltage controller <NUM> includes a first input terminal 42b, a second input terminal 42c, and an output terminal 42d. The rectifier circuit controller <NUM> includes an input terminal 44b and an output terminal 44c. The speed controller <NUM> includes a first input terminal 46b, a second input terminal 46c, and an output terminal 46d. The inverter controller <NUM> includes an input terminal 48b, a first output terminal 48c, a second output terminal 48d, and a third output terminal 48e. The controller <NUM> includes a low pass filter 43a between the output terminal 42d of the DC link voltage controller <NUM> and the input terminal 44b of the rectifier circuit controller <NUM>. The controller <NUM> includes a low pass filter 43b on the upstream side of the second input terminal 46c of the speed controller <NUM>.

A target DC link voltage vDC* is input to the first input terminal 42b of the DC link voltage controller <NUM>. The current DC link voltage vDC is input to the second input terminal 42c. The DC link voltage controller <NUM> obtains target capacitor power pc* based on the difference ΔvDC (not shown) between vDC* and vDC and outputs the difference from the output terminal 42d.

The target capacitor power PC* that is output from the output terminal 42d of the DC link voltage controller <NUM> is branched into two at a branch point v3, and one is input to the low pass filter 43a. The low pass filter 43a absorbs high frequency components from PC* to generate a target average capacitor power <PC>* and outputs the target average capacitor power <PC>*. <PC>* output from the low pass filter 43a is branched into two at a branch point v4, and one is added to the target average inverter output <PINV>* output from the output terminal 46d of the speed controller <NUM>. As a result, a target average rectified power <PPFC>* is calculated as <PPFC>* = <PC>* + <PINV>*. The calculated <PPFC>* is input to the input terminal 44b of the rectifier circuit controller <NUM>. The other <PC>* branched at the branch point v4 is subtracted from the other PC* branched at the branch point v3, and an input power pulsation pC,AC is generated. In other words, the input power pulsation pC,AC is obtained by extracting only the pulsation part from the target capacitor power PC*. The input power pulsation pC,AC is subtracted from target rectified power pPFC* so as to calculate target motor power PM* (PM* = PPFC* - pC,AC). The pM* that has been calculated is input to the input terminal 48b of the inverter controller <NUM>.

As described above, the target motor power pM* that is input to the inverter controller <NUM> is obtained by subtracting the input power pulsation pC,AC from the target rectified power pPFC*. In other words, the pulsation ΔpDC of the DC link is input to the three-phase motor <NUM>. The three-phase motor <NUM> compensates for this pulsation by the inertia possessed by a load connected to the three-phase motor <NUM>. As a result, the pulsation of the DC link is absorbed, and pM = pG is established. In other words, the motor power pM agrees with the input power pG.

The speed ω of the three-phase motor <NUM> pulsates at the frequency 2fg, which is twice the frequency fG of the input power pG, due to compensation of the input power pG by the three-phase motor <NUM>. Accordingly, high frequency components of ω are removed using a low pass filter as shown in the following. The current motor speed ω is input to the low pass filter 43b. The low pass filter 43b removes the high frequency components from ω to generate the current average speed <ω> of the motor and inputs the current average speed to the second input terminal 46c of the speed controller <NUM>. A target average speed <ω>* of the three-phase motor <NUM> is input to the first input terminal 46b of the speed controller <NUM>. The speed controller <NUM> obtains target average inverter output <PINV>* based on the difference Δω (not shown) between <ω>* and <ω> and outputs the target average inverter output <PINV>* from the output terminal 46d.

The rectifier circuit controller <NUM> controls the rectifier circuit <NUM> so as to keep the DC link voltage vDC constant by feedforward. The target average inverter output <PINV>* that has been output from the output terminal 46d of the speed controller <NUM> is added to the target average capacitor power <PC>* that has been output from the low pass filter 43a. As a result, the target average rectified power <PPFC>* is calculated as <PPFC>* = <PC>* + <PINV>*. The calculated <PPFC>* is input to the input terminal 44b of the rectifier circuit controller <NUM>. The rectifier circuit controller <NUM> calculates a target input current iG* (not shown) based on the <PPFC>* that has been input, obtains an output duty ratio dB from the inductor current difference, and outputs this from the output terminal 44c. The output duty ratio dB that has been output is input to the rectifier circuit <NUM> via a pulse width modulator (not shown) such that desired control is realized.

According to the present embodiment, the power pulsation can be absorbed by using the load of the motor by the controllers <NUM>, <NUM>, and <NUM> specifically configured as described above. This eliminates the need to use a large-capacity DC link capacitor and makes it possible to achieve the further miniaturization and densification of the entire motor drive system, reduce the cost, and extend the service life.

In the sixth embodiment, each of DC links vdc1, vdc2, and vdc3 provided on the downstream side of the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, respectively, includes a capacitor. These capacitors absorb the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage.

In a typical example, when the rectifier circuit <NUM> operates at several kW and several 100V, the capacitance of these capacitors is of the order of mF.

According to the present embodiment, the power pulsation can be absorbed without providing a special controller.

In the seventh embodiment, the controllers <NUM>, <NUM>, and <NUM> control the switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, respectively, and the inverter circuit modules <NUM>, <NUM>, and <NUM>, respectively, such that input power from the three-phase AC power supply is evenly distributed to all the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>. In other words, the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> each evenly output one-third of the three-phase AC output power to the inverter circuit modules <NUM>, <NUM>, and <NUM>. In this case, since the same amount of power is evenly supplied to the windings WS<NUM>, WS<NUM>, and WS<NUM> of the three-phase motor, the motor is driven smoothly.

According to the present embodiment, smooth motor drive can be realized.

In the eighth embodiment, the controllers <NUM>, <NUM>, and <NUM> control the switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, respectively, and the inverter circuit modules <NUM>, <NUM>, and <NUM>, respectively, such that the input power from the three-phase AC power supply is evenly distributed to the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> at different ratios. For example, the controllers <NUM>, <NUM>, and <NUM> may calculate the motor drive efficiency of each phase and obtain power distribution that allows the motor to be driven most efficiently. As a result, for example, <NUM>%, <NUM>%, and <NUM>% of the input power are distributed to the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM>, respectively, or <NUM>%, <NUM>%, and <NUM>% are distributed, respectively (in this case, the input power is evenly distributed to the U-phase and V-phase modules, and the W-phase module is stopped).

According to the present embodiment, efficient motor drive can be realized.

In the ninth embodiment, the controllers <NUM>, <NUM>, and <NUM> calculate the power supply voltage of each phase of the three-phase AC power supply, and control the switching elements constituting the single-phase rectifier circuit modules <NUM>, <NUM>, and <NUM> and the inverter circuit modules <NUM>, <NUM>, and <NUM> such that the amount of power distributed to a single-phase rectifier circuit module corresponding to a phase with a high power supply voltage is larger than the amount of power distributed to a single-phase rectifier circuit module corresponding to a phase with a low power supply voltage. When there is imbalance between the phases of the power supply voltage, this compensates for the imbalance by supplying more power to a load corresponding to a phase with a high power supply voltage. As a result, the motor can be driven with optimum efficiency even when there is imbalance between the phases of the power supply voltage.

The above explanation is made based on the embodiments of the present invention. These embodiments are intended to be illustrative only, and it will be obvious to those skilled in the art that various modifications and changes can be developed within the scope of the claims of the present invention and that such modifications and changes are also within the scope of the claims of the present invention. Therefore, the descriptions and figures in the specification should be treated demonstratively instead of being treated in a limited manner.

Claim 1:
An AC-AC converter (<NUM>) comprising:
n single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>), where n is a multiple of three, that are configured to convert an AC voltage of each phase of a three-phase AC input voltage supplied from a three-phase AC power supply into a DC voltage;
the same number of inverter circuit modules (<NUM>, <NUM>, <NUM>) as the single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>) that are each configured to convert the DC voltage into a three-phase AC output voltage; and
controllers (<NUM>, <NUM>, <NUM>) that are configured to control switching elements constituting the single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>) and the inverter circuit modules (<NUM>, <NUM>, <NUM>),
characterized in that
the n single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>) being connected to one another using a delta connection or a star connection; and
the controllers (<NUM>, <NUM>, <NUM>) are configured to control the switching elements such that when any one of the n single-phase rectifier circuit modules fails, the inverter circuit modules (<NUM>, <NUM>, <NUM>) connected to the remaining single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>) and to the one of the single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>) evenly output three-phase AC output voltage; and by a switching unit (<NUM>) that is configured to switch between the delta connection and the star connection of the single-phase rectifier circuit modules (<NUM>, <NUM>, <NUM>), in accordance with a magnitude of the AC input voltage.