JP5471498B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device having a function of compensating an output voltage error caused by so-called dead time.

  In a refrigeration apparatus such as an air conditioner, a power converter is often used to supply AC power to a motor that drives a compressor. Such a power converter includes a so-called inverter circuit. There is. For example, in an inverter circuit, a plurality of switching legs formed by connecting two switching elements in series with each other are connected in parallel between the DC buses, and a DC voltage is converted into an AC voltage by ON / OFF operation of the switching elements of each switching leg. Some are designed to output. In the inverter circuit with this configuration, during the on / off operation, if the switching elements connected in series in any switching leg are simultaneously turned on, a short circuit occurs between the DC buses, so the two switching elements constituting the switching leg are The on / off operation is performed while providing a dead time which is an off period. Since the output voltage deviates from a desired voltage value when the dead time is provided in this way, there is an inverter circuit having a function of compensating for an output voltage error. There are various methods for compensating the output voltage error. For example, there is a method of correcting the switching timing of the switching element according to the direction of the phase current (see, for example, Patent Document 1).

JP 2009-106110 A

  However, for example, in applications such as an air conditioner having a chiller, there is a thing that needs to pass a larger current (for example, a current of 400 A) than an air conditioner for home use, and an inverter that handles such a large current The inventor of the present application finds that when the phase voltage value is controlled to be smaller when the output voltage error is compensated for in the circuit, a phenomenon may occur in which the deviation of the output voltage with respect to the target value increases. It was. As will be described in detail later, the phase voltage does not switch immediately even when the switching element is switched on / off due to the influence of the capacitor component formed in the switching element, and the assumed error voltage (target output voltage) This is probably because an error different from the difference between the actual value and the actual output voltage may occur.

  The present invention has been made paying attention to the above problems, and in a power converter, even when the phase voltage does not immediately switch even when the switching element is switched on / off, an appropriate output voltage error can be compensated. The purpose is to do so.

In order to solve the above problems, the first invention is
In a power conversion device that switches input power and converts it into predetermined AC power,
An inverter circuit (3) having a plurality of sets of switching elements (3a, 3a) connected in series between buses (P, N) to which the input power is supplied and supplying the AC power to a predetermined load (6) )When,
While providing a dead time (Td) in which both of the series-connected switching elements (3a, 3a) are off, the on-off relationship of the series-connected switching elements (3a, 3a) is controlled in reverse. A switching control unit (5) for compensating an output voltage error of the inverter circuit (3) due to the provision of the dead time (Td);
With
The switching control unit (5) compensates for the output voltage error according to a phase voltage (Vx, Vz) that changes in a period from the start of the dead time (Td) to the phase voltage (Vx, Vz) switching. It is characterized by setting an amount.

  In this configuration, the output voltage error takes into account the phase voltage that changes in the period from the start of the dead time (Td) (that is, switching of the on / off state of one switching element (3a)) to the phase voltage switching. Is set. As a result, even when the phase voltage does not immediately switch even when the on / off state of the switching element is switched, the compensation amount is appropriately determined.

The first invention,
Before SL switching controller (5), the period the switching element in the ON state (3a) is from switched off until the switching element connected in series with the switching element (3a) (3a) is turned on The compensation amount is set in accordance with the phase voltage (Vx, Vz) changed to.

  In this configuration, the switching element (3a) that is paired with the switching element (3a) is turned on after the switching element (3a) in the on state (that is, the switching element (3a) in which current flows) is switched to the off state. In some cases, the phase voltage (Vx, Vz) may be switched. Even in such a case, the phase voltage (Vx, Vx, V) is changed during the period from when the switching element (3a) in the on state is switched off until the switching element (3a) connected in series with the switching element (3a) is turned on. By setting the compensation amount according to Vz), it becomes possible to set the compensation amount more accurately.

In addition, the second invention,
In the power converter of the first invention,
A storage unit (5a) that stores a line graph, an approximate curve, or a table indicating the relationship between the compensation amount and the phase current (Iu, Iw),
The switching control unit (5) compensates for the output voltage error based on a compensation amount stored in the storage unit (5a).

  In this configuration, information stored in the storage unit (5a) (for example, information indicating a relationship between the compensation amount and the phase current (Iu, Iw) indicated by a line graph) and a phase current (Iu, Iw) The amount of compensation can be obtained by comparing the magnitude of

In addition, the third invention,
In power conversion device of the first or second aspect of the invention,
The compensation amount stored in the storage unit (5a) is set based on the line voltage in the inverter circuit (3).

In this configuration, the relationship between the compensation amount and the phase current (Iu, Iw) is set more accurately, thereby making it possible to determine the compensation amount more appropriately.

In addition, the fourth invention is
In any one of the power converters according to the first to third aspects of the invention,
The switching control unit (5) is characterized in that the compensation amount is reduced or the compensation of the output voltage error is stopped as the value of the phase current (Iu, Iw) becomes smaller.

  In this configuration, the correction amount is appropriately set under the condition that the capacitor component formed in the switching element easily affects the output voltage.

  According to the first invention, even when the phase voltage does not switch even when the dead time starts, the compensation amount is appropriately determined. Therefore, in the power converter, an output voltage closer to the target value can be obtained. become.

Further, according to the first invention, the compensation amount can be obtained more accurately, and the output voltage error can be compensated more appropriately.

Further, according to the second invention, the compensation amount can be easily obtained.

In addition, according to the third aspect of the invention, the amount of compensation can be obtained more accurately, so that the output voltage error can be compensated more appropriately.

According to the fourth aspect of the invention, the output voltage is appropriately controlled in a region where the phase currents (Iu, Iw) are relatively small, and an output voltage closer to the target value can be obtained.

FIG. 1 is a block diagram showing a configuration of a power converter according to an embodiment of the present invention. FIG. 2A is a diagram illustrating a waveform of a switching command given to each switching element during one period of the carrier signal, and FIG. 2B is a phase assumed when the switching command is applied. It is a figure which shows a voltage. FIG. 3 is a diagram showing a difference (error voltage) between the voltage command indicating the target value of the output voltage of the inverter circuit and the actual phase voltage. FIG. 4 is a block diagram for explaining the concept of output voltage error compensation performed by the switching control unit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are essentially preferable examples, and are not intended to limit the scope of the present invention, its application, or its use.

  Below, the example of the power converter device used for the air conditioner with a chiller is demonstrated as embodiment of this invention. In applications such as an air conditioner having a chiller, it is necessary to pass a larger current (for example, a current of 400 A) than an air conditioner for home use. The power converter of this embodiment also handles such a current.

<Configuration of power converter>
FIG. 1 is a block diagram showing a configuration of a power conversion device (1) according to an embodiment of the present invention. In this example, the power conversion device (1) includes a DC power supply unit (2), an inverter circuit (3), a detection unit (4), and a switching control unit (5). The DC power supply unit (2) supplies DC power (voltage (Vdc)) to the inverter circuit (3). The inverter circuit (3) converts the output of the DC power supply unit (2) into an alternating current of a predetermined voltage and outputs it to a connected load (for example, the motor (6)). In FIG. 1, the motor (6) is schematically shown by an inductance component (L) and a DC resistance component (R).

  Specifically, in the inverter circuit (3) of the present embodiment, a plurality of switching elements (3a) are bridge-connected. In this example, the switching element (3a) is an IGBT (Insulated Gate Bipolar Transistor) switching element, and a free-wheeling diode (3b) is connected in antiparallel to each switching element (3a). In the inverter circuit (3), the output alternating current is a single-phase alternating current, and the inverter circuit (3) requires four switching elements (3a). That is, the inverter circuit (3) has two switching legs (L1, L2) in which two switching elements (3a, 3a) are connected in series between DC buses (P, N) (see FIG. 1). Two sets of switching legs (L1, L2) are connected in parallel to each other. The intermediate points (M1, M2) of each switching leg (L1, L2) are output nodes (Pu, Pw) corresponding to each phase (U, W) of single-phase AC, and these output nodes (Pu, Pw) Is connected to the motor (6) (load). In the inverter circuit (3), the on / off operation of these switching elements (3a) converts the DC power into AC power and outputs the AC power from each output node (Pu, Pw).

  The detection unit (4) detects the current or voltage at a predetermined location of the inverter circuit (3), and determines the direction and magnitude of the phase current (Iu, Iw) of each phase (U, W) of the output AC. Output to (5). The detection unit (4) may be configured to detect current and voltage for each phase (U, W), or measure the current (voltage) with the negative DC bus (N), You may make it obtain | require by calculating the phase current value of each phase (U, W) from a measured value.

  The switching control unit (5) performs PWM control (PWM: Pulse Width Modulation) on the inverter circuit (3). Specifically, the switching control unit (5) generates a switching command (Tu, Tx, Tw, Tz) to be applied to the gate of each switching element (3a) and controls on / off of each switching element (3a). . In this PWM control, both the series-connected switching elements (3a, 3a) are turned on so that the series-connected switching elements (3a, 3a) are simultaneously turned on and the DC buses (P, N) are not short-circuited. The reverse switching control of the on / off relationship of the serially connected switching elements (3a) is performed while providing a period during which is turned off (so-called dead time).

  FIG. 2A is a diagram exemplifying waveforms of switching commands (Tu, Tx, Tw, Tz) given to the respective switching elements (3a) during one period of the carrier signal (carrier period (Ts)). In this figure, the direction in which the W-phase phase current (Iw) flows from the output node (Pw) to the motor (6) (load) side is positive, and the phase current (Iw) is positive (that is, the phase current ( The switching command (Tu, Tx, Tw, Tz) of (when Iu) is negative) is illustrated. In FIG. 2A, the switching command (Tu) and the switching command (Tx) are the upper arm side (DC bus (P) side) and the lower arm side (DC bus (N) side) of the switching leg (L1). Switching command given to each switching element (3a). Similarly, the switching command (Tw) and the switching command (Tz) are switching commands given to the switching element (3a) on the upper arm side and the lower arm side of the switching leg (L2), respectively.

  In FIG. 2A, during the period when each switching command (Tu, Tx, Tw, Tz) is displayed at a high level (H level), the switching element (3a) corresponding to the switching command is on. Conversely, during the period when the switching command (Tu, Tx, Tw, Tz) is displayed at the low level (L level), the switching element (3a) corresponding to the switching command is off. As shown in FIG. 2A, in this inverter circuit (3), the switching command (Tu) rises after a lapse of a predetermined period (dead time (Td)) from the falling edge of the switching command (Tx), and the switching command (Tu) Tx) rises after the dead time (Td) has elapsed from the fall of the switching command (Tu). Also, the switching command (Tw) rises after the dead time (Td) has elapsed since the falling of the switching command (Tz), and the switching command (Tz) only takes the dead time (Td) from the falling of the switching command (Tw). Stands up after the lapse. That is, the switching control unit (5) controls the upper and lower arms in the inverter circuit (3) so as not to short-circuit by providing a dead time (Td).

  And in this power converter device (1), the switching control part (5) implement | achieves the compensation function of the output voltage error by having provided the dead time (Td). Specifically, the switching control unit (5) compensates for the output voltage error by correcting the voltage command (V *) indicating the target value of the output voltage of the inverter circuit (3). The present embodiment is characterized by setting the compensation amount of the voltage command (V *).

  FIG. 2B is a diagram showing phase voltages (Vx, Vz) that are assumed when the switching commands (Tu, Tx, Tw, Tz) of FIG. 2A are applied. More specifically, in FIG. 2B, the solid line indicates the phase voltage waveform assumed in the conventional knowledge, and the broken line is a phenomenon newly found by the inventor of the present application, which is as large as in this embodiment. The phase voltage waveform assumed in the inverter circuit (henceforth a high capacity | capacitance inverter circuit) which handles an electric current is shown. Generally, in an inverter circuit, it was originally considered that the phase voltage (Vx) is switched when the switching command (Tx) is switched to the L level. However, in the inverter circuit (3), as shown in FIG. 2 (B), even if the dead time (Td) starts (that is, even if the on / off state of one switching element (3a) is switched), Phase voltage (Vx) is not switched to Vdc voltage. In the example of FIG. 2B, the phase voltage (Vx) is switched after the switching command (Tu) rises. Similarly, when the switching command (Tw) is switched to the L level, the phase voltage (Vz) should be switched to the Vdc voltage, but the phase voltage (Vz) gradually changes until the switching command (Tz) rises. Yes.

  Such a phenomenon occurs when the phase current is controlled to be small because the capacitance of the capacitor existing between the collector and the emitter is relatively large in the large-capacity switching element (3a) as in this embodiment (for example, This is because the charge of the capacitor is considered to affect the phase voltage when the switching element (3a) is controlled to about 1/10 of the rating. FIG. 3 is a diagram showing a difference (error voltage) between the voltage command (V *) for the inverter circuit (3) and the actual phase voltage. As shown in FIG. 3, the error voltage (VV *) due to the provision of the dead time (Td) itself is considered to be substantially constant regardless of the magnitude of the phase current (“dead time (Td in FIG. 3)”. ) “Equivalent error voltage”). However, in the inverter circuit (3), as shown in FIG. 3, it changes according to the magnitude of the phase current (see “error voltage of large-capacity inverter circuit” in FIG. 3). There are various causes for this change. In the inverter circuit (3) that handles a relatively large current, if the phase current values (Iu, Iw) are controlled to be relatively small, the dead time (Td) In addition to the influence, an error of the output voltage is caused by the influence of the capacitor existing between the collector and the emitter of the switching element (3a).

  The inventor of the present application who discovered the phenomenon described above, the phase voltage (Vx, Vz) that changes in the period from the start of the dead time (Td) (switching of the switching element (3a)) until the phase voltage (Vx, Vz) switches. ), The switching control unit (5) is configured to set the compensation amount of the output voltage error. In particular, the phase voltage (Vx, Vz) changed in the period from when the switching element (3a) in the on state is switched to the off state until the switching element (3a) connected in series with the switching element (3a) is turned on. ) Is taken into account when setting the compensation amount. In the inverter circuit (3), after the switching element (3a) of the upper arm or the lower arm is switched to the off state, the switching element (3a) paired with the switching element (3a) is switched to the on state. This is because the phase voltage (Vx, Vz) is switched. For example, in the example of FIG. 2, the period from when the W-phase (upper arm) switching element (3a) is turned off until the Z-phase (lower arm) switching element (3a) is turned on. When the phase voltage (Vz) gradually changes and the Z-phase (lower arm) switching element (3a) is turned on, the phase voltage (Vz) is switched. Therefore, in this example, the period from when the W-phase switching element (3a) is switched from the ON state (that is, the phase current is flowing) to the OFF state until the Z-phase switching element (3a) is turned on. The compensation amount is set in consideration of the phase voltage (Vz) that has changed to. In this way, a more accurate compensation amount can be set.

  In this embodiment, the switching control unit (5) includes a storage unit (5a) (for example, a nonvolatile memory) that stores information indicating the relationship between the compensation amount and the phase current, and is obtained from the detection unit (4). The compensation amount is determined in consideration of the information on the phase current value and the direction of the phase current and the information in the storage unit (5a) (specific operation will be described later). Using this “information indicating the relationship between compensation amount and phase current”, depending on the phase voltage (Vx, Vz) that changes in the period from the start of the dead time (Td) to the phase voltage (Vx, Vz) switching The compensation amount can be set. In this example, the information stored in the storage unit (5a) is the actual dead time (Td) adopted in the power conversion device (1), and the phases measured in advance by switching to various target voltages. Based on the voltage, each point of the line graph indicating the relationship between the compensation amount and the phase current is obtained and set. As can be seen from FIG. 3, since the error voltage decreases as the phase current decreases, the compensation amount decreases as the phase current decreases. By measuring the phase voltage in the actual operating state of the power converter (1) in this way, the phase voltage that has changed between the start of the dead time (Td) and the phase voltage switching is also taken into account, A compensation amount is set. When measuring the phase voltage, it is preferable to measure so that the line voltage (difference between Vx and Vz in the example of FIG. 1) can be detected. Further, depending on the characteristics of the inverter circuit (3), the switching control unit (5) may perform control such that the compensation amount is zero, that is, the compensation of the output voltage error is stopped.

  The information indicating the relationship between the compensation amount and the phase current stored in the storage unit (5a) may be stored in the form of an approximate curve or a table. The switching control unit (5) may be configured to correct the phase voltage in consideration of the voltage drop of the switching element. In this case, the compensation amount due to the voltage drop is preferably reduced as the phase current decreases.

<< Compensation for output voltage error of power converter (1) >>
FIG. 4 is a block diagram for explaining the concept of output voltage error compensation performed by the switching controller (5). When Vdef (n + 1) is given as a voltage command, the switching control unit (5) of the present embodiment first detects information (current phase current value (I (n)) and direction of phase current of the detection unit (4). ) To obtain the next target current value I (n + 1). Next, the switching control unit (5) compares the obtained current value I (n + 1) with information stored in the storage unit (5a) to determine a compensation amount. Then, the switching control unit (5) obtains a value obtained by adding the correction value to Vdef (n + 1) as a new voltage command (V *), and gives the switching command (Tu, Tx, Tw, Tz) is generated. By this new voltage command (V *), the duty ratio of the switching command (Tu, Tx, Tw, Tz) is determined. When each switching element (3a) is switched in the inverter circuit (3) by this switching command (Tu, Tx, Tw, Tz), each output node (Pu) is corrected with the corrected phase voltage (Vx, Vz). , Pw), AC power is supplied to the load (motor (6)).

<< Effect of this embodiment >>
As described above, in the power converter (1), in addition to the direction of the phase current, the magnitude of the phase current is also detected, and the phase voltage that changes in the period from the start of the dead time (Td) to the phase voltage switching is determined. The compensation amount is determined in consideration. This makes it possible to appropriately compensate for the output voltage error when the phase voltage does not switch even when the on / off state of the switching element (3a) is switched. Therefore, according to this embodiment, an output voltage (phase voltage (Vx, Vz)) closer to the target value can be obtained.

<< Other Embodiments >>
Note that the circuit configuration of the inverter circuit (3) is an example, and the present invention can be applied to a power conversion device that has other circuit configurations and compensates for an output voltage error. That is, the present invention is useful for an inverter circuit in which a phenomenon that the phase voltage does not switch even when the on / off state of the switching element is switched is assumed.

  Further, the inverter circuit (3) may be configured to provide three sets of switching legs to output a three-phase alternating current.

  The magnitude of the current handled by the inverter circuit (3) is also an example.

  The present invention is useful as a power converter having a function of compensating for an output voltage error caused by so-called dead time.

DESCRIPTION OF SYMBOLS 1 Power converter 3 Inverter circuit 3a Switching element 5 Switching control part 5a Memory | storage part 6 Motor (load)

Claims (4)

In a power conversion device that switches input power and converts it into predetermined AC power,
An inverter circuit (3) having a plurality of sets of switching elements (3a, 3a) connected in series between buses (P, N) to which the input power is supplied and supplying the AC power to a predetermined load (6) )When,
While providing a dead time (Td) in which both of the series-connected switching elements (3a, 3a) are off, the on-off relationship of the series-connected switching elements (3a, 3a) is controlled in reverse. A switching control unit (5) for compensating an output voltage error of the inverter circuit (3) due to the provision of the dead time (Td);
With
The switching control unit (5) compensates for the output voltage error according to a phase voltage (Vx, Vz) that changes in a period from the start of the dead time (Td) to the phase voltage (Vx, Vz) switching. In the period from when the switching element (3a) in the on state is switched to the off state until the switching element (3a) connected in series with the switching element (3a) is in the on state A power conversion device characterized in that the compensation amount is set according to the changed phase voltage (Vx, Vz). In the power converter device of Claim 1 ,
A storage unit (5a) storing a line graph, an approximate curve, or a table indicating the relationship between the compensation amount and the phase current (Iu, Iw),
The switching control unit (5) compensates for the output voltage error based on a compensation amount stored in the storage unit (5a). In power converter according to claim 1 or claim 2,
The compensation amount stored in the storage unit (5a) is set based on the line voltage in the inverter circuit (3). In any one power converter device in any one of Claims 1-3 ,
The switching control unit (5) reduces the compensation amount or stops the compensation of the output voltage error as the phase current (Iu, Iw) becomes smaller.

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