JP5326913B2 - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect a duration of actual dead time which is required, when carrying out dead time compensation. <P>SOLUTION: The power converter includes an inverter circuit (4) containing a plurality of switching parts (4a), including switching elements (Sp and Sn) which allow reversal conduction, and a control part (10) which outputs an on-signal to the switching elements (Sp and Sn), at a predetermined timing, such as a current in the direction opposite to the switching element (Sp and Sn) flows in the inverter circuit (4), after the switching elements (Sp and Sn) of the plurality of switching parts (4a) are so turned off as to provide dead time to the inverter circuit (4); and it also includes a dead time detecting part (20) which detects a duration of a dead time, based on the on-voltage drop that occurs at the switching part (4a), when the current flows in that opposite direction during the dead time. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a power conversion device including an inverter circuit having a plurality of switching elements and a switching control unit that controls driving of the switching elements.

  2. Description of the Related Art Conventionally, there is known a power conversion device including an inverter circuit having a plurality of switching elements and a switching control unit that controls driving of the switching elements. Such a power conversion device is widely used for home appliances and industrial devices that need to control the rotational speed and torque of a motor, for example.

  By the way, in the inverter circuit, generally, the upper and lower arms are constituted by a pair of switching elements, and switching control is performed so that either one of the pair of switching elements is turned on. Is configured to supply predetermined power. In such a configuration, when both of the pair of switching elements constituting the upper and lower arms are turned on, an arm short circuit occurs. For this reason, conventionally, when switching on / off of the pair of switching elements, a dead time for turning off both of the switching elements is provided.

  However, if the dead time is provided, an error with respect to the command signal of the output voltage is generated accordingly, and thus the output current and torque are distorted. On the other hand, as disclosed in Patent Document 1, for example, a configuration is considered in which a voltage command to the inverter circuit is corrected in consideration of a voltage component caused by dead time.

JP 2004-64948 A

  However, since the actual dead time is affected by the switching time of the switching element and the like, the actual dead time varies depending on the operating environment such as the individual difference of the switching element that affects the switching time and the temperature, not the fixed time. Therefore, it has been difficult to accurately grasp the length of the dead time that is most important when performing dead time compensation as described in Patent Document 1.

  The present invention has been made in view of the above points, and an object of the present invention is to obtain a configuration capable of accurately detecting the length of an actual dead time necessary for performing dead time compensation. It is in.

  In order to achieve the above object, in the power converter (1) according to the present invention, when a current in the reverse direction of the switching element (Sp, Sn) flows in the inverter circuit (4) during the dead time, Focusing on the point at which the on-voltage drop occurs, the length of the dead time is detected based on the on-voltage drop.

  Specifically, the first invention provides an inverter circuit (4) having a plurality of switching units (4a) including switching elements (Sp, Sn) capable of reverse conduction, and dead time in the inverter circuit (4). After turning off the switching elements (Sp, Sn) of the plurality of switching sections (4a) so as to be provided, a predetermined timing at which current in the reverse direction of the switching elements (Sp, Sn) flows in the inverter circuit (4) In the control unit (10) that outputs an ON signal to the switching element (Sp, Sn), and when the current flows in the reverse direction during the dead time, the switching unit (4a) generates And a dead time detector (20) for detecting the length of the dead time based on the ON voltage drop.

  With this configuration, since the dead time is detected based on a phenomenon actually occurring in the inverter circuit (4), the length of the dead time can be detected with high accuracy. That is, during the dead time, a current in the reverse direction of the switching element (Sp, Sn) flows in the inverter circuit (4), so that an on-voltage drop occurs in the switching unit (4a). By detecting this on-voltage drop, it becomes possible to detect the dead time when the switching element (Sp, Sn) is off.

  Moreover, by using a switching element (Sp, Sn) capable of reverse conduction as the switching element, the switching element (Sp, Sn) is turned on in the reverse direction at the timing when the reverse current flows in the inverter circuit (4). Thus, the conduction loss in the switching unit (4a) can be reduced, and the potential difference between when the switching element (Sp, Sn) is on and when it is off can be easily detected.

  In the first invention, the dead time detection unit (20) compares the voltage between the controlled terminals of the switching element (Sp, Sn) with a predetermined comparison voltage, and the period during which the on-voltage drop appears. It is assumed that the length of the dead time is detected by extracting (second invention).

  Thereby, it is possible to easily detect a period in which the on-voltage drop occurs in the switching unit (4a) during the dead time. Therefore, the configuration of the first invention can be easily realized. Here, between the controlled terminals of the switching element (Sp, Sn) means between the two terminals of the switching element (Sp, Sn) whose current conduction and non-conduction are switched by the control terminal (eg, gate terminal) (eg, MOSFET) Means between drain and source.

  In the first or second aspect of the invention, the control unit (10) is configured so that the dead time detected by the dead time detection unit (20) so that the output voltage of the inverter circuit (4) becomes a desired value. It is assumed that the output period of the ON signal can be changed based on the length of the signal (third invention).

  By doing this, the output period of the ON signal is changed based on the detected dead time length so that the output voltage becomes a desired value, so that the error of the output voltage due to the influence of the dead time is reduced. It becomes possible. That is, the above-described configuration can reduce the influence of the dead time on the output voltage.

  In the first or second aspect of the invention, the ON signal output setting time determined from the output voltage command signal in the control unit (10) and the dead time length detected by the dead time detection unit (20) Based on this, it is assumed that an output voltage calculation unit (16) for calculating the output voltage is further provided (fourth invention).

  As a result, the output voltage is calculated in consideration of the voltage error due to the dead time, so it is more accurate than the conventional output voltage calculation method that calculates based on the ON signal output setting time determined from the command signal. The output voltage can be obtained well. Therefore, for example, in so-called sensorless control in which the position of the rotor of the motor is detected without using a sensor and the motor is controlled, an accurate value is used as the voltage value as basic data for calculating the position of the rotor. Therefore, the motor can be controlled with high accuracy.

  In the first or second aspect of the invention, the control unit (10) includes the switching elements (Sp, Sn) so that the length of the dead time detected by the dead time detection unit (20) is shortened. ), The dead time setting time as an interval for outputting the ON signal can be changed (fifth invention).

  By doing so, the length of the dead time itself can be shortened as much as possible, so that the error of the output voltage can be reduced accordingly.

  In any one of the first to fifth inventions, the switching element (Sp, Sn) is a unipolar element (sixth invention). By doing so, switching elements (Sp, Sn) capable of reverse conduction can be easily configured by MOSFETs, JFETs, or the like. Thereby, the configurations of the first to fifth aspects of the invention can be easily realized.

  In any one of the first to sixth inventions, the switching element (Sp, Sn) is made of a wide band gap semiconductor (seventh invention). Thereby, for example, in the case of a configuration in which a parasitic diode is formed inside a switching element made of a wide band gap semiconductor, the on-voltage drop when a current flows through the parasitic diode during the dead time is reduced in the switching element made of Si. Therefore, the on-voltage drop during the dead time can be detected with higher accuracy. Therefore, with the above-described configuration, the dead time can be detected with higher accuracy.

  As described above, according to the first invention, since the length of the dead time is detected based on the on-voltage drop caused by the current flowing in the reverse direction in the switching unit (4a) during the dead time, The length of the dead time can be detected with high accuracy.

  In addition, according to the second invention, the voltage between the controlled terminals of the switching element (Sp, Sn) is compared with the comparison voltage to obtain the on-voltage drop. The configuration can be realized.

  According to the third invention, since the output period of the ON signal is changed based on the detected dead time length so that the output voltage of the inverter circuit (4) becomes a desired value, The influence on the output voltage due to time can be reduced.

  Further, according to the fourth invention, since the output voltage is calculated in consideration of the length of the detected dead time, the actual output voltage can be obtained with high accuracy, and the motor can be controlled with high accuracy. it can.

  Further, according to the fifth invention, in order to change the dead time setting time as an interval for outputting the ON signal to the plurality of switching elements (Sp, Sn) so that the detected dead time is reduced, The influence of dead time on the output voltage can be minimized.

  According to the sixth invention, since the switching element (Sp, Sn) is a unipolar element, the configurations of the first to fifth inventions can be easily realized.

  Furthermore, according to the seventh invention, since the switching element (Sp, Sn) is made of a wide band gap semiconductor, the dead time can be detected with higher accuracy.

FIG. 1 is a diagram illustrating a schematic configuration of a power conversion device according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating the operation of a pair of upper and lower arms in the inverter circuit. FIG. 3 is a time chart showing the waveform of the ON signal and the waveform of the output voltage with respect to the voltage command. FIG. 4 is a time chart showing each signal generated by the dead time detection unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

Embodiment 1
-Overall configuration of power converter-
FIG. 1 shows a power conversion apparatus (1) according to Embodiment 1 of the present invention. The power converter (1) includes a converter circuit (2), a capacitor circuit (3), and an inverter circuit (4). In addition, the said power converter device (1) is used, for example in order to drive the electric motor (5) (henceforth a motor) of the compressor provided in the refrigerant circuit of the air conditioning apparatus. Here, the refrigerant circuit of the air conditioner is not particularly shown, but the compressor, the condenser, the expansion mechanism, and the evaporator are connected to form a closed circuit, and the refrigerant circulates to form a vapor compression refrigeration. It is configured to perform a cycle. By this refrigerant circuit, in the cooling operation, air cooled by the evaporator is supplied into the room, and in the heating operation, air heated by the condenser is supplied into the room.

  The converter circuit (2) includes a plurality of diodes (2a) and is configured to rectify AC power output from the commercial power supply (6). Although not particularly illustrated, the converter circuit (2) includes a plurality of (for example, six in the case of three-phase alternating current) diodes (2a) connected in a bridge shape, thereby constituting a rectifier circuit. In the present embodiment, the converter circuit (2) is configured by a plurality of diodes (2a). However, the present invention is not limited to this, and the switching circuit is configured by a switching element so that the AC power is rectified to DC power. The element may be driven and controlled.

  The capacitor circuit (3) includes a capacitor (3a) connected in parallel to the output side of the converter circuit (2). By providing this capacitor circuit (3), the voltage rectified by the converter circuit (2) can be smoothed. Thereby, DC power can be stably supplied to the inverter circuit (4) side.

  The inverter circuit (4) is connected in parallel to the converter circuit (2) together with the capacitor circuit (3). This inverter circuit (4) is formed by bridge-connecting a plurality of switching elements (S, for example, six in the case of three-phase alternating current). That is, although not particularly illustrated, the inverter circuit (4) is composed of three switching legs in which two switching elements (S, S) are connected in series to each other, and these switching elements (S ) To convert the DC voltage into an AC voltage and supply it to the motor (5).

  The switching element (S) is a unipolar element such as a MOSFET or JFET, and is made of a wide band gap semiconductor such as SiC or GaN. The switching element (S) is configured to be conductive in the reverse direction.

  Here, in the present embodiment, a diode (D) is connected in antiparallel to each of the switching elements (S), and the switching element (S) and the diode (D) are used for switching in the present invention. Part (4a) is configured. In the present embodiment, the diode (D) is constituted by a parasitic diode formed in a chip constituting the switching element (S).

The power conversion device (1) includes a switching control unit (11) that outputs ON signals Gp and Gn (gate drive signals) to the switching elements (S) of the inverter circuit (4) at a predetermined timing. And an inverter control unit (15) for outputting a voltage command Vo ^* (command signal) to the switching control unit (11). That is, each switching element (S) of the inverter circuit (4) is configured to perform an on / off operation based on the voltage command Vo ^* output from the inverter control unit (15). As shown in FIG. 3, the voltage command has a signal waveform that turns on in a predetermined output period Ton with respect to the unit time T of the carrier cycle (not particularly shown in the case of FIG. 3). However, the average voltage per unit time T of the carrier period is V ^* . Hereinafter, this V ^* is simply referred to as the average voltage in the voltage command Vo ^* .

  Here, the switching control unit (11) and the inverter control unit (15) constitute the control unit (10) of the present invention.

The switching control unit (11) determines the timing of outputting the ON signals Gp and Gn to each switching element (S) based on the voltage command Vo ^* output from the inverter control unit (15). It is configured. The switching control unit (11) is configured to turn on the two switching elements (S, S) so that only one of the two switching elements (S, S) connected in series is turned on. Gp and Gn are output. That is, the switching control unit (11) sets the ON set time Tp ^* corresponding to the voltage command Vo ^* for the two switching elements (S, S). As will be described in detail later, the switching control section (11) is configured to turn on signals Gp, Gn so as to provide a dead time Td in which both of the two switching elements (S, S) are turned off. Is output.

The inverter control unit (15) is a sensorless sensor that detects the load demand on the electric motor (5) driven by the inverter circuit (4) and the rotational position of the rotor of the electric motor (5) ( The output current i, DC voltage Vdc, ON set time Tp ^* ) of the inverter circuit (4) is received as a signal, and the voltage command Vo ^* is output to the switching control unit (11) based on these signals. It is configured. In addition, when the detection signal of the dead time Td detected by the dead time detection unit (20) described later is input to the inverter control unit (15), the voltage command Vo ^* is set in consideration of the dead time Td. It is configured to correct.

Here, the inverter control unit (15) includes an output voltage calculation unit (16) for calculating an output voltage calculation value V ′ necessary for detecting the rotational position of the rotor of the electric motor (5) without a sensor. ing. In the output voltage computing section (16), and on the output set time Tp ^* that is set by the output period Ton of the on-signal in the voltage command Vo ^*, by using the unit of carrier cycle time T, Tp ^* / T × Vdc Is used to calculate the output voltage calculation value V ′. The output voltage calculation value V ′ is an average voltage per unit time of the carrier cycle, and is different from the output voltage Vo that is a detected value and an instantaneous value.

  Further, the inverter control unit (15) is configured such that a current flows through a diode (D) connected in antiparallel to one switching element (S) of two switching elements (S, S) connected in series. The switching element (S) is configured to output an on signal to turn it on. By performing such switching control, it is possible to flow a reverse current to the switching element (S) side, so that loss can be reduced compared to the case of flowing a reverse current to the diode (D) side. it can.

  Here, after the predetermined timing is OFF in the switching circuit (Sp, Sn) of the plurality of switching units (4a) so as to provide a dead time for the inverter circuit (4) in the present invention, the inverter circuit ( 4) Corresponds to the predetermined timing in which the current in the reverse direction of the switching element (Sp, Sn) flows.

  The dead time detector (20) is configured to detect the dead time Td based on the voltage in the inverter circuit (4). As will be described in detail later, the dead time detection unit (20) includes a voltage detection unit (21) that detects the voltage Vo in the inverter circuit (4), and a voltage comparison unit that compares the detected voltage Vo with the comparison voltage Vr. (22), a pulse width calculation unit (23) that outputs the pulse width of the comparison result as a signal, and a dead time calculation unit (24) that calculates the dead time Td based on this signal.

-Dead time detection-
Next, the operation of the inverter circuit (4) when an ON signal is output from the switching control unit (11) to each switching element (S) will be described. In the following description, for the sake of simplification, as shown in FIG. 2, a capacitor (3a) serving as a DC power source and two switching elements connected in series ( In the description, the switching elements will be described using a circuit consisting of: Sp and Sn.

  Here, in the circuit shown in FIG. 2, diodes (Dp, Dn) are connected in antiparallel to the switching elements (Sp, Sn) connected in series. Thereby, the switching elements (Sp, Sn) and the diodes (Dp, Dn) constitute the switching units (4a, 4a), respectively. And the midpoint of these switching parts (4a, 4a) is connected to the load which is not illustrated. Note that the symbols gp and gn in FIG. 2 indicate the gate terminals of the switching elements (Sp and Sn), respectively.

In the circuit of FIG. 2, when a voltage command Vo ^* as shown in FIG. 3 is input from the inverter control unit (15) to the switching control unit (11), the switching control unit (11) On signals Gp and Gn (gate drive signals) corresponding to the voltage command Vo ^* are output to (Sp). When such an ON signal Gp is input to the switching element (Sp) and the switching element (Sp) is turned on, for example, when the output current i flows to the load side in the circuit of FIG. > 0), since current flows through the switching element (Sp), the output voltage Vo (between controlled terminals of the lower arm switching element (Sn) (for example, between drain and source in the case of MOSFET)) Is equivalent to Vdc-Vs obtained by subtracting the on-voltage drop Vs of the switching element (Sp) from the voltage Vdc of the capacitor (3a). On the other hand, when the switching element (Sp) is turned off, unless the lower arm switching element (Sn) is turned on, a current flows through the diode (Dn) connected in reverse parallel to the switching element (Sn). The output voltage Vo becomes −Vd corresponding to the ON voltage drop of the diode (Dn).

  Here, when the switching element (Sn) of the lower arm is turned on at the timing when the current flows to the diode (Dn), the current flows to the switching element (Sn) side with less loss during conduction than the diode (Dn). And loss of the inverter circuit (4) can be reduced.

However, in such a control method, when a signal as indicated by a broken line in FIG. 3 is input to the gate terminals (gp, gn) of two switching elements (Sp, Sn) connected in series, the 2 Two switching elements (Sp, Sn) may both be turned on and short-circuited. Therefore, normally, a dead time is provided for an ON signal input to two switching elements (Sp, Sn) connected in series. Specifically, the switching control unit (11) has a gate drive signal that delays the ON signal by the dead time setting time Td ^* so as to provide a dead time (solid lines of Gp and Gn in FIG. 3). Is generated.

  By doing so, during the dead time, current flows through the diode (Dn) connected in reverse parallel to the lower arm switching element (Sn), and the output voltage Vo flows through the diode (Dn). -Vd, which is the on-voltage drop at that time. When the lower arm switching element (Sn) is turned on at a predetermined timing, a current flows through the switching element (Sn). Therefore, the output voltage Vo is equal to the on-voltage drop of the switching element (Sn). -Vs corresponding to.

  On the other hand, when the output current i is i <0 (when the output current i flows into the circuit of FIG. 2), it is connected in reverse parallel to the switching element (Sp) of the upper arm during the dead time. Since the current flows through the diode (Dp), the output voltage Vo becomes Vdc + Vd obtained by adding Vd, which is the on-voltage drop of the diode (Dp), to the DC voltage Vdc of the capacitor (3a). When the upper arm switching element (Sp) is on, a current flows through the switching element (Sp). Therefore, the output voltage Vo is equal to the voltage Vdc corresponding to the on-voltage drop of the switching element (Sp). Vdc + Vs obtained by adding a certain Vs. Since the current flows through the switching element (Sn) when the lower arm switching element (Sn) is on, the output voltage Vo is equal to Vs corresponding to the on-voltage drop of the switching element (Sn). Become.

Incidentally, when providing the dead time as described above, a short circuit while can be prevented reliably between the upper and lower arms, as shown in FIG. 3, if the output current i> 0, the output voltage relative to the voltage command Vo ^* When the output period Vo is shortened and the output current i <0, the output voltage Vo is output with respect to the voltage command Vo ^* . Then, an error occurs in the actual output voltage with respect to the required output voltage. On the other hand, so-called dead time immobilization, in which output voltage is corrected according to dead time, has been conventionally performed.

However, since the dead time varies depending on the operating environment such as the individual difference of the switching elements (Sp, Sn) and the temperature, the same length as the dead time setting time (Td ^* ) by the switching control unit (11). It does not always become. Therefore, in order to perform accurate dead time compensation, it is necessary to accurately detect the length of the actual dead time Td.

  On the other hand, the inventors of the present invention, as a result of diligent efforts, as described above, during the dead time Td during which the switching elements (Sp, Sn) of the upper and lower arms are off, the diode (Dn) The point where the on-voltage drop Vd appears was found, and a configuration for detecting the length of the dead time Td based on the on-voltage drop Vd was devised. As a result, the actual length of the dead time Td can be accurately detected, and the output voltage error due to the dead time Td can be reduced. Hereinafter, detection of the length of the dead time Td will be described.

  In the present invention, as shown in FIG. 1, the dead time Td is detected by the dead time detector (20). As described above, the dead time detection unit (20) is preset with the voltage detection unit (21) for detecting the output voltage Vo and the output voltage Vo detected by the voltage detection unit (21). A voltage comparison unit (22) for comparing the predetermined comparison voltage Vr, a pulse width calculation unit (23) for converting the pulse width of the comparison result into the amplitude of the signal, and the length of the dead time Td based on the amplitude And a dead time calculation unit (24) for obtaining the height.

  The voltage detector (21) is configured to detect the output voltage Vo of the circuit of FIG. 2, that is, the voltage between the controlled terminals of the lower arm switching element (Sn).

  The voltage comparison unit (22) extracts the on-voltage drop of the diode (Dp, Dn) from the output voltage Vo, and converts the on-voltage drop into a signal w1 having a pulse width corresponding to its duration. It is configured as follows. Specifically, for example, when the output voltage Vo has a waveform as shown in FIG. 4 (when the output current i> 0), the voltage comparison unit (22) causes the output voltage Vo to be equal to or less than the negative comparison voltage Vr. Only when the signal is high, a high signal is output. When the output current i <0, as shown in FIG. 3, the output voltage (Vdc + Vs) when the upper arm switching element (Sp) is on due to the on-voltage drop of the diode (Dp, Dn). Therefore, the voltage comparator (22) outputs a high signal only when the output voltage Vo is equal to or higher than the positive comparison voltage Vr.

  The pulse width calculation unit (23) is configured to convert the signal w1 into a signal w2 having an amplitude proportional to the pulse width of the High signal output by the voltage comparison unit (22) and output the signal w2. Yes. As a result, a period in which the on-voltage drop of the diode (Dp, Dn) appears can be converted into an amplitude, and a signal having a triangular wave shape in the period can be obtained.

  The dead time calculation unit (24) is configured to hold the peak of the amplitude of the signal w2. As a result, the maximum value of the amplitude of the signal w2, that is, the maximum value of the dead time Td can be obtained. The dead time calculation unit (24) may be configured to output an average value of dead times Td within a predetermined period and each dead time Td. When calculating the average value of the dead times Td, the dead time calculation unit (24) is constituted by, for example, a filter circuit having a time constant.

  In the configuration as described above, the length of the dead time Td is detected as follows.

  When the output voltage Vo as shown in FIG. 4 is detected by the voltage detector (21), the output voltage Vo is compared with the comparison voltage Vr by the voltage comparator (22), and a diode ( Only the on-voltage drop of Dp, Dn) is extracted. At this time, the voltage comparison unit (22) outputs a high signal during a period in which the output voltage Vo is lower than the negative comparison voltage Vr (when i <0, it is higher than the positive comparison voltage Vr). A signal w1 having a pulse width corresponding to a period in which the on-voltage drop continuously appears is generated.

  Thereafter, the signal w1 is input to the pulse width calculator (23), and the pulse width calculator (23) generates a signal w2 whose amplitude changes according to the pulse width of the signal w1. Thereby, the signal w1 from which the High signal is output in a rectangular wave shape is converted into a signal w2 having a triangular wave portion. When the signal w2 is input to the dead time calculation unit (24), the maximum value of the amplitude of the signal w2 is calculated by the dead time calculation unit (24). In this way, the maximum value of the dead time Td can be obtained.

  With the above configuration, the actual length of the dead time Td can be accurately detected based on the on-voltage drop Vd of the diode (Dp, Dn). Here, as in this embodiment, the switching element (Sp, Sn) is composed of a wide band gap semiconductor such as SiC or GaN, and the switching element (Sp, Sn) is used as the diode (Dp, Dn). ) Is used, the on-voltage of the diodes (Dp, Dn) is about 3V. Therefore, the on-voltage of the diode (Dp, Dn) can be increased as compared with the parasitic diode (on-voltage is about 1 V) of a chip using general Si, and the dead time Td of the above-described configuration can be reduced. The length can be easily detected.

−Dead time compensation−
In consideration of the length of the dead time Td obtained as described above, the inverter control unit (15) performs the following dead time compensation.

That is, when the detected value of the dead time Td is input from the dead time detection unit (20), the inverter control unit (15) turns on the switching element (Sp) of the upper arm by the dead time Td. A voltage command Vo ^* that changes the signal output period is output. More specifically, as shown in FIG. 3, when i> 0 in which the output period of the output voltage Vo is shortened due to the influence of the dead time Td, an ON signal is output based on the voltage command Vo ^* before the dead time compensation. When the output period of the output voltage Vo becomes longer due to the influence of the dead time Td while the output period of the ON signal is the sum of the dead time Td and the period Ton, the output period A voltage command Vo ^* is output from the inverter control section (15) so as to set the output period of the ON signal by subtracting the dead time Td from Ton.

As a result, an on-output setting period Tp ^* that is an ideal on-signal output period not including dead time is also Ton + Td when i> 0, and Ton−Td when i <0. Thus, the voltage V per unit time T of the carrier cycle in the actual output voltage (hereinafter simply referred to as the average output voltage V) can be matched with the average voltage V ^* (desired value in the present invention) in the voltage command Vo ^* . it can.

  When i> 0

  When i <0

As described above, the average output voltage V ^* equal to the average voltage V ^* in the voltage command Vo ^* is changed by changing the output period Ton of the ON signal based on the voltage command Vo ^* using the actual dead time Td detected with high accuracy. Can be output. That is, by changing the ON signal output period Ton in consideration of the dead time Td, an error in the average output voltage V due to the dead time Td can be reduced.

-Effect of Embodiment 1-
As described above, according to this embodiment, the diode (Dp) connected in antiparallel to the switching element (Sp, Sn) during the dead time Td when the switching element (Sp, Sn) of the upper and lower arms is turned off. , Dn), the point at which the on-voltage drop Vd appears in the output voltage Vo is detected, and the dead time Td is detected based on the on-voltage drop Vd. Can be detected with high accuracy.

  In addition, when the dead time Td is detected, the output voltage Vo and the comparison voltage Vr are compared and the High voltage is output while the on-voltage drop Vd continues, so the on-voltage drop Vd Can be easily converted into the pulse width of the signal, and the duration of the on-voltage drop Vd, that is, the length of the dead time Td can be easily detected.

Then, by changing the ON signal output period based on the voltage command Vo ^* by the detected dead time Td, the error of the average output voltage V with respect to the average voltage V ^* in the voltage command Vo ^* is reduced. be able to.

<< Embodiment 2 >>
The second embodiment of the present invention will be described below. This embodiment is different from the first embodiment in the configuration of the output voltage calculation unit (16) of the inverter control unit (15) and the dead time compensation method. In the following description, the same parts as those in the first embodiment are denoted by the same reference numerals, and only different parts will be described.

Specifically, the output voltage calculation unit (16) in the present embodiment uses the ON output setting time Tp ^* set by the output period Ton of the ON signal in the voltage command and the unit time T of the carrier cycle, The output voltage calculation value calculated by Tp ^* / T × Vdc is configured to take into account the dead time Td detected in the first embodiment. That is, the output voltage calculation unit (16) subtracts the actual dead time Td detected from Tp ^* when i> 0 and subtracts Tp ^* when i <0, as shown in the following equation. By adding the detected actual dead time Td, the same output voltage calculation value V ′ as the actual average output voltage V is calculated.

  When i> 0

  When i <0

  The output voltage calculation value V ′ obtained in this way is used for sensorless control for controlling the rotation of the motor without using a position sensor, for example. Therefore, as described above, the motor can be controlled with high accuracy by using a highly accurate calculation method that can calculate the same value as the actual output voltage V.

-Effect of Embodiment 2-
As described above, according to this embodiment, when the output voltage is obtained by calculation, the output voltage calculation value that is the same as the actual average output voltage V is obtained by taking into account the actual dead time Td detected in the first embodiment. V ′ can be obtained, and the calculation accuracy of the output voltage can be improved.

Therefore, even if an error occurs in the actual average output voltage V with respect to the average voltage V ^* of the voltage command Vo ^* the influence of the dead time Td, since the output voltage calculation value V 'can be determined accurately, the output The motor can be accurately controlled using the voltage calculation value V ′.

<< Embodiment 3 >>
Hereinafter, Embodiment 3 of the present invention will be described. Since this embodiment also differs from the first embodiment only in the dead time compensation method as in the second embodiment, the same reference numerals are given to the same parts as those in the first embodiment in the following description. Only different parts will be described.

  First, the influence of the dead time Td on the actual average output voltage V and the output voltage calculation value V ′ will be described.

Assuming that the on-set time Tp ^* for the switching element (Sp) of the upper arm is Tp ^* = Ton, the actual average output voltage V is the above dead with respect to the average voltage V ^* in the voltage command V ^* as shown in the following equation. An error corresponding to the time Td is generated. That is, the output time of the voltage is shortened by the dead time Td with respect to the on-set time Tp ^* (in the case of i <0, it becomes long), and thus the average voltage V in the voltage command Vo ^* . It becomes an error of average output voltage V with respect to ^* . In the following expression, the on-voltage drops Vs and Vd are ignored.

  When i> 0

  When i <0

Further, the output voltage calculation value V ′ calculated using the on-set time Tp ^* and the voltage Vdc is also an error with respect to the actual average output voltage V by the dead time Td as shown in the following equation. Have

  When i> 0

  When i <0

Since the above-described error is caused by the dead time Td, in this embodiment, the dead time Td is made as small as possible. Specifically, in the switching control unit (11), the dead time setting directly related to the dead time Td is set so that the dead time Td is reduced to such an extent that the switching elements (Sp, Sn) of the upper and lower arms are not short-circuited. Time Td ^* is adjusted. That is, the switching control unit (11) is configured to reduce the dead time setting time Td ^* based on the dead time Td detected in the first embodiment so that the dead time Td is reduced. ing.

-Effect of Embodiment 3-
As described above, according to this embodiment, the dead time setting time Td ^* is reduced based on the detected dead time Td so that the dead time Td is reduced. The error of the voltage calculation value V ′ can be reduced.

<< Other Embodiments >>
About the said embodiment, it is good also as the following structures.

  In each of the above embodiments, a parasitic diode formed in a chip constituting the switching element (Sp, Sn) is used as the diode (Dp, Dn). However, the present invention is not limited to this, and the switching element (Sp, Sn) It may be a diode formed separately from the chip. Further, the switching element (Sp, Sn) may be constituted by a JFET that can conduct in the reverse direction. In this case, a diode connected in antiparallel to the switching element (Sp, Sn) is not necessary. Here, in the switching control when there is no diode as described above, the switching element (S) is turned on at a predetermined timing when a current in the reverse direction flows through the switching element (S). In this case, the predetermined timing is OFF after switching elements (Sp, Sn) of the plurality of switching units (4a) are turned off so as to provide a dead time for the inverter circuit (4) in the present invention. This corresponds to a predetermined timing at which a current in the reverse direction of the switching element (Sp, Sn) flows in the circuit (4).

  In each of the above embodiments, the dead time detection unit (20) compares the output voltage Vo with the comparison voltage Vr, extracts the on-voltage drop from the output voltage Vo, performs signal processing, and then performs the on-state. The period in which the voltage drop occurs is obtained. However, the present invention is not limited to this, and the period in which the on-voltage drop occurs is directly obtained by starting a timer according to the value of the output voltage Vo. Any configuration may be used as long as the period during which the on-voltage drop occurs can be detected.

In the first embodiment, the inverter controller (15) outputs the voltage command Vo ^* in consideration of the dead time Td detected by the dead time detector (20). However, the present invention is not limited to this. The dead time Td may be taken into account when the switching control unit (11) determines the ON signal output period based on the voltage command Vo ^* .

  As described above, the present invention is useful for a power conversion device that performs switching control to turn on a switching element at a predetermined timing when a current in the reverse direction of the switching element flows in the inverter circuit.

DESCRIPTION OF SYMBOLS 1 Power converter 3 Capacitor circuit 3a Capacitor 4 Inverter circuit 4a Switching part 5 Electric motor 10 Control part 11 Switching control part 15 Inverter control part 16 Output voltage calculation part 20 Dead time detection part 21 Voltage detection part 22 Voltage comparison part 23 Pulse width calculation Unit 24 dead time calculation unit S, Sp, Sn switching element D, Dp, Dn diode gp, gn gate terminal

Claims (7)

An inverter circuit (4) having a plurality of switching units (4a) including switching elements (Sp, Sn) capable of reverse conduction;
After the switching elements (Sp, Sn) of the plurality of switching units (4a) are turned off so as to provide a dead time in the inverter circuit (4), the switching elements (Sp, Sn) in the inverter circuit (4) A control unit (10) for outputting an ON signal to the switching element (Sp, Sn) at a predetermined timing when a current in the reverse direction of
A dead time detection unit (20) for detecting a length of the dead time based on an on-voltage drop generated in the switching unit (4a) when a current flows in the reverse direction during the dead time period; A power conversion device comprising: The power conversion device according to claim 1,
The dead time detection unit (20) compares the voltage between the controlled terminals of the switching element (Sp, Sn) with a predetermined comparison voltage, and extracts the period in which the on-voltage drop appears, thereby A power converter configured to detect a length of dead time. In the power converter device according to claim 1 or 2,
The control unit (10) is configured to output the on signal based on the length of the dead time detected by the dead time detection unit (20) so that the output voltage of the inverter circuit (4) becomes a desired value. The power conversion device is configured to be capable of changing the output period. In the power converter device according to claim 1 or 2,
Output voltage for calculating the output voltage based on the ON signal output setting time determined from the output voltage command signal in the control unit (10) and the dead time length detected by the dead time detection unit (20) A power converter, further comprising a calculation unit (16). In the power converter device according to claim 1 or 2,
The control unit (10) outputs an ON signal to the plurality of switching elements (Sp, Sn) so that the length of the dead time detected by the dead time detection unit (20) is shortened. A power conversion device configured to be able to change a dead time setting time. In the power converter according to any one of claims 1 to 5,
The switching element (Sp, Sn) comprises a unipolar element. In the power converter according to any one of claims 1 to 6,
The switching element (Sp, Sn) is made of a wide band gap semiconductor, and is a power conversion device.

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