JP6987268B2 - Power converter, motor drive and air conditioner - Google Patents

Description

The present invention relates to a power conversion device, a motor drive device, and an air conditioner that convert AC power into DC power.

There is a power conversion device that converts the supplied AC power into DC power and outputs it by using a bridge circuit composed of switching elements. By turning the switching element on and off, the power conversion device can perform a step-up operation for boosting the voltage of AC power and a synchronous rectification operation for rectifying AC power.

In Patent Document 1, the power conversion device sets two of the four switching elements according to the voltage of the AC power supplied from the AC power source and the current flowing through the AC power source according to the voltage polarity. A technique for controlling and controlling the other two switching elements according to the polarity of the current is disclosed. In the power conversion device described in Patent Document 1, when the polarity of the current is positive, one of the two switching elements controlled according to the polarity of the current is the switching element when the absolute value of the current value becomes the determination value a or more. Is turned on, and when the absolute value of the current value becomes a judgment value b or less, which is smaller than the judgment value a, one of the switching elements is turned off. Further, in the power conversion device described in Patent Document 1, when the polarity of the current is negative, the other of the two switching elements controlled according to the polarity of the current, when the absolute value of the current value becomes the determination value a or more, the other. The switching element is turned on, and when the absolute value of the current value becomes the determination value b or less, the other switching element is turned off. The power conversion device described in Patent Document 1 uses two determination values to lengthen the on-period of the switching element and improve the efficiency.

Japanese Unexamined Patent Publication No. 2018-7326

However, the power conversion device described in Patent Document 1 turns off the switching element when the absolute value of the current value becomes a determination value b or less, which is smaller than the determination value a. Therefore, depending on the setting of the determination value b, the power conversion device described in Patent Document 1 turns off after the current value becomes zero if the process of turning off the switching element is delayed, and the DC is applied in the synchronous rectification operation. There is a problem that a backflow current from the voltage side to the AC power supply side may be generated.

The present invention has been made in view of the above, and an object of the present invention is to obtain a power conversion device capable of improving efficiency in synchronous rectification operation while suppressing the generation of backflow current.

In order to solve the above-mentioned problems and achieve the object, the power conversion device according to the present invention has a reactor having a first end portion and a second end portion, and the first end portion is connected to an AC power supply. A bridge circuit that is connected to the second end of the reactor and has at least one or more switching elements to convert the AC voltage output from the AC power supply to a DC voltage, and a current detector that detects the current of the AC power supply. A control unit that controls on / off of the switching element according to the current value detected by the current detection unit is provided, and the control unit includes a first current value and a current that are current values previously detected by the current detection unit. The predicted value of the current of the AC power supply at the timing after the timing when the second current value is detected is calculated by using only the second current value which is the current value newly detected by the detection unit, and the predicted value is calculated. It is used to control the on / off of the switching element.

The power conversion device according to the present invention has an effect that the efficiency in the synchronous rectification operation can be improved while suppressing the generation of the backflow current.

The figure which shows the structural example of the power conversion apparatus which concerns on Embodiment 1. Schematic cross-sectional view showing the schematic structure of a MOSFET The first figure which shows the path of the current flowing through the power conversion apparatus which concerns on Embodiment 1 when the absolute value of the power supply current is larger than the current threshold value, and the power supply voltage polarity is positive. The first figure which shows the path of the current which flows through the power conversion apparatus which concerns on Embodiment 1 when the absolute value of the power supply current is larger than the current threshold value, and the power supply voltage polarity is negative. The second figure which shows the path of the current flowing through the power conversion apparatus which concerns on Embodiment 1 when the absolute value of the power supply current is larger than the current threshold value, and the power supply voltage polarity is positive. The second figure which shows the path of the current which flows through the power conversion apparatus which concerns on Embodiment 1 when the absolute value of the power supply current is larger than the current threshold value, and the power supply voltage polarity is negative. The figure which shows the timing which the control part turns on a switching element in the power conversion apparatus which concerns on Embodiment 1. The figure which shows the process which the control part of the power conversion apparatus which concerns on Embodiment 1 calculates the predicted value of the current value which is detected next by a power supply current detection part. A flowchart showing processing for a switching element in which the control unit of the power conversion device according to the first embodiment controls on / off according to the polarity of the power supply current. The figure which shows an example of the hardware configuration which realizes the control part provided in the power conversion apparatus which concerns on Embodiment 1. The figure which shows the timing which the control part of the power conversion apparatus which concerns on Embodiment 2 turns on a switching element. The figure which shows the structural example of the motor drive device which concerns on Embodiment 3. The figure which shows the structural example of the air conditioner which concerns on Embodiment 4.

Hereinafter, the power conversion device, the motor drive device, and the air conditioner according to the embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a diagram showing a configuration example of the power conversion device 100 according to the first embodiment of the present invention. The power conversion device 100 is a power supply device having an AC / DC conversion function that converts the AC power supplied from the AC power supply 1 into DC power and applies it to the load 50 by using the bridge circuit 3. As shown in FIG. 1, the power conversion device 100 includes a reactor 2, a bridge circuit 3, a smoothing capacitor 4, a power supply voltage detection unit 5, a power supply current detection unit 6, a bus voltage detection unit 7, and a control unit. It is provided with 10. The reactor 2 includes a first end portion and a second end portion, and the first end portion is connected to the AC power supply 1.

The bridge circuit 3 is a circuit including two arms in which two switching elements in which diodes are connected in parallel are connected in series, and two arms are connected in parallel. Specifically, the bridge circuit 3 includes a first arm 31 which is a first circuit and a second arm 32 which is a second circuit. The first arm 31 includes a switching element 311 and a switching element 312 connected in series. A parasitic diode 311a is formed on the switching element 311. The parasitic diode 311a is connected in parallel between the drain and the source of the switching element 311. A parasitic diode 312a is formed on the switching element 312. The parasitic diode 312a is connected in parallel between the drain and the source of the switching element 312. Each of the parasitic diodes 311a and 312a is a diode used as a freewheeling diode.

The second arm 32 includes a switching element 321 and a switching element 322 connected in series. The second arm 32 is connected in parallel to the first arm 31. A parasitic diode 321a is formed on the switching element 321. The parasitic diode 321a is connected in parallel between the drain and the source of the switching element 321. A parasitic diode 322a is formed on the switching element 322. The parasitic diode 322a is connected in parallel between the drain and the source of the switching element 322. Each of the parasitic diodes 321a and 322a is a diode used as a freewheeling diode.

Specifically, the power conversion device 100 includes a first wiring 501 and a second wiring 502, each of which is connected to an AC power supply 1, and a reactor 2 arranged in the first wiring 501. Further, the first arm 31 includes a switching element 311 which is a first switching element, a switching element 312 which is a second switching element, and a third wiring 503 having a first connection point 506. The switching element 311 and the switching element 312 are connected in series by the third wiring 503. The first wiring 501 is connected to the first connection point 506. The first connection point 506 is connected to the AC power supply 1 via the first wiring 501 and the reactor 2. The first connection point 506 is connected to the second end of the reactor 2.

The second arm 32 includes a switching element 321 which is a third switching element, a switching element 322 which is a fourth switching element, and a fourth wiring 504 including a second connection point 508, and is a switching element. The 321 and the switching element 322 are connected in series by the fourth wiring 504. The second wiring 502 is connected to the second connection point 508. The second connection point 508 is connected to the AC power supply 1 via the second wiring 502. The bridge circuit 3 may be provided with at least one switching element and may be capable of converting an AC voltage output from the AC power supply 1 into a DC voltage.

The smoothing capacitor 4 is a capacitor connected in parallel to the bridge circuit 3, specifically, the second arm 32. In the bridge circuit 3, one end of the switching element 311 is connected to the positive side of the smoothing capacitor 4, the other end of the switching element 311 and one end of the switching element 312 are connected, and the other end of the switching element 312 is the negative of the smoothing capacitor 4. It is connected to the side.

The switching elements 311, 312, 321, 322 are composed of MOSFETs. The switching elements 311, 312, 321 and 322 are composed of wide band gap (WBG) semiconductors such as gallium nitride (GaN), silicon carbide (SiC), diamond or aluminum nitride. A MOSFET can be used. By using a WBG semiconductor for the switching elements 311, 312, 321, 322, the withstand voltage resistance is high and the allowable current density is also high, so that the module can be miniaturized. Since the WBG semiconductor has high heat resistance, it is possible to reduce the size of the heat dissipation fins of the heat dissipation part.

The control unit 10 operates a drive pulse for operating the switching elements 311, 312, 321, 322 of the bridge circuit 3 based on the signals output from the power supply voltage detection unit 5, the power supply current detection unit 6, and the bus voltage detection unit 7, respectively. To generate. The power supply voltage detection unit 5 is a voltage detection unit that detects the power supply voltage Vs, which is the voltage value of the output voltage of the AC power supply 1, and outputs an electric signal indicating the detection result to the control unit 10. The power supply current detection unit 6 is a current detection unit that detects the power supply current Is, which is the current value of the current output from the AC power supply 1, and outputs an electric signal indicating the detection result to the control unit 10. The power supply current Is is the current value of the current flowing between the AC power supply 1 and the bridge circuit 3. The bus voltage detection unit 7 is a voltage detection unit that detects the bus voltage Vdc and outputs an electric signal indicating the detection result to the control unit 10. The bus voltage Vdc is a voltage obtained by smoothing the output voltage of the bridge circuit 3 with the smoothing capacitor 4. The control unit 10 controls the on / off of the switching elements 311, 312, 321, 322 according to the power supply voltage Vs, the power supply current Is, and the bus voltage Vdc. The control unit 10 may control the on / off of the switching elements 311, 312, 321, 322 by using at least one of the power supply voltage Vs, the power supply current Is, and the bus voltage Vdc.

Next, the basic operation of the power conversion device 100 according to the first embodiment will be described. Hereinafter, the switching elements 311, 321 connected to the positive side of the AC power supply 1, that is, the positive electrode terminal of the AC power supply 1 may be referred to as an upper switching element. Further, the switching elements 312 and 322 connected to the negative side of the AC power supply 1, that is, the negative electrode terminal of the AC power supply 1, may be referred to as a lower switching element.

In the first arm 31, the upper switching element and the lower switching element operate in a complementary manner. That is, when one of the upper switching element and the lower switching element is on, the other is off. As will be described later, the switching elements 311, 312 constituting the first arm 31 are driven by a PWM (Pulse Width Modulation) signal, which is a drive signal generated by the control unit 10. The on or off operation of the switching elements 311, 312 according to the PWM signal is also referred to as a switching operation below. In order to prevent a short circuit of the smoothing capacitor 4 via the AC power supply 1 and the reactor 2, when the absolute value of the power supply current Is output from the AC power supply 1 is equal to or less than the current threshold value, both the switching element 311 and the switching element 312 are turned off. It becomes. Hereinafter, the short circuit of the smoothing capacitor 4 is referred to as a capacitor short circuit. Capacitor short circuit is a state in which the energy stored in the smoothing capacitor 4 is released and the current is regenerated in the AC power supply 1.

The switching elements 321 and 322 constituting the second arm 32 are turned on or off by the drive signal generated by the control unit 10. The switching elements 321 and 322 are basically turned on or off depending on the polarity of the power supply voltage, which is the polarity of the voltage output from the AC power supply 1. Specifically, when the power supply voltage polarity is positive, the switching element 322 is on and the switching element 321 is off, and when the power supply voltage polarity is negative, the switching element 321 is on and switching. The element 322 is off. Note that FIG. 1 shows a drive signal for controlling the on / off of the switching elements 321 and 322 with an arrow directed from the control unit 10 to the bridge circuit 3, and the above-mentioned PWM signal for controlling the on / off of the switching elements 311, 312.

Next, the relationship between the state of the switching element in the first embodiment and the path of the current flowing through the power conversion device 100 according to the first embodiment will be described. Prior to this description, the structure of the MOSFET will be described with reference to FIG.

FIG. 2 is a schematic cross-sectional view showing a schematic structure of a MOSFET. FIG. 2 illustrates an n-type MOSFET. In the case of an n-type MOSFET, a p-type semiconductor substrate 600 is used, as shown in FIG. A source electrode S, a drain electrode D, and a gate electrode G are formed on the semiconductor substrate 600. High-concentration impurities are ion-implanted into the portions in contact with the source electrode S and the drain electrode D to form an n-type region 601. Further, in the semiconductor substrate 600, an oxide insulating film 602 is formed between the portion where the n-type region 601 is not formed and the gate electrode G. That is, the oxide insulating film 602 is interposed between the gate electrode G and the p-type region 603 in the semiconductor substrate 600.

When a positive voltage is applied to the gate electrode G, electrons are attracted to the boundary surface between the p-shaped region 603 and the oxide insulating film 602 in the semiconductor substrate 600, and the boundary surface is negatively charged. Where the electrons are gathered, the density of the electrons becomes higher than the hole density and the n-type is formed. This n-type portion serves as a current path and is called a channel 604. Channel 604 is an n-type channel in the example of FIG. By controlling the MOSFET on, the flowing current flows through the channel 604 more than the parasitic diode formed in the p-type region 603.

FIG. 3 is a first diagram showing a path of a current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is larger than the current threshold value and the power supply voltage polarity is positive. In FIG. 3, the power supply voltage polarity is positive, the switching element 311 and the switching element 322 are on, and the switching element 312 and the switching element 321 are off. In this state, the current flows in the order of the AC power supply 1, the reactor 2, the switching element 311, the smoothing capacitor 4, the switching element 322, and the AC power supply 1. As described above, in the first embodiment, the synchronous rectification operation is performed by the current flowing through each channel of the switching element 311 and the switching element 322, instead of the current flowing through the parasitic diode 311a and the parasitic diode 322a. In FIG. 3, the switching elements that are turned on are indicated by circles. The same shall apply in the following figures.

FIG. 4 is a first diagram showing a path of a current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is larger than the current threshold value and the power supply voltage polarity is negative. In FIG. 4, the power supply voltage polarity is negative, the switching element 312 and the switching element 321 are on, and the switching element 311 and the switching element 322 are off. In this state, current flows in the order of the AC power supply 1, the switching element 321, the smoothing capacitor 4, the switching element 312, the reactor 2, and the AC power supply 1. As described above, in the first embodiment, the synchronous rectification operation is performed by the current flowing through each channel of the switching element 321 and the switching element 312, instead of the current flowing through the parasitic diode 321a and the parasitic diode 312a.

FIG. 5 is a second diagram showing a path of a current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is larger than the current threshold value and the power supply voltage polarity is positive. In FIG. 5, the power supply voltage polarity is positive, the switching element 312 and the switching element 322 are on, and the switching element 311 and the switching element 321 are off. In this state, a current flows in the order of the AC power supply 1, the reactor 2, the switching element 312, the switching element 322, and the AC power supply 1, and a power supply short-circuit path that does not pass through the smoothing capacitor 4 is formed. As described above, in the first embodiment, the power short-circuit path is formed by the current flowing through each channel of the switching element 312 and the switching element 322, instead of the current flowing through the parasitic diode 312a and the parasitic diode 322a. ..

FIG. 6 is a second diagram showing a path of a current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is larger than the current threshold value and the power supply voltage polarity is negative. In FIG. 6, the power supply voltage polarity is negative, the switching element 311 and the switching element 321 are on, and the switching element 312 and the switching element 322 are off. In this state, a current flows in the order of the AC power supply 1, the switching element 321, the switching element 311, the reactor 2, and the AC power supply 1, and a power supply short-circuit path that does not pass through the smoothing capacitor 4 is formed. As described above, in the first embodiment, the power supply short-circuit path is formed by the current flowing through each channel of the switching element 311 and the switching element 321 instead of the current flowing through the parasitic diode 311a and the parasitic diode 321a. ..

The control unit 10 can control the values of the power supply current Is and the bus voltage Vdc by controlling the switching of the current path described above. The power conversion device 100 continuously switches between the load power supply mode shown in FIG. 3 and the power short-circuit mode shown in FIG. 5 when the power supply voltage polarity is positive, and the load shown in FIG. 4 when the power supply voltage polarity is negative. By continuously switching between the power supply mode and the power supply short-circuit mode shown in FIG. 6, operations such as an increase in the bus voltage Vdc and synchronous rectification of the power supply current Is are realized. Specifically, the control unit 10 sets the switching frequency of the switching elements 311, 312 that perform the switching operation by PWM higher than the switching frequency of the switching elements 321 and 322 that perform the switching operation according to the polarity of the power supply voltage Vs. Therefore, the on / off of the switching elements 311, 312, 321, 322 is controlled. In the following description, when the switching elements 311, 312, 321, and 322 are not distinguished, they may be simply referred to as switching elements. Similarly, when the parasitic diodes 311a, 312a, 321a, and 322a are not distinguished, they may be simply referred to as parasitic diodes.

Next, the timing at which the control unit 10 turns the switching element on and off will be described. FIG. 7 is a diagram showing the timing at which the control unit 10 turns on the switching element in the power conversion device 100 according to the first embodiment. In FIG. 7, the horizontal axis is time. In FIG. 7, Vs is the power supply voltage Vs detected by the power supply voltage detection unit 5, and Is is the power supply current Is detected by the power supply current detection unit 6. FIG. 7 shows that the switching elements 311, 312 are current-synchronized switching elements whose on / off is controlled according to the polarity of the power supply current Is, and the switching elements 321 and 322 correspond to the polarity of the power supply voltage Vs. It indicates that it is a voltage-synchronized switching element whose on / off is controlled. Further, in FIG. 7, Is indicates a current threshold value. Although FIG. 7 shows one cycle of the AC power output from the AC power supply 1, the control unit 10 shall perform the same control as the control shown in FIG. 7 in the other cycles.

When the power supply voltage polarity is positive, the control unit 10 turns on the switching element 322 and turns off the switching element 321. Further, when the power supply voltage polarity is negative, the control unit 10 turns on the switching element 321 and turns off the switching element 322. In FIG. 7, the timing at which the switching element 322 is turned from on to off and the timing at which the switching element 321 is turned from off to on are the same timing, but the timing is not limited to this. The control unit 10 may provide a dead time during which the switching elements 321 and 322 are both turned off between the timing at which the switching element 322 is turned from on to off and the timing at which the switching element 321 is turned from off to on. Similarly, the control unit 10 provides a dead time during which the switching elements 321 and 322 are both turned off between the timing at which the switching element 321 is turned from on to off and the timing at which the switching element 322 is turned from off to on. May be good.

When the power supply voltage polarity is positive, the control unit 10 turns on the switching element 311 when the absolute value of the power supply current Is becomes equal to or higher than the current threshold value Is. After that, the control unit 10 turns off the switching element 311 when the absolute value of the power supply current Is becomes smaller and the absolute value of the power supply current Is becomes smaller than the current threshold value Is. Further, when the power supply voltage polarity is negative, the control unit 10 turns on the switching element 312 when the absolute value of the power supply current Is becomes equal to or higher than the current threshold value Is. After that, the control unit 10 turns off the switching element 312 when the absolute value of the power supply current Is becomes smaller and the absolute value of the power supply current Is becomes smaller than the current threshold value Is.

When the absolute value of the power supply current Is is equal to or less than the current threshold Is, the control unit 10 controls so that the switching element 311 and the switching element 321 of the upper switching element do not turn on at the same time, and the switching element of the lower switching element. It is controlled so that the 312 and the switching element 322 are not turned on at the same time. As a result, the control unit 10 can prevent a capacitor short circuit in the power conversion device 100.

Here, the power conversion device 100 does not actually detect the power supply current Is continuously, but detects the power supply current Is at each control cycle. That is, the power conversion device 100 may not be able to accurately detect the moment when the power supply current Is reaches the current threshold value Is in the detection of the power supply current Is in the control cycle unit. Therefore, in the present embodiment, the control unit 10 has a first current value which is the current value previously detected by the power supply current detection unit 6 and a second current which is the current value detected this time by the power supply current detection unit 6. Using the value and the value, the predicted value of the current value to be detected next by the power supply current detection unit 6 is calculated. The first current value detected last time is the current value previously detected by the power supply current detection unit 6, and the second current value detected this time is the current newly detected by the power supply current detection unit 6. The value. The control unit 10 controls the on / off of the switching elements 311, 312 according to the calculated predicted value. In this way, the control unit 10 controls the on / off of the switching elements 311, 312 using the past current values detected by the power supply current detection unit 6.

FIG. 8 is a diagram showing a process in which the control unit 10 of the power conversion device 100 according to the first embodiment calculates a predicted value of the current value next detected by the power supply current detection unit 6. Further, FIG. 8 shows the actual power supply current flowing through the power conversion device 100 and the power supply current Is detected by the power conversion device 100 with respect to the power supply current Is shown in FIG. 7. FIG. 8 shows a portion of the power supply current Is shown in FIG. 7 in which the polarity of the power supply current Is is positive. In FIG. 8, the horizontal axis represents time and the vertical axis represents current value. In FIG. 8, Is indicates a current threshold. Id (n-1) is a current value detected by the power supply current detection unit 6 at the time of the n-1th control timing, and corresponds to the above-mentioned first current value. Id (n) is a current value detected by the power supply current detection unit 6 at the nth control timing, and corresponds to the above-mentioned second current value. Ie (n) predicts the current value to be detected next by the power supply current detection unit 6 at the time of the nth control timing, and corresponds to the above-mentioned predicted value. Ts is a cycle in which the power supply current detecting unit 6 detects the current value, and is the above-mentioned control cycle. In such a case, the control unit 10 can calculate the predicted value Ie (n) using the following equation (1).

Ie (n) = Id (n) + ((Id (n) -Id (n-1)) / Ts) × Ts ... (1)

In equation (1), ((Id (n) -Id (n-1)) / Ts) linearly approximates the change in power supply current Is during the period from the n-1st control timing to the nth control timing. It is the inclination when it is done. The control unit 10 uses the current value Id (n-1), the current value Id (n), and the control cycle Ts in which the power supply current detection unit 6 detects the current value to obtain a value calculated using the current value Id (n). The predicted value Ie (n) is calculated by adding to. The equation (1) can be modified as in the following equation (2).

Ie (n) = Id (n) + (Id (n) -Id (n-1)) ... (2)

That is, the control unit 10 can calculate the predicted value Ie (n) by adding the difference between the current value Id (n) and the current value Id (n-1) to the current value Id (n). can. The control unit 10 may use the predicted value Ie (n) as the predicted value Ie (n) obtained by multiplying the value calculated and obtained as in the right side of the equation (1) or the equation (2) by a specified coefficient. As a result, the control unit 10 can cope with the case where the change in the power supply current Is is steep.

FIG. 9 is a flowchart showing processing for switching elements 311, 312 in which the control unit 10 of the power conversion device 100 according to the first embodiment controls on / off according to the polarity of the power supply current Is. As an example, a case where the polarity of the power supply current Is is positive will be described. The control unit 10 calculates the predicted value Ie (n) (step S1). The method of calculating the predicted value Ie (n) in the control unit 10 is as described above. The control unit 10 compares the absolute value of the predicted value Ie (n) with the current threshold value Is (step S2). When the absolute value of the predicted value Ie (n) is equal to or less than the current threshold value Is (step S3: Yes), the control unit 10 next detects the absolute value of the current value detected by the power supply current detection unit 6 to be equal to or less than the current threshold value Is. Of the switching elements controlled according to the polarity of the current, the on switching element 311 is turned off (step S4). When the absolute value of the predicted value Ie (n) is larger than the current threshold value Is (step S3: No), the control unit 10 assumes that the absolute value of the current value detected by the power supply current detection unit 6 is larger than the current threshold value Is. Of the switching elements controlled according to the polarity of the current, the switched element 311 that is turned on remains on (step S5). When the polarity of the power supply current Is is negative, the control unit 10 performs the same processing as described above for the switching element 312. Regarding the control cycle Ts, the interval is set so that the power supply current detection unit 6 detects the current value so that the predicted value Ie (n) calculated by the control unit 10 becomes −Ith ≦ Ie (n) ≦ It. ..

When the absolute value of the predicted value Ie (n) becomes equal to or less than the current threshold value Ith by calculating the predicted value Ie (n) of the current value detected by the power supply current detecting unit 6, the control unit 10 actually The switching element can be turned off before the absolute value of the current value of the current flowing through the power converter 100 reaches the current threshold value Is. That is, the power conversion device 100 can prevent the generation of a backflow current from the smoothing capacitor 4 to the AC power supply 1 due to the delay in turning off the switching element due to the control delay. Therefore, the user who uses the power conversion device 100 can set the current threshold value Is to a smaller value than before. As a result, the power converter 100 can realize a highly accurate synchronous rectification operation. Further, the power conversion device 100 can prolong the period in which the switching elements 311, 312, which are controlled according to the polarity of the current, are turned on, suppress the decrease in efficiency, reduce the loss, and obtain a highly efficient system. be able to.

The control unit 10 controls the on / off of the switching elements 311, 312 by comparing the absolute value of the calculated predicted value Ie (n) with the current threshold value Is, but the present invention is not limited to this. If the control cycle Ts is such that the power supply current detection unit 6 frequently detects the current value, the control unit 10 turns on / off the switching elements 311, 312 depending on whether or not the calculated predicted value Ie (n) becomes zero. May be controlled. Specifically, the control unit 10 controls according to the polarity of the current when the calculated predicted value Ie (n) becomes zero or when the polarity is different from the current value Id (n). Of the switching elements, the on switching element is turned off. When the predicted value Ie (n) has a different polarity from the current value Id (n), the current value Id (n) is positive and the predicted value Ie (n) is negative, or the current value Id (n). ) Is negative and the predicted value Ie (n) is positive.

Here, the configuration of the switching element will be described. In the power conversion device 100, one of the methods for increasing the switching speed of the switching element is to reduce the gate resistance of the switching element. As the gate resistance becomes smaller, the charge / discharge time to the gate input capacitance becomes shorter, and the turn-on period and the turn-off period become shorter, so that the switching speed becomes faster.

However, there is a limit to reducing the switching loss by reducing the gate resistance. Therefore, by configuring the switching element with a WBG semiconductor such as GaN or SiC, the loss per switching can be further suppressed, the efficiency is further improved, and high frequency switching becomes possible. Further, by enabling high frequency switching, the reactor 2 can be miniaturized, and the power conversion device 100 can be miniaturized and lightened. Further, by using the WBG semiconductor for the switching element, the switching speed is improved and the switching loss is suppressed, so that it is possible to simplify the heat dissipation measures so that the switching element can continue the normal operation. Further, by using a WBG semiconductor for the switching element, the switching frequency can be set to a sufficiently high value, for example, 16 kHz or more, so that noise caused by switching can be suppressed.

Further, in a GaN semiconductor, a two-dimensional electron gas is generated at the interface between the GaN layer and the aluminum gallium nitride layer, and the two-dimensional electron gas causes high carrier mobility. Therefore, a switching element using a GaN semiconductor can realize high-speed switching. Here, when the AC power supply 1 is a commercial power supply of 50 Hz / 60 Hz, the audible range frequency is in the range of 16 kHz to 20 kHz, that is, in the range of 266 to 400 times the frequency of the commercial power supply. The GaN semiconductor is suitable for switching at a frequency higher than this audible frequency. When a switching element 311, 312, 321, 322 made of silicon (Si), which is the mainstream semiconductor material, is driven at a switching frequency of several tens of kHz or more, the ratio of switching loss increases and heat dissipation measures are essential. Become. On the other hand, the switching element 311, 312, 321, 322 made of a GaN semiconductor has a very large switching loss even when driven at a switching frequency of several tens of kHz or more, specifically, a switching frequency higher than 20 kHz. small. Therefore, heat dissipation measures are not required, or the size of the heat dissipation member used for heat dissipation measures can be reduced, and the power conversion device 100 can be made smaller and lighter. Further, since high frequency switching is possible, the reactor 2 can be miniaturized. The switching frequency is preferably 150 kHz or less in order to prevent the primary component of the switching frequency from entering the measurement range of the noise terminal voltage standard.

Further, since the WBG semiconductor has a smaller capacitance than the Si semiconductor, the generation of recovery current due to switching is small, and the generation of loss and noise due to the recovery current can be suppressed, so that it is suitable for high frequency switching. ..

Since the on-resistance of the SiC semiconductor is smaller than that of the GaN semiconductor, the switching elements 311, 312 of the first arm 31 having a larger number of switching times than the second arm 32 are composed of the GaN semiconductor, and the number of switching times is higher. The switching elements 321 and 322 of the second arm 32, which are few in number, may be made of a SiC semiconductor. This makes it possible to make the best use of the characteristics of the SiC semiconductor and the GaN semiconductor. Further, by using the SiC semiconductor for the switching elements 321 and 322 of the second arm 32, which has a smaller number of switching times than the first arm 31, the ratio of the conduction loss to the loss of the switching elements 321 and 322. Will increase, and turn-on loss and turn-off loss will decrease. Therefore, the increase in heat generation due to the switching of the switching elements 321 and 322 is suppressed, the chip area of the switching elements 321 and 322 constituting the second arm 32 can be made relatively small, and the yield at the time of chip manufacturing is low. Can be used effectively.

Further, a Super Junction (SJ)-MOSFET may be used for the switching elements 321 and 322 of the second arm 32 having a small number of switchings. By using the SJ- MOSFET, it is possible to suppress the demerit that the capacitance is high and recovery is likely to occur while taking advantage of the low on-resistance which is the merit of the SJ- MOSFET. Further, by using the SJ- MOSFET, the manufacturing cost of the second arm 32 can be reduced as compared with the case of using the WBG semiconductor.

Further, the WBG semiconductor has higher heat resistance than the Si semiconductor and can operate even at a high junction temperature. Therefore, by using the WBG semiconductor, the first arm 31 and the second arm 32 can be configured by a small chip having a large thermal resistance. In particular, SiC semiconductors, which have a low yield during chip manufacturing, can be used for small chips to reduce costs.

Further, even when the WBG semiconductor is driven at a high frequency of about 100 kHz, the increase in the loss generated in the switching element is suppressed, so that the loss reduction effect due to the miniaturization of the reactor 2 becomes large, and a wide output band, that is, a wide load is obtained. Under the conditions, a highly efficient converter can be realized.

Further, the WBG semiconductor has higher heat resistance than the Si semiconductor and has a high heat generation allowable level for switching due to the bias of the loss between the arms, and is therefore suitable for the first arm 31 in which the switching loss due to high frequency driving occurs.

Next, the hardware configuration of the control unit 10 included in the power conversion device 100 will be described. FIG. 10 is a diagram showing an example of a hardware configuration that realizes the control unit 10 included in the power conversion device 100 according to the first embodiment. The control unit 10 is realized by the processor 201 and the memory 202.

The processor 201 is a CPU (Central Processing Unit, central processing unit, processing unit, arithmetic unit, microprocessor, microprocessor, processor, DSP (Digital Signal Processor)), or system LSI (Large Scale Integration). The memory 202 is non-volatile or volatile such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (registered trademark) (Electrically Erasable Programmable Read-Only Memory). The semiconductor memory of the above can be exemplified. Further, the memory 202 is not limited to these, and may be a magnetic disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc).

As described above, according to the present embodiment, in the power conversion device 100, the control unit 10 includes the current value Id (n-1) previously detected by the power supply current detection unit 6 and the power supply current detection unit 6. Using the current value Id (n) detected this time, the predicted value Ie (n) of the current value next detected by the power supply current detection unit 6 is calculated. The control unit 10 decides to control the on / off of the switching elements 311, 312 according to the calculated predicted value Ie (n). As a result, the power conversion device 100 can improve the efficiency in the synchronous rectification operation while suppressing the generation of the backflow current.

As shown in FIG. 8, when the polarity of the current value is positive, the control unit 10 may calculate the predicted value Ie (n) even if the current value is increasing. Similarly, when the polarity of the current value is negative, the control unit 10 may calculate the predicted value Ie (n) even when the current value is decreasing.

In the example of FIG. 8, the control unit 10 calculates the predicted value Ie (n) in the control cycle Ts at regular intervals, but the present invention is not limited to this. In the example of FIG. 8, it is assumed that the absolute value of the current value next detected by the power supply current detection unit 6 does not become equal to or less than the current threshold value Is when the current value is increasing. That is, the control unit 10 does not need to frequently calculate the predicted value Ie (n) in the situation where the current value is increasing. Therefore, when the polarity of the current value is positive, the control unit 10 calculates the predicted value Ie (n) while the current value is decreasing, rather than the frequency of calculating the predicted value Ie (n) while the current value is increasing. To raise. Similarly, when the polarity of the current value is negative, the control unit 10 calculates the predicted value Ie (n) while the current value is increasing from the frequency of calculating the predicted value Ie (n) while the current value is decreasing. Increase the frequency. As a result, the control unit 10 can reduce the processing load.

Further, the control unit 10 does not have to calculate the predicted value Ie (n) when the current value Id (n) is zero. This is because the absolute value of the predicted value Ie (n) is already within the current threshold value Is, so that it does not affect the process of turning off the switching element in the control unit 10. Similarly, in this case, the control unit 10 can reduce the processing load.

Further, the case where the MOSFET is used as the switching element used in the power conversion device 100 has been described, but it is an example and is not limited thereto. The process of this embodiment can be applied to a switching element other than the MOSFET as long as it is a switching element in which a backflow current may be generated due to a delay in the switching process.

Further, in the present embodiment, the control unit 10 of the power conversion device 100 predicts the current value subsequently detected by the power supply current detection unit 6 using the current value detected by the power supply current detection unit 6. However, it is not limited to this. Using the same method, the control unit 10 can predict the voltage value detected by the power supply voltage detection unit 5 next using the voltage value detected by the power supply voltage detection unit 5.

In the present embodiment, the control unit 10 controls the on / off of the switching elements 321 and 322 according to the polarity of the power supply voltage Vs, and controls the on / off of the switching elements 311, 312 according to the polarity of the power supply current Is. It was, but it is not limited to this. The control unit 10 may control the on / off of the switching elements 311, 312 according to the polarity of the power supply voltage Vs, and may control the on / off of the switching elements 321 and 322 according to the polarity of the power supply current Is.

Embodiment 2.
In the first embodiment, in the power conversion device 100, the control unit 10 controls the on / off of the switching elements 311, 312 according to the calculated predicted value Ie (n). Therefore, the control unit 10 may turn off the switching elements 311, 312 early even when the absolute value of the current value of the current actually flowing through the power conversion device 100 is larger than the current threshold value Is. In the second embodiment, the control unit 10 estimates the time when the absolute value of the current value of the current flowing through the power conversion device 100 becomes the current threshold value Is, and turns off the switching elements 311, 312 at the estimated time.

In the second embodiment, the configuration of the power conversion device 100 is the same as that of the first embodiment shown in FIG. In the second embodiment, the control unit 10 determines that when the absolute value of the predicted value Ie (n) becomes equal to or higher than the current threshold value Is, the absolute value of the predicted value Ie (n) is the same as the current threshold value Is. , Estimate the time when the absolute value of the predicted value Ie (n) becomes the current threshold value Is. In the equation (1) described in the first embodiment, the predicted value Ie (n) is replaced with the current threshold value Is, and the last control cycle Ts indicating the elapsed time is set to the time when the predicted value Ie (n) becomes the current threshold value Is. When replaced with the estimated time Tith shown, the following equation (3) is obtained.

Is = Id (n) + ((Id (n) -Id (n-1)) / Ts) × Tith ... (3)

From the equation (3), the equation (4) for obtaining the estimated time Tith can be obtained.

Tith = ((Id (n) -Ith) / (Id (n-1) -Id (n))) × Ts ... (4)

When the absolute value of the predicted value Ie (n) becomes equal to or less than the current threshold value Is, the control unit 10 controls according to the polarity of the current after the estimated time Thith has elapsed from the time of the nth control timing. Control is performed to turn off the on switching element among the switching elements. Alternatively, when the absolute value of the predicted value Ie (n) becomes equal to or less than the current threshold value Is, the control unit 10 controls according to the polarity of the current from the time of the nth control timing to the estimated time Tith. Control is performed to turn off the on switching element among the switching elements. FIG. 11 is a diagram showing the timing at which the control unit 10 of the power conversion device 100 according to the second embodiment turns on the switching element. The control unit 10 uses, for example, a control signal that generates a control cycle Ts so that the switching element can be turned off after the estimated time Tith has elapsed from the timing shown in FIG. 11, that is, the time of the nth control timing. The control unit 10 generates a control signal by using, for example, a switching timer that counts the control cycle Ts. For example, the control unit 10 generates a compare-match power supply current from the detected current value, and performs compare-match using the compare-match power supply current and the control signal. The power supply current for compare match is a signal whose current value is set to a level that does not intersect with the control signal while the power supply current Is is increasing. The control unit 10 turns off the switching element 311 at the timing when the compare match power supply current and the control signal overlap. When the current value has a positive polarity, the control unit 10 may not perform a compare match while the current value increases.

Although the control unit 10 has described an example of calculating Tith when the absolute value of the predicted value Ie (n) is equal to or less than the current threshold value Is, the present invention is not limited to this. The control unit 10 may calculate Tith before the absolute value of the predicted value Ie (n) becomes equal to or less than the current threshold value Is.

Further, when the control unit 10 controls the on / off of the switching elements 311, 312 depending on whether or not the calculated predicted value Ie (n) becomes zero, the predicted value Ie (n) is estimated to be zero. Calculate the time T0. Specifically, by replacing "Ith" with "0" in the equation (4), the following equation (5) can be obtained.

T0 = (Id (n) / (Id (n-1) -Id (n))) × Ts ... (5)

As described above, according to the present embodiment, in the power conversion device 100, the control unit 10 tells the power conversion device 100 when the absolute value of the calculated predicted value Ie (n) is equal to or less than the current threshold Is. The time when the absolute value of the current value of the flowing current becomes the current threshold Is is estimated, and the switching element is turned off at the estimated time. As a result, the power conversion device 100 can further improve the efficiency in the synchronous rectification operation as compared with the first embodiment while suppressing the generation of the backflow current.

Embodiment 3.
In the third embodiment, the motor drive device including the power conversion device 100 described in the first and second embodiments will be described.

FIG. 12 is a diagram showing a configuration example of the motor drive device 101 according to the third embodiment. The motor drive device 101 drives the motor 42, which is a load. The motor drive device 101 includes the power conversion device 100 of the first and second embodiments, an inverter 41, a motor current detection unit 44, and an inverter control unit 43. The inverter 41 drives the motor 42 by converting the DC power supplied from the power conversion device 100 into AC power and outputting it to the motor 42. Although an example in which the load of the motor drive device 101 is the motor 42 is described, it is an example, and the device connected to the inverter 41 may be a device to which AC power is input, and the motor 42 may be used. Devices other than the above may be used.

The inverter 41 is a circuit in which switching elements such as an IGBT (Insulated Gate Bipolar Transistor) have a three-phase bridge configuration or a two-phase bridge configuration. The switching element used in the inverter 41 is not limited to the IGBT, and may be a switching element composed of a WBG semiconductor, an IGCT (Integrated Gate Commutated Thyristor), a FET (Field Effect Transistor), or a MOSFET.

The motor current detection unit 44 detects the current flowing between the inverter 41 and the motor 42. The inverter control unit 43 uses the current detected by the motor current detection unit 44 to generate a PWM signal for driving the switching element in the inverter 41 so that the motor 42 rotates at a desired rotation speed. Is applied to the inverter 41. The inverter control unit 43 is realized by a processor and a memory like the control unit 10. The inverter control unit 43 of the motor drive device 101 and the control unit 10 of the power conversion device 100 may be realized by one circuit.

When the power conversion device 100 is used for the motor drive device 101, the bus voltage Vdc required for controlling the bridge circuit 3 changes according to the operating state of the motor 42. Generally, it is necessary to increase the output voltage of the inverter 41 as the rotation speed of the motor 42 increases. The upper limit of the output voltage of the inverter 41 is limited by the input voltage to the inverter 41, that is, the bus voltage Vdc which is the output of the power conversion device 100. The region where the output voltage from the inverter 41 saturates beyond the upper limit limited by the bus voltage Vdc is called an overmodulation region.

In such a motor drive device 101, it is not necessary to boost the bus voltage Vdc in the range of low rotation, that is, in the range where the motor 42 does not reach the overmodulation region. On the other hand, when the motor 42 rotates at a high speed, the overmodulation region can be set to a higher rotation side by boosting the bus voltage Vdc. As a result, the operating range of the motor 42 can be expanded to the high rotation side.

Further, if it is not necessary to expand the operating range of the motor 42, the number of turns of the winding around the stator provided in the motor 42 can be increased accordingly. By increasing the number of turns of the winding, the motor voltage generated at both ends of the winding increases in the low rotation region, and the current flowing through the winding decreases by that amount, so that the switching operation of the switching element in the inverter 41 The loss caused by the can be reduced. When both the effects of expanding the operating range of the motor 42 and improving the loss in the low rotation region are obtained, the number of turns of the winding of the motor 42 is set to an appropriate value.

As described above, according to the present embodiment, by using the power conversion device 100, the bias of heat generation between the arms is reduced, and a highly reliable and high output motor drive device 101 can be realized.

Embodiment 4.
In the fourth embodiment, the air conditioner provided with the motor drive device 101 described in the third embodiment will be described.

FIG. 13 is a diagram showing a configuration example of the air conditioner 700 according to the fourth embodiment. The air conditioner 700 is an example of a refrigeration cycle device, and includes the motor drive device 101 and the motor 42 of the third embodiment. The air conditioner 700 includes a compressor 81 having a built-in compression mechanism 87 and a motor 42, a four-way valve 82, an outdoor heat exchanger 83, an expansion valve 84, an indoor heat exchanger 85, and a refrigerant pipe 86. .. The air conditioner 700 is not limited to a separate type air conditioner in which the outdoor unit is separated from the indoor unit, and the compressor 81, the indoor heat exchanger 85, and the outdoor heat exchanger 83 are provided in one housing. It may be a body type air conditioner. The motor 42 is driven by the motor drive device 101.

Inside the compressor 81, a compression mechanism 87 for compressing the refrigerant and a motor 42 for operating the compression mechanism 87 are provided. A refrigerating cycle is configured by circulating the refrigerant in the compressor 81, the four-way valve 82, the outdoor heat exchanger 83, the expansion valve 84, the indoor heat exchanger 85, and the refrigerant pipe 86. The components of the air conditioner 700 can also be applied to equipment such as a refrigerator or a freezer equipped with a refrigeration cycle.

Further, in the fourth embodiment, a configuration example in which the motor 42 is used as the drive source of the compressor 81 and the motor 42 is driven by the motor drive device 101 has been described. However, the motor 42 may be applied to the drive source for driving the indoor unit blower and the outdoor unit blower (not shown) included in the air conditioner 700, and the motor 42 may be driven by the motor drive device 101. Further, the motor 42 may be applied to the drive source of the indoor unit blower, the outdoor unit blower, and the compressor 81, and the motor 42 may be driven by the motor drive device 101.

Further, in the air conditioner 700, the operation under the intermediate condition where the output is less than half of the rated output, that is, the operation under the low output condition is dominant throughout the year, so that the contribution to the annual power consumption under the intermediate condition is high. Become. Further, in the air conditioner 700, the rotation speed of the motor 42 tends to be low, and the bus voltage Vdc required to drive the motor 42 tends to be low. Therefore, it is effective from the viewpoint of system efficiency to operate the switching element used in the air conditioner 700 in a passive state. Therefore, the power conversion device 100 capable of reducing the loss in a wide range of operation modes from the passive state to the high frequency switching state is useful for the air conditioner 700. As described above, the reactor 2 can be miniaturized by the interleave method, but since the air conditioner 700 is often operated under intermediate conditions, it is not necessary to miniaturize the reactor 2, and the configuration and operation of the power conversion device 100 However, it is effective in terms of harmonic suppression and power factor.

Further, since the power conversion device 100 can suppress the switching loss, the temperature rise of the power conversion device 100 is suppressed, and even if the size of the outdoor unit blower (not shown) is reduced, the substrate mounted on the power conversion device 100 Cooling capacity can be secured. Therefore, the power converter 100 is suitable for an air conditioner 700 having high efficiency and a high output of 4.0 kW or more.

Further, according to the present embodiment, since the bias of heat generation between the arms is reduced by using the power conversion device 100, the reactor 2 can be miniaturized by driving the switching element at a high frequency, and the air conditioner 700 can be reduced in size. The increase in weight can be suppressed. Further, according to the present embodiment, by driving the switching element at high frequency, the switching loss is reduced, the energy consumption rate is low, and the highly efficient air conditioner 700 can be realized.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations as long as it does not deviate from the gist of the present invention. It is also possible to omit or change the part.

1 AC power supply, 2 reactor, 3 bridge circuit, 4 smoothing capacitor, 5 power supply voltage detector, 6 power supply current detector, 7 bus voltage detector, 10 control unit, 31 first arm, 32 second arm, 41 Inverter, 42 motor, 43 inverter control unit, 44 motor current detector, 50 load, 81 compressor, 82 four-way valve, 83 outdoor heat exchanger, 84 expansion valve, 85 indoor heat exchanger, 86 refrigerant piping, 87 compression mechanism , 100 power converter, 101 motor drive, 201 processor, 202 memory, 311, 312, 321, 322 switching elements, 311a, 312a, 321a, 322a parasitic diode, 501 first wiring, 502 second wiring, 503 3rd wiring, 504 4th wiring, 506 1st connection point, 508 2nd connection point, 600 semiconductor substrate, 601,603 area, 602 oxide insulating film, 604 channel, 700 air conditioner.

Claims (9)

A reactor that has a first end and a second end, and the first end is connected to an AC power supply.
A bridge circuit connected to the second end of the reactor, comprising at least one switching element, and converting an AC voltage output from an AC power supply into a DC voltage.
A current detector that detects the current of the AC power supply and
A control unit that controls on / off of the switching element according to the current value detected by the current detection unit, and a control unit.
Equipped with
The control unit uses only the first current value, which is the current value previously detected by the current detection unit, and the second current value, which is the current value newly detected by the current detection unit . A power conversion device that calculates a predicted value of the current of the AC power supply at a timing after the timing at which the current value of 2 is detected, and controls the on / off of the switching element using the predicted value. When the polarity of the current value is positive, the control unit calculates the predicted value while the current value is decreasing more frequently than the frequency of calculating the predicted value while the current value is increasing.
The power conversion device according to claim 1. When the polarity of the current value is negative, the control unit calculates the predicted value while the current value is increasing more frequently than the frequency of calculating the predicted value while the current value is decreasing.
The power conversion device according to claim 1. The control unit does not calculate the predicted value when the second current value is zero.
The power conversion device according to claim 1. When the absolute value of the predicted value is equal to or less than the current threshold value, the control unit turns off the on switching element among the switching elements controlled according to the polarity of the current.
The power conversion device according to claim 1. When the absolute value of the predicted value is equal to or greater than the current threshold value, the control unit calculates the time when the absolute value of the current value becomes the current threshold value.
The power conversion device according to claim 1. By the estimated time, the control unit turns off the on switching element among the switching elements controlled according to the polarity of the current.
The power conversion device according to claim 6. It is a motor drive device that drives a motor.
The power conversion device according to any one of claims 1 to 7.
An inverter that converts DC power output from the power conversion device into AC power and outputs it to the motor.
A motor drive device. With the motor
The motor drive device according to claim 8 and
Air conditioner equipped with.

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