Power conversion device and air conditioner

Abstract

To provide a power conversion device which can easily be manufactured and has high reliability.SOLUTION: A power conversion device 100 includes: an inverter circuit 50 which has a parallel connection body of a plurality of switching elements S1a and S1b for each output phase, converts DC voltage into AC voltage and applies the AC voltage to a motor; a control unit 80 for controlling the inverter circuit 50; and current detection units 61a and 61b for individually detecting output current of the plurality of switching elements S1a and S1b. The device further includes a comparison unit 70 for individually comparing a detection value of output current and a plurality of thresholds different in sizes for the plurality of switching elements S1a and S1b. The control unit 80 performs load adjustment control for reducing rotational speed of the motor based on a comparison result by the comparison unit 70.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device and the like. [Background technology]

[0002] With regard to an inverter circuit configured with multiple switching elements connected in parallel, the techniques described in Patent Documents 1 and 2 are known, for example. That is, Patent Document 1 describes adjusting the impedance of the gate wiring so that the gate current of each semiconductor module has the same value during off operation. Furthermore, Patent Document 2 describes changing the timing of turning on semiconductor elements based on the detected value of a temperature sensor provided in each of a plurality of semiconductor elements connected in parallel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-156304 [Patent Document 2] Patent No. 7051008 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 requires prior sorting of semiconductor modules into those with high and low gate threshold voltages. Furthermore, the need to adjust the impedance of the gate wiring to match the characteristics of each semiconductor module complicates the manufacturing process.

[0005] Furthermore, the technology described in Patent Document 2 prevents turn-on loss (switching loss) by delaying the timing of the on-operation of the semiconductor element with the higher temperature among multiple semiconductor elements connected in parallel. In this case, the reverse recovery current of two semiconductor elements flows through the semiconductor element with the lower temperature, which increases the induced electromotive force of the parasitic inductance, and this may lead to malfunction of the semiconductor element.

[0006] Therefore, an object of the present disclosure is to provide a power conversion device or the like that is easy to manufacture and highly reliable. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the power conversion device according to the present disclosure includes an inverter circuit having a parallel connection of a plurality of switching elements for each output phase, converting a DC voltage into an AC voltage and applying the AC voltage to a motor, a control unit that controls the inverter circuit, a current detection unit that individually detects the current flowing through each of the plurality of switching elements, and a comparison unit that individually compares the detection value of the current detection unit with a plurality of threshold values ​​of different magnitudes for the plurality of switching elements, and the control unit performs load adjustment control to reduce the rotational speed of the motor based on the result of the comparison by the comparison unit. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a power conversion device and the like that is easy to manufacture and highly reliable. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram of a power conversion device according to a first embodiment. [Figure 2] 1 is a configuration diagram including an inverter circuit of a power conversion device according to a first embodiment. [Figure 3]3 is an explanatory diagram showing the relationship between the range of currents related to switching elements, the magnitude of the currents, and the voltages output from the current detection units in the power conversion device according to the first embodiment. FIG. [Figure 4] 1 is a configuration diagram including a comparison unit and a control unit of a power conversion device according to a first embodiment. [Figure 5] 4 is an explanatory diagram showing the correspondence relationship between the current value of a switching element, the output voltage of each comparator, and the input voltage of a second comparison unit in the power conversion device according to the first embodiment. FIG. [Figure 6A] 4 is a flowchart of a process executed by a control unit of the power conversion device according to the first embodiment. [Figure 6B] 4 is a flowchart of a process executed by a control unit of the power conversion device according to the first embodiment. [Figure 7] 4 is a time chart showing an example of the operation of the power conversion device according to the first embodiment. [Figure 8A] 6 is a time chart showing an example of the operation of the power conversion device according to the modified example of the first embodiment. [Figure 8B] 6 is a time chart showing an example of the operation of the power conversion device according to the modified example of the first embodiment, including the operation of the MCU. [Figure 8C] 10 is a time chart showing an example of the operation of the power conversion device according to the modified example of the first embodiment, relating to the motor current, the value of k, and the load adjustment flag. [Figure 9] FIG. 10 is a configuration diagram including an inverter circuit of a power conversion device according to a second embodiment. [Figure 10] FIG. 10 is a configuration diagram including an inverter circuit of a power conversion device according to a third embodiment. [Figure 11] FIG. 10 is a configuration diagram of an air conditioner according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment <Configuration of power conversion device> FIG. 1 is a configuration diagram of a power conversion device 100 according to the first embodiment. The power conversion device 100 shown in Fig. 1 is a device that converts three-phase AC power supplied from an AC power source E1 into DC power, converts this DC power into a predetermined AC power, and outputs it to a motor M1. The motor M1 may be, for example, a permanent magnet synchronous motor, or may be another type of motor. As shown in Fig. 1, the power conversion device 100 includes a converter circuit 10, a smoothing capacitor 20, a DC voltage detection unit 30, a shunt resistor 40, an inverter circuit 50, a plurality of current detection units 61a, 61b, ... (see Fig. 2), a comparison unit 70, and a control unit 80.

[0011] The converter circuit 10 is a power converter that converts AC voltage applied from an AC power source E1 into DC voltage (pulsating DC voltage). Such a converter circuit 10 may be a full-wave rectifier circuit configured with a plurality of diodes (not shown) connected in a bridge configuration, or may be a switching type rectifier. The output side of the converter circuit 10 is connected to the inverter circuit 50 via a positive DC line K1 and also connected to the inverter circuit 50 via a negative DC line K2.

[0012] The smoothing capacitor 20 is an element that smoothes the DC voltage (pulsating DC voltage) on the output side of the converter circuit 10. An electrolytic capacitor may be used as the smoothing capacitor 20, or other types of capacitors such as a film capacitor may be used. As shown in Fig. 1, the positive electrode of the smoothing capacitor 20 is connected to one DC line K1, and the negative electrode is connected to the other DC line K2.

[0013] The DC voltage detection unit 30 detects the DC voltage across the smoothing capacitor 20. That is, the DC voltage detection unit 30 detects the DC voltage between the pair of DC lines K1 and K2. The detection value of the DC voltage detection unit 30 is output to the control unit 80. The shunt resistor 40 is a resistive element for detecting the bus current flowing through the DC line K2, and is provided on this DC line K2. The detected value of the shunt resistor 40 is output to the control unit 80. The detected values ​​of the DC voltage detection unit 30 and the shunt resistor 40 are used for well-known vector control.

[0014] The inverter circuit 50 is a power converter that converts the DC voltage of the smoothing capacitor 20 into a predetermined AC voltage and applies this AC voltage to the motor M1. Details of the inverter circuit 50 will be described later. The current detection units 61a, 61b, ... (see FIG. 2) individually detect the current flowing through each of the multiple switching elements S1a, S1b, ... (see FIG. 2) of the inverter circuit 50. The detection values ​​of the current detection units 61a, 61b, ... (see FIG. 2) are output to the comparison unit 70.

[0015] The comparison unit 70 compares the detection values ​​of the current detection units 61a, 61b, ... (see FIG. 2) with a plurality of threshold values ​​of different magnitudes for each of the switching elements S1a, S1b, ... (see FIG. 2). The comparison results by the comparison unit 70 are output to the control unit 80.

[0016] The control unit 80 is, for example, an MCU (Micro Controller Unit), and although not shown, is configured to include electronic circuits such as a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and various interfaces. The control unit 80 reads out a program stored in the ROM and loads it into the RAM, and the CPU executes various processes. The control unit 80 controls the inverter circuit 50 based on the detection values ​​of the DC voltage detection unit 30 and the shunt resistor 40, as well as the result of comparison by the comparison unit 70.

[0017] As shown in FIG. 1, the control unit 80 includes a load adjustment unit 81 and a rotational speed control unit 82. The load adjustment unit 81 executes load adjustment control based on the result of the comparison by the comparison unit 70. The "load adjustment control" described above is a control that reduces the rotational speed of the motor M1 to reduce the current flowing through the parallel connection of switching elements S1a, S1b, ... (see FIG. 2) (performs load adjustment). This load adjustment control is performed by the control unit 80 (rotational speed control unit 82) controlling the inverter circuit 50.

[0018] The rotational speed control unit 82 switches each switching element of the inverter circuit 50 on and off in a predetermined manner based on PWM control (Pulse Width Modulation). This converts the DC voltage of the smoothing capacitor 20 into a three-phase AC voltage. This AC voltage is applied to the U-phase, V-phase, and W-phase windings of the motor M1. Furthermore, when a rotational speed command value related to load adjustment control is input from the load adjustment unit 81, the rotational speed control unit 82 executes PWM control based on this rotational speed command value. Details of the processing by the control unit 80 will be described later.

[0019] FIG. 2 is a configuration diagram including an inverter circuit 50 of the power conversion device. 2, the inverter circuit 50 has a first leg (reference numeral not shown, same below) corresponding to the U phase, a second leg corresponding to the V phase, and a third leg corresponding to the W phase. These first, second, and third legs are connected in parallel to the smoothing capacitor 20 (see FIG. 1).

[0020] The first leg corresponding to the U phase is configured by connecting in series a parallel connection of switching elements S1a and S1b in the upper arm and a parallel connection of switching elements S2a and S2b in the lower arm. Using a parallel connection of switching elements in this manner allows for a larger capacity of the inverter circuit 50. Furthermore, since less current flows through each switching element, conduction loss in the switching elements can be reduced, resulting in higher efficiency. The second leg corresponding to the V phase and the third leg corresponding to the W phase are configured in a similar manner. Thus, the inverter circuit 50 has a parallel connection of multiple switching elements for each output phase (U phase, V phase, and W phase).

[0021] As shown in FIG. 2, the connection point between the parallel connection of the upper arm switching elements S1a and S1b and the parallel connection of the lower arm switching elements S2a and S2b is connected to a U-phase winding (not shown) of the motor M1 via a wire (the same applies to the V-phase and W-phase windings).

[0022] In order to prevent destruction of the switching elements due to commutation in the first, second, and third legs, a freewheeling diode (not shown) is connected in anti-parallel to each switching element. Note that if the switching elements have a parasitic diode, this parasitic diode will function as the freewheeling diode, so there is no need to provide a separate freewheeling diode.

[0023] In the example of Fig. 2, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as multiple switching elements that constitute the first, second, and third legs. In particular, using SJ-MOSFETs, which have low on-resistance, as switching elements can reduce loss and improve efficiency. Note that the type of switching elements in the inverter circuit 50 is not limited to SJ-MOSFETs, and SiC-MOSFETs and IGBTs (Insulated Gate Bipolar Transistors) may also be used.

[0024] 2 (for example, gate resistors R1a, R1b, R2a, and R2b for the U phase) and a gate driver circuit 51. The gate resistor R1a is an element for adjusting the switching time of the switching element S1a and reducing ringing, and is connected to the gate of the switching element S1a. The same applies to the remaining gate resistors R1b, R2a, R2b, and so on.

[0025] The gate driver circuit 51 is a circuit that amplifies the voltage of the PWM signal output from the control unit 80 (see FIG. 1) to a predetermined voltage required to drive each switching element. The voltage amplified by the gate driver circuit 51 is applied to the gate of each switching element, thereby switching each switching element on and off in a predetermined manner.

[0026] The current detection unit 61a shown in FIG. 2 detects the current (drain current) flowing through the switching element S1a. For example, a resistor or a current sensor is used as this current detection unit 61a. In the example of FIG. 2, the current detection unit 61a is provided on the wiring on the source side of the switching element S1a. Similarly, the remaining switching elements S1b, S2a, S2b, etc. are provided with current detection units 61b, 62a, 62b, etc. for individually detecting the currents therein. The detection values ​​of these current detection units 61a, 61b, 62a, 62b, etc. are output to the comparison unit 70.

[0027] In the following, we will mainly explain matters related to the switching elements S1a and S1b of the upper arm of the first leg corresponding to the U phase, but the same applies to the other switching elements S2a, S2b, S3a, S3b, S4a, S4b, S5a, S5b, S6a, and S6b.

[0028] <Current imbalance> As described above, the upper arm of the U phase is provided with a parallel connection of switching elements S1a and S1b. A predetermined voltage is applied to the gates of switching elements S1a and S1b from gate driver circuit 51, thereby switching on and off switching elements S1a and S1b. Ideally, switching on and off switching elements S1a and S1b is performed simultaneously by the voltage from gate driver circuit 51, and current flows equally through each of switching elements S1a and S1b.

[0029] However, the characteristics of the switching elements S1a and S1b are not necessarily identical. There is some variation in these characteristics, and there is often variation in the impedance of the inverter circuit 50 (main circuit) and the gate driver circuit 51. As a result, the on / off timing of the switching elements S1a and S1b may be off. The main causes of characteristic variation are variations in the gate-source threshold voltage and transconductance of the switching elements S1a and S1b. The aforementioned "threshold voltage" refers to the threshold voltage between the gate and source when current begins to flow through the switching element. Furthermore, "transconductance" refers to the degree of change in drain current in response to a change in the input gate voltage.

[0030] For example, if the threshold voltages of switching elements S1a and S1b are different, during on-state current begins to flow through the one with the lower threshold voltage. As a result, a larger current flows through the one with the lower threshold voltage, causing current to flow unevenly through switching elements S1a and S1b. During off-state current, the one with the higher threshold voltage stops flowing first, and then current concentrates in the one with the lower threshold voltage. In other words, during both on-state and off-state current, current concentrates in the switching element with the lower threshold voltage, causing a current imbalance.

[0031] If an excessive current repeatedly flows through one of the parallel-connected switching elements, the amount of heat generated (loss) per unit time increases, which may lead to deterioration of the switching element and a shortened lifespan.Furthermore, an increase in the induced electromotive force of the parasitic inductance may cause the switching element to malfunction.

[0032] Therefore, in the first embodiment, the control unit 80 performs load adjustment control based on a comparison between the detected value of the current of each switching element in the inverter circuit 50 and a plurality of threshold values ​​of different magnitudes. As described above, the "load adjustment control" is a control that reduces the current flowing through the switching elements by slowing down the rotation speed of the motor M1. This prevents excessive current from flowing through the switching elements, thereby preventing shortened lifespans and malfunctions.

[0033] FIG. 3 is an explanatory diagram showing the relationship between the range of current related to the switching element, the magnitude of the current, and the voltage output from the current detection unit. The "current range" shown in FIG. 3 is a range between two thresholds I High ,I Low The range is divided into three ranges: "High", "Middle", and "Low". In the following explanation, the current threshold I High ,I Low and the voltage threshold V High ,V Low For convenience, the terms "High" and "Low" are used to indicate the magnitude of the current so that the correspondence between them can be easily understood.

[0034] As shown in Figure 3, when the drain current of the switching element exceeds the threshold I High The current range above this threshold is defined as "High." Low That's all, I High The current range where the drain current of the switching element is less than the threshold I is defined as "Middle." LowThe current range below this is considered "Low."

[0035] The "current" shown in Fig. 3 indicates the magnitude of the drain current of the switching element, similar to the "current range." In other words, the "current" shown in Fig. 3 indicates the value of the current detected by each of the current detection units 61a, 61b, ... (see Fig. 2).

[0036] The "voltage" shown in FIG. 3 indicates, for example, the voltage output from the current detection unit 61a (see FIG. 2) to the comparison unit 70 (see FIG. 2). As a specific example, if a resistive element is used as the current detection unit 61a, the voltage across this resistive element is proportional to the magnitude of the drain current of the switching element S1a (see FIG. 2). In other words, the voltage across the resistive element indicates the magnitude of the drain current of the switching element S1a. The voltage across the resistive element is applied to the non-inverting input terminals (+ terminals) of the comparators 1a and 2a (see FIG. 4) of the comparison unit 70. The same can be said for the voltages output from the other current detection units 61b, 62a, 62b, etc. (see FIG. 2).

[0037] The voltage threshold V shown in Figure 3 High is the current threshold I High For example, when the drain current of the switching element S1a (see FIG. 2) exceeds the threshold I High If the voltage is equal to or greater than the threshold voltage V High It will be higher than this.

[0038] Also, the voltage threshold V Low is the current threshold I Low For example, when the drain current of the switching element S1a (see FIG. 2) exceeds the threshold I Low If the voltage is less than the threshold voltage V (included in the "Low" range), the voltage output from the current detection unit 61a (see FIG. 2) to the comparison unit 70 (see FIG. 2) is equal to or lower than the threshold voltage V Low The height will be less than

[0039] FIG. 4 is a configuration diagram of the power conversion device 100 including a comparison unit 70 and a control unit 80. 4 illustrates the switching elements S1a and S1b of the upper arm of the first leg corresponding to the U phase in the inverter circuit 50, and does not illustrate the remaining switching elements. High ,V Low corresponds to that explained in Figure 3.

[0040] 4, the comparison unit 70 includes a first comparison unit 71 and a second comparison unit 72. The first comparison unit 71 compares the detected values ​​of the current detection units 61a and 61b with the detected values ​​of the multiple threshold values ​​V for each of the multiple switching elements S1a and S1b that are components of the parallel connection. High ,V Low and outputs a predetermined voltage corresponding to the result of this comparison to the second comparing section 72. As shown in FIG. 4, the first comparing section 71 includes comparators 1a, 1b, 2a, and 2b, and resistive elements 21a, 22a, 21b, 22b, and 23.

[0041] The comparator 1a is connected to the output voltage of the current detection unit 61a and the threshold V High The comparator 1a is a circuit that compares the magnitudes of the voltages of and and outputs the comparison result. That is, the comparator 1a judges whether the magnitude of the drain current of the switching element S1a is within the "High" range (see FIG. 3). The output voltage of the current detection unit 61a is applied to the non-inverting input terminal (+ terminal) of the comparator 1a. The inverting input terminal (- terminal) of the comparator 1a is applied to the threshold voltage V High A DC voltage of is applied.

[0042] Another comparator 2a is connected to the output voltage of the current detection unit 61a and a threshold V LowThe comparator 2a is a circuit that compares the magnitudes of the voltages of and and outputs the comparison result. That is, the comparator 2a judges whether the magnitude of the drain current of the switching element S1a is within the above-mentioned "Low" range (see FIG. 3). The output voltage of the current detection unit 61a is applied to the non-inverting input terminal (+ terminal) of the comparator 2a. The inverting input terminal (- terminal) of the comparator 2a is applied with a threshold voltage V Low A DC voltage of is applied.

[0043] As shown in Fig. 4, the output terminals of the comparators 1a and 2a are connected to each other via a wiring K3. This wiring K3 is provided with a series connection of resistor elements 21a and 22a. The resistor elements 21a and 22a have the same resistance value. The connection point between the resistor elements 21a and 22a is connected to another wiring K6 via a wiring K4.

[0044] The comparator 1b is connected to the output voltage of the current detection unit 61b and the threshold V High The comparator 1b is a circuit that compares the magnitudes of the voltages of and and outputs the comparison result. That is, the comparator 1b determines whether the magnitude of the drain current of the switching element S1b is within the "High" range (see FIG. 3). The output voltage of the current detection unit 61b is applied to the non-inverting input terminal (+ terminal) of the comparator 1b. The inverting input terminal (- terminal) of the comparator 1b is applied with a threshold V High A DC voltage of is applied.

[0045] Another comparator 2b is connected to the output voltage of the current detection unit 61b and a threshold V Low The comparator 2b is a circuit that compares the magnitudes of the voltages of and and outputs the comparison result. That is, the comparator 2b determines whether the magnitude of the drain current of the switching element S1b is within the "Low" range (see FIG. 3). The output voltage of the current detection unit 61b is applied to the non-inverting input terminal (+ terminal) of the comparator 2b. The inverting input terminal (- terminal) of the comparator 2b is applied to the threshold voltage V Low A DC voltage of is applied.

[0046] The output terminals of the comparators 1b and 2b are connected to each other via a wiring K5. A series connection of resistor elements 21b and 22b is provided on this wiring K5. The resistor elements 21b and 22b have the same resistance value. One end of a wiring K6 is connected to the connection point between the resistor elements 21b and 22b. The other end of this wiring K6 is connected to the inverting input terminal (negative terminal) of the comparator 72a of the second comparing section 72. A predetermined DC voltage VD is applied to the wiring K6 via a resistor element 23.

[0047] 4 outputs a predetermined ON signal or OFF signal to the control unit 80 (load adjusting unit 81) based on the voltage output from the first comparing unit 71 (the voltage applied to the inverting input terminal of the comparator 72a). Specifically, the second comparing unit 72 outputs an ON signal to the control unit 80 when the voltage output from the first comparing unit 71 becomes equal to or greater than a first threshold. The first threshold (also referred to as an ON threshold) is a voltage threshold that serves as a criterion for determining whether or not the second comparing unit 72 should output an ON signal to the control unit 80, and is set in advance.

[0048] Furthermore, after outputting the ON signal, the second comparing unit 72 outputs an OFF signal to the control unit 80 (load adjusting unit 81) when the voltage output from the first comparing unit 71 becomes equal to or lower than the second threshold. In this way, the second comparing unit 72 functions as a hysteresis comparator. The second threshold (also referred to as OFF threshold) is a voltage threshold that serves as a criterion for determining whether or not the second comparing unit 72 should output an OFF signal to the control unit 80, and is set in advance. The second threshold is set to a value lower than the first threshold.

[0049] 4, the second comparing section 72 includes a comparator 72a and resistor elements 72b, 72c, 72d, 72e, and 72f. The resistor elements 72b and 72c are connected in series. A predetermined DC voltage VS is applied to one end (the resistor element 72b side) of the series connection of the resistor elements 72b and 72c, and the other end is at ground potential. The connection point between the series connection of the resistor elements 72b and 72c is connected to the non-inverting input terminal (+ terminal) of the comparator 72a via another resistor element 72d.

[0050] The output terminal of the comparator 72a is connected to the load adjusting unit 81 via a wiring K7, and is also connected to the non-inverting input terminal (+ terminal) of the comparator 72a via another wiring K8 (i.e., positive feedback is applied). As shown in Fig. 4, a resistor element 72e is provided on the wiring K8. A predetermined DC voltage VP is applied to the wiring K7 via another resistor element 72f.

[0051] The comparison unit 70 shown in Fig. 4 corresponds to the parallel connection of the switching elements S1a and S1b. Therefore, a comparison unit 70 having the same configuration as that shown in Fig. 4 is provided individually for each of the six pairs of parallel connections shown in Fig. 2.

[0052] FIG. 5 is an explanatory diagram showing the correspondence between the current value of the switching element, the output voltage of each comparator, and the input voltage of the second comparison section (also see FIG. 4 as appropriate). The states α to λ shown in FIG. 5 correspond to the combinations of the rows (horizontal rows) in the explanatory diagram of FIG. 5. The "61a" and "61b" written in the "Current Value" column in FIG. 5 indicate the symbols of the current detection units 61a and 61b, in that order. For example, the "61a" column indicates "High," "Middle," and "Low" as candidates for the range that includes the detection value of the current detection unit 61a (i.e., the drain current of the switching element S1a). These "High," "Middle," and "Low" correspond to those explained using FIG. 3 (the same applies to the "61b" column).

[0053] In Figure 5, "1a" in "Output voltage of each comparator" indicates the symbol for comparator 1a. "H" in the "1a" column indicates that the output voltage of comparator 1a becomes high. Also, "L" in the "1a" column indicates that the output voltage of comparator 1a becomes low. The same applies to "1b," "2a," and "2b" in "Output voltage of each comparator."

[0054] 5, "72a: - terminal" in "Input voltage" indicates the voltage applied to the inverting input terminal (- terminal) of comparator 2a of second comparing section 72. For example, when the magnitudes of the drain currents of parallel-connected switching elements S1a and S1b are all within the "High" range, an "H" signal is output from each of four comparators 1a, 1b, 2a, and 2b. When "H" is the same potential as DC voltage VD, a voltage of "1.00 × VD" is applied to the inverting input terminal (- terminal) of comparator 72a of second comparing section 72.

[0055] Furthermore, for example, when the magnitude of the drain current of switching element S1a is within the "High" range and the magnitude of the drain current of the other switching element S1b is within the "Middle" range, the following signals are output. That is, "H" signals are output from comparators 1a, 2a, and 2b, and an "L" signal is output from comparator 1b. When "H" is the same potential as DC voltage VD and "L" is 0V, a voltage of "0.50 × VD" is applied to the inverting input terminal (negative terminal) of comparator 72a of the second comparing section 72.

[0056] In this way, the combination of the magnitude of each drain current of the switching elements S1a, S1b ("High", "Middle", or "Low"), the combination of the output voltages "H" and "L" of the comparators 1a, 1b, 2a, and 2b, and the value of the voltage applied to the inverting input terminal (- terminal) of the comparator 72a of the second comparison section 72 are pre-associated.

[0057] Although FIG. 5 shows the settings related to the parallel connection of the switching elements S1a and S1b, it is assumed that the same settings as those in FIG. 5 are made in advance for each of the total six pairs of parallel connections shown in FIG. 2.

[0058] <Processing of control section> 6A and 6B are flowcharts of the processing executed by the control unit of the power conversion device (see also FIG. 4 as appropriate). The following mainly describes the processing for the parallel connection of switching elements S1a and S1b, but it is assumed that similar processing is performed for the remaining five parallel connection pairs. Note that it is not necessary to know in advance the differences in characteristics (differences in threshold voltage, etc.) of the parallel connection of switching elements S1a, S1b, etc. Also, it is assumed that the driving of motor M1 begins at "START" in Figure 6A.

[0059] In step S101, control unit 80 sets the value of k to zero. Here, k is a value that is incremented (S103) each time an ON signal is input from second comparison unit 72 to load adjustment unit 81. Note that instead of the processing of step S101, control unit 80 may reset the value of k to zero when load adjustment control, which will be described later, is stopped (S114 in FIG. 6B).

[0060] Next, in step S102, the control unit 80 determines whether or not an ON signal has been input from the second comparing unit 72. As will be described in detail later, if the detected values ​​of the drain currents of the switching elements S1a and S1b are both within the "High" range (state α in FIG. 5), or if one is "High" and the other is "Middle" (states β and δ in FIG. 5), the second comparing unit 72 outputs an ON signal to the control unit 80. In other words, if the total value of the drain currents of the parallel-connected switching elements S1a and S1b is equal to or greater than a certain value and the drain current of each element is increasing to the point where it is likely to become an overcurrent, the second comparing unit 72 outputs an ON signal to the control unit 80.

[0061] If an ON signal is not input from the second comparing unit 72 in step S102 (S102: No), the control unit 80 repeats the determination process of step S102. If an ON signal is input from the second comparing unit 72 in step S102 (S102: Yes), the process of the control unit 80 proceeds to step S103. In step S103, the control unit 80 increments the value of k. Specifically, the control unit 80 increments the value of k from zero to one.

[0062] In step S104, the control unit 80 determines whether the value of k is equal to or greater than a first predetermined value. Here, the "first predetermined value" is a preset threshold value (e.g., two or three times) of the number of ON signals that serves as a criterion for determining whether the control unit 80 starts load adjustment control (S107). If the value of k is less than the first predetermined value in step S104 (S104: No), the control unit 80 proceeds to step S105.

[0063] In step S105, the control unit 80 determines whether a predetermined number of PWM periods (e.g., five periods) have elapsed since the value of k was most recently reset. Here, the "predetermined number of times" refers to a preset threshold value for the number of PWM periods that serves as a criterion for determining whether or not to reset the value of k to zero (S106). In step S105, if the predetermined number of PWM periods has not elapsed since the value of k was reset (S105: No), the process of the control unit 80 returns to step S102. In addition, in step S105, if the predetermined number of PWM periods has elapsed since the value of k was reset (S105: Yes), the process of the control unit 80 proceeds to step S106.

[0064] In step S106, the control unit 80 resets the value of k to 0. After performing the process of step S106, the process of the control unit 80 returns to step S102. If the value of k is equal to or greater than the first predetermined value in step S104 (S104: Yes), the control unit 80 proceeds to step S107.

[0065] In step S107, the control unit 80 starts the load adjustment control. In this way, when the number of times that the second comparison unit 72 outputs an ON signal becomes equal to or greater than a predetermined number of times during a period of multiple cycles of PWM control (S104: Yes), the control unit 80 performs the load adjustment control (S107). As described above, the "load adjustment control" is a control that reduces the rotation speed of the motor M1. By performing the load adjustment control in this way, the current flowing through the parallel connection of the switching elements is reduced, thereby suppressing deterioration and malfunction of the switching elements.

[0066] It is preferable that the control unit 80 performs load adjustment control when an ON signal is input consecutively a predetermined number of times or more (for example, two or more times) from the second comparison unit 72. This makes it possible to prevent unnecessarily frequent load adjustment control even when the current flowing through the switching element temporarily increases due to the influence of a transient phenomenon or noise.

[0067] 2, for example, a total of six pairs of parallel-connected switching elements are provided. In such a configuration, when the number of times that an ON signal is output from at least one of the total of six second comparators 72 corresponding to each parallel-connected pair reaches a predetermined number or more over a period of multiple cycles of PWM control, the control unit 80 may perform load adjustment control.

[0068] After the process of step S107 is started, the load adjustment control is continued until the process of step S114 in FIG. 6B (stop of the load adjustment control) is executed. It should be noted that the control unit 80 does not need to continue reducing the rotation speed of the motor M1 while the load adjustment control is being executed. For example, the control unit 80 may reduce the rotation speed of the motor M1 from a first rotation speed before the load adjustment control is started to a second rotation speed, and then maintain the second rotation speed. Furthermore, the control unit 80 may reduce the rotation speed of the motor M1 in stages after the load adjustment control is started. Alternatively, for example, the control unit 80 may reduce the rotation speed of the motor M1 at a predetermined speed change rate (temporal change rate) after the load adjustment control is started.

[0069] Next, in step S108 of FIG. 6B, the control unit 80 resets the value of k to zero. In step S109, the control unit 80 determines whether a predetermined period has elapsed since the value of k was reset. Here, the "predetermined period" may be, for example, a period of multiple PWM periods, or a period of multiple electrical or mechanical angle periods. In step S109, if the predetermined period has not elapsed since the value of k was reset (S109: No), the control unit 80 proceeds to step S110.

[0070] In step S110, the control unit 80 determines whether or not an ON signal has been input from the second comparing unit 72. If an ON signal has not been input from the second comparing unit 72 in step S110 (S110: No), the process of the control unit 80 returns to step S109. If an ON signal has been input from the second comparing unit 72 in step S110 (S110: Yes), the process of the control unit 80 proceeds to step S111.

[0071] In step S111, the control unit 80 increments the value of k. After performing the process of step S111, the process of the control unit 80 returns to step S109. Furthermore, in step S109, if a predetermined period of time has elapsed since the value of k was reset (S109: Yes), the process of the control unit 80 proceeds to step S112.

[0072] In step S112, the control unit 80 determines whether the value of k is equal to or less than a second predetermined value. Here, the "second predetermined value" is a preset threshold value of the number of ON signals (for example, 1 time) that is used as a criterion for determining whether the control unit 80 should stop the load adjustment control (S114). If the value of k is greater than the second predetermined value in step S112 (S112: No), the process of the control unit 80 proceeds to step S113.

[0073] In step S113, the control unit 80 resets the value of k to 0. After performing the process of step S113, the process of the control unit 80 returns to step S109. In this case, the load adjustment control continues as is. If the value of k is equal to or less than the second predetermined value in step S112 (S112: Yes), the process of the control unit 80 proceeds to step S114.

[0074] In step S114, the control unit 80 stops the load adjustment control. Thus, after the load adjustment control is started (S107 in FIG. 6A), if the number of times that the second comparison unit 72 outputs an ON signal becomes equal to or less than a predetermined number of times within a predetermined period (S112: Yes in FIG. 6B), the control unit 80 stops the load adjustment control (S114) and increases the rotational speed of the motor M1, or maintains the rotational speed of the motor M1 at the rotational speed at the time when the load adjustment control was stopped (immediately before the stop). If the rotational speed is to be increased, the control unit 80 increases the rotational speed of the motor M1 and returns the motor to normal operation. If the rotational speed is to be maintained, the motor is returned to normal operation after a certain time has elapsed or when the command rotational speed is reset.

[0075] For example, in the configuration shown in Fig. 2, a total of six pairs of parallel-connected switching elements are provided. In such a configuration, when the number of times that an ON signal is output from all of the six second comparators 72 corresponding to the respective parallel-connected elements falls below a predetermined number within a predetermined period, the control unit 80 may stop the load adjustment control. After performing the process of step S114, the process of the control unit 80 returns to "START" in Fig. 6A (RETURN).

[0076] FIG. 7 is a time chart showing an example of the operation of the power conversion device (also see FIG. 4 as appropriate). 7 represents time. The vertical axes of the time charts in FIG. 7 represent, from the top of the page, the drain currents of the switching elements S1a and S1b, the output voltages of the comparators 1a, 2a, 1b, and 2b, the input voltage of the inverting input terminal (negative terminal) of the comparator 72a of the second comparing section 72, and the output voltage of the second comparing section 72. The threshold V shown in FIG. ON is a "first threshold value" that is a criterion for determining whether or not to switch the output voltage of the second comparing section 72 to an ON signal, and is set in advance. OFFis a "second threshold value" that is a criterion for determining whether or not to switch the output voltage of the second comparing section 72 to an OFF signal, and is set in advance.

[0077] As shown by the time scale ("100 ns") at the top right of Fig. 7, the period from time t1 to t11 is actually very short. "High," "Middle," and "Low" shown at the right edge of the drain current time chart in Fig. 7 correspond to those explained in Fig. 3.

[0078] Assume that a predetermined voltage is applied to each gate of switching elements S1a and S1b from gate driver circuit 51 immediately before time t1 in Fig. 7. In the example of Fig. 7, the drain current of switching element S1a increases more steeply from time t1 than that of switching element S1b. This shows that switching element S1a has a lower threshold voltage than switching element S1b.

[0079] During the period from time t2 to t3 in FIG. 7, the drain current of the switching element S1a is in the "Middle" range, and the drain current of the other switching element S1b is in the "Low" range. As a result, the output voltage of the comparator 2a becomes "H" (High), and the output voltages of the remaining comparators 1a, 1b, and 2b become "L" (Low). In other words, during the period from time t2 to t3, the state ζ shown in FIG. 5 is reached, and therefore the input voltage at the inverting input terminal (- terminal) of the comparator 2a of the second comparing section 72 becomes "0.25×VD". This "0.25×VD" is the on-threshold threshold V ON Since the output voltage of second comparing unit 72 is set to be lower than the reference voltage L1, the output voltage of second comparing unit 72 is set to the value L1 during the period from time t2 to t3. As a result, an OFF signal is output from second comparing unit 72 to load adjusting unit 81.

[0080] 7, the drain current of the switching element S1a is in the "High" range, and the drain current of the other switching element S1b is in the "Middle" range. As a result, the output voltages of the comparators 1a, 2a, and 2b are "H", and the output voltage of the remaining comparator 1b is "L". In other words, during the period from time t4 to t5, the state is as shown in FIG. 5, and therefore the input voltage at the inverting input terminal (- terminal) of the comparator 72a of the second comparing section 72 is "0.50×VD". This "0.50×VD" is the on-threshold threshold V ON Since the output voltage of second comparing unit 72 is set to be higher than the output voltage of load adjusting unit 81, the output voltage of second comparing unit 72 is set to the value H1 during the period from time t4 to t5. As a result, an ON signal is output from second comparing unit 72 to load adjusting unit 81.

[0081] In this way, when the magnitude of the drain current of one of the switching elements S1a and S1b is within the "High" range and the magnitude of the drain current of the other is within the "Middle" range (states β and δ in FIG. 5), the voltage of the inverting input terminal (- terminal) of the comparator 72a is equal to or lower than the on-threshold threshold V ON It is set to be equal to or greater than (first threshold value).

[0082] Note that even when the magnitude of the drain current of each of the switching elements S1a and S1b is within the "High" range (state α in FIG. 5), the voltage at the inverting input terminal (-terminal) of the comparator 72a does not exceed the threshold V ON This threshold V ON is a voltage threshold value that is a criterion for determining whether or not to output an ON signal from the second comparison unit 72 to the load adjustment unit 81, and is set in advance. For example, the voltage threshold value V is set to a value that is higher than 0.33×VD (see FIG. 5) and lower than 0.50×VD (see FIG. 5). ON is set.

[0083] In the example of Figure 7, after reaching state ζ between times t2 and t3, the states transition sequentially to state ε (times t3 to t4), state β (times t4 to t5), state ε (times t5 to t6), state ζ (times t6 to t7), state λ (times t7 to t10), state ζ (times t10 to t11), and state λ (after time t11), as described in Figure 5.

[0084] For example, during the period from time t4 to time t7, the input voltage of the inverting input terminal (- terminal) of the comparator 72a is equal to or exceeds the threshold voltage V OFF Since the drain current of each of the switching elements S1a and S1b is kept higher than the threshold voltage V, the load regulation control continues. After that, at time t7, the magnitude of the drain current of each of the switching elements S1a and S1b is included in the "Low" range, and therefore the input voltage at the inverting input terminal (- terminal) of the comparator 72a becomes equal to or lower than the threshold voltage V OFF As a result, the second comparing section 72 outputs an OFF signal to the load adjusting section 81.

[0085] In this way, when the magnitude of each drain current of the switching elements S1a and S1b is included in the "Low" range (state λ in FIG. 5), the voltage of the inverting input terminal (- terminal) of the comparator 72a is equal to or lower than the threshold V OFF (second threshold) is set to be equal to or less than this threshold V OFF is a voltage threshold value that is a criterion for determining whether or not to switch the signal from the second comparison unit 72 to the load adjustment unit 81 from an ON signal to an OFF signal, and is set in advance. For example, the threshold value V is set to a value lower than 0.25×VD (see FIG. 5). OFF is set.

[0086] <Effects> According to the first embodiment, if the second comparison unit 72 inputs an ON signal a predetermined number of times or more within a predetermined period, the control unit 80 performs load adjustment control to reduce the rotational speed of the motor M1. This reduces the drain current of the switching element, thereby suppressing heat generation in the switching element and preventing its deterioration. Furthermore, the induced electromotive force in the parasitic inductance between the drain and source is reduced, thereby preventing malfunction of the switching element. Furthermore, it is possible to prevent conduction loss and thermal breakdown due to a large current flowing through the switching element.

[0087] Furthermore, in the first embodiment, the voltage at the inverting input terminal (negative terminal) of the second comparator 72 is changed based on whether the current of each of the two parallel-connected switching elements S1a and S1b falls within one of three ranges: "High," "Middle," or "Low." This makes it possible to prevent unnecessarily frequent load adjustment control (i.e., deceleration of the motor M1) compared to when separate second comparators 72 are provided for the switching elements S1a and S1b or when the number of current ranges is limited to two, "High" and "Low." Therefore, it becomes easier to ensure an operating range for the rotational speed of the motor M1, allowing the motor M1 to be driven at a relatively high speed.

[0088] Furthermore, according to the first embodiment, there is no particular need for the manufacturer to know the individual characteristics of the switching elements in advance, and there is also no particular need to adjust the impedance of the circuit in accordance with the characteristics of the switching elements, which facilitates the manufacture of the power conversion device 100. In this way, according to the first embodiment, it is possible to provide a power conversion device 100 that is easy to manufacture and highly reliable.

[0089] <Modification of the First Embodiment> FIG. 8A is a time chart showing an example of the operation of the power conversion device according to the modification of the first embodiment. The configuration and processing contents of the power conversion device 100 (see FIG. 1) are assumed to be the same as those in the first embodiment. The horizontal and vertical axes of each time chart in FIG. 8A and the waveforms of the drain current are assumed to be the same as those in FIG. 7.

[0090] In the example of Figure 8A, the drain current threshold I Low The magnitude of the threshold V is set to a value smaller than that of the first embodiment (see FIG. 7). High (See Figure 3) and threshold V Low (See Figure 3) Low ) the value of the current of the switching element (threshold I Low ) is set to a value smaller than the steady-state current (current from time t8 to t9) after the switching elements S1a and S1b are turned on.

[0091] As a result, after a steady-state current flows through the switching elements S1a and S1b from time t8 to t9, the output voltage of the second comparing unit 72 changes from value H1 to value L1 when the switching elements are turned off (time t10). Therefore, the time during which the second comparing unit 72 outputs an ON signal to the control unit 80 (times t4 to t10 in FIG. 8A) is longer than the output time of the ON signal in the first embodiment (times t4 to t7 in FIG. 7). The output time in this embodiment is several tens of microseconds or more when the PWM frequency is on the order of several kilohertz. Because the output time of the ON signal is thus sufficiently ensured, the control unit 80 can more easily detect the ON signal from the second comparing unit 72 compared to the first embodiment. An example of the control unit 80 is an MCU, and when the H1 signal of the second comparison unit 72 can be continuously acquired at intervals of several microseconds in a single PWM period, for example, by incrementing k (S102 to S103 in FIG. 6A, S110 to S111 in FIG. 6B), it is possible to prevent erroneous detection of the ON signal due to noise, etc. (see FIG. 8B for details, which will be described later).

[0092] 7 used in the first embodiment, the output time of the ON signal output from the second comparing section 72 is quite short, such as several hundred nanoseconds, but an integrated circuit that can read such an ON signal may be used as the control section 80. This allows the control section 80 to appropriately detect the ON signal etc. from the second comparing section 72.

[0093] FIG. 8B is a time chart showing an example of the operation of the power conversion device according to the modified example of the first embodiment, including the operation of the MCU (see also FIG. 4 as appropriate). The horizontal axis of each time chart in Fig. 8B represents time. The vertical axis of each time chart in Fig. 8B represents, from top to bottom, the drain currents of the switching elements S1a and S1b, the PWM timer, the drain currents in a partially enlarged waveform from times t21 to t24, the PWM timer, the output voltage of the second comparing unit 72, and the value of k. Here, k is a value that is incremented each time an on signal is input from the second comparing unit 72 to the load adjusting unit 81, as described in the flowcharts of Figs. 6A and 6B.

[0094] As shown in Figure 8B, the PWM signal is turned on and off cyclically. At the start of a PWM cycle, the PWM timer value is set to zero, after which the PWM timer value increases linearly and monotonically, and at the end of the PWM cycle (i.e., at the start of the next PWM cycle), the PWM timer value returns to zero.

[0095] As shown by "sampling interval" in Fig. 8B, the control unit 80 (MCU) may read the output voltage of the second comparing unit 72 at a predetermined sampling interval (e.g., several microseconds) during one PWM period. Then, when the number of consecutive ON signals output from the second comparing unit 72 reaches a predetermined number (four times in the example of Fig. 8B) (corresponding to S102: Yes in Fig. 6A), the control unit 80 increments the value of k (S103 in Fig. 6A). By performing such processing, it is possible to prevent erroneous ON signal detection due to the influence of noise, etc.

[0096] FIG. 8C is an example of the operation of the power conversion device according to the modification of the first embodiment, and is a time chart relating to the motor current, the value of k, and the load adjustment flag (also see FIG. 4 as appropriate). The horizontal axis of each time chart in Fig. 8C represents time. The vertical axis of each time chart in Fig. 8C represents, from top to bottom, the motor current, the value of k, and the load adjustment flag. Here, the "load adjustment flag" is a flag that indicates whether or not load adjustment control is being executed.

[0097] 8C, in response to an ON signal from the second comparing unit 72, the value of k is sequentially incremented from time t31, and reaches k=3 (a first predetermined value, as an example) at time t32 (S104: Yes in FIG. 6A). Therefore, the control unit 80 switches the value of the load adjustment flag from 0 to 1 at time t32, and starts load adjustment control (S107 in FIG. 6A).

[0098] Furthermore, at time t32, when the load adjustment control starts, the control unit 80 resets k to 0 (S108 in FIG. 6B). In the example of FIG. 8C, the value of k is sequentially incremented from time t33 during the execution of the load adjustment control, and reaches k = 4 (S112: No in FIG. 6B). It is assumed that the second predetermined value in step S112 in FIG. 6B is set to, for example, 1. Therefore, at time t34, when a predetermined period has elapsed since the reset of k, the control unit 80 resets k to 0 (S113 in FIG. 6B) while continuing the load adjustment control, and further reduces the rotational speed of the motor M1. This reduces the drain current of the switching element, thereby suppressing heat generation in the switching element and suppressing its deterioration.

[0099] In the example of FIG. 8C, after the value of k is incremented to k=1 at time t35 (S111 in FIG. 6B), at time t36, a predetermined period after k was reset, k remains at 1 and is equal to or less than a second predetermined value (e.g., 1) (S112: Yes in FIG. 6B). Therefore, at time t36, the control unit 80 switches the value of the load adjustment flag from 1 to 0 and stops the load adjustment control. In the example of FIG. 8C, after the load adjustment control is stopped, the rotation speed of the motor M1 is maintained at the rotation speed at the time when the load adjustment control was stopped (time t36). Incidentally, in the example of FIG. 8C, the rotation speed of the motor M1 changes (decreases) over a time period corresponding to approximately three cycles of the motor current, but this is not limited to this. That is, FIG. 8C is merely an example, and it may take a longer time for the control unit 80 to change the rotation speed of the motor M1.

[0100] Second Embodiment The second embodiment differs from the first embodiment in that non-contact Hall sensors 61Aa, 61Ab, ... (see FIG. 9) are used as elements for detecting the current of the switching elements. Note that other configurations and processing contents are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0101] FIG. 9 is a configuration diagram including an inverter circuit 50 of a power conversion device 100A according to the second embodiment. 9, the power conversion device 100A includes non-contact Hall sensors 61Aa, 61Ab, 62Aa, 62Ab, etc. The Hall sensor 61Aa detects the drain current of the switching element S1a and is installed near the switching element S1a. The Hall sensor 61Aa has a Hall element (not shown) and is configured to detect a change in magnetic flux accompanying the drain current of the switching element S1a using the Hall element.

[0102] Similarly, the other Hall sensors 61Ab, 62Aa, 62Ab, etc. are provided in one-to-one correspondence with the switching elements S1b, S2a, S2b, etc. The detection values ​​of the Hall sensors 61Aa, 61Ab, 62Aa, 62Ab, etc. are output to a comparison unit 70. Note that the processing of the comparison unit 70 and the control unit 80 is the same as in the first embodiment, and therefore description thereof will be omitted.

[0103] Incidentally, a non-contact type magneto-impedance sensor (MI sensor, Magneto-Impedance Sensor) may be used instead of the non-contact type Hall sensors 61Aa, 61Ab, 62Aa, 62Ab, etc. A magneto-impedance sensor is a sensor that detects current by utilizing the magneto-impedance effect. The "magneto-impedance effect" mentioned above is a phenomenon in which the impedance of a magnetic material such as amorphous wire changes with a change in the magnetic field. Even when a magneto-impedance sensor is used in this way, the current of each of the switching elements S1b, S2a, S2b, etc. can be detected individually.

[0104] <Effects> According to the second embodiment, a non-contact type Hall sensor or magnetic impedance sensor is used to detect the current of the switching elements S1a, S1b, S2a, S2b, etc. Therefore, compared to the first embodiment in which a resistive element is used to detect the current, the generation of thermal energy is suppressed, thereby achieving low loss and high efficiency.

[0105] Third Embodiment The third embodiment differs from the first embodiment in that temperature sensors 61Ba, 61Bb, ... (see FIG. 10) are used as elements for detecting the current of the switching elements. Note that other configurations and processing contents are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0106] FIG. 10 is a configuration diagram including an inverter circuit 50 of a power conversion device 100B according to the third embodiment. As shown in FIG. 10, the power conversion device 100B includes temperature sensors 61Ba, 61Bb, 62Ba, 62Bb, etc. The temperature sensor 61Ba detects the surface temperature of the switching element S1a. For example, a Si diode or an NTC thermistor is used as the temperature sensor 61Ba. The temperature sensor 61Ba may be in contact with the switching element S1a or may not be in contact with the switching element S1a. Similarly, the other temperature sensors 61Bb, 62Ba, 62Bb, etc. are provided in one-to-one correspondence with the switching elements S1b, S2a, S2b, etc.

[0107] Furthermore, the "current detection unit" may have a temperature sensor (e.g., temperature sensor 61Ba) that individually detects the surface temperature of each switching element (e.g., switching element S1a), and the detected value of this temperature sensor may be converted into the value of the current of the switching element. The current value is output to the comparison unit 70. Alternatively, the detected value of the temperature sensor may be output directly to the comparison unit 70 without being converted into a current value. The same applies to the current detection of the other switching elements S1b, S2a, S2b, .... The processing of the comparison unit 70 and the control unit 80 is the same as in the first embodiment, so a description thereof will be omitted.

[0108] <Effects> According to the third embodiment, a temperature sensor is used to detect the current of the switching elements S1a, S1b, S2a, S2b, etc. Therefore, compared to the first embodiment in which a resistive element is used to detect the current, it is possible to achieve lower loss and higher efficiency.

[0109] Fourth Embodiment In the fourth embodiment, an air conditioner W1 (see FIG. 11) including the power conversion device 100 (see FIG. 1) configured as described in the first embodiment will be described. Note that the configuration and processing contents of the power conversion device 100 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0110] FIG. 11 is a configuration diagram of an air conditioner W1 according to the fourth embodiment. The solid arrows in FIG. 11 indicate the flow of the refrigerant in the heating cycle. The dashed arrows in FIG. 11 indicate the flow of refrigerant in the cooling cycle. The air conditioner W1 is a device that performs air conditioning such as cooling and heating. As shown in Fig. 11, the air conditioner W1 includes components provided in the outdoor unit U1, such as a compressor 91, an outdoor heat exchanger 92, an outdoor fan 93, an expansion valve 94, and a four-way valve 95. The air conditioner W1 also includes components provided in the indoor unit U2, such as an indoor heat exchanger 96 and an indoor fan 97.

[0111] Although not shown in Fig. 11, the air conditioner W1 is equipped with a power conversion device 100 (see Fig. 1) having the same configuration as that of the first embodiment. This power conversion device 100 is mounted on a circuit board (not shown) of the outdoor unit U1.

[0112] The compressor 91 is a device that compresses a low-temperature, low-pressure gas refrigerant and discharges it as a high-temperature, high-pressure gas refrigerant. For example, a scroll compressor or a rotary compressor is used as this compressor 91. Although not shown in Fig. 11, an accumulator for separating the refrigerant into gas and liquid is connected to the suction side of the compressor 91. A motor M1 that is a drive source of the compressor 91 is connected to the output side of the inverter circuit 50 (see Fig. 1) of the power conversion device 100 (see Fig. 1).

[0113] The outdoor heat exchanger 92 is a heat exchanger in which heat is exchanged between the refrigerant flowing through its heat transfer tubes and the outside air sent in from the outdoor fan 93. The outdoor fan 93 is a fan that sends outside air to the outdoor heat exchanger 92. The outdoor fan 93 has an outdoor fan motor 93a that serves as a drive source, and is installed near the outdoor heat exchanger 92.

[0114] The expansion valve 94 is a valve that reduces the pressure of the refrigerant condensed in the "condenser" (one of the outdoor heat exchanger 92 and the indoor heat exchanger 96). The refrigerant reduced in pressure by the expansion valve 94 is led to the "evaporator" (the other of the outdoor heat exchanger 92 and the indoor heat exchanger 96). The indoor heat exchanger 96 is a heat exchanger in which heat is exchanged between the refrigerant flowing through its heat transfer pipes (not shown) and the indoor air (air in the air-conditioned room) sent in from the indoor fan 97. The indoor fan 97 is a fan that sends the indoor air to the indoor heat exchanger 96. The indoor fan 97 has an indoor fan motor 97a that serves as a drive source, and is installed near the indoor heat exchanger 96.

[0115] The four-way valve 95 is a valve that switches the refrigerant flow path depending on the operating mode of the air conditioner W1. For example, during cooling operation (see the dashed arrow in FIG. 11), the refrigerant circulates sequentially through the compressor 91, outdoor heat exchanger 92 (condenser), expansion valve 94, and indoor heat exchanger 96 (evaporator). During heating operation (see the solid arrow in FIG. 11), the refrigerant circulates sequentially through the compressor 91, indoor heat exchanger 96 (condenser), expansion valve 94, and outdoor heat exchanger 92 (evaporator). The air that has exchanged heat with the refrigerant flowing through the indoor heat exchanger 96 is then blown out of the indoor unit U2 into the air-conditioned room.

[0116] <Effects> According to the fourth embodiment, the air conditioner W1 is equipped with the power conversion device 100 (see FIG. 1) having the same configuration as in the first embodiment, and therefore the reliability of the air conditioner W1 can be improved.

[0117] <<Variations>> The power conversion devices 100, 100A, 100B and the air conditioner W1 according to the present disclosure have been described in the above embodiments, but they are not limited to these descriptions and can be modified in various ways. For example, in the first embodiment, the inverter circuit 50 (see FIG. 2) includes a parallel connection of two switching elements, but this is not limiting. That is, the inverter circuit 50 may include a parallel connection of three or more switching elements. The same can be said for the second and third embodiments.

[0118] In the first embodiment, the detection values ​​of the current detection units 61a, 61b, etc. (see FIG. 2) and the two threshold values ​​V High ,V Low Although the comparison unit 70 compares the magnitudes of (see FIG. 3) and (see FIG. 3) in the above description, the present invention is not limited to this, and the number of threshold values ​​may be three or more. The same can be said for the second and third embodiments.

[0119] In the first embodiment, the inverter circuit 50 (see FIG. 2) is a three-phase inverter circuit having three legs, but the present invention is not limited to this. For example, a single-phase inverter circuit having two legs or a half-bridge circuit having one leg may be used as the inverter circuit.

[0120] Furthermore, in each embodiment, the AC power supply E1 (see FIG. 1) is a three-phase AC power supply, but the present invention is not limited to this, and a single-phase AC power supply may also be used. Furthermore, the second embodiment and the fourth embodiment may be combined, and in a configuration in which Hall sensors 61Aa, 61Ab, ... are used to detect current (second embodiment), the motor M1 connected to the inverter circuit 50 may be used as a drive source for the compressor 91 of the air conditioner W1 (fourth embodiment). Similarly, the third embodiment and the fourth embodiment may also be combined.

[0121] In the fourth embodiment (see FIG. 11), the power converter 100 (see FIG. 1) is connected to the motor M1 of the compressor 91, but the present invention is not limited to this. For example, the power converter 100 may be connected to the outdoor fan motor 93a (see FIG. 11). Furthermore, the power converter 100 may be connected to the motor M1 of the compressor 91, and the power converter 100 may be connected to the outdoor fan motor 93a.

[0122] Furthermore, in the fourth embodiment (see FIG. 11), a configuration has been described in which the air conditioner W1 is equipped with a four-way valve 95, but this is not limiting. That is, the four-way valve 85 may be omitted as appropriate, and the air conditioner may be dedicated to cooling or heating. The fourth embodiment (see FIG. 11) can be applied to various types of air conditioners, such as commercial air conditioners and multi-air conditioners for buildings, in addition to room air conditioners. The fourth embodiment can also be applied to other types of equipment, such as water heaters, refrigerators, and air-conditioning and hot water supply systems.

[0123] Furthermore, each embodiment has been described in detail to clearly explain the present disclosure, and is not necessarily limited to having all of the configurations described. Furthermore, some of the configurations of each embodiment can be added to, deleted from, or replaced with other configurations. Furthermore, the mechanisms and configurations described above are those that are considered necessary for the explanation, and do not necessarily represent all mechanisms and configurations of the product. [Explanation of symbols]

[0124] 10 Converter circuit 20 smoothing capacitor 30 DC voltage detection section 40 Shunt resistor 50 Inverter circuit 61a, 61b, 62a, 62b, 63a, 63b, 64a, 64b, 65a, 65b, 66a, 66b Current detection section 61Aa, 61Ab, 62Aa, 62Ab, 63Aa, 63Ab, 64Aa, 64Ab, 65Aa, 65Ab, 66Aa, 66Ab Hall sensor (current detection part) 61Ba, 61Bb, 62Ba, 62Bb, 63Ba, 63Bb, 64Ba, 64Bb, 65Ba, 65Bb, 66Ba, 66Bb Temperature sensor (current detection section) 70 Comparison Section 71 First Comparison Section 72 Second Comparison Section 80 Control Unit 81 Load adjustment section 82 Rotational speed control section 91 Compressor 92 Outdoor heat exchanger 93 Outdoor fan 94 Expansion valve 95 Four-way valve 96 Indoor heat exchanger 97 Indoor fan 100 Power conversion device E1 AC power supply K1, K2 DC lines M1 motor S107 Step (load adjustment control) S1a, S1b, S2a, S2b, S3a, S3b, S4a, S4b, S5a, S5b, S6a, S6b switching elements W1 Air Conditioner

Claims

1. an inverter circuit having a plurality of switching elements connected in parallel for each output phase, converting a DC voltage into an AC voltage and applying the AC voltage to a motor; a control unit that controls the inverter circuit; a current detection unit that individually detects the current flowing through each of the plurality of switching elements; a comparison unit that compares the detection value of the current detection unit with a plurality of threshold values ​​having different magnitudes for each of the plurality of switching elements; The control unit performs load adjustment control to reduce the rotation speed of the motor based on a result of the comparison by the comparison unit.

2. The comparison unit a first comparison unit that compares a detection value of the current detection unit with a plurality of threshold values ​​for each of the plurality of switching elements that are components of the parallel connection unit, and outputs a predetermined voltage corresponding to the comparison result; a second comparison unit which is a hysteresis comparator that outputs an ON signal or an OFF signal to the control unit based on the voltage output from the first comparison unit, the second comparison unit outputs an ON signal to the control unit when the voltage output from the first comparison unit becomes equal to or greater than a first threshold, and outputs an OFF signal to the control unit when the voltage becomes equal to or less than a second threshold after outputting the ON signal; The second threshold is set to a value lower than the first threshold. The power conversion device according to claim 1 .

3. The control unit performs the load adjustment control when the number of times that the second comparison unit outputs an ON signal becomes equal to or greater than a predetermined number of times during a period of multiple cycles of PWM control. The power conversion device according to claim 2 .

4. When the number of times that the second comparison unit outputs an ON signal becomes equal to or less than a predetermined number of times within a predetermined period after the load adjustment control is started, the control unit stops the load adjustment control and increases the rotation speed of the motor, or maintains the rotation speed of the motor at the rotation speed at the time when the load adjustment control was stopped. The power conversion device according to claim 2 .

5. The current value corresponding to the smallest one of the plurality of threshold values ​​having different magnitudes is set to a value smaller than the steady-state current after the switching element is turned on. The power conversion device according to claim 1 .

6. The current detection unit is a non-contact type Hall sensor or a non-contact type magnetic impedance sensor. The power conversion device according to claim 1 .

7. The current detection unit has a temperature sensor that detects the surface temperature of each of the switching elements individually, and converts the detected value of the temperature sensor into the value of the current. The power conversion device according to claim 1 .

8. The power conversion device according to any one of claims 1 to 7 is provided, The air conditioner includes a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger. The air conditioner, wherein the motor serving as a drive source for the compressor is connected to the output side of the inverter circuit.

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