Modulation signal generation device

Abstract

To set a non-conductive section of upper side and lower side conduction elements constituting a power conversion unit even when a signal which can be used for carrier waves of modulation control is limited.SOLUTION: A modulation signal generation device of an embodiment comprises: a current detection unit constituted by connecting three sets of upper side and lower side conduction elements in parallel with one another to detect three-phase current flowing to a power conversion unit which converts DC power into AC power to drive a three-phase electric motor; and a signal generation unit which generates a three-phase modulation signal to be output to the power conversion unit on the basis of the current. The signal generation unit comprises: a clock unit; and a non-conductive section setting unit which uses a specific phase of carrier waves used for generation of the modulation signal as a reference phase, starts clocking by the clocking part at a point of time of the reference phase, and sets a non-conductive section for making both of the upper side and lower side conduction elements into a non-conductive state in the modulation signal according to a clock value by the clock unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a modulation signal generating device that drives a three-phase electric motor by modulation signal control. [Background technology]

[0002] For example, when a three-phase pulse width modulation (PWM) signal, which is a rectangular wave modulation signal, is output to an inverter circuit to drive a motor, it is necessary to prevent switching elements such as MOSFETs that constitute the upper and lower arms of the inverter circuit from simultaneously turning on, causing a short-circuit current to flow. Therefore, when switching the upper and lower arms on and off, it is common to provide a period during which the upper and lower arms are simultaneously off, known as a dead time. Furthermore, when detecting the current flowing through the motor to control it, a method known as a single-shunt current detection method is used, in which only one resistive element is placed in the DC section of the inverter circuit and the three-phase current is detected from the current flowing through that resistive element.

[0003] Compared to the three-shunt method, the one-shunt current detection method has a limited timing for detecting three-phase currents, so a method for improving the current detection rate by shifting the pulse phase of the three-phase PWM signal has been proposed, for example, in Patent Document 1. Hereinafter, this method will be referred to as the shifted PWM method.

[0004] Patent Document 1 also mentions the generation of dead time, but does not disclose the specific method by which the dead time is generated. It is assumed that Patent Document 1 uses a dedicated microcomputer that generates PWM signals, and that the microcomputer hardware is equipped with a function that can automatically set the dead time.

[0005] Another shift PWM method is shown in Figure 15. This method achieves two-phase modulation by setting the duty ratio of one of the three phases to 0% or 100% every two cycles. This method utilizes the so-called two-phase modulation upper and lower arm method, which inverts the duty value of one of the modulated phases to shift the energized phase by 180 degrees. A triangular wave is used as the carrier wave, and the phase current is converted to analog and digital form and sampled at the timings when the triangular wave reaches its minimum value (bottom) and its maximum value (peak). As shown by the hatching in the figure, pulse shift is achieved by inverting the PWM signal of the phase to be sampled at the bottom of the triangular wave every two cycles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-32403 Summary of the Invention [Problem to be solved by the invention]

[0007] Let's consider setting a dead time for the PWM signal generated by the two-phase modulation upper and lower arm method. Patent Document 1 also discloses using carrier waves with different waveforms for each phase to achieve the shift PWM method. While this allows for more diverse settings for the timing of the signal waveform, more common microcontrollers have limited hardware resources for generating the carrier waves.

[0008] For example, as shown in Figure 16, assume that a triangular wave A is used as the carrier wave, and a triangular wave B, which has the same frequency as triangular wave A but a certain amplitude greater than that of triangular wave A, is used to generate the dead time. As a result, a dead time section is generated in which both the upper and lower arms are off, as shown in the figure.

[0009] However, in the two-phase modulation upper and lower arm method, if PWM signals with the same waveform are inverted, both the upper and lower arms will turn on and a through current will flow, as shown in Figure 17. Therefore, this method cannot be applied. Therefore, a modulation signal generating device is provided that can set non-conducting sections of the upper and lower conductive elements that make up the power conversion unit even when signals that can be used as carrier waves for modulation control are limited. [Means for solving the problem]

[0010] The modulation signal generating device of the embodiment includes a current detecting unit that detects three-phase currents flowing in a power converting unit that converts DC power into AC power and drives a three-phase motor, the power converting unit including three pairs of upper and lower conductive elements connected in parallel; a signal generating unit that generates a three-phase modulation signal to be output to the power converting unit based on the current, The signal generation unit A timing unit; a non-conduction section setting unit that sets a non-conduction section in the modulated signal, in which a specific phase of a carrier wave used to generate the modulated signal is set as a reference phase, causes the timer unit to start timing at the point of the reference phase, and sets a non-conduction section in the modulated signal, in which both the upper conductive element and the lower conductive element are in a non-conduction state, according to a time value measured by the timer unit; Equipped with. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a functional block diagram illustrating a configuration of a PWM signal generating unit according to a first embodiment. [Figure 2] A diagram showing the selector of the output control section [Figure 3] A block diagram showing a functional section that performs vector control in a control device. [Figure 4] Flowchart (part 1) showing the processing performed by the PWM signal generator [Figure 5] Flowchart (part 2) showing the processing performed by the PWM signal generator [Figure 6]FIG. 1 is a diagram showing sectors corresponding to a two-phase modulation upper and lower arm system, and the phase currents detected or calculated corresponding to each sector. [Figure 7] A diagram showing the priority levels of each interrupt cause [Figure 8] An example of a timing chart corresponding to the processing in the flowchart (part 1) [Figure 9] Figure 2 shows an example of a timing chart corresponding to the processing in the flowchart. [Figure 10] A timing chart showing an example of a section in which a dead time is set. [Figure 11] A diagram showing an example of a normal PWM method that is intended for switching between medium and high speed ranges of a motor [Figure 12] FIG. 1 is a longitudinal sectional front view showing a schematic configuration example of a refrigerator; [Figure 13] FIG. 1 is a diagram showing a schematic configuration example of a refrigeration cycle of a refrigerator. [Figure 14] Diagram showing the conventional two-phase modulation upper and lower arm method [Figure 15] FIG. 10 is a diagram illustrating a configuration for providing a dead time in an output protection unit according to a second embodiment. [Figure 16] FIG. 1 shows an example of a waveform before inversion of the comparison result between the modulated wave and the carrier wave in a two-phase modulation upper and lower arm system. [Figure 17] FIG. 10 is a diagram showing an example of a waveform obtained by inverting the comparison result. DETAILED DESCRIPTION OF THE INVENTION

[0012] (First embodiment) A first embodiment will be described below with reference to FIGS. 1 to 13. The motor to be driven in this embodiment is assumed to be a motor built into a compressor that constitutes the refrigeration cycle of a refrigerator, so the refrigerator will be described first. A refrigerator 10 shown in FIG. 12 includes a rectangular insulated box 11 that forms the outer shell of the refrigerator. Various items, such as food, can be stored inside the storage boxes 12, 13, 14, and 15. While not shown in detail, the insulated box 11 includes a thermal insulator between the inner box and the outer box. The thermal insulator for the insulated box 11 can be, for example, a vacuum insulation panel, urethane foam, or a thermally insulated molded body made of a thermally insulating material.

[0013] The front openings of the storage compartments 12, 13, 14, and 15 are configured to be openable and closable by storage compartment doors (not shown). The storage compartment doors (not shown) may be, for example, pivotable storage compartment doors that are provided to be pivotable in the left-right direction, or drawer-type storage compartment doors that are provided to be movable in the front-rear direction.

[0014] In this case, the storage compartment 12 is a refrigerator compartment maintained in a refrigerator temperature range. Hereinafter, the storage compartment 12 may be referred to as the "refrigerator compartment 12." In this case, the storage compartment 13 is a switchable compartment maintained in a refrigerator temperature range. Hereinafter, the storage compartment 13 may be referred to as the "switchable compartment 13." In this case, the switchable compartment 13 is provided inside the refrigerator compartment 12. That is, the switchable compartment 13 is formed by partitioning off a portion of the space inside the refrigerator compartment 12. The switchable compartment 13 is a storage compartment known as a "chilled compartment." Note that the switchable compartment 13 may be provided outside the refrigerator compartment 12. That is, the switchable compartment 13 may be an independent storage compartment separate from the refrigerator compartment 12.

[0015] In this case, storage compartment 14 is a freezing compartment maintained in the freezing temperature range. Hereinafter, storage compartment 14 may be referred to as "freezing compartment 14." In this case, storage compartment 15 is an ice-making compartment maintained in the freezing temperature range. Hereinafter, storage compartment 15 may be referred to as "ice-making compartment 15." In this case, ice-making compartment 15 is provided as an independent storage compartment separate from freezing compartment 14. Note that ice-making compartment 15 may be provided inside freezing compartment 14. In other words, ice-making compartment 15 may be formed by partitioning off a portion of the space within freezing compartment 14.

[0016] The refrigerator 10 also includes a refrigeration cycle 20 illustrated in Fig. 13. The refrigeration cycle 20 configures a circulation cycle in which a compressor 21, a radiator 22, a switching valve 23, a refrigeration throttle 24, a refrigeration cooler 25, a freezing throttle 26, and a freezing cooler 27 are connected by a refrigerant pipe 28. The compressor 21 compresses the refrigerant and sends it under pressure to the radiator 22. The radiator 22 receives the refrigerant sent from the compressor 21 and radiates heat.

[0017] The switching valve 23 is a three-way valve with one inlet and two outlets, and is configured to be switchable between a refrigeration switching state in which the refrigerant flowing in from the radiator 22 flows out to the refrigeration cooler 25 side, and a freezing switching state in which the refrigerant flows out to the freezing cooler 27 side. When the switching valve 23 is switched to the refrigeration switching state, the refrigerant is supplied to the refrigeration cooler 25 via the refrigeration throttle 24. This cools the refrigeration cooler 25. The refrigerant that has passed through the refrigeration cooler 25 is returned to the compressor 21.

[0018] On the other hand, when the switching valve 23 is switched to the freezing switching state, the refrigerant is supplied to the freezing cooler 27 via the freezing throttle 26. This cools the freezing cooler 27. Then, the refrigerant that has passed through the freezing cooler 27 is returned to the compressor 21. A check valve 29 is provided in the refrigerant pipe 28 at a portion connecting the compressor 21 and the refrigeration cooler 27. The check valve 29 prevents the refrigerant from flowing back from the compressor 21 side to the refrigeration cooler 27 side.

[0019] Refrigerator 10 also includes a refrigeration blower and a freezing blower (not shown). Refrigerator 10 is configured to be able to supply cold air generated by refrigeration cooler 25 into at least one of storage compartments, refrigeration compartment 12 and switchable compartment 13, by driving the refrigeration blower when refrigeration cycle 20 is cooling refrigeration cooler 25. Refrigerator 10 is also configured to be able to supply cold air generated by refrigeration cooler 27 into at least one of storage compartments, refrigeration compartment 14 and ice-making compartment 15, by driving the refrigeration blower when refrigeration cycle 20 is cooling refrigeration cooler 27.

[0020] The motor 30 corresponding to the electric motor shown in FIG. 3 is a so-called compressor motor built into the compressor 21. The figure shows, in functional blocks, a configuration that mainly performs vector control calculations in a control device 31 that controls the motor 30. A q-axis current command Iqref and a d-axis current command Idref are input to current control units 32q and 32d, respectively. The q-axis current command Iqref is generated, for example, by performing a proportional integral (PI) calculation on the difference between a speed command ωref input from a higher-level device or the like and a motor speed ω obtained, for example, from a rotor position estimation unit 33, so that they coincide with each other. The d-axis current command Idref is set to a negative value when the motor 30 is, for example, a brushless DC motor and is subjected to field-weakening control, but is set to zero otherwise.

[0021] The current control unit 32 generates and outputs q-axis and d-axis voltage commands Vq and Vd by, for example, performing PI calculation on the difference between the input q-axis current command Iqref and d-axis current command Idref and the currents Iq and Id input from the rotational coordinate conversion unit 34. The three-phase to two-phase conversion unit 35 converts the phase currents Iu, Iv, and IW detected by the shunt resistor 36, amplifier 37, ADC, and three-phase current detection unit 38, which correspond to the current detection unit, into orthogonal currents Iα and Iβ. Based on the rotation angle θ of the rotor estimated by the rotor position estimation unit 33, the rotation coordinate conversion unit 34 converts the orthogonal currents Iα and Iβ into currents Iq and Id of the q-axis and d-axis coordinates used for vector control.

[0022] A fixed coordinate conversion unit 39 converts d-axis and q-axis voltage commands Vd and Vq into orthogonal voltage commands Vα and Vβ based on the rotation angle θ. A space vector conversion unit 40 converts the orthogonal voltage commands Vα and Vβ into three-phase voltage commands Vu, Vv, and Vw, and generates three-phase PWM signals U, V, W, X, Y, and Z from these three-phase voltage commands. These signals are output to a motor driver 41. The motor driver 41 is an inverter circuit, and is configured by connecting three arms, each of which has a series connection of switching elements such as MOSFETs, in parallel for three phases. A DC power supply (not shown) is connected to the motor driver 41, which is a power conversion unit, as a driving power supply. The motor driver 41 converts DC power to AC power to drive the motor 30. Hereinafter, the switching elements on the power supply side of each arm will be referred to as upper arms corresponding to upper conductive elements, and the switching elements on the ground side will be referred to as lower arms corresponding to lower conductive elements.

[0023] A shunt resistor 36, which is a current detection element, is connected between the lower arm and ground. The terminal voltage of the shunt resistor 36 is amplified by an amplifier 37 and input to an ADC and a three-phase current detection unit 38. In this embodiment, two-phase currents are directly detected within the carrier wave period of PWM control, and the third-phase current is calculated by the three-phase current detection unit 38.

[0024] FIG. 1 shows the configuration of the PWM signal generation unit 42 built into the space vector conversion unit 40. The PWM signal generation unit 42 corresponds to the signal generation unit. The PWM signal generation unit 42 plus the shunt resistor 36, amplifier 37, ADC, and three-phase current detection unit 38 corresponds to the modulation signal generation device. The comparison unit 43 receives a triangular carrier wave signal generated by a carrier wave generation unit 44 and modulation wave signals for the U, V, and W phases. Hereinafter, these will be referred to as the carrier wave and modulation wave, respectively. The comparison unit 43 compares the levels of these modulation waves for each phase with the level of the carrier wave, and when it generates three-phase PWM signals as coincidence signals, it outputs these PWM signals to the output control unit 45.

[0025] In this embodiment, the modulation control is square wave width modulation control, and the modulation signal is a PWM signal. PWM control corresponds to square wave width modulation control, and the PWM signal corresponds to a square wave width modulation signal. The carrier wave generating unit 44 can also be called a carrier wave generating unit, and the carrier wave it generates is not limited to a triangular wave, and may be another waveform such as a sawtooth wave.

[0026] The output control unit 45 includes a dead time generation unit 46 corresponding to the non-energized section setting unit. The dead time generation unit 46 includes a counter 47, an interrupt generation unit 48, a dead time setting unit 49, and registers E, S, and C. The counter 47, which is a timing unit, counts using the same clock signal as the carrier wave generation unit 44. A carrier wave is input to the interrupt generation unit 48, and the above-mentioned coincidence signal is input to the dead time setting unit 49. The register values ​​of registers E, S, and C are also input to the interrupt generation unit 48.

[0027] The interrupt generating unit 48 generates a bottom interrupt INT_B and a top interrupt INT_T by comparing the value of the carrier wave with the minimum and maximum values ​​of the carrier wave amplitude. That is, the bottom interrupt INT_B occurs at the timing of the bottom when the amplitude value of the carrier wave is at its minimum, and the top interrupt INT_T occurs at the timing of the top when the amplitude value is at its maximum. These interrupt signals are input to the counter 47. The counter 47 starts counting operation using the input of these interrupt signals as a trigger. The phases at which the carrier wave amplitude indicates its minimum and maximum values ​​correspond to a specific reference phase. The bottom interrupt INT_B and top interrupt INT_T correspond to reference phase interrupts.

[0028] The interrupt generating unit 48 also generates interrupts INT_E, INT_S, and INT_C by comparing the value of the carrier wave with the values ​​of registers E, S, and C. These interrupt signals are input to a dead time setting unit 49. The interrupt generating unit 48 also generates an AD conversion end interrupt INT_AD with a timing slightly delayed from the timing of generation of the bottom interrupt INT_B. The dead time setting unit 49 sets dead times corresponding to the non-energized sections in the three-phase PWM signals based on the interrupts INT_E, S, and C. Details of these operations will be described later.

[0029] The output control unit 45 outputs three-phase PWM signals to which dead times generated by the dead time generation unit 46 are added. These PWM signals are output as gate signals to the six switching elements that make up the motor driver 41 via the output protection unit 50. The output protection unit 50 has a function of cutting off the output of the PWM signals when an abnormality such as an overcurrent is detected.

[0030] The output control unit 45 also includes a selector 51 (see FIG. 2). The PWM signal with the dead time is output via a general-purpose port, which is an internal terminal. Meanwhile, the PWM signal without the dead time, i.e., the match signal output by the comparator 43, is also output via a dedicated port, which is an internal terminal. Hereinafter, the match signal may be referred to as a complementary PWM signal. The "0" side of the selector 49, which corresponds to the selector, is connected to a general-purpose port, and the "1" side is connected to a dedicated port. The "0" or "1" side of the selector 51 is selected by writing the corresponding value to the port function switch register 52, and the input signal on the selected side is output to an external terminal, i.e., the output protection unit 50. The functions of the control device 31 shown in FIGS. 1 to 3 are realized by the cooperation of hardware and software functions constituting a microcomputer.

[0031] Next, the operation of this embodiment will be described with reference to Figs. 4 to 11. The PWM signal is generated by a two-phase modulation upper and lower arm method shown in Fig. 14. Figs. 4 and 5 are flowcharts showing the processing mainly performed by the dead time generation unit 46 of the control device 31. Hereinafter, the interrupt INT_B will be referred to as a "bottom interrupt," and the interrupt INT_T will be referred to as a "top interrupt." Also, the AD conversion end interrupt INT_AD will be referred to as an "AD conversion end interrupt."

[0032] First, when a bottom interrupt occurs (S1; YES), the counter 47 is cleared and started, and the energized phase to be two-phase modulated is determined according to the sector determination result. As shown in Fig. 6, the sectors are modulated by the upper and lower arm method of two-phase modulation, and one cycle in which the phase with a duty ratio set to 0% or 100% switches from V to W to U is divided into 12 equal parts, resulting in sectors 0 to 11. For example, the energized phases in sectors 1 to 4 are the U and W phases.

[0033] 6 also shows two-phase currents directly detected by AD conversion in each sector, and the current of the remaining phase calculated by the ADC and three-phase current detection unit 38. In the figure, Idc1 and Idc2 are currents Ib and It obtained by AD conversion at the bottom and top of the carrier wave, respectively (b and t are u, v, or w), and Idc0 is zero. −(Ib+It) is the third-phase current calculated from the currents Ib and It.

[0034] In step S2, the values ​​of registers E and S are calculated (S2). Register E is a register that sets the interrupt timing near the end of the conduction period of the current conduction phase, and register S is a register that sets the interrupt timing near the start of the conduction period of the next conduction phase. The values ​​of registers E and S are set to a value that slightly reduces the pulse width from the bottom of the carrier wave to the pulse edge corresponding to the duty ratio. This causes the dead time period to start from the timing immediately before the arrival of the pulse edge.

[0035] Next, when an AD conversion end interrupt occurs (S3; YES), a vector control calculation is executed (S4). Since AD ​​conversion is performed at the timing when the top interrupt and bottom interrupt occur, the interrupt generating unit 48 generates an AD conversion end interrupt when a predetermined time has elapsed since the bottom interrupt. As a result of the vector control calculation, the duty ratio of the PWM signal to be used in the next cycle is determined.

[0036] Next, it is determined whether the absolute value of the difference between the values ​​of registers E and S is equal to or less than a certain value (S5). As will be described later, the interrupt generation unit 48 compares the values ​​of registers E and S with the count value of counter 47, and if the two match, a so-called compare match interrupt is generated. The compare match interrupt generated by register E is interrupt INT_E, and the compare match interrupt generated by register S is interrupt INT_S. Hereinafter, these will be referred to as interrupts E and S. These are interval generation interrupts, corresponding to the end point interrupt and the start point interrupt, respectively. If the timing of the occurrence of interrupts E and S is too close, the respective interrupt processes will interfere with each other, and it may be impossible to provide the dead time as intended. Therefore, the certain value here is set as a threshold value at which it becomes impossible to set the dead time as intended in response to the occurrence of each of interrupts E and S.

[0037] If the absolute value of the difference is not equal to or less than a certain value (S5; NO), the dead time setting unit 49 sets (S20) a dead time in which the upper and lower arm outputs are turned off for a certain period of time from the time when interrupt E occurs (S19; YES). Next, from the time when interrupt S occurs (S23; YES), the dead time is set in the same manner (S24).

[0038] If the absolute value of the difference is equal to or less than a certain value (S5; YES), the interrupt generating unit 48 compares the values ​​of registers E and S (S6). If the former value is greater (YES), interrupt S will occur first, but the processing of interrupt E, which occurs later, will interfere with the processing of interrupt S. Therefore, interrupt E is prohibited from occurring (S7), and a dead time is set (S9) from the point in time when interrupt S occurs (S8; YES). The timing chart shown in FIG. 9 illustrates a case where the dead time is set in step S9. In this case, the dead time is set longer than when it is normally set in step S24, taking into account the time difference between the interrupts.

[0039] On the other hand, if the value of register E is equal to or less than the value of register S (S6; NO), the opposite of the above occurs: interrupt E occurs first, but the processing of interrupt S that occurs after that interferes with the processing of interrupt E. Therefore, the generation of interrupt S is prohibited (S21), and a dead time is set (S9) from the point when interrupt E occurs (S22; YES).

[0040] In step S10 following step S9, it is determined whether there will be a change in the conduction phase when the next top interrupt occurs. The change in the conduction phase when the top interrupt occurs corresponds to the timing of transitions from sector 0 to 1, sector 2 to 3, sector 4 to 5, sector 6 to 7, sector 8 to 9, and sector 10 to 11 shown in FIG. 6. If it corresponds to one of these transition timings (S10; YES), a dead time is set (S12) from the time when interrupt C occurs (S11; YES). Interrupt C is generated by a compare match of the value of register C.

[0041] The timing of the above switching is the point at which a top interrupt occurs. Therefore, the value of register C is set to a fixed value so that it is the timing just before the carrier amplitude reaches its maximum value. Note that FIG. 8 does not show the timing of switching the energized phase, but shows the dead time set by steps S11 and S12. Then, the process proceeds to step S13. Also, if the determination in step S10 is "NO," the process proceeds to step S13.

[0042] When a top interrupt occurs (S13; YES), counter 47 is cleared and started as in step S2, and the values ​​of registers E and S are calculated (S14). In addition, the values ​​of the modulated waves of each energized phase, which were calculated by the vector control calculation in step S4 and are to be used in the next carrier cycle, are updated. In the following steps S15 to S18, the same processes as in steps S19, S20, S23, and S24 are performed, and then the process returns to step S1.

[0043] The intervals in which the dead time is set by the above processing are shown, for example, in Figures 8 and 9. The "W-phase modulated wave [shift]" in the figures indicates that the W-phase modulated wave is set to 100% or 0%. Therefore, the signal generation logic is reversed between the U-phase upper and lower arm signals and the W-phase upper and lower arm signals. In Figure 10, the intervals in which the dead time is set over two periods of the carrier wave are indicated by hatching.

[0044] 7 shows an example of the priority levels of each interrupt cause in the above process. The bottom interrupt and top interrupt have the highest priority level of "14", the interrupts C, E, and S caused by compare matches of registers C, E, and S have a priority level of "13", and the AD conversion end interrupt has a priority level of "12".

[0045] It is also possible to apply the above-described two-phase modulation upper and lower arm method and shift PWM method to the startup and low-speed regions of the motor 30, and then apply the normal PWM method shown in Fig. 11 to the medium and high-speed regions following the low-speed region. This normal PWM method is the same two-phase modulation as the shift PWM method, but the duty ratio of the W phase is set to 0% during the period when the current conduction phases are the U and V phases, the duty ratio of the U phase is set to 0% during the period when the current conduction phases are the V and W phases, and the duty ratio of the V phase is set to 0% during the period when the current conduction phases are the W and U phases.

[0046] The current detection trigger, i.e., the timing for AD conversion, is set twice, starting from the bottom of the carrier amplitude. For example, during the period when the current is conducted to the U and V phases, the negative W-phase current is detected when both U and V are on, and the U-phase current is detected when only the U-phase is conducted. Furthermore, instead of the method shown in FIG. 11, for example, by applying the third embodiment shown in FIGS. 14 and 15 of Patent Document 1, a shift PWM method may be performed with three-phase modulation using only a triangular wave as a carrier.

[0047] As described above, according to this embodiment, the ADC and three-phase current detection unit 38 detects three-phase currents flowing through the motor driver 41 that drives the motor 30, based on the voltage generated across the shunt resistor 36. The PWM signal generation unit 42 generates three-phase PWM signals to be output to the motor driver 41 based on the three-phase currents. The PWM signal generation unit 42 also includes a dead time generation unit 46. The dead time generation unit 46 starts timing with the counter 47 at the reference phase when the amplitude of the single carrier wave used to generate the PWM signal indicates the minimum and maximum values, and sets a dead time in the PWM signal according to the count value of the counter 47. Therefore, even if the microcomputer constituting the PWM signal generating unit 42 has limited hardware resources for generating a carrier wave, the dead time can be set at any timing by software processing.

[0048] The ADC and three-phase current detection unit 38 performs AD conversion on the current detected by the shunt resistor 36. The PWM signal generation unit 42 generates a PWM signal based on the bottom interrupt, top interrupt, interrupts E and S generated based on the counting operation of the counter 47, and the AD conversion end interrupt. The relative priorities of the three interrupts are set as follows: bottom interrupt and top interrupt first, interrupts E and S second, and AD conversion end interrupt third. This ensures that processing corresponding to the bottom interrupt and top interrupt, which are the reference timing for generating dead time, can be executed reliably. Even if there are interrupt causes other than the above three, the bottom interrupt and top interrupt are set to the highest priority.

[0049] Furthermore, if the time difference between the occurrence of interrupts E and S is shorter than the set dead time, the dead time generation unit 46 prohibits the later occurring interrupt and sets the dead time starting from the earlier occurring interrupt. This prevents the later occurring interrupt processing from interfering with the earlier occurring interrupt processing, and allows the dead time to be set reliably.

[0050] (Second embodiment) The second embodiment shown in FIG. 14 describes a case where the dead time is set using the function of the output protection unit 50. As described above, the output protection unit 50 has the function of cutting off the output of the PWM signal when an abnormality such as an overcurrent is detected. For this reason, for example, as shown in FIG. 14, the signal input from the output control unit 45 is received on the "0" side of the selector 53, and the "1" side is set to ground level. The arm output protection switch 54 normally selects the "0" side, but when an abnormality is detected, it selects the "1" side, simultaneously turning off the upper and lower arms to a non-conductive state, i.e., turning them off, cutting off the output of the motor driver 41. Note that the selector 53 may cut off all phases at once or cut off each phase individually.

[0051] Using the above function, set the dead time as follows: In the selector 51 shown in FIG. 2, the complementary PWM signal on the "1" side is selected. The arm output protection switch 54 is controlled by the interrupts E, S, and C generated by the interrupt generating unit 48, and the selector 53 is set to "1" for a certain period of time at the timing of each interrupt occurrence. This allows dead time to be added.

[0052] Here, including the first and second embodiments, the methods assumed when setting a dead time in a PWM signal using the functions of a microcomputer will be roughly classified as follows. Dead time setting by complementary PWM output (mainly microcontroller hardware) Dead time setting by interrupt and general-purpose port function (mainly microcontroller software) Dead time setting by interrupt and function to turn off each phase arm output (software-based) Dead time setting by interrupt and function to turn off all phase arm output (software-based)

[0053] (Other embodiments) The carrier wave used for PWM control does not necessarily have to be limited to a triangular wave, and it is not necessarily required to use only one waveform signal. The current detection element is not limited to one that uses only one shunt resistor 36, and may be applied to, for example, a three-shunt current detection method. The counter 47 may be located outside the dead time generating unit 46 . Instead of the rotor position estimation unit 33, a rotational position sensor may be used.

[0054] The compressor incorporating the electric motor is not necessarily limited to one that constitutes a heat exchanger applied to a refrigerator, but may be one that is applied to other equipment such as an air conditioner or a washing machine. Furthermore, the modulation signal generating device is not limited to being applied to an electric motor built into a compressor motor.

[0055] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0056] In the drawing, 10 denotes a refrigerator, 20 denotes a refrigeration cycle, 21 denotes a compressor, 31 denotes a motor, 36 denotes a shunt resistor, 38 denotes an ADC and three-phase current detection unit, 40 denotes a space vector conversion unit, 41 denotes a motor driver, 42 denotes a PWM signal generation unit, 43 denotes a comparison unit, 44 denotes a carrier wave generation unit, 45 denotes an output control unit, 46 denotes a dead time generation unit, 47 denotes a counter, 48 denotes an interrupt generation unit, 49 denotes a dead time setting unit, and 51 denotes a selector.

Claims

1. a current detection unit configured by connecting three pairs of upper and lower conduction elements in parallel, the current detection unit detecting three-phase currents flowing in a power conversion unit that converts DC power into AC power to drive a three-phase motor; a signal generating unit that generates a three-phase modulation signal to be output to the power converting unit based on the current, The signal generation unit A timing unit; a non-conduction section setting unit that sets a non-conduction section in the modulated signal, in which a specific phase of a carrier wave used to generate the modulated signal is set as a reference phase, causes the timer unit to start timing at the point of the reference phase, and sets a non-conduction section in the modulated signal, in which both the upper conductive element and the lower conductive element are in a non-conduction state, according to a time value measured by the timer unit; A modulation signal generating device comprising:

2. 2. The modulated signal generating device according to claim 1, wherein said signal generating section uses only one of said carrier waves.

3. The current detection unit converts the detected current value into a numerical value, The signal generating unit generates a reference phase interrupt at the time of the reference phase; a section generation interrupt that is generated based on the time measurement by the time measurement unit; generating the modulated signal by processing based on a conversion interrupt generated at the end of the conversion; 2. The modulation signal generating device according to claim 1, wherein the priority of the three interrupts is set so that the reference phase interrupt is first, the section generation interrupt is second, and the conversion interrupt is third.

4. the non-energized section setting unit generates, as the section generation interrupt, an end point interrupt which is generated in response to an end point of a current energized phase and a start point interrupt which is generated in response to a start point of a next energized phase; A modulation signal generating device as described in claim 3, wherein when the time difference between the occurrence of the end point interrupt and the occurrence of the start point interrupt is shorter than the non-powered interval set under normal circumstances, the interrupt that occurs later is prohibited and the non-powered interval is set using the interrupt that occurs earlier as the starting point.

5. an output cutoff unit that turns off upper and lower conductive elements of all or each phase when an abnormality is detected in the power conversion unit; the signal generating unit has a dedicated internal terminal for outputting a complementary modulated signal generated by comparing the carrier wave with the modulated wave of each phase; The modulation signal having the non-energized section set therein is output via a general-purpose internal terminal, a selection unit that selects either the dedicated internal terminal or the general-purpose internal terminal and connects it to an external terminal; 2. The modulation signal generating device according to claim 1, wherein the selection unit selects the dedicated internal terminal, and the output cutoff unit is used as a functional unit for setting the non-energized section in the non-energized section setting unit.

6. the current detection unit includes one current detection element disposed in a DC part of the power conversion unit, 2. The modulation signal generating device according to claim 1, wherein the three-phase currents are detected based on a voltage generated in the current detecting element.

7. 7. The modulation signal generating device according to claim 1, wherein the electric motor is built in a compressor that constitutes a device that circulates a refrigerant to perform heat exchange.

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