Inverter unit and indoor unit

Abstract

To provide an inverter device that can suppress power loss. [Solution] The inverter device comprises a boost circuit, an inverter circuit, a boost circuit control unit, and an inverter circuit control unit. The boost circuit increases the voltage of the DC power. The inverter circuit converts the DC power increased by the boost circuit into AC power and supplies it to the motor. The boost circuit control unit controls the boost circuit. The inverter circuit control unit controls the inverter circuit. In the second region, the inverter circuit control unit controls the motor with one pulse. In the second region, the motor load is higher than in the first region. In the first region, the boost circuit control unit does not boost the voltage in the boost circuit. In the second region, the boost circuit control unit continuously boosts the voltage in the boost circuit so that the boosting speed is less than or equal to a predetermined first value.

Description

Technical Field

[0001] It relates to an inverter device.

Background Art

[0002] Patent Document 1 (Japanese Patent Laid-Open No. 2012-110088) describes an inverter device that performs a control method generally called one-pulse control. In one-pulse control, by setting the voltage command as a rectangular wave, the number of switchings can be significantly reduced, and power loss can be suppressed. Conventionally, in an inverter device that performs this one-pulse control, in order to suppress power loss, when the required voltage of the load is low, normal PWM control is performed, and when the required voltage of the load rises and approaches rated operation, one-pulse control is performed.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In the method of Patent Document 1, on the contrary, power loss may increase.

Means for Solving the Problems

[0004] The inverter device of the first aspect includes a boost circuit, an inverter circuit, a boost circuit control unit, and an inverter circuit control unit. The boost circuit boosts the voltage of the DC power. The inverter circuit converts the DC power boosted by the boost circuit into AC power and supplies it to the motor. The boost circuit control unit controls the boost circuit. The inverter circuit control unit controls the inverter circuit. The inverter circuit control unit performs one-pulse control on the motor in the second region. In the second region, the load of the motor is higher than that in the first region. The boost circuit control unit does not boost the boost circuit in the first region. The boost circuit control unit continuously boosts the boost circuit so that the boost speed becomes a predetermined first value or less in the second region.

[0005] According to this inverter device, voltage loss can be suppressed.

[0006] The inverter device of the second perspective is the inverter device of the first perspective, and the first value is 0.2 to 1.0 V / 10 msec.

[0007] The inverter device in the third perspective is an inverter device in the first or second perspective, which maintains a boosted voltage in the third region. In the third region, the motor load is higher than in the second region.

[0008] The inverter device in the fourth perspective is an inverter device of any of the first to third perspectives, and in the first region, the inverter circuit control unit performs PWM control. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram illustrates a conceptual configuration of an inverter device. [Figure 2] This figure shows how the DC voltage output from the boost circuit and the inverter output voltage output from the inverter circuit change in response to the compressor load. [Figure 3] This figure shows an example of a voltage command value for single-pulse control. [Figure 4] This figure shows an example of a voltage command value for 6-step control. [Figure 5] This figure shows an example of voltage command value, carrier, and output voltage. [Figure 6] This figure shows an example of voltage command value, carrier, and output voltage. [Figure 7] This figure shows an example of a voltage command value. [Figure 8] This figure shows an example of a voltage command value. [Figure 9] This figure shows a comparison between PWM control and single-pulse control. [Figure 10] This figure shows an example of voltage command values, carriers, and output voltages in a 6-step control system. [Modes for carrying out the invention]

[0010] Embodiments of the present disclosure will be described below with reference to the drawings. These embodiments are essentially preferred examples and are not intended to limit the scope of the present disclosure, its applications, or its uses. Furthermore, the embodiments, modifications, and other examples described below can be combined or partially replaced to the extent that the present disclosure is implementable.

[0011] (1) Overall structure The inverter device 100 supplies power to a motor 70 that rotates, for example, the compressor of an air conditioning system.

[0012] As shown in Figure 1, the inverter device 100 includes a rectifier circuit 10, a boost circuit 20, an inverter circuit 30, a boost circuit control unit 40, and an inverter circuit control unit 50.

[0013] (2) Detailed configuration (2-1) Rectifier circuit 10 The rectifier circuit 10 rectifies the AC power from the AC power supply 60. In this embodiment, the rectifier circuit 10 has six rectifier diodes 10a to 10d. The rectifier diodes 10a to 10d are connected in a bridge configuration.

[0014] (2-2) Boost circuit 20 The boost circuit 20 increases the voltage of the rectified DC power.

[0015] The boost circuit 20 includes a boost reactor 21, a boost diode 22, and a boost switching element 23. One end of the boost reactor 21 is connected to the rectifier circuit 10, and the other end is connected to the anode of the boost diode 22. The cathode of the boost diode 22 is connected to the inverter circuit 30. One end of the boost switching element 23 is connected to the connection point between the boost reactor 21 and the boost diode 22, and the other end is connected to the rectifier circuit 10 and the inverter circuit 30.

[0016] A smoothing capacitor 80 is arranged between the boost circuit 20 and the inverter circuit 30. The smoothing capacitor 80 smooths the output of the boost circuit 20.

[0017] (2-3) Inverter Circuit 30 The inverter circuit 30 converts the DC power boosted by the boost circuit 20 into AC power and supplies it to the motor 70.

[0018] The inverter circuit 30 has switching elements S1 to S6 and diodes D1 to D6.

[0019] [[ID=1,4]]The switching elements S1 to S6 are, for example, insulated gate bipolar transistors or field effect transistors. Each of the switching elements S1 to S3 is provided between each of the output terminals Pu, Pv, Pw and the input terminal P1. Hereinafter, the switching elements S1 to S3 are also referred to as upper switching elements. The anodes of the diodes D1 to D3 are connected to the output terminals Pu, Pv, Pw, respectively, and the diodes D1 to D3 are connected in parallel with the switching elements S1 to S3, respectively. Each of the switching elements S4 to S6 is provided between each of the output terminals Pu, Pv, Pw and the input terminal P2. Hereinafter, the switching elements S4 to S6 are also referred to as lower switching elements. The anodes of the diodes D4 to D6 are connected to the input terminal P2, and the diodes D4 to D6 are connected in parallel with the switching elements S4 to S6, respectively.

[0020] Switching signals are respectively given from the inverter circuit control unit 50 to the switching elements S1 to S6. Each of the switching elements S1 to S6 is turned on by the switching signal. By the inverter circuit control unit 50 giving switching signals to the switching elements S1 to S6 at appropriate timings, the inverter circuit 30 converts the DC voltage into an AC voltage. Note that, under the control of the inverter circuit control unit 50, the switching elements S1 and S4 conduct mutually exclusively, the switching elements S2 and S5 conduct mutually exclusively, and the switching elements Sз and S6 conduct mutually exclusively. This is to prevent a large current from flowing through the switching elements due to the input terminals P1 and P2 being short-circuited.

[0021] The inverter device 100 can drive, for example, the motor 70 of a compressor. The motor 70 is connected to output terminals Pu, Pv, and Pw. The motor 70 rotates in accordance with the AC voltage applied by the inverter circuit 30.

[0022] (2-4) Boost circuit control unit 40 The boost circuit control unit 40 controls the boost circuit 20.

[0023] The boost circuit control unit 40 includes a boost circuit voltage command generation unit 41 and a boost circuit switching control unit 42.

[0024] The boost circuit voltage command generation unit 41 determines the required voltage value based on the value of the motor load 70 detected from an external control device (hereinafter referred to as the "motor load detection value"). The boost circuit voltage command generation unit 41 generates a voltage command (hereinafter referred to as the "voltage command V***") and outputs it to the boost circuit switching control unit 42. Based on the voltage command V***, the boost circuit switching control unit 42 generates a control signal to control the on / off state of the boost switching element 23 of the boost circuit 20 and outputs it to the boost switching element 23.

[0025] The boost circuit control unit 40 includes a microcomputer and a memory device. The microcomputer executes each processing step described in the program. The memory device can consist of one or more of various memory devices, such as ROM (Read Only Memory), RAM (Random Access Memory), rewritable non-volatile memory (EPROM (Erasable Programmable ROM), etc.), and hard disk drives. The memory device stores various information and data, stores the program executed by the microcomputer, and provides a workspace for executing the program. The microcomputer can also be understood as functioning as various means corresponding to each processing step described in the program, or as realizing various functions corresponding to each processing step. Furthermore, the boost circuit control unit 40 is not limited to these, and some or all of the various procedures, means, or functions executed by the boost circuit control unit 40 may be realized in hardware.

[0026] (2-5) Inverter circuit control unit 50 The inverter circuit control unit 50 controls the inverter circuit 30.

[0027] The inverter circuit control unit 50 generates control signals to control the on / off states of the switching elements S1 to S6 of the inverter circuit 30 based on motor load detection values ​​input from an external control device, and outputs these signals to the inverter circuit 30.

[0028] The inverter circuit control unit 50 includes a voltage command generation unit 51, a carrier generation unit 52, and a switching control unit 53.

[0029] The voltage command generation unit 51 generates a voltage command value V** for the phase voltage (hereinafter also referred to as "output voltage") output by the inverter device 100 and outputs it to the switching control unit 53.

[0030] The carrier generation unit 52 generates two different carriers C1 and C2 with a predetermined period, and supplies either carrier C1 or C2 to the switching control unit 53.

[0031] The switching control unit 53 outputs a switch signal to the switching elements S1 to S6 based on a comparison between the second voltage command value V** from the voltage command generation unit 51 and the carrier from the carrier generation unit 52.

[0032] The inverter circuit control unit 50 includes a microcomputer and a memory device. The microcomputer executes each processing step described in the program. The memory device can consist of one or more of various memory devices, such as ROM (Read Only Memory), RAM (Random Access Memory), rewritable non-volatile memory (EPROM (Erasable Programmable ROM), etc.), and hard disk drives. The memory device stores various information and data, stores the program executed by the microcomputer, and provides a workspace for executing the program. The microcomputer can also be understood as functioning as various means corresponding to each processing step described in the program, or as realizing various functions corresponding to each processing step. Furthermore, the inverter circuit control unit 50 is not limited to this, and some or all of the various procedures, means, or functions executed by the inverter circuit control unit 50 may be realized in hardware.

[0033] (3) Operation and control method of inverter device 100 In the inverter device 100, the control method changes according to the load on the compressor motor 70. As shown in Figure 2, the motor 70 is divided into three regions: a first region, a second region, and a third region, depending on the load. In the second region, the load on the motor 70 is higher than in the first region. In the third region, the load on the motor 70 is higher than in the second region. The first region is, for example, the region where the rotational speed of the motor 70 is above the minimum rotational speed and near or below the rated rotational speed. The minimum rotational speed is the minimum rotational speed required for the motor 70 to drive the compressor. The second region is, for example, the region where the rotational speed of the motor 70 exceeds the rated rotational speed and is below the maximum rotational speed. The third region is, for example, the region where the rotational speed of the motor 70 exceeds the maximum rotational speed.

[0034] In the first region, the boost circuit control unit 40 does not boost the voltage of the boost circuit 20. In the first region, the inverter circuit control unit 50 performs conventional PWM control.

[0035] In the second region, the boost circuit control unit 40 continuously boosts the voltage in the boost circuit 20 so that the boosting speed is less than or equal to a predetermined first value. In the second region, the inverter circuit control unit 50 controls the motor 70 with one pulse.

[0036] In the third domain, the boost circuit control unit 40 causes the boost circuit 20 to maintain the boosted voltage.

[0037] (3-1) Boost Circuit Control The voltage command generation process performed by the boost circuit voltage command generation unit 41 starts when the motor 70 is operated.

[0038] In the first region, the boost circuit voltage command generation unit 41 generates a zero voltage command V*** and outputs it to the boost circuit switching control unit 42.

[0039] The zero voltage command V*** is a voltage command that indicates that the boost circuit 20 should not perform a voltage boost. When the zero voltage command is input to the boost circuit switching control unit 42, it turns off the boost switching element 23. As a result, in the first region, the boost circuit 20 is in a stopped state.

[0040] The boost circuit voltage command generation unit 41 determines the required voltage based on the motor load detection value input from an external control device. The boost circuit voltage command generation unit 41 determines whether the input voltage is insufficient to meet the required voltage. If the determination is negative, the output of a zero voltage command continues.

[0041] On the other hand, if the determination is positive, the boost circuit voltage command generation unit 41 generates a boost voltage command V*** in the second region and outputs it to the boost circuit switching control unit 42. At this time, the boost circuit control unit 40 boosts the voltage in the boost circuit 20 so that the boost speed is in line with the rate of increase of the voltage required for the motor 70. Here, the voltage required for the motor 70 increases continuously. Therefore, the boost circuit control unit 40 continuously boosts the voltage in the boost circuit 20 so that the boost speed is less than or equal to a predetermined first value, following the curve C in Figure 2. The first value is 0.2 to 1.0 V / 10 msec. The preferred lower limit of the first value is 0.3 V / 10 msec, and more preferably 0.4 V / 10 msec. The preferred upper limit of the first value is 0.9 V / 10 msec, and more preferably 0.8 V / 10 msec. Here, "continuously boosting" means boosting the voltage steplessly. More specifically, "continuously increasing the voltage" means increasing the voltage at least once per second. "Continuously increasing the voltage" can also mean, for example, increasing the voltage linearly.

[0042] Next, the boost circuit voltage command generation unit 41 determines, based on the motor load detection value, whether the motor 70's rotational speed has reached its maximum rotational speed. If the determination is negative, the output of the boost voltage command V*** for the required voltage continues.

[0043] On the other hand, if the result is positive, a constant voltage command V*** is generated and output to the boost circuit switching control unit 42. The constant voltage command V*** is a voltage command that boosts the voltage to output a constant DC voltage.

[0044] (3-2) PWM control In the first region, the inverter circuit 30 generates a PWM signal based on a control signal sent from the inverter circuit control unit 50 and outputs it to each switching element S1 to S6. This causes the inverter circuit control unit 50 to perform switching operations on each switching element S1 to S6. The switching operations of each switching element S1 to S6 apply a voltage to the coil of the motor 70.

[0045] (3-3) 1-pulse control The inverter circuit control unit 50 performs 1-pulse control in the second region. For example, based on the motor load detection value, the inverter circuit control unit 50 starts 1-pulse control when the rotational speed of the motor 70 reaches the rated rotational speed.

[0046] One-pulse control is a control method that uses a 180-degree energization system. In detail, as shown in Figure 3, it is a control method in which each phase voltage has only one square wave pulse that energizes for 180 degrees within one 360-degree cycle. In the example in Figure 3, the phase voltage has only one pulse in one cycle of AC, but it is sufficient if it has approximately one pulse waveform.

[0047] The term "approximately one-pulse waveform" as used here includes the following types of pulses. For example, in a half-cycle where the phase voltage V takes on a low voltage value, the phase voltage may maintain a high voltage value for a very short period. That is, the phase voltage may contain very narrow pulses. This very short period is shorter than the minimum period required for detecting DC current, and the minimum period is, for example, the sum of the transient period, the conversion period, and the turn-on period of the switching element. However, in addition to the transient period, fluctuation period, and turn-on period, there are other periods that should be considered as the period required for current detection. Such other periods are common technical knowledge for those skilled in the art and are naturally assumed. Similarly, in a half-cycle where the phase voltage V takes on a high voltage value, the phase voltage V may maintain a low voltage value for a very short period. This very short period is shorter than the minimum period mentioned above. In short, an approximately one-pulse waveform is one in which the waveform obtained by ignoring the period shorter than the minimum period during which the phase voltage V continuously takes on a high or low voltage value has only one square wave pulse.

[0048] An example of the specific operation of the voltage command generation unit 51 will be explained with reference to Figure 4. The voltage command generation unit 51 generates a voltage command value V**. In the example in Figure 4, the period enclosed by two adjacent dashed lines each has a predetermined period T1. At the start of period T10, the voltage command value V** rises from its minimum value V2 (e.g., 0) to a predetermined value, and at the end of period T10, it rises to its maximum value V1. From period T11 to period T12, the voltage command value V** takes the maximum value V1, falls to a predetermined value at the start of period T13, the period after period T12, and falls to a minimum value V2 at the end of period T13. From the period after period T13 to period T14, the voltage command value V** takes the minimum value V2, rises again from the minimum value V2 to a predetermined value at the start of period T15, the period after period T14, and rises to the maximum value V1 at the end of period T15.

[0049] Furthermore, the voltage command value V** illustrated in Figure 4 is generated, for example, as follows. That is, the voltage command generation unit 51 receives the uncorrected voltage command value V* (hereinafter simply referred to as the voltage command value V*), corrects the voltage command value V*, and generates the voltage command value V**.

[0050] The voltage command value V* is a square wave, alternating between a maximum value V1 and a minimum value V2. Here, the period during which the voltage command value V* reaches its maximum value V1 is equal to the period during which it reaches its minimum value V2. In the example in Figure 4, the voltage command value V* rises from the minimum value V2 to the maximum value V1 within period T10, falls from the maximum value V1 to the minimum value V2 within period T13, and then rises again from the minimum value V2 to the maximum value V1 within period T15.

[0051] The voltage command generation unit 51 does not correct the voltage command value V* when, for example, the voltage command value V* does not change during each period. In other words, it uses the value of the voltage command value V* as is to generate the voltage command value V**. For example, as shown in Figure 4, the voltage command value V* remains constant during periods T11, T12, and T14. Therefore, during these periods, the voltage command value V** matches the voltage command value V*. Also, for example, when the voltage command value V* changes during each period, the voltage command generation unit 51 corrects the voltage command value V* for that period to an intermediate value between the maximum and minimum values ​​of the voltage command value V* for that period to generate the voltage command value V**. For example, as shown in Figure 4, the voltage command value V* changes during periods T10, T13, and T15. Therefore, during these periods, the voltage command value V** uses an intermediate value between the maximum value V1 and the minimum value V2. Through the above operation, the voltage command value V** exemplified in Figure 4 is generated.

[0052] Through this operation, the microcontroller, which recognizes values ​​at predetermined cycles T1, can recognize the voltage command value V* as the voltage command value V**. Furthermore, if the voltage command value V** is generated by correcting the voltage command value V*, the voltage command generation unit 51 can also be understood as the voltage command value correction unit.

[0053] The carrier generation unit 52 generates carriers C1 and C2 having a predetermined period T1. More specifically, as illustrated in Figure 5, the carrier generation unit 52 generates a monotonically decreasing carrier C1 that decreases monotonically in each period, and a monotonically increasing carrier C2 that increases monotonically in each period. The periods of both carriers C1 and C2 are equal to the predetermined period T1. Carrier C1 is, for example, a right-angle triangular wave with a negative slope, and decreases proportionally with the passage of time from a maximum value V1 to a minimum value V2 in each period. Carrier C2 is, for example, a right-angle triangular wave with a positive slope, and increases proportionally with the passage of time, for example, from a minimum value V2 to a maximum value V1 in each period. Carriers C1 and C2 are called so-called sawtooth waves. Note that carriers C1 and C2 do not need to be proportional with the passage of time and may be curved. This point is also true for other embodiments described later, so repeated explanations will be avoided.

[0054] The carrier generation unit 52 outputs either carrier C1 or C2 to the switching control unit 53 based on information from the voltage command generation unit 51.

[0055] The voltage command generation unit 51 generates the voltage command value V** in a period prior to the period in which it is output. For example, the voltage command value V** to be output in period T11 is generated before period T10. Therefore, the voltage command generation unit 51 can recognize the value of the voltage command value V** output in a given period and the value of the voltage command value V** to be output in the next period. The voltage command generation unit 51 then notifies the carrier generation unit 52 that the next period is the period in which the voltage command value V** falls from its maximum value V1 to a predetermined value (for example, period T13).

[0056] The carrier generation unit 52 outputs carrier C1 to the switching control unit 53 unless it receives notification from the voltage command generation unit 51. On the other hand, if it receives notification from the voltage command generation unit 51, the carrier generation unit 52 outputs carrier C2 to the switching control unit 53 for the next period. Therefore, in the examples in Figures 4 and 5, carrier C2 is used during period T13.

[0057] The switching control unit 53 controls the switching elements S1 to S6 based on a comparison between the voltage command value V** and the carrier. For example, when the voltage command value V** is greater than or equal to the carrier, the switching control unit 53 makes the upper switching element conduct and the lower switching element deconduct, and when the voltage command value V** is less than or equal to the carrier, it makes the upper switching element deconduct and the lower switching element conduct.

[0058] Now, due to the operation of the voltage command generation unit 51 and the carrier generation unit 52 described above, carrier C2 is adopted during the period when the voltage command value V** falls from its maximum value V1 to a predetermined value (for example, period T13). Since carrier C2 increases monotonically during this period, the voltage command value V** is greater than or equal to carrier C2 in the first half of this period. Therefore, the upper switching element conducts and the lower switching element does not conduct during the first half of this period. On the other hand, in the period immediately preceding this period (for example, period T12), the voltage command value V** takes its maximum value V1, so it is greater than or equal to carrier C1. Therefore, during this period, the upper switching element conducts and the lower switching element does not conduct. In other words, the switch patterns of the upper and lower switching elements do not change before and after the boundary between these two periods (for example, periods T12 and T13). To put it another way, the output voltage V does not fall before and after the boundary between these two periods, but maintains a high potential.

[0059] Furthermore, carrier C1 is used during periods other than the period when the voltage command value V** falls from its maximum value V1 to a predetermined value. Therefore, carrier C1 is also used during the period when the voltage command value V** rises from its minimum value V2 to a predetermined value (for example, periods T10 and T15). Since carrier C1 decreases monotonically during this period, the voltage command value V** becomes greater than or equal to carrier C1 in the latter half of this period. Therefore, the upper switching element conducts and the lower switching element does not conduct in the latter half of this period. On the other hand, in the next period after this period (for example, periods T11 and the period after T15), the voltage command value V** takes its maximum value V1, so the upper switching element conducts and the lower switching element does not conduct. In other words, the switch patterns of the upper and lower switching elements do not change before and after the boundary between these two periods (for example, periods T10, T11, T15 and the following period). In other words, before and after the boundary between these two periods, the output voltage V does not fall but continues to maintain a high potential.

[0060] Furthermore, in the period following period T13, the voltage command value V** takes its minimum value V2, so the upper switching element is non-conductive and the lower switching element conducts. In period T13, as described above, carrier C2 is used, so in the latter half of that period, the upper switching element is non-conductive and the lower switching element conducts. Therefore, the switch patterns of the upper and lower switching elements do not change before and after the boundary between period T13 and the following period. In other words, the output voltage V remains at a low potential before and after the boundary between these two periods.

[0061] Furthermore, during period T14, the voltage command value V** takes its minimum value V2, so the upper switching element is non-conductive and the lower switching element conducts. In period T15, which follows period T14, carrier C1 is adopted as described above, so the upper switching element is non-conductive and the lower switching element conducts during the first half of period T15. Therefore, the switch patterns of the upper and lower switching elements do not change before and after the boundary between periods T14 and T15. In other words, the output voltage V remains at a low potential before and after the boundary between these two periods.

[0062] Therefore, as illustrated in Figures 4 and 5, the inverter device 100 outputs an output voltage V having only one pulse within one period (i.e., period T2). In other words, it can output an AC voltage with the fewest number of switches.

[0063] On the other hand, if the falling and rising points of the voltage command value V* are located at either the boundary of each period, the voltage command value V** has the same shape as the voltage command value V*. In this case, regardless of whether a triangular wave or a right-angle triangular wave carrier is used, the inverter device 100 can output an output voltage V having only one pulse within one period. However, in order to achieve this, the predetermined period T1 must be an integer fraction of the period T2 of the voltage command value V*. Therefore, the predetermined period T1 must be changed every time the period T2 changes, making control difficult. On the other hand, in this embodiment, it is not necessary to make the predetermined period T1 an integer fraction of the period T2, making control easy.

[0064] In the examples in Figures 4 and 5, the maximum value V1 and minimum value V2 of the voltage command value V** coincide with the maximum and minimum values ​​of carriers C1 and C2, respectively, but this is not the only case. Simply put, in Figures 3 and 4, it is sufficient that the voltage command value V** is greater than or equal to the maximum value of the carrier during the period when the voltage command value V** takes its maximum value V1, and that the voltage command value V** is less than or equal to the minimum value of carrier C during the period when the voltage command value V** takes its minimum value V2.

[0065] This can also be expressed as follows: The voltage command value V** is less than or equal to the minimum value of the carrier for at least one period (for example, a period before period T10), and at the start of the following period (for example, period T10), it rises from a value less than or equal to the minimum value of the carrier to a predetermined value. This predetermined value is greater than the minimum value of the carrier and less than the maximum value of the carrier. Then, at the end of this period, the voltage command value V** rises to a value greater than or equal to the maximum value of the carrier, and maintains a value greater than or equal to the maximum value of the carrier for at least one subsequent period (for example, periods T11 to T12). Furthermore, at the start of the following period (for example, period T13), the voltage command value V** falls from a value greater than or equal to the maximum value of the carrier C to a predetermined value. This predetermined value is also greater than the minimum value of the carrier and less than the maximum value of the carrier. Then, at the end of this period, the voltage command value V** falls to a value less than or equal to the minimum value of the carrier C, and again maintains a value less than or equal to the minimum value of the carrier for at least one subsequent period.

[0066] As a result, similar to Figures 4 and 5, the inverter device 100 outputs an output voltage V having only one pulse within one period (i.e., period T2). In other words, it is possible to output an AC voltage with the fewest number of switches. This point is also true in other embodiments described later, so we will avoid repeating the explanation.

[0067] Furthermore, the carrier generation unit 52 may output carrier C2 to the switching control unit 53 unless notified by the voltage command generation unit 51. In this case, the voltage command generation unit 51 notifies the carrier generation unit 52 as follows: That is, when the next period is the period during which the second voltage command value V** rises from the minimum value V2 to a predetermined value (for example, period T10), the voltage command generation unit 51 notifies the carrier generation unit 52 to that effect. Upon receiving this notification, the carrier generation unit 52 outputs carrier C1 to the switching control unit 53 during the next period. Even in this way, the inverter device 100 can output the same output voltage V as in Figures 4 and 5.

[0068] Furthermore, while the voltage command value V** takes its maximum value V1 (for example, from period T11 to period T12), the output voltage V maintains a high potential regardless of the carrier, and while the voltage command value V** takes its minimum value V2, the output voltage V maintains a low potential regardless of the carrier. Therefore, as illustrated in Figure 6, during the period when the voltage command value V** takes its maximum value V1 or minimum value V2, a carrier C3, such as an isosceles triangular wave, which has the same period as the control period T1 and increases and decreases in each period, may be used.

[0069] In short, a monotonically decreasing carrier C1 is used during periods T10 and T15, and a monotonically increasing carrier C2 is used during period T13. This allows the inverter device 100 to output AC voltage with the fewest number of switches.

[0070] The switching control unit 53 may also make the upper switching element conductive and the lower switching element non-conductive when the voltage command value V** is less than or equal to the carrier.

[0071] Furthermore, in periods T10, T13, and T15, it is desirable that the voltage command value V** is the average of the voltage command values ​​V* in each respective period. In other words, the above intermediate value is the average value of the voltage command value V* in each period. Such an average value can be derived as follows. That is, let period Tv1 be the period in which the voltage command value V* takes its maximum value V1, and let period Tv2 (=T1-Tv1) be the period in which the voltage command value V* takes its minimum value V2. In this case, the voltage command value V** in each of these periods satisfies the following equation.

[0072] V**=(V1·Tv1+V2·Tv2) / T1 Formula (1) By adopting such a voltage command value V**, theoretically, the average value of the voltage command value V** over period T2 can be made equal to the average value of the voltage command value V* over period T2.

[0073] Furthermore, since the average value of the voltage command value V** over period T2 can be brought closer to the average value of the voltage command value V** over period T2, the average value of the output voltage V over period T2 can also be brought closer to the average value of the voltage command value V**. In other words, the difference (imbalance) between the period in which the output voltage V takes its maximum value and the period in which the output voltage V takes its minimum value can be reduced. In the example in Figure 6, theoretically the average value of the voltage command value V** is equal to the average value of the voltage command value V*, so the imbalance of the output voltage V can be theoretically eliminated.

[0074] Furthermore, if the predetermined period T1 is set to an integer fraction of the period T2, a similar effect can be achieved through control based on a comparison between the voltage command value V* and the carrier. However, this requires changing the predetermined period T1 based on the period T2, necessitating calculations or processing to change the predetermined period T1. Therefore, the control becomes more complex. On the other hand, according to this embodiment, it is not necessary to set the predetermined period T1 to an integer fraction of the period T2 of the voltage command value V*. Therefore, the control can be simplified.

[0075] Furthermore, by increasing the predetermined period T1, imbalance can also be reduced by control based on a comparison between the voltage command value V* and the carrier. However, increasing the predetermined period T1 increases the required computational processing power, which in turn leads to increased manufacturing costs. On the other hand, according to this embodiment, there is no need to increase the predetermined period T1, so such an increase in manufacturing costs can be suppressed.

[0076] <An example of a specific method for generating the second voltage command value V**> The first voltage command value V* is assumed to be a square wave, falling at an electrical angle of 30 degrees and rising at an electrical angle of 210 degrees. Figure 7 shows an enlarged example of voltage command values ​​V* and V**. Figure 7 shows the vicinity of the falling portion of the voltage command value V*. The voltage command value V* falls from its maximum value V1 to its minimum value V2 at an electrical angle of 30 degrees.

[0077] The voltage command generation unit 51 corrects the voltage command value V* and generates a voltage command value V** for each control cycle T1. For example, at the midpoint of each period, it generates the voltage command value V** for the next period.

[0078] Here, if we let δ[N] (where N is an integer) be the electrical angle of the voltage command value V* at the midpoint of each period, then geometrically the following equation is satisfied.

[0079] δ[n+1]-δ[n]:30°-δ[n]=T1:Tv1-T1 / 2 Formula (2) By rearranging equation (2), we can derive period Tv1, and by further considering Tv2 = T1 - Tv1, we can derive period Tv2.

[0080] Tv1=T1·(1 / 2+(30°-δ[n]) / (δ[n+1]-δ[n])) Equation (3) Tv2=T1·(1 / 2-(30°-δ[n]) / (δ[n+1]-δ[n])) Equation (4) Here, assuming that the control period T1 is constant and the period T2 of the voltage command value V* is constant, the following equation holds: δ[n+1]-δ[n]=δ[n]-δ[n-1]=k (constant) (n is an integer). This assumption means, for example, that motor 70, which is an example of an inductive load, is driven at a constant rotational speed. By rearranging equations (3) and (4) considering δ[n+1]-δ[n]=δ[n]-δ[n-1]=k, the following equation is derived.

[0081] Tv1=T1·(1 / 2+(30°-δ[n-1]-k) / k) Equation (5) Tv2=T1·(1 / 2-(30°-δ[n-1]-k) / k) Equation (6) By substituting the periods Tv1 and Tv2 into equation (1), the voltage command generation unit 51 can determine the voltage command value V** for period T11. Note that if δ[n] and δ[n+1] are known at the time of calculating the voltage command value V** for period T11, the voltage command value V** may be calculated using equations (3) and (4).

[0082] Figure 8 shows a magnified view of another example of voltage command values ​​V* and V**. Figure 8 shows the vicinity of the falling portion of the voltage command value V*. The voltage command value V* falls from its maximum value V1 to its minimum value V2 at an electrical angle of 30 degrees, for example. Compared to the example in Figure 7, the electrical angle δ[n] is greater than the electrical angle (e.g., 30 degrees) at which the voltage command value V* falls. In this case, for example, the following equation is geometrically satisfied.

[0083] δ[n]-δ[n-1]:δ[n]-30°=T1:T1 / 2-Tv1 (7) Equation (7) is expressed using electrical angles δ[n] and δ[n-1]. In other words, electrical angles δ[n] and δ[n-1] close to the point at which the voltage command value V* rises are adopted. Rearranging this equation (7) gives us the period Tv1, and considering Tv2 = T1 - Tv1, we can derive the period Tv2.

[0084] Tv1=T1·(1 / 2+(30°-δ[n]) / (δ[n]-δ[n-1])) Equation (8) Tv2=T1·(1 / 2-(30°-δ[n]) / (δ[n]-δ[n-1])) Equation (9) Here, assuming that the electrical angular velocity does not change abruptly, the equation δ[n+1]-δ[n]=δ[n]-δ[n-1]=k holds. Using this, equations (8) and (9) can be transformed to derive equations (5) and (6).

[0085] By substituting the periods Tv1 and Tv2 into equation (1), the voltage command generation unit 51 can determine the voltage command value V** for period T11. Note that if δ[n-1] and δ[n] are known at the time of calculating the voltage command value V** for period T11, the voltage command value V** may be calculated using equations (8) and (9).

[0086] Note that while we assumed the voltage command value V* falls at an electrical angle of 30 degrees, it may rise at any electrical angle. In equations (2) to (9), simply replace "30°" with the desired electrical angle.

[0087] Furthermore, in the example above, the voltage command value V* at time δ is used, but if the voltage command value V* takes a single value for each control cycle T1, then that value should be used. For example, if the voltage command value V* is generated by a program executed by the microcomputer of the inverter circuit control unit 50, then, for example, one voltage command value V* is generated for each control cycle T1.

[0088] Furthermore, it is not always necessary to adopt the above formula; for example, the voltage command value V** may be generated based on the current control period T1 and any two or all of the voltage command values ​​V* from the control periods before and after it.

[0089] (4) Features (4-1) The inverter device 100 includes a boost circuit 20, an inverter circuit 30, a boost circuit control unit 40, and an inverter circuit control unit 50. The boost circuit 20 increases the voltage of the DC power. The inverter circuit 30 converts the DC power increased by the boost circuit 20 into AC power and supplies it to the motor 70. The boost circuit control unit 40 controls the boost circuit 20. The inverter circuit control unit 50 controls the inverter circuit 30. In the second region, the inverter circuit control unit 50 controls the motor 70 with one pulse. In the second region, the load on the motor 70 is higher than in the first region. In the first region, the boost circuit control unit 40 does not boost the voltage to the boost circuit 20. In the second region, the boost circuit control unit 40 continuously boosts the voltage to the boost circuit 20 so that the boosting speed is less than or equal to a predetermined first value.

[0090] In Figure 2, the dashed curve A shows the voltage required for the compressor motor 70. The dashed line B shows the voltage when conventional control is performed. The solid curve C shows the voltage for control according to this embodiment. The dashed arrow D indicates the period during which conventional 1-pulse control is performed. The solid arrow E indicates the period during which 1-pulse control is performed according to this embodiment.

[0091] As shown in Figure 9, when using PWM control, the number of switching cycles per revolution is, for example, 180. In this case, power loss is large. Therefore, conventionally, as shown by line B in Figure 2, PWM control is performed until the rotational speed of the motor 70 approaches the rated speed, and in the region indicated by the dashed arrow D, which is above the rated speed, 1-pulse control (6-step control in Figure 9) is performed as shown in the right-hand diagram of Figure 9. With 1-pulse control, the number of switching cycles per revolution is 6, which significantly reduces the number of switching cycles. Therefore, power loss can be reduced.

[0092] However, when using single-pulse control, at the point when the motor 70 reaches its rated rotational speed and single-pulse control begins, the input voltage will be boosted to exceed the voltage required for the compressor (curve B in Figure 2). Therefore, immediately after the start of single-pulse control, the difference between the boosted input voltage and the required voltage (the difference indicated by the downward arrow in Figure 2) is large. Consequently, using single-pulse control may cause the operating point of the motor 70 to move away from the point of maximum efficiency, potentially leading to increased power loss.

[0093] In the inverter device 100 according to this embodiment, in the second region, the voltage is continuously boosted to the boost circuit 20 along curve B in Figure 2 so that the boost speed is less than or equal to a predetermined first value. Therefore, the inverter device 100 can boost the voltage by the required amount. As a result, voltage loss can be suppressed.

[0094] (4-2) In the inverter device 100, the first value is 0.2 to 1.0 V / 10 msec.

[0095] Here, the difference between the input voltage and the required voltage is sufficiently small. Therefore, voltage loss can be minimized.

[0096] (4-3) In the inverter device 100, the boosted voltage is maintained in the third region. In the third region, the load on the motor 70 is higher than in the second region.

[0097] (4-4) In the inverter device 100, the inverter circuit control unit 50 performs PWM control in the first region.

[0098] (5) Variant (5-1) Variation A In the above embodiment, the inverter device 100 performs 1-pulse control in the second region. However, the inverter device 100 may also perform 6-step control, which is a type of 1-pulse control, in the second region. In 6-step control, a switching operation is performed once on the rising and falling edges of both ends of a 1-pulse. In 6-step control, control is performed with 3 pulses within 360 degrees.

[0099] In detail, in this modified example A, as shown in Figure 10, the command value V** is compared with the carrier C of the isosceles triangular wave to control the switching elements S1 to S6. In this modified example A, the phase voltage V output by the inverter device 100 has three pulses in period T2. Therefore, three pulses mean that each switching element S1 to S6 switches six times.

[0100] (5-2) Variation B In the above embodiment, the inverter device 100 performs PWM control in the first region. However, the inverter device 100 may also perform overmodulated PWM control in the first region. [Examples]

[0101] We compared air conditioning systems by controlling the inverter device using different control methods, with the motor power range set to 2300W.

[0102] In Example 1, the inverter circuit control unit performed PWM control in the first region and 1-pulse control in the second region. The boost circuit control unit did not boost the voltage in the boost circuit in the first region, but continuously boosted the voltage in the boost circuit in the second region so that the boost speed was 0.5V / 10msec or less.

[0103] In Example 2, the inverter circuit control unit performed PWM control in all regions.

[0104] As a result, in Example 1, the inverter efficiency was improved by 0.65% compared to Example 2.

[0105] While embodiments of this disclosure have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of this disclosure as described in the claims. [Industrial applicability]

[0106] This inverter device can be used in air conditioning systems. [Explanation of Symbols]

[0107] 20: Boost Circuit 30: Inverter Circuit 40: Boost Circuit Control Unit 50: Inverter circuit control unit 100: Inverter device [Prior art documents] [Patent Documents]

[0108] [Patent Document 1] Japanese Patent Publication No. 2012-110088

Claims

1. A boost circuit (20) that increases the voltage of DC power, An inverter circuit (30) converts the DC power boosted by the aforementioned boost circuit into AC power and supplies it to the motor, A boost circuit control unit (40) that controls the boost circuit, An inverter circuit control unit (50) that controls the inverter circuit, Equipped with, The inverter circuit control unit controls the motor with one pulse in the second region where the motor load is higher than in the first region. The boost circuit control unit does not boost the voltage in the boost circuit in the first region, and continuously boosts the voltage in the boost circuit in the second region such that the boost speed is less than or equal to a predetermined first value. Inverter device.

2. The first value is 0.2 to 1.0 V / 10 msec. The inverter device according to claim 1.

3. In the third region where the load on the motor is higher than in the second region, the boosted voltage is maintained. The inverter device according to claim 1.

4. In the first region, the inverter circuit control unit performs PWM control. An inverter device according to any one of claims 1 to 3.

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