WO2023067697A1

WO2023067697A1 - Power conversion device and heat pump device

Info

Publication number: WO2023067697A1
Application number: PCT/JP2021/038620
Authority: WO
Inventors: 和徳畠山; 慎也豊留; 翔英堤
Original assignee: 三菱電機株式会社
Priority date: 2021-10-19
Filing date: 2021-10-19
Publication date: 2023-04-27
Also published as: JPWO2023067697A1

Abstract

A power conversion device (100) comprises: a rectifier (3) that is a converter for rectifying AC power supplied from an AC power supply (1); a smoothing unit (4) that is connected to the output end of the converter and smooths power output by the converter; an inverter (5) that is connected to both ends of the smoothing unit and generates AC power to be output to a load (6); a current detector (7) that detects the current flowing between the smoothing unit and the inverter; and a control unit (9) that controls the inverter. The control unit divides, on the basis of a voltage vector indicating the state of each switching element constituting the inverter, a unit time that is a period having a predetermined length into a plurality of current detection intervals, calculates, for each of the plurality of current detection intervals, the products of the time widths of the current detection intervals and the current values detected by the current detector in the current detection intervals, and controls the inverter so that the sum value of the calculated products per unit time becomes constant for each unit time.

Description

Power conversion equipment and heat pump equipment

The present disclosure relates to a power converter and a heat pump device using the power converter.

In the control of electric motors that drive single-rotary compressors and twin-rotary compressors applied to heat pump devices such as air conditioners and refrigerators, for example, power consumption can be reduced by appropriately compensating for the pulsating component of torque according to the state of the electric motor. There is a technique for suppressing an increase in electric power (see Patent Document 1, for example).

JP 2016-178814 A

The motor control device described in Patent Document 1 controls a motor that drives a load whose load torque pulsates periodically. However, in the case of a power conversion device equipped with a converter that converts AC power supplied from an AC power source into DC power, when the load torque pulsates at a frequency asynchronous to the power source frequency, the charging/discharging current flowing from the converter to the smoothing capacitor is reduced by the power source. An unbalanced state occurs between positive and negative voltages. As a result, the harmonics of the power supply current may increase.

Further, the electric motor control device described in Patent Document 1 estimates a three-phase alternating current flowing in the electric motor from the detection result of the current flowing between the converter that rectifies the alternating current power supply and the inverter, and converts the estimated three-phase alternating current into generate a control signal based on Patent Literature 1 also describes that a shunt resistor can be used to detect the current flowing between the converter and the inverter.

However, when current detection is performed using a shunt resistor, detection is possible only at a predetermined timing. In general, current detection is performed periodically at predetermined time intervals, so only instantaneous values can be detected, making it difficult to obtain accurate current values. If an accurate current value cannot be obtained, it becomes difficult to accurately control the inverter. Note that there is a minimum value in the time interval for current detection, and current detection cannot be performed at intervals shorter than the minimum value.

The present disclosure has been made in view of the above, and an object of the present disclosure is to obtain a power conversion device capable of increasing the accuracy of load control performed based on an instantaneous value of current obtained at a predetermined timing. do.

In order to solve the above-described problems and achieve the object, the power converter according to the present disclosure includes a converter that rectifies AC power supplied from an AC power supply, and power that is connected to the output terminal of the converter and output by the converter. a smoothing unit that smoothes the current, an inverter that is connected to both ends of the smoothing unit and generates AC power to be output to the load, a current detector that detects current flowing between the smoothing unit and the inverter, and controls the inverter and a control unit. The control unit divides a unit time, which is a period of a predetermined length, into a plurality of current detection intervals based on voltage vectors representing the state of each switching element that constitutes the inverter, and for each of the plurality of current detection intervals , calculates the product of the time width of the current detection section and the current value detected by the current detector in the current detection section, and controls the inverter so that the total value of the calculated product per unit time is constant for each unit time. .

According to the present disclosure, it is possible to realize an electric power conversion device capable of highly accurate control of a load based on an instantaneous value of current obtained at a predetermined timing.

1 is a diagram showing a configuration example of a power converter according to a first embodiment; FIG. FIG. 4 is a diagram for explaining how the control unit generates a control signal for the inverter; FIG. 4 shows switching patterns of switching elements that make up an inverter FIG. 4 is a diagram showing an example of current and voltage waveforms when the power converter according to the first embodiment operates; FIG. 4 is a diagram showing frequency components included in an input current Is in a state where symmetry is lost when the frequency of the power supply voltage Vs is 50 Hz; A diagram showing an example of current and voltage waveforms when the power conversion device operates the load at a constant current Diagram for explaining a general method of detecting load current FIG. 4 is a diagram for explaining a method of detecting a direct current Idc flowing from an inverter of a power conversion device to a load; FIG. 2 is a diagram showing an example of a hardware configuration that realizes a control unit included in the power converter according to the first embodiment; FIG. FIG. 10 is a diagram showing a configuration example of a heat pump device according to a second embodiment;

A power conversion device and a heat pump device according to embodiments of the present disclosure will be described below in detail based on the drawings.

Embodiment 1.
1 is a diagram illustrating a configuration example of a power converter according to a first embodiment; FIG. The power conversion device 100 includes a reactor 2 , a rectifier 3 that is a converter, a smoothing section 4 , an inverter 5 , a current detector 7 , a voltage detector 8 and a control section 9 . The power conversion device 100 is connected to an AC power supply 1 , converts AC power supplied from the AC power supply 1 into three-phase AC power, and supplies the three-phase AC power to a load 6 .

A power supply voltage Vs input from an AC power supply 1 is rectified by a rectifier 3 via a reactor 2, and is accumulated in capacitors 4a and 4b constituting a smoothing section 4 connected to the output end of the rectifier 3, thereby smoothing the voltage. After that, it is supplied to the inverter 5 . When the side of the output terminal of the AC power supply 1 connected to the reactor 2 is positive, the capacitor 4a of the smoothing unit 4 is charged when the power supply voltage Vs is positive, and the capacitor 4b is charged when the power supply voltage Vs is negative. When the battery is charged.

Here, the AC power supply 1 may be a commercial power supply of 50 Hz or 60 Hz, or an AC voltage generated by a distributed power supply such as a stationary storage battery or solar power generation.

In addition, the reactor 2 may be an EI-shaped or EE-shaped one in which electromagnetic steel sheets are laminated, or may be one using an iron core such as ferrite or amorphous. The winding material is copper, aluminum, or the like.

The rectifier 3 is realized, for example, by arranging diodes in a bridge shape. The rectifier 3 may be configured by a power semiconductor such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) instead of the diode. Also, power semiconductors such as diodes and MOSFETs may be of general silicon material or may be wide bandgap semiconductors with lower loss.

The capacitors 4a and 4b are aluminum electrolytic capacitors, small-capacity film capacitors, or the like.

The configuration of the rectifier 3 is not limited to that shown in FIG. The power converter 100 according to the present embodiment may be of any type as long as it includes a circuit for rectifying AC power and a capacitor for smoothing the rectified DC power.

An inverter 5 is connected to both ends of the smoothing section 4, that is, to both ends of a series circuit composed of a capacitor 4a and a capacitor 4b connected in series, and a load 6 is connected to the inverter 5. A load 6 that consumes the AC power generated by the inverter 5 includes an electric motor. The inverter 5 has a plurality of series-connected switching elements arranged in parallel, and operates to apply a multiphase AC voltage to the electric motor included in the load 6 . A diode is connected in parallel to each of the switching elements forming inverter 5 . IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs are widely used as switching elements. In the case of a MOSFET, a parasitic diode is built in, and the diode connected in parallel may not be separately connected.

Silicon (Si) materials are widely used for switching elements, and in recent years, due to the demand for higher efficiency, MOSFETs with a super junction structure are also widely used. In addition, wide bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond have been used for further efficiency improvement. There is no problem, and switching elements made of any material can be used as long as they are capable of switching operation so as to apply a voltage to the motor.

Regarding the electric motor, there are induction motors and synchronous motors, but there is no problem with the electric motor of any configuration. For example, in the case of a synchronous motor, the stator may be concentrated winding or distributed winding, and the winding may be made of any material such as copper or aluminum wire that allows current to flow. As for the rotor, there are surface magnet type, embedded magnet type, etc. as those using a permanent magnet synchronous motor, but any type may be used as long as it has a structure capable of generating a rotational force.

When such a motor is used to implement, for example, a refrigeration cycle device, the motor is used to operate a compression mechanism that compresses the refrigerant or drive a fan for heat exchange.

Further, the control unit 9 controls the switching element to control the voltage supplied to the load 6 by the inverter 5 based on the DC current Idc detected by the current detector 7 and the DC voltage Vdc detected by the voltage detector 8. A pulse width modulation (PWM: Pulse Width Modulation) signal is sent out. It should be noted that the current detector 7 may be a shunt resistor or a DCCT (Direct Current Current Transformer) or any other device that can detect current.

A method for the control unit 9 to generate a PWM signal as a control signal for the inverter 5 will be described. FIG. 2 is a diagram for explaining how the control section 9 generates a control signal for the inverter 5. As shown in FIG.

As shown in the upper part of FIG. 2, the control unit 9 controls a carrier signal whose amplitude is 1/2 of the DC voltage Vdc and a command for each of the U-phase, V-phase, and W-phase voltages to be applied to the motor included in the load 6. The values Vu*, Vv*, and Vw* are compared to generate a PWM signal for operating each switching element of the inverter 5 . V* is the amplitude of the voltage command value (Vu*, Vv*, Vw*) of each phase. The PWM signal generated by the controller 9 is shown in the lower part of FIG. 2, UP is a control signal for the upper left switching element of the inverter 5 shown in FIG. 1, UN is a control signal for the lower left switching element, VP is a control signal for the middle upper switching element, and VN is the middle lower switching element. , WP is a control signal for the upper right switching element, and WN is a control signal for the lower right switching element.

FIG. 3 is a diagram showing switching patterns of switching elements that constitute the inverter 5. FIG. Specifically, FIG. 3 shows the direction of the voltage applied to the motor (voltage direction) in each switching pattern of the switching elements that make up the inverter 5, and the rectifier 3 and the inverter 5 when the voltage vector (V0 to V7) is output. and the PWM signals (UP, VP, WP, UN, VN, WN). A voltage vector represents the state of each switching element that constitutes inverter 5 . Note that the numerical values (0 to 7) combined with "V" correspond to the states of the switching elements UP, VP, and WP.

The direction of the voltage applied to the electric motor, which is described as "voltage direction" in FIG. A current detector 7 detects a direct current Idc described as "detected current". In FIG. 3, the current flowing from the rectifier 3 to the inverter 5 is assumed to be positive. Generally, in controlling a motor connected to an inverter, current is detected at a specific moment when a PWM signal corresponding to a voltage vector is output to the inverter, and the detected instantaneous value is used for controlling the motor. Since such an electric motor control method is publicly known, a detailed explanation is omitted.

Next, consider control for suppressing speed pulsation by controlling the torque of the electric motor in accordance with the pulsation of the load torque, as in the technology described in Patent Document 1 above. FIG. 4 is a diagram showing an example of current and voltage waveforms when the power converter 100 according to the first embodiment operates. FIG. 4 shows waveforms when the speed pulsation is suppressed by controlling the torque of the electric motor according to the pulsation of the load torque.

When controlling the torque of the electric motor in accordance with the pulsation of the load torque, the power converter 100 increases or decreases the active power output to the electric motor in accordance with the pulsation of the load torque. Therefore, as shown in FIG. 4, the DC current Idc pulsates, and electric charges are consumed from the capacitors 4a and 4b forming the smoothing section 4 in accordance with the pulsation of the load torque. Therefore, the charging timing of the capacitors 4a and 4b with the power supply voltage Vs becomes asynchronous with the power supply frequency, and the symmetry between positive and negative input current Is is lost. Each of the waveforms shown in FIG. 4 represents, from top to bottom, the power supply voltage Vs, the input current Is, the DC voltage Vdc, the motor currents Iu, Iv, Iw, the DC current Idc, and the voltage vector. When the symmetry between the positive waveform and the negative waveform of the input current Is is lost, harmonics contained in the input current Is increase.

When the input current Is and the power supply voltage Vs are synchronized, the input current Is has odd-order harmonics such as the 3rd, 5th, 7th, etc., with the component of the same frequency as the frequency of the power supply voltage Vs as the fundamental wave. component becomes dominant, and the generation of even-order harmonics is slight. However, if the input current Is flows irregularly and asynchronously with the power supply voltage Vs, the symmetry of the waveform of the input current Is is lost as described above. As a result, current components other than odd-order harmonics, specifically, even-order harmonics and inter-harmonics are generated. Interharmonics are harmonics that are neither odd nor even harmonics of the input current Is. For example, if the frequency of the fundamental wave is 50 Hz, the second harmonic is 100 Hz. A frequency component between 50 Hz and 100 Hz.

Here, the harmonic current of the power supply current (corresponding to the input current Is in the power converter 100) is the limit value in 61000-3-2 of the standard stipulated by JIS (Japanese Industrial Standards) and IEC (International Electrotechnical Commission). is determined. The standard sets higher limits for odd harmonics than for even harmonics. Therefore, in cases where components other than odd-order harmonics are generated, the even-order harmonics increase and easily exceed the limit value. As for the interharmonics, the handling method is determined in 61000-4-7 of the standard defined by JIS and IEC. According to this standard 61000-4-7, interharmonics are grouped by frequency within a specific range and added to adjacent odd-order or even-order harmonics. Therefore, as the interharmonics increase, the harmonics treated as odd-order harmonics and the harmonics treated as even-order harmonics also increase. Therefore, the generation of interharmonics cannot be ignored, and it is important to suppress the generation.

In the case of FIG. 4, due to the imbalance of the input current Is, there are places where the charging current per charge is large (for example, the charging current on the positive side in the first cycle from the left) and places where it is small (for example, the fourth cycle from the left). (positive charging current in the second cycle) appears, and in the region where the charging current is particularly large, the input current Is flowing through the reactor 2 increases, which causes the inductance to decrease, and the rectifier 3 to flow an excessive current. There are concerns about worsening losses. Therefore, it is necessary to perform control to prevent such current from flowing, that is, to prevent the charging current per charge from increasing.

When the DC current Idc is small, the drop in the DC voltage Vdc is small, and the amount of charge due to the power supply voltage Vs is small, so the input current Is is reduced. Also, when the power supply voltage Vs is low (close to zero) and the DC current Idc is large, the DC voltage Vdc drops significantly. If a positive or negative peak occurs in power supply voltage Vs in such a state, the charging current to capacitors 4a and 4b increases and input current Is increases. In such an unbalanced state where the symmetry of the input current Is is lost, the input current Is contains the following components. As an example, FIG. 5 shows current components included in the input current Is when the power supply frequency is 50 Hz. FIG. 5 is a diagram showing frequency components included in the input current Is in a state where the symmetry is lost when the frequency of the power supply voltage Vs is 50 Hz. In the case where the power supply frequency is 60 Hz, the frequency component included in the input current Is in which the symmetry is lost can also be obtained in the same manner as described below.

The frequencies (0, 5, 10, . . . , 100) described in the leftmost column of FIG. is the fluctuation frequency of For convenience of explanation, this frequency may hereinafter be referred to as the load current fluctuation frequency.

The range of numerical values (75 to 125, 125 to 175, . . . , 275 to 325) shown in the first row of FIG. . That is, in the grouping according to the above standard 61000-4-7, the interharmonics included in each range shown in the first line of FIG. 5 are grouped. For example, interharmonics in the range of 75-125 Hz belong to the same group. The numerical values described in each column other than the leftmost column from the third row onward in FIG. 5 indicate the frequency of the interharmonics included in the input current Is.

Descriptions other than the leftmost column on the second row in FIG. 5 (second, third, . show. For example, the interharmonics (75 Hz, 80 Hz, . Half of the interharmonics of the frequencies (125Hz, 175Hz, 225Hz, etc.) that form the boundaries of the ranges to be grouped are odd-order harmonics corresponding to the two ranges that include these interharmonics. one of the waves and the even harmonics and the other half is added to the other.

A specific current component generated when the DC current Idc flowing through the load 6 is periodically changed will be described. In the following description, the frequency (50 Hz) of the fundamental wave component of the power supply voltage Vs is described as power supply frequency 1f, and the frequencies (100Hz, 150Hz, 200Hz, . . . ) of the harmonic components of power supply voltage Vs are referred to as power supply frequency 2f , power frequency 3f, power frequency 4f, . Also, in order to prevent the explanation from becoming complicated, the DC current Idc flowing through the load 6 may be referred to as a load current.

As a current component that occurs regardless of fluctuations in the load current of the AC power supply 1, there is a current component with the frequency shown in (1) below.

(1) Power frequency 1f, power frequency 3f, power frequency 5f, ..., power frequency (2n-1)f, (n = 1, 2, 3, ...)

"Power supply frequency 1f" represents the frequency of the fundamental wave of the power supply current, and "Power supply frequency (2n-1)" represents the frequency of the 2n-1st harmonic of the power supply current. That is, the fundamental wave component and the odd-order harmonic component are generated regardless of fluctuations in the load current of the AC power supply 1 .

Current components with frequencies shown in (2) to (7) below are current components generated in the input current Is due to the influence of the fundamental wave component of the load current. "Power supply frequency 3f" represents the frequency of the third harmonic of the power supply current, and "Power supply frequency 5f" represents the frequency of the fifth harmonic of the power supply current.

(2) Power frequency 1f- {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency|}
(3) Power frequency 1f + {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency|}
(4) Power frequency 3f- {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency|}
(5) Power frequency 3f + {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency|}
(6) Power frequency 5f- {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency|}
(7) Power frequency 5f + {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency|}

In addition, current components with frequencies shown in (8) to (13) below are current components generated in the input current Is due to the influence of the secondary harmonic components of the load current. Note that these are shown in parentheses in FIG. 5 (for example, "(80, 120)" corresponds).

(8) Power frequency 1f- {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency x 2|}
(9) Power frequency 1f + {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency x 2|}
(10) Power frequency 3f-{Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency x 2|}
(11) Power frequency 3f + {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency x 2|}
(12) Power frequency 5f- {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency x 2|}
(13) Power frequency 5f + {Power frequency 1f-|Power frequency 1f-Load current fluctuation frequency x 2|}

In this way, the current components other than the frequency shown in (1) are generated depending on the power supply frequency and the load current fluctuation frequency, and the generated amount increases as the fluctuation range of the load current increases. As shown in FIG. 5, it is mostly the interharmonics in between, rather than the odd and even harmonics that are multiples of 50 Hz (power supply frequency). When the grouping process defined by the above standard 61000-4-7 is performed, for example, when the load current fluctuation frequency is 30 Hz, current components with frequencies of 80 Hz, 90 Hz, 110 Hz, and 120 Hz are generated. is grouped at 100 Hz of the even harmonics, resulting in an increase in the even harmonics. Since even-order harmonics are set to a low limit value in the above-mentioned standard 61000-3-2, etc., when inter-order harmonics grouped into even-order harmonics are generated, even-order harmonics are generated. You are more likely to exceed your limits.

The interharmonics of the frequencies shown in (2) to (13) above do not occur if the load current fluctuation frequency becomes zero, that is, if the load current becomes direct current. Therefore, if the control unit 9 controls the load 6 so that the load current becomes direct current, it is clear that the imbalance of the input current Is does not occur as shown in FIG. be. FIG. 6 is a diagram showing an example of current and voltage waveforms when the power converter 100 operates the load 6 with a constant current.

In this way, by operating the load 6 with a constant current so as to always consume a constant amount of electric charge from the capacitors 4a and 4b that constitute the smoothing section 4, variations in charging and discharging of the capacitors 4a and 4b are eliminated. As a result, the power supply voltage Vs and the input current Is have synchronized waveforms, and the input current Is has a waveform containing many odd-order harmonics. In general, the power supply current (corresponding to the input current Is in this embodiment) is synchronized with the power supply voltage Vs and contains many odd-order harmonics. Therefore, as described above, in the standard 61000-3-2, the limit value of odd-order harmonics is set high, and the limit value of even-order harmonics is set low. Therefore, it is necessary to suppress the generation of interharmonics that are grouped into even orders.

From the above, in order not to generate even-order harmonics, it is necessary to suppress the AC component generated in the DC current Idc flowing from the inverter 5 to the load 6, and it is necessary to accurately detect the DC current Idc.

Here, conventionally, as shown in FIG. 7, the current is detected at the timing of outputting the voltage vector shown in FIG. 3 within one cycle of the carrier signal, and the inverter is controlled using this detection result. there is FIG. 7 is a diagram for explaining a general method of detecting load current. The upper part of FIG. 7 shows the relationship between the carrier signal and the voltage commands (Vu*, Vv*, Vw*) of each phase applied to the motor. The lower part of FIG. 7 shows the current flowing through the motor and the timing of detecting the current (corresponding to current measurement points represented by ●). In the load current detection method shown in FIG. 7, the current is detected once during the period from when the voltage vector changes until the next change.

However, in reality, as can be seen from FIG. 7, current flows continuously in the motor, and the current changes even in sections where the voltage vector is the same. Therefore, the detected value may change depending on the detection timing, and an accurate value may not be obtained. In addition, since there are sections in which no current flows, detection is not easy. There is also a method of finer current detection timing, but the period of the carrier signal is several tens of microseconds to several hundreds of microseconds, whereas the speed of analog-to-digital conversion of general microcomputers is about several microseconds. , the time resolution may be insufficient. Moreover, frequent analog-to-digital conversion may affect the processing time of the entire microcomputer, which is not realistic.

Therefore, in the power conversion device 100 according to the present embodiment, current detection is performed using a method as shown in FIG. FIG. 8 is a diagram for explaining a method of detecting the direct current Idc flowing from the inverter 5 to the load 6 of the power converter 100. As shown in FIG. In the method shown in FIG. 8, one carrier cycle is defined as a unit time that is a period of a predetermined length, and a current value (instantaneous value) detected at a certain timing within one carrier cycle is output to the inverter 5. Based on the PWM signal, the average value of the DC current Idc per unit time is obtained.

In the power conversion device 100, a real vector is output from the control unit 9 to the inverter 5 based on the relationship between the carrier signal used to generate the PWM signal for the inverter 5 and the voltage commands Vu*, Vv*, and Vw*. It is possible to guess the time. Note that the real vector here means a voltage vector other than the V0 vector and the V7 vector shown in FIG. The control unit 9 can estimate the time during which each of the V1 vector to V6 vector is output. For example, in the case of time t1 shown in FIG. 8, the time during which the real vector is output is the difference between the point where the voltage command Vw* and the carrier signal intersect and the point where the voltage command Vv* and the carrier signal intersect. It's time. In this regard, the carrier signal rising timing is set to v=a×t+b, voltage commands Vv* and Vw* are substituted for v, t is obtained, and the difference is obtained. Note that v is the voltage command value on the vertical axis in FIG. 8, t is the time on the horizontal axis in FIG. 8, and a and b are constants. By obtaining the product of t1 obtained in this way and the current I1 detected in that section, the area can be obtained. Similarly, I2×t2, I3×t3, and I4×t4 shown in FIG. 8 are calculated and added. By dividing this by the carrier cycle time, the average load current, which is the average value of the current flowing through the load 6 in one carrier cycle, can be obtained. By using such a method, even when fine current detection timing is difficult, such as when using an inexpensive shunt resistor, the occurrence of detection errors in the average load current is suppressed, and the DC current Idc flowing through the load 6 is kept constant. It is possible to control

It should be noted that the current detection timing in the current detection section, which is the time section (t1 to t4) corresponding to each voltage vector, is preferably near the center of each current detection section. By performing detection near the center of the current detection section, it is possible to suppress current detection errors and calculate the area with high accuracy. However, if the width of the current detection section is narrow and detection is performed near the center, ringing will occur when the current detection section switches, and it will continue to near the center, which will affect the detection accuracy. there is a possibility. Therefore, when the width of the current detection section is narrow, detection may be performed after waiting until the influence of ringing disappears.

Also, the peak current of the direct current Idc pulsates at a frequency six times that of the current flowing in the motor. Therefore, the average value may be obtained by adding the areas of the currents as described above in the period of six times the frequency. In addition, in order to eliminate the influence of other pulsations, the average value may be obtained in a period other than one carrier period. For example, the average value of the DC current Idc per unit time may be obtained by using a period that is an integral multiple of one carrier period as a unit time.

In addition, although FIG. 8 shows an example in which current measurement is performed once in each current detection section, it is also possible to perform current measurement multiple times in one current detection section, average the measured values, and use them for the above area calculation. good.

By controlling the torque generated by the motor so that the current value (direct current Idc) obtained by such a method is constant, the electric charge consumed from the capacitors 4a and 4b is reduced according to the cycle of the load torque pulsation. The amount becomes uniform in each cycle of the load torque pulsation, making it possible to reduce the harmonics of the input current Is. As a result, the harmonic current can be effectively reduced even when the capacity of the reactor 2 and the capacitors 4a and 4b is small, and the size and weight of the device can be reduced and the cost can be reduced.

A method of controlling the torque generated by the electric motor so that the DC current Idc flowing through the load 6 is constant can be easily realized using a known technique. For example, the control unit 9 compensates the q-axis current command value, which is the torque current of the motor, so that the direct current Idc flowing through the load 6 is constant, and operates the motor, thereby easily manipulating the active power. is possible, and the DC current Idc flowing through the load 6 can be controlled to be constant.

In addition, the charging and discharging of the capacitors 4a and 4b are affected by the electromotive force and voltage drop due to the reactor 2 and the capacitance of the capacitors 4a and 4b. When the capacity of the reactor 2 and the capacitors 4a and 4b is sufficiently large (reactor 2 is several milliseconds, and the capacitors 4a and 4b are several hundreds of microfarads), fluctuations in the DC voltage Vdc become small, and pulsations are superimposed on the DC current Idc. Also, components other than odd-order harmonics are less likely to occur in the input current Is. Therefore, while considering the amount of current generated other than the odd-order harmonics, it is possible to use the conventional control of pulsating the load torque. By doing so, it is possible to achieve both a reduction in vibration of the compressor driven by the motor to be controlled and a reduction in harmonic current.

In general single-rotary compressors and twin-rotary compressors, which are connected to a load connected to an electric motor, in order to suppress the increase in vibration accompanying speed fluctuations due to pulsation of the load torque, the torque output by the electric motor is reduced to the load torque. The speed fluctuation is prevented by making it substantially coincide with the pulsation of the In addition, it is operated to suppress the output torque of the electric motor so that the power consumption does not become too large.

In such an operation, the DC current Idc flowing through the load 6 fluctuates according to the load torque, and the harmonic current of the input current Is deteriorates as described above. In the case of an inverter that drives a motor, the load power is determined by the product of the mechanical angular frequency ω and the torque τ of the motor. Therefore, by varying the mechanical angular frequency ω or varying the torque τ, it is possible to control the DC current Idc so as to approach a constant value.

However, if the operation is performed so as to suppress the pulsation of the DC current Idc flowing through the load 6 so that the power supply harmonic current does not further increase, there is a concern that the vibration will increase. In general, for electric motors, the power fluctuation is proportional to the load torque and inversely proportional to the moment of inertia. If the fluctuation of the DC current Idc flowing through the load 6 due to the load torque is unacceptable, it can be dealt with by designing to increase the moment of inertia. By taking such measures, it is possible to achieve both suppression of vibration and suppression of power supply harmonic current.

In addition, in the load of an electric motor such as a conventional single rotary compressor or twin rotary compressor, in order to suppress the increase in vibration accompanying the speed fluctuation due to the pulsation of the load torque, the torque output by the electric motor is reduced to the load torque. Speed fluctuation is prevented by substantially matching the pulsation, and in addition, the output torque of the electric motor is controlled so as to prevent power consumption from becoming too large.

In the case of such operation, the load current fluctuates according to the load torque, and the harmonic current of the input current deteriorates as described above. In the case of an inverter that drives an electric motor, the load power is determined by the product of the mechanical angular frequency ω and the torque τ. Therefore, by varying the mechanical angular frequency ω or varying the torque τ, it is possible to control the DC current Idc, which is the load current, to be nearly constant.

However, there is a concern that the oscillation of the power supply current will increase if the load current pulsation is suppressed to prevent the power supply harmonic current from increasing further. In the case of a general electric motor, power fluctuation is proportional to load torque and inversely proportional to moment of inertia. If the amount of load current variation due to load torque variation is unacceptable, it can be dealt with by designing to increase the moment of inertia. By taking such measures, it is possible to achieve both suppression of vibration and suppression of power supply harmonic current. That is, the control unit 9 of the power conversion device 100 sets the amount of fluctuation of the DC current Idc detected by the current detector 7 to be within an allowable range, in other words, the amount of fluctuation of the DC current Idc is set to a value The load 6 is controlled via the inverter 5 so that: The permissible range is the range in which the even-order harmonics affected by the generation of inter-harmonics of the power supply current can be maintained below the standard limit value, and the inductance of the reactor 2 and the static of the capacitors 4a and 4b. It is determined in advance in consideration of the electric capacity and the like.

The switching frequency of the inverter for driving the compressor for air conditioning is higher than 2 kHz (when the power main frequency is 50 Hz) or 2.4 kHz (when the power frequency is 60 Hz) of the 40th harmonic, which is the power harmonic regulation value. . The load current in the inverter has a pulse shape corresponding to the switching frequency, but this pulse shape current does not easily affect the harmonics of the power supply. Therefore, the pulsating component of the load current should be suppressed below the frequency of the 40th harmonic, which is the power supply harmonic regulation value.

Next, the hardware configuration of the control unit 9 included in the power converter 100 will be described. FIG. 9 is a diagram illustrating an example of a hardware configuration that implements the control unit 9 included in the power converter 100 according to the first embodiment. The control unit 9 of the power conversion device 100 is realized by, for example, a processor 91 and a memory 92 shown in FIG. 9 .

The processor 91 is a CPU (Central Processing Unit, also referred to as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, DSP (Digital Signal Processor)). The memory 92 is RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (registered trademark) (Electrically Erasable Programmable Read Only Memory), or the like. Note that the memory 92 stores a program for operating as the control unit 9 of the power conversion device 100, and the control unit 9 is realized by the processor 91 reading and executing this program. The above program stored in the memory 92 may be provided to the user or the like while being written on a storage medium such as a CD (Compact Disc)-ROM, a DVD (Digital Versatile Disc)-ROM, etc. Alternatively, it may be provided via a network.

The control unit 9 can also be realized by a dedicated processing circuit, for example, a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a circuit combining these. be.

As described above, in the power conversion device 100 according to the present embodiment, the control unit 9 that controls the inverter 5 sets the unit time to an integral multiple of one period of the carrier signal, and sets the unit time based on the voltage vector. It is divided into a plurality of current detection intervals, and for each of the plurality of current detection intervals, the product of the time width of the current detection interval and the DC current Idc detected by the current detector 7 in the current detection interval is calculated. The inverter 5 is controlled so that the total value per unit time is constant for each unit time. As a result, even when a shunt resistor or the like, which is difficult to improve the resolution of current detection, is used as the current detector 7, the DC current flowing between the smoothing section 4 and the inverter 5 can be detected with high accuracy. It is possible to improve the accuracy of the control of the load 6 based on the instantaneous value of the current obtained at the timing.

Embodiment 2.
In this embodiment, a device that can be realized by applying the power conversion device 100 described in the first embodiment will be described. As an example, a heat pump device using the power conversion device 100 described in Embodiment 1 will be described.

FIG. 10 is a diagram showing a configuration example of the heat pump device 200 according to the second embodiment. A heat pump device 200 according to the second embodiment includes the power conversion device 100 described in the first embodiment.

In addition, the heat pump device 200 includes a four-way valve 902, a compressor 903 that constitutes the load 6 shown in FIG. It has a refrigeration cycle in a mounted configuration.

The compressor 903 is provided with a compression mechanism 904 that compresses the refrigerant circulating in the refrigerant pipe 912 and an electric motor 905 that operates the compression mechanism 904 . The electric motor 905 constitutes the load 6 shown in FIG. 1 and is driven by being supplied with electric power from the power converter 100 .

The heat pump device 200 having such a configuration can be used, for example, in air conditioners, heat pump water heaters, refrigerators, refrigerators, and the like.

The configurations shown in the above embodiments are only examples, and can be combined with other known techniques, or can be combined with other embodiments, without departing from the scope of the invention. It is also possible to omit or change part of the configuration.

1 AC power supply, 2 reactor, 3 rectifier, 4 smoothing unit, 4a, 4b capacitor, 5 inverter, 6 load, 7 current detector, 8 voltage detector, 9 control unit, 100 power conversion device, 200 heat pump device, 902 square valve, 903 compressor, 904 compression mechanism, 905 electric motor, 906, 910 heat exchanger, 908 expansion valve, 912 refrigerant piping.

Claims

a converter for rectifying AC power supplied from an AC power supply;
a smoothing unit connected to the output end of the converter for smoothing power output from the converter;
an inverter connected to both ends of the smoothing unit and generating AC power to be output to a load;
a current detector that detects a current flowing between the smoothing unit and the inverter;
a control unit that controls the inverter;
with
The control unit divides a unit time, which is a period of a predetermined length, into a plurality of current detection intervals based on voltage vectors representing states of respective switching elements forming the inverter. For each of the above, the product of the time width of the current detection section and the current value detected by the current detector in the current detection section is calculated, and the total value of the calculated products per unit time is constant for each unit time. controlling the inverter to
Power converter.
The unit time is an integral multiple of one cycle of a carrier signal used to generate a control signal to be output to the inverter;
The power converter according to claim 1.
configuring the current detector with a shunt resistor;
The power converter according to claim 1 or 2.
A heat pump device comprising the power conversion device according to any one of claims 1 to 3.