Power converters and air conditioning systems

Abstract

This invention provides a power conversion device that suppresses oscillation in the control of harmonic currents. [Solution] The power conversion device is connected to a power source and consists of upper and lower arms of semiconductor switching elements. It comprises a power conversion circuit that converts AC to DC, and a controller that controls the upper and lower arms based on a first target value of a first current on the AC side and a second target value of a second current with a lower frequency than the first current. The switching signal includes a dead time for the upper and lower arms. d [s], the carrier cycle is T c [s], the DC voltage is V dc Let [V] be the value of the first current and when the second current is not outputting, the average value of the gain characteristics from the first target value to the first current in a defined frequency band be G0 [dB]. When the first current is outputting and the second current is outputting, the average value of the gain characteristics from the first target value to the first current (G0) is less than the gain characteristic (G(i)) given by the following formula, when the second current is i [A]. TIFF2026166443000008.tif13155

Description

[Technical Field]

[0001] This disclosure relates to a power converter and an air conditioning system. [Background technology]

[0002] Patent Document 1 discloses an active filter device connected to a harmonic generating device, comprising: a current source that supplies a compensation current (Ic) to the power system to which the harmonic generating device is connected in order to improve the power factor; and a power factor controller that determines the magnitude of the compensation current by adding a set value corresponding to the reactive current in devices other than the harmonic generating device to the load current of the current flowing from the power system to the harmonic generating device. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-191375 [Overview of the project] [Problems that the invention aims to solve]

[0004] Power converters connected to a power source may output fundamental currents in addition to harmonic currents to compensate for the voltage of the power system. When a power converter outputs fundamental currents in addition to harmonic currents, oscillation may occur in the control of the harmonic currents. This disclosure aims to suppress oscillation in the control of harmonic currents when a power converter outputs a fundamental wave current in addition to harmonic currents. [Means for solving the problem]

[0005] A power conversion device according to a first aspect is connected to a power supply, and includes: a power conversion circuit that is constituted by upper and lower arms of semiconductor switching elements and converts between AC power and DC power; and a controller that generates a switching signal for controlling the upper and lower arms of the power conversion circuit based on a first target value that is a target value of a first current flowing on the AC side of the power conversion circuit, and a second target value that is a target value of a second current having a lower frequency than the first current, wherein a dead time set so that the upper and lower arms are not simultaneously turned on in the switching signal is T d [s], and a carrier period of the controller is T c [s], and a voltage on the DC side of the power conversion circuit is V dc [V], and when an average value of gain characteristics from the first target value to the first current in a predetermined frequency band when the second current is not output is defined as G0[dB], the average value of the gain characteristics from the first target value to the first current in the frequency band when the first current is being output and the second current is output is lower than a gain characteristic (G(i)) calculated by formula (1), where i[A] is the second current output in this state. In this case, when the power conversion device outputs a fundamental wave current in addition to a harmonic current, oscillation in control of the harmonic current can be suppressed.

[0006]

Mathematical Formula

[0007] A power conversion device according to a second aspect is the power conversion device according to the first aspect, wherein the first current is a current having a plurality of zero cross points in one cycle on the AC side of the power conversion circuit, and the one cycle is one cycle of the voltage of the power supply when the AC side of the power conversion circuit is connected to the power supply, and is one cycle of the current of the load when the AC side of the power conversion circuit is connected to the load. A power conversion device according to a third aspect is the power conversion device according to the second aspect, wherein a current obtained by superimposing the first current and the second current has a reduced number of zero cross points in the one cycle as compared with the first current. The power converter according to the fourth aspect is a power converter according to any of the first to third aspects, wherein the AC side of the power converter circuit is connected to the power supply, and it is a power converter that controls the first current and the second current flowing to the power supply, and the upper limit of the predetermined frequency band is 40 times or less the frequency of the power supply. In this case, oscillation in the control of harmonic currents can be suppressed in the control band of the power converter circuit. The power converter according to the fifth aspect is a power converter according to any of the first to fourth aspects, wherein the difference between the average value of the gain characteristics (G0) when the second current is not output and the average value of the gain characteristics when the second current is output is within 3 dB. In this case, even if the second current increases, oscillation of the harmonic current control can be suppressed. The power converter according to the sixth aspect is a power converter according to any of the first to fifth aspects, wherein the controller sets the control gain of the first current based on the second current or the second target value. The power converter according to the seventh aspect is a power converter according to any of the first to sixth aspects, wherein the controller controls the first current and the second current separately. In this case, control performance according to frequency can be obtained by setting the control responses separately. The air conditioning system of the eighth aspect incorporates a power converter of any of the first to seventh aspects. In this case, when the power converter outputs a fundamental wave current in addition to harmonic currents, oscillation in the control of harmonic currents can be suppressed. The air conditioning system according to the ninth aspect comprises multiple power converters according to any of the first to seventh aspects, and these multiple power converters share the output of the first current and the second current. In this case, the output amount per power converter can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of the configuration of the active filter device according to this embodiment. [Figure 2] This figure shows an example of an inverter circuit configuration. [Figure 3] This figure shows an example of an inverter circuit configuration when the AC side is connected to a load. [Figure 4] This diagram defines one cycle of the AC side when the AC side of an inverter circuit is connected to an AC power source, with (a) showing the voltage waveform of the AC power source and (b) showing the waveform of the harmonic current. [Figure 5] This diagram defines one cycle of the AC side when the AC side of an inverter circuit is connected to a load. (a) shows the waveform of the load current flowing through the load, and (b) shows the waveform of the harmonic current. [Figure 6] This diagram shows the waveforms of the harmonic current, fundamental current, and the superimposed current output by the inverter circuit. [Figure 7] This figure shows the repetitive control in a harmonic current controller. [Figure 8] This diagram shows the movement of the upper and lower arms of the inverter circuit. [Figure 9] This figure shows the relationship between the fundamental wave current output by the inverter circuit and the dead time voltage error. (a) shows the waveform of the compensation current when the magnitude of the fundamental wave current output by the inverter circuit is changed, and (b) shows the relationship between the magnitude of the fundamental wave current output by the inverter circuit and the average dead time voltage error. [Figure 10] This figure shows the relationship between the fundamental wave current output by the inverter circuit and the gain characteristics from the command value of the harmonic current in the harmonic current control to the output harmonic current, when the harmonic current controller does not adjust the control gain. [Figure 11] This figure shows the adjustment of the control gain according to this embodiment. [Figure 12] This figure shows the gain characteristics calculated by equation (1). [Figure 13] This figure shows the relationship between the fundamental wave current output by the inverter circuit and the gain characteristics of the harmonic current control when the harmonic current controller adjusts its control gain. [Figure 14]This figure shows an example of limiting the gain characteristics using an index other than the one calculated using equation (1). [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the attached drawings. <Configuration of an active filter device> Figure 1 shows an example configuration of the active filter device 100 according to this embodiment. Figure 1 shows the case where the active filter device 100 is incorporated into the air conditioning system 36. The active filter device 100 is an example of a power conversion device.

[0010] The air conditioning system 36 is installed in buildings, factories, apartment buildings, etc. Power is supplied to these buildings, etc., from the power source 20 via distribution lines. Here, the power source 20 and the distribution lines 21 are collectively referred to as the power distribution system. The distribution lines 21 have an impedance 22 of the distribution line or transformer. The power source 20 is, for example, a three-phase AC power source (commercial power). The air conditioning system 36 is equipped with a refrigerant circuit (not shown) that circulates a refrigerant to perform refrigeration cycle operation, and is used to cool or heat rooms in buildings and the like. The refrigerant circuit of the air conditioning system 36 is equipped with a compressor that compresses the refrigerant. The air conditioning system 36 includes a power converter 60.

[0011] As shown in Figure 1, the power converter 60 of the air conditioning unit 36 ​​comprises a converter circuit 61, a reactor 62, a capacitor 63, an inverter circuit 64, a motor 65, and a noise filter 66. The converter circuit 61 is a circuit that converts alternating current (AC) to direct current (DC). The converter circuit 61 is, for example, a diode bridge circuit. The capacitor 63 smooths the output of the converter circuit 61. The inverter circuit 64 converts the DC smoothed by the capacitor 63 into AC of a predetermined frequency and voltage. The inverter circuit 64 comprises, for example, multiple switching elements and converts the input DC into AC by switching them.

[0012] The motor 65 of the power converter 60 of the air-conditioning apparatus 36 is, for example, an IPM motor (Interior Permanent Magnet Motor). The motor 65 drives a compressor provided in a refrigerant circuit. The motor 65 is an example of a load. Here, if no measures are taken, the operation of the motor 65 causes the current of the power distribution system (hereinafter referred to as system current I S ) to have a harmonic current superimposed thereon. The power converter 60 is an example of a device that generates a harmonic current.

[0013] The active filter device 100 includes a current source 110, a control unit 120, and a PWM controller 141. The active filter device 100 is connected in parallel with the power converter 60 to the power supply 20. The control unit 120 and the PWM controller 141 are an example of a controller. The active filter device 100 supplies a compensation current I from the current source 110 C to the power distribution system, thereby improving the voltage of the power distribution system and suppressing the harmonic current of the power converter 60 in the air-conditioning apparatus 36. Here, the compensation current I C is defined as positive in the direction flowing from the current source 110 to the power distribution system. The system current I S and the compensation current I C are assumed to be equal to the load current I that flows from the power supply 20 to the power converter 60 which is an example of a load. L

[0014] If an inverter circuit is included in the load connected to the power distribution system, the inverter circuit performs switching at a frequency higher than the fundamental wave frequency, so that a harmonic current is added to the current of the power distribution system and affects the power supply. Accordingly, the active filter device 100 supplies a compensation current to the power distribution system to suppress the harmonic current. Further, from the viewpoint of reducing the capacity of facilities included in the power distribution system and saving energy, improvement of the fundamental wave power factor is required. The active filter device 100 has a function of improving the fundamental wave power factor, and is configured to output a compensation current of the fundamental wave current in addition to the harmonic current. The harmonic current is an example of a first current. The fundamental wave current is an example of a second current.

[0015] ​ The fundamental wave is a sine wave consisting of the frequency components of the power supply 20. For example, if the frequency of the power supply is 50 Hz, the fundamental wave frequency will be 50 Hz. Harmonics are frequency components that are integer multiples of the fundamental wave. Integer multiples are 2 or more. The fundamental wave is not included in harmonics. In this disclosure, the fundamental wave component of the current is referred to as the fundamental wave current, and the harmonic component of the current is referred to as the harmonic current. Furthermore, the harmonic current dealt with in this disclosure is a current that includes harmonic components from the 2nd order to the 40th order. In other words, the current control bandwidth of the harmonic current controller 121 dealt with in this disclosure is 40th order or less. 40th order is an example of a predetermined upper limit of the frequency bandwidth.

[0016] The current source 110 comprises an inverter circuit 111 and a capacitor 113. The inverter circuit 111 is an example of a power conversion circuit. The capacitor 113 is composed of, for example, an electrolytic capacitor. The inverter circuit 111 provides a compensation current I C The capacitor 113 is charged and discharged by inputting and outputting. In this example, the inverter circuit 111 is connected to the power distribution system via a three-phase reactor 146. The inverter circuit 111, like the inverter circuit 64, is composed of multiple (six in this case) semiconductor switching elements. The inverter circuit 111 changes the switching state (on / off state) of the multiple switching elements in synchronization with the drive signal G of a predetermined frequency output by the PWM controller 141, thereby generating a compensation current I including the fundamental wave current and harmonic current. C It inputs and outputs. In Figure 1, the compensation current I C A low-pass filter 145, which removes ripple, is provided between the reactor 146 and the connection point between the power distribution system and the power converter 60. The low-pass filter 145 is a so-called LC filter. The configuration and operation of the inverter circuit 111 will be described later.

[0017] The control unit 120 comprises a harmonic current controller 121 and a fundamental wave current controller 122. Specifically, the main part of the control unit 120 can be configured using a microcomputer and a memory device containing software for operating it.

[0018] The harmonic current controller 121 controls the harmonic current using an algorithm such as feedback control (for example, so-called PID control) based on the deviation between the commanded value and the measured value of the harmonic current. The adjustment of the control gain by the harmonic current controller 121 will be described later. The fundamental wave current controller 122 controls the fundamental wave current using an algorithm such as feedback control (for example, so-called PID control) based on the deviation between the commanded value and the measured value of the fundamental wave current.

[0019] The harmonic current controller 121 controls harmonic currents of 100 Hz or higher or 120 Hz or higher, while the fundamental wave current controller 122 controls fundamental wave currents of 60 Hz or 50 Hz. The current control response of the harmonic current controller 121 and the current control response of the fundamental wave current controller 122 can be set separately. Note that control delay occurs as the frequency increases, so the control response of the harmonic current controller 121 must be set higher than that of the fundamental wave current controller 122 depending on the frequency component being controlled. By having separate current controllers corresponding to the frequency components of the controlled material, it is possible to set separate control responses and obtain control performance according to the frequency.

[0020] The PWM controller 141 generates a drive signal G to drive the current source 110 based on the output of the harmonic current controller 121 and the output of the fundamental wave current controller 122. The PWM controller 141 performs so-called PWM (pulse width modulation) control and supplies a compensating current I to the current source 110. C The PWM controller 141 can be configured using a microcomputer and a memory device that stores the software for operating it.

[0021] Figure 2 shows an example of the circuit configuration of the inverter circuit 111. The inverter circuit 111 consists of six semiconductor switching elements SW1, SW2, SW3, SW4, SW5, and SW6. Switching elements SW1 and SW2, SW3 and SW4, and SW5 and SW6 each form an upper and lower arm. Each upper and lower arm is controlled by a PWM controller 141 so that they do not turn on simultaneously. In the following, the arm equipped with switching element SW1 will be referred to as the upper arm 114, and the arm equipped with switching element SW2 will be referred to as the lower arm 115.

[0022] Harmonic currents are currents that have multiple zero-crossing points within one cycle of the fundamental wave on the AC side of the inverter circuit 111. The AC side of the inverter circuit 111 is connected to an AC power source and / or load. In the examples shown in Figures 1 and 2, the AC side of the inverter circuit 111 is connected to a power source 20, which is an AC power source. One cycle of the AC side is one cycle of the voltage of the AC power source when the AC side of the inverter circuit 111 is connected to an AC power source.

[0023] Figure 3 shows an example of the circuit configuration of the inverter circuit 111 when the AC side is connected to a load. As shown in Figure 3, the capacitor 113 of the inverter circuit 111 is connected to the power supply 35 via the rectifier 37. The AC side of the inverter circuit 111 is connected to the load, which is the motor 30. In the case shown in Figure 3, one cycle on the AC side is one cycle of the current flowing through the load, which is the motor 30. The inverter circuit 111 is an example of a power conversion device.

[0024] Figure 4 is a diagram that defines one cycle of the AC side when the AC side of the inverter circuit 111 is connected to an AC power source. Figure 4(a) shows the voltage waveform of the AC power source, and Figure 4(b) shows the waveform of the harmonic current. In Figure 4(a), the horizontal axis represents the phase (rad) and the vertical axis represents the power supply voltage (V). In Figure 4(b), the horizontal axis represents the phase (rad) and the vertical axis represents the harmonic current (A). As shown in Figure 4, one cycle on the AC side corresponds to one cycle of the AC power supply voltage. As shown in Figure 4(b), the harmonic current has multiple zero-crossing points within one cycle on the AC side. A zero-crossing point is a point where the current intersects with 0A.

[0025] Figure 5 is a diagram that defines one cycle on the AC side when the AC side of the inverter circuit 111 is connected to a load. Figure 5(a) shows the waveform of the load current flowing through the load, and Figure 5(b) shows the waveform of the harmonic current. In Figure 5(a), the horizontal axis represents the phase (rad) and the vertical axis represents the load current (A). In Figure 5(b), the horizontal axis represents the phase (rad) and the vertical axis represents the harmonic current (A). As shown in Figure 5, one cycle on the AC side corresponds to one cycle of the load current. As shown in Figure 5(b), the harmonic current has multiple zero-crossing points within one cycle on the AC side.

[0026] Figure 6 shows the waveforms of the harmonic current, fundamental current, and the superimposed current output by the inverter circuit 111. In Figure 6, the horizontal axis represents phase (rad) and the vertical axis represents current (A). As shown in Figure 6, the current obtained by superimposing the harmonic current and the fundamental wave current has fewer zero-crossing points in one cycle on the AC side compared to the harmonic current alone.

[0027] <Repeat control> Figure 7 shows the repetitive control in the harmonic current controller 121. The harmonic current controller 121 includes a PI current controller 1211 and a repetitive controller 1212. The PI current controller 1211 receives the deviation between the first target value, which is the command value of the harmonic current, and the harmonic current as input. The PI current controller 1211 outputs a value calculated by performing proportional-integral control on the input deviation. The repetitive controller 1212 stores one cycle of the input signal and performs repetitive control by delaying the output by one cycle. When the harmonic current controller 121 outputs, it adds the value from one cycle prior to the output by the repetitive controller 1212 and outputs that value. Repetitive control enables control that compensates for the phase delay caused by the delay in harmonic current control, thereby improving the performance of harmonic current compensation. Note that the configuration of the harmonic current controller 121 is not limited to the form shown in Figure 6.

[0028] In cases where this embodiment is not applied, if the power converter outputs a fundamental wave current in addition to harmonic currents, oscillation may occur in the control of the harmonic currents. Below, using Figures 8 to 10, we will explain how the repetitive control of harmonic currents causes oscillation.

[0029] Figure 8 shows the operation of the upper arm 114 and lower arm 115 of the inverter circuit 111. The switching element SW1 on the upper arm 114 and the switching element SW2 on the lower arm 115 are exclusively controlled by the PWM controller 141, so that when one is ON, the other is OFF. In addition, to suppress the formation of a short circuit caused by switching elements SW1 and SW2 being ON at the same time, a dead time T is set when both switching elements SW1 and SW2 are OFF. d A system will be established.

[0030] Dead Time T d By providing this, the voltage command value V to the inverter circuit 111 * d And the output voltage V of the inverter circuit 111 d Error (dead time voltage error V) dead ) occurs. Dead time is T d (s) The carrier period of the PWM controller 141 is set to T c (s) The DC voltage of the inverter circuit 111 is V dc(V), the compensation current, which is the sum of the fundamental wave current and harmonic currents output by the inverter circuit 111, is I C (A) When the dead time voltage error is V dead This can be expressed as shown in equation (2).

[0031]

number

[0032] Figure 9 shows the compensation current I output by the inverter circuit 111. C and dead time voltage error V dead This figure shows the relationship between the inverter circuit 111 and the compensation current I. C The compensation current I when the magnitude of the fundamental wave current superimposed on it is changed. C This figure shows the waveform. Figure 9(b) shows the magnitude of the fundamental wave current output by the inverter circuit 111 and the average dead time voltage error V dead This figure shows the relationship between the two. The average dead time voltage error is the average value of the dead time voltage error per cycle on the AC side. In Figure 9(a), the horizontal axis is phase (rad), and the vertical axis is compensation current (I C Figure 9(b) shows (A). In Figure 9(b), the horizontal axis represents the fundamental wave current (A), and the vertical axis represents the average dead time voltage error (V).

[0033] As shown in equation (2), the dead time voltage error V dead This is generated in the opposite direction to the current polarity and interferes with the current output by the inverter circuit 111. As shown in Figure 9(a), increasing the fundamental wave current increases the compensation current I C The number of points where the current polarity switches (the number of zero-crossing points) decreases. Therefore, as shown by the arrow in Figure 9(b), increasing the fundamental wave current increases the dead time voltage error V that occurs in a direction that opposes the output of the harmonic current. dead It decreases.

[0034] Figure 10 shows the relationship between the fundamental wave current output by the inverter circuit 111 and the gain characteristics from the command value of the harmonic current controlled by the harmonic current control, when the harmonic current controller 121 does not adjust the control gain. In Figure 10, the horizontal axis represents frequency (Hz) and the vertical axis represents gain (dB). The gain characteristics are obtained by measuring and plotting the frequency response of the harmonic current. Figure 10 shows the input-output ratio plotted for each frequency. The gain characteristics were measured using a frequency sweep range of 100 Hz to 10 kHz. The total number of measurement data points was 1024, and the frequency was varied using a logarithmic sweep, with the gain characteristics measured at each frequency. The ideal curve shown by the dashed line in Figure 10 represents the dead time voltage error V dead The gain characteristics when = 0 are shown. As mentioned above, increasing the fundamental wave current increases the dead time voltage error V dead This decreases, resulting in a voltage command value V to the inverter circuit 111. * d And the output voltage V of the inverter circuit 111 d The error becomes smaller.

[0035] Increase the fundamental wave current to reduce the dead time voltage error V dead As the fundamental wave current decreases, the gain characteristic of the harmonic current control increases and approaches the ideal curve. When the gain characteristic of the harmonic current control increases, the difference from the gain characteristic when the fundamental wave current is not output becomes large. The repetitive control of the harmonic current is set based on the case when the fundamental wave current is not output. Therefore, when the fundamental wave current increases, the gain margin decreases, and the repetitive control oscillates.

[0036] In this embodiment, oscillation in the repetitive control is suppressed by adjusting the control gain of the harmonic current control according to the magnitude of the fundamental wave current. The adjustment of the control gain will be described below.

[0037] <Adjusting the control gain> Figure 11 shows the adjustment of the control gain according to this embodiment. The PWM controller 141 generates a drive signal G that drives the inverter circuit 111 of the current source 110 based on the output of the harmonic current controller 121 and the output of the fundamental current controller 122. The inverter circuit 111, in synchronization with the drive signal G, generates a compensation current I that includes the fundamental current and the harmonic current. C Input and output. Compensation current I C The signal passes through a high-pass filter (HPF) 116 or a low-pass filter (LPF) 117 to separate the harmonic current from the fundamental current.

[0038] The harmonic currents that have passed through the high-pass filter 116 are input to the harmonic current controller 121. The fundamental wave currents that have passed through the low-pass filter 117 are input to the fundamental wave current controller 122. The fundamental wave current controller 122 performs feedback control based on the deviation between the second target value, which is the command value of the fundamental wave current, and the measured value of the fundamental wave current output from the low-pass filter 117.

[0039] The harmonic current controller 121 includes a controller 124 (denoted as β in Figure 11) that sets a control gain for a first target value, which is the command value of the harmonic current. The harmonic current controller 121 also includes a controller 123 (denoted as α in Figure 11) that sets a control gain for the deviation between the first target value and the measured value of the harmonic current output from the high-pass filter 116. The harmonic current controller 121 sets the control gain of controller 123 or controller 124 based on the magnitude of the fundamental wave current or a second target value, which is the command value of the fundamental wave current, thereby suppressing oscillation in the repetitive control.

[0040] The harmonic current controller 121 controls the inverter circuit 111 so that the average value of the gain characteristic from the command value of the harmonic current to the output harmonic current in the frequency band of the 40th order or less is less than the gain characteristic calculated by equation (1). The gain characteristic from the command value of the harmonic current to the output harmonic current is the ratio (amplification factor) of the output obtained to the command value. The gain characteristic from the command value of the harmonic current to the output harmonic current is measured using a measuring device such as a servo analyzer. The gain characteristic in the frequency band of the 40th order or less is extracted from the measurement results and the average value is calculated. The average value of the gain characteristic may be measured experimentally or calculated by simulation. In equation (1), T d The dead time (s) is T c V represents the carrier period (s). dc is the DC voltage (V) of the inverter circuit 111, and i is the fundamental wave current (A) in the dq coordinate output by the inverter circuit 111. G0 represents the average value of the gain characteristics from the command value of the harmonic current to the output harmonic current in the frequency band of the 40th order or lower, when the inverter circuit 111 does not output a fundamental wave current. G0 can be expressed as shown in equation (3) or equation (4). Equation (3) uses a method of sweeping by changing the frequency at which the gain characteristics are measured on a logarithmic scale. Equation (4) uses a method of sweeping by changing the frequency at which the gain characteristics are measured on a linear scale. Either equation (3) or equation (4) can be used to calculate G0. In equations (3) and (4), f min f is the minimum frequency (Hz) at which the gain characteristics are measured. max n is the maximum frequency (Hz) at which the gain characteristics are measured. max represents the total number of measurement data points. Also, in equations (3) and (4), MEAS() represents the measured value (dB) of the gain characteristic, and the argument is frequency (Hz).

[0041]

number

[0042]

number

[0043]

number

[0044] Figure 12 shows the gain characteristics calculated by equation (1). In Figure 12, the horizontal axis represents the fundamental wave current (A) in dq coordinates, and the vertical axis represents the gain (dB). The dashed line in Figure 12 shows the gain characteristics calculated by equation (1). The gain when the fundamental wave current is 0A is G0. If the harmonic current controller 121 does not set the control gain of controller 123 or controller 124 based on the second target value, the gain characteristic follows the dashed line shown in Figure 12. The harmonic current controller 121 adjusts the control gain so that the gain characteristic is smaller than the dashed line shown in Figure 12.

[0045] Figure 13 shows the relationship between the fundamental wave current output by the inverter circuit 111 and the gain characteristics of the harmonic current control when the harmonic current controller 121 adjusts its control gain. In Figure 13, the horizontal axis represents frequency (Hz) and the vertical axis represents gain (dB). Figure 13 plots the input-output ratio for each frequency. Similar to Figure 10, the ideal curve is shown as a dashed line in Figure 13. By adjusting the control gain with the harmonic current controller 121, the change in gain characteristics due to changes in the magnitude of the fundamental wave current is canceled out, and the gain characteristics become similar to those when no fundamental wave current is output. This suppresses oscillation in the repetitive control. Note that the gain characteristics at a fundamental current of 0A shown in Figures 10 and 13, and point G0 at a fundamental current of 0A shown in Figures 12 and 14, are V dc , T d , T c This is an example under specific conditions, including [mentioning specific conditions]. The two results do not necessarily represent the same conditions.

[0046] <Variation> The above embodiment is merely an example and is not limited thereto. For example, the harmonic current controller 121 may set the control gain using an index other than the gain characteristic calculated by equation (1). Figure 14 shows an example of limiting the gain characteristics using an index other than the one calculated by equation (1). In Figure 14, the horizontal axis represents the fundamental wave current (A), and the vertical axis represents the gain (dB). The dashed line shown in the graph of Figure 14 represents the gain characteristics calculated by equation (1). The gain characteristic G0 is when the fundamental wave current is 0A. The solid line shown in the graph of Figure 14 represents a gain 3 dB higher than G0 calculated by equation (3).

[0047] The harmonic current controller 121 adjusts its control gain so that its gain characteristics are smaller than the dashed and solid lines shown in Figure 14. The gain characteristics are adjusted so that the difference between the gain characteristics from the command value of the harmonic current to the output harmonic current (G0) in the frequency band of the 40th harmonic order and below, when the inverter circuit 111 does not output a fundamental wave current, is within 3 dB. When designing the harmonic current controller 121, a gain margin of 3 dB is ensured, taking into account the variation in the element constants of the active filter device 100. If the gain characteristics increase due to the output of the fundamental wave current and exceed the margin, the control system becomes unstable. Therefore, the variable gain is adjusted to keep the difference in the gain characteristics with respect to G0 within 3 dB. By keeping the difference with respect to G0 within 3 dB, oscillation due to repetitive control is suppressed even when the fundamental wave current increases.

[0048] Furthermore, although this embodiment describes a case in which the active filter device 100 is incorporated into the air conditioning system 36, it is not limited to this. The active filter device 100 may not be incorporated into the air conditioning system 36, but may be provided outside the air conditioning system 36. Alternatively, the control of harmonic currents and fundamental wave currents may be performed by a single controller.

[0049] Furthermore, multiple active filter devices 100 are incorporated into the air conditioning system 36 and share the responsibility of providing compensation current (IC The configuration may also output a compensation current (I C ) is output. Multiple active filter devices 100 have a compensation current (I C The harmonic currents and fundamental currents contained in the signal may be equally divided and output, or they may be divided into an active filter device 100 that outputs only the harmonic currents and an active filter device 100 that outputs only the fundamental currents.

[0050] <Effects> The active filter device 100 in the first aspect is connected to a power supply 20 and comprises an inverter circuit 111 that converts AC power to DC power and is composed of upper and lower arms of semiconductor switching elements, and a controller that generates a switching signal to control the upper and lower arms of the inverter circuit 111 based on a first target value which is a target value for a first current flowing on the AC side of the inverter circuit 111 and a second target value which is a target value for a second current with a lower frequency than the first current, and the switching signal includes a dead time T set so that the upper and lower arms are not turned on at the same time. d [s], the carrier period of the controller is set to T c [s] The DC voltage of the inverter circuit 111 is V dc Let [V] be the value of the gain characteristics from the first target value to the first current in a predetermined frequency band when the second current is not outputting, and let G0 [dB] be the average value of the gain characteristics from the first target value to the first current in a predetermined frequency band when the first current is outputting and the second current is outputting, then when the second current outputting in that state is i [A], the average value of the gain characteristics from the first target value to the first current in the frequency band is less than the gain characteristic (G(i)) calculated by equation (1). In this case, when the active filter device 100 outputs a fundamental wave current in addition to the harmonic current, oscillation in the control of the harmonic current can be suppressed. The active filter device 100 in the second aspect is the active filter device 100 in the first aspect, wherein the first current is a current having multiple zero-crossing points in one cycle of the AC side of the inverter circuit 111, and one cycle is one cycle of the voltage of the power supply 20 when the AC side of the inverter circuit 111 is connected to the power supply 20, and one cycle of the load current when the AC side of the inverter circuit 111 is connected to a load. The active filter device 100 in the third aspect is the active filter device 100 in the second aspect, wherein the current obtained by superimposing the first current and the second current has a reduced number of zero-crossing points in one period compared to the first current. The active filter device 100 in the fourth aspect is an active filter device 100 according to any of the first to third aspects, wherein the AC side of the inverter circuit 111 is connected to the power supply 20, and the active filter device 100 controls the first current and the second current flowing to the power supply 20, and the upper limit of the predetermined frequency band is 40 times or less the frequency of the power supply 20. In this case, oscillation in the control of harmonic currents can be suppressed in the control band of the inverter circuit 111. The active filter device 100 according to the fifth viewpoint is an active filter device 100 according to any of the first to fourth viewpoints, wherein the difference between the average value of the gain characteristics (G0) when the second current is not output and the average value of the gain characteristics when the second current is output is within 3 dB. In this case, even if the second current becomes large, oscillation of the harmonic current control can be suppressed. The active filter device 100 of the sixth aspect is an active filter device 100 of any of the first to fifth aspects, wherein the controller sets the control gain of the first current based on the second current or the second target value. The active filter device 100 in the seventh aspect is an active filter device 100 according to any of the first to sixth aspects, wherein the controller controls the first current and the second current separately. In this case, the control response can be set separately to obtain control performance according to the frequency. The air conditioning system 36 according to the eighth aspect incorporates an active filter device 100 according to any of the first to seventh aspects. In this case, when the active filter device 100 outputs a fundamental wave current in addition to harmonic currents, oscillation in the control of harmonic currents can be suppressed. The air conditioning system 36 according to the ninth aspect comprises multiple active filter devices 100 according to any of the first to seventh aspects, and the multiple active filter devices 100 share the output of the first current and the second current. In this case, the output amount per active filter device 100 can be suppressed.

[0051] Although embodiments have been described above, the technical scope of this disclosure is not limited to the embodiments described above. It is clear from the claims that combinations of two or more of the above embodiments, as well as various modifications or improvements to the above embodiments, are also included in the technical scope of this disclosure. [Explanation of Symbols]

[0052] 20...Power supply, 60...Power converter, 100...Active filter device, 110...Current source, 111...Inverter circuit, 120...Control unit, 121...Harmonic current controller, 122...Fundamental current controller

Claims

1. Connected to a power source, A power conversion circuit consisting of upper and lower arms of semiconductor switching elements that converts AC power to DC power, The power conversion circuit comprises a controller that generates a switching signal to control the upper and lower arms of the power conversion circuit based on a first target value which is a target value for a first current flowing on the AC side of the power conversion circuit, and a second target value which is a target value for a second current with a lower frequency than the first current. The switching signal is given a dead time T such that the upper and lower arms do not turn on simultaneously. ｄ [s] The carrier period of the controller is set to T ｃ [s] The voltage on the DC side of the power conversion circuit is V ｄｃ Let [V] be the value, and G be the average value of the gain characteristics from the first target value to the first current in a predetermined frequency band when the second current is not being output. ０ A power converter wherein, when the first current is output and the second current is output, the average gain characteristic from the first target value to the first current in the frequency band is less than the gain characteristic (G(i)) calculated by equation (1), where i [A] is the second current output in that state. [Math 1]

2. The first current is a current having multiple zero-crossing points during one cycle on the AC side of the power conversion circuit, The power conversion device according to claim 1, wherein the aforementioned one cycle is one cycle of the voltage of the power supply when the AC side of the power conversion circuit is connected to the power supply, and one cycle of the current of the load when the AC side of the power conversion circuit is connected to a load.

3. The power conversion device according to claim 2, wherein the current obtained by superimposing the first current and the second current has a reduced number of zero-crossing points during one cycle compared to the first current.

4. The AC side of the power conversion circuit is connected to the power supply. A power conversion device that controls the first current and the second current flowing to the power supply, The power conversion device according to any one of claims 1 to 3, wherein the upper limit of the predetermined frequency band is 40 times or less the frequency of the power supply.

5. The average value of the gain characteristic (G) when the second current is not being output. ０ )and, The power conversion device according to any one of claims 1 to 3, wherein the difference between the average value of the gain characteristics when the second current is output is within 3 dB.

6. The power conversion device according to any one of claims 1 to 3, wherein the controller sets the control gain of the first current based on the second current or the second target value.

7. The power conversion device according to any one of claims 1 to 3, wherein the controller separately controls the first current and the second current.

8. An air conditioning system incorporating a power conversion device according to any one of claims 1 to 3.

9. An air conditioning system comprising a plurality of power converters according to any one of claims 1 to 3, wherein the plurality of power converters share the output of the first current and the second current.

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