JP2023140713A - Electric power conversion system - Google Patents

Abstract

To provide an electric power conversion system that can appropriately monitor a power supply voltage to continue operation properly.SOLUTION: An electric power conversion system is equipped with: electric power converters that are connected to power supply lines of a three-phase AC power supply, which are connected to the power supply lines through passive filters to perform electric power conversion by switching; a voltage detecting part that detects voltages between power-distribution paths extending from the power supply lines to the passive filters and predetermined positions in the electric power converters; a rectangular wave removing filter that removes rectangular wave components generated accompanying the switching from voltages detected by the voltage detecting part; and a control part that estimates values of the power supply voltages of the three-phase AC power supply on the basis of the voltages having the rectangular wave components removed therefrom by the rectangular wave removing filter and zero-phase voltages superposing on potentials at the predetermined positions in the electric power converters, and controls the switching of the electric power converters on the basis of the estimated results.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to a power conversion device connected to each power line of a three-phase AC power source.

BACKGROUND ART Power conversion devices, such as multilevel converters and converters, which are connected to each power line of a three-phase AC power source and perform power conversion by switching, are known.

This power conversion device needs to be protected by monitoring the power supply voltage of the three-phase AC power supply and stopping operation if an abnormality occurs in the power supply voltage.

Patent No. 6453108

The power supply voltage of a three-phase AC power supply changes depending on the operating state of the power supply and the operating state of other electrical equipment connected to the three-phase AC power supply. Accurately capturing this change has become an important issue.

An object of the embodiments of the present invention is to provide a power conversion device that can accurately monitor power supply voltage with a simple configuration.

The power converter of the embodiment is connected to each power line of a three-phase AC power source, and includes: a power converter that is connected to each power line through a passive filter and performs power conversion by switching; a voltage detection unit that detects a voltage between a current-carrying path from each power supply line to the passive filter and a predetermined position in the power converter; detecting a rectangular wave component accompanying the switching from the voltage detected by the voltage detection unit; a rectangular wave removal filter to be removed; estimating the value of the power supply voltage of the three-phase AC power supply based on the voltage passing through the rectangular wave removal filter and a zero-phase voltage superimposed on the potential at the predetermined position in the power converter; , and a control unit that controls switching of the power converter based on the estimation result.

FIG. 1 is a block diagram showing the configuration of the first embodiment. The figure which shows the structure of each unit converter in 1st Embodiment. FIG. 3 is a diagram showing the configuration of a rectangular wave removal filter in the first to third embodiments. FIG. 3 is a diagram showing main parts of a control section in the first embodiment. FIG. 4 is a diagram showing the cutoff frequency of the low-pass filter in FIG. 3; FIG. 7 is a diagram showing the value of power supply voltage due to the presence of a lead compensator in the first embodiment. FIG. 7 is a diagram showing the value of the power supply voltage when there is no lead compensator in the first embodiment. FIG. 2 is a block diagram showing the configuration of a second embodiment. FIG. 3 is a block diagram showing the configuration of a converter in second and third embodiments. 10 is a diagram showing another example of the configuration of the converter in FIG. 9. FIG. 10 is a diagram showing still another configuration example of the converter in FIG. 9. FIG. FIG. 7 is a diagram showing main parts of a control unit in a second embodiment. FIG. 7 is a block diagram showing the configuration of a third embodiment.

[1] First embodiment
A first embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a load, such as an air conditioner 2, is connected to power lines Lr, Ls, and Lt of a three-phase AC power source 1. The air conditioner 2 includes a rectifier circuit 3 that rectifies the power supply voltages Vr, Vs, and Vt of the three-phase AC power supply 1 using a plurality of bridge-connected diodes, and the output voltage of the rectifier circuit 3 is applied via a DC reactor 4. It includes a capacitor 5, an inverter 6 connected between both ends of the capacitor 5 and converting the DC voltage into an AC voltage of a predetermined frequency and outputting the same, a compressor motor 7 operated by the output of the inverter 6, and the like. Note that the three-phase AC power supply 1 may be a commercial three-phase AC power supply or a privately generated three-phase AC power supply.

A power conversion device 10 is connected in parallel with the air conditioner 2 to power lines Lr, Ls, Lt to which the air conditioner 2 is connected.

The power converter 10 includes an LC filter 11, interconnection reactors 14r, 14s, 14t, a passive filter consisting of the LC filter 11 and interconnection reactors 14r, 14s, 14t, and power supply lines Lr, Ls, Lt through the passive filter. A multi-level converter (converter) 20 is provided. Furthermore, the power conversion device 10 is arranged at a position closer to the air conditioner 2 than the connection position of the LC filter 11 in the power lines Lr, Ls, Lt, and converts currents (load currents) Ir, Is, It flowing into the air conditioner 2. Among the detection unit 15 that detects, the detection unit 16 that detects the currents Icr, Ics, and Ict flowing in the energization paths between the interconnection reactors 14r, 14s, and 14t and the multilevel converter 20, and the power supply lines Lr, Ls, and Lt. For example, between each energizing path from the power supply lines Lr, Ls to the passive filter (LC filter 11 and interconnection reactors 14r, 14s, 14t) and a neutral point (predetermined position) A, which will be described later, in the multilevel converter 20. A voltage detecting section 17 that detects the voltages Vr_n and Vs_n of the voltage detecting section 17, a rectangular wave removal filter 18 that removes the rectangular wave components associated with the switching of the multilevel converter 20 from the voltages Vr_n and Vs_n detected by the voltage detecting section 17, The power supply voltage Vr of each phase of RST of the three-phase AC power supply 1 is determined based on the voltages Vr_n, Vs_n that have passed through the wave removal filter 18 and the zero-phase voltage Vo superimposed on the potential of a neutral point A, which will be described later, in the multilevel converter 20. , Vs, Vt and the phase θ, and controls switching of the multilevel converter 20 according to the estimation results and the detection results of the detection units 15 and 16.

The LC filter 11 includes an LC circuit consisting of a reactor 12r and a capacitor 13r, an LC circuit consisting of a reactor 12s and a capacitor 13s, and an LC circuit consisting of a reactor 12t and a capacitor 13t for each phase of the RST.

The multilevel converter 20 includes clusters 21r, 21s, and 21t that selectively generate and output DC voltages of three or more levels for each phase of the power lines Lr, Ls, and Lt, and the air conditioner 2 that is the load. It functions as an active filter that suppresses harmonic components of the current generated from the rectifier circuit 3 and flowing to the rectifier circuit 3. Hereinafter, each cluster 21r, 21s, 21t has the same configuration and will be collectively referred to as cluster 21.

The cluster 21r is a so-called multi-level converter formed by connecting in series (cascade connection) a plurality (three) unit converters (cells) 22r, each of which selectively generates and outputs a multi-level DC voltage by switching. It is a series converter cluster, and generates and outputs an alternating current voltage Vcr0 by adding up the output voltages (cell output voltages) Vcr of each unit converter 22r.

Similarly, the cluster 21s has a plurality of unit converters 22s connected in series, and generates and outputs an AC voltage Vcs0 by adding together the output voltages Vcs of the unit converters 22s.

The cluster 21t has a plurality of unit converters 22t connected in series, and generates and outputs an alternating current voltage Vct0 by adding together the output voltages Vct of the unit converters 22t. The output voltage of each cluster 21 has a waveform close to a sine wave to reduce harmonics.

One end of each cluster 21 is interconnected (star connection) to become a neutral point A, and the other end of each cluster 21 is connected to the power supply line Lr via a passive filter (LC filter 11 and interconnection reactors 14r, 14s, 14t). , Ls, and Lt, respectively.

Since the configuration of each cluster 21 is the same, the configuration of each unit converter 22r in the cluster 21r is shown in FIG. 2 as a representative example.

Each unit converter 22r has a pair of output terminals, switch elements Q1, Q2, Q3, Q4 each having a free wheel diode D, and a capacitor (DC capacitor) C connected to the output terminal via these switch elements Q1 to Q4. , includes a voltage detection unit Cx that detects the voltage Vcr of the capacitor C and notifies it to the control unit 30, and generates multiple levels of DC voltage by selectively forming a plurality of conductive paths by switching (ON, OFF) the switching elements Q1 to Q4. Generate and output. When MOSFETs are used as the switching elements Q1 to Q4, the parasitic diodes of the MOSFETs can also be used as freewheeling diodes D.

The control unit 30 sets an AC voltage command value for causing the cluster 21r to generate an AC voltage with almost the same waveform as the AC voltage Vr of the three-phase AC power supply 1, and uses the same number of unit converters 22r to set the phase of each unit converter 22r. By pulse width modulation (PWM) that compares the voltage level of each triangular wave-shaped carrier signal with a different voltage and the voltage level of its AC voltage command value, the switching drive signal ( gate signal). When generating this drive signal, the control section 30 controls the switching elements Q1 and Q2 arranged in series in each unit converter 22r between on and off, and the switching elements Q3 and Q4 arranged in series with each other. A dead time is ensured between the on and off times of the off-state to prevent short circuits.

In the case of switching using two-level modulation, each unit converter 22r selectively generates and outputs two-level DC voltages of "positive level" and "negative level." In the case of switching using three-level modulation, each unit converter 22r selectively generates and outputs three-level DC voltages of "positive level," "zero level," and "negative level."

The configuration and switching of each unit converter 22r of the cluster 21r described above is the same for the configuration and switching of each unit converter 22s of the cluster 21s, and the same is true for the configuration and switching of each unit converter 22t of the cluster 21t. be.

The voltage detection unit 17 detects voltages Vr_n and Vs_n between each current-carrying path from the two power supply lines Lr and Ls to the passive filter and the neutral point A in the multilevel converter 20. Specifically, the voltage detection unit 17 includes a series circuit of resistors R1 and R2 connected between the current-carrying path from the power line Lr to the passive filter and the neutral point A, and a series circuit of resistors R1 and R2 connected between the power line Lr and the passive filter. It includes a series circuit of resistors R3 and R4 connected between the current-carrying path and the neutral point A, and detects the voltage Vr_n generated between the interconnection point of the resistors R1 and R2 and the neutral point A, Resistor R3. The voltage Vs_n generated between the interconnection point of R4 and the neutral point A is detected.

As shown in FIG. 3, the rectangular wave removal filter 18 includes lead compensators 41 and 42 that compensate for the phase delay of the voltages Vr_n and Vs_n detected by the voltage detection unit 17, and a voltage Vr_n that has passed through the lead compensators 41 and 42. , Vs_n, which remove rectangular wave components associated with switching of the multilevel converter 20. The voltages Vr_nm and Vs_nm that have passed through the low-pass filters 43 and 44 are sent to the control section 30.

The control unit 30 uses the voltages Vr_nm and Vr_nm that have passed through the rectangular wave removal filter 18 and the zero-phase voltage Vo in the multilevel converter 20, and uses the potential at the neutral point A of the multilevel converter 20 as a reference potential to The values and phase θ of the power supply voltages Vr, Vs, and Vt of the phase AC power supply 1 are estimated. As this estimating means, the control unit 30 includes a phase locked circuit (PLL circuit) shown in FIG.

Subtraction units 51 and 52 calculate a zero-sequence voltage (zero-sequence voltage superimposed on the potential of neutral point A) Vo calculated by a subsequent zero-sequence voltage calculation unit 59 from voltages Vr_nm and Vr_nm that have passed through the square wave removal filter 18. By subtracting , the values of power supply voltages Vr and Vs are obtained. The subtraction unit 53 captures the difference between the values of the power supply voltages Vr and Vs captured by the subtraction units 51 and 52 as the value of the power supply voltage Vt.
Vr=Vr_nm-Vo, Vs=Vs_nm-Vo, Vt=-Vr-Vs
Regarding the zero-sequence voltage Vo, when the multilevel converter 20 stops switching operation, the value is 15% of the value of the power supply voltages Vr, Vs, Vt, and the frequency is 3 times the frequency of the power supply voltages Vr, Vs, Vt. The doubled zero-sequence voltage Vo is superimposed on the potential at the neutral point A of the multilevel converter 20.

The values of the power supply voltages Vr, Vs, and Vt captured by these subtraction units 51, 52, and 53 become the estimation results of the control unit 30. In addition, the control unit 30 includes a coordinate transformation unit 54, a subtraction unit 55, a PI control unit 56, an addition unit 57, an integration unit 58, A zero-phase voltage calculation section 59 is included.

The coordinate conversion unit 54 converts the values of the power supply voltages Vr, Vs, and Vt captured by the subtraction units 51 to 53 using the phase θ obtained by the integrating unit 58 in the subsequent stage, thereby converting the values of the power supply voltages Vr, Vs, and Vt. A d-axis voltage Vd corresponding to the d-axis voltage Vd and a q-axis voltage Vq whose level is "0 (zero)" are obtained. The subtraction unit 55 captures the deviation between the q-axis voltage Vq obtained by the coordinate conversion unit 54 and the target value “0”. The PI control unit 56 determines the frequencies ω of the power supply voltages Vr, Vs, and Vt by PI control using the deviation captured by the subtraction unit 55 as input.

The addition unit 57 deals with the fact that the frequency ω determined by the PI control unit 56 is not yet known at the time of start of operation, and adds a value corresponding to the power frequency of the three-phase AC power supply 1 to the frequency ω determined by the PI control unit 56. Add reference frequency ωo. The integrating section 58 integrates the frequency ω passed through the adding section 57 to obtain the phase θ of the power supply voltages Vr, Vs, and Vt. The obtained phase θ becomes the estimation result of the control unit 30.

The zero-sequence voltage calculating section 59 calculates the zero-sequence voltage Vo superimposed on the potential at the neutral point A based on the phase θ obtained by the integrating section 58 and the d-axis voltage Vd obtained by the coordinate converting section 54. The calculated zero-sequence voltage Vo is fed back to the subtraction units 51 and 52.

With the above configuration, the values and phase θ of the power supply voltages Vr, Vs, and Vt can be accurately monitored. Thereby, the appropriate operation of the multilevel converter 20 under the control of the control unit 30 can be continued.

Note that since the control unit 30 estimates the values and phase θ of the power supply voltages Vr, Vs, and Vt based on the potential of the neutral point A superimposed with the zero-sequence voltage Vo, the control unit 30 and the multilevel converter 20 is not required. As a countermeasure against power supply disturbances, the control unit 30 controls the contents of control for each unit converter of the multilevel converter 20, such as control gain, when the estimated values of power supply voltages Vr, Vs, and Vt vary by more than a predetermined value. By changing the target voltage, target current, repetitive control memory, etc. in accordance with the amount of variation in the estimated values of the power supply voltages Vr, Vs, and Vt, harmonics can be stably reduced.

[Cutoff frequency fx of low-pass filters 43 and 44]
The LC filter 11 and interconnection reactors 14u, 14v, and 14w remove the switching frequency components of the pulse width modulation (PWM) control of the control unit 30 so that they do not flow into the system on the three-phase AC power supply 1 side. An LCL resonant circuit is formed for this purpose. Figure 5 shows the gain characteristics of this LCL resonant circuit.
Since the multilevel converter 20 multilevels the output voltage for each phase by each cluster 21, the actual switching frequency (switching frequency of the switching elements Q1 to Q4 in each unit converter) fs is the same as that of the LCL resonant circuit. Even if it is lower than the resonant frequency (cutoff frequency) fc, the equivalent switching frequency of the multilevel converter 20 is higher than the resonant frequency fc as "N x fs" (N is the number of stages of each unit converter in one cluster). Become.

The cutoff frequency fx of the low-pass filters 43 and 44 in the rectangular wave removal filter 18 is set between the resonant frequency fc of the LCL resonant circuit and the equivalent switching frequency "N×fs" of the multilevel converter 20. By providing the low-pass filters 43 and 44 with this cutoff frequency fx, the control unit 30 can detect an abnormality in the power supply voltages Vr, Vs, and Vt when resonance occurs in the LCL resonant circuit. That is, the low-pass filters 43 and 44 do not detect the equivalent switching frequency "N x fs" which is higher than the cutoff frequency fx, but generate the resonant frequency fc of the LCL resonant circuit lower than the cutoff frequency fx. can be detected. For example, the switching frequency fs of the switching elements Q1 to Q4 is 3kHz, and in this case, the equivalent switching frequency "N x fs" for the multilevel converter 20 is 9kHz, and the switching frequency fs of the switching elements Q1 to Q4 is 9kHz. The resonance frequency fc is set to 5kHz, and the cutoff frequency fx is set to 8kHz.

[Advance compensation of square wave removal filter 18]
A phase delay occurs in the voltages Vr_n and Vs_n detected by the voltage detection unit 17 due to the effects of sampling and filter characteristics. If this is done as it is, there is a possibility that the control unit 30 may not be able to make an appropriate estimation.

In consideration of this point, advance compensators 41 and 42 such as incomplete differentials are provided in the rectangular wave removal filter 18 to compensate for the phase lag of the voltages Vr_n and Vs_n.

FIG. 6 shows the values of the power supply voltages Vr, Vs, and Vt estimated by the control unit 30 when the lead compensators 41 and 42 are provided. If the lead compensators 41 and 42 are not provided, as shown in FIG. 7, distortion will occur in the values of the power supply voltages Vr, Vs, and Vt estimated by the control unit 30, making it impossible to detect accurate values.

[Other controls of control unit 30]
The control unit 30 includes means for estimating the values of the power supply voltages Vr, Vs, and Vt based on the capacitor voltages (detected voltages of the voltage detection unit Cx) in each unit converter of the multilevel converter 20, and is stopped, the estimation result based on the capacitor voltage is compared with the estimation result based on the voltages Vr_nm, Vs_nm passed through the rectangular wave removal filter 18 and the zero-phase voltage Vo. Note that the power supply voltages Vr, Vs, and Vt based on the voltages Vr_nm and Vs_nm that have passed through the square wave removal filter 18 and the zero-sequence voltage Vo can be estimated regardless of whether the load 2 is operating or not and/or whether the power converter 10 itself is operating or not. However, estimation of the power supply voltages Vr, Vs, and Vt based on the capacitor voltages can only be used when the multilevel converter 20 is stopped. When the multilevel converter 20 is stopped, the d-axis voltage Vd obtained by the coordinate converter 54 corresponds to the values of the power supply voltages Vr, Vs, and Vt, and corresponds to the value of the capacitor C in each unit converter in one cluster. Assuming that the average voltage value is Vc and the number of stages of each unit converter in one cluster is N, it is expressed by the following formula. The values of power supply voltages Vr, Vs, and Vt can be estimated from this d-axis voltage Vd.

なお、数1中の（N・Vc）は、１つのクラスタ内の各単位変換器２２におけるコンデンサＣの電圧値の積算値と等しいので、こちらを使用しても良い。

Note that (N·Vc) in Equation 1 is equal to the integrated value of the voltage value of the capacitor C in each unit converter 22 in one cluster, so it may be used.

When the multilevel converter 20 is stopped, if there is no abnormality in the power supply voltages Vr, Vs, Vt, the values of the power supply voltages Vr, Vs, Vt estimated by the capacitor voltage Vc and the above-mentioned square wave removal filter The values of the power supply voltages Vr, Vs, and Vt estimated based on the voltages Vr_n, Vs_n and the zero-sequence voltage Vo that have passed through 18 should be the same, respectively.

However, if there is an abnormality in any of the clusters 21 in the multilevel converter 20 or the unit converter 22 therein, there is a high probability that a puncture has occurred in the capacitor C in the unit converter 22. There is a difference between the two estimation results. Therefore, the control unit 30 calculates the difference between the estimated power supply voltages in each phase, and if this difference is less than a predetermined threshold value in all phases, the multilevel converter 20 is deemed to be normal and does not start up. However, if the difference in any one phase is greater than the threshold value, the multilevel converter 20 is not activated based on the determination that there is an abnormality somewhere in the multilevel converter 20. This prevents failure or damage caused by starting the multilevel converter 20 in an abnormal state.

[2] Second embodiment
A second embodiment of the present invention will be described. In the drawings, the same parts as in the first embodiment are given the same reference numerals, and detailed explanation thereof will be omitted.

As shown in FIG. 8, a converter 60 is connected to the power lines Lr, Ls, Lt of the three-phase AC power supply 1 via a passive filter consisting of an LC filter 11 and interconnection reactors 14r, 14s, 14t. A load, for example, an air conditioner 2, is connected to the positive output terminal P and negative output terminal N of the converter 60. The air conditioner 2 includes an inverter 6 that converts the output voltage Vdc of the converter 60 into an alternating current voltage of a predetermined frequency and outputs it, a compressor motor 7 operated by the output of the inverter 6, and the like.

The converter 60 is connected to a switching circuit 61 that converts the power supply voltages Vr, Vs, Vt of the three-phase AC power supply 1 into DC voltages by switching according to a drive signal from the control unit 30, and an output terminal of this switching circuit 61. A DC capacitor (smoothing capacitor) 62 is included.

A DC voltage detection section 63 that detects the output voltage Vdc of the converter 60 is connected between the positive output terminal P and the negative output terminal N of the converter 60. The DC voltage detection unit 63 connects resistors 63a and 63b having the same resistance value in series, and outputs a voltage Vdc generated between the interconnection point of the resistors 63a and 63b and the negative output terminal N as the output of the converter 60. Detected as voltage. This voltage Vdc is sent to the control section 30.

The power conversion device 10 is configured by the passive filter, the converter 60, the DC voltage detection section 63, the voltage detection section 17, the square wave removal filter 18, and the control section 30.

For example, as shown in FIG. 9, the switching circuit 61 of the converter 60 includes a series circuit of switching elements T1 and T2 provided for each phase of the power supply lines Lr, Ls, and Lt, and a DC capacitor 62 connected to these three series circuits. It is a two-level output type. Alternatively, as shown in FIG. 10, the switching circuit 61 includes a series circuit of switch elements T1 and T2, and a series circuit of switch elements T3 and T4 connected to the interconnection point of the switch elements T1 and T2. It is a three-level output type in which a series circuit is provided for each phase of the power supply lines Lr, Ls, and Lt, and DC capacitors 62a and 62b, which are two halves of the DC capacitor 62, are connected to these series circuits. As shown in FIG. 11, it includes a series circuit of diodes D1 and D2, and a series circuit of switch elements T3 and T4 connected to the interconnection point of these diodes D1 and D2, and these series circuits are connected to power supply lines Lr and Ls. A three-level output type may be used as the switching circuit 61, which is provided for each phase of Lt and in which DC capacitors 62a and 62b, which are two parts of the DC capacitor 62, are connected to these series circuits.

The voltage detection unit 17 connects two of the power supply lines Lr, Ls, Lt, for example, to each current path from the power supply lines Lr, Ls to the passive filter (LC filter 11 and interconnection reactors 14r, 14s, 14t) and the negative of the converter 60. Voltages Vr_n and Vs_n between the side output terminal (predetermined position) N are detected.

The rectangular wave removal filter 18 includes the same compensators 41 and 42 and low-pass filters (LPF) 43 and 44 as in the first embodiment, and removes the rectangular wave component from the detected voltages Vr_n and Vs_n of the voltage detection unit 17.

The control unit 30 controls the power supply of the three-phase AC power supply 1 based on the voltages Vr_nm, Vr_nm that have passed through the rectangular wave removal filter 18 and the zero-phase voltage Vo in the converter 60, and with the potential of the negative output terminal N of the converter 60 as a reference potential. The values and phase θ of voltages Vr, Vs, and Vt are estimated. As this estimating means, the control unit 30 includes a phase locked circuit (PLL circuit) shown in FIG. 12.

The calculation unit 70 calculates a value of 1/2 of the voltage detected by the DC voltage detection unit 63 (the output voltage of the converter 60) Vdc. The subtraction units 51 and 52 subtract the output voltage “Vdc/2” of the calculation unit 70 from the voltages Vr_n and Vr_n that have passed through the square wave removal filter 18, and the zero-phase voltage calculated by the subsequent zero-phase voltage calculation unit 59. By subtracting the voltage (zero-phase voltage superimposed on the potential of the negative output terminal N) Vo, the values of the power supply voltages Vr and Vs are obtained. The subtraction unit 53 captures the difference between the values of the power supply voltages Vr and Vs captured by the subtraction units 51 and 52 as the value of the power supply voltage Vt.
Vr=Vr_n-(Vdc/2)-Vo, Vs=Vs_n-(Vdc/2)-Vo, Vt=-Vr-(Vdc/2)-Vs
The potential at the interconnection point of resistors 63a, 63b corresponds to the midpoint potential of DC capacitor 62, and the interconnection point of resistors 63a, 63b acts as a virtual neutral point of converter 60, which is a converter. The potential of the negative output terminal N seen from this virtual neutral point is "-Vdc/2", and the voltages Vr_n, Vr_n and zero-sequence voltage Vo, which are based on the potential of the negative output terminal N, are the voltage " Vdc/2” is included. Therefore, the voltage "Vdc/2" is subtracted from the voltages Vr_n, Vr_n and the zero-phase voltage Vo.

Zero-phase voltage Vo changes depending on the operating condition of converter 60. For example, when sinusoidal modulation is applied to switching control of converter 60, zero-phase voltage Vo becomes 0 (zero). When the converter 60 stops its switching operation or when the third-order harmonic superimposition method is applied to the switching control of the converter 60, the frequency is set to 15% of the value of the power supply voltages Vr, Vs, and Vt. A zero-phase voltage Vo having a frequency three times the frequency of the power supply voltages Vr, Vs, and Vt is superimposed on the potential of the negative output terminal N.

The values of the power supply voltages Vr, Vs, and Vt captured by these subtraction units 51, 52, and 53 become the estimation results of the control unit 30. In addition, the control unit 30 includes a coordinate transformation unit 54, a subtraction unit 55, a PI control unit 56, an addition unit 57, an integration unit 58, A zero-phase voltage calculation section 59 is included. The configurations of the coordinate conversion section 54 to the integration section 58 are the same as in the first embodiment, so their explanation will be omitted.

The zero-sequence voltage calculating section 59 calculates the zero-sequence voltage Vo superimposed on the potential of the negative output terminal N based on the phase θ obtained by the integrating section 58 and the d-axis voltage Vd obtained by the coordinate converting section 54. The calculated zero-phase voltage Vo is fed back to the subtraction units 51 and 52.

With the above configuration, the values and phase θ of the power supply voltages Vr, Vs, and Vt can be accurately monitored. Thereby, the appropriate operation of converter 60 under the control of control unit 30 can be continued. That is, control unit 30 stably reduces harmonics by controlling the switching operation of the switching circuit of converter 60 based on the estimated values of power supply voltages Vr, Vs, and Vt. For example, the control unit 30 changes the timing of the switching operation and changes the control gain, target voltage, target current, memory for repetitive control, etc. in the control of the switching operation according to the estimated values of the power supply voltages Vr, Vs, and Vt. Control the duration.

Note that since the control unit 30 estimates the values and phase θ of the power supply voltages Vr, Vs, and Vt based on the potential of the negative output terminal N on which the zero-sequence voltage Vo is superimposed, the control unit 30 and the converter 60 No electrical insulation is required between the two.

[3] Third embodiment
A third embodiment of the present invention will be described.
As shown in FIG. 13, the power conversion device 10 includes a converter 60 and a DC voltage detection section 63 of the second embodiment in place of the multilevel converter 20 of the first embodiment. Converter 60 functions as an active filter that suppresses harmonic components of the current flowing through rectifier circuit 3 of air conditioner 2 .
Other configurations and controls are the same as in the first and second embodiments. Therefore, the explanation thereof will be omitted.

[4] Modification example
In the first embodiment, a case has been described in which the number of unit converters in the clusters 21r, 21s, and 21t is three for each phase, but the number can be set as appropriate, and three or more is desirable. Considering the number of drive signals for each unit converter 22, it is desirable that the number is an odd number.

The embodiments and modifications described above are presented as examples, and are not intended to limit the scope of the invention. These embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the gist of the invention. The scope of these embodiments and modifications is included in the gist of the invention, and is also included in the scope of the invention described in the claims and its equivalents.

1... Three-phase AC power supply, Lr, Ls, Lt... Power line, 3... Air conditioner (load), 10... Power converter, 11... LC filter, 14u, 14v, 14w... Grid-connected reactor, 17... Voltage detection 18... Rectangular wave removal filter, 20... Multilevel converter (converter), 30... Control unit, 60... Converter (converter), 63... DC voltage detection unit.

Claims (13)

A power conversion device connected to each power line of a three-phase AC power supply,
a power converter that is connected to each of the power supply lines through a passive filter and performs power conversion by switching;
a voltage detection unit that detects a voltage between a current-carrying path from each of the power supply lines to the passive filter and a predetermined position in the power converter;
a rectangular wave removal filter that removes a rectangular wave component associated with the switching from the voltage detected by the voltage detection section;
The value of the power supply voltage of the three-phase AC power supply is estimated based on the voltage that has passed through the square wave removal filter and the zero-phase voltage superimposed on the potential at the predetermined position in the power converter, and the value of the power supply voltage of the three-phase AC power supply is estimated based on the estimation result. a control unit that controls switching of the power converter;
A power conversion device comprising: The power converter includes a plurality of clusters configured by connecting a plurality of unit converters in series, each consisting of a switch element and a capacitor, and one end of each cluster is interconnected to serve as a neutral point, and each cluster has a neutral point. a multilevel converter whose other end is connected to each of the power lines via the passive filter;
The voltage detection unit detects a voltage between a current-carrying path from each power supply line to the passive filter and the neutral point,
The control unit estimates the value of the power supply voltage based on the voltage that has passed through the square wave removal filter and the zero-phase voltage superimposed on the potential at the neutral point, and performs the multilevel conversion based on the estimation result. control device switching,
The power conversion device according to claim 1. The power converter is a converter that is connected to each of the power supply lines via the passive filter and includes a switching circuit that converts the power supply voltage into a DC voltage, and a DC capacitor connected to the output end of the switching circuit,
The voltage detection unit detects a voltage between a current-carrying path from each power supply line to the passive filter and a negative output terminal of the converter,
The control unit estimates the value of the power supply voltage based on the voltage that has passed through the square wave removal filter and the zero-sequence voltage that is superimposed on the potential at the negative output terminal of the converter, and based on the estimation result. controlling switching of the converter;
The power conversion device according to claim 1. The voltage detection unit detects a voltage between two current-carrying paths from two of the power supply lines to the passive filter and the neutral point or the negative terminal.
The power conversion device according to claim 2 or 3. The control unit estimates the value and phase of the power supply voltage by subtracting the zero-sequence voltage from the voltage that has passed through the square wave removal filter, and controls the switching of the multilevel converter or the converter based on this estimation result. control,
The power conversion device according to claim 2 or 3. The square wave removal filter is a low-pass filter having a cutoff frequency between the resonant frequency of the passive filter and the equivalent switching frequency of the multilevel converter or the converter.
The power conversion device according to claim 2 or 3. The square wave removal filter includes a lead compensator that compensates for a phase lag of the voltage detected by the voltage detection section.
The power conversion device according to claim 6. The control unit includes means for estimating the value of the power supply voltage based on the voltage of the capacitor in each unit converter, and when the multilevel converter is stopped, the estimation result based on the voltage of the capacitor is and not starting the multilevel converter if the difference between the voltage passing through the square wave removal filter and the estimation result based on the zero-sequence voltage is equal to or more than a threshold value;
The power conversion device according to claim 2. The control unit includes means for estimating the value of the power supply voltage based on the voltage of the DC capacitor, and when the converter is stopped, the control unit estimates the value of the power supply voltage based on the voltage of the DC capacitor and the square wave removal filter. not starting the converter if the difference between the voltage passed through the voltage and the estimation result based on the zero-sequence voltage is equal to or more than a threshold;
The power conversion device according to claim 3. The control unit estimates the value of the power supply voltage using the potential of the neutral point or the negative terminal as a reference potential.
The power conversion device according to claim 2 or 3. The multilevel converter or the converter selectively generates and outputs DC voltages of three or more levels for each phase of each power supply line.
The power conversion device according to claim 2 or 3. The multilevel converter or the converter functions as an active filter that suppresses harmonic components of a current flowing to a load connected to the power supply line.
The power conversion device according to claim 2 or 3. The control unit changes the control content for each unit converter of the multilevel converter in accordance with the amount of variation when the estimation result has a variation of more than a predetermined value.
The power conversion device according to claim 2.

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