JP2007300709A - Ac-ac direct converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an AC power supply side from having a leading power factor due to an LC filter on the AC power supply side. <P>SOLUTION: In power factor control where the input power factor is sustained at "1" by a controller 4 performing PWM control of each two-way switch by inserting an AC-AC direct conversion circuit 3 constituted of an input LC filter 2 and a two-way switch into each phase of an AC power supply 1, a power factor compensation circuit 5 determines the compensation value of filter lead component of power supply voltage Vs by means of a coefficient unit 5A having the filter constants as coefficients and corrects a power supply current command value Isref by the product of the power supply voltage Vs and the compensation value to obtain an input current command Ismcref. It also include to estimate an input current command value, to estimate a power conversion efficiency, and the like, and to take account of the inductance of the AC power supply in the filter constant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an AC-AC direct conversion device (matrix converter) that converts a voltage or frequency input from a single-phase or multi-phase AC power source into an arbitrary voltage or frequency and outputs the voltage or frequency. The present invention relates to power factor control of power supply current in consideration of the impedance of an input filter of a converter.

  This type of AC-AC direct conversion device that has existed in the past switches a bidirectional switch using a self-extinguishing semiconductor element at high speed, and converts a single-phase or multi-phase AC input to power of an arbitrary voltage or frequency. FIG. 8 shows a basic configuration of a conversion device for conversion. An input filter (InputFilter) 2 and an AC-AC direct conversion circuit 3 having bidirectional switches S1 to S9 are inserted in the R, S, and T phases of the three-phase AC power source 1, and both are controlled by a controller (controller) 4. By performing PWM control of the direction switch at a frequency sufficiently higher than the power supply frequency, an AC output of U, V, W controlled to an arbitrary voltage or frequency is obtained while directly applying an input voltage to a load Load such as a motor.

  The switching pattern of the bidirectional switch in the AC-AC direct conversion device includes, for example, a PWM converter pattern that is a signal synchronized with the input voltage and a PWM inverter pattern that is created according to the output frequency and voltage in the case of a modulation method using carrier amplitude. And the AND condition. As a result, the input current of the AC-AC direct conversion device is limited by the PWM converter pattern, the output voltage and frequency are controlled by the PWM inverter pattern, and the input current is converted to a sine wave and output while keeping the input power factor “1”. Realizes waveform sine wave and frequency conversion at the same time. The bidirectional switch may be configured by using a plurality of unidirectional switches as shown in the figure.

  In the AC-AC direct conversion device as shown in FIG. 8, the input filter (LC filter) 2 inserted on the power supply side is frequency-converted and controlled by the switching operation of the bidirectional switch without the input AC voltage passing through the DC smoothing circuit. Therefore, the harmonics of this switching frequency component are reduced. When this input filter 2 is inserted, even if power factor 1 control is performed at the inlet of the AC-AC direct conversion device (after the filter), there is an influence of the impedance of the input filter, and the power source 1 at the grid connection point. Current does not reach a perfect power factor of 1, and a component is generated.

  As a method for improving the power factor in the PWM converter, the present applicant has already proposed a control method that takes into account the influence of the input filter in the combination of the PWM converter and inverter via a DC circuit in the middle with the power supply side (for example, , See Patent Document 1). In this control method, as the PWM control of the PWM converter, the switching element of each phase is turned on or off by comparing the amplitudes of the fundamental wave command signal and the carrier wave signal. In a PWM converter that behaves like this, control errors due to the influence of the input filter are eliminated by setting the converter current command value in consideration of the filter characteristics of each element of the T-type filter and the characteristics of the proportional term gain and integral term gain. .

  As another power factor adjustment method, the PWM cycloconverter corrects the impedance of the input filter by adding the input power factor compensation angle ε to the power supply voltage information detected from the AC power supply to create a switching pattern. A method of controlling the input power factor to “1” has been proposed (see, for example, Patent Document 2).

As another power factor adjustment method, there is a method that realizes power factor 1 control in a PWM cycloconverter by taking an input current and an input voltage and giving a command to correct a mutual phase difference to a control circuit ( For example, see Patent Document 3).
JP 2004-254429 A JP 2000-299984 A JP 2001-309660 A

  The power factor adjustment method of Patent Document 1 is applied to a PWM converter alone, and even when applied to an AC-AC direct conversion device having a different behavior, the same power factor improvement effect cannot be obtained.

  Further, in Patent Document 2, the input power factor compensation angle ε needs to be adjusted each time so that the input power factor or the phase difference between the input voltage waveform and the current waveform becomes 1, and the power factor is 1; Every time the behavior of the AC direct conversion device fluctuates, the input power factor compensation angle ε must be adjusted.

  In Patent Document 3, a power factor detection device is required, and in particular, an instrument transformer or an instrument current transformer must be attached to the power supply side of the filter, which is not suitable for downsizing and cost reduction of the device. The advantages of the AC-AC direct conversion device, which is said to be possible to reduce the size and cost without the need for reactors and capacitors, cannot be used. In addition, a delay in control responsiveness due to a detection delay of these instrument transformers and instrument current transformers causes a problem that the control accuracy is lowered and power factor control cannot be performed with high accuracy.

  An object of the present invention is to provide an AC-AC direct conversion device that can prevent an AC power supply side from advancing and becoming a power factor by an LC filter on the AC power supply side.

  The present invention for solving the above-described problems is characterized by the following configuration.

(1) Each phase of a single-phase or multi-phase AC power supply is connected to a load via an input LC filter for suppressing harmonics and an AC-AC direct conversion circuit having a bidirectional switch configuration, and the PWM of each bidirectional switch In an AC-AC direct conversion device that obtains an output obtained by converting the voltage or frequency of the AC power source into an arbitrary voltage or frequency by a control device that performs control,
A power supply voltage Vs and a power supply current command value Isref are input, and a compensation value of a filter advance component of the input LC filter that cancels a phase difference between the power supply voltage Vs and the power supply current Is of the AC-AC direct conversion circuit is obtained. A power factor compensation circuit that corrects the power supply current command value Isref with a product value of the power supply voltage Vs and the compensation value and outputs the input current command value Ismcref of the AC-AC direct conversion circuit to the control device;
The power supply current Is is controlled to a power factor “1”.

  (2) The power factor compensation circuit estimates the power supply current command value Isref from the output phase voltage command value Vrefp of the AC-AC direct conversion circuit, and an estimated value Isref ′ (estimated value of the power supply current command value) The product value of the unit input current command value iref is corrected with the product value of the power supply voltage Vs and the compensation value, and the input current command value Ismcref is output to the control device.

  (3) The power factor compensation circuit includes the estimated value Isref ″ and the unit of the power supply current command in consideration of the total power conversion efficiency η including the power conversion efficiency of the AC-AC direct conversion circuit and the power loss of the filter. The product of the vector of the input current command value iref is corrected with the product value of the product of the power supply voltage Vs and the compensation value, and the input current command value Ismcref is output to the control device.

(4) Each phase of the single-phase or multi-phase AC power supply is connected to a load via an input LC filter for suppressing harmonics and an AC-AC direct conversion circuit having a bidirectional switch configuration, and the PWM of each bidirectional switch In an AC-AC direct conversion device that obtains an output obtained by converting the voltage or frequency of the AC power source into an arbitrary voltage or frequency by a control device that performs control,
The input voltage command value Vsmcref of the AC-AC direct conversion circuit is obtained from the power supply current command value Isref and the power supply voltage Vs, and the phase difference Δθmcref between the input voltage command value Vsmcref and the input current command value Ismcref is output to the control device. A power factor compensation circuit is provided.

  (5) The power factor compensation circuit obtains the compensation value by adding an inductance component of the AC power source to an inductance of the filter constant.

  (6) The power factor compensation circuit is characterized in that the detection value of the power supply phase voltage Vs or the input voltage command value Vsmc can be selected.

  As described above, according to the present invention, it is possible to prevent the AC power supply side from proceeding to the power factor by the LC filter on the AC power supply side in the AC-AC direct conversion device. Moreover, power factor compensation according to the behavior of the AC-AC direct conversion device can be performed. In addition, power factor compensation can be performed accurately without the need for a power factor detection device on the AC power source side.

(Embodiment 1)
FIG. 1 shows a circuit configuration diagram of the present embodiment. The difference from FIG. 8 is that a power factor compensation circuit 5 for adding a compensation value of a filter advance component in advance to an input current command value to the control device 4 is added. is there. Hereinafter, this power factor compensation will be described in principle.

In the general three-phase AC-AC direct conversion device as shown in FIG. 8, the single-phase equivalent circuit of the input filter and the AC-AC direct conversion circuit is as shown in FIG. As basic control of the AC-AC direct conversion device, usually, the power supply voltage Vs and the output current I ₀ are detected, and the three-phase input voltage is cut in accordance with the output voltage command to perform PWM control. The input side performs PWM control by chopping the three-phase output current. Therefore, in FIG. 2, the input side of the conversion circuit is considered as a current source, and the output side of the conversion circuit is considered as a voltage source, and the input and output are mutually dependent.

  Here, paying attention to the control on the input side, the input voltage of the AC-AC direct conversion circuit is Vsmc shown in FIG. 2, that is, the voltage across the filter capacitor unit (including the resonance suppression resistor). However, since the power source voltage Vs is normally detected and the power factor 1 control of the input current Ismc is performed so as to match the phase, the actual power source current Is causes a phase difference from the power source voltage Vs.

  When the circuit equation of the input filter unit is derived based on the single-phase equivalent circuit of FIG. 2, Equation (1) is obtained. In the following equations, each voltage and current indicated by an arrow “→” is a vector quantity.

  When the power supply current Is is arranged, the equation (2) is obtained.

  When the AC-AC direct conversion circuit is controlled using the input current Ismc of the conversion circuit as an input current command, the first term of equation (2) functions as a secondary low-pass filter, and the second term is an error term related to the power supply voltage Vs. This affects the power supply current Is. FIG. 3 shows an example of a Bode diagram for the power supply current Is of each term in an arbitrary filter parameter. Focusing on the error term, it can be seen that the phase of the power supply current Is advances by 90 degrees with respect to the power supply voltage Vs, and has a gain of about one hundredth of the power supply voltage Vs in the vicinity of the 50 [Hz] fundamental wave.

  In order to eliminate the influence of this error term, a term for canceling the error term is added in advance to the input current command value of the AC-AC direct conversion circuit. That is, the input current command value Ismcref is expressed by equation (3).

  In this equation (3), Isref is a desired ideal power supply current command value. When the expression (3) is substituted into the expression (2), the power supply current Is becomes only the low-pass filter (LPF) term, and Is≈Isref in the fundamental wave component.

  Further, the input voltage Vsmc of the AC-AC direct conversion circuit is expressed by equation (4) from equations (1)-(3).

  From the above, the power supply current Is can be controlled to a power factor of 1 by adding the compensation value of the filter advance component in advance to the input current command value Ismcref.

  From the above, in this embodiment, as shown in FIG. 1, a power factor compensation circuit 5 is added to the configuration of FIG. In the figure, the power factor compensation circuit 5 includes a coefficient unit 5A and a subtractor 5B, and the coefficient unit 5A multiplies the power supply voltage Vs of the AC-AC direct conversion circuit 3 by the coefficient of the second term of the equation (3). The subtractor 5B subtracts the output of the coefficient unit 5A from the power supply side input current command value Isref to obtain the input current command value Ismcref of the AC-AC direct conversion circuit 3. That is, the power supply voltage Vs that is input to the AC-AC direct conversion circuit is obtained through a low-pass filter whose coefficient is the filter constant of the input LC filter to obtain a compensation value of the filter advance component, and the power supply current command value Isref is calculated from the power supply voltage Vs. A power factor compensation circuit that corrects with the product value and outputs the input current command value Ismcref to the control device prevents the AC power source from leading to a power factor.

  With this configuration, the input current command of the conversion circuit compensates for the advance component due to the influence of the input filter, so that the power factor of the AC power supply can be improved.

(Embodiment 2)
In the case of directly giving not only the phase but also the magnitude of the input current command as in the first embodiment, the filter advance component can be compensated by the equation (3), but normally, the output voltage command is given to the load and the AC-AC direct In many cases, the converter is controlled and the magnitude of the input current is given depending on the required load current.

  Therefore, in the present embodiment, the input current command value ismcref is estimated from the output phase voltage command value Vrefp, and the filter advance component is compensated using the estimated value, which will be described in detail below.

  When it is considered that the exchange of the active power of the input / output of the AC-AC direct conversion device basically matches, the equation (5) is established.

  However, the output phase voltage command value Vrefp is the phase conversion value of the output line voltage command, cos θ is the input power factor, and cos φ is the output power factor.

In the above equation (5), the input power factor cos θ is set to 1 in order to remove the influence of the filter. Further, the output power factor cos φ is obtained by the phase calculation from the output phase voltage command value Vrefp and the detected value of the output current I ₀ .

  The magnitude | Is | of the estimated input current obtained by substituting the above into the expression (5) is the unit input current command value iref obtained from the detected value of the power supply voltage Vs (vector of magnitude 1 that matches the power supply voltage phase). ) To obtain Isref, which is then substituted into the filter compensation equation of equation (3) to derive the input current command value Ismc of the conversion circuit as in equation (6).

  According to the above formula, the input filter advance power factor can be improved when the output voltage command value is given without giving the input current command.

  From the above, in this embodiment, the power factor compensation circuit 6 shown in FIG. 4 is used instead of the power factor compensation circuit 5 shown in FIG. In FIG. 4, the coefficient unit 6A and the subtractor 6B are the same as the coefficient unit 5A and the subtractor 5B in FIG. Instead of the power source side current command value Isref of the subtractor 5B, the power source current command value Isref is obtained by the arithmetic elements 6C to 6H according to the equations (5) and (6).

  6C calculates the magnitude (absolute value) of the output phase voltage command value Vrefp. 6D calculates the magnitude (absolute value) of the detected value of the output current Io. 6E obtains the phase angle (cosφ) between the output phase voltage command value Vrefp and the detected value of the output current Io. 6F obtains the coefficient of the first term of the equation (6) from each calculation output of 6C to 6E, the detected value of the power supply voltage Vs, and the power supply power factor command value cosθref.

  6G obtains a unit input current command value iref from the detected value of the power supply voltage Vs. 6H multiplies the unit input current command value iref by using the calculation result of 6F as a coefficient to obtain an estimated value of the power supply side input current command value corresponding to the first term of the equation (6), which is used as the input of the subtractor 6B. .

  Therefore, according to the present embodiment, when the input current command value is not given, the power factor can be improved by estimating the input current command value from the relationship between the input and output active power based on the output voltage command.

(Embodiment 3)
The estimation of the input current command value according to the second embodiment is a theoretical value, and is established when the total power conversion efficiency including the power conversion efficiency of the AC-AC direct conversion circuit and the power loss of the filter is 100%. Depending on the load, capacity, device configuration, etc., the value is about 90%. Therefore, in this embodiment, the input current is estimated according to the equation (7) corrected by the total power conversion efficiency η in the equation (6).

  FIG. 5 shows the power factor compensation circuit 7 in accordance with the equation (7). Each calculation element incorporates the total power conversion efficiency η into the calculation in the calculation element 6F with the power factor compensation circuit 6, and this total power conversion efficiency η The calculation of the first term of the equation (7) is performed.

  As for the total power conversion efficiency η, an efficiency table or the like corresponding to the load is prepared in advance, and the estimated efficiency is determined from the load current detection value via the table. As a result, the power supply current estimated value becomes a more accurate value, and the filter compensation accuracy is improved.

(Embodiment 4)
In the first, second, and third embodiments, the case where the input current command value Ismcref of the conversion circuit is given to the control device 4 is shown. In this embodiment, the phase difference between the input current command value Ismcref and the input voltage command value Vsmcref is shown. Δθmc is calculated to obtain phase difference data for power factor control. Equation (8) can be used to calculate the phase difference Δθmc.

  Note that the subscripts α and β in the equation (8) mean values obtained by three-phase / two-phase conversion.

  FIG. 6 shows the arithmetic circuit 8 for the phase difference Δθmc. The coefficient unit 8A multiplies the power supply current command value Isref by the second term coefficient of the equation (4), and the subtractor 8B subtracts the output of the coefficient unit 8A from the power supply voltage Vs. Thus, the input voltage command value Vsmcref is obtained. The phase calculator 8C obtains the phase θvsmc of the input voltage command value Vsmcref by the calculation of the second term of the equation (8), and the phase calculator 8D calculates the phase of the input current command value Ismcref obtained in the power factor compensation circuits 5-7. θismc is obtained by the calculation of the first term of equation (8). The adder 8E obtains a phase difference command value Δθmcref between the phase θvsmc and the phase θismc.

  Although the effect of this embodiment is the same as that of the former, in the load current value at that time, the phase difference between the current and voltage of the AC power source due to the influence of the filter can be grasped in advance.

(Embodiment 5)
In the embodiments described above, the influence of the power source impedance is not considered. Actually, the inductance component of the power source impedance has an effect on the filter parameter Lf. This delays the current phase as compared with the case where the filter compensation formula is given only with pure filter parameters. In other words, the intention to delay the lead current component by the filter to a power factor of 1 (phase matching) often results in overcompensation and conversely a lag current.

  In the present embodiment, in consideration of the inductance component of the power source impedance, the inductance value Lfs of the power source impedance is added to the filter parameter Lf of Formula (2) and Formula (4) as shown in Formula (9).

  Here, Lf ′ is a filter parameter considering the power supply impedance, Lf is a filter parameter, and Lfs is an inductance value of the power supply impedance.

  Although the power source impedance component cannot be generally described because it depends on the characteristics of the power source to which the apparatus is connected, it is preferable to obtain the average value of actually measured values, but it may be given as an estimated value.

  According to this embodiment, the compensation component can be further improved by adding the filter parameter Lf in consideration of the inductance component of the power source impedance.

(Embodiment 6)
When the influence of the filter is taken into consideration, the input voltage Vsmc of the AC-AC direct conversion circuit is expressed by equation (4), but is usually controlled by using the detected value of the power supply voltage Vs. If the control is performed in consideration of the influence of the filter, the equation (4) should be used originally, but the equation is differential, and if used as it is, it may become unstable depending on the conditions.

  In the present embodiment, the detected value of the power supply voltage Vs is used as it is for power factor compensation or the input voltage Vsmc obtained by the equation (4) can be selected and used separately. When Vs and Vsmc are compared by substituting filter parameters that are actually used, if there is no significant difference in position difference, or if Vsmc is unstable, Vs is used as it is for control. To do.

  According to the present embodiment, as the input voltage value of the AC-AC direct conversion circuit, either the power supply voltage Vs or the input voltage Vsmc in consideration of the filter parameter can be selected according to the condition, thereby enabling the power factor control. Stabilization can be achieved.

(simulation)
It was verified by simulation that the power factor compensation circuit according to the present invention can prevent the grid interconnection point from being advanced and becoming a power factor due to the influence of the LC filter inserted on the AC input side of the AC-AC direct conversion circuit.

  FIG. 7A shows the case without filter advance compensation, and the phase of the voltage V and the current I at the grid connection point do not match. On the other hand, FIG. 7B shows a case where the filter advance compensation is performed, and the phase of the voltage V and the current I at the grid connection point coincide, that is, a power factor “1” can be obtained.

The circuit block diagram which shows Embodiment 1 of this invention. The single-phase equivalent circuit diagram of an input filter and an AC-AC direct conversion circuit. The Bode diagram with respect to the power supply current Is. The circuit block diagram which shows Embodiment 2 of this invention. The circuit block diagram which shows Embodiment 3 of this invention. The circuit block diagram which shows Embodiment 4 of this invention. Simulation waveform diagram. The basic block diagram of an alternating current-alternating current direct conversion apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Input LC filter 3 AC-AC direct conversion circuit 4 Controller 5, 6, 7 Power factor compensation circuit 8 Phase difference calculation circuit

Claims (6)

Each phase of the single-phase or multi-phase AC power supply is connected to a load via an input LC filter for suppressing harmonics and an AC-AC direct conversion circuit having a bidirectional switch configuration, and PWM control of each bidirectional switch is performed. In an AC-AC direct conversion device that obtains an output obtained by converting the voltage or frequency of the AC power source into an arbitrary voltage or frequency by a control device,
A power supply voltage Vs and a power supply current command value Isref are input, and a compensation value of a filter advance component of the input LC filter that cancels a phase difference between the power supply voltage Vs and the power supply current Is of the AC-AC direct conversion circuit is obtained. A power factor compensation circuit that corrects the power supply current command value Isref with a product value of the power supply voltage Vs and the compensation value and outputs the input current command value Ismcref of the AC-AC direct conversion circuit to the control device;
An AC-AC direct conversion device, wherein the power source current Is is controlled to a power factor “1”.   The power factor compensation circuit estimates the power supply current command value Isref from the output phase voltage command value Vrefp of the AC-AC direct conversion circuit, and estimates the value Isref ′ (estimated value of the power supply current command value) and unit input current. 2. The AC− of claim 1, wherein an input current command value Ismcref is output to the control device by correcting a product value of the vector of the command value iref with a product value of the power supply voltage Vs and a compensation value. AC direct conversion device.   The power factor compensation circuit takes into account the total power conversion efficiency η including the power conversion efficiency of the AC-AC direct conversion circuit and the power loss of the filter, and the estimated value Isref ″ of the power source current command and the unit input current command 3. The input current command value Ismcref is output to the control device by correcting a product value of the value iref with a vector by a product value of the power supply voltage Vs and a compensation value. AC-AC direct conversion device. Each phase of the single-phase or multi-phase AC power supply is connected to a load via an input LC filter for suppressing harmonics and an AC-AC direct conversion circuit having a bidirectional switch configuration, and PWM control of each bidirectional switch is performed. In an AC-AC direct conversion device that obtains an output obtained by converting the voltage or frequency of the AC power source into an arbitrary voltage or frequency by a control device,
The input voltage command value Vsmcref of the AC-AC direct conversion circuit is obtained from the power supply current command value Isref and the power supply voltage Vs, and the phase difference Δθmcref between the input voltage command value Vsmcref and the input current command value Ismcref is output to the control device. An AC-AC direct conversion device comprising a power factor compensation circuit.   5. The AC-AC direct according to claim 1, wherein the power factor compensation circuit obtains the compensation value by adding an inductance component of the AC power source to an inductance of the filter constant. 6. Conversion device. 6. The AC-AC direct conversion according to claim 1, wherein the power factor compensation circuit can select a detection value of the power supply phase voltage Vs or the input voltage command value Vsmc. apparatus.

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