JP4931129B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device for accurately supplying a desired current to a load.

  For example, in a power converter for an electromagnetic coil, it is necessary to supply current to a load following a current reference that changes with time. In such a power converter, a control circuit is generally composed of a main loop of a constant current control circuit and a minor loop of a constant voltage control circuit having a fast response speed (see, for example, Patent Document 1). .

Moreover, in a power converter using a voltage type power converter, a main circuit configuration of self-excited voltage type rectifier + voltage type power converter is often used. In this case, a smoothing capacitor is connected to the output side of the self-excited voltage type rectifier to suppress fluctuations in the DC voltage, and the voltage applied to the smoothing capacitor is controlled by the self-excited voltage type rectifier. (For example, refer to Patent Document 2).
Japanese Patent Publication No. 8-33778 (page 3-5, FIG. 1) JP 2006-74849 A (page 3-5, FIG. 1)

  As described above, the circuit configuration for converting an AC voltage to a DC voltage using a self-excited voltage type rectifier as an AC / DC converter has an advantage that the DC voltage can be controlled to be constant by the self-excited voltage type rectifier. There are problems that the number of parts increases and the control circuit becomes complicated. On the other hand, if a diode rectifier is used instead of a self-excited voltage rectifier to convert AC voltage to DC voltage, the number of parts is small, the configuration is simple, and control is not required. Will improve.

  However, when converting from an AC power source to a DC voltage using a diode rectifier, there arises a problem that the input DC voltage of the power conversion device fluctuates with the temporal change of the output current. When the input DC voltage fluctuates, the control characteristics of the output current of the power converter are adversely affected, and the control accuracy is reduced.

  The present invention has been made in view of the above problems, and has high-accuracy follow-up characteristics with respect to a current reference value that changes with time even when a diode rectifier is used as an input AC / DC converter circuit. An object is to provide a power converter.

In order to achieve the above object, a power converter of the present invention includes a diode rectifier that converts an AC voltage of an AC power source into a DC voltage, a smoothing capacitor that smoothes the output of the diode rectifier,
A DC converter applied to the smoothing capacitor is provided as an input, and includes a power converter that supplies a desired current to the load, and a control unit that controls the power converter. The control unit includes a current reference value and the current converter. A constant current control circuit that adjusts a current control manipulated variable that is an output so that a deviation of an output current of the power converter is minimized; a feedforward control circuit that outputs a feedforward manipulated variable according to the current reference value; First correction means for correcting the feedforward manipulated variable in order to correct a control characteristic fluctuation accompanying input voltage fluctuation of the power converter, and a feedforward manipulated variable in which the output voltage of the power converter is corrected. And a voltage control means for controlling to follow an operation amount obtained by adding the current control operation amount.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where a diode rectifier is used as an input AC / DC conversion circuit, it is possible to provide a power converter having a high-accuracy tracking characteristic with respect to a current reference value that changes with time It becomes.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of a power conversion apparatus according to Embodiment 1 of the present invention.

  The AC voltage supplied from the AC power source 1 is converted to DC by the diode rectifier 2. This DC voltage is smoothed by the smoothing capacitor 3 and supplied to the power converter 4. The power converter 4 supplies a current pattern that changes with time to the load 5 in accordance with a control command from the control unit 6. A typical configuration of the power converter 4 is a chopper using a self-extinguishing type element. In this case, the self-extinguishing type element is on / off controlled by a gate pulse from the control unit 6 and a desired current pattern is applied to the load 5. give.

  The input voltage of the power converter 4 is detected by the voltage detector 7 and given to the control unit 6. Further, the output current of the power converter 4 is detected by the current detector 8 and given to the control unit 6. The internal configuration of the control unit 6 will be described below.

The load current Iout detected by the current detector 8 is compared with the current reference value Iref by the comparator 61, and the deviation is input to the constant current control circuit 62. The constant current control circuit 62 adjusts the output current control manipulated variable Ec _ACR so that the input deviation becomes zero. The current control manipulated variable Ec _ACR becomes one input of the adder 63.

The current reference value Iref is also given to the feedforward control circuit 64. The feedforward control circuit 64 outputs the feed-forward operation amount _{Ec FF} as the current reference value Iref supplied. This feedforward manipulated variable Ec _FF is given to the correction calculator 65, and the output of the correction calculator 65 becomes one input of the adder 63. The correction calculator 65 is supplied with the input voltage of the power converter 4 detected by the voltage detector 7, and the correction calculator 65 corrects the feedforward manipulated variable Ec _FF so as to be inversely proportional to the input voltage.

  The operation amount Ec, which is the output of the adder 63 obtained in this way, is converted into a gate signal that is an on / off pulse by the PWM control circuit 66, and is given to the gate of the self-extinguishing element constituting the power converter 4. It is done. That is, the PWM control circuit 66 performs a voltage control operation such that the output current of the power converter 4 becomes the current reference value Iref.

Hereinafter, the operation of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. 1 will be described with reference to FIG. FIG. 2 shows the waveform of each part when the current reference value Iref is changed to a substantially triangular wave shape with a period of _τIREF . As shown in the figure, the current reference value Iref increases in the interval of τ1 _IREF , decreases to the original value in the interval of τ2 _IREF , and thereafter becomes a predetermined small current. The output current Iout of the power converter 4 is controlled according to this current reference value Iref. In order to output such an output current Iout, the output voltage Vout of the power converter 4 becomes a pseudo rectangular wave as illustrated. This is because the output voltage Vout applied to the load 5 is based on the inductance value L of the load 5, the resistance value R of the load 5, and the output current Iout of the power converter 4 flowing through the load 5.
Vout = L (dIout / dt) + R × Iout (1)
This is because Further, since the diode rectifier 2 is used as the input AC / DC converter, the input power from the AC power source 1 increases when the output current Iout increases, and the influence of the voltage drop due to the impedance of the line, the voltage drop of the diode element, and the like. As shown in the figure, the input DC voltage Vin of the power converter 4 decreases in the interval τ1 _IREF . Conversely, when the output current Iout decreases in the interval of τ2 _IREF, the input DC voltage Vin increases because the input power decreases.

Between the input DC voltage Vin, the output voltage Vout, and the operation amount Ec given to the PWM control circuit 66,
Vout∝Vin × Ec (2)
Therefore, when the input DC voltage Vin decreases, the loop transfer function gain of the entire power converter decreases, and the control response performance deteriorates.

  Further, when the relationship among the current reference value Iref, the voltage reference value Vref, the feedforward manipulated variable Ecff, and the input DC voltage Vin is obtained using the equations (1) and (2), the following equation (3) is obtained. Become.

Ecff∝Vref / Vin
= {L (dIref / dt) + R × Iref} / Vin (3)
Accordingly, the feedforward control circuit 64 calculates the voltage reference value Vref from the current reference value Iref and the load characteristic of the load 5 as shown by the relationship of the expression (3), and calculates the manipulated variable Ec and the converter output voltage Vout. The necessary feedforward manipulated variable Ec _FF is calculated from the relationship. The voltage reference value Vref in the above may be given from the outside in advance.

However, the feedforward control circuit 64 shown in FIG. 1, for giving only the current reference value Iref as a variation, the other parameters so that calculates the feedforward manipulated variable Ec _FF as constant, for example, the input DC voltage When Vin varies, the accurate feedforward manipulated variable Ec _FF cannot be calculated, and the calculation accuracy of Ec _ff decreases.

Therefore, the correction arithmetic unit 65 to the output of the feed forward control circuit 64 is provided to correct the feed-forward operation amount Ec _FF. The correction calculator 65 corrects the Ec _ff to increase when the input DC voltage Vin decreases, and corrects the Ec _ff to decrease when the input DC voltage Vin increases. Since the feedforward manipulated variable Ec _FF and the input DC voltage Vin are inversely proportional as shown in the equation (3), when the input DC voltage Vin decreases, the feedforward manipulated variable Ec _FF is increased so that the input DC voltage Vin is The calculation accuracy of Ec _ff can be improved by performing a substantially inversely proportional correction that decreases the feedforward manipulated variable Ec _FF when it rises.

  Further, the control response of the feedforward control circuit 64 and the correction calculator 65 is the frequency response of the current reference value Iref itself, and is very slow with respect to the response of the constant current control circuit 62. It will never be.

As described above, according to the first embodiment, since the feedforward system in which the calculation accuracy of the feedforward manipulated variable Ec _FF is improved is used, it is possible to follow the current reference value that changes with time with high accuracy. It is possible to provide a power conversion device having characteristics.

  FIG. 3 is a block diagram of the power conversion apparatus according to the second embodiment of the present invention. In the second embodiment, the same parts as those in the circuit configuration diagram of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. The second embodiment is different from the first embodiment in that a ripple removing circuit 67 is provided and a voltage detected by the voltage detecting circuit 7 is supplied to the correction arithmetic unit 65 via the ripple removing circuit 67.

  Since the input DC voltage Vin is obtained by rectifying the AC voltage of the AC power supply 1 with the diode rectifier 2, the detected value of the input DC voltage Vin includes a ripple component corresponding to the frequency of the AC power supply 1. Therefore, by removing this ripple component by the ripple removing circuit 67, the stability of the control system can be improved.

In the third embodiment, the ripple removing circuit 67 is constituted by a primary delay circuit. In this case, the time constant τ of the first-order lag circuit is τ _IN <when the maximum value of the ripple component period included in the input signal of the ripple removal circuit 67 is τ _IN and the period of the current reference value Iref is τ _IREF. Select so that τ <τ _IREF .

The ripple component can be removed by selecting the time constant τ of the first-order lag circuit so that τ> τ _IN. On the other hand, the correction arithmetic unit 65 causes the control characteristic variation due to the variation of the input DC voltage Vin. In order to correct, a signal having a frequency component equivalent to the time constant τ _{V in} which the input DC voltage Vin varies is necessary. Further, since the fluctuation of the input DC voltage Vin is caused by the fluctuation of the output current Iout, the fluctuation time constant τ _V of the input DC voltage Vin becomes about the period τ _IREF of the ripple component of the current command value Iref. Therefore, if τ <τ _IREF , a signal having a necessary frequency component is not removed.

For example, when the triangular wave-like current reference in FIG. 2 is τ1 _IREF = 2.0 s, τ2 _IREF = 1.0 s, and τ _IREF = 4.0 s, the input DC voltage Vin varies fastest during the period of τ2 _IREF. Therefore, in order to correct the fluctuation of the control characteristic accompanying the fluctuation of the input DC voltage Vin, the frequency component having the time constant of τ2 _IREF needs to pass through the first-order lag circuit. Therefore, the time constant τ of the first-order lag circuit should be τ = 0.1 s with a margin of about 10 times. For example, when the frequency of the AC power supply is 50 Hz and the input diode rectifier 2 is configured with 12 phases, the ripple component included in the input DC voltage Vin is 600 Hz (period 1.67 ms) and 600 Hz double wave. , Τ = 0.1 s primary delay circuit, it is possible to remove the ripple component included in the detected value of the input DC voltage Vin.

  In the second embodiment, the case where the ripple removing circuit 67 is a first-order lag circuit has been described. However, this first-order lag circuit may be configured by hardware using a CR filter, and in the case of digital control, it may be implemented by software. It may be realized. In addition, a secondary delay circuit can be applied to the ripple removing circuit 67. In the case of a second-order lag circuit, it may be configured by hardware using an LCR filter, or may be realized by software in the case of digital control.

  FIG. 4 is a block diagram of a power conversion apparatus according to Embodiment 3 of the present invention. In the third embodiment, the same parts as those in the circuit configuration diagram of the power conversion device according to the first embodiment of the present invention shown in FIG. The third embodiment is different from the first embodiment in that the voltage detection circuit 7 is omitted and the output current Iout of the power converter 4 is input to the correction calculator 65A instead of the input DC voltage Vin. .

As can be seen from the waveform shown in FIG. 2, the input DC voltage Vin decreases when the output current Iout increases, and conversely increases when it decreases. Therefore, in order to enhance the operation amount of the feedforward value Ec _ff when the input DC voltage Vin is decreased, it is sufficient to perform the correction substantially proportional correction calculator 65A in the output current Iout.

  In order to perform the calculation in the correction calculator 65A in more detail, the voltage drop due to the impedance of the input circuit of the diode rectifier 2, the voltage drop of the diode rectifier 2, and the voltage drop of the DC circuit are obtained by calculation and input from the output current Iout. What is necessary is just to obtain | require DC voltage Vin. The voltage drop of the diode rectifier 2 includes a diode on-resistance and a commutation overlap angle increase. The voltage drop due to the increase of the commutation overlap angle can be obtained by calculation from the commutation reactance.

  According to the third embodiment, since the voltage detector 7 can be omitted, it is not necessary to add a new detector to the conventional configuration.

  As can be seen from the waveform shown in FIG. 2, it is apparent that the same effect can be obtained even if the current reference value Iref is used instead of the output current Iout of the power converter 4.

  FIG. 5 is a block diagram of a power conversion apparatus according to Embodiment 4 of the present invention. In the fourth embodiment, the same parts as those in the circuit configuration diagram of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. The fourth embodiment differs from the first embodiment in that a current detector 9 for detecting the input current Iac_in of the diode rectifier instead of the voltage detection circuit 7, a voltage detector 10 for detecting the input voltage Vac_in of the diode rectifier, and the input current An input power calculator 68 that calculates input power from Iac_in and the input voltage Vac_in is provided, and an output Pin of the input power calculator 68 is provided to the correction calculator 65B.

  As described above, since the decrease and increase of the input DC voltage Vin are caused by the increase and decrease of the input power, the fluctuation of the input DC voltage Vin can be derived from the input power calculation value Pin. Therefore, the control characteristic of the feedforward system is improved by using the input power calculation value Pin for the fluctuation of the input DC voltage Vin in the power converter, and the tracking characteristic with high accuracy with respect to the current reference value changing with time. It is possible to provide a power conversion device having

Here, the correction calculator 65B corrects the feedforward manipulated variable Ec _FF approximately in proportion to the input power calculation value Pin. However, the correction calculator 65B performs more detailed correction by performing a calculation equivalent to the calculation described in the third embodiment. It becomes possible.

  According to the fourth embodiment, since the AC power that does not pulsate according to the system frequency is detected and corrected, the necessity of using the ripple removing means described in the second embodiment is reduced.

  FIG. 6 is a block diagram of a power conversion apparatus according to Embodiment 5 of the present invention. In each part of the fifth embodiment, the same parts as those in the circuit configuration diagram of the power conversion apparatus according to the first embodiment of the present invention shown in FIG. The fifth embodiment is different from the first embodiment in that the output of the constant current control circuit 62 is supplied to the adder 63 via the correction calculator 69.

  The correction calculator 69 is input with the input DC voltage Vin, and has an inverse proportional characteristic that decreases the output when the input DC voltage Vin increases as in the correction calculator 65.

  As shown in the fifth embodiment, in addition to the control loop by the feedforward control circuit 64, the control characteristic is further improved by adding the control correction by the input voltage fluctuation in the feedback control loop by the constant current control circuit 62. Is possible.

  Note that a ripple removal circuit as shown in the second embodiment may be provided so that the voltage detected by the voltage detection circuit 7 is supplied to the correction computing unit 69 via the ripple removal circuit. Further, as shown in the third embodiment. Alternatively, the output current Iout or the current reference value Iref of the power converter 4 may be input to the correction calculator 69 and the correction calculator 69 may perform a correction substantially proportional to this value. Further, as shown in the fourth embodiment, a configuration in which AC input power is supplied to the correction computing unit 69 may be adopted.

The block block diagram of the power converter device which concerns on Example 1 of this invention. Operation waveforms of each part for explaining the operation of the first embodiment. The block block diagram of the power converter device which concerns on Example 2 of this invention. The block block diagram of the power converter device which concerns on Example 3 of this invention. The block block diagram of the power converter device which concerns on Example 4 of this invention. The block block diagram of the power converter device which concerns on Example 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Diode rectifier 3 Smoothing capacitor 4 Power converter 5 Load 6 Control part 7 Voltage detector 8 Current detector 9 Current detector 10 Voltage detector

61 Comparator 62 Constant Current Control Circuit 63 Adder 64 Feedforward Control Circuit 65, 65A, 65B Correction Calculator 66 PWM Control Circuit 67 Ripple Removal Circuit 68 Input Power Calculator 69 Correction Calculator

Claims (9)

A diode rectifier that converts the AC voltage of the AC power source into a DC voltage;
A smoothing capacitor for smoothing the output of this diode rectifier,
A power converter that inputs a DC voltage applied to the smoothing capacitor and supplies a desired current to the load;
A control unit for controlling the power converter,
The controller is
A constant current control circuit for adjusting a current control operation amount as an output so that a deviation between a current reference value and an output current of the power converter is minimized;
A feedforward control circuit that outputs a feedforward manipulated variable according to the current reference value;
First correction means for correcting the feedforward manipulated variable in order to correct the control characteristic fluctuation accompanying the input voltage fluctuation of the power converter;
And a voltage control unit configured to control the output voltage of the power converter so as to follow an operation amount obtained by adding the corrected feedforward operation amount and the current control operation amount. The feedforward control circuit is
The voltage to be output by the power converter is obtained by calculation from the current reference value and the impedance of the load, and the feedforward manipulated variable is output in proportion to the voltage to be output. The power conversion device according to claim 1. Voltage detecting means for detecting an input voltage of the power converter;
3. The power converter according to claim 1, wherein the first correction unit corrects the feedforward operation amount substantially in inverse proportion to the detected voltage. 4. The voltage detection means includes
The power conversion device according to claim 3, further comprising a ripple removing unit that removes a voltage ripple included in the input voltage. The ripple removing means is a first-order lag circuit with a time constant τ,
When the period of the current reference value is τ _IREF and the maximum value of the ripple component included in the input signal of the primary delay circuit is τ _IN , the time constant τ of the primary delay circuit is τ _IN <τ <τ _IREF The power converter according to claim 4, wherein the power converter is selected to be The first correction means includes
The power converter according to claim 1 or 2, wherein the feedforward manipulated variable is corrected according to at least one of an output current of the power converter and the current reference value. Power detection means for detecting the input power of the power converter;
3. The power converter according to claim 1, wherein the first correction unit corrects the feedforward operation amount substantially in inverse proportion to the detected power. 4. In order to correct the control characteristic fluctuation accompanying the input voltage fluctuation of the power converter,
The power converter according to any one of claims 1 to 7, further comprising a second correction unit that corrects an output of the constant current control circuit. Voltage detecting means for detecting an input voltage of the power converter;
9. The power conversion apparatus according to claim 8, wherein the second correction unit corrects the output of the constant current control circuit in substantially inverse proportion to the detected voltage.

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