JP4940933B2 - PWM inverter output voltage control device - Google Patents

Description

  The present invention relates to a PWM inverter that is used in a UPS (uninterruptible power supply) or a parallel type sag compensator and supplies alternating current power to a load. The present invention relates to a controller for compensation.

  A circuit configuration example of the UPS is shown in FIG. In normal times, the AC input is converted to DC by the forward converter 1 to charge the storage battery 2 and supply power to the PWM inverter 3. The inverter 3 converts this DC power into AC power and supplies it to the load 4. The UPS with this configuration converts AC to DC, then converts it back to AC and supplies it to the load. Therefore, it loads stable quality power that is not affected by voltage fluctuations, frequency fluctuations, and waveform distortion of the AC input power supply. Can supply. Moreover, at the time of an AC input power failure, DC power is supplied from the storage battery 2, and the inverter 3 can continue to supply stable AC power to the load without a power failure.

  The AC filter 5 removes harmonic components from the AC input current, and the AC filter 6 removes harmonic components (carrier components) included in the PWM output of the inverter 3.

  The inverter voltage control block of UPS is shown in FIG. An AVR control (automatic voltage control) unit 11 that keeps the effective voltage value at the command value, a distortion correction control unit 12 based on the deviation between the inverter output voltage instantaneous value and the normal voltage instantaneous value, and an L portion (inductance) of the AC filter 6 The voltage compensation control unit 13 compensates for the voltage drop due to.

  FIG. 8 shows an example of the circuit configuration of the parallel type voltage sag compensator (see, for example, Patent Document 1). In normal times, power is supplied to the load 4 via the high-speed switch 7. The AC / DC converter 8 having a bidirectional power conversion function stops or normally charges the electric double layer capacitor 9 as a DC power source. At the time of a power failure in the system, the high speed switch 7 is disconnected, the DC power stored in the electric double layer capacitor 9 is converted into AC power by the AC / DC converter 8, and the power is supplied to the load 4 through the AC filter 6 without interruption. The control device performs the same detection and control as in the case of UPS during the sag compensation operation.

  Here, when the load 4 includes a rectifier load or the like, the output voltage of the inverter 3 or the AC / DC converter 8 is affected by the load current and is distorted. In order to shape this voltage waveform distortion into a normal voltage waveform, distortion correction control is performed.

Similarly, when viewed from the AC system power source, the UPS forward converter 1 and the AC / DC converter of the parallel type voltage sag compensator become a rectifier load, and the harmonic current flowing therethrough distorts the system voltage. The suppression of the harmonic current is generally performed by an LC filter, and an active filter may be provided in the AC system.
JP 2005-73410 A

  As described above, the AC filter 6 for removing the PWM carrier is provided between the PWM inverter and the load. Due to the influence of the AC filter and the load current flowing therethrough, there is a problem that the inverter output voltage (load end voltage through the AC filter) does not follow the inverter voltage command value.

  That is, the distortion correction control unit 12 based on the deviation between the inverter output voltage instantaneous value and the normal voltage instantaneous value adds the difference from the normal voltage to the voltage command value. On the other hand, the voltage correction controller 13 that compensates for the voltage drop due to the AC filter L adds the differential (sLI) of the L current to the voltage command value. Even if these distortion correction and voltage correction control command values are added to the voltage command values as they are, high-accuracy control cannot be performed due to the influence of the AC filter and the load current flowing therethrough.

  An object of the present invention is to provide an output voltage control device for a PWM inverter that can compensate for the output voltage distortion of the inverter due to the output stage AC filter and load current of the PWM inverter with high accuracy.

  In order to solve the above-described problems, the present invention creates a voltage command value in consideration of an AC filter and a load by a voltage control unit of a PWM inverter, and has the following configuration.

( 1 ) A PWM carrier removing AC filter having an LCL filter configuration in which a series connection circuit of a capacitor Cf and a resistor Rf is provided at a series connection point of the reactors L1 and L2 between the PWM inverter and the load, and the control device Is a device for controlling the output voltage of the PWM inverter according to the output voltage command,
A first calculation element having a load current instantaneous value Iload as an input and having a transfer function G (s) below;

  The deviation between the normal voltage instantaneous value Vref of the PWM inverter and the output voltage instantaneous value Vout of the PWM inverter is added to the normal voltage instantaneous value Vref. A second arithmetic element having the following transfer function H (s) as an input obtained by adding the corresponding automatic voltage control (AVR) output;

  A voltage control unit is provided which adds the calculation outputs of the first and second calculation elements to obtain a voltage command value of the PWM inverter.

( 2 ) AC filter for PWM carrier removal having an LC filter configuration in which a reactor L1 is interposed between the PWM inverter and the load, and a series connection circuit of a capacitor Cf and a resistor Rf is provided at a connection point between the reactor L1 and the load. The control device is a device that controls the output voltage of the PWM inverter according to the output voltage command,
A first calculation element having a load current instantaneous value Iload as an input and having a transfer function G (s) below;

  The deviation between the normal voltage instantaneous value Vref of the PWM inverter and the output voltage instantaneous value Vout of the PWM inverter is added to the normal voltage instantaneous value Vref, and this is added to the deviation of the normal voltage effective value Vrefrms and the output voltage effective value Voutrms of the PWM inverter. A second arithmetic element having the following transfer function H (s) as an input obtained by adding the corresponding automatic voltage control (AVR) output;

  A voltage control unit is provided which adds the calculation outputs of the first and second calculation elements to obtain a voltage command value of the PWM inverter.

( 3 ) The voltage control unit
Control means for performing proportional differentiation (PD) control on the deviation between the normal voltage instantaneous value Vref and the inverter output voltage instantaneous value Vout and adding the normal voltage instantaneous value Vref as an input;
Control means for performing proportional differentiation (PD) control on the instantaneous current value Iload of the load and inputting the transfer function G (s);
It is provided with.

  As described above, according to the present invention, the output voltage distortion of the inverter due to the output stage AC filter of the PWM inverter and the load current can be compensated with high accuracy.

(Embodiment 1)
FIG. 1 is a block configuration diagram of a control device according to the present embodiment. A portion different from the voltage control block diagram shown in FIG. 7 is replaced with an AVR control unit 11, a distortion correction unit 12, and a voltage correction control unit 13. The control unit 14 is provided.

  The voltage control unit 14 obtains a voltage control signal through which the load current instantaneous value Iload is input through the transfer function G (s), and the normal voltage instantaneous value Vref is input through the transfer function H (s). A calculation element 14B that obtains a voltage control signal and a calculation element 14C that uses a result obtained by adding the calculation results of both calculation elements 14A and 14B as a voltage command value of the inverter 3 are provided. Hereinafter, the voltage command value calculation by the transfer functions G (s) and H (s) in the voltage control unit 14 will be described in principle.

  In FIG. 1, the circuit configuration of the AC filter 6 inserted between the PWM inverter 3 of the UPS and the load 4 is an LCL in which a series connection circuit of a capacitor Cf and a resistor Rf is provided at the series connection point of the reactors L1 and L2. Filter configuration.

  In this filter configuration, when the circuit equation is established as the current Iinv0 of the reactor L1, the current Iinv1 of the reactor L2, the current of the capacitor Cf and the resistor Rf (Iinv1-Iinv0), the output voltage Vinv of the inverter 3 and the voltage Vload of the load 4 are as follows: (1) and (2). s is a Laplace operator.

  The above formulas (1) and (2) are summarized as the following formula (3).

  The above equation (3) can be expressed by the following equation (4).

  When the load voltage Vload is solved from the above equations (4) and (5) to (8), the following equation (9) is obtained.

  From this equation (9), it can be seen that there is an error in Vinv and Vload. In equation (9), in order to make Vload coincide with the normal voltage instantaneous value Vref of the inverter, Vinv may be set to the value of the following equation (10).

  In the above equation (10), transfer functions H (s) and G (s) are

In other words, the inverter output voltage Vinv may be controlled by calculation according to the following equation (13).

  From the above, the voltage control unit 14 in the present embodiment obtains the voltage command value by the calculation based on the above equation (13). Among these, the transfer function H (s) receives the normal voltage instantaneous value Vref as an input, and performs calculation according to the equation (11). The transfer function G (s) receives the load current instantaneous value Iload as input, and performs calculation according to the equation (12). The sum of these calculation results is used as the voltage command value for the inverter.

  According to the present embodiment, the output voltage control is performed in consideration of the AC filter and the load current. Therefore, the high-accuracy control that compensates for the output voltage distortion can be performed as compared with the conventional control device. Moreover, since an inverter voltage command value can be calculated | required only by feedforward calculation, responsiveness can be improved. Further, the amount of calculation can be reduced as compared with the second and third embodiments described below.

(Embodiment 2)
In the present embodiment, instead of the voltage control unit 14 of FIG. 1, the voltage control unit 15 having the arithmetic block configuration shown in FIG. 2 is used.

  The transfer function H (s) of the voltage control unit 15 has an input obtained by adding a deviation between the normal voltage instantaneous value Vref and the inverter output voltage instantaneous value Vout to the normal voltage detection value Vref, and follows the equation (11). Perform the operation. The transfer function G (s) receives the load current instantaneous value Iload as input, and performs calculation according to the equation (12).

  According to the present embodiment, the feedback of the inverter output voltage is applied as compared with the first embodiment, so that more accurate control can be performed.

(Embodiment 3)
In the present embodiment, the voltage control unit 16 shown in FIG. 3 is used instead of the voltage control unit 15 shown in FIG.

  In the control block of FIG. 3, in addition to the calculation block of the voltage control unit 15 of FIG. 2, the AVR command value obtained by the AVR unit 11 is added to the transfer function H (s). The transfer function H (s) is obtained by inputting the sum of the deviation between the normal voltage instantaneous value Vref and the inverter output voltage instantaneous value Vout to the normal voltage detection value Vref and the AVR command value. Perform operations according to

  According to this embodiment, the fundamental wave component of the inverter output voltage matches the normal voltage by AVR control. Therefore, compared to the second embodiment, the control burden based on the deviation between the inverter output voltage instantaneous value and the normal voltage instantaneous value is reduced.

(Embodiment 4)
The present embodiment is a voltage control device in the case where the AC filter 6 has an LC filter configuration (a configuration in which the reactor L2 in FIG. 1 is omitted).

  When the load voltage Vload is solved from the above equations (4) and (5) to (8), it can be expressed by the following equation (14).

  From this equation (14), it can be seen that an error occurs in Vinv and Vload due to the load current Iinv1. In equation (14), in order to make Vload coincide with the normal voltage instantaneous value Vref of the inverter, Vinv may be set to the value of the following equation (15).

  By substituting the following equation (16) for the above equations (14) and (15), the load voltage Vload can be matched with the inverter voltage command value Vref when the inverter voltage control system is ideal.

  In this equation (16), transfer functions H (s) and G (s) are set as the following equations (17) and (18),

  The above equation (15) is expressed as the following equation (19).

  Here, when the AC filter is an LC configuration instead of the LCL configuration of FIG. 1, in the above formulas (17) and (18), the value of the reactor L2 of FIG. (S) and G (s) are the following expressions (20) and (21), respectively, and can be expressed by simple expressions.

  From the above, this embodiment is a voltage control device having a calculation block configuration shown in FIG. The voltage control unit 17 in the figure obtains a voltage command value by calculation based on the above equations (19) to (21). Among these, the transfer function H (s) indicated by 17B has an input obtained by adding a deviation between the normal voltage instantaneous value Vref and the inverter output voltage instantaneous value Vout to the normal voltage detected value Vref, and follows the equation (20). Perform the operation. The transfer function G (s) indicated by 17A takes the load current instantaneous value Iinv1 (= load) as an input and performs a calculation according to the equation (21). The sum of these calculation results is used as the voltage command value for the inverter.

  Here, the terms input to the transfer functions G (s) and H (s) in the equation (19) will be described. Since there is a deviation between the normal voltage instantaneous value Vref and the inverter output voltage Vout that are input to the transfer function H (s), the gain by the proportional (P) operation by the amplifier 17D, the differential term calculation unit 17E and the amplifier The control characteristic is improved by the differential (D) operation by 17F, that is, PD control is performed. Then, the normal voltage instantaneous value Vref is added to this value and input to H (s). Similarly, the term input to the transfer function G (s) is a value obtained by subjecting the load current instantaneous value Iinv1 to PD control by the amplifier 17G, the differential term calculation unit 17H, and the amplifier 17I.

  According to the present embodiment, PD control based on the deviation between the inverter output voltage instantaneous value and the normal voltage instantaneous value can be performed, and a voltage command value can be created in consideration of the AC filter and the load. Therefore, it becomes possible to improve the gain and control characteristics by PD control and remove the influence of the AC filter, and to perform voltage control with higher accuracy than the conventional method.

(Embodiment 5)
The present embodiment is a voltage control device in which an AVR command value is added to the arithmetic block configuration shown in the fourth embodiment.

  FIG. 5 shows a voltage control unit 18 that uses the AVR command value obtained by the AVR unit 11 as an addition input to the transfer function H (s) in addition to the calculation block of the voltage control unit 17 of FIG. The transfer function H (s) is obtained by inputting the sum of the deviation between the normal voltage instantaneous value Vref and the inverter output voltage instantaneous value Vout and adding it to the normal voltage detected value Vref and the AVR command value, The calculation according to the equation (20) is performed.

  According to the present embodiment, the fundamental component of the inverter output voltage matches the normal voltage by AVR control. Therefore, as compared with the fourth embodiment, the control burden based on the deviation between the inverter output voltage instantaneous value and the normal voltage is reduced.

  The PD control in the fourth and fifth embodiments can be applied to the first to third embodiments to improve the gain and control characteristics.

The block block diagram of the control apparatus which shows Embodiment 1 of this invention. The block block diagram of the control apparatus which shows Embodiment 2 of this invention. The block block diagram of the control apparatus which shows Embodiment 3 of this invention. The block block diagram of the control apparatus which shows Embodiment 4 of this invention. The block block diagram of the control apparatus which shows Embodiment 5 of this invention. The circuit diagram of UPS (uninterruptible power supply). The conventional UPS voltage control block block diagram. The circuit diagram of a parallel type voltage sag compensator.

Explanation of symbols

3 PWM inverter 4 Load 6 AC filter 11 AVR control unit 12 Distortion correction unit 14-18 Voltage control unit

Claims (3)

A PWM carrier removing AC filter having an LCL filter configuration in which a series connection circuit of a capacitor Cf and a resistor Rf is provided at the series connection point of the reactors L1 and L2 is interposed between the PWM inverter and the load. A device for controlling the output voltage of the PWM inverter according to a command,
A first calculation element having a load current instantaneous value Iload as an input and having a transfer function G (s) below;

The deviation between the normal voltage instantaneous value Vref of the PWM inverter and the output voltage instantaneous value Vout of the PWM inverter is added to the normal voltage instantaneous value Vref. A second arithmetic element having the following transfer function H (s) as an input obtained by adding the corresponding automatic voltage control (AVR) output;

An output voltage control device for a PWM inverter, comprising: a voltage control unit that adds the calculation outputs of the first and second calculation elements to obtain a voltage command value of the PWM inverter. A reactor L1 is interposed between the PWM inverter and the load, and an AC filter for PWM carrier removal having an LC filter configuration in which a series connection circuit of a capacitor Cf and a resistor Rf is provided at a connection point between the reactor L1 and the load is inserted. The control device is a device for controlling the output voltage of the PWM inverter according to the output voltage command,
A first calculation element having a load current instantaneous value Iload as an input and having a transfer function G (s) below;

The deviation between the normal voltage instantaneous value Vref of the PWM inverter and the output voltage instantaneous value Vout of the PWM inverter is added to the normal voltage instantaneous value Vref. A second arithmetic element having the following transfer function H (s) as an input obtained by adding the corresponding automatic voltage control (AVR) output;

An output voltage control device for a PWM inverter, comprising: a voltage control unit that adds the calculation outputs of the first and second calculation elements to obtain a voltage command value of the PWM inverter. The voltage controller is
Control means for performing proportional differentiation (PD) control on the deviation between the normal voltage instantaneous value Vref and the inverter output voltage instantaneous value Vout and adding the normal voltage instantaneous value Vref as an input;
Control means for performing proportional differentiation (PD) control on the instantaneous current value Iload of the load and inputting the transfer function G (s);
The output voltage control apparatus of the PWM inverter according to claim 1 or 2 , further comprising:

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