JP2015046985A - Electric power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion apparatus capable of suppressing voltage fluctuation when a load is rapidly changed without using a sensor for detecting a load current and a capacitor of a large capacity for suppressing the voltage fluctuation.SOLUTION: An electric power conversion apparatus 10 includes: an electric power conversion circuit 11 which outputs an electric current corresponding to an electric current command value to thereby convert an input DC power or AC power into a constant DC power; a capacitor 12 connected to an output part of the electric power conversion circuit; and voltage control means 14 for outputting the electric current command value to the electric power conversion circuit in order to control the voltage of the capacitor to a set value. The voltage control means calculates the electric current command value from a process value Vand a set value Vof the voltage of the capacitor.

Description

Embodiments described herein relate generally to a power conversion apparatus.

  A power converter that converts input DC or AC power into constant DC power is connected to a power converter circuit such as a 6-arm PWM (Pulse Width Modulation) converter, a DC / DC converter, and the power converter. And a capacitor for generating a DC voltage. Since the PWM converter and the DC / DC converter are switching circuits to which a self-extinguishing element is applied, the output voltage can be controlled to an arbitrary voltage by controlling the switching operation by feeding back the capacitor voltage.

  Incidentally, the power conversion circuit controls the output current to a constant value. A load is connected in parallel with the capacitor to the power conversion circuit. Therefore, the current controlled by the power conversion circuit flows to the capacitor and the load side. For this reason, when a transitional fluctuation such as a sudden change in the load occurs, the capacitor voltage fluctuates due to the current flowing through the load acting as a disturbance, which disturbs the control operation of the power conversion circuit.

  Therefore, the current flowing through the load (load current) is detected, and the control signal is compensated according to this load current (for example, feedforward control is applied), so that the intended current flows through the capacitor, and the voltage at the time of sudden load change Variations can be suppressed.

Masakatsu Kawada, Katsuhiro Nishioka "Easy Control Engineering with MATLAB / Simulink", Morikita Publishing, p66

  However, in order to incorporate the load current into the control system, a sensor for detecting the load current and a circuit for constructing a new control system are required, which increases the cost of the control device. On the other hand, in order to suppress the fluctuation of the capacitor voltage at the time of sudden load change, it is conceivable to provide a capacitor having a large capacity. However, an increase in the volume and cost of the power conversion device due to the installation of the large capacity capacitor is caused.

  The present invention has been made in order to solve the above-described problems, and is capable of suppressing voltage fluctuation at the time of sudden load change without using a sensor for detecting load current and a large-capacity capacitor for suppressing voltage fluctuation. An object is to provide a conversion device.

  According to an embodiment of the present invention for solving the above problems, a current conversion circuit that converts a DC or AC power input by outputting a current corresponding to a current command value into a constant DC power; A capacitor connected to the output section of the current conversion circuit; and a voltage control means for outputting the current command value to the current conversion circuit for controlling the voltage of the capacitor to a set value. Thus, a power conversion device that obtains the current command value from the process value and set value of the voltage of the capacitor can be obtained.

The figure which shows the control block of the power converter device of 1st Embodiment. The figure which shows the control block of the power converter device of the variation of 1st Embodiment. The figure which shows the control block of the power converter device of 2nd Embodiment. The figure which shows the control block of the power converter device of 3rd Embodiment. The figure which shows the structure of the power converter device examined prior to the power converter device of 1st Embodiment.

[First embodiment]
Before describing the power converter of the first embodiment, problems in the conventional power converter will be described.

  FIG. 5 is a diagram illustrating a configuration of the power conversion device studied prior to the power conversion device according to the first embodiment.

  The power conversion device 10 converts AC power input from the AC power source 5 into DC power and supplies the DC power to the load 6. The current detector 7 provided outside the power conversion device 10 detects the load current and outputs it to the power conversion device 10.

  The power conversion apparatus 10 includes a power conversion circuit 11, a capacitor 12, a voltage detector 13, a DC voltage control circuit 14, a current control circuit 15, a current detector 16, a gate signal generation circuit 17, and a gate drive circuit 18. .

The power conversion circuit 11 is a PWM converter in which the switching element 11a is configured with six arms. The power conversion circuit 11 drives the switching element 11a to generate the output current i _conv from the input current i _in . The current control circuit 15 outputs a control signal for executing PWM from the input current i _in detected by the current detector 16 and the current command value i _{conv_ref} . The gate signal generation circuit 17 generates a gate signal for driving the gate of the switching element 11a based on the control signal. The gate drive circuit 18 operates the switching element 11a based on the gate signal.

The generated output current i _conv branches into a current i _c flowing through the capacitor 12 and a current i _load flowing through the load 6. Charge is accumulated in the capacitor 12 by the current _ic , and a voltage is generated across the capacitor 12. The voltage detector 13 detects the voltage V _{DC of the} capacitor 12 and outputs it to the DC voltage control circuit 14. The current detector 7 detects the current i _load flowing through the load 6 and outputs it to the DC voltage control circuit 14.

The DC voltage control circuit 14 generates a control signal based on a deviation between the voltage V _{DC of the} capacitor 12 (voltage between the output terminal P and the output terminal N) and the voltage command value V _{DC_ref} and generates a current as a current command value i _{conv_ref.} Output to the control circuit 15.

As described above, the DC voltage control circuit 14 _{obtains the} current command value i _{conv_ref} from the voltage _{VDC of the} capacitor 12, and the current control circuit 15 performs voltage control by flowing a current corresponding to the command value to the capacitor. Therefore, the DC voltage control circuit 14 and the current control circuit 15 constitute cascade control.

Here, the process value (PV) input to the DC voltage control circuit 14 is a voltage value generated by the current _ic flowing through the capacitor 12. On the other hand, the current value output current _{i conv} controlling the current control circuit 15 is a value which is the sum of the current _{i load} flowing through the current _{i c} and the load 6 flowing through the capacitor 12. As described above, the power conversion circuit 11 operates the total value of the current flowing through the capacitor 12 and the load 6, but cannot directly operate the voltage of the capacitor 12. Therefore, when a transient change occurs in the load 6, the voltage of the capacitor 12 changes.

Therefore, the power conversion device 10 shown in FIG. 5 detects the current i _load flowing through the load 6, and newly adds a value obtained by adding a signal corresponding to the current i _load to the current command value i _{conv_ref} obtained by the DC voltage control circuit 14. By setting the current command value i _{conv_ref} to a _correct value, the intended current _ic is supplied to the capacitor 12 to suppress voltage fluctuation when the load 6 suddenly changes.

  As described above, the power conversion method shown in FIG. 5 requires a sensor for detecting the load current and a circuit for configuring a new control system as described above. There is a problem of rising.

  Then, the structure of the power converter device 10 of 1st Embodiment is demonstrated.

  FIG. 1 is a diagram illustrating a control block of the power conversion device 10 according to the first embodiment. The power conversion device 10 of the first embodiment is different from the power conversion device 10 shown in FIG. 5 in the control method.

  The control block of the power conversion apparatus 10 includes a voltage control block 20 and a current control block 21.

  The voltage control block 20 is a block showing the control function of the DC voltage control circuit 14. The current control block 21 is a block showing control functions including the current control circuit 15, the current detector 16, the gate signal generation circuit 17, the gate drive circuit 18, and the power conversion circuit 11 described in FIG. 5.

However, the current control block 21 is a control block that executes an operation of generating an output current i _conv corresponding to the current command value i _{conv_ref} by a switching operation, and has a function of controlling the switching operation by taking in the variation of the load 6. Not. Therefore, in the present embodiment, the current control block 21 is handled as a proportional operation block having a gain conversion function, and control elements such as a delay element due to a switching operation are considered in the voltage control block 20.

  Although the AC power supply 5 is not explicitly shown in FIG. 1, the power conversion circuit 10 of the present embodiment is not limited to the input of the AC power supply, and a capacitor (capacitance) is provided on the output side. It should be noted that all the power conversion circuits 10 of the type including the component are targeted.

  Next, the configuration of the voltage control block 20 will be described.

In FIG. 1, the relationship between the power conversion circuit output current i _conv , the current i _c flowing through the capacitor 12 connected to the output, and the load current i _load is expressed by Equation (1).

Here, when the voltage between the output terminals PN in FIG. 1 is _VDC , the voltage between PN is a capacitor voltage, and therefore, the capacitor current is expressed by equation (2).

Here, if the capacitor voltage differential value shown in Equation (2) is used for load current estimation as it is, the influence of high-frequency noise due to switching of the power conversion circuit 11 appears and the control system becomes unstable. Therefore, a first-order lag element (incomplete differentiation) for suppressing high-frequency noise is inserted. The estimated value of the capacitor current _{ic including} the first-order lag element is expressed by Expression (3) when expressed using the differential operator s.

Since the current i _c can be estimated from the capacitor voltage V _{DC, the} load current i _load can be estimated if the output current i _conv can be obtained. However, in general, the power conversion circuit 10 capable of operating the current does not include a sensor for detecting the output current, and thus cannot directly _{determine the} output current i _conv . Therefore, the current command value i _{conv_ref} is used as means for knowing the output current i _conv . However, the current command value i _{conv_ref} cannot be used as it is as the output current i _conv . This is because the power conversion circuit output current i _conv and the current command value i _{conv_ref} at the time when the capacitor voltage is detected do not match. Therefore, by adding a delay element such as a first-order lag filter to the current command value i _{conv_ref} and using a past value for a predetermined time, the output current i _conv when the capacitor voltage is detected from the current command value i _{conv_ref} is estimated. To do. The output current of the power conversion circuit estimated using the first-order lag element is expressed by Equation (4).

From the above, the load current i _load can be expressed by equation (5).

On the other hand, as shown in FIG. 1, the output of the control compensation block and the estimated load current i _load are added to obtain the current command value i _{conv_ref} by Expression (6).

By arranging the equations (5) and (6), the transfer function of the voltage control block 20 for deriving the current command value i _{conv_ref} from the capacitor voltage V _DC can be obtained. And by performing control according to this transfer function, voltage fluctuation suppression can be realized.

[Variation of the first embodiment]
In the first embodiment, and using a constant T _f time constant T _D and the output current estimation when the capacitor current estimation. In the variation of the first embodiment, the transfer function is simplified as time constant T _D = time constant T _f .

Here, the time constant _Tf is a first-order lag element for controlling the power conversion circuit 11 and is a physically determined value. The constant T _D when contrast is a value introduced in order to achieve a practical control as a primary delay element for suppressing high-frequency noise (inexact differential) as described above. Both values have the same order value. Therefore, replacing the constant T _D with the time constant T _f time is a reasonable response.

By this simplification, Expression (5) can be expressed by Expression (7).

  FIG. 2 is a diagram illustrating a control block of the power conversion device 10 according to the variation of the first embodiment.

By arranging the equations (6) and (7), the transfer function of the voltage control block 20 for deriving the current command value i _{conv_ref} from the capacitor voltage V _DC can be obtained. And by performing control according to this transfer function, voltage fluctuation suppression can be realized. According to the configuration of this variation, the circuit configuration of the DC voltage control circuit 14 can be simplified, and the processing efficiency can be improved.

[Second Embodiment]
The second embodiment is different from the first embodiment in that the power conversion device is configured to convert power from a DC power supply. Parts having the same or similar functions as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 3 is a diagram illustrating a control block of the power conversion device 10 according to the second embodiment.

Input current _{i in} of the direct current power supply 8 of the input voltage _{V in} is supplied via the reactor 9 is converted to the power conversion circuit output current _{i conv} The power conversion circuit 11. Here, unlike the configuration of FIG. 5, the power conversion circuit 11 is configured by a two-arm PWM converter, which converts AC power in FIG. 5, whereas in the second embodiment, it is DC power. Is to convert.

Further, the current control block 21 is newly provided with a gain block. A proportional gain is set in the gain block, and a gain calculation is performed on the current command value i _{conv_ref} obtained by each block shown in the variation (FIG. 2) of the first embodiment. Then, the corrected current command value i _{conv_ref0} after the gain calculation is output to the current control circuit 15 as a command value.

Here, the reactor 9, the power conversion circuit 11, and the capacitor 12 shown in FIG. 3 constitute a step-up chopper. Therefore, the relationship of Expression (8) is established among the input voltage V _in , the input current i _in , the power conversion circuit output current i _conv, and the output voltage V _out .
V _in × i _in = V _out × i _conv (8)
That is, since the input voltage V _in is boosted to the voltage V _out by configuring the boost chopper, the input current i _in is reduced and output at a ratio of voltage V _in / voltage V _out . Accordingly, the current control block 21 multiplies the current command value i _{conv_ref} obtained by the control calculation by a reciprocal coefficient (= V _out / V _in ) _{in the} gain block. Then, the obtained corrected current command value i _{conv_ref0} is output to the current control circuit 15.

[Third embodiment]
The third embodiment is different from the second embodiment in that the power conversion device is configured to convert power from an AC power supply. Parts having the same or similar functions as those of the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 4 is a diagram illustrating a control block of the power conversion device 10 according to the third embodiment.

  In the third embodiment, an AC power supply 5 is used. Therefore, the power conversion circuit 11 is composed of a 6-arm PWM converter. Since the configuration other than this is the same as that of the second embodiment, detailed description thereof is omitted.

Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.
For example, the control block disclosed in each of the above-described embodiments is not limited to the mode configured by the illustrated control block, and can be configured by hardware and software having similar functions.

  Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 5 ... AC power source, 6 ... Load, 7 ... Current detector, 8 ... DC power source, 9 ... Reactor, 10 ... Power converter, 11 ... Power converter circuit, 12 ... Capacitor, 13 ... Voltage detector, 14 ... DC voltage Control circuit, 15 ... current control circuit, 16 ... current detector, 17 ... gate signal generation circuit, 18 ... gate drive circuit, 20 ... voltage control block, 21 ... current control block.

Claims (4)

A power conversion circuit that converts DC or AC power input by outputting a current corresponding to a current command value into a constant DC power;
A capacitor connected to the output of the power conversion circuit;
Voltage control means for outputting the current command value to the power conversion circuit to control the voltage of the capacitor to a set value;
The power control device, wherein the voltage control means obtains the current command value from a process value and a set value of the voltage of the capacitor. The voltage control means includes
Control compensation means for calculating and outputting a control signal from a deviation between a process value and a set value of the voltage of the capacitor;
Subtracting means for subtracting a current value flowing through the capacitor from a current command value in the past for a predetermined time to obtain a load current flowing through a load connected to the power conversion circuit;
The power converter according to claim 1, further comprising an adding unit that adds the control signal and the estimated load current to obtain the current command value. A DC power source is connected to the input part of the power conversion circuit,
The power conversion device according to claim 1, wherein the power conversion circuit is a two-arm PWM converter. An AC power supply is connected to the input part of the power conversion circuit,
The power conversion device according to claim 1, wherein the power conversion circuit is a 6-arm PWM converter.