JP4251030B2 - Power converter - Google Patents

Description

  The present invention relates to a series-parallel power converter including a series converter connected in series to an AC power supply and a parallel converter connected in parallel. The present invention relates to a power converter that compensates for supplying a constant voltage to a load and that a parallel converter compensates only for energy required for compensation by a series converter.

FIG. 7 is a circuit diagram showing a conventional technique of this type of power conversion device, which is, for example, a circuit substantially similar to that described in Non-Patent Document 1 described later.
In FIG. 7, 1 is an AC power source, 2 and 9 are filter capacitors, 3 and 8 are reactors, 4 is a current detector, 5 is a parallel converter, 6 is an electrolytic capacitor as a converter power source provided in the DC link unit, 7 Indicates a series converter and 10 indicates a load.

Here, as shown in FIG. 8, for example, the parallel converter 5 and the series converter 7 are formed by connecting semiconductor switching elements 51 to 54 and 71 to 74 such as IGBTs having anti-reflective diodes connected in antiparallel to each other by a single-phase bridge connection. It is configured. An insulation transformer (not shown) is connected to the AC input side of the parallel converter 5 or the output side of the series converter 7 as necessary.
The series converter may be configured as a half bridge by replacing one upper and lower arms of the parallel converter 5 or one upper and lower arms of the series converter 7, for example, a series circuit of the switching elements 71 and 72 with a series circuit of capacitors. good.

  In the configuration of FIG. 7, since the voltage obtained by adding the voltage of the AC power supply 1 and the output voltage of the series converter 7 is applied to the load 10, the series converter 7 operates as a series compensation voltage source. For example, even if the voltage of the AC power supply 1 fluctuates and decreases, the AC voltage supplied to the load 10 can be made constant by adding the output voltage of the series converter 7 to the AC power supply voltage. For this reason, although not shown, the voltage across the load 10 is detected, and the switching elements in the series converter 7 are controlled to be turned on and off so that the deviation from the command value becomes zero.

  On the other hand, the parallel converter 5 operates as a parallel compensation current source in order to compensate and keep constant the voltage fluctuation of the DC link part (electrolytic capacitor 6) accompanying the switching operation of the series converter 7. Charge / discharge operation is performed between. As a result, the energy supplied to the load 10 passes only through the series converter 7, and only the energy used for voltage compensation by the series converter 7 passes through the parallel converter 5. Therefore, the loss in the parallel converter 5 is reduced and high efficiency is achieved. Can be realized.

Next, the operation of the parallel converter 5 will be described below together with the configuration of the control circuit in FIG.
A deviation between the voltage reference value V _dcref of the DC link unit and the voltage detection value V _dc is obtained by the adder 15, and the deviation is input to the multiplier 17 via the PI regulator 16 as the first adjusting means. On the other hand, to obtain a sine wave command Sin-wt and a power supply voltage V _in and the reference sine wave Sin-ref is synchronized by the PLL circuit 11. The sine wave command Sin-wt is input to the multiplier 17 and multiplied by the output signal of the PI regulator 16 to obtain an amplitude command ASin-wt of the input current of the parallel converter 5. This amplitude command ASin-wt is input to the adder 12 together with the input current I _pc detected by the current detector 4, and the PI adjuster 13 and the PWM as the second adjusting means so that the deviation between them becomes zero. A PWM pattern is generated via the circuit 14, and a gate pulse according to this PWM pattern is applied to the switching element of the parallel converter 5 for on / off control.
Thereby, it is possible to control the input current waveform of the parallel converter 5 in a sine wave _shape while maintaining the voltage of the DC link unit at the voltage reference value V _dcref .

Yasuhiro Nakai and two others, “Variable AC Electronic Transformer Using Series-Parallel Active Filters”, Proceedings of National Conference of Industrial Application Division, IEEJ, p. 227-230 (Fig.3)

  In the conventional technology described above, the parallel converter 5 performs switching over the entire period of the power supply voltage cycle (commercial cycle) in order to make the input current follow the amplitude command ASin-wt. For this reason, although the parallel converter 5 has less energy to be compensated for the series converter 7, the parallel converter 5 operates to pass a sine wave current, so that the number of times of switching increases, switching loss and element conduction. There was a problem that the loss increased.

  Therefore, the present invention seeks to provide a power conversion device that improves the conversion efficiency by reducing the switching frequency of the parallel converter and reducing the switching loss and the like.

In order to solve the above problems, the invention described in claim 1 is a series converter connected in series between an AC power source and a load and provided with a capacitor as a converter power source, and connected in parallel to the AC power source. The parallel converter is a power conversion device connected via a DC link unit having the capacitor, and the supply voltage to the load is kept constant by compensating the voltage fluctuation of the AC power supply by the switching operation of the series converter. In the power converter for compensating for the voltage fluctuation of the capacitor due to the compensation operation of the series converter by the charge / discharge operation between the parallel converter and the AC power source,
The amplitude command of the input current of the parallel converter generated for PWM control of the parallel converter is a waveform synchronized with the AC power supply voltage, and the width is narrower than 180 degrees centering on the peak value of the positive / negative half cycle The waveform command is based on the reference waveform .

The invention described in claim 2 is the power conversion device according to claim 1,
Means for generating a reference waveform command synchronized with the AC power supply voltage, first adjusting means for adjusting the voltage detection value of the DC link unit to match the voltage reference value, the output signal of this means and the reference waveform Means for multiplying the command to generate an amplitude command of the input current of the parallel converter, second adjusting means for adjusting the amplitude of the input current of the parallel converter to follow the amplitude command of the input current, And a means for generating a PWM signal for the parallel converter from the output signal of the second adjusting means.

  According to the present invention, in a so-called series-parallel power converter, the waveform command for the parallel converter is intermittently made to shorten the switching period. Thereby, the switching frequency of a parallel converter can be reduced, switching loss and element conduction loss can be reduced, and conversion efficiency of the apparatus can be improved and running cost can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a circuit diagram showing an embodiment of the present invention. The same components as those of FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted. Hereinafter, different parts will be mainly described.

1 differs from FIG. 7 in the following manner. That is, in FIG. 1, to obtain a reference waveform command Wave-wt and a power supply voltage V _in and the reference waveform Wave-ref is synchronized by the PLL circuit 11, the output of the reference waveform command Wave-wt and PI controller 16 The signal is multiplied by the multiplier 17 to obtain the amplitude command AWave-wt of the input current of the parallel converter 5.

  Here, FIG. 2 conceptually shows an example of the reference waveform Wave-ref. As shown in the figure, only the section from 30 degrees to 150 degrees and the section from 210 degrees to 330 degrees are continuously displayed. A waveform having a value is set as the reference waveform Wave-ref. By multiplying the reference waveform command Wave-wt based on the reference waveform Wave-ref by the output signal of the PI regulator 16 by the multiplier 17, the reference waveform Wave is used as an amplitude command of the input current of the parallel converter 5. The amplitude command AWave-wt synchronized with -ref is obtained.

A deviation between the amplitude command AWave-wt and the input current I _pc of the parallel converter 5 is obtained by the adder 12, and the switching element of the parallel converter 5 is connected via the PI controller 13 and the PWM circuit so that the deviation becomes zero. A gate pulse for is generated.
For this reason, the input current I _pc of the parallel converter 5 is controlled so as to follow the amplitude command AWave-wt, and the current only flows for a period of 2/3 of one cycle. The number of times of switching is 2/3 as compared with the case where a current is passed over the entire period of one cycle. Therefore, it is possible to reduce the switching loss of the parallel converter 5 and the conduction loss of the element and increase the conversion efficiency.

  As for the control on the side of the series converter 7, as in the conventional technique, the voltage across the load 10 is detected and the switching element in the series converter 7 is turned on and off so that the deviation from the voltage command value becomes zero. Is done.

  In this embodiment, the harmonic input component is expected to increase because the waveform of the AC input current is distorted as compared with the case where the amplitude command is a sine wave. However, the present invention has a relatively small capacity (for example, about 1 KVA). When applied to a power converter, the so-called harmonic guideline is not applicable and there is no problem.

Further, as described above, only the current corresponding to the energy used for the voltage compensation by the series converter 7 flows through the parallel converter 5 and the value thereof is relatively small. The impact is small.
For example, FIG. 3 is an explanatory diagram of a case where the series converter 7 is operated so as to maintain a normal AC power supply voltage (100%) when the voltage of the AC power supply 1 is reduced by 20%. A normal current (100%) is supplied from the AC power supply 1 via the series converter 7, and a current corresponding to the voltage compensation by the series converter 7 (for example, 25%) flows only in the parallel converter 5. (Thus, the AC input current is 125%).
These AC input current, parallel converter 5 current, and AC output current (output current of the series converter 7) are schematically shown in FIGS. 4 (a), 4 (b), and 4 (c). Since the current flowing through the circuit is very small, the distortion of the AC input current is not a problem.

Next, FIG. 5 shows a current waveform when the input current of the parallel converter 5 is controlled using the reference waveform Wave-ref as shown in FIG. This is shown for each of the cases where the flow period is 180 degrees (that is, during continuous flow), 150 degrees, 120 degrees, 90 degrees, and 60 degrees. Assuming that the average value of the current is constant, the peak value of the current increases as the conduction period becomes shorter.
Hereinafter, the switching loss in the parallel converter 5 when the conduction period is changed as described above will be considered.

Here, the switching loss in each current waveform of FIG. 5 was calculated by the following simple calculation formula.
P _LOSS = (E _d × I) / 6 × T × f _crr
P _LOSS : Switching loss E _d : DC link voltage I: _Peak value of each current waveform T: Current period f _crr : Current frequency

FIG. 6 shows a result obtained by normalizing the value calculated by the above calculation formula with the switching loss of the conduction period of 180 degrees (during continuous conduction) as 1. FIG.
When the conduction period is short, the cutoff current increases as a whole, so that one switching loss increases. However, as is apparent from FIG. 6, the conduction period is shortened to reduce the number of times of switching by PWM control. As a result, it is understood that the loss is reduced by about 10 to 20 percent as compared with the continuous flow. This loss reduction effect becomes more remarkable as the flow period is shorter.

  Note that the same effect can be obtained even when the reference waveform Wave-ref is a modulatable waveform centered on the peak portion of the positive and negative half cycles.

It is a circuit diagram of a power converter to which an embodiment of the present invention is applied. It is a conceptual diagram of the reference waveform in the embodiment. It is operation | movement explanatory drawing of embodiment. It is a current waveform figure of each part in an embodiment. It is an input current waveform figure of the parallel converter at the time of intermittent operation in an embodiment. It is explanatory drawing of the switching loss reduction effect at the time of the intermittent operation in embodiment. It is a circuit diagram which shows a prior art. It is a circuit diagram which shows the principal part of FIG.

Explanation of symbols

1: AC power supply 2, 9: Filter capacitor 3, 8: Reactor 4: Current detector 5: Parallel converter 51-54: Semiconductor switching element 6: Electrolytic capacitor 7: Series converter 71-74: Semiconductor switching element 10: Load 11 : PLL circuit 12, 15: Adder 13, 16: PI controller 14: PWM circuit 17: Multiplier

Claims (2)

A series converter connected in series between an AC power source and a load and provided with a capacitor as a converter power source, and a parallel converter connected in parallel to the AC power source via a DC link unit having the capacitor A connected power converter, wherein the voltage fluctuation of the AC power supply is compensated by the switching operation of the series converter to keep the supply voltage to the load constant, and the voltage fluctuation of the capacitor due to the compensation operation of the series converter. In a power conversion device that compensates for charging / discharging operation with an AC power source by the parallel converter,
The amplitude command of the input current of the parallel converter generated for PWM control of the parallel converter is a waveform synchronized with the AC power supply voltage, and the width is narrower than 180 degrees centering on the peak value of the positive / negative half cycle A power conversion device characterized by using a waveform command based on a reference waveform .
The power conversion device according to claim 1,
Means for generating a reference waveform command synchronized with the AC power supply voltage;
First adjusting means for adjusting the voltage detection value of the DC link unit to match the voltage reference value;
Means for multiplying the output signal of this means and the reference waveform command to generate an amplitude command of the input current of the parallel converter;
Second adjusting means for adjusting the amplitude of the input current of the parallel converter so as to follow the amplitude command of the input current;
Means for generating a PWM signal for the parallel converter from the output signal of the second adjusting means;
A power conversion device comprising:

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