JPH01321868A - Pwm electric power converting device and control thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a PWM power converter, and more particularly to a method for reducing ripple current in a smoothing capacitor to reduce its capacitance.

[Conventional technology]

In a converter device that converts single-phase alternating current to direct current, there is a method in which a series resonant circuit that resonates with the frequency of the rectified ripple current is provided to absorb the rectified ripple current and thereby reduce the size of the smoothing capacitor. 197
4th year) pages 135 to 142 (Elektrisch
e Bahnen 45 (1974) pp135-1
42).

[Problem to be solved by the invention]

However, the above conventional technology
There is no mention of the absorption of DC current ripple associated with WM control, nor is there any mention of the reduction in the ripple current absorption effect when the resonant frequency of the series resonant circuit fluctuates, and how to deal with it.

The object of the present invention is to provide a PWM power converter that effectively absorbs ripple components contained in the DC current of the PWM power converter, suppresses the pull current flowing into the smoothing capacitor, and downsizes the smoothing capacitor. In addition, a method for controlling a PWM power converter is provided that can effectively absorb ripple current at all times and reduce the capacitance of the smoothing capacitor even if the capacitance and inductance values of the capacitor and reactor of the ripple absorbing series resonant circuit vary due to temperature, etc. It is about providing.

[Means to solve the problem]

The above purpose is to install a series resonant circuit in parallel with the smoothing capacitor of the PWM power converter to absorb the ripple current accompanying PWM control, and to adjust the carrier frequency of the PWM control so that the magnitude of the current ripple flowing through the smoothing capacitor is minimized. This is achieved through control.

[Effect]

A series resonant circuit consisting of a capacitor and a reactor is provided in parallel with the smoothing capacitor of the PWM power converter, and the carrier frequency of PWM control is varied so that the amplitude of the ripple component of the current flowing through the smoothing capacitor is minimized. As a result, the resonant frequency of the series resonant circuit and the frequency of the pull current component match, so that the ripple component is absorbed by the resonant current flowing through the series resonant circuit, and almost no pull current flows through the smoothing capacitor. Also.

Even if the values of the capacitor and reactor of the series resonant circuit change due to temperature rise, etc., the carrier wave frequency is controlled so that the resonance condition is always satisfied.

In other words, changes in the resonance frequency can be detected from the ripple component flowing through the smoothing capacitor, and since the carrier frequency of PWM control is varied so that this ripple component is minimized, the ripple component can be effectively absorbed by the resonant circuit at all times. can do. As a result, the smoothing capacitor capacity of the PWM power converter can be reduced.

[Embodiment] FIG. 1 shows an embodiment in which the present invention is applied to a PWM inverter. In FIG. 1, a PWM inverter 6 converts a DC voltage applied from a DC power supply 1 into an AC voltage. The inverter 6 is a Graetz-connected self-extinguishing element T.
UP, TVP, ... TWN and feedback diodes DUP, DVP, ... connected in antiparallel to each self-extinguishing element.
...DWN. As the self-extinguishing element, a switching element such as a transistor or a gate turn-off thyristor is used. Each phase U of the inverter 6,
V.

An induction motor 7 is connected to the AC output terminal of W.

A speed command signal from speed command circuit 15 is applied to voltage-frequency converter 14 . The voltage-frequency converter 14 outputs a frequency command signal in response to the speed command signal. The output frequency of the inverter 1 (the primary frequency of the motor 7) is determined by the frequency command signal. The voltage command circuit 13 generates a voltage command pattern signal Vt11 with an amplitude proportional to the magnitude of the frequency command signal and a 120° phase difference whose frequency is proportional to the frequency command signal.
゜Vv''yV- is outputted to the comparators 12U, 12V, and 12W.The output signal of the oscillator 10, which generates a carrier wave signal for pulse width modulation control, is outputted to the comparator 12U.

12V, 12W is applied for 1m. Comparator 12U.

12V and 12W are voltage command pattern signals Vu''.

A switching element TUP that compares Vv*pV- with a carrier signal and configures a PWM inverter 6.

TVP, . . . outputs pulse width modulated pulses for turning on and off TWN to the gate circuit 11. The gate circuit 11 provides gate signals to the switching elements TUP, TVP, . . . TWN in response to the pulse width modulation pulse.

The DC voltage of the DC power supply 1 is applied to the smoothing capacitor 2, the series resonant circuit 18, and the inverter 6.

The series resonant circuit 18 is composed of an inductance 4 and a capacitor 5. The current flowing through the smoothing capacitor 2 is detected by the current detector 3, and the detected current signal is applied to the filter circuit 8. The filter circuit 8 extracts a ripple component associated with PWM control included in the detected current signal and applies it to the tracking control circuit 9. Tracking control circuit 9
calculates a frequency command that minimizes the magnitude of the ripple component and applies it to the oscillator 10. The oscillator 10 varies the oscillation frequency based on the output signal of the tracking control circuit 9 and sends the output signal to the comparators 12U and 12V.

Add to 12W.

First, its operation will be briefly explained. FIG. 1 shows a V/f control inverter device, which supplies an AC output with a constant value of output voltage/output frequency of an inverter 6 to an electric motor 7.

Next, the operation of the present invention will be explained with reference to FIGS. 2 and 3. The DC input current of the PWM inverter 6 is
A ripple current associated with the M operation is included, which flows into a smoothing capacitor (usually an electrolytic capacitor), increasing its temperature. Therefore, a large capacity smoothing capacitor 2 is provided in the DC circuit depending on the ripple current. However, since the magnitude of this ripple current increases in proportion to the magnitude of the output current of the inverter 6, the smoothing capacitor 2 in the inverter has a large capacitance due to the large capacitance Pw. Therefore, in the present invention, focusing on the fact that the frequency of the ripple current is an integral multiple of fc related to the carrier frequency fc of PWM control, a series resonant circuit that absorbs this ripple current
8 is provided in parallel with the smoothing capacitor 2. The resonant frequency f of the series resonant circuit 18 is the size L of the inductance 4.
It is determined from x and the size C2 of the capacitor 5. FIG. 2 is an equivalent circuit of a DC circuit. In FIG. 2, rs.

r'i and rz are resistances caused by wiring, and Q8 is inductance on the power supply side. 8de is a ripple voltage expressed at the terminal of the smoothing capacitor 2. The current 11 flowing through the smoothing capacitor 2, the current iz flowing through the series resonant circuit 18, the resonance frequency fr, and the resonance sharpness Q are expressed by the following equations. however,
ω=2πfc.

Here, the resonant frequency of the series resonant circuit 18! , and the ripple current frequency fc, the current component due to the fluctuation of the DC voltage flows through the series resonant circuit 18, and the smoothing capacitor 2
It doesn't flow.

However, as current flows through the series resonant circuit 18, the values of the capacitor 5 and the reactor 4 change due to temperature rise, etc., and the resonance frequency f no longer matches the frequency fc of the ripple current. As a result, the pull current flowing into the smoothing capacitor 2 increases.

Therefore, in the ninth test, the series resonant circuit 18 is further operated so that the resonant frequency f and the frequency fc of the pull current always match. Next, this will be explained.

The current iz of the series resonant circuit 18 and the current 11 of the smoothing capacitor 2 have the relationship shown in the following equation and FIG. 3 as (1), (2)
It is obtained from Eq.

Figure 3 shows that the resonance sharpness Q of the series resonant circuit 18 is 100 and 6.
For the case 0, liz/izl for fc/f,
The size of is calculated. From Figure 3, the resonance frequency! deviates from the fluctuation frequency fC of the DC voltage, the current flowing through the smoothing capacitor 2 increases. Therefore, in the present invention, the current of the smoothing capacitor 2 is detected by the current detector 3, and only the ripple current component is detected via the filter circuit 8, and the frequency value at which the magnitude thereof is minimized is determined by the relationship shown in FIG. The tracking control circuit 9 calculates the carrier frequency of the PWM inverter 6 based on the resonant frequency f.
control. If the magnitude of the ripple current is greater than or equal to a predetermined value, the tracking control circuit 9 determines a frequency value that minimizes the magnitude of the ripple current using the following procedure. Increase the current carrier frequency f by Δf>O, check the polarity of the change in ripple current magnitude ΔA, and if ΔA>O, lower the carrier frequency f, and conversely, if ΔA×O, increase the carrier frequency f. I'm going to raise it. As a result, when the magnitude A of the ripple current becomes less than or equal to a predetermined value, the frequency value is held.

As a result, the ripple current accompanying PWM operation can be effectively absorbed by the series resonant circuit 18, and the capacitance of the smoothing capacitor 2 can be reduced.

FIG. 4 shows another embodiment in which the present invention is applied to a PWM converter. Components that are the same as those in the first embodiment are given the same numbers, and therefore their description will be omitted. In Figure 4, PWM
Converter 16 converts AC voltage applied from AC power supply 17 into DC voltage. The converter 16 includes self-extinguishing elements GUP and GVP.

...Feedback diodes DUP, DVP, ...DWN connected in antiparallel to GWN and each self-extinguishing element
It consists of As the self-extinguishing element, a switching element such as a gate turn-off thyristor or a transistor is used. The control configuration of the converter is such that Vde'' from a DC voltage command 19 and a detection signal from a terminal voltage detector 21 of a smoothing capacitor 2 are added to an adder 20, and the output of the adder 20 is added to a voltage regulator 22. The output signal of voltage regulator 22 and the detection signal of voltage detector 24 of AC power supply 17 are applied to power factor regulator 23, and converter 16
The instantaneous value command pattern signal of the input current is calculated and added to the adder 25. The adder 25 calculates the deviation between the detection signal of the current detector 26 of the input current of the converter and the output signal of the power factor regulator 23, and adds the deviation to the current regulator 27.

Current regulator 27 calculates output voltage commands Vu*, Vv*, and V- for each phase of converter 16, and applies them to comparators 12U, 12V, and 12W, respectively.

Next, the operation will be briefly explained. Control of the converter 16 is as follows:
A voltage regulator 22 for controlling the DC output voltage, a power factor regulator 23 for outputting an instantaneous input current value command for the converter 16 to achieve a predetermined power factor based on the AC power supply voltage, and an instantaneous input current value command for the converter 16. current regulator 27 and comparator 12U-12 to control the converter input current to match
This is performed by a PWM control circuit composed of W or the like.

The PWM control is performed at a carrier frequency that matches the frequency value calculated by the tracking control circuit 9 so that the amplitude of the ripple current flowing through the smoothing capacitor 2 of the output voltage of the converter 16 is minimized. As a result, P of converter 16
The ripple component included in the DC current accompanying the WM operation is absorbed by the series resonant circuit 18 provided in parallel with the smoothing capacitor 2, and the flow of ripple current into the smoothing capacitor 2 can be suppressed, so the capacitance of the smoothing capacitor 2 can be reduced. can be reduced.

FIG. 5 shows another embodiment in which the present invention is applied to a PMW converter. Components that are the same as those in the second embodiment shown in FIG. 4 are given the same numbers, and therefore their explanation will be omitted. The difference from the second embodiment is that the current detector 3 is provided in the series resonant circuit 18. As shown in equation (2), the series resonant circuit 18
The current has a resonant frequency f, and a direct current pull frequency fc
is maximum when they match. This relationship is exactly opposite to the characteristic shown in FIG. Therefore, in this embodiment, the tracking control circuit 9 detects the current of the series resonant circuit 18 and determines the frequency value so that the ripple component is maximized.
Control carrier frequency. The tracking control circuit 9 is
The frequency value is determined by the following procedure so that the magnitude A of the ripple current becomes the maximum value. The current carrier frequency J is Δf>
The polarity of the change ΔA in the magnitude of the ripple current is checked, and if ΔA>O, the carrier wave frequency f is increased, and conversely, if ΔA<O, the carrier wave frequency J is decreased.

As a result, the frequency value is held when the change ΔA of the ripple current falls within a range of width equal to or less than a predetermined value.

This embodiment also provides the same effects as the second embodiment.

Furthermore, the present invention can also be implemented with the same configuration as the second embodiment by detecting the magnitude of the pull component from the terminal voltage of the smoothing capacitor 2 based on the same idea.

FIG. 6 shows another embodiment in which the present invention is applied to a PWM converter. Components that are the same as those in the second embodiment shown in FIG. 4 are given the same numbers, and therefore their explanation will be omitted. The difference from the second embodiment is that the series resonant circuit 18 is connected to the PWM converter 1.
6, and further a reactor 28 is provided between the series resonant circuit 18 and the smoothing capacitor 2.

The reactor 28 acts to prevent ripple current components associated with the PWM operation of the PWM converter 16 from flowing into the smoothing capacitor 2 . As a result, the smoothing capacitor ripple current can be further effectively reduced.

Further, based on the same idea, a resistor element can be used instead of the reactor 28, and even if a reactor or a resistor is provided in series with the smoothing capacitor 2, the same effect can be obtained.

FIG. 7 shows another embodiment of the invention. 3 shown in Figure 5.
Components that are the same as those in the embodiment are given the same numbers, and therefore their description will be omitted. The difference from the third embodiment is that the PWM converter 1
Series resonant circuit 18A for 6 and PWM converter 6
A series resonant circuit 18B is provided for each of the series resonant circuits 18A and 18B, and currents flowing through the respective series resonant circuits 18A and 18B are detected by current detectors 3A and 3B.
Detected with.

The point is that the carrier wave frequencies of the PWM converter 16 and the PWM inverter 6 are controlled so that the magnitude thereof is maximized.

This embodiment also provides the same effects as the first and second embodiments.

The embodiments in which the present invention is applied to a PWM inverter and a PWM converter have been described above, but the present invention can also be applied to power converters that perform other PWM operations, and is not limited to the control configuration of power converters. It can also be implemented with analog and digital control.

〔Effect of the invention〕

In FIG. 8, conventionally, in order to keep the ripple current flowing through the smoothing capacitor below the allowable value, it was necessary to make the ripple current larger than point P of curve A, but in the embodiment of the present invention, as shown in curve B, the smoothing capacitor Since the ripple current flowing into the capacitor can be reduced, its capacitance can be reduced. Therefore,
According to the present invention, it is possible to reduce the ripple current flowing into the smoothing capacitor of a PWM power conversion device and reduce the capacitance of the smoothing capacitor, so the device can be downsized.
Furthermore, the energy accumulated in the smoothing capacitor is reduced, making it easier to protect the power converter in the event of a failure.

[Brief explanation of the drawing]

FIG. 1 is a control configuration diagram showing an embodiment of the present invention. Fig. 2 is an equivalent circuit diagram for evaluating the characteristics of the series resonant circuit used in the present invention, Fig. 3 is a characteristic diagram explaining the operating principle of the present invention, and Fig. 4 shows a second embodiment of the present invention. Control configuration diagram, FIG. 5 is a control configuration diagram showing a third embodiment of the present invention, FIG. 6 is a control configuration diagram showing a fourth embodiment of the present invention, and FIG. 7 is a control configuration diagram showing a fifth embodiment of the present invention. The control configuration diagram shown in FIG. 8 is a characteristic diagram illustrating the effect on the capacitance of the smoothing capacitor according to the present invention. 2... Smoothing capacitor, 3... Current detector, 6...
・PWM inverter, 9...tracking control circuit,
10... Oscillator, 16... PMW converter, 18
... Series iron rule 1 Figure 2 - Figure 3 + c/ f, CP, u, J Figure 6 Figure 8 - Flat A ↑ Kon i ton - Lease pull tc

Claims (1)

[Scope of Claims] 1. A power conversion device that performs PWM control, which includes a series resonant circuit in parallel with a smoothing capacitor, and generates the series resonance at the frequency of a ripple component included in the DC current of the power conversion device accompanying PWM control. A PWM power conversion device characterized in that the resonant frequency of a circuit is matched within a predetermined range. 2. In a power conversion device that performs PWM control, a series resonant circuit is provided in parallel with a smoothing capacitor, and the resonant frequency of the series resonant circuit is set to a frequency of a ripple component included in a direct current of the power conversion device accompanying PWM control. A PWM power conversion device characterized in that the carrier wave frequency of the PWM control is varied so as to match within a range. 3. A power conversion device that performs PWM control, including a series resonant circuit in parallel with a smoothing capacitor, and means for varying the carrier frequency of the PWM control, so that the carrier frequency matches the resonant frequency of the series resonant circuit. 1. A method for controlling a PWM conversion device, characterized in that the control method is performed as follows. 4. A power conversion device that performs PWM control, comprising a smoothing capacitor of a DC circuit, a series resonant circuit, a means for varying the carrier frequency of the PWM control, and a means for detecting a current flowing through the smoothing capacitor, and a means for detecting a current flowing through the smoothing capacitor. A method for controlling a PWM power conversion device, characterized in that the carrier frequency of the PWM control is controlled based on the PWM control. 5. A power conversion device that performs PWM control, comprising a smoothing capacitor of a DC circuit, a series resonant circuit, a means for varying the carrier frequency of the PWM control, and a means for detecting a current flowing through the series resonant circuit, and a means for detecting a current flowing through the series resonant circuit, and a means for detecting a current flowing through the series resonant circuit. A method for controlling a PWM power conversion device, characterized in that the carrier frequency of the PWM control is controlled based on the following. 6. The PWM power conversion device according to claim 1 or 2, further comprising a plurality of series resonant circuits connected in parallel with the smoothing capacitor, and each series resonant circuit has a different resonance frequency. 7. The PWM power conversion device according to claim 1 or 2, characterized in that a reactor or a resistance element is connected in series to the smoothing capacitor. 8. The PWM power conversion device according to claim 1 or 2, wherein the series resonant circuit is connected to a side closer to the power conversion device than a smoothing capacitor of the DC circuit. 9. The PWM power converter according to claim 8, characterized in that a reactor or a resistance element is connected between the DC circuit connection point of the smoothing capacitor and the same connection point of the series resonant circuit. 10. Claim 1 or Claim 2, wherein the series resonant circuit is a series circuit of a capacitor and a reactor.
The described PWM power conversion device.