JPH11215849A - Pulse width modulated power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PWM(pulse width modulated) power converter operable continuously when power supply or a load varies, and operable with a sufficiently higher efficiency as well by reducing losses to be generated by switching elements. SOLUTION: A control command signal CTR outputted from a load condition detecting circuit 28 is supplied to a logic circuit 24, and supply of firing commands 12a-12f to switching elements 2a-2f is prevented, when the magnitude of a DC current between a converter section 2 and an inverter section 4 is less than a specified value. Here, the switching elements 2a-2f are PWM- controlled, only when it is the specified value or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting AC power into DC power by pulse width modulation of a switching element, and more particularly to a power converter suitable as a forward converter in an inverter device.

[0002]

2. Description of the Related Art A typical example of a converter for converting AC power into DC power is a known diode bridge circuit. However, this diode bridge circuit has a problem that the power supply current includes many harmonics.
Since there is no reverse conversion function, there is a problem that power regeneration cannot be performed.

On the other hand, as a converter circuit which can cope with the problem of the diode bridge circuit, for example, a PWM circuit
There is a (pulse width modulation) power converter. However, this PW
The M power conversion device requires a control device that is not required in the diode bridge circuit, and also has a problem in that a switching loss occurs in the diode bridge circuit due to a switching element that does not exist in principle.

Therefore, as one method for reducing the problems of such a PWM power converter, a simple control method in which instantaneous current value control is omitted is disclosed in, for example, the following document. 1990, IEEJ Transactions on Journal D, 110, 7
No., “Power factor control system, three-phase voltage type pulse width modulation control power converter”

[0005] The prior art disclosed in this document will be described below. This prior art relates to an inverter device for converting DC power converted by a converter device into AC power of a variable frequency. 1 is a three-phase AC power supply, 2 is a converter unit for converting three-phase AC to DC (mainly a power conversion unit used for forward conversion), 3 is a capacitor for smoothing a DC voltage, Reference numeral 4 denotes an inverter unit (mainly a power conversion unit used for forward conversion).

First, a converter section 2 is for power conversion between an AC power supply and a DC section, and is a self-extinguishing type switching element 2a to 2f connected in Grenz and a diode connected in anti-parallel to each of these switching elements. 2g to 2l (L)
It is composed of Next, the inverter unit 4 is for power conversion between the DC unit and the AC load, and is also a self-extinguishing type switching element 4a to 4f and diodes 4g to 4l connected in anti-parallel to each switching element. It is composed of The output of the inverter 4 on the AC side is connected to an induction motor 5.

[0007] Next, reference numeral 6 denotes a reactor, which functions to suppress a PWM frequency component in harmonics included in the AC current, and 7 denotes an AC voltage / current detector, which includes a current transformer 7a and an instrument transformer. The detector 7b functions to detect an AC voltage and an AC current, respectively, 8 is a DC voltage detector, 9 is a power factor detector, and based on the AC voltage and the AC current detected by the AC voltage / current detector 7, It functions to detect the power factor.

Reference numeral 10 denotes a PLL control circuit which outputs a phase command α for keeping the power factor constant. Reference numeral 11 denotes a DC voltage control circuit which converts the DC voltage detected by the DC voltage detector 8 to a set value. A sine wave PWM control signal generator 12 outputs a modulation degree command M for adjustment, and is a firing (ON) / extinguishing (OFF) command 12 for the switching elements 2a to 2f.
a is a sine wave PWM control signal generator on the inverter side, which outputs switching elements 4a to 4f.
It outputs the firing (ON) / extinguishing (OFF) commands 13a to 13f of f.

FIG. 10 shows a sine wave PWM control signal generator 1.
2 is a diagram for explaining the operation of FIG. 2, in which a modulated wave having an amplitude modulation rate M is synthesized at a phase advanced by α from the AC voltage signal ER,
Switching element 2 according to magnitude of triangular waveform carrier
The firing / extinguishing commands 12a and 12d are output to a and 2d.

FIG. 11 shows an AC power supply voltage ER, a current IR,
A one-phase vector diagram showing the relationship between the AC reactor voltage drop EX and the converter voltage EC. If the modulation factor M is equal to or greater than the critical modulation factor MC determined by the load state, the power factor is always adjusted by adjusting the phase command α. It is said that control to set to 1 is possible.

When the load fluctuation on the inverter side is small, the modulation factor M may be fixed to a value close to 1, and in this case, the DC voltage control circuit 11 for adjusting the modulation factor M is not necessarily required. Is not required.

Therefore, according to the converter unit 2 of the inverter device shown in FIG. 9, the higher harmonic current can be suppressed as compared with the diode bridge circuit, and the AC current control required in the ordinary PWM power converter is omitted. can do.

[0013]

In the above prior art, it cannot be said that sufficient consideration has been given to maintaining the stability of operation and improving the efficiency. There is a problem in continuity of operation and reduction of loss in the switching element. According to the above prior art, higher harmonic currents can be suppressed than in the diode bridge circuit, and the AC current control required in the ordinary PWM power converter can be omitted.

However, when it is necessary to continue the operation even when the AC power supply voltage drops or becomes unbalanced, the inductance value of the AC reactor 6 is increased to suppress the overcurrent, or the converter 2 is constructed. There is a problem that it is necessary to increase the capacity of the elements and components that are used so as to sufficiently withstand overcurrent.

Further, in the above-mentioned prior art, the DC voltage control circuit can be omitted. In this case, even if the load fluctuation on the inverter side is small normally, the DC voltage control circuit is transiently connected directly to, for example, an AC motor having an inverter load. For example, when the load torque of the used machine suddenly increases, there is a problem that the DC voltage drop becomes large and the operation cannot be continued.

An object of the present invention is to maintain continuous operation in the event of power supply fluctuations and load fluctuations without controlling the AC current and DC voltage, and to sufficiently obtain high efficiency by reducing the loss due to switching elements. PWM that can be used
An object of the present invention is to provide a power converter.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to provide a power conversion unit by a Grenz connection of an arm composed of a self-extinguishing type switching element and a diode element which are connected in anti-parallel with each other. In a PWM power conversion device configured to perform power conversion between DC loads, means for switching an operation mode of the power conversion unit to one of a diode bridge rectification mode and a PWM power conversion mode is provided. This is achieved by selecting the operation mode of the power conversion unit according to the following. At this time, the state of the load may be determined by the value of the DC current,
The determination may be made based on the value of the DC voltage.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a PWM power converter according to the present invention will be described in detail with reference to the illustrated embodiments. First, FIG. 1 shows an embodiment of the present invention, and the same reference numerals are given to the same elements as those in the prior art described with reference to FIG. 9, and therefore, detailed description thereof will be omitted.

In FIG. 1, first, 16 is a voltage-current transformer, which functions to detect an AC waveform signal, and then, 17 is a reactive power detector, which is based on an AC waveform signal inputted from the voltage-current transformer 16. It functions to detect the reactive power and generate the detected value Qm. A reactive power control circuit 18 outputs a phase correction command α.

FIG. 2 shows an embodiment of the reactive power control circuit 18 in which the difference between the command value Qref and the reactive power detection value Qm is expressed by:
It is configured to be input to a proportional integration circuit including an amplifier 181 and an integrator 182 with upper and lower limit output limiters, and to output a phase correction command α via a limiter circuit 183.
The phase correction command α is added to adders 19a to 19c.
And the phase θ of each phase is corrected.

Therefore, in this embodiment, control for converging the operating power factor of the inverter unit 2 to the command value Qref always works.
Should be set to 0. Note that, for this reason, Qref =
Normally, it is set to 0 and operated. Next, reference numeral 20 denotes a voltage phase detector using a digital arithmetic unit, which functions to output the voltage phases θ _R , θ _S , and θ _T of each phase of the AC power supply.
As a specific calculation method at this time, a method using a moving Fourier transform is known.
According to Japanese Patent Publication No. 31682 and Japanese Patent Application Laid-Open No. 1-283015, a voltage phase calculation method further considering a malfunction inside the calculation device is disclosed, and these may be used. The phase detection signals representing the voltage phases θ _R , θ _S , and θ _T of the respective phases are supplied to the reactive power control circuit 1 by the adders 19a to 19c.
8 is corrected by the correction value α output from

Next, reference numerals 21a to 21c denote function generators for calculating the duty ratio. For example, an R-phase function generator 21a is used as an example.
FIG. 3 shows an example of those characteristics. This figure 3
In the example, the function characteristic is approximated by a polygonal line passing through the points A and B. As a result, at θ = 30 °, the function characteristic passes through the point C with a conduction ratio of 0.5. Further, at point C, the value is reduced to 0.866, and before and after, it changes linearly to 1; at point D, it is increased to 0.134, and similarly, it changes to 0 linearly before and after. ing.

For the S phase and the T phase, the phase signals input to the function generators 21b and 21c are signals having a positive peak value θ = 0 as in the case of the R phase. May be set the same as the R phase. Next, 22a-22
Reference numeral c denotes a comparator which compares the magnitude of the carrier signal from the carrier generator 23 with the duty ratio command, and generates a firing command to the switching element connected to each RST phase.

Reference numeral 24 denotes an OR circuit, which is a control command signal C
When TR is at level 0, it functions to prevent the outputs of the comparators 22a to 22c from being supplied to the amplifier 25. Then, the outputs of the amplifier 25 become firing commands 26a to 26f, which are supplied to the switching elements 2a to 2f, respectively, and subjected to PWM control.

It should be noted that, in FIG.
The PWM power conversion device excluding the DC current detector 27, the load state detection circuit 28, and the electromagnetic switch 29 is a PWM power conversion device described in the specification of Japanese Patent Application No. 9-162967 filed by the present applicant. Therefore, according to the embodiment of FIG. 1, it is possible to maintain a continuous operation at the time of power supply fluctuation and load fluctuation without controlling the AC current and the DC voltage, and Since the switching frequency of the (circuit) can be reduced, switching loss is reduced, and high efficiency can be maintained.

The DC current detector 28 functions to detect a current between the converter 2 on the power supply side and the inverter 4 on the load side to generate a DC current signal IDC. The load state detection circuit 28 has a function of determining the magnitude of the load according to the DC current signal IDC and outputting a control command signal CTR and a switching command Mg for the electromagnetic switch 29. The electromagnetic switch 29 is provided with an auxiliary contact so that a signal for confirming the switching operation can be obtained.

FIG. 4 shows the current comparison characteristics of the load state detection circuit 28, in which the DC current IDC is equal to the set value ID.
When it becomes C1 or more, the load detection signal IDOV becomes level 1. Here, in this embodiment, the current comparison characteristic is given a history characteristic, and as shown in FIG.
Unless C becomes smaller than the set value IDC2, the load detection signal IDOV does not return to level 0.

FIG. 5 shows an example of the load state detection circuit 28 in the case of being constituted by a relay protection interlocking circuit.
The load detection signal IDOV described above is represented as a contact point. At this time, the level 1 of the load detection signal IDOV corresponds to the contact ID.
OV is shown in a closed state, at this time relay C30
Is excited, and the contact C30 (normally open contact) is closed.

First, the relay R1 is controlled by a start command STR and a stop command STP by a manual switch, and the electromagnetic switch 29 (FIG. 1) is controlled by its two contacts R1.
The opening / closing command Mg and the timer T1 are controlled.

As a result, at the time of starting, the time from when the electromagnetic switch 29 is turned on by the relay R1 until the smoothing capacitor 3 is charged by the output of the diode circuit of the converter unit 2 is determined by the delay time of the timer T1. Secured
Thereafter, the closing operation of the timer contact T1 causes the contact C30.
Is ready, the control ready signal RD
Y becomes level 1 and the switching operation of the converter unit 2 is enabled.

When the control preparation completion signal RDY goes to level 1, the control command signal CTR goes to level 1 on condition that the contact Z86 is closed, and as a result, the OR circuit 24 opens to fire. The blocking of the command is released, and the firing commands 26a to 26f are supplied to the switching elements 2a to 2f of the converter unit 2, so that the switching operation starts and the operation state as a normal PWM converter is started.

Here, the contact Z86 is a normally closed contact that is controlled to open and close by another emergency stop protection device (not shown), for example, an overcurrent protection relay. Opening stops the switching operation and provides a protection function.

Next, the operation of this embodiment will be described. Now, the converter unit 2 under a certain load
Assuming that the load decreases during the operation, the level of the DC current signal IDC output from the DC current detector 27 also decreases due to the decrease in the load current. Then, the level of the DC current signal IDC is equal to the set value IDC of FIG.
If it becomes 2 or less, the load detection signal IDOV, which has been at level 1 until then, changes to level 0.

As a result, the excitation of the relay C30 is cut off,
Since the contact C30 is opened, the control command signal CTR becomes level 0, the OR circuit 24 is closed, and the firing command is blocked. Therefore, the operation state of the converter unit 2 at this time is only the operation in the diode bridge rectification mode, that is, the operation by the rectification action of the diode bridge circuit including the diodes 2g to 2l. .

Next, in this state, if the load increases this time, the load current decreases, and the DC current signal ID output from the DC current detector 27 is output.
The level of C rises. And this DC current signal ID
If the level of C becomes equal to or more than the set value IDC1 in FIG.
Changes to level 1.

As a result, the relay C30 is excited again,
Since the contact C30 is closed, the control command signal CTR goes to level 1, the OR circuit 24 is opened to stop the ignition command, and the switching element 2a of the converter unit 2 is again turned on.
To 2f are supplied with firing commands 26a to 26f, and a switching operation is started.

Then, the operation of the converter unit 2 at this time is a PWM power conversion operation mode, that is, an operation as a normal PWM converter by a PWM switching operation of the switching elements 2a to 2f, whereby a load current is supplied. To a state where

Therefore, according to the embodiment of FIG. 1, the operation mode of the converter section 2 is switched in accordance with the size of the load, and operates at the time of low load by operating in the diode bridge rectification mode by the diodes 2g to 2l. Sometimes PW due to the switching operation of the switching elements 2a to 2f
It will operate in the M power conversion mode.

Here, in the diode bridge rectification mode, since there is no switching loss, high efficiency can be obtained even with a light load. On the other hand, in the PWM converter operation mode, harmonic suppression is obtained, which is advantageous when the load becomes large. Therefore, according to the above embodiment, both high efficiency when the load is light and suppression of harmonics when the load becomes large can be obtained, and the PW having excellent performance can be obtained.
An M converter device can be easily provided.

Next, FIG. 6 shows another embodiment of the present invention, in which 30 is a DC voltage detector, 31 is a regenerative state detecting circuit, and other configurations are the same as those of the embodiment of FIG. Therefore, the embodiment of FIG. 6 is different from the embodiment of FIG. 1 in that the DC voltage detector 3 is used instead of the DC current detector 27.
0 is provided, and a regeneration state detection circuit 31 is provided instead of the load state detection circuit 28 in the same manner.

First, the DC voltage detector 30 is connected to the capacitor 3
, Ie, the voltage of the DC portion, and generates a voltage signal VDC. Next, the regenerative state detection circuit 31 determines whether or not the load is in a regenerative state according to the voltage signal VDC, and outputs a control command signal CTR and an open / close command Mg for the electromagnetic switch 29.

FIG. 7 shows a voltage comparison characteristic of the regenerative state detection circuit 31. When the value of the DC voltage signal VDC becomes equal to or more than the set value VDC1, the regenerative detection signal VDOV
Is set to level 1. FIG. 8 shows a regenerative state detecting circuit 31 in the case of being constituted by a relay protection interlocking circuit.
The regenerative detection signal VDOV is indicated by a contact.

Therefore, the regenerative state detecting circuit 31 shown in FIG. 8 corresponds to a circuit provided with a relay V30 instead of the relay C30 in the load state detecting circuit 28 in FIG.
Other configurations are the same. As a result, in the embodiment of FIG. 6, the operation mode of converter unit 2 is switched in accordance with the terminal voltage of capacitor 3, and the value of DC voltage signal VDC is low when the voltage is low. 7 is smaller than the set value VDC1 shown in FIG. 7 and operates in the diode bridge rectification mode by the diodes 2g to 21. At a high voltage, that is, when the value of the DC voltage signal VDC is equal to or more than the set value VDC1 shown in FIG. The operation is performed in the PWM power conversion mode by the switching operation of the switching elements 2a to 2f.

Here, with respect to the terminal voltage of the capacitor 3, this voltage is low when the load is taking in power, and is high when the load is generating power, that is, in the regenerative state.

Therefore, according to the embodiment of FIG. 6, the operation mode of converter unit 2 is switched according to the operation state of the load, and when power is running, that is, when the load is consuming power, diodes 2g-2l are connected. , And operates in the PWM power conversion mode by the switching operation of the switching elements 2a to 2f during regeneration, that is, when the load is generating power.

For the regenerative operation, the converter section 2 needs to perform the reverse conversion operation, and therefore cannot be performed in the diode bridge rectification mode. However, according to the embodiment of FIG. 6, when the load enters the regenerative state, the operation mode of the converter unit 2 automatically shifts to the PWM power conversion mode,
Therefore, according to this embodiment, it is possible to always accurately cope with the state of the load, including the regenerative operation, and to maintain a stable operation state.

[0047]

According to the present invention, continuous operation can be maintained even when the power supply or the load fluctuates without controlling the AC current and the DC voltage, so that the configuration can be simplified and the pulse width with high reliability can be maintained. A power converter of a modulation method can be easily provided. Further, according to the present invention, since the switching frequency of the switching element can be reduced, the switching loss is reduced, and a high-efficiency pulse width modulation power converter can be easily provided.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a pulse width modulation power converter according to the present invention.
FIG. 2 is a block circuit diagram showing the embodiment.

FIG. 2 is a block diagram illustrating an example of a reactive power control circuit according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating an example of a setting characteristic of a function generator according to the first embodiment.

FIG. 4 is a characteristic diagram illustrating an example of a current comparison characteristic of the load state detection circuit according to the first embodiment.

FIG. 5 is a circuit diagram illustrating an example of a load state detection circuit according to the first embodiment.

FIG. 6 shows a second embodiment of the pulse width modulation power converter according to the present invention.
FIG. 2 is a block circuit diagram showing the embodiment.

FIG. 7 is a characteristic diagram illustrating an example of a voltage comparison characteristic of the regenerative state detection circuit according to the second embodiment.

FIG. 8 is a circuit diagram illustrating an example of a regenerative state detection circuit according to the second embodiment. FIG. 3 is a block diagram illustrating a specific example of a reactive power control circuit.

FIG. 9 is a block circuit diagram showing a conventional example of a pulse width modulation power converter.

FIG. 10 shows a sine wave P in the pulse width modulation power converter.
FIG. 4 is a waveform chart for explaining the operation of the WM control signal generator.

FIG. 11 is a vector diagram for explaining the operation of the pulse width modulation power converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 3-phase alternating current power supply 2 Converter part 3 Smoothing capacitor 4 Inverter part 5 Induction motor 6 Reactor 16 Voltage-current transformer 17 Reactive power detector 18 Reactive power control circuit 20 Voltage phase detector 21a-21c Function generator 22a-22c Comparator 23 Carrier generator 27 DC current detector 28 Load state detection circuit 29 Magnetic contactor 30 DC voltage detector 31 Regeneration state detection circuit

Claims (3)

[Claims] 1. An electric power converter comprising a self-arc-extinguishing switching element and a diode element, which are connected in antiparallel with each other, by a Grenz connection of an arm, and
In a pulse width modulation power conversion device configured to perform power conversion between an AC power supply and a DC load, the operation mode of the power conversion unit is switched to one of a diode bridge rectification mode and a pulse width modulation power conversion mode. Means, wherein an operation mode of the power conversion unit is selected according to a state of a load. 2. An electric power converter comprising a self-arc-extinguishing type switching element and a diode element, which are connected in antiparallel with each other, by a Grenz connection of an arm.
In a pulse width modulation power conversion device configured to perform power conversion between an AC power supply and a DC load, the operation mode of the power conversion unit is switched to one of a diode bridge rectification mode and a pulse width modulation power conversion mode. Control means, and voltage detection means for detecting a voltage on the DC side of the power conversion unit, wherein an operation mode of the power conversion unit is selected according to a detection result of the voltage detection means. A pulse width modulation power converter. 3. An electric power converter comprising a self-arc-extinguishing type switching element and a diode element, which are connected in antiparallel with each other, by a Grenz connection of an arm.
In a pulse width modulation power conversion device configured to perform power conversion between an AC power supply and a DC load, the operation mode of the power conversion unit is switched to one of a diode bridge rectification mode and a pulse width modulation power conversion mode. Control means, and current detection means for detecting a current on the DC side of the power conversion unit, wherein an operation mode of the power conversion unit is selected according to a detection result of the current detection means. A pulse width modulation power converter.