JPH08182330A - Power converter - Google Patents

Abstract

PURPOSE: To enable a power converter to have a lagged-phase current which offsets a leading current generated from a capacitor by adding a sinusoidal waveform which is lagged in phase by a specific angle and the output of a multiplier to a reference sinusoidal waveform and using the sum as the input current commanding value of a capacitor output section. CONSTITUTION: The second output waveform of a reference sinusoidal waveform generating section 76 given to a multiplier 77c is lagged in phase from a reference sinusoidal waveform by 90 deg.C. The phase of the second output waveform is lagged from that of the current 1c of a capacitor 5 by 180 deg.C. The sum of a waveform ILAG* obtained by multiplying the second output waveform by an appropriate coefficient and another waveform Id* is found by means of an adder 77b and the sum is used as the new input current command 1* of a capacitor output section 4. The input current IL4 of the section 4 following the command 1* has the same waveform as the command 1* has and this current IL4 is composed of the leading current flowing to the capacitor 5 and the opposite-phase current ILAG. A lagged-phase current which offsets the leading current can be generated by making the gain Ic of the multiplier 77c a little larger.

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 an AC voltage into a DC voltage or a DC voltage into an AC voltage and controlling an AC current into a sine wave having a power factor of 1 with respect to the AC voltage. It relates to the device.

[0002]

2. Description of the Related Art FIG. 4 shows the configuration and control method of a conventional sine wave converter as a power converter. In the figure, 1 is an AC power supply, 2 is a converter device, 3 is an inverter circuit for driving a motor or an uninterruptible power supply device, and a DC load circuit such as a storage battery. The converter device 2 includes a converter output unit 4 including a semiconductor switching element, a capacitor 5, a reactor 6, a control circuit 7, and a current detector 8. Here, the capacitor 5 and the reactor 6 form a filter circuit. The control circuit 7 includes a DC voltage control unit 71, a reference sine wave generation unit 72, a current command unit 73, a current control unit 74, and a gate amplification unit 75.

The DC voltage control unit 71 takes in the DC voltage of the converter device 2 and uses the adder 71a to set the DC voltage setting signal.
The deviation from 71b is obtained, and the voltage control signal is output via the control amplifier 71c. The reference sine wave generator 72 outputs a reference sine waveform of constant amplitude whose phase matches the voltage of the input terminal of the converter device 2. The current command unit 73 is a multiplier 73a
The current required for the phase to match the input terminal voltage of the converter device 2 and the amplitude by multiplying the voltage control signal from the DC voltage control unit 71 by the reference sine waveform from the reference sine wave generation unit 72. A sinusoidal waveform proportional to
This sine waveform is the input current command Id of the converter output unit 4.
* The current controller 74 includes an adder 74a and a control amplifier 74b.
Consists of. Here, the deviation between the input current command Id * waveform and the current waveform fetched from the current detector 8 is obtained by the adder 74a and sent to the converter output unit 4 via the control amplifier 74b and the gate amplifying unit 75, whereby the converter output The input current of the unit 4 can be controlled to be the same as the input current command Id * waveform.

FIG. 5 shows the relationship between the converter device 2 and the AC power supply in FIG. 4 by an equivalent circuit. 1a is an equivalent circuit of the AC power supply 1, 4a is an equivalent circuit of the converter unit 4, and 9 is an AC power supply. 1 is a wiring impedance between the converter 1 and the converter device 2 or a power source impedance. In Figure 6,
The vector diagram of the voltage / current of each part obtained from the equivalent circuit of FIG. 5 is shown. The symbols in FIG. 6 are the symbols shown with the arrows in FIG. In both FIGS. 5 and 6, the solid line arrow indicates current, and the alternate long and short dash line arrow indicates voltage. When the voltage Vc of the capacitor 5, which is the input terminal voltage of the converter device 2, is used as a reference, a current Ic having a phase leading by 90 degrees from Vc flows through the capacitor 5.

In FIG. 4, the input current command Id * of the converter output section 4, which is the output of the multiplier 73a, has exactly the same phase as the voltage Vc of the capacitor 5 as described above, and the input current of the converter output section 4 is the same. And reactor 6
The current IL4 of is also in phase with the voltage Vc of the capacitor 5.
The current I of the capacitor 5 is applied to the power source 1a and the reactor 9.
current IL2 which is the sum of c and the current IL4 to the converter output unit 4
Flows. This current IL2 is more than the voltage Vc of the capacitor 5.
Due to the component of the current Ic which leads the phase by 90 degrees, the capacitor 5
The voltage becomes a phase leading current from the voltage Vc. Since the phase difference between the voltage Vc of the capacitor 5 and the electromotive voltage E of the power source 1a is small, the current IL2 flowing in the reactor 9 such as the power source 1a and the wiring is as follows when viewed from the electromotive voltage E of the power source 1a as shown in FIG. The phase is advanced.

[0006]

When the power source has a sufficient margin with respect to the capacity of the converter device, the phase of the current flowing through the power source does not matter, but the power source is a generator and the capacity is not sufficient. In this case, when a current is passed through the generator, the generator causes self-excitation and raises the output voltage.
Outputs excessive voltage. The voltage can reach 1.5 times the normal voltage, which may damage the device due to overvoltage. Further, if the power factor of the power supply current is advanced or delayed and the power factor is reduced to less than 1, and reactive power is generated, a large power supply facility capacity is required, which is uneconomical.

[0007]

In order to avoid such a problem, the present invention provides a reference sine wave generator for outputting a reference sine wave whose phase matches the voltage of an AC power supply, an output DC voltage and a setting signal. A DC voltage control unit that amplifies the deviation between, a multiplier that receives the output of the reference sine wave generator and the DC voltage control unit, and a power converter that uses the output of the multiplier as the input current command value of the converter output unit, A sine waveform delayed by 90 degrees and a multiplier output are added to the reference sine waveform, and the output is used as the input current command value of the converter output section.

Alternatively, the product of the sine waveform delayed by 90 degrees in phase from the reference sine waveform and the AC power supply voltage value is added to the multiplier output, and the output is used as the input current command value of the converter output section. Similarly, the problem can be resolved.

[0009]

By doing so, the input current command Id * of the converter output section always has a delay current component that cancels the advance current Ic due to the capacitor, and it is possible to prevent the advance current from flowing to the power source. Moreover, the power factor of the power supply current can be set to 1.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration according to the first embodiment of the present invention. In FIG. 1, 7'is a control circuit, 76 is a reference sine wave generator,
77 is a current command unit, 77a is a multiplier, 77b is an adder, 77c
Indicates a multiplier. The same reference numerals as those in FIG. 4 indicate the same elements. Here, the multiplier 77a is the same as the multiplier 73a of FIG. The difference between the reference sine wave generator 72 and the reference sine wave generator 76 is that the reference sine wave generator 76 outputs a second output, and this output is delayed by 90 degrees in phase from the reference sine wave. It is a point that has a corrugated waveform. In terms of circuitry, this waveform can be easily obtained by delaying the phase of the reference sine wave by a filter circuit or shifting the reading point of the data table representing the sine wave by software processing of a microcomputer. In the case of a three-phase AC power supply, for example, if the waveform delayed by 90 degrees from the R phase, the difference between the S phase voltage or the reference sine wave and the T phase voltage or the reference sine wave is calculated by software. You can ask for it either in the circuit or in the circuit.

The difference between the current command unit 73 and the current command unit 77 is that the current command unit 77 includes an adder 77b and a multiplier 77c in addition to the multiplier. The second output of the reference sine wave generator 76 is input to the multiplier 77c, and the output of the multiplier 77c and the output of the multiplier 77a are added by the adder 77b. By doing so, the waveform whose phase is delayed by 90 degrees from the reference sine waveform is multiplied by the multiplier 77c by a coefficient according to the value of the advance current due to the capacitor 5, and the adder 77b is used to convert the conventional converter output unit 4 The new input current command I * is added to the input current command Id *.

FIG. 2 shows a vector diagram of the voltage and current of each part according to this embodiment. In FIG. 2, the same symbols as those in FIG. 6 denote the same components. In FIG. 2, as in the conventional example, the waveform obtained by multiplying the output of the DC voltage control unit 71 and the reference sine waveform from the reference sine wave generation unit 76 by the multiplier 77a has the phase at the input terminal voltage. It is a sine waveform that matches and is proportional to the amplitude of the current required for DC voltage control, and the vector of this sine waveform is Id *. This sine waveform is purely a current component required for DC voltage control. Also, a multiplier 77c
The second output waveform of the reference sine wave generator 76 given to the above is a waveform whose phase is delayed by 90 degrees from the reference sine waveform, and is a waveform whose phase is 180 degrees opposite to that of the current Ic of the capacitor 5. The adder 77b obtains the sum of the waveforms ILAG * and Id * obtained by multiplying this waveform by an appropriate coefficient by the multiplier 77c, and gives a new input current command I * for the converter output section 4.

The input current IL4 of the converter output unit 4 according to this input current command I * has the same waveform as I *, and this current is a component IR necessary for purely controlling the DC voltage.
And a leading current IC flowing through the capacitor 5 and a current ILAG having an opposite phase. Therefore, ILAG is I
By setting the gain of the multiplier 77c so as to be equal to or slightly larger than c, the input current IL2 of the converter device is made purely only the component necessary for the direct current control, and the input terminal voltage Vc of the device is It is possible to have the same phase or slightly delayed phase. FIG. 2 shows an example in which IL2 is slightly delayed with respect to the input terminal voltage Vc of the device.
At this time, the phase of the power supply current IL2 seen from the power supply and the generator is also delayed, so that the generator does not cause self-excitation and it is possible to prevent generation of an excessive voltage.

FIG. 3 shows a second embodiment of the present invention. FIG.
7 ”is a control circuit, and 79 is a power supply voltage value detector for detecting the magnitude of the power supply voltage. Here, the multiplier 77c of FIG. 1 is replaced with a multiplier 78d, and a reference sine wave generator 76 is provided. 2 is multiplied by the output of the power supply voltage value detector 79. That is, the magnification of the multiplier 77c is made variable so that the magnification is proportional to the power supply voltage value. Further, the multiplier 78a is the same as the multiplier 73a and the multiplier 77a.

In the first embodiment, the delay current command ILAG for canceling the advance current Ic by the capacitor 5 is used.
* Was constant. However, the lead current Ic due to the capacitor 5 changes in proportion to the magnitude of the power supply voltage Vc. Therefore, under the condition of the power supply voltage in which the delay current command ILAG * is constant, the advance current and the delay current I by the capacitor 5 are
The LAGs cancel each other out, and the power supply current IL2 has the same phase as the power supply voltage. However, if the power supply voltage Vc changes and the advance current due to the capacitor 5 increases or decreases, the phase of the power supply current IL2 deviates from the power supply voltage Vc, and the power factor I can't keep 1. In particular, when the power supply voltage Vc rises and the advance current of the capacitor 5 becomes large, the power supply current IL2 advances with respect to the power supply voltage Vc, and the above-mentioned problem occurs. Further, if the delay current command ILAG * is set to a large value so that the power supply current IL2 is a delay current with respect to the power supply voltage Vc even with respect to the maximum power supply voltage, the power supply current IL2 is larger than the power supply voltage Vc at the normal power supply voltage. The delay becomes large, the power supply power factor decreases, and a large power supply capacity is required. In order to eliminate such a problem, in the second embodiment, the delay current command ILAG * is changed in proportion to the magnitude of the power supply voltage, and the delay current I in FIG.
The LAG is always controlled to a value that just cancels the leading current Ic due to the capacitor 5. As a result, the power supply current IL2 can always be in phase with the power supply voltage Vc.

[0016]

As described above, according to the present invention, in addition to the current command in phase with the power supply voltage required for DC voltage control, a delay current component for canceling the advance current of the capacitor is used as an offset. By superimposing the converter current command, it is possible to prevent the power supply current from advancing and becoming in phase, prevent self-excitation of the generator, generate excessive voltage in the generator, and damage the converter device and load device. It is possible to provide a power conversion device that can be prevented from being given and can perform stable operation even in a severe power supply environment. Furthermore, by changing the magnitude of the offset of the lagging current component in proportion to the magnitude of the power supply voltage, the power factor of the power supply can always be kept at 1 even when the power supply voltage changes, and the power supply equipment capacity can be effectively utilized.

[Brief description of drawings]

FIG. 1 is a circuit configuration showing a first embodiment of the present invention.

FIG. 2 is a vector diagram of each part according to the first embodiment.

FIG. 3 is a circuit configuration showing a second embodiment of the present invention.

FIG. 4 is an example of a conventional circuit configuration.

FIG. 5 is an equivalent circuit for one phase.

FIG. 6 is a vector diagram of each unit according to a conventional example.

[Explanation of symbols]

 1 AC power supply 2 Converter device 3 DC load circuit 4 Converter output unit 5 Capacitor 6 Reactor 7 Control circuit 7'Control circuit 7 "Control circuit 8 Current detector 9 Reactor 71 DC voltage control unit 71a Adder 71b DC voltage setting signal 71c Control Amplifier 72 Reference sine wave generator 73 Current command unit 73a Multiplier 74 Current controller 74a Adder 74b Control amplifier 75 Gate amplifier 76 Reference sine wave generator 77 Current command unit 77a Multiplier 77b Adder 77c Multiplier 78 Current command Part 78a Multiplier 78b Adder 78d Multiplier 79 Power supply voltage value detector

Claims (2)

[Claims] 1. A reference sine wave generator that outputs a reference sine wave whose phase matches the voltage of an AC power supply, a DC voltage controller that amplifies the deviation between the output DC voltage and a setting signal, a reference sine wave generator, and a direct current. A multiplier that receives the output of the voltage controller
In a power converter that uses the output of the multiplier as the input current command value of the converter output section, a sine waveform delayed by 90 degrees with respect to the reference sine waveform and the multiplier output are added, and the output is the converter output. An electric power converter configured to use an input current command value of a section. 2. A reference sine wave generator that outputs a reference sine waveform whose phase matches the voltage of the AC power supply, a DC voltage controller that amplifies the deviation between the output DC voltage and the setting signal, a reference sine wave generator and a DC. A multiplier that receives the output of the voltage controller
In a power converter that uses the output of the multiplier as the input current command value of the converter output section, the product of the sine waveform delayed by 90 degrees in phase with the reference sine waveform and the AC power supply voltage value, and the multiplier output Is added and the output thereof is set as the input current command value of the converter output section.