JPS62230358A - Parallel operation circuit for converter - Google Patents

Abstract

PURPOSE:To obtain a stable output at all times by inputting a winding output detecting no output voltage to a chopper type stabilizing circuit through a capacitor-input type rectifier circuit. CONSTITUTION:A switching element Ql is ON-OFF controlled, and outputs Vl, V2 are lde out of the secondary side through a converter transi c Af former Tl. The output Vl is compared with referencc voltage, and the switching transistor Ql is controlled in response to the difference of comparison. An output from a winding N2 is inputted to a capacitor-input type rectifying smoothing circuit corsisting of a diode Dl and a capacitor C3, an output from the rectifying smoothing circuit is inputted to a chopper circuit constituted of a transistor Q2, a commutation diode D2, a choke coil Ll, a capacitor Cl and a control section A2, and the output Vl is led out.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an AC/DC conversion circuit using a PWM converter, and particularly relates to performance improvement when many PWM converters are operated in parallel. It is something.

(Prior art) Rectifier circuits using semiconductor elements such as thyristors are often used as AC/DC converters to convert alternating current to direct current, but harmonics caused by power factor of AC input and distortion of voltage and current waveforms are a problem. In this case, instead of the conventional rectifier circuit that uses a thyristor to perform phase control, a PWM converter may be used to control the power factor to 1 and to make the current waveform closer to a sine wave. It has become.

In order to bring the waveform of the AC input current closer to a sine wave and reduce harmonics, it is necessary to increase the frequency of the sine wave of the PWM converter. PWM
A method has been adopted in which multiple converters are connected in parallel and the phases of the modulated waves of the respective PWM converters are shifted by a predetermined electrical angle.

When parallel operation is performed by shifting the phase of the modulated waves of the PWM converters by a certain electrical angle, the combined input current changes as if it were modulated at a modulation frequency several times the modulation frequency of the individual PWM converters in parallel, Improves waveform control performance.

FIG. 5 shows, as an example of the prior art, a case in which the outputs of two PWM converters CON1 and C0NV2 (7) are connected in parallel to perform dual operation. Power from the AC power supply PS flows through the primary winding N1 of the transformer as a primary current 11, and flows through the two secondary windings N21 and N22 as a secondary current I21.
．． induces I22. These secondary currents flow through reactors Ll, L2 to PWN4 converter C0NVI, C
0NV2.

Each PWM converter C0NV1, C0NV2 has 4 G
While connecting the TO thyristors T1 to T4 in a bridge,
It is constructed by connecting diodes D1 to D4 in antiparallel to each GTO thyristor, and these PWM converters C0
The outputs of NV1 and CONV2 are connected in parallel, smoothed by a parallel capacitor C, and then supplied to the load.

Figure 6 shows the PWM converters C0NV1 and C0N mentioned above.
It shows the temporal relationship between the modulated wave of V2, the input current waveform, and the primary side input current waveform.

In the PWM converter C0NVI, the gate signal of the GTO thyristor is obtained by performing pulse width modulation by comparing the modulated wave shown in FIG. 6(a) with the sine wave signal obtained from the control circuit. The input current I21 of the PWM converter C0NVI subjected to pulse width modulation changes as shown in FIG. 6(b).

Similarly, in PWM converter C0NV2, Fig. 6 (a>
Pulse width modulation is performed by comparing the modulated wave shown in FIG. 6 with a sine wave signal obtained from the control circuit, and the input current I22 changes as shown in FIG. 6(C).

The current of these two PWM converters I21°122
The primary current 11 of the transformer TR that induces
).

In this way, the primary current 11 is shown in FIGS. 6(d) and 6(b),
As is clear from comparing (C), it becomes much smoother. In addition, PWM converters C0NV1 and C0N
The modulated waves of V2 are shifted by 90 degrees in electrical angle, and are in a relationship such that increases and decreases in the input currents of the two PWM converters cancel each other out.

However, in this way, two PWM converters can be
For heavy operation, the two PWM converters are connected to transformer TR
Since the secondary winding N of transformer TR
Due to the influence of the magnetic coupling between 21 and N22, a cross current occurs between the input currents I2+ and 122 of the two PWM converters, which may even increase waveform distortion and harmonics.

In order to minimize the influence between the two secondary windings, it is necessary to arrange the windings of the transformer TR away from each other so that they are not influenced by each other, and it is necessary to have a special design for the transformer TR. It arises.

Another method is to relatively reduce the influence between the windings of the transformer TR by setting the reactors Ll and L2 to sufficiently large values, but this method may cause the equipment to become unnecessarily large. This is not a good idea as it would be complicated. Further, if the modulated waves of the two PWM converters are operated in the same phase, cross current between the two windings can be prevented, but there is a drawback that low harmonic waves cannot be controlled.

(Problems to be solved by the invention) As mentioned above, in the conventional method, in order to reduce the influence between the two windings, it is necessary to make the transformer special, and the structure is also complicated. It has no choice but to be large in appearance. Furthermore, the reactor between the transformer and the PWM converter needs to have a larger value than necessary, and the external size also becomes large.

The present invention has been made in order to eliminate the above-mentioned drawbacks in the background art, and aims to eliminate the influence of mutual interference between the windings of a transformer and prevent the transformer and reactor from increasing in size. .

[Structure of the Invention] (Means for Solving the Problems) The parallel operation circuit of the PWM converter of the present invention includes a transformer having a plurality of secondary windings, and a transformer connected to each of these secondary windings. A PWM converter parallel operation circuit comprising a PWM converter and a reactor connected between the secondary winding of the transformer and the PWM converter, and in which DC outputs of the PWM converter are connected in parallel,
The present invention is characterized in that at least two or more of the plurality of parallel circuits are set as a set, and the reactors of the set of circuits are magnetically coupled so that changes in the current flowing through each reactor cancel each other out.

(Function) As described above, in the circuit of the present invention, a set includes at least two circuits of a plurality of PWM converters whose output sides are connected in parallel, and the reactors of the circuits of the set are used to control the current flowing through each reactor. Since the reactors are magnetically coupled so that the changes in the reactors cancel each other out, the capacitance of each reactor can be reduced.

(Embodiment) FIG. 1 shows a parallel dual operation circuit of a PWM converter according to the present invention. PS is an AC power supply, TR is a transformer, Ll and L2 are reactors, T1 to T4 are GTO zyristors, r) 1 to D4 are diodes, C is a capacitor,
C0NV1 and C0NV2 indicate PWM converters. Also, N1 is the primary winding of the transformer, N2 + and N22 are the secondary windings of the transformer, I1 is the primary side input current, I21, I22
indicates the input current of the PWM converter C0NV1.2.

In the circuit shown in Figure 1, the current I flowing through the reactors Ll and L2 is
BM and I22 are coupled to each other so as to suppress the current. In addition, two PWM converters C0N
V1. As shown in FIG. 2, the modulated waves of C0NV2 have the same frequency, and the temporal relationship of the modulated waves is shifted by 90 degrees in electrical angle.

The operation of the input currents 12+ and I22 of each converter and the reactor LIL2 at this time will be explained with reference to FIG.

Figure 3 is a partially centered view of Figure 1, with V2+
is the voltage of the secondary winding N21 of the transformer TR, 22 is the voltage of the secondary winding N22, and VCl is the pwM converter C0.
Input voltage of NV1, ■o2 is PWM converter C0NV
2 input voltages are shown.

Furthermore, if the self-inductance of Ll is L(Ll>, the self-inductance of L2 is L(L2), and the mutual inductance of LI and L2 is M, then Ll and L2 are coupled so that this mutual inductance M is negative. .

The voltage equation of this circuit is PWM converter C0NV1.
The calculation for each of 2 is as follows.

For C0NVI, L(LI > dI+/dt-MdI2/dt=V2+
-VCI ・・・・・・・・・ ■For C0NV2 L (L2) d I2 /Cjt-Md I 1/
d t= V 22 V (2...
■For formula ■, as explained in Figure 6,
The phase angle of the modulated waves of the two PWM converters is set to 90 degrees with respect to each other.
If control is performed so that the difference between )d
I+/dt and the second term -MdI2/dt are always added.

Therefore, the mutual inductance M always tends to increase the inductance of the entire circuit, and the inductance becomes larger than when the two reactors Ll and L2 are not coupled.

In this way, by providing the necessary inductance for the entire circuit with the mutual inductance M, the reactor L
The self-inductance of L and L2 can be reduced, and the structure can be made small. Also, the fact that the mutual inductance acts negatively means that the currents I21 and ■22 of the two PWM converters are in a relationship that suppresses their respective changes, making it difficult for cross current to flow through the transformer TR, reducing the influence between the windings. can be reduced.

Other Embodiments) FIG. 4 shows a case where four PWM converters are connected in parallel and operated. In this circuit, PWM converter C0
The phases of the modulated waves of NVI and CONV2 are shifted by 90', and the reactors L1 and L2 are coupled so that their mutual inductance is negative. Further, the phases of the modulated waves of the PWM converters C0NV3 and C0NV4 are shifted by 90 degrees, and the reactors L3 and L4 are coupled so that their mutual inductance becomes negative. Further, the phase differences between the modulated waves of the PWM converters C0NV1, C0NV2, C0NV3, and C0NV4 are each set to 45 degrees.

Even when four PWM converters are operated in parallel in this way, it is possible to eliminate the influence between the windings of the transformer, downsize the reactor, and reduce harmonics.

Further, although the above-described embodiments have been described with respect to a multiple parallel operation circuit of a PWM converter in a single-phase circuit, the present invention is not limited thereto, and can be applied to a three-phase circuit in exactly the same manner.

[Effects of the Invention] As described above, according to the present invention, even when multiple PWM converters are operated in parallel, the influence between each PWM converter due to the coupling between the windings of the transformer can be prevented, and the phase of the modulated wave can be maintained. The harmonics of the input current can be reduced by staggered operation, and the reactor can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a parallel operation circuit for a PWM converter according to the present invention, FIG. 2 is a modulation waveform diagram thereof, and FIG.
The figure is a circuit diagram explaining the operation of the parallel operation circuit of a PWM converter according to the present invention, FIG. 4 is a schematic diagram showing another embodiment of the present invention, and FIG. 5 is a circuit diagram of a conventional parallel operation circuit of a PWM converter. , FIG. 6 is a waveform diagram explaining its operation. PS...AC power supply TR...Transformer L1-L4...Reactor T1-T4...GTO thyristor D1-D4...Diode C...Capacitor

Claims (2)

[Claims] (1) A transformer with multiple secondary windings, and these two
A PWM (Pulse Width Modulation) converter connected to each secondary winding, and a reactor connected between the secondary winding of the transformer and the PWM converter, respectively,
A PWM in which the DC outputs of the PWM converters are connected in parallel.
In a parallel operation circuit of a converter, at least two of the plurality of parallel circuits are set as a set, and the reactors of the set of circuits are magnetically coupled so that changes in the current flowing through each reactor cancel each other out. A parallel operation circuit for a PWM converter characterized by the following. (2) At least two or more circuits are set as a set, and the reactors of the set of circuits are magnetically coupled so that changes in the current flowing through each reactor cancel each other out, and at least two sets of the magnetically coupled circuits are 2. A parallel operation circuit for PWM converters according to claim 1, wherein the PWM converter has at least one PWM converter, and is set so that the phase difference of the modulated wave of each PWM converter is shifted by equal intervals in electrical angle.