JPS62247758A - Series operation circuit of dc-dc converter - Google Patents

Abstract

PURPOSE:To eliminate unbalance of voltage distribution, by a method wherein two sets of DC-DC converters are connected in series to a DC power source, aud two sets of output windings are provided in respective output transformers and coupled with each other, and power is supplied to respective loads. CONSTITUTION:ON/OFF operation of DC voltage is performed by GTO thyristors 11-22 and two sets of DC-DC converters are used to take any voltage from output transformers 10, 20, and separate input filter capacitors 17, 27 are installed in parallel at input side of each converter thereby a series operation circuit of the converter is constituted. In this case, the output transformers 10, 20 are provided with two sets of output windings (first windings 10B, 10C and second windings 10C, 20C) mutually insulated. The first windings 10B and 20B are connected in series and DC power is supplied to one load 16, and also the second windings 10C and 20C are connected in series and DC power is supplied to other load 26. Thereby supply power to both loads 16, 26 is balanced and distributed to each converter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a circuit that operates by connecting two sets of DC-DC converters in series with a DC power source.

(Prior art and its problems) DC power is input and the voltage is different from this input, and the DC power is isolated from the input.
Direct current converters (hereinafter referred to as DC/Do converters) have many uses. For example, in electric railways, high-voltage DC power collected from overhead wires or third rails is converted to low-voltage DC power and used as a control power source in the train or a power source for service equipment, so the above-mentioned: o o
/DO converter is often used. However, in recent years, the capacitance of semiconductor switching elements has increased and high voltage
As it has become possible to use large currents, large-capacity Do/Do converters are now being manufactured, and in electric railways, they are also used in the main circuits in vehicles, such as the DC motors that drive electric cars. It's starting to happen.

Figure 3 shows the series field current of a DC series motor.

FIG. 3 is a main circuit connection diagram showing an example of control using a /Do converter. In Fig. 3, the reference numeral 2 is the DC motor armature, and the reference numeral 2F is the DC motor field winding. By connecting these two in series, a DC series motor is constructed. Volume 11211= is TM, column is Do
A /Do converter 4 is connected, and an inductive shunt 3 is connected in parallel to the series circuit of the field winding 2F and the Do/Do converter 4. D O / D O
When the output voltage of the converter 4 is VE%, and the armature current flowing through the motor armature 2A is IA, the motor field winding 2F is
The series field current IF flowing through is expressed by the following equation (1). However, 1 and are constants.

1F = K, VE -IK2-IA -----
--(1) That is, the series field current F can be adjusted by changing the output voltage VE of the DC/Do controller 4, but it can also be seen that it can be changed by the armature current IA. In this way, the series field current IF is the armature current)A
This means that when the power supply voltage of an electric car changes suddenly, the armature current IA changes accordingly.
It has the effect of preventing a sudden increase or decrease in the amount of water and improving stability.

Furthermore, in the circuit shown in Figure 3, in addition to performing continuous field weakening control when the electric vehicle is running in forward motion, it is also possible to change the direction of the armature current IA by strengthening the field. It is also possible to shift to regenerative braking operation without changing the connection.

The above circuit is called an additive excitation circuit, and this Do
A converter used in place of the /Do converter 4 has already been put into practical use. By the way, a DC electric car is equipped with multiple main motors to drive the electric car.
These traction motors are usually divided into two groups, and the field current of these drive traction motors is controlled individually for each group.
A DC converter or a Da/DC converter that has two outputs and can individually control the voltage of each output is required.

Therefore, conventional examples of Do/Do converters used to meet the above-mentioned requirements and their problems will be described below.

FIG. 4 is a circuit diagram showing a conventional example in which two sets of DO/DO converters are connected in parallel. In FIG. 4, reference numeral 11 is a gate turn-off thyristor (hereinafter referred to as GT
12 is a freewheeling diode for circulating the excitation current of the output transformer;
3 is the output transformer, 14 is the output diode, and 15 is the output diode.
is a freewheeling diode for freewheeling the output current,
These GTO thyristor 11, freewheeling diode 12, output transformer 13, output diode 14, and freewheeling diode 15 constitute one DC/DO converter. Similarly, the other Do/Do converter is configured by the GTO thyristor 21 as switching elements, a freewheeling diode 22, an output transformer 23, an output diode 24, and a freewheeling diode 25, and supplies DC power to a load 26. . Furthermore, each DO/
The DO converter will hereinafter be referred to as a unit converter or simply a converter.

The outline of the operation of the unit converter is as follows. In other words, when two sets of GTO thyristors 11 on opposite sides of a bridge circuit composed of a GTO thyristor 11 and a free-wheeling diode 12 are simultaneously turned on, a voltage is applied to the input winding of the output transformer 13. A voltage is induced in the output winding. This voltage becomes an output voltage through the output diode 14 and supplies power to the load 16. Next G
When the TO thyristor 11 is turned off, the output transformer 1
The excitation current No. 3 flows through two sets of freewheeling diodes 12 forming opposite sides of the bridge circuit, and during this time, the input winding voltage and output winding voltage of the output transformer 13 are different from those when the GTO thyristor 11 is in the on state. The polarity is reversed. Therefore, the output diode 14 is turned off, and instead the freewheeling diode 15 is turned on, and current continues to flow through the load 16, but during this time the output voltage is zero. While the GTO thyristor 11 is in the off state, the excitation current of the output transformer 13 gradually decreases, but when this excitation current becomes zero, the freewheeling diode 12 also turns off, and the output winding voltage of the output transformer 13 becomes zero. . At this time, the output diode 14 remains off and the freewheeling diode 15 remains on, so the output voltage remains zero. If the GTO thyristor 11 is now turned on, the above-mentioned state is repeated again. The average value of the output voltage of such a unit converter can be adjusted to an arbitrary value by changing the ratio of on-time in one cycle in which the GTO thyristor 11 repeats on-state and off-state, that is, the conduction rate.

In the conventional circuit shown in FIG. 4, two sets of unit converters operating as described above are connected in parallel, and separate loads 16 and 26 are connected to each unit converter. Further, a DC power supply 5, an input filter reactor 6, and an input filter capacitor 7 are provided in common to both unit converters to supply DC power to them. Here, the input filter reactor 6 and the input filter capacitor 7 function to prevent harmonic currents generated during the operation of these unit converters from flowing out to the power supply side.

By the way, in the conventional circuit shown in FIG. 4, even if the two sets of loads 16 and 26 require different power, by separately controlling the voltage of each unit converter, each can meet the demands of the loads. Although there is an advantage, when the DC power supply 5 is a high voltage, the GTO thyristors 11, 21, . and freewheeling diode 12.
No. 22 has the disadvantage that it is expensive because it requires the use of high-voltage elements. Furthermore, if a high-voltage element cannot be obtained, it is necessary to use a plurality of elements connected in series as shown in FIG. 4, which increases the weight and volume of the device. Furthermore, consideration must be given to balancing the voltages applied to the elements connected in series, which also has the disadvantage of increasing the cost.

FIG. 5 is a circuit diagram showing a conventional example in which two sets of Do/Do converters are connected in series. In FIG. 5, a GTo thyristor 11, a freewheeling diode 12, an output transformer 13, an output diode 14, and a freewheeling diode 15 constitute one unit converter, and the output of this unit converter is supplied to a load 16. Similarly, the other unit converter is also a GTO thyristor 21. It is composed of a freewheeling diode 22, an output transformer 23, an output diode 24, and a freewheeling diode 25, and is designed to supply power to a load 26. These two unit converters are connected in series to the DC power supply 5. Further, input filter capacitors 17 and 27 are separately connected in parallel to the input sides of these unit converters. Furthermore, code 6
is the input filter reactor.

In the conventional example circuit shown in FIG. 5, two sets of unit converters are connected in series to the DC power supply 5, so the input voltage of each unit converter is / of the power supply voltage, and therefore the GTO thyristor 11°21 or freewheeling diode 12
．． 22 has the advantage that it is not necessary to use high-voltage elements, and it is not necessary to use a plurality of elements in series.

However, in order to keep the input voltage of each unit converter equal, the average input current of each unit converter must be equal.

Now, if we were to increase the output current by increasing the current flow rate of the unit converter on the positive side, the average input current of this positive side converter would increase, and as a result, the input filter capacitor 17 on the positive side would be discharged and its output current would increase. The voltage decreases, and conversely, the input filter capacitor 27 on the negative side is charged, and its electric power increases. If the conduction rates of the positive and negative converters are automatically controlled to maintain the output current at a predetermined value, the output voltage of the positive converter will decrease as the input voltage decreases. Since the current decreases, the control system of this positive side converter tries to suppress this decrease in output current by further increasing the conduction rate, but as the conduction rate increases, the average input current increases. As a result, the input voltage of the positive side converter further decreases. On the negative side, the input voltage of the unit comparator increases, so in order to keep the output current at a predetermined value, the conduction rate decreases, but as a result, the average input current decreases and the input voltage further increases. It will rise.

In other words, in the conventional circuit shown in Fig. 5, when attempting to obtain different output powers by controlling the voltages of two series-connected unit converters separately, the input voltages of each unit converter become unbalanced, and the input voltage becomes unbalanced. Since there is a risk that the withstand voltage of the side elements will be insufficient, there is a drawback that the voltages of both unit converters cannot be controlled separately.

(Object of the Invention) The present invention provides a DC-DC converter in which two sets of DO/DO converters are connected in series to a DC power source, and the output power of each Do/Do converter can be controlled separately without any trouble. The purpose is to provide a series operation circuit for.

(Summary of the Invention) This invention extracts any DC voltage isolated from the input voltage from the output winding of the transformer by turning on and off the DC voltage applied to the input winding of the transformer. 2 of the Do/Do converters configured to be able to
The transformer has two sets connected in series to the DC power source, a separate input filter capacitor connected in parallel to the input side of each Do/Do converter, and two sets having an equal number of turns and isolated from each other. with an output winding of one DO
/The first output winding of the transformer for DC converter and the other 0)D
A circuit that supplies DC power to the first load using the first output winding and output diode of the o/DO converter transformer, and a circuit that supplies DC power to the first load using the first output winding and output diode of the o/DO converter transformer, and a circuit that supplies DC power to the first load using the first output winding and output diode of the transformer, and a By configuring a circuit that supplies DC power to 2 loads, both DCs connected in series
This is intended to equalize the sharing of input voltage when the c converters are controlled with the same duty ratio.

(Example of the invention) FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In FIG. 1, of the two unit converters connected in series, the unit converter connected to the positive side is a GTO thyristor 11 as a switching element.
, a freewheeling diode 12, an output transformer 10, an output diode 14, and a freewheeling diode, and the unit converter connected to the negative electrode side similarly includes a GTO thyristor 21 as a switching element, a freewheeling diode 22, and an output transformer 20. , an output diode 24, and a freewheeling diode 25. Input filter capacitors 17 and 27 are connected in parallel to the input sides of the positive and negative converters, respectively.

In the present invention, the output transformers 10 and 20 provided in both converters have two sets of output windings that are insulated from each other, that is, the first output windings 10B and 20B and the second output windings 100 and 20B. 200, these first windings 10B and 20B are connected in series to supply DC power to one load 16, and these second windings 100 and 200 are connected in series to supply DC power to the other load 16. The first winding and the second winding have the same number of turns.

In the circuit configured as described above, the GT of both converters is
If the O-thyristors 11 and 21 are controlled to have the same conduction rate, even if there is an imbalance between the loads 16 and 26,
Both output transformers 10 and 20 will share half of the power supplied to load 16 and half of the power supplied to load 26.

Therefore, if we ignore the slight difference in winding impedance between the output transformers 10 and 20 and the slight difference in the forward voltage drop of each diode or each GTO thyristor, then from the primary side of the output transformers 10 and 20, input becomes equal. As a result, the voltages shared by the input filter capacitors 17 and 27 connected in parallel to the input side of each Do/Do converter are also balanced.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention,
The positive side converter is G'I' as a switching element.
An arm formed by connecting an O-thyristor 31 and a free-wheeling diode 32 in antiparallel is connected to the output transformer 10 through a bridge connection. Similarly, the negative side converter has a bridge connection of an arm formed by an antiparallel connection of a GTO thyristor 41 as a switching element and a freewheeling diode 42, which is connected to the output transformer 20, but the other parts, that is, the DC power supply 5 , the input filter reactor 6, the free wheel diodes 15 and 25, the loads 16 and 26, and the input filter capacitors 17 and 27 have the same names, uses, and functions as those already described in FIG.

A first output winding 10 provided on both transformers 10 and 20
B and 20B are output diodes 14B and 24B, respectively.
are connected in parallel to each other via the second output winding 1
00 and 200 also have output diodes 140 and 240 respectively.
and are connected in parallel to each other. Here each GT
By turning the O thyristors 31 and 41 on and off, both output transformers 1o and 20 alternately supply power to the loads 16 and 26 every half wave of their input AC voltage, so that as shown in FIG. Similarly to the circuit described above, the power and voltage sharing on the input side of the two output transformers 10 and 20 can be made equal.

(Effect of the invention) According to this invention, two sets of DO/D O converters are connected in series to a DC power supply, and each DC/D
When using input filter capacitors connected in parallel on the input side of a C converter, each output transformer has two sets of mutually isolated output windings with equal windings, and the first output windings are combine to power one load,
If the circuit is configured to supply power to the other load by connecting the second output windings, and if both Do/Do converters are operated at the same conduction rate, the power to each load will be / 2
Since each Do/Do converter can bear the burden of
Since the withstand voltage of the elements used in the O/DO converter is only half of the power supply voltage, the device can be made low-cost and compact. It also has the advantage of eliminating the risk of element damage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the invention, and FIG. 2 is a circuit diagram showing a second embodiment of the invention. Figure 3 shows the series field current of a DC series motor. 4 is a main circuit connection diagram showing an example of control using a /DC converter, FIG. 4 is a circuit diagram showing a conventional example in which two sets of DO/Do converters are connected in parallel, and FIG. FIG. 2 is a circuit diagram showing a conventional example in which a set of Do/Do converters is connected in series and used. 2A: DC motor armature, 2F: DC motor field winding,
3: Inductive shunt, 4: DO/Do converter, 5'
If current power supply, 6: Input filter reactor, ? , 17.
27 n manual filter capacitor, 10°13, 20
．． 23: Output transformer, IOA, 20A: Input winding, IOB, 20B: First output winding, 100°20
0 = second output winding, 11.21.31.41 GTO thyristor as a switching element, 12°22
．． 32, 42: Freewheeling diode, 14.14B, 140
゜24.24B, 240: Output diode, 15.
257 Freewheeling diode, 16.26: Load.

Claims (1)

[Claims] 1) The input DC voltage applied to the input winding of the transformer is turned on and off by a switching element, and an arbitrary voltage isolated from the input DC voltage is generated from the output winding of the transformer via an output rectifying element. In a device that uses two sets of DC-DC converters configured to obtain a DC power of each transformer has an output winding composed of two sets of windings having an equal number of turns, a first output winding of one transformer and a first output winding of the other transformer. a circuit that connects the line and supplies power to a load via a rectifying element, and a second output winding of one transformer and a second output winding of the other transformer;
1. A series operation circuit for DC-DC converters, comprising a circuit for supplying power to another load via another rectifying element.