JP3328094B2 - DC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter for converting a DC voltage to a second DC voltage, and more particularly to a DC / DC converter having improved voltage control stability and improved control characteristics.

[0002]

2. Description of the Related Art DC / DC converters have been used which convert a DC voltage into an alternating voltage at a predetermined modulation period and then convert it into a second DC voltage again. This type of conventional DC / DC converter used for a vehicle or the like will be described with reference to FIG.

[0003] A pantograph 1 receives a DC voltage Ed1 from a fed overhead wire, and receives a reactor 2, a thyristor (or G).
The capacitor 4 is charged via the (TO) 3. The DC voltage Ed1 charged in the capacitor 4 is applied to an inverter circuit 9 composed of switching elements 5 to 8, is converted into a rectangular wave alternating voltage Ea1 whose polarity is alternately inverted, and is input to the primary winding of the transformer 10. . AC voltage E induced in the secondary winding of the transformer 10
a2 is full-wave rectified by a rectifier 15 composed of diodes 11 to 14, and a filter 18 composed of a reactor 16 and a capacitor 17 is provided.
Is output as a smoothed second DC voltage Ed2.

The control of the inverter circuit 9 is performed as follows. The voltage controller 20 compares the second DC voltage Ed2, which is insulated and detected via the voltage detector 19, with the voltage reference Er, and reduces the voltage deviation ΔE so that the voltage control signal Vc becomes zero. Output. This voltage control signal Vc is input to the comparator 24, and as shown in FIG.
Signal Ca of a sawtooth wave with a constant period T1
Is output as a PWM control signal P1 that has been pulse-width modulated. Further, the modulation signal generator 29 outputs the modulation signal C
A synchronous pulse Cp having a narrow width is output at every fixed period T1 in synchronism with a.
Outputs a signal Ga whose logic value is inverted every time is input. Further, it outputs a signal Gb having a logic value opposite to that of the signal Ga. Therefore, the signal Ga Gb becomes a signal having a cycle twice as long as the cycle T1 of the modulation signal Ca, and becomes active alternately every half cycle T1. The PWM control signal P1 is input to the AND circuits 26 and 27, and is alternately output as a PWM control signal Da Db every half cycle T1 by the signal Ga Gb output from the flip-flop 25. The elements 5, 8 and the switching elements 6, 7 are turned on alternately. Thus, the alternating voltage Ea1 output from the inverter circuit 9 is
The power supply time in the half cycle T1 is adjusted, and the second DC voltage Ed2 is controlled to a desired value.

[0005]

However, in the above-mentioned conventional apparatus, the value of the voltage control signal Vc becomes small at a light load, the output voltage becomes high due to the influence of noise, and the output voltage rises. Oscillation may occur and become unstable. Further, the control response of the voltage control must be set to be slow in order to prevent the unstable phenomenon, and there is a problem that the control response of the normal voltage control is also slow.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a DC / DC converter capable of preventing an unstable phenomenon and improving the control response of voltage control. Is to do.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an inverter for converting a DC voltage into a rectangular wave alternating voltage and applying the converted voltage to a primary winding of a transformer, and a secondary winding of the transformer. A rectifier for converting an alternating voltage output from the line into a second DC voltage, a filter circuit for smoothing the second DC voltage, and controlling to reduce a deviation between a voltage reference and the second DC voltage A voltage control unit that outputs a signal, a correction unit that corrects the control signal based on an instantaneous value of a current flowing through a primary winding of the transformer, and compares the corrected control signal and the modulation signal to generate a square wave signal. Pulse width modulation means for outputting a drive signal for the inverter so as to adjust the width.

Further, the correction means obtains an absolute value of an instantaneous value of a current flowing through a primary winding of the transformer, and subtracts an absolute value of an instantaneous value of the current from the control signal to obtain a corrected control signal. Calculation means for obtaining.

Further, the operation response time of the correction means is set to be later than the cycle of the modulation signal and earlier than the operation response time of the voltage control section. Means for holding a peak value of a current flowing through the primary winding of the transformer for each cycle of the modulation signal, and outputting a voltage correction signal corresponding to the peak value; and correcting the voltage reference with the voltage correction signal. Means for reducing the second DC voltage in accordance with the output current to have a drooping characteristic.

[0010]

In the above arrangement, the voltage control section outputs a control signal so as to reduce the deviation between the voltage reference and the second DC voltage, and the pulse width modulation means compares the control signal with the modulation signal. The inverter outputs a drive signal.The inverter converts the DC voltage to a rectangular wave alternating voltage, applies the converted voltage to the primary winding of the transformer, rectifies the alternating voltage output from the secondary winding with a rectifier, and forms a filter circuit. And output as a smoothed second DC voltage. In this case, the correction unit corrects the control signal based on the instantaneous value of the current flowing through the primary winding of the transformer, and the pulse width modulation unit compares the corrected control signal with the modulation signal to generate the square wave. A drive signal for the inverter is output so as to adjust the width, and the voltage control is stabilized by the instantaneous value of the current flowing through the primary winding of the transformer.

[0011] Further, the correction means may include:
The absolute value of the instantaneous value of the current flowing through the primary winding of the transformer is obtained, and the corrected control signal is obtained by subtracting the absolute value of the instantaneous value of the current from the control signal.

Further, by setting the operation response time of the correction means later than the cycle of the modulation signal and earlier than the operation response time of the voltage control section, stable voltage control can be performed. The control response time of the voltage control unit can be made shorter than before.

Further, the voltage reference is corrected based on the peak value of the current flowing through the primary winding of the transformer, and the second DC voltage is reduced in accordance with the output current to have a drooping characteristic, thereby stabilizing the voltage control. In addition, when a plurality of DC / DC converters are operated in parallel, the load current can be automatically balanced.

[0014]

FIG. 1 shows an embodiment corresponding to claims 1 and 2 of the present invention. In FIG. 1, reference numeral 30 denotes a current detector for detecting an instantaneous value ia1 of an alternating current flowing through the primary winding of the transformer 10, and 31
Is a signal converter for converting the detected AC current ia1 to an absolute value signal ia1a, and 32 is a control signal Vc output from the voltage controller 20, subtracts the absolute value signal ia1a from the control signal Vc, and outputs a corrected control signal Vc1. It is an arithmetic unit. The comparator 24 compares the corrected control signal Vc1 with the modulation signal Ca and outputs a PWM control signal P1. Others are the same as the conventional one (FIG. 5), so the same reference numerals are given and the description is omitted.

As described above, as a minor loop of the voltage control loop, the control signal Vc of the voltage control based on the instantaneous value of the current is performed.
Is formed. In the above configuration, the voltage control unit 20 compares the voltage reference Er with the second DC voltage Ed2 detected via the voltage detector 19, and outputs a control signal Vc so as to reduce the deviation. PW as well as
An M control signal Da Db is output, the switching elements 5, 8 and the switching elements 6, 7 are turned on alternately via the drive circuit 28, and an alternating voltage Ea1 is output from the inverter circuit 9, and the power supply in the half cycle T1 is supplied. By adjusting the time, the second DC voltage E
d2 is controlled to the value of the voltage reference Er.

In the case of this embodiment, when a current ia1 flows through the primary winding of the transformer 10 due to the output of the alternating voltage Ea1, the current ia1 is detected via the current detector 30, and as shown in FIG. The signal ia1 of the absolute value of the alternating current ia1 from the signal converter 31
a is output, and the arithmetic unit 32 subtracts the absolute value signal ia1a from the control signal Vc to output a corrected control signal Vc1. Then, the corrected control signal Vc1 is compared with the sawtooth wave modulation signal Ca to generate a PWM control signal P1.

As described above, the corrected control signal Vc1 becomes a signal that changes at a rate of change in accordance with the degree of the current change by being corrected with the signal ia1a, and a signal having a certain magnitude even under a light load. Become. Therefore, at a light load, the degree of change in the pulse width due to the influence of noise is reduced, and the jumping phenomenon of the output voltage is suppressed,
Unstable phenomena such as intermittent oscillation are eliminated.

The operation response time of the correction means comprising the current detector 30, the signal converter 31, and the calculator 32 is determined by the modulation signal generator.
By setting the period to be shorter than the period T1 of the modulation signal Ca of the saw-tooth wave output from 29 and earlier than the operation response time of the voltage control unit 20, it becomes possible to prevent an unstable phenomenon, Even if the operation response time is set shorter than in the past, stable control can be achieved. (Claim 3) An embodiment corresponding to claim 4 of the present invention is shown in FIG. FIG.
(a) shows the configuration of the main part of the present embodiment, and 33 is the maximum value of the signal ia1a of the absolute value of the AC instantaneous value ia1 output from the signal conversion unit 31 and is held at the maximum value. A peak hold circuit that outputs a corresponding voltage correction signal Vcmp, 34
Is an arithmetic unit for subtracting the voltage correction signal Vcmp from the voltage reference Er. Others are the same as FIG.

In the above configuration, when the current of the load supplied with the second DC voltage Ed2 increases or decreases, the current ia1 of the primary winding of the transformer 10 increases or decreases, and the signal converter 31 responds to the increase or decrease of the load current. Signal ia1a of the absolute value of the instantaneous alternating current value ia1
Is output. This signal ia1a is input to the arithmetic unit 32,
The control signal Vc is corrected and the peak hold circuit 33 is corrected.
And holds the maximum value of the signal ia1a and outputs a voltage correction signal Vcmp corresponding to the maximum value. The arithmetic unit 34 outputs the corrected voltage reference Er1 by subtracting the voltage correction signal Vcmp from the voltage reference Er, and the voltage controller 20 outputs the corrected voltage reference Er1.
And an output voltage (second DC voltage) Ed2, and outputs a control signal Vc so as to reduce the deviation. Since the voltage correction signal Vcmp output from the peak hold circuit 33 increases and decreases according to the increase and decrease of the load current, the corrected voltage reference Er1 is corrected so as to decrease as the load current increases.

Therefore, as shown in FIG. 3 (b), it is possible to provide a drooping characteristic in which the second DC voltage Ed2 decreases in proportion to an increase in the load current, and to perform more stable voltage control. it can. Further, according to this embodiment, a plurality of DCs
When the / DC converters are operated in parallel, it is possible to automatically control to keep the load current balanced.

[0021]

According to the present invention, a rectangular wave alternating voltage is obtained from a DC power supply by PWM control, rectified through a transformer,
In the case of outputting the smoothed second DC voltage, it is possible to perform a stable voltage control by suppressing the intermittent oscillation and the jumping phenomenon at a light load, and to improve the DC control response characteristic.
/ DC converter can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment corresponding to claims 1 and 2 of the present invention.

FIG. 2 is a timing chart for explaining the operation of the embodiment.

FIGS. 3A and 3B are views showing an embodiment according to claim 4 of the present invention, wherein FIG. 3A is a configuration diagram of a main part thereof, and FIG. 3B is a special drawing of an output voltage with respect to a load current.

FIG. 4 is a configuration diagram of a conventional device.

FIG. 5 is a timing chart for explaining the operation of the conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pantograph 2 ... Reactor 3 ... Thyristor 4 ... Capacitor 5-8 ... Self-extinguishing switch element 10 ... Transformer 11-14 ... Diode 15 ... Rectifier 16 ... Reactor 17 ... Capacitor 18 ... Filter 19 ... Voltage detector 20 ... Voltage Control unit 24 Comparator 25 Flip-flops 26 and 27 AND circuit 28 Gate drive circuit 29 Modulation signal (sawtooth wave) generation unit 30 Current detector 31 Signal conversion unit 32 Computing unit 33 Peak hold Circuit 34 ... Calculator

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-3678 (JP, A) JP-A-62-268066 (JP, A) JP-A-7-59342 (JP, A) JP-A-5-59342 260741 (JP, A) JP-A-5-38158 (JP, A) JP-A-3-50980 (JP, U) JP-A-1-76184 (JP, U) JP-A-63-164382 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/335 H02M 7/48 H02M 7/5387

Claims (4)

(57) [Claims] 1. An inverter which converts a DC voltage into a rectangular wave alternating voltage and applies the same to a primary winding of a transformer, and converts an alternating voltage output from a secondary winding of the transformer into a second DC voltage. A rectifier, a filter circuit for smoothing the second DC voltage, a voltage control unit for outputting a control signal to reduce a deviation between a voltage reference and the second DC voltage, and a primary winding of the transformer Correction means for correcting the control signal according to the instantaneous value of the current flowing through the inverter, and a pulse width for outputting a drive signal for the inverter so as to adjust the width of the rectangular wave by comparing the corrected control signal with the modulation signal. A DC / DC converter comprising a modulation means, wherein voltage control is stabilized by an instantaneous value of a current flowing through a primary winding of the transformer. 2. The DC / DC converter according to claim 1, wherein said correction means obtains an absolute value of an instantaneous value of a current flowing through a primary winding of said transformer, and obtains an instantaneous value of said current from said control signal. A DC / DC converter comprising an arithmetic unit for obtaining a corrected control signal by subtracting an absolute value of a value. 3. The DC / DC converter according to claim 1, wherein an operation response time of said correction means is set later than a period of said pulse width modulation signal and earlier than an operation response time of said voltage control section. A DC / DC converter, characterized in that: 4. The DC / DC converter according to claim 1, wherein a peak value of a current flowing through a primary winding of the transformer is held for each cycle of the modulation signal, and a voltage correction signal corresponding to the peak value is held. And a means for correcting the voltage reference with the voltage correction signal, wherein the second DC voltage is reduced in accordance with an output current to have a drooping characteristic.