FR2467505A1 - CONVERTER CIRCUIT USING VARIABLE WIDTH PULSE MODULATION - Google Patents

Abstract

A voltage conversion and regulation circuit and method using variable width pulse modulation to vary the periodic excitation of a tuned circuit 21 used to control a transformer and an associated rectifier. A direct current source 34 periodically energizes the tuned circuit 21 at a fixed rate but for changeable periods of time during each cycle, in order to produce in the tuned circuit an alternating current of fixed frequency for its subsequent transformations and rectifications into current. continuous at a determined and regulated level. The PWM modulator is connected in a feedback loop between output terminals 44, 46 and switches 26, 28 which serve to ensure the periodic excitation. By modifying the duration of the actuation time of the switches according to the changes in the level of the output voltage, the desired regulating control is obtained. Application to all systems requiring controlled tension. (CF DRAWING IN BOPI)

Description

The present invention relates to a circuit and a method for

  ensure the conversion and regulation of a DC voltage by the exci-

  selective and periodic tapping of a tuned resonant circuit.

  Relevant examples of such circuits include those described in US Pat. No. 3,953,779 issued to Schwarz, an article entitled "A 95-Percent Efficient 1kW DC Converter with an Internal Frequency of 50kHz" by F. C. Schwarz and J. B. Klaassens of

  Power Electronics Laboratory of the Electrotechnical Department of the U

  State University of Technology in Delft (Holland), and the American patent

  No. 3,596,165 issued to Andrews and assigned to the assignee of the present invention. Such circuits operate fundamentally by periodic excitation of a resonant circuit from a source

  of direct current, in order to produce alternating current in the

  cooks tuned and then turning the alternating current to a level

  producing, after rectification, a desired DC potential.

  It is also possible to obtain a limited regulation by modifying the rate

  of excitation in accordance with the changes in

  inlet or on-demand supply at the exit.

  In the circuits described by both Schwarz and Andrews, the

  tuned elements are excited at an offset rate of some

  The disadvantage of such circuits is that their regulating capacity is limited to a range of charges of about 2 to 1, ie between about half and

about the entire load.

  The object of the present invention is to provide a con-

  initiator and its process for ensuring the conversion and

  tion of a DC voltage over a wide range of

  from the power supply to the input, from the demand to the output. More by-

  In particular, the circuit according to the present invention comprises a converter circuit similar in many respects to that described in the Andrews reference cited above, except that the operation of the circuit is controlled by variable width pulse modulation.

  instead of frequency modulation.

  The circuit according to the present invention comprises a circuit

  tuned resonant, switch devices to periodically excite

  the circuit from an AC source having a constant frequency substantially equal to the resonant frequency of the circuit, output means for producing an output in response to the alternating current, and a modulator which operates by varying the width. pulses in order to modify the duration of each periodic excitation in

  function of the level of the output. The circuit granted includes an inductive

  and a capacitor connected in series with the primary winding of an output transformer whose secondary winding is in turn connected to a conventional diode-capacitor rectifying circuit, in order to

  produce a final DC output. During the course

  As the input power level or the output demand level changes, so as to affect the output level of the circuit, the variable width pulse modulator provides the increment or decrement of the duration. periodic excitation of the tuned circuit,

  in a way that tends to maintain the output at a regulated and

  As. As mentioned above, with the exception of the use of variable width pulse modulation for controlling

  excitation of the circuit, the circuit of the present invention is

  in many respects to the one described in Andrews

mentioned above.

  The main advantages of the circuit and the process of the pre-

  invention are their simplicity, both of understanding and of

  their ability to maintain effective regulation of the

  on a relatively wide range of variations in

  out, and more particularly, over a wider range

  than the one that can be dealt with the Andrews circuit.

  Therefore, the main object of the present invention

  to provide a circuit and a method for converting and regulating a DC voltage over a wide range of variations

  of the input power supply and output demand.

  One of the features of the present invention lies in

  the fact that the conversion and regulation of the effective voltage

  by a tuned resonant circuit whose resonant elements proper are periodically excited from a DC source at a constant rate of determined value, but for periods of varying duration depending on the power supply.

  entrance and demand at the exit.

  The aims and features set forth above, as well as the advantages that characterize the present invention, will be better understood

  if we refer to the detailed description below made in

  Referring to the figures of the accompanying drawing, in which FIGURE 1 is a simplified schematic representation of a

  an embodiment, given by way of example only, of the circuit

  energizer and regulator made according to the present invention; FIGS. 2 and 3 each show a series of waveforms to illustrate how the circuit of FIG. 1 operates, and FIG. 4 is a simplified schematic representation of an alternative embodiment of the converter and regulator circuit of FIG.

present invention.

  If we first refer to Figure 1, we see

  schematically, an embodiment, given for the sole purpose of

  non-limiting, of the converter and regulator circuit following the

  invention, which comprises: an inductor 22 and a condenser

  24 which together form a tuned resonant circuit 21 connected in series with the primary winding 25 of an output transformer 20

  whose secondary 41 is coupled to two output terminals 44, 46 in step

  by a conventional rectifier device with diode and capacitor 36 and 40; switches 26 and 28 and two respective diodes 30 and 32 connected in parallel to selectively energize the tuned circuit 21 and the primary winding 25 of the transformer 20 from a DC source 34; and a variable width pulse modulator 42 connected between the output terminals 44, 46 and the switches 26, 28 to control the operation of the latter,

  in a way that will be described in more detail later. Both

  interrupters 26, 28 may be of any suitable type, provided

  on the one hand to achieve rapid rates of

  in the 25 kWz zone and secondly to use an electronic control. A typical example of such switches is the combination of transistors described in the Andrews reference cited above. Similarly, the variable width pulse modulator 42 may be of any suitable type capable of controlling the undervoltage and de-energizing state of the two switches 26, 28.

  according to a voltage level existing at the two terminals 44 and 46.

  A typical example of such a device is that marketed under the reference 3524 by manufacturers such as Silicon General and Texas Instruments. In use, the variable width pulse modulator 42 actuates in turn the two switches 26, 28 so as to

  generated in the tuned circuit 21 and the winding 25 of the transforma-

  alternating current, the size and duration of which are

  sufficient to produce at output terminals 44, 46, after tranforma-

  transformer and the subsequent rectification, a DC potential of determined and controlled value. The detail of the circuit of FIG. 1 will be better understood if we examine the waveforms of FIGS. 2 and 3 where the curve designated by the acronym CLK defines a clock signal (of which two adjacent pulses represent a single cycle). to refer to the timed operation of modulator 42 by variable width pulses, while the curve designated by the word DRIVE indicates the state of power on or off of

  two switches 26 and 28, the curve e1 representing the voltage applied to

  plicated through the circuit formed by the tuned circuit 21 and the

  transformer bearing 25 during operation of the interrupters.

  tors; finally, the curves designated by the symbols e i and i. re-

  present respectively the voltage and the intensity obtained in the single primary winding. The four curves of Figure 2 which are designated by the symbols i to i are component segments pri <I1) pri (4)

  of the i.ri curve that have been separated or detached for purposes of illustration.

  Each of the voltage and intensity curves, respectively,

  between them by a series of broken lines and the synchronization marks t, to indicate the appearance of important phenomena

  during their generation. An arrow marked T indicates the relationship

  between a half-cycle of the CLK curve and the periodicity of the remaining curves of these Figures. For simplicity, it will be assumed that the inductor 22 and the capacitor 24 forming the tuned circuit 21 are purely reactive and the primary winding 25 will be considered as

  being essentially parallel resistance with capacitance

  plotted to a diode. It can be emphasized that in the DRIVE curve

  2 and 3, the solid line designated by the symbol S26 represents

  the state of the switch 26 and that the dashed line S28 represents the state of the switch 28, with a high level, in each case, to indicate a state of closure or under voltage and a low level indicating an open or unpowered state. Can also

  note that switches 26 and 28, although potentially open,

  at the same time, can not under any circumstances close at the same time

  time, because it is obvious that this would actually

circuit the input source 34.

  To take a starting point, we can assume for example

  at a specific moment, located just before time t1,

  switches 26 and 28 are open, as shown by the DRIVE curve of the

  Figure 2, and that the current i pri flows in a positive direction, what

  the arrow 50 in Figure 1, through the circuit

  22, the capacitor 24, the primary winding 25 of the transformer

  21 and the diode 32 polarized in the conductive direction, the source

  current i being constituted by the release of an emma-

  gasined in the capacitor 24 during a previous operation of the circuit. At time t i, modulator 42 operating in pulses of variable width closes switch 26, as indicated by the curve DRIVE

  of Figure 2, which has the effect of applying the voltage E 1 of the source

  this of direct current 34 at the terminals of the tuned circuit 21 and the

  primary bearing 25, as shown in the following curve e1 of Figure 2. This results in a sharp increase of the current ir in the positive direction, as indicated by the curve i.ri (1), until reaching a maximum value at the instant t 2, after which this current

  decreases in accordance with the characteristic transient response of a

  baked LC in series has a stepped wave. (It is assumed in this context that the reader is familiar with the problem of the transient

  characteristic of such an LC circuit with stepped functions as

  only negative). It may be noted in passing that the diode 32 is polarized upside down by the application of the voltage of the source

  E. and that the traj and followed by the i.r current is now

  to the source 34. If the switch 26 was left closed, the current i 2 ,. would oscillate around zero at the resonance frequency of the circuit

  LC while being amortized exponentially as indicated by the

  in dashed lines of the curve i. <r 1).

  At time t 3, although the switch 26 is open and the voltage source Ei is isolated from the circuit, the current i pi, instead of falling back to zero, is maintained for a short period by the weakening field of the inductor 22, and made to continue to flow through the circuit which once again comprises the diode 32 polarized in the conductive direction, until falling back to zero at time t 4 At this time, the field of the inductor 22 is dissipated and the capacitor 24, charged to the maximum potential, greater than that of the source 34, circulates the current i.Pr in the opposite direction, passing beyond

  of the diode 32 again polarized in the opposite or non-con-

  conductor, and through the diode 30 polarized in the conductive direction, to return to the source 34 itself. This phenomenon is indicated by a comparison of the curves e1 and i ri (2) of Figure 2. (It should be recalled that the tuned circuit LC high value of Q, excited at its resonant frequency, will produce a voltage across the capacitor

  with a peak value of approximately Q times the excitation voltage,

  so, if Ei = 300 Volts and Q = 10, the voltage across the con-

  denser will be approximately 3,000 volts, as a first approximation.

  As the charge of the capacitor 24 dissipates, the current i ri increases in magnitude until it reaches a maximum at time t5 where it begins to decrease again and to approach zero. If we left the circuit as it is, ipri current would drop to zero and then flow in the positive direction through the diode 32 which would then be polarized in the conductive direction, as indicated by the part in

  interrupted lines of the curve i. (2), until weakening

pri

to fall to zero.

  At time t6, the switch 28 closes and the current i pri flowing in the opposite direction through the source 34 is suddenly set

  in shunt through the zero resistance of the switch device.

  This has the effect of producing a sudden increase in the magnitude of the current ipri, as indicated by the curve i ri (3), always in the opposite direction, until it reaches its peak at time t7, after which this Current returns to zero. As in the previous case, if we left the switch 28 closed, the current i. would oscillate around zero, in characteristic transient response to the suppression of a stepped wave of an LC series circuit. However, at time t8, the switch 28 is opened again and the current i i maintained during a short

  instant by the weakening field of the inductor 22 is repressed a se-

  conde times through the diode 30 polarized in the conductive direction and to the source 34, until it drops to zero at time t9

  when the capacitor 24, now charged to its negative potential

  ximal by the reverse current that previously flowed there, begins to discharge and to send current in the conductive direction, as indicated by the curve ii (4), through the diode 32. As the load that contains the capacitor 24 dissipates, the current ip reaches a maximum value at the instant t10, then begins to decrease until the instant to the switch 26 is closed and the process

repeating itself.

  As mentioned above, the four segments of

  rant ipri (1) to i ri (4) form in combination the current i pri which circulates

  actually flows through the winding 25 of the transformer 20.

  Although the current i pri is of a somewhat sinusoidal nature, the voltage epri produced across the primary winding 25 of the trans-

  trainer 20 essentially follows the curve of a square wave, in

  first place because of the load used in the circuit o the diodes 36 and 38 provide the charge of the capacitor 40. For a load of fully resistive alternating current, the voltage e. would be good

  less a square wave and more similar to the sinusoid of the neck.

rant i ..

  The control of the two switches 26 and 28 to obtain the operation described above is carried out by means of a modulator 42 operating in pulses of variable width, connected between the output terminals 44 and 46 (designated by the acronym PWM in Figures 1 and 4),

  on the one hand, and the two aforementioned switches 26 and 28, on the other hand.

  During normal operation and at rest, modulator 42 operating

  pulses of variable width produces a series of pulses, such as

  the ones indicated by the DRIVE curve of FIG. 2, and this at a constant rate, preferably equal to the resonance frequency of the tuned circuit 21, and with a sufficient width or period of time for each of the switches 26 and 28 to closes for about

  % of each operating cycle, defined as

  diamed higher by two cycles of the CLK curve, and opens during

  the remaining part of the cycle. Whenever there is disturbance of

  output voltage of the DC voltage produced by the circuit, for example as a result of a change occurring either in the demand at the output or in the input power supply, the modulator 42 operating in pulses of variable width automatically varies the width of the individual pulses which constitute the pulse current which controls the operation of the two switches 26

and 28.

  Thus, for example, if the output voltage at the terminals 44 and 46 decreases, for example as a result of an increase in the demand at the output, the pulse-width modulator 42 intervenes

  to increase the pulse width in the pulse current.

  This intervention is represented by the curves in Figure 3, some of which are individually designated to identify them in relation to each other.

  to the corresponding curves in Figure 2. As can be seen in Figure

  In FIG. 3, the frequency of the pulse current is maintained at a value equal to that of FIG. 2, but the width, or duration in time, of each pulse is increased to a considerable extent. As a result, as explained above, the current i i produces

  in the same way as previously indicated, amounts to

  than a larger size and encloses a larger area under its

  curve. Therefore, the output voltage measured at the output terminals

  44 and 46 is also increased. Increasing the width of the pulses is limited by the feedback loop operation of the modulator 42 to a measure just sufficient to increase the voltage.

  exit from the circuit to the level that was his before the

  turbation. If, on the contrary, the output voltage has increased, for example

  as a result of an increase in the input supply or a decrease in

  When the demand is output, the pulse width of the DRIVE curve will be reduced to less than that of the pulses in Figure 2 to produce a reduced current i i in the primary

  of the transformer and a corresponding decrease in the voltage

  held at the output terminals. When the demand (load) drops to a very low level, the operation of the circuit of FIG. 1 becomes in fact discontinuous, the pulses of the DRIVE curve having a width

  barely sufficient to maintain an alternative charge in the con-

denser 24.

  In practice, a very small change in the width of the pulses is sufficient to compensate for changes in the output voltage due to variation in the output demand.

  whereas most of this change is due to international variation

  came in the food at the entrance.

  Examples of suitable values for different components of the circuit of FIG. 1, which include an inductor 22 of 0.4 milliherry, a capacitor 24 of 0.1 microfarad, a transformer 20 having an inductor, can be indicated by way of example. magnetization of about 400 millihenry, and a capacitor 40 of 5, 000 microfarads. The operating voltages may be for example an input voltage of about 300 volts, and an output voltage of about 100 volts, the difference being

  mainly due to the turns ratio of the transformer 20. Frequency

  The preferred operating frequency would be approximately 25 kHz for the resonance frequency of its tuned circuit 21. Such a circuit

  is able to provide a regulated output for input voltages

  killed between about 270 volts and about 500 volts, and outgoing demands in the range of about o volts and about the maximum rated load. If we briefly examine the circuit shown in Figure 3, we see the two-phase equivalent of the circuit of Figure 1. To facilitate the establishment of a correlation, the components of the circuit of Figure 4 are designated so to correspond to those of the circuit of Figure 1, except for the use of the distinctive sign "prime" ('). The operation of the circuit of Figure 4 is in many ways similar to that of Figure 1, and those skilled in the art will understand it without difficulty. The main difference observed between the voltage and intensity curves obtained by the operation of such a circuit is that the voltage curve e1 alternates

  between + E. and -Ei, instead of alternating between + E. and zero in the case

  i i cedent. Moreover, the curves of FIGS. 2 and 3 apply to the circuit of FIG. 4, except for changes in magnitude due to two-phase current characteristics, in contrast to FIG.

  to those of the half-wave current, of the circuit considered.

  Therefore, it is clear that we have described above a

  converter circuit and energy regulator that operates

  pulse width, to produce a voltage

  in direct current of a determined and regulated size.

  Of course, certain modifications and variations can be made in the practical implementation of the invention without, however, departing from the basic principles thereof, as will be apparent from the present invention.

  to any technician knowledgeable in this area.

Claims (9)

  1. Energy conversion and regulation circuit, characterized in that it comprises: a) a tuned circuit, (21) b) means for periodically exciting this tuned circuit, (21) from a source of direct current (34) to produce in this tuned circuit, (21) a current alternating constant frequency.   c) means coupled to said tuned circuit, (21) for receiving an output in response to said alternating current, and d) means responsive to said output for changing   the duration of each periodic excitation of said circuit   d & according to the level of said output. -   2. Energy conversion and regulation circuit   according to Claim 1, characterized in that the means (b)   periodically energizing said tuned circuit (a) includes switches (26,28) for selectively connecting said tuned circuit to said DC power source, and   means (d) responsive to said tuned circuit, (21) comprising   a device coupled to said switches in order to   hold each connection above for a period of time   which is a function of the level of said output.   - 3. Energy conversion and regulation circuit according to claim 1, characterized in that the means (d) responsive to said output comprise a device adapted to increase the duration of each periodic excitation dudLt tuned circuit, (21) in response to a decrease in level of said output.   -30 4. Power conversion and regulation circuit according to claim 1, characterized in that said sensitive means (d) comprise devices adapted to reduce the duration of each periodic excitation of said tuned circuit in response to an increase in the level of said output.   5. An improved power conversion and regulation circuit of the kind comprising a tuned circuit (21) means for periodically energizing said step circuit (219 1 1 from a DC source, (34) so as to generating AC current in that circuit, means coupled to said tuned circuit, (21) for receiving an output in response to said AC current, and   means responsive to said output for modifying the excitation   periodically said tuned circuit according to the level of said output characterized in that there is provided means for causing said excitation of the tuned circuit (21) to occur at a fixed rate in order to generate in this tuned circuit ' an alternating current of constant frequency, and means to ensure that the duration of each periodic excitation increases as the level of the output decreases, and decreases at   as the level of said output increases.   6. A process of energy conversion and regulation   characterized in that the phases consisting of a) providing a tuned circuit, (21) b) periodically exciting said tuned circuit (21).   from a DC power source (34) to pro-   dulre in this circuit an alternating current of constant frequency, c) receiving an output in response to said alternating current produced in said tuned circuit, (21), and d) in relation to said output, modifying the duration of each periodic excitation of said tuned circuit ( 21)   function of the level of said output.   A method of converting and regulating energy according to Claim 6, characterized in that the step b) comprises selectively connecting said tuned circuit (21) to said DC source, (34) is said phase d) comprises maintaining each of the aforementioned connections for a period of time whose duration depends on the level of said output.   8. A method of converting and regulating energy according to claim 6, characterized in that said phase   (d) increase the duration of each periodic excitation   said tuned circuit (21) in response to a decrease the level of said output.   9. A method of converting and regulating energy according to Claim 6, characterized in that said phase d) consists in reducing the duration of each periodic excitation of said tuned circuit (21) in response to a   increasing the level of said output.