RU2588051C1 - Device for limiting charge current of load capacitor - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention can be applied to devices for limiting charge current of load capacitors, in particular, used for output voltage filtration from source designed to supply different DC loads. Device for limiting charge current of load capacitor comprises voltage source of direct current, switch, control unit, current setting device, time delay unit, current sensor, and terminals for connection of load capacitor, as well as reactor and diode.

EFFECT: reduced current loads on supply DC voltage source and load capacitor, and protection of supply voltage source from overload currents, which increases reliability of operation and widens field of device application.

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Description

The invention relates to electrical engineering, in particular to devices for limiting the charging current of a capacitor, in particular for limiting the charging current of a capacitor connected to an inverter input.

A device is known for limiting the charging current of a capacitor, (http://electrum-av.com/ru/, Novikov PA. A smooth charge of a capacitance: what to choose? Fig. 1).

A known device for limiting the charging current of a load capacitor consists of a resistor connected between a power source and a load capacitor, a relay with a make contact, connected in parallel with the resistor, and a control system that enables the relay to operate when the voltage on the load capacitor increases to a predetermined level or after a certain time from the moment of inclusion.

The disadvantages of the device are due to the fact that the relay coil in the main mode of operation of the device remains connected to the network, which reduces the resource of its operation and increases the likelihood of failure.

A device for limiting the charging current of a load capacitor, the closest in technical essence to the claimed device. (http://electrum-av.com/ru/, Novikov P.A. Smooth capacity charge: what to choose? Fig. 3) - prototype.

A known device for limiting the charging current of a load capacitor consists of a key, the power terminals of which are connected between the first output of the power source and the first output of the load capacitor, and the second output of the power source is connected to the second output of the load capacitor directly, and the control unit, the output of which is connected to the control terminal the key. When the power source is turned on, the control system generates control pulses in accordance with the specified algorithm, which causes a periodic key short circuit and a gradual charge of the load capacitor with a corresponding limitation of the charging current value.

A disadvantage of the known device for limiting the charging current of the load capacitor is due to the fact that it does not control pulsed values of the charge current in the intervals of the key conductivity. However, when combining the process of charging a load capacitor with possible random changes in the voltage of the power source in the form of voltage spikes, the limitation of the charge current will differ from the programmed one, and the amplitude of the current pulses at individual switching intervals can exceed the permissible value.

The basis of the claimed invention is tasked to eliminate this drawback, i.e. introduce a limitation of the charge current, thereby increasing the reliability of the device, and also introduce the function of protection against overload currents in the steady state after the end of the charge of the capacitor.

The problem is solved in that in the device for limiting the charging current of the load capacitor containing a DC voltage source, a key and a control unit, the output of which is connected to the control input of the key, and the first output of the DC voltage source is connected to the first terminal of the key, the device is additionally introduced a current setpoint, a current sensor, a reactor, a diode and a time delay unit, while the second terminal of the key is connected through the reactor to the first terminal for connecting the load capacitor, the second terminal is a voltage sensor through a current sensor is connected to a second terminal for connecting a load capacitor, the output of the current setting device is connected to the first input of the control unit, and the output of the current sensor through a time delay unit is connected to the second input of the control unit, between the second output of the switch and the second output of the voltage source A direct current diode is connected by a cathode to the second terminal of the switch.

In the claimed device for limiting the charging current of the load capacitor, the common essential features for him and for his prototype are:

- DC voltage source;

- key;

- Control block;

- the output of the control unit is connected to the control input of the key;

- the first terminal of the DC voltage source is connected to the first terminal of the switch.

A comparative analysis of the essential features of the claimed device for limiting the charging current of the load capacitor and its prototype shows that the first, in contrast to the prototype, has the following distinctive features:

- introduced a current sensor connected between the second terminal of the DC voltage source and the second terminal for connecting the load capacitor;

- a current setting device has been introduced, the output of which is connected to the first input of the control unit;

- a time delay block has been introduced through which the output of the current sensor is connected to the second input of the control unit;

- a reactor is connected between the second terminal of the key and the first terminal for connecting the load capacitor;

- introduced a diode connected between the second terminal of the key and the second terminal of the DC voltage source by the cathode to the second terminal of the key.

The sign: "... a current sensor is inserted, connected between the second terminal of the DC voltage source and the second terminal for connecting the load capacitor" provides a measurement of the charging current of the load capacitor.

The signs "... a current setting device is introduced, the output of which is connected to the first input of the control unit, ... a time delay unit is introduced, through which the output of the current sensor is connected to the second input of the control unit", the mismatch between the set value of the charging current of the load capacitor and the actual its value and maintaining by the control unit a predetermined level of current limitation, and the time delay unit in the current feedback circuit between the output of the current sensor and the second input ohm control unit allows to obtain the desired value of the frequency and amplitude of the charging current fluctuations in the transient charge load capacitor.

The sign "... a reactor is connected between the second terminal of the switch and the first terminal for connecting the load capacitor, ... a diode is connected between the second terminal of the switch and the second terminal of the DC voltage source by the cathode to the second terminal of the switch" provides a sequential voltage increment on the load capacitor in the process its charge with a limitation of the amplitude of the current pulse in the range of key conduction.

Based on the foregoing, we can conclude that the set of essential features of the claimed invention has a causal relationship with the achieved technical result, i.e. Thanks to this combination of essential features of the invention, it became possible to solve the problem - introducing a limitation of the charge current, thereby increasing the reliability of the device, as well as additionally introducing the function of protection against overload current in the steady state mode after the end of the charge of the capacitor.

 These essential features that distinguish the claimed device for limiting the charging current of the load capacitor from the prototype, together with the features common to it and the prototype, ensure the achievement of the claimed technical result in all cases to which the scope of legal protection applies.

The invention is illustrated by drawings, where in FIG. 1 is a functional diagram of a device for limiting the charging current of a load capacitor; FIG. 2 - graphs of the voltage change across the load capacitor and the load current, taken during the full-scale experiment.

A device for limiting the charging current of a load capacitor from a DC voltage source 1 contains a key 2, a control unit 3, a current setting device 4, a time delay unit 5, a current sensor 6, a reactor 7, a diode 8, and terminals 9, 10 for connecting a load capacitor, wherein the first output of source 1 is connected to the first output of key 2, the second output of key 2 through reactor 7 is connected to the first terminal 9 for connecting a load capacitor, the second output of source 1 through a current sensor 6 is connected to second terminal 10 for connecting condensate load, the output of the current setting device 4 is connected to the first input of the control unit 3, the output of the current sensor 6 through the time delay unit 5 is connected to the second input of the control unit 3, and the output of the control unit 3 is connected to the control input of the key 2, and between the second output of the source 1 and the second output of the key 2 is connected by a diode 8 cathode to the second output of the key 2.

A device for limiting the charging current of a load capacitor operates as follows.

When you turn on the DC voltage source 1 at the initial time, the current in the capacitor charge circuit is less than the set limit level, therefore, switch 2 is in the closed state. The current begins to increase, and its rate of change is limited due to the smoothing effect of the reactor inductance 7. The measured value of I _{T of the} charging current from the output of the current sensor 6 through the time delay unit 5 is fed to the second input of the control unit 3, where it is compared with a given level I _{ЗТ of the} charging limit current, which is supplied to the first input of the control unit 3 from the output of the current setting device 4.

As a result, depending on the mismatch sign Δ = I _ЗТ -I _Т , the key 2 is self-oscillating. The delay of the current feedback signal carried out in block 5 causes an increase in the mismatch A, at which the key 2 is switched, and, at the same time, reduces the switching frequency of the charge circuit to the desired value. This property allows you to provide an acceptable range of oscillations of the charging current I _T relative to the level of the specified limit I _ZT and reduce switching losses on the key 2 to the desired value in the transient charge capacitor of the load.

In the interval of conductivity of the key 2, the load capacitor current I _T of the load flows from the direct current source 1 through the public key 2 and reactor 7, which causes a voltage increment in the load capacitor while limiting the current rise rate due to the smoothing effect of the reactor inductance 7. In the interval of the key 2 pause the energy of the reactor 7 is discharged through the load capacitor and diode 8, and in each interval, the instantaneous value of the current I _T is measured by the current sensor 6. With each subsequent switching pulse, the voltage on the load capacitor increases and if the voltage of the source 1 and the voltage on the capacitor are equal, the switching process of the switch 2 stops, while the switch 2 remains in the closed state.

In the event of an overload of source 1 or a short circuit in the load circuit, the current limiting process occurs similarly, i.e. when the current consumption I _T from source 1 increases and its value reaches the set limit I _ZT , a self-oscillating mode of switching key 2 occurs with automatic duty cycle adjustment so that the current consumed from source 1 is maintained within the deviation Δ = I _ZT -I _T from the level set restrictions. When overload is removed, the device automatically returns to the stationary operating mode.

In FIG. 2 is a screenshot of an oscilloscope showing the transient process of connecting the device to a DC voltage source 1, where I (t) and U (t) are graphs of changes in the charging current and voltage across the load capacitor, respectively. The turning-on time is indicated by t ₀ , the time t ₁ corresponds to the completion of the self-oscillation mode of the key with the charging current limited to I _max , from the moment t _{2 the} device goes into stationary mode with steady currents I ₀ corresponding to the connected device load, and the voltage across the capacitor reaches steady-state value U ₀ equal to the voltage of the power source.

Claims (1)

A device for limiting the charging current of a load capacitor containing a DC voltage source, a key and a control unit, the output of which is connected to a control input of the key, and the first output of the DC voltage source is connected to the first output of the switch, characterized in that the task device is additionally introduced a current sensor, a current sensor, a reactor, a diode and a time delay unit, the second key terminal being connected through the reactor to the first terminal for connecting the load capacitor, the second source terminal the voltage through the current sensor is connected to the second terminal for connecting the load capacitor, the output of the current setting device is connected to the first input of the control unit, and the output of the current sensor through the time delay unit is connected to the second input of the control unit, between the second output of the switch and the second output of the voltage source A direct current diode is connected by a cathode to the second terminal of the switch.

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