EP1036432A1

EP1036432A1 - Capacitor supply unit

Info

Publication number: EP1036432A1
Application number: EP98963437A
Authority: EP
Inventors: Marco Honsberg
Original assignee: Leopold Kostal GmbH and Co KG
Current assignee: Leopold Kostal GmbH and Co KG
Priority date: 1997-12-06
Filing date: 1998-11-10
Publication date: 2000-09-20
Also published as: JP2002509690A; US6366058B1; DE19754239A1; AU1871699A; BR9810539A; WO1999030408A1

Abstract

The invention relates to a capacitor supply unit, comprising a charging capacitor for charging up another capacitor (storage capacitor) for operating an electrical consumer, a rectifier (4, 5) which is located between the charging capacitor (2) and the storage capacitor (3), and a switching element (6, 12) which is located between the charging capacitor (2) and the storage capacitor (3) in circuit terms. Said switching element (6, 12) has a control input (7) to which the output of a switching time determining element (9) is applied. The switching time determining element (9) is subjected to a reference voltage Uprot which is small in comparison with the alternate current supply voltage U SIMILAR , and determines the instant at which the switching element (6, 12) switches from a switch position in which the storage capacitor (3) is charged to a switch position in which the charging process is interrupted, according to the voltage Us being applied to the charging capacitor (2) at the output end. The output of a charge status determining element (10) for determining the charge status of the storage capacitor (3) is also applied to said control input (7). Interconnected to represent a logical AND operation, the interconnecting switching time determining element (9) and the charge status determining element (10) act upon the control input of the switching element (6, 12) in such a way that both switching operations of the switching element (6, 12) - switching the capacitor supply unit (1) into charging mode or switching the same to interrupt the charging process - take place at a time when the voltage Us being applied to the charging capacitor (2) at the output end is less than or equal to the reference voltage Uprot.

Description

Capacitor power supply

The invention relates to the field of power supplies for supplying electronic assemblies. In particular, the invention relates to a condenser power supply comprising a charging capacitor for charging a further capacitor (storage capacitor) for operating a current consumer, a rectifier arranged between the charging capacitor and the storage capacitor and a switching means arranged in terms of circuitry between the charging capacitor and the storage capacitor with a control input at which Control input, the outputs of a switching time determination element, which is acted upon with a reference voltage that is small compared to the AC line voltage, for determining the switching time for switching the switching means from a switch position charging the storage capacitor into a switch position interrupting the charging process, depending on the voltage present on the output side of the charging capacitor and a charging state determination element for determining the Charge state of the storage capacitor present. The invention further relates to a method for operating a capacitor power supply.

Capacitor power supplies are often used to generate auxiliary power supplies that are not separated from the mains. Such auxiliary voltages are usually used to supply electronic assemblies, for example to supply the electronics used for speed control of drilling machines. The principle of a capacitor power supply is based on the cyclical recharging of the charging capacitor, which serves as a charge pump for the storage capacitor and charges the latter during each network cycle. A breakdown diode is used to stabilize such a capacitor power supply. In the context of these statements, the term breakdown diode refers to all diodes which are reverse-biased and are also known as zener diodes or avalanche diodes. For small output powers with an almost constant load, capacitor power supplies are widely used due to their simple and inexpensive design. However, the use of such a capacitor power supply is problematic if the load is relatively large and the operating point is subject to strong fluctuations. This load change can lead to an extreme load on the breakdown diode, which can ultimately lead to destruction of both the breakdown diode and the storage capacitor and thus the entire power supply. This effect is particularly serious when such a capacitor power supply is cast in a housing, for example, so that the heat occurring in the breakdown diode cannot be dissipated, or can be dissipated only to a very inadequate extent, so that the thermal load can lead to unsoldering of the breakdown diode . The capacitor power supply is then no longer functional.

To reduce these disadvantages, capacitor power supplies have been developed, as described for example in DE 38 01 399 A1, in which the switching process for switching the switching means from a switch position charging the storage capacitor into a switch position interrupting the charging process is provided at a point in time at which the Switching means is only slightly energized. Consequently, no steep switching edges should be generated in this switching process. This is achieved in that a control device is connected upstream of the switching means, by means of which control device the switching means is brought into its switch position which interrupts the charging process when the voltage on the output side of the charging capacitor is correspondingly low to the cycle of the mains voltage. At such a switching time, the switching means is only slightly energized. This capacitor power supply is switched back to the charging mode when the output voltage of the storage capacitor falls below a predetermined target value. This switching process depends solely on the state of charge of the storage capacitor and can therefore be carried out at any time with regard to the cycle of the mains voltage. Even if the switch at this point in time can at best only be under a low voltage, the switching means is, however, supplied with a relatively high current, so that generation of current peaks cannot be ruled out. If the current consumer is operated continuously, the required current is continuously drawn from the storage capacitor. Through the control of the switching means described in this document, it is continuously switched back and forth between the two operating positions in accordance with the frequency of the network cycle or the rectified voltage half-waves. Because of the power loss that occurs, in particular when the switching means is switched to the charging mode of the storage capacitor, there is a risk that the electronic components can be heated up to their destruction.

Based on this discussed prior art, the invention is therefore based on the object of providing a capacitor power supply unit which is also suitable for continuous operation of the current consumer connected to it.

Another object of the invention is to provide a corresponding method for operating a capacitor power supply.

According to the invention, the device-related object is achieved in that the switching time determination element and the state of charge determination element, which represent a logical AND function, interconnected and act on the control input of the switching means, so that both switching operations of the switching means - the switching of the capacitor power supply to the charging mode or the switching thereof Interruption of the charging operation - take place at a point in time at which the voltage applied to the charging capacitor on the output side is less than or equal to the reference voltage.

The method-related problem is solved according to the invention in that the method for operating a capacitor power supply with a switching means has the following steps, starting from a charging mode for charging a storage capacitor:

Comparing the phase-dependent voltage applied to a charging capacitor on the output side with a reference voltage,

- Providing a control signal with a switching time determination element for controlling the switching means when the applied Voltage is less than or equal to the reference voltage,

Determining the state of charge of the storage capacitor with a state of charge determination element,

Providing a control signal for controlling the switching means, if the state of charge of the storage capacitor is greater than a predetermined limit value, which steps relating to the state of charge can take place simultaneously with the steps relating to the switching instant,

- Switching the switching means for interrupting the charging process of the storage capacitor when both the state of charge of the storage capacitor exceeds a predetermined limit value and the voltage applied to the charging capacitor on the output side is less than or equal to the reference voltage and

- Switching back of the switching means to the charging mode when both the state of charge of the storage capacitor falls below or is equal to a predetermined limit value and the voltage applied to the charging capacitor on the output side is less than or equal to the reference voltage.

In the capacitor power supply unit according to the invention, the switching time determination element and the state of charge determination element are electronically connected to one another by a logical AND function and in this way act on the control input of the switching means. A switching process is therefore only triggered if corresponding control signals are present at the control input of the switching means both from the switching time determination element and from the state of charge determination element. The charge state determination element can provide two control signals, one of which represents the state of the storage capacitor, in which its output voltage is greater than a predetermined setpoint, reproducing the limit value of the output voltage, and another of which represents the state of the storage capacitor, in which its output voltage is less than or equal to the setpoint. If the first control signal is present, it is not necessary to recharge the storage capacitor. If, however, the latter control signal is present, it is no longer fully charged and can be reloaded. Actual actuation of the switching means, causing the capacitor power supply in its charging mode is switched to charge the storage capacitor, however, only takes place when a control signal is provided by the switching time determination element in which it is ensured that the switching means is currentless or quasi currentless. For this purpose, the switching time determination element is acted upon by a reference voltage which is very low compared to the mains alternating voltage, advantageously about 0 V or equal to 0 V. The control signal of the switching time determination element is provided when the voltage applied to the charging capacitor on the output side is less than or equal to the reference voltage. This ensures that the switching means is only switched when the switching means is de-energized or essentially de-energized. Furthermore, the logical AND operation of the two control signals acting on the control input of the switching means causes the switching means not to be switched when the power consumption connected to the capacitor power supply is in continuous operation, but to remain in its open position, which represents the charging operation of the capacitor power supply until the operation of the power consumer has been stopped and the output voltage at the storage capacitor has exceeded the setpoint due to the recharging.

Due to the selection of the switching times and the low number of switching operations compared to known capacitor power supply units, the capacitor and the network are only exposed to a very low pulse load with regard to the electromagnetic compatibility, which can be far below the prescribed limit value.

The capacitor power supply according to the invention thus implements a principle of controlled recharging of the storage capacitor using a soft switching process to interrupt and switch on the charging process. Therefore, the capacitor power supply is subject to only insignificant heating even with relatively large loads that fluctuate depending on the operating point. Such a capacitor power supply can thus also be used to control a relay, for example, without having to take additional cooling measures. A comparator element is expediently provided as the switching time determination element, by means of which the applied voltage is compared with a predetermined reference voltage as a function of the phase of the voltage curve. The reference voltage is selected so that it represents a voltage in the region of the zero crossing of the voltage curve present on the output side of the charging capacitor. A particularly favorable reference voltage is 0 V, so that actuation of the switching means is only possible when the switching means is de-energized.

It is particularly expedient to provide the elements required for the capacitor power supply as electronic circuits or switching elements. If such a capacitor power supply is provided, an electronic semiconductor switch, in particular a thyristor, is advantageously used, at the gate of which the outputs of the switching time determination element and the state of charge determination element are present. Depending on the configuration of the capacitor power supply, it may be expedient for the control input of the switching means to be preceded by a memory element for storing the control signals generated by the switching time determination element and the charging state determination element. In this connection it should be noted that the use of a thyristor is exemplary and that other equivalent electronic switching means, such as triacs, can also be used.

In a capacitor power supply unit with electronic components, the switching time determination element implemented by a circuit and the state of charge determination element likewise implemented by a circuit are connected in the form of an AND function (a so-called wired AND function). The reference voltage can be applied externally to the switching time determining element or - as provided in a preferred exemplary embodiment - by a zener diode assigned to the switching time determining element.

Further advantages and developments of the invention are part of further subclaims and the following description of a preferred exemplary embodiment. Show it: 1: a schematic block diagram of a capacitor power supply with a switching means in charging mode,

2: the capacitor power supply unit of FIG. 1 in its position which interrupts the charging operation,

Fig. 3: a circuit diagram of a capacitor power supply according to the in

Figures 1 and 2 block diagrams shown and

4: a plurality of state and condition diagrams arranged one above the other to illustrate the condition-dependent switching of a switching means used in a capacitor power supply according to FIGS. 1 to 3.

FIG. 1 shows a capacitor power supply 1 in a schematic block diagram. The capacitor power supply 1 comprises a charging capacitor 2 which is arranged for charging a storage capacitor 3. The capacitance of the storage capacitor 3 is many times greater than the capacitance of the charging capacitor 2. The ratio of the two capacitors to one another is coordinated such that the ripple of the output voltage U _{a of} the storage capacitor 3 is limited to the required value specified by the load . Two diodes 4, 5 are provided for rectifying the AC voltage U_ applied to the network. Consequently, this rectifier 4, 5 provides voltage half-waves separated in time by one voltage half-wave.

In terms of circuitry, a switching means 6 is arranged between the charging capacitor 2 and the storage capacitor 3, which is in its position shown in FIG. 1 in the position “0” for charging the storage capacitor 3. The switching means 6 has a control input 7 at which the output of a memory element 8 is connected. The memory element 8 is acted upon by the control signals of both a switching time determination element 9 and a state of charge determination element 10. The switching time determination element 9 is connected on the input side to a charging line 11 connecting the charging capacitor 2 and the storage capacitor 3 via the diode 5 , the tap provided on the charging capacitor side in front of the diode 5 is. The input of the state of charge determination element 10 is arranged for tapping the output voltage of the storage capacitor 3.

The switching time determination element 9 compares the voltage U _{s present} in the charging line 11 with a reference voltage U _prot , which is either present at another input of the switching time determination element 9 or is provided electronically. The switching time determination element 9 then generates a control signal which is passed on to the switching means 6 when the voltage U _{s of} the charging line 11 is less than or equal to the reference voltage U _prot . In the exemplary embodiment shown, the reference voltage U _prot is 7 V. In order that the switching means 6 is actually switched from the “0” position to the “1” position that interrupts the charging process (as shown in FIG. 2), provision or generation is also required a control signal of the charge state determination element 10. This then generates a control signal when the tapped output voltage U _{a of} the storage capacitor 3 exceeds a predetermined limit value U _max . The memory element 8 transmits a control signal to the switching means 6 for switching it from the position "0" to the position "1" when the two AND-linked conditions mentioned are met.

If both conditions are met, the switching means 6 switches to the "1" position, as a result of which the charging process of the storage capacitor is interrupted by diverting the current flow to the ground. By switching at a time when the phase of the Voltage curve in the region of its zero crossing - in the illustrated embodiment at a voltage <± 7 V - there is no risk of overcurrent peaks which could lead to the destruction of the switching means 6; likewise, the network and the capacitor power supply 1 is only one exposed to low pulse loads.

The capacitor power supply 1 switches back to the charging mode recharging the storage capacitor 3 when both the output voltage U _{a of} the storage capacitor 3 drops below the limit value U _max and a control signal is provided by the switching time determination element, according to which the output side is connected to the charging capacitor. voltage U _{a is} less than or equal to the reference voltage U _prot .

FIG. 3 shows the circuit diagram of the capacitor power supply 1 in one embodiment. A thyristor 12 serves as switching means, the gate 13 of which is connected to the outputs of the switching time determination element 9 and of the charge state determination element 10. The switching time determination element 9 is implemented by two resistors R1, R2, a diode D2, a Zener diode Z1 and a transistor T1 as an inverter. The reference voltage of 7 V is provided by the Zener diode Z1 in the switching point determination element 9 shown. The state of charge determination element 10 is implemented by two resistors R3, R4 and a Zener diode Z2. The two rectifying diodes are identified by the reference numerals 4 and 5.

In addition, in the exemplary embodiment shown, a choke L1 is arranged on the output side of the charging capacitor 2 to limit the current rise in the first switch-on moment of the device and the critical current rise of the thyristor 12 in the stationary case. From the circuit diagram shown in FIG. 3, it can be seen that the switching time determination element 9 and the charge state determination element 10 represent, in terms of circuitry, a UN D link - a so-called wired AND function.

In the diagrams of FIG. 4, time is plotted in the direction of the x-axes and voltages or states are plotted on the y-axes. The top diagram shows the profile of the voltage U _a applied to the storage capacitor 3 on the output side _, the profile of the voltage U _s applied to the charging capacitor 2 on the output side, the reference voltage U _prot and the limit value of the output voltage U _max (setpoint) of the storage capacitor 3. The time interval in which the condition that the output voltage U _{a of} the storage capacitor 3 is greater than the limit voltage U _max can be seen in the diagram below. The times in which the further condition is fulfilled that the voltage U _s <U _{prot applied to} the charging capacitor 2 is shown in the third diagram. The two diagrams below show the time period in which the switching means is energized and the switch status. The voltage diagram U_ on the mains side is shown in the bottom diagram.

Starting from a state of the storage capacitor 3 in which its output voltage U _a <U _max , the capacitor power supply 1 is in its charging mode for charging the storage capacitor 3. At time t, the voltage U _{a present} on the output side at the storage capacitor 3 exceeds the limit value of Output voltage U _max , so that one switching condition U _a > U _max for switching the capacitor power supply 1 or its switching means 6, 12 is fulfilled. Switching of the switching means 6, 12 takes place, however, only at a point in time when the further condition U _s U U _{prot is} fulfilled. This point in time is identified as t ₂ . As a result of the fulfillment of the two conditions necessary to interrupt the charging operation, the switching means 6, 12 is closed; the switch state from this point in time in position "1" (see FIG. 2).

The maximum of the voltage U _a or U _s corresponds to the maximum in time of the voltage curve U_ applied to the network. The voltage U _{s present} on the output side at the charging capacitor 2 drops with the cycle of the mains voltage U_ until this voltage U _s falls below the value of the reference voltage U _prot at the instant t ₂ . In the cycle of the voltage curve U_ applied to the network, the voltage U _s at time t ₃ , which represents the negative maximum of the voltage curve U_ in this cycle, exceeds the reference voltage U _prot . Starting at time t ₃ , the switching means 6, 12 is energized. It is now not possible to actuate the switching means 6, 12, since the condition U _s <U _{prot is} not fulfilled in this period.

As the output voltage U _{a of} the storage capacitor 3 decreases, it falls below the limit value U _max at the time t ₄ . Beginning at time t ₄ , the condition for switching the switching means 6, 12 to the charging mode is therefore fulfilled again. However, switching of the switching means 6, 12 at time t ₄ is not possible, since the further condition U _s <U _{prot is} not met at this time. Only at the time of the next positive ven maximum of the line voltage curve U_ - the time t ₅ - the voltage U _{s present} on the output side at the charging capacitor 2 drops again below U _prot . Only at this point in time t ₅ is the further condition U _s <U _{prot also} met, so that the switching means 6, 12 now switches to its charging position “0” again.

In a further exemplary embodiment, not shown in the figures, which is essentially designed in accordance with the exemplary embodiment shown in FIG. 3, a capacitor is connected in parallel with the resistor R2. This causes a time delay of the time t ₂ shown in FIG. 4, so that a switching operation is only possible when U _{s is} less than U _prot .

When using such a capacitor, provision can also be made to use the low switch-on voltage - for example 0.7 V - of the transistor T1 shown in FIG. 3 as a quasi-indirect reference _voltage , U _prot then assuming the value of 0 V. In such a case, it is not necessary to use the diodes Z1, D2. The delay in the switch-on possibility caused by the use of said capacitor ensures that a switching operation is only carried out if the phase of U _{s is} less than U _prot , where U _prot corresponds to an assumed voltage of 0 V. In this case, U _s is negative. Therefore, there is no current supply in the switching means at the time of switching, so that no current peaks can be generated during a switching operation.

Compilation of the reference symbols

1 capacitor power supply

2 charging capacitor

3 storage capacitor

4 diode

5 diode

6 switching means

7 control input

8 memory element

9 switching time determination element

10 state-of-charge determination element

11 charging line

12 thyristor

13 gate

R1 resistance

R2 resistance

D2 diode

Z1 zener diode

T1 transistor

R3 resistance

R4 resistance

Z2 zener diode

L1 choke

U _s input voltage

U _a output voltage

Uprot reference voltage u _max limit value of the output voltage

Claims

claims

1. capacitor power supply comprising a charging capacitor for charging a further capacitor (storage capacitor) for

Operating a current consumer, a rectifier (4, 5) arranged between the charging capacitor (2) and the storage capacitor (3) and a switching means (6, 12) arranged between the charging capacitor (2) and the storage capacitor (3) in terms of circuitry Control input (7), at which

Control input (7) the outputs of a switching time determination element (9) which is acted upon by a reference voltage (U _prot ) which is small compared to the mains alternating voltage (U_) for determining the switching time for switching the switching means (6, 12) from a switch position charging the storage capacitor (3) to a the switch interrupting the charging process as a function of the voltage (U _s ) present on the output side of the charging capacitor (3) and a state of charge determining element (10) for determining the state of charge of the storage capacitor (3), characterized in that the

Switching time determination element (9) and the state of charge determination element (10), representing a logical AND function, interconnected and act upon the control input of the switching means (6, 12), so that both switching operations of the switching means (6, 12) - the switching of the capacitor power supply (1) in the

Charging mode or the switching thereof to interrupt the charging mode - take place at a time when the voltage (U _s ) applied to the output capacitor (2) is less than or equal to the reference voltage (U _prot ).

2. Capacitor power supply according to claim 1, characterized in that the output voltage of the storage capacitor (3) can be detected by the state of charge determination element (10).

3. Capacitor power supply according to claim 1 or 2, characterized in that an electronic semiconductor switch (12) is provided as switching means.

4. Capacitor power supply according to claim 3, characterized in that the semiconductor switch (6) is a thyristor (12), at the gate (13) of which the outputs of the switching time determination element (9) and the charge state determination element (10) are present.

5. capacitor power supply according to one of claims 1 to 3, characterized in that the control input (7) of the switching means (6, 12), a memory element (8) is connected upstream.

6. capacitor power supply according to one of claims 1 to 5, characterized in that the reference voltage (U _prot ) is in the range of 0 V or 0 V.

7. Capacitor power supply according to claim 6, characterized in that the reference voltage is 0 V and the switching voltage for actuating the switching means is the switch-on voltage of a transistor arranged in the switching time determination element.

8. A method for operating a capacitor power supply (1) with a switching means (6, 12), comprising the following steps starting from a charging mode for charging a storage capacitor

(3):

Comparing the phase-dependent voltage (U _s ) present on the output side of a charging capacitor (3) with a reference voltage (U _prot ),

- Providing a control signal with a switching time determination element (9) for controlling the switching means (6, 12) when the applied voltage (U _s ) is less than or equal to the reference voltage (U _prot ),

- Determining the state of charge of the storage capacitor (3) with a state of charge determination element (10),

- Providing a control signal for controlling the switching means (6, 12) when the state of charge of the storage capacitor (3) is greater than a predetermined limit value (U _max ), which the

Charging state-related steps can take place simultaneously with the steps relating to the switching time, - Switching the switching means (6, 12) to interrupt the charging process of the storage capacitor (3) when both the state of charge of the storage capacitor (3) exceeds a predetermined limit value (U _max ) and the voltage (U _s. ) On the output side of the charging capacitor (2) ) is less than or equal to the reference voltage (U _prot ) and

- Switching back of the switching means (6, 12) to the charging mode if both the state of charge of the storage capacitor (3) falls below or is equal to a predetermined limit value (U _max ) and also the output side of the charging capacitor

(2) applied voltage (U _s ) is less than or equal to the reference voltage (U _prot ).

9. The method according to claim 8, characterized in that the reference voltage is in the near-phase region of the zero crossing of the voltage curve (U _s ) applied to the output capacitor (2) or is equal to zero.

10. The method according to claim 8 or 9, characterized in that the switching means (6, 12) controlling control signals are buffered before or when they are applied to the control input (7) of the switching means (6, 12).