WO2005096484A1

WO2005096484A1 - Method for recharging a dc link

Info

Publication number: WO2005096484A1
Application number: PCT/EP2005/003143
Authority: WO
Inventors: Michael Sleven; Jürgen Lamparter
Original assignee: Bosch Rexroth Ag
Priority date: 2004-03-30
Filing date: 2005-03-24
Publication date: 2005-10-13
Also published as: DE102004016062A1

Abstract

Disclosed is a method for charging a DC link capacitor (13). The aim of the invention is to create a method that ensures gentle charging of the capacitor (13) while reducing the number of components required and ensuring operation that is as protected as possible. Said aim is achieved by the fact that a sequence control system (10) causes the capacitor (13) to be charged during a precharging stage by means of an active valve (11) while said sequence control system (10) monitors the DC link voltage and opens or blocks active valves (11) in accordance with a comparison between at least one setpoint value and an actual value.

Description

Method for charging a DC link

The invention discloses a method for charging a DC intermediate circuit according to the preamble of claim 1.

10 DC intermediate circuits of drive controllers, power converters or frequency inverters contain a smoothing capacity which usually does not contain any charge or only a partial charge before commissioning. Therefore, before connecting a load, it must be ensured that the capacity is at the desired level

15 DC link voltage is precharged, for example to prevent a short circuit or an excessive current increase that may be harmful to components when the mains voltage is switched on. Typical values for the intermediate circuit voltage are 560 volts (- 15%) to 800 volts (+ 10%), whereby a function must be guaranteed both at 50 heart (EUROPA) and at 60 Hz (USA) mains frequency.

20., ^• DE 197 10 371 Cl shows a charging device for the intermediate circuit capacitor of an intermediate circuit connected to a semi-controlled three-phase bridge circuit, which operates by means of a charging resistor R ade) and by means of the diodes (D1-D3) which become thyristors (Thl-Th3) after completing the

25 charging process ignited. The Norladesistor R de used here, as a rule, has very large dimensions (10-30 cm) relative to the other components, quickly becomes very hot, generates power loss and increases the risk of fire.

The invention is based on the object of specifying a method for the gentle charging 30 of the capacitance of a DC intermediate circuit, the component expenditure should be kept as low as possible and operation which is largely secured should be ensured.

5

BESTÄTIGUΝGSKOPIE This object is achieved in that a sequence control causes the capacity to be charged by means of an active valve during a precharging stage, and the sequence control monitors the intermediate circuit voltage and enables or blocks active valves in accordance with a comparison between at least one setpoint and one actual value. This has the advantage that the precharging gently charges the capacitance, with no precharging resistance being required and thus the component expenditure being kept as low as possible. The requirement for reduced component expenditure is primarily met by the electrically controlled precharging without the need for additional components, which further results in a reduced printed circuit board area.

Monitoring the DC link voltage ensures largely safe operation and enables the device to be switched off in the event of a fault, which makes the DC link practically short-circuit proof, causes gentle handling of the components, and minimizes the risk of burn-up in the event of a fault. All in all, the process protects the components of the circuit from one. Destruction. The comparison of target and actual values can also include temporal processes, so that a certain value must have occurred within a certain period. ^' This period is then taken into account in the monitoring.

As a decision criterion for switching valves on or off, an actual value is expediently derived from the intermediate circuit voltage and a setpoint value is derived from the mains voltage. For a release of the active valves, for example, the correspondence between the DC voltage in the intermediate circuit and a setpoint value derived from the line voltage could be decisive, this setpoint value preferably corresponding to the rectification value of the line voltage. The rectification value is the average of all function values that occur with a rectified, periodic variable within a period. When using the rectification value of the mains voltage, a good orientation value is obtained for measuring the charge required to be introduced into the capacitance. To implement this, a comparator can detect the mains voltage and compare it with the DC link voltage, hereinafter referred to as ZKS, during the charging process. Only when the ZKS at least 90% the mains voltage has reached, the comparator responds and ends the precharging process. As long as the threshold is not reached, reloading or possibly! another predeterminable measure is initiated after a definable time.

It is also advantageous to block the active valves because of the failure of at least one network phase and / or one that has been derived from the intermediate circuit and has not been reached

Actual value and / or a monitoring of the voltage rise dU / dt on the

DC link capacity to e.g. positive change. In this way, sources of error can be detected prematurely, evaluated and appropriate countermeasures initiated.

A pre-charge despite a possible short circuit could thus be prevented. During the entire precharging process, which can usually be between 2-5 seconds as described below, the DC link should be checked for an existing short circuit by analyzing it for a positive voltage change du / dt.

A phase failure in the nominal voltage range from 340 volts to 550 volts is recognized as follows. Two phase voltages (U / V and U / W) measured by means of differential amplifiers are monitored for a predefinable threshold by means of a comparator. If the threshold is undershot, which must be due to a phase failure, this is recognized by the comparator. A phase failure during the precharge leads to a termination of the precharge. If the phase can be regenerated again, a new precharge attempt is automatically initiated by the sequence control. This is particularly important because otherwise the progressive ignition angle (see also below) would result in a very large surge current.

Disadvantageously, during the second stage, i.e. in the case of feeding a connected load, the active valves are ignited in blocks regardless of the phase position of the mains voltage, because a network-independent release of the active valves with high frequency and. Using square wave signals, for example, minimizes the circuitry and power loss. If the bridge circuit is designed as a six-pulse bridge circuit (B6) with three branches and each branch as an active valve, a thyristor and as a passive valve, ie as a non-controllable valve, a diode, the first stage comprising a sequence control Phase gating control is carried out, which continuously changes the control angle to control the gate of a thyristor, then the manufacturing costs can be reduced. drastically reduce the arrangement on which the method is based and increase reliability due to the reduced number of components and the elimination of charging resistors. This results in a controlled precharge of the intermediate circuit capacitance via thyristors.

The control angle is expediently changed by a certain number of degrees and / or the charging time is dimensioned such that the voltage applied to the intermediate circuit capacitance. when the final value for the steering angle is reached essentially corresponds to the target value. This causes a "soft" charging of the intermediate circuit capacitance by limiting the charging current to avoid a short circuit within a predefinable charging time.

Specifically, the charging current is limited without influencing the current by continuously changing the control angle from 180 ° to 90 ° and / or the charging time is dimensioned such that the intermediate circuit capacity contains the desired precharge when a control angle of 90 ° is reached. The variable ignition and control angle adjustment for DC link pre-charging is used and components (diode bridge, pre-charging resistors) are saved.

The ignition timing for a thyristor in the proposed arrangement is derived directly from the current mains voltage, the voltage between two phases (U / W or U / V) as a trigger source depending on the direction of rotation of this 3-phase mains voltage (U / V / W) is used. For this purpose, both voltages are recorded using a differential amplifier. A subsequent circuit determines the direction of rotation and depending on this, either the phase voltage U / W or U / V is then used with the aid of a comparator to generate the ignition pulse. With the start of the pre-charging of the DC link capacitance is at the time ignited the zero crossing of the phases of the mains voltage. At this point the effective voltage at the thyristor = 0 volts and the current flow angle is zero. The comparison voltage Uref for the comparator at this time is equal to the mean value of the phase voltage U / W or U / V of the network. Now the comparison voltage Uref on the comparator is reduced during the precharging process. As a result, as the precharge progresses, the time of advance is continuously advanced and the current flow angle becomes larger. So it is related to the sine half-wave; fired earlier and earlier. The ignition angle therefore changes from 180 ° to 90 °. The comparison voltage Uref for the comparator is further reduced. When a control angle of 90 ° is reached, the pre-charging is finished. The control angle is adjusted more or less continuously. With a set slope of, for example, 280V / s and 560 volts DC link voltage (mains voltage 400V, 5GHz), there are 100 ignitions to cause a pre-charge within 2 seconds. The range of the ignition angle, which is passed through during the precharging, is 180 ° -90 ° = 90 °. This corresponds to a step size of 0.9 ° per ignition or per 5.6 volt step (see also below). If the voltage changes in 5.6 volt steps are continuously positive, the precharging process is maintained. , If the DC link voltage does not rise in the expected sequence of steps, a short circuit or other error in the DC link may be assumed, as already described above, and the charging process terminated. The remaining, not yet active, thyristors are only released when the intermediate circuit voltage has reached a certain setpoint, for example 85% of the peak value (more stationary value of the voltage in the intermediate circuit) of the mains voltage.

It is advantageous if the sequence control automatically selects the optimal ignition timing for the thyristors. According to the invention, the optimum ignition point is reached when the voltage between the anode and cathode of the thyristor is positive and has reached a desired amount ΔU. ΔU is calculated from the number of firing operations on the thyristors per second and the level of the mains voltage. Example: With 100 ignition processes and 400 volt mains voltage (560V intermediate circuit voltage), ΔU results in 560 volt. / 100 = 5.6 volts. The The DC link voltage rises by 5.6V per ignition process until it reaches 560V in steps of 5.6 volts and almost linearly.

An advantage of the invention is that the precharging time of the capacity during the first precharging stage brought about by the sequential control system is dependent on the amount of mains voltage. The precharge time is determined using the slope of the DC link voltage and its final value. This slope is, for example, 560 volts DC link voltage (at 400 V mains voltage) and .2 seconds precharge time 280 volts / s. The DC link capacity is charged with this slope. The advantage of this dependency is that this effect has a limiting effect on the maximum mains current. And theoretically, any precharge times can be realized. However, the shorter the precharge time, the higher the charging current and the demands on the supply network. Usual times are between 2 and 5 seconds with an assumed mains voltage of 400 to 600 V.

A relatively high cost saving per precharge circuit can be achieved if this DC link is used as an intermediate circuit of a drive controller for servomotors, a converter or a frequency converter in large quantities.

figure description

Figure 1 schematically shows an embodiment of the invention. A sequence control 10, active valves 11, passive valves 12, intermediate circuit capacitance (ZKK) .13, phases of the mains voltage 14 and lines 15 and a phase tap 16 can be seen.

FIG. 1 shows a three-phase arrangement for precharging a ZKK. The sequence control 10 is implemented as a thyristor driver, the active valves 11 are implemented by means of thyristors (Thl to Th3) and the passive valves 12 are implemented by means of diodes (D3 to D6). The diodes and thyristors are connected as a B6 bridge (six-flushing bridge) and feed the ZKK 13 depending on the operating mode (pre-charging or load case) over one, two or all three phases of the mains voltage 14. The thyristor driver grasps all phases of the mains voltage 14 by means of the phase tap 16 from to internally this to have available for phase detection.

When the mains voltages 14 are applied, the circuit of the thyristor driver 10 recognizes the direction of rotation of the network, which is important for correct synchronization. If all three phases in the nominal voltage range from 340V to 550 V are recognized as present, the direction of rotation of the network is initially saved as binary information. This storage can take place, for example, by means of a flip-flop. After saving, an asynchronous. Switching mechanism activated, for example a monostable multivibrator (monpflop), in order to initiate a first precharge of the ZKK for testing the DC link for a predefinable test time period (here around 500 ms). If it is recognized during this test phase that the voltage at the ZKK increases, the precharging process is continued, otherwise it is terminated and further measures are initiated if necessary. If it is aborted, there is either a fault in the network or in the intermediate circuit, for example a short circuit or a phase fault. If a DC link short circuit is detected, the precharging is stopped completely and immediately. A renewed precharge attempt is only started when all phases of the connected network 14 are present again. Under the. Assuming a correctly working circuit, the DC link is still checked for a possible short circuit during the entire precharge. The change in voltage at the ZKK is analyzed relative to time (requirement: du / dt> 0). If there is no short circuit, i.e. du / dt is always positive, the precharging continues until a setpoint for the voltage at the ZKK is reached. The nominal value is around 85% of the peak value of the mains voltage. During the precharge, a single thyristor selected for the precharge is activated in such a way that the control angle is continuously changed from 180 ° to 90 ° in accordance with a phase control, so that the desired charge is contained in the ZKK when a control angle of 90 ° is reached.

If the actual value and the setpoint are close to each other (preferably identity), the thyristor driver switches over from the precharging stage to the operating stage, which includes switching on all further thyristors 11, since the precharging is carried out only via one of the three thyristors 11.

As soon as the network 14 falls below a minimum voltage, this is recognized by the thyristor driver and the control is switched off. A new precharging process would only be started again when the mains voltage is at the permissible minimum value for the network under consideration (here 340 volts) or and continues to rise.

A phase failure after completion of the precharging process, i.e. in the event of a load, on the other hand does not lead to a change in the operating state, ie in this case the circuit continues to work undeterred. Due to the wide voltage range of the network 14 from 340 to 550 V, the circuit can be used both in the USA and in Europe, or in all other countries in which network voltages prevail in these areas. The field of application is very wide. The circuit is preferably used for charging the intermediate circuits of drive controllers, servomotors, converters or converters. reference numeral

Sequence control active valve passive valve DC link capacitor (ZKK) mains voltage phase connections phase tap

Claims

Expectations

1. A method for charging the capacitance of a DC voltage intermediate circuit, the charging being carried out at least by means of an alternating, in particular multiphase, mains voltage and a bridge circuit and each branch of the bridge circuit contains at least one active valve which is electrically controllable, characterized in that a sequence control (10) during a precharging stage, the capacitance (13) is charged by means of an active valve (11), the sequence controller (10) monitors the intermediate circuit voltage and, based on a comparison between at least one setpoint and one actual value, active valves (11) releases or blocks.

2. The method according to claim 1, characterized in that the actual value is derived from the intermediate circuit voltage and the setpoint is derived from the mains voltage.

3. The method according to any one of the preceding claims, characterized in that a blocking of the active valves (11) results from the failure of at least one network phase (14) and or an actual value derived from the intermediate circuit and / or monitoring of the voltage rise at the intermediate circuit capacitance ( 13).

4. The method according to any one of the preceding claims, characterized in that during the second stage (load case), the active valves (11) are controlled independently of the phase position of the mains voltage (14).

5. The method according to any one of the preceding claims, wherein the bridge circuit is a six-pulse bridge circuit (B6) with three branches and each branch as an active valve (11) a thyristor and as a passive valve (12), ie as a non-controllable valve, comprises a diode, characterized in that the precharging stage is carried out by means of a phase gating control circuit included in the sequence control (10), which continuously changes the control angle for driving the gate electrode of a thyristor (11).

6. The method according spoke 5 characterized in that the control angle is changed by a certain number of degrees and / or the charging time is dimensioned such that the voltage applied to the intermediate circuit capacitance (13) essentially corresponds to the desired value when the final value for the control angle is reached.

7. The method according to any one of claims 5 or 6, characterized in that the control angle is continuously changed from 180 ° to 90 ° and / or the charging time is dimensioned such that the intermediate circuit capacitance (13) on reaching a control angle of 90 ° the desired Contains subpoena.

8. The method according to any one of the preceding claims, characterized in that the sequence control selects the optimal ignition timing for the thyristors (11). ,

9. The method according to any one of the preceding claims, characterized in that the charging time is dependent on the mains voltage level.

10. The method according to any one of the preceding claims, characterized in that it is the DC link to the DC link

Drive controller for servomotors, a converter or a frequency converter.