Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/10—Regulating voltage or current 
  • G05F1/46—Regulating voltage or current  wherein the variable actually regulated by the final control device is DC
  • G05F1/56—Regulating voltage or current  wherein the variable actually regulated by the final control device is DC using semiconductor devices in series with the load as final control devices
  • G05F1/565—Regulating voltage or current  wherein the variable actually regulated by the final control device is DC using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor
  • G05F1/569—Regulating voltage or current  wherein the variable actually regulated by the final control device is DC using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for protection

Definitions

• the invention relates to a protective device for a power converter, preferably having a capacitive input, such as a power supply unit, inverter or DC voltage converter, which is adjustable with an energy source via a
• Resistor current limiting device is connected, the resistance value for protecting the power converter is changed as a function of the difference between the voltage present at the input of the protective device and the voltage present at the input of the power converter, where the adjustable resistor may have a fixed current limiting resistor stood in parallel.
• a protective device of a corresponding type is e.g. known from EP-A 0 250 158.
• the current limiting device in the known protective device consists of a fixed ohmic resistor, to which a transistor is connected in parallel as an adjustable resistor.
• the emitter-collector path of a bipolar transistor is connected in parallel to two resistors arranged in series.
• a further resistor is arranged in the emitter circuit of the transistor, through which the entire current fed into the power converter flows.
• the further resistor is connected at its connection not connected to the emitter via two diodes arranged in series with the base of the transistor, which is further connected to an operating voltage source powered by the power converter, which is supplied with voltage by an auxiliary winding of the transformer of the power converter.
• the capacitive input of the power converter is charged via the fixed resistor with a current that is limited in height by the resistance value, until the transistor is controlled by a base current.
• the transistor gradually saturates, so that most of the current flows through the transistor. If undesired high voltages occur at the input of the protective device when the transistor is saturated, the increasing current increases the negative feedback voltage in the emitter circuit of the transistor.
• the associated reduction in the base-emitter potential increases the resistance of the emitter-collector path, so that the emitter current in turn decreases.
• the current is therefore also limited when the input voltages on the protective device exceed the nominal voltage during operation of the power converter.
• the invention is based on the object of further developing a protective device of the type described at the outset such that, in particular, the power converter is protected against undesirably high voltages at the input.
• the charging of the energy-storing and capacitive input of the power converter should also take place more quickly even at input voltages below the nominal voltage on the protective device. .
• the adjustable resistor is an actuator in a voltage and current control loop, that the actual value of the voltage of at least one capacitive element of the power converter or of this itself and the actual value of the current from a shunt is tapped and that the voltage control loop, the current control loop is connected in parallel or subordinate.
• the shunt can also be replaced by an equivalent element such as a Hall generator.
• this can be made very high-impedance, so that the charging current can be limited to a desired small value when the energy source is switched on.
• the current control circuit subordinate or connected in parallel, causes a current corresponding to the current setpoint to flow in the adjustable resistor.
• the capacitor is therefore not only with the Charged current flowing through the charging current limiting resistor, whereby the charging is accelerated.
• a desired current profile can be achieved by coordinating the charging current limiting resistor and the current setpoint. .
• the voltage supply for the voltage and current control loop is obtained from the input voltage of the protective device.
• the voltage setpoint can preferably be set so high that even with the minimum value of the adjustable resistor, the maximum nominal input voltage is not sufficient for the voltage setpoint to be reached at the capacitor.
• the adjustable resistance then has its lowest value at the nominal input voltage, which results in the lowest current heat losses. This has a favorable effect on the efficiency of the
• the control circuit prevents the occurrence of high undesired voltages on the capacitive elements or the downstream circuits.
• the input voltage can therefore z. B. which according to VDE or. VG guidelines accept permissible peak voltages for the defined period of time without inadmissibly high voltages occurring on the capacitor itself or the downstream circuits, in particular the semiconductors.
• the value of the charging current limiting resistor preferably corresponds to the quotient of the maximum permissible static nominal input voltage and the no-load current flowing to the power converter at this nominal input voltage.
• An expedient embodiment consists in that the capacitive element and a voltage setpoint transmitter are connected to a comparison device, which is followed by a control amplifier to which an additional comparison device connected to a current actual value transmitter is connected, the Another control amplifier is connected downstream, the output of which feeds the control electrode of a transistor forming the actuator, which is arranged in series with the shunt.
• the active filter i.e. the protective device is supplied by a separate power supply, which in turn is obtained from the nominal input voltage, in particular in autonomous operation
• the protective device is switched to inactive in order to prevent idling currents from the energy source when the device is ready for operation.
• the capacitive laser is connected to a switching regulator for generating a regulated direct voltage, which contains a transformer which is connected to a
• Control amplifier is provided in the control loop of the active filter. De
• the active filter can be supplied, in particular in the case of autonomous operation, by its own voltage supply, which in turn is obtained from the nominal input voltage.
• an auxiliary voltage supplied to a chopper stage is fed from the supply voltage via the chopper stage and a transformer to the current control circuit voltage.
• the current limiting resistor can be omitted and by means of, for example. a remote-controlled switch-off signal, the active filter can be switched to inactive to prevent idle currents from the energy source while still ready for operation.
• Both the supply voltage for the voltage current control circuit and the downstream power stage or power stages can be immediately switched inactive via a remote control signal.
• one proposal is characterized in that the chopper stage is activated immediately with a remote control signal, and the power stage or power stages are activated with a time delay via a link to the minimum limit voltage.
• Actual voltage control variable (actual current value variable) and a voltage setpoint generator (current setpoint generator) are connected to comparison devices which are followed by control amplifiers, the outputs of which feed the control electrode of the transistor.
• the actual voltage value is measured on the capacitive element and the actual current value on the shunt.
• the current control loop can be replaced by a plurality of current control loops connected in parallel and each having the actuator.
• Fig. 1 is a block diagram of a protective device
• Fig. 2 the protective device according to Fig. 1 in self-sufficient operating mode.
• the invention is described using a power converter in the form of a power supply unit, without this being intended to impose a restriction.
• a power supply unit for generating a DC voltage contains a rectifier (1), e.g. a full-wave rectifier, which is fed by its AC voltage inputs with its AC voltage inputs (2), (3).
• the rectifier (1) is connected to the DC voltage outputs (4), (5) in each case to a charge current limiting resistor (6) and to the drain electrode of a field effect transistor (13), which has a drain-source path in series with one capacitive element (10) is placed, which is connected to the DC voltage output (5) of the rectifier (1).
• a switching stage consisting of the switching transistor (7) designed as a field-effect transistor and the transformer (9) is connected in parallel with the capacitive element (10), the capacitive element (10) being used in particular for smoothing and energy storage of the rectified AC mains voltage.
• a further rectifier not shown, along with smoothing devices, which feeds a load.
• the gate electrode of the field effect transistor (7) is connected to a control and regulating circuit (12) which actuates the field effect transistor (7) with pulse duration modulation in order to generate a regulated DC voltage at the output of the power supply.
• the control and regulating circuit (12) forms a switching regulator with the transformer (9), the rectifier on the secondary side of the transformer (9) as well as with the smoothing means and a voltage actual value transmitter.
• the control electrode of the transistor (13) is. connected to the output of a control amplifier (15) whose input is on a comparison device (16) is connected, which is connected to the current sensor (14) and via a resistor (17) to the output of another control amplifier (18).
• a voltage limiting device (19) e.g. Zener diode (19) connected.
• the control amplifier (18) is connected at its input to a comparison device (26) to which a voltage setpoint generator (20), e.g. a Zener diode, and a resistor (21) which connects one electrode (reference point (32)) of the capacitive element (10).
• a voltage setpoint generator (20) e.g. a Zener diode
• resistor (21) which connects one electrode (reference point (32)) of the capacitive element (10).
• the transformer (9) contains an auxiliary winding (22) which is arranged in series with a diode (23) which feeds a capacitor (24) on which the operating voltage for the control amplifiers (15), (18) is tapped.
• the capacitor (24) is arranged in parallel with the series connection of the auxiliary winding (22) and the diode (23), and has an electrode with the shunt (14) (reference symbol (30)) and the capacitive element (10) (reference characters 31)) in connection (potential in points (30) and (31) is the same).
• the charging current limiting resistor (6) is of high impedance. It limits the inrush or inrush current of the AC mains voltage when the maximum overvoltage value is applied. It is at a value which is as large as the current flowing into the capacitor when the power supply is idling. Charging the capacitive element (10) builds up a voltage that reaches a limit above which the control and regulating circuit (12) begins to function, the switching regulator starting to work by means of the field effect transistor (7). As a result, the control amplifiers (15), (18) are also supplied with operating voltage via the auxiliary winding (22), the diode (23) and the capacitor (24).
• the nominal value of the voltage at the comparison device (26) corresponds to the maximum nominal input voltage. If the
• Control amplifier (18) receives operating voltage, occurs at the
• Comparison device (26) therefore has a high control deviation, through which the control amplifier (18) generates a high DC output voltage, which is set, for example, by means of the resistor (17) and the Zener diode (19) so that it corresponds as a reference variable to a permissible current value.
• This voltage which corresponds to the maximum permissible current value, has the effect via the comparison device (16) and the control amplifier (15) that the transistor (13) is turned on and feeds the maximum permissible current setpoint in a controlled manner into the capacitive element (10) and the downstream circuits .
• the transistor (13) has a resistance corresponding to the current setpoint. When the transistor (13) is operating, a negligibly small current flows through the high-impedance charging current limiting resistor (6).
• the resistor (21), the voltage setpoint generator (20), the comparison device (28), the control amplifier (18), the resistor (17), the Zener diode (19), the comparison device (16) and the control amplifier (15) Components of the control circuit described above, which contains the transistor (13) as an actuator and influences the voltage drop across the capacitor (10) or the current flowing through the shunt (14) as the control variable.
• This control circuit (reference symbol (28)) contains a current control circuit (33) with the transistor (13) as actuator, the current sensor (14) as current actual value transmitter, the control amplifier (15) and the comparison device (16) as well as a voltage control circuit (34) with the voltage sf-cooler (21) as the actual voltage transmitter, the voltage setpoint transmitter (20), the control amplifier (18) and the comparison device (26).
• the current and voltage control circuit (33) or (34) can also act directly (in parallel) on the actuator (13) with their respective output and not as shown.
• the current flowing into the capacitive element (10) and the downstream circuits would increase indefinitely without the current control circuit (33).
• the transistor (13) receives less control current or control voltage when the input voltage rises, as a result of which its resistance is increased, ie the current setpoint is retained since the actual voltage value remains lower than the voltage setpoint. This means that the voltage control loop (34) does not become active. If the voltage at the input rises even further, above the set voltage setpoint, the voltage falling across the capacitive element (10) is regulated, i.e. the downstream circuits do not receive a DC voltage that rises in the same way above the input voltage.
• the voltage control loop (34) therefore limits the voltage at the capacitive element (10) to a system-compatible value. High input voltages therefore cause voltage drops across the current limiting resistor (6) and across the adjustable resistor (13) connected in parallel. Therefore, the power supply can generate a regulated output voltage with secured functionality even with dynamic overvoltage.
• a voltage limiting circuit (27) is expediently arranged parallel to the capacitive element (10), the response threshold of which is higher than the voltage setpoint (20) present at the comparison device (26).
• This voltage limiting circuit (27) can protect the capacitive element at very high input voltages and the resulting current through the resistor (6) when the input voltage is too high and especially when the device is idling. It is advantageous if the value of the charging current limiting resistor corresponds to the quotient of the difference between the maximum permissible static overvoltage and the voltage setpoint at the capacitive element (10) and the no-load current of the power converter.
• Fig. 2 is that with reference to FIG. 1 described protective device modified so that an autonomous mode of operation is possible. Otherwise, with the exception of the charging current limiting resistor (6), the circuit elements and the structure of the circuit are preserved.
• an auxiliary voltage (36) is taken from the DC voltage outputs (4) and (5), which is fed to a chopper stage (37) and then via a transformer with the primary winding (35) is fed into the secondary winding (22).
• the function of the circuit according to Fig. 2 corresponds otherwise to that of FIG. 1.
• FIG. 2 shows the possibility of switching the power supply inactive or inhibit with an extremely low quiescent current.
• a remote control signal (39) is connected to the chopper stage (37) and a linkage stage (40), optionally with a downstream one
• the chopper stage (37) and thus the current voltage control circuit (28) are activated immediately and the power stage (12) or several power stages connected in parallel (circuit (41)) are activated with a time delay using the AND link (40).
• the lower switch-on threshold (31), (32) of the power level is detected.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Automation & Control Theory (AREA)
• Dc-Dc Converters (AREA)

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Citations (5)

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• 1988
  • 1988-02-10 DE DE3804074A patent/DE3804074A1/de active Granted
• 1989
  • 1989-02-09 EP EP89902253A patent/EP0402367B1/de not_active Expired - Lifetime
  • 1989-02-09 DE DE8989902253T patent/DE58904360D1/de not_active Expired - Lifetime
  • 1989-02-09 WO PCT/EP1989/000121 patent/WO1989007853A1/de active IP Right Grant

Patent Citations (5)

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