Patent Publication Number: US-2022224326-A1

Title: Device for controlling semiconductor circuit breakers in the high-voltage range

Description:
The invention relates to a device for simultaneously controlling a plurality of semiconductor power switches in the case of pulsed loads in the high-voltage range. 
     The control of semiconductor power switches by means of conventional devices of the type mentioned in the introduction will be explained with reference to  FIGS. 1 and 2 . 
     As shown in  FIG. 1 , for the control of two semiconductor power switches (MOSFETs, IGBTs, bipolar transistors), the voltage of 15 V required for control at the control input (gate, base), with the switch turned on, must always have a defined potential difference with respect to a reference level. If this were not the case, the switch could not be switched on. In the worst case, this can even lead to the destruction of the semiconductor power switch. In the high-voltage application shown in  FIG. 1 , the reference level can be e.g. at 0 V (circuit variant on the left in  FIG. 1 ) or 500 V (circuit variant on the right in  FIG. 1 ), and it can even jump from 0 V to 500 V when the power switch is turned off or turned on (high-side problem). 
     For the application in the high-voltage range as shown by way of example in  FIG. 2 , driver voltages UL 1 , UH 1  and UH 2  are generated by means of a transformer with a plurality of output voltages, which provide the driver voltages at different reference levels in a galvanically isolated manner. In specific detail, a first load Load  1  and a second load Load  2  are cyclically connected to the zero potential HV− and the positive potential HV+ of 500 volts, for example, respectively via a pair of electronic power switches S 1 , S 12  and S 2 , S 21 . The driver voltage UL 1  for controlling the switch S 1  is tapped off from a first secondary winding of the transformer (the lower secondary voltage of the transformer in  FIG. 2 ). The driver voltage Uh 1  for controlling the switch S 12  is tapped off from a second secondary winding of the transformer (the upper secondary voltage of the transformer in  FIG. 2 ). The driver voltage Uh 2  for controlling the switch S 21  is tapped off from a third secondary winding of the transformer (the upper secondary voltage of the transformer in  FIG. 2 ). The high voltage is applied to the respective load Load  1  and Load  2  when switches S 1 , S 12  and S 2 , S 21  are closed, and is disconnected from said load when the switches are open. 
     On account of the compact winding construction, electromagnetic interference caused by clocking of the power semiconductors is transmitted to the primary side of the transformer. In automotive applications, the interference generated in the HV part of the device is thus transmitted to the low-voltage side. Moreover, the interference generated can lead to voltage spikes on the further secondary windings of the transformer. Said interference has to be reduced in a relatively complex manner with the aid of EMC filter components. A further disadvantage of the method is the use of a transformer having a plurality of secondary windings. The latter are complex and expensive owing to the required dielectric strength and the use of high-quality and thus more expensive insulation materials. 
     It is an object of the invention to provide a device such that said device can be produced in an optimized manner in terms of EMC and cost-effectively. 
     This object is achieved by means of the features of claim  1 . Advantageous developments of the invention are defined in the dependent claims. 
     The invention accordingly provides a device for controlling a plurality of semiconductor power switches by means of driver voltages for the clocked operation of a plurality of loads in the high-voltage range. They are provided via a transformer, wherein the driver voltages for the semiconductor power switches are derived from a single secondary winding of the transformer. Voltage level shifter circuits are provided, which obtain driver voltages with the required voltage level from the voltage generated in the secondary winding of the transformer. 
     It is preferably provided that only one transformer having only one secondary winding is required. The driver voltages for an arbitrary number of PWM-controlled loads are preferably generated in each case by way of simple electronic voltage level shifter circuits. 
     The device according to the invention is more compact in comparison with that according to the prior art with a plurality of secondary windings and has less EMC interference. 
     The outlay for transformer and EMC filter components is reduced and results in a significant cost saving. 
     The electronic voltage level shifter circuits are based on the concept of a charge pump. The term charge pump encompasses a plurality of different electrical circuits which increase the value of electrical voltages or reverse the polarity of DC voltages. 
     Charge pumps can be used as voltage shifters wherever high output currents are not required or suitable magnetic components such as coils cannot be used. 
     Charge pumps set their voltages to a different value by means of a temporal sequence between charging of capacitors and cascading. This is realized by periodic switching over of switches. 
     The processes are similar to those of a reciprocating piston pump. Charging of the capacitors corresponds to the filling of the cylinder, and cascading corresponds to the raising of the cylinder. Diodes preferably act as electronic switches, which diodes are switched by potential differences in each case into off-state or on-state ranges and charge capacitors or boost their voltage. Charge pumps, multiply cascaded, can generate very high DC voltages. Such circuits are referred to as a high-voltage cascade. 
     It is advantageous that the clocking of the respective load serves for the clocking of the respective charge pump; in particular, the PWM pulse of the respective load is used for the clocking of the charge pump. Its circuit design is greatly simplified as a result. 
     Preferably, the clocking of the device is effected in each case via a switch which is connected to the secondary winding of the transformer, which charges the charge pump in the closed state, and which applies the driver voltage generated in the charge pump to the respective semiconductor power switch in the open state. The charge pump clocking is preferably effected in each case via a PWM-switched power switch Sn. In this regard, e.g. in the closed state of S 1 , the capacitor C 1  is charged to voltage UL 1  via D 1 -R 1 . In the open state, C 1  is discharged via D 12  to C 12 . Diode D 1  turns off and the charged capacitor is set to the reference level of the power switch S 12 . With Uh 1 =UL 1 =15V the driver of S 12  is supplied with the necessary voltage. 
    
    
     
       The invention is explained in greater detail below with reference to the drawing, in which: 
         FIG. 1  shows generally the control of semiconductor power switches (MOSFETs, IGBTs, bipolar transistors) in accordance with the prior art, 
         FIG. 2  shows an application of the control from  FIG. 1  in the high-voltage range by means of a transformer for the galvanic isolation of the respective driver voltages for the power switches, wherein the driver voltages for the power switches are galvanically isolated by means of secondary windings of the transformer, and 
         FIG. 3  shows an embodiment of the device according to the invention for controlling power switches by means of a transformer having a single secondary winding, from which the various driver voltages for the power switches are derived. 
     
    
    
       FIGS. 1 and 2  have been explained in the introductory part concerning the prior art. 
     An embodiment of the device according to the invention is shown in  FIG. 3 . This embodiment differs from the device shown in  FIG. 2  in the use of a transformer having a single secondary winding for providing the driver voltage UL 1  for the electronic load switches S 1 , S 2 , to put it more precisely to the two electronic load switches S 1  and S 2  by means of the lower secondary winding of the transformer with three levels of the zero potential HV−. 
     For the device in  FIG. 3 , the driver voltages Uh 1  and Uh 2  for controlling the electronic load switches S 12  and S 21  are not provided by further secondary windings of the transformer, but rather are derived from the single secondary winding of the transformer by means of charge pumps. 
     The charge pump for providing the driver voltage Uh 1  comprises a capacitor C 1  connected at one end to that end of the load Load  1  which is connected to the switch S 1 , and at the other end via a series resistor R 1 , the other end of which is connected to a diode D 1  at UL 1  potential. The driver voltage Uh 1  generated from the voltage UL 1  by way of the charge pump is applied via a diode D 12  to the electronic switch S 12  bridged by a capacitor C 12  on the input side. 
     The charge pump for providing the driver voltage Uh 2  comprises a capacitor C 2  connected at one end to that end of the load Load  2  which is connected to the switch S 2 , and at the other end via a series resistor R 2 , the other end of which is connected to a diode D 2  at UL 1  potential. The driver voltage Uh 2  generated from the voltage UL 1  by way of the charge pump is applied via a diode D 12  to the electronic switch S 12  bridged by a capacitor C 21  on the input side. 
     If the switch S 1  is closed, the capacitor C 1 , C 2  is charged to the driver voltage potential UL via the series resistor R 1 , R 2  and the blocking diode D 1 , D 2 . 
     If the switch S 1 , S 2  is opened, the capacitor C 12 , C 21  is charged with the charge of the capacitor C 1 , C 2 . The potential Uh 1 (Uh 2 )=UL required for controlling the switch S 12 , S 21  is thus available. This process is repeated cyclically with the clocking of the switches S 1 , S 2 . 
     The device according to the invention has been explained on the basis of an embodiment with two semiconductor power switches. However, the invention is not restricted thereto. Rather, more than two switches of this type are taken into consideration for the device for controlling semiconductor power switches.