Abstract:
An air-cooled power converter with gate turn-off power semiconductors, is described in which the cooling capacity is such that the temperature of the gate turn-off power semiconductor does not exceed a critical temperature limit, the power converter having optimized heat sinks, at least some of which are thermally connected in parallel, and the power converter is designed to operate at a continuous load of 1 to 20 megawatts, preferably of 2 to 10 megawatts.

Description:
FIELD OF THE INVENTION 
     The present invention concerns an air-cooled power converter with a gate turn-off. 
     BACKGROUND INFORMATION 
     Water-cooled megawatt power converters are known. However, conventional power converters are expensive to manufacture and maintain. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a power converter in a capacity range of 1 to 10 MW that can be manufactured more advantageously compared to the conventional power converters. It is particularly desirable that a power converter in the capacity range of 1 to 20 MW be provided, which is easier and less expensive to operate and maintain than conventional power converters. 
     Air cooling for power converters operating in the range of 1 to 20 MW is considered unsuitable by experts in the field. It has, however, been shown that power converters in the above-mentioned capacity range with air cooling are feasible. Such air-cooled power converters have proven to be particularly cost-effective and require little maintenance compared to known water-cooled power converters. 
     In an advantageous embodiment of the present invention, heat sinks electrically connect gate turn-off power semiconductors. This electrical connection also represents a good heat connection, so that the heat generated in the power semiconductors is sufficiently dissipated. It has also proven to be advantageous to use heat sinks with such a high heat capacity that they react inertially to peak loads. 
     In another advantageous embodiment of the present invention, the power converter has a fan that supplies ambient air or pre-cooled air to the heat sinks or that advantageously draws ambient air through the heat sinks. 
    
    
     Other advantageous and inventive details are presented in the following description of the embodiment with reference to the drawing and in conjunction with the subclaims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a motor supplied by a power converter with a diode power rectifier on the line side; 
     FIG. 2 shows a motor supplied by a power converter with a self-commutated power rectifier and power inverter also on the line side; 
     FIG. 3 shows a power converter arrangement with an automation device connected via optical fibers; 
     FIG. 4 shows a three-point power inverter with GTO thyristors (main circuit without RC circuit); 
     FIG. 5 shows a three-point power inverter with RC GTOs and RC circuit; 
     FIG. 6 shows a power converter arrangement for supplying a three-phase motor with a three-point power converter section on the line and load side; 
     FIG. 7 shows a power converter arrangement for double-sided supply of a three-phase motor having an open winding with a three-point power converter section; 
     FIG. 8 shows the mechanical construction of a power converter according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a motor  15  supplied by a power converter with a diode power rectifier  2  on the line side. The power converter arrangement is preferably designed as a series connection of two B 6  diode bridges. The line-side connection is implemented using a transformer  1  with two secondary winding systems preferably electrically offset by 30° to achieve a 12-pulse phase effect. Diode power rectifier  2  is connected to the load-side power inverter  4  via voltage link  3  on the dc side. The voltage link is preferably connected across three poles—the positive link pole, the negative link pole, and the dc neutral. Load-side power inverter  4  is designed as self-commutated three-point power inverter to whose output three-phase motor  15  is connected using three conductors. 
     FIG. 2 shows a motor  9  supplied by a power converter with self-commutated power rectifier  6  and power inverter  8  on the line side. The power converter arrangement has a line-side self-commutated power rectifier  6 , connected on the dc side to load-side power inverter  8  via voltage link  7 . Both power converter sections  6  and  8  have a three-point design, and the voltage link is preferably connected via three poles—the positive link, the negative link, and the DC neutral. Load-side self-commutated power rectifier  6  is connected to the line via transformer  5 . The circuit is preferably of the same design as that of load-side power inverter  8  and allows operation both as a power rectifier and as a power inverter for energy recovery, for example in braking motor  9 . The output of load-side power inverter is connected to the three-phase motor via three conductors. 
     FIG. 3 shows a power converter arrangement with an automation device  14  for controlling power converter  16 , the entire information exchange taking place over an optical fiber connection  13 . Power converter  16  has a line-side power converter section  10 , a voltage link  11 , and a load-side power converter section  12 . The power connections of the power converter sections with the line and the motor can be implemented as shown in FIGS. 1 and 2, for example. Power converter  10  contains all the sensors required for operation and monitoring, so that no other outside connections are needed. It is not shown that both the power converter and the automation device require an auxiliary power supply or a battery. 
     FIG. 4 shows the main circuit of a three-point power inverter. Positive-side link capacitor  54  and negative-side link capacitor  55  are connected in series between positive DC pole  56  and negative DC pole  57 . Their point of connection forms DC neutral point  58 . Phase modules  50 ,  51 ,  52 , each with four GTOs connected in series and free-wheeling diodes connected in anti-parallel, are connected between the positive and negative DC poles. The point of connection between the first and second GTOs of a phase module and the third and fourth GTO of a phase module is connected to two additional diodes connected in series and in anti-parallel to the GTOS; the neutral point of these two diodes is connected to DC neutral point  58 . The point of connection between the second and third GTO of a phase module forms the respective output terminal connected to motor  53 . 
     FIG. 5 shows a three-point power inverter component with RC GTOs and RC circuit. The series connection of an inductance L 1 , four RC GTOs (reverse conducting gate-turn-off thyristors) V 1 , V 2 , V 3 , V 4  and inductance L 2  between the positive DC pole  24  and the negative DC pole  26  form together with the two neutral point diodes V 15  and V 16  the main circuit of a phase module of a three-point power inverter. The anode of V 15  is connected to DC neutral point  25  and its cathode is connected to the connection point of first RC GTO Vl with second RC GTO V 2 . The cathode of X 16  is connected to DC neutral point  25  and its anode is connected to the connection point of third RC GTO V 3  with fourth RC GTO V 4 . The connection point between the second RC GTO V 2  and the third RC GTO V 3  forms the ac output of phase module V (V or W). 
     L 1  and L 2  are used to limit the current rise rate; RC circuits V 21  and V 22  with C 7  and C 1 , as well as V 24  and V 23  with C 17  and C 11  are used to limit the voltage rise rate when switching the GTOs. The energy stored in the respective RC circuits in each switching operation is converted into heat at resistors R 3  and R 4  and the overcharging of capacitors C 1  and C 11  is prevented or reversed. 
     The two RCD protection circuits R 11 , C 9 , V 25  and R 21 , C 19 , V 26  are used as additional protection of the two middle RC GTOs V 2  and V 3 . They are advantageously used in high-capacity power converters with the resulting large physical dimensions for preventing voltage surges in design-related parasitic inductances of GTOs V 2  and V 3 . 
     FIG. 6 shows a power converter arrangement for supplying a three-phase motor with the line-side power converter section  33  and load-side power converter section  34  having the same three-point design with GTOs. The main circuit of each phase module is illustrated with their respective RC circuits  40  and  41 . Positive-side link capacitor  37  forms, together with negative-side link capacitor  39 , the DC voltage link, over which the two power converter sections are connected. The positive-side RC charge reversal resistor  36  and the negative-side RC charge reversal resistor  38  are connected to the respective sides of RC circuits  40  and  41 . The output of line-side power converter section  33  is connected to line  30  via transformer  31  and circuit breaker  32 . The output of load-side power converter section  34  is connected to three-phase motor  35 . 
     In the arrangement of FIG. 7, the output of a first power converter  74  and the output of a second power converter  75  are connected to a side  71  and  72 , respectively, of the open three-phase winding of three-phase motor  73 . With this arrangement, a particularly advantageous operating condition is achieved in addition to doubling the capacity, since, as assumed according to the tuned pulse method, a largely sinusoidal current is achieved in the motor with low harmonics even at low switching frequencies. 
     On the line side, first power converter  74  is connected to power supply line  60  via an optional line-side additional inductance  63  and a first star/delta connected transformer  61 , for example. The second power converter  75  is connected to power supply line  60  via an optional line-side additional inductance  64  and a second transformer  62 , preferably electrically offset with respect to the first transformer by 30° (e.g., star/star connected). With this arrangement, particularly advantageous line reaction conditions are obtained, especially when, as in the present example, the power converter is composed of three-point connected power converter sections. Even at a fundamental component load of the self-commutated line power converter, a sinusoidal current is obtained with very little harmonics. 
     The two power converters  74  and  75  have line-side power converter sections  66  and  65  and load-side power converter sections  69  and  70 , respectively, each of which is connected via DC voltage link  67  and  68 , respectively. The two DC voltage links  67  and  68  are electrically insulated from one another. All power converter sections  66 ,  65 ,  69 ,  70  are three-point connected, preferably with RC GTOs. 
     FIG. 8 shows the mechanical construction of an air-cooled power converter according to the present invention. The semiconductor elements are mounted in this embodiment on a pull-out power rectifier module  81 . Power rectifier module  81  can be inserted into a support  82 . Support  82  is shown in FIG. 8 without side walls or doors. The unit is cooled using an air current generated by fan  80  and blown through support  82  and inserted power rectifier module  81 . The semiconductors of power rectifier  81  are preferably arranged between heat sinks  83 , which are also cooled by the air stream.