text: fig1 depicts a drive system in which input a - c energy received over line 10 is rectified in input bridge rectifier circuit 11 , passed over line 12 , filter 13 and line 14 to provide a d - c energizing voltage for inverter 15 . the output a - c voltage produced by the inverter is passed over line 16 to energize any suitable load , such as motor 17 which is depicted driving a shaft 18 . in addition , the input a - c energy is also passed from line 10 over line 20 to a logic circuit 21 which rectifies the energy and , through logical circuit components , provides ( 1 ) gating signals on line 22 to regulate the turn - on and turn - off of at least one controllable component ( not shown ) in the input bridge rectifier , and ( 2 ) appropriate gating signals over line 23 for the individual semiconductor switches ( not shown ) within inverter 15 . as shown the gating signal for the input bridge rectifier 11 is delayed in a time delay circuit 24 before being applied over line 25 to the rectifier circuit 11 . the output voltage from pre - charge circuit 26 is applied over line 27 to inverter 15 , to charge the commutating capacitors described above before the input bridge rectifier is activated . it is noted that although a time delay circuit 24 is illustrated as the means for delaying the application of a d - c voltage over line 14 to the inverter 15 , other systems for delaying the application of the bus voltage can be substituted for the illustrated arrangement without departing from the spirit and scope of the present invention . fig2 depicts three input conductors 10a , 10b , and 10c for receiving a three phase a - c voltage in a manner well - known and understood in the art . similarly , the input bridge rectifier circuit 11 includes six thyristors or controllable components 31 - 36 , so that selective gating of these thyristors under the regulation of logic circuit 21 governs the amplitude of the d - c voltage provided on conductors 12a , 12b . of course , in a single - phase system only two input conductors 10a , 10b are needed , and the system could operate with only a single controllable component 31 , with the thyristor 32 replaced by a diode in a manner well - known and understood in the art . the d - c voltage is filtered by the filter 13 , which includes a series - connected inductor 37 and a parallel - connected capacitor 38 . the resultant filtered d - c energizing voltage is supplied over the bus conductors 14a , 14b to energize phase circuit a of the three - phase aux - comm inverter represented by the numeral 15 in fig1 . only one phase circuit of the inverter is shown in fig2 as that is sufficient for an understanding of the pre - charge arrangement of the present invention , and in fact would be the arrangement if a single - phase inverter were utilized . the phase a inverter system comprises main thyristors 40 , 41 and auxiliary thyristors 42 , 43 . the series circuit including commutating capacitor 44 and commutating inductor 45 is connected between the common connection between the main thyristors and the common connection between the auxiliary thyristors . a first inductor 46 is coupled between bus conductor 14a and the anodes of thyristors 40 , 42 , and a second inductor 47 is coupled between the other bus conductor 14b and the common connection of the cathodes of the thyristors 41 , 43 . such an aux - comm inverter circuit is now known and has been successfully utilized for circuits with relatively high voltages , of the order of a thousand volts , applied to the bus conductors . the energy return diodes 48 , 50 are connected between the bus conductors in a well - known manner . one suitable circuit actually tested and successfully operated included a commutating capacitor 44 of the order of 70 microfarads , and its associated inductor 45 was a seven microhenry inductor . each of the inductors 46 , 47 was approximately 12 microhenries . it is apparent that the commutating inductor 45 cooperates with either of the inductors 46 , 47 , depending on which of the main thyristors 40 , 41 is being turned off at any one time , and thus it is the total inductance of inductor 45 and the then - connected inductor 46 or 47 which is important in determining the characteristics of the commutating circuit . a pre - charge transformer 52 has a single primary winding 53 , coupled to the supply conductors 20a , 20b , and has three secondary windings 54 , 55 and 56 . secondary winding 54 is coupled to a half - wave rectifier circuit including a pair of series - connected rectifiers 55 , 56 . resistors 57 , 58 are coupled in parallel with the diodes 55 , 56 to ensure accurate voltage division across these two diodes in a manner well - known and understood in this art . particularly in accordance with this invention , the rectified voltage from the first pre - charge circuit output conductor 60 is applied over an isolation resistor 61 and conductor 62 directly to one side of commutating capacitor 44 . the other output conductor 63 of the pre - charge circuit is likewise coupled over another isolation resistor 64 and another conductor 65 to the other side of the commutating capacitor 44 . it has been found that this system is effective to charge the capacitor 44 to an effective commutating voltage level with only a slight delay , of the order of 20 to 30 seconds , provided by time delay circuit 24 before the one or more controllable components in rectifier circuit 11 are energized to produce the d - c bus voltage at conductors 14a , 14b . thus this arrangement has saved the expense and physical volume previously attributed to an additional relay utilized to selectively make the connection over conductors 62 , 65 and then interrupt the connection after the appropriate pre - charge voltage was applied across capacitor 44 . those skilled in the art will appreciate that the time delay provided by stage 24 need not be in the circuit which delays energization of the input bridge rectifier , but can be any suitable arrangement for delaying the application of the d - c input voltage to the bus conductors of the inverter . in the appended claims the term &# 34 ; connected &# 34 ; means a d - c connection between two components with virtually zero d - c resistance between those components . the term &# 34 ; coupled &# 34 ; indicates there is a functional relationship between two components , with the possible interposition of other elements between the two components described as &# 34 ; coupled &# 34 ; or &# 34 ; inter - coupled &# 34 ;. while only a particular embodiment of the invention has been described and claimed herein , it is apparent that various modifications and alterations of the invention may be made . it is therefore the intention in the appended claims to cover all such modifications and alterations as may fall within the true spirit and scope of the invention .