Patent Publication Number: US-2023147990-A1

Title: Power supply unit and power supply system with dynamic current sharing

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to a power supply unit and a power supply system with dynamic current sharing, and more particularly to a power supply unit and a power supply system with continuous and fast dynamic current sharing for an output current of a load. 
     Description of Related Art 
     The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art. 
     With the development of the Internet and the increasing demand for computing, the functions and performance of the central processing unit (CPU) and graphics processing unit (GPU), which act as the basic computing engine, are becoming more and more powerful. As a result, the dynamic load changes of the system become more and more severe so the dynamic load current-sharing performance of the power supply becomes more important. 
     Please refer to  FIG.  1   , which shows a schematic waveform of the dynamic load test for a graphic processing unit. The continuous dynamic load waveform (i.e., electric data peak processing, EDPP) shown in  FIG.  1    may show: the peak load (or maximum load) can reach to more than 200% of the rated load, and the time duration is less than 200 µs (that is, the time length of T1). At T2 (less than 1 ms), it is 150% of the rated load. Therefore, the dynamic load state sequentially descends. 
     For parallel-connected power supply units (PSUs), when the above-mentioned EDPP is used for load testing, if only the general current-sharing technology is used, the uneven (not equal) output currents of the power supply units will easily occur. 
     For example, multiple power supply units are connected to the system load by connecting outputs thereof together to supply power to the system load. If only the general active current-sharing technology is used, a current-sharing bus is provided to connect between multiple power supply units, and by subtracting the signal on the current-sharing bus with the current detection signal inside the power supply unit, the output voltage of the power supply unit with lower output current is increased to achieve the purpose of current sharing, thereby achieving the accurate current-sharing performance under the stable load. However, its disadvantage is that it is unable to provide instant (quick) load response for continuous dynamic load conditions. 
     Specifically, the active current sharing is achieved by comparing the current signal I SHARE_BUS  of the current-sharing bus with the current signal I LOCAL   _BUS  of each power supply unit (i.e., the current subtraction). In particular, the current signal of the current-sharing bus is the maximum output current of the plurality of power supply units (or a current signal that is directly proportional to the maximum output current). According to the comparison of the two currents, therefore, the difference between the output current of each power supply unit and the maximum output current of all power supply units (i.e., I SHARE   _   BUS -I LOCAL   _BUS ) can be realized. Furthermore, the error amount (i.e., the current difference) after the subtraction of the two currents is generated through a controller (for example, but not limited to, a PI (proportional-integral) controller) to generate a voltage increase, and then the voltage increase is provided to the reference voltage so that the output current of the power supply unit can be increased to achieve the effect of current sharing. Under continuous dynamic load operation, I SHARE   _   BUS  and I LOCAL   _BU  will vary with the load conditions, which is limited by the signal response speed and the controller bandwidth. Therefore, when the load changes (variations) more drastically, the voltage compensation speed will not be able to catch up with the load changes, resulting in poor dynamic current-sharing performance. 
     In addition, another general current-sharing technology is called droop current-sharing technology. For the droop current-sharing technology, there is no need to connect all the power supply units with the current-sharing bus as the previously-disclosed active current-sharing technology, only the internal current signal of each power supply unit is used. The principle is that the output voltage of the power supply unit will decrease as the loading becomes larger, as shown in  FIG.  6 A . Therefore, through the droop current-sharing technology, the output voltage can be naturally changed in response to changes in the load conditions, thereby achieving the purpose of current sharing. In usual, the circuit is realized by using an operational amplifier (OPA) and a current-sensing resistor. The differential amplifier circuit composed of the operational amplifier amplifies the voltage difference generated by the load current through the current-sensing resistor, and then adds this amplified signal to the voltage feedback circuit, that is, when the load current increases, the output voltage decreases; when the load current decreases, the output voltage increases. 
     In general, the droop current-sharing technology is mostly used in the power over Ethernet (PoE) system. Since the output voltage of the power supply device (i.e., the power supply unit) of the PoE system is relatively high (usually 54 volts), and the voltage may vary widely, therefore, through a simple droop current-sharing technology, the current sharing (uniformity in current) can be achieved. However, its disadvantage is that in order to achieve a high accuracy (precision) current-sharing effect, the droop slope must be large, but the load regulation of the output voltage will be sacrificed. In addition, since the accuracy of the droop slope must be high, the design requirements are more stringent. In other words, it is relatively difficult to design a droop slope to achieve both a good current-sharing effect and load regulation rate. 
     SUMMARY 
     An object of the present disclosure is to provide a power supply unit to solve the problems of the existing technology. 
     In order to achieve the object, the power supply unit includes a power converter, a current detection circuit, a detection signal peripheral circuit, and a control processor. The power converter provides an output current and an output voltage. The current detection circuit detects the output current, and provides a current signal corresponding to the magnitude of the output current. The detection signal peripheral circuit receives the output voltage, the current signal, and a current-sharing bus signal, and respectively converts the output voltage, the current-sharing bus signal, and the current signal into an output voltage signal, a first current signal, and a second current signal. The control processor receives the output voltage signal, the first current signal, and the second current signal, and performs an active current-sharing control, a current-averaging error compensation control, and a droop current control according to the output voltage signal, the first current signal, and the second current signal so as to generate a control signal to control the output voltage and adjust the magnitude of the output current. 
     Accordingly, the active current-sharing control, the average current difference compensation control, and the droop current-sharing control are integrated/combined to acquire the advantages of each current sharing control, that is, achieving continuous and fast dynamic current sharing for the output current of the load, and increasing voltage compensation speed and current sharing accuracy so that the output currents of the parallel-connected power supply units are approximately equal to implement the optimized current-sharing effect. 
     Another object of the present disclosure is to provide a power supply system with dynamic current sharing to solve the problems of the existing technology. 
     In order to achieve the object, the power supply system with dynamic current sharing includes a current-sharing bus and a plurality of power supply units. The current-sharing bus provides a first current signal. The plurality of power supply units connected to each other through the current-sharing bus. Each power supply unit includes a local current bus for providing a second current signal. Each power supply unit includes a control processor. The control processor includes an active current-sharing unit, an average current unit, a droop current unit, and an integration calculation unit. The active current-sharing receives the first current signal and the second current signal, and compares the second current signal with the first current signal to generate a compensation voltage. The average current unit receives the first current signal and the second current signal, and compares an average value of the first current signal with an average value of the second current signal to generate an average voltage. The droop current unit receives the second current signal to generate a droop compensation voltage. The integration calculation unit receives the compensation voltage, the average voltage, and the droop compensation voltage to make output currents of the power supply units be approximately equal according to the compensation voltage, the average voltage, and the droop compensation voltage. 
     Accordingly, the active current-sharing control, the average current difference compensation control, and the droop current-sharing control are integrated/combined to acquire the advantages of each current sharing control, that is, achieving continuous and fast dynamic current sharing for the output current of the load, and increasing voltage compensation speed and current sharing accuracy so that the output currents of the parallel-connected power supply units are approximately equal to implement the optimized current-sharing effect. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the present disclosure as claimed. Other advantages and features of the present disclosure will be apparent from the following description, drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawing as follows: 
         FIG.  1    is a schematic waveform of the dynamic load test for a graphic processing unit. 
         FIG.  2    is a block diagram of a single power supply unit of a power supply system according to the present disclosure. 
         FIG.  3    is a schematic block diagram of multiple parallel-connected power supply units of the power supply system according to the present disclosure. 
         FIG.  4    is a block diagram of control processors of the power supply system to perform a dynamic current sharing according to the present disclosure. 
         FIG.  5    is a detailed block diagram of the control processor of the power supply unit according to the present disclosure. 
         FIG.  6 A  is a waveform designed for the slope of load current and output voltage used in traditional droop current sharing. 
         FIG.  6 B  is a waveform designed for the slope of load current and output voltage used in droop current sharing of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to the drawing figures to describe the present disclosure in detail. It will be understood that the drawing figures and exemplified embodiments of present disclosure are not limited to the details thereof. 
     The power supply system with dynamic current sharing disclosed in the present disclosure may be applied to, for example, but not limited to, power supplies in related fields such as servers, networking, etc., for example, multiple power supplies connected in parallel are used as a redundant power supply architecture. 
     Moreover, the present disclosure introduces existing current-sharing technology, including the active current-sharing control, the average current difference compensation control, and the droop current-sharing control, which are integrated/combined to acquire the advantages of each current sharing control, that is, achieving continuous and fast dynamic current sharing for the output current of the load, and increasing voltage compensation speed and current sharing accuracy. Hereinafter, the current-sharing control of the present disclosure will be described in detail. 
     Please refer to  FIG.  2   , which shows a block diagram of a single power supply unit of a power supply system according to the present disclosure. The single power supply unit PSU 1 -PSU N  includes a current detection circuit  101 , a detection signal peripheral circuit  102 , a digital control processor  103 , a current-sharing bus signal peripheral circuit  104 , a switch drive circuit  105 , and a switched power converter  106 . Please refer to  FIG.  3   , multiple power supply units are used in parallel as a redundant power supply architecture. In this embodiment, two power supply units PSU 1 -PSU 2  are taken as an example but not for limitation of the present disclosure. In this parallel-connected system, output voltages V OUT  of all power supply units PSU 1 -PSU 2  are connected in parallel. The first power supply unit PSU 1  provides a first output current Iout1 and the second power supply unit PSU 2  provides a second output current Iout2 to commonly provide a total output current I out_total  to supply power to a load of the system. In addition, the power supply units PSU 1 -PSU 2  are connected to each other through a current-sharing bus I SB . 
     Please refer to  FIG.  2    again, the current detection circuit  101  is used to detect the output current I OUT  of the power supply unit PSU (i.e., a load current), and provides a current signal V ILOCAL_1  of amplifying the output current I OUT . In practice, the current detection circuit  101  may be, for example, but not limited to, a resistive component, and therefore the output current I OUT  flowing through a resistance value R of the resistive component (such as a resistor) generates a voltage difference (Vsense=Iout*R). A differential amplifier circuit composed of OPA may detect the magnitude of the voltage difference (corresponding to the output current I OUT ), which represents the amplified current signal Y ILOCAL_1 . 
     The detection signal peripheral circuit  102  is used to receive three detection signals, including the output voltage V OUT , the current-sharing bus I SB , and the amplified current signal V ILOCAL   _1  (corresponding to the output current I OUT  of the power supply unit). Moreover, the detection signal peripheral circuit  102  adjusts (for example, steps down) the received detection, and provides the adjusted detection signal to the digital control processor  103  to meet the voltage level (magnitude) that the digital control processor  103  can operate. In other words, after processing by the detection signal peripheral circuit  102 , the output voltage V OUT  is step down (reduced) to V OUT   _SENSE , the current signal V ILOCAL_1  is step down (reduced) to the second current signal S I21 -S I2N , and the current-sharing bus signal I SB  is step down (reduced) to the first current signal S I1 . 
     The digital control processor  103  digitally filters the second current signal S I2  (i.e., the local current detection signal), and calculates the filtered second current signal S I2  to generate the corresponding current-sharing signal I SHARE  to the current-sharing bus signal peripheral circuit  104 . The current-sharing bus signal peripheral circuit  104  amplifies the current-sharing signal I SHARE  and provides the amplified current-sharing signal I SHARE  to the current-sharing bus I SB  connected to the current-sharing bus signal peripheral circuit  104 . Incidentally, since the current signal on the current-sharing bus I SB  is the maximum output current of all power supply units, when all power supply units provide (transmit) the amplified current-sharing signals I SHARE  to the current-sharing bus signal peripheral circuit  104 , the current-sharing bus I SB  reserves the maximum output current as the current signal of the current-sharing bus I SB . 
     The digital control processor  103  performs an active current-sharing control, an average current difference compensation control, and a droop current-sharing control inside the processor according to the output voltage signal V OUT   _SENSE , the second current signal S I21 -S I2N , and the first current signal S I1  provided by the detection signal peripheral circuit  102  to generate the corresponding reference voltage command and PWM control signal (the detailed description will be made as follows). Therefore, the switch drive circuit  105  is used to control the output voltage V OUT  of the switched power converter  106 , i.e., the output voltage V OUT  of the power supply unit, thereby achieving continuous and fast dynamic current sharing for the output current of the load. 
     Please refer to  FIG.  4   , which shows a block diagram of control processors of the power supply system to perform a dynamic current sharing according to the present disclosure, and also refer to  FIG.  3   . The power supply system includes a current-sharing bus I SB  and a plurality of a plurality of power supply units PSU 1 -PSU N . The current-sharing bus I SB  provides a first current signal S I1 . The power supply units PSU 1 -PSU N  are connected to each other through the current-sharing bus I SB . A digital control processor  103   1 - 103   N  of each power supply unit PSU 1 -PSU N  includes an active current-sharing unit  11 , an average current unit  12 , a droop current unit  13 , and an integration calculation unit  14 . A plurality of local current bus I LB1 -I LBN  correspondingly provide the second current signals S I21 -S 12N . That is, a current signal of the output current provided by the local current bus I LB1 ) of the first power supply unit PSU 3  is the first current signal S I21 , a current signal of the output current provided by the local current bus I LB2  of the second power supply unit PSU 2  is the second current signal S I22 , and so on, and the detail description is omitted here for conciseness. The digital control processor  103  receives the output voltage signals V OUT_SENSEI - V OUT_SENSEN , the first current signal S I1 , and the second current signals S I21 -S I2N  provided from the detection signal peripheral circuit  102  shown in  FIG.  2   . 
     As shown in  FIG.  4   , the active current-sharing unit  11  of each power supply unit PSU 1 -PSU N  receives the first current signal S I1  and the second current signal S I21 -S I2N , and compares the second current signal S I21 -S I2N  with the first current signal S I1  to generate the compensation voltage V COMPI -V COMPN . Specifically, the first power supply unit PSU 1  receives the first current signal S I1  provided by the current-sharing bus I SB  and the second current signal S I21  provided by the first local current bus I LB1 . The second power supply unit PSU 2  receives the first current signal S I1  provided by the current-sharing bus I SB  and the second current signal S I22  provided by the second local current bus I LB2 , and so on. The N th  power supply unit PSU N  receives the first current signal S I1  provided by the current-sharing bus I SB  and the second current signal S I2N  provided by the N th  local current bus I LBN . In particular, the magnitude of the first current signal S I1  provided by the shared (commonly-used) current-sharing bus I SB  is equal to the maximum value of the second current signals S I21 -S I2N . That is, the current signal (i.e., the first current signal S I1 ) provided by the current-sharing bus I SB  corresponds to the maximum output current I OUT  of all power supply units PSU 1 -PSU N . 
     Please refer to  FIG.  5   , which shows a detailed block diagram of the control processor of the power supply unit according to the present disclosure. The active current-sharing unit  11   includes a voltage comparison unit  111  and a compensation unit  112 . The voltage comparison unit  111  receives the first current signal S I1  and the second current signal S I21 -S I2N , and subtracts the second current signal S I21  from the first current signal S I1  (take the first power supply unit PSU 1  as an example) so as to acquire/realize a current difference I DIF  between the output current I OUT1 -I OUTN  of each power supply unit PSU 1 -PSU N  and the maximum output current of all power supply units PSU 1 -PSU N . Furthermore, the compensation unit  112  is used to calculate the current difference I DIF . In one embodiment, the compensation unit  112  may be a digital controller, for example, but not limited to, a proportional-integral (PI) controller to generate the compensation voltages V COMP1 -V COMPN . Therefore, when the current difference between the first current signal S I1  and the second current signal S I21  is larger, the active current-sharing unit  11  provides a larger compensation voltage; otherwise, it provides a smaller compensation voltage. Incidentally, since the first current signal S I1  corresponds to the maximum output current, the aforementioned current value subtraction calculation is the difference acquiring by subtracting the second current signal S I21  from the first current signal S I1 . 
     As shown in  FIG.  4   , the average current unit  12  receives the first current signal S I1  and the second current signal S I21 -S I2N , respectively calculates an average value of the first current signal S I1  as a first current average value S I1AVG  and an average value of the second current signal S I21 -S I2N  as a second current average value S I21AVG -S I2NAVG , and calculates a difference value between the first current average value S I1AVG  and the second current average value S I21AVG -S I2NAVG  to generate the average voltage V AVG1 -V AVGN . 
     Specifically, as shown in  FIG.  5   , the average current unit  12  includes a first average current calculation unit  121 , a second average current calculation unit  122 , and an average current difference calculation unit  123 . The first average current calculation unit  121  receives the first current signal S I1 , and calculates an average value of the first current signal S I1  as a first current average value S I1AVG . The second average current calculation unit  122  receives the second current signal S I21 -S I2N , and calculates an average value of the second current signal S I21 -S I2N  as a second current average value S I21   AVG -S I2NAVG . The average current difference calculation unit  103  receives the first current average value S I1AVG  and the second current average value S I21AVG  (take the first power supply unit PSU 1  as an example), and calculate a difference value between the first current average value S I1AVG  and the second current average value S I21AVG  to generate the average voltage V AVG1 . In particular, the main purpose of average current compensation is to help parallel-connected power supply units to compensate the average voltage error caused by the current detection and the active current-sharing delay in the continuous dynamic load. 
     As shown in  FIG.  4   , the droop current unit  13  receives the second current signal S I21 -S I2N  to generate the droop compensation voltage V DROOP1 -V DROOPN . Specifically, as shown in  FIG.  5   , the droop current unit  13  includes a droop function calculation unit  131 . The droop function calculation unit  131  receives the second current signal S I21 -S I2N  to generate the droop compensation voltage V DROOPI -V DROOPN  according to the magnitude of the second current signal S I21 -S I2N . Please refer to  FIG.  6 B , the voltage compensation effect is implemented by the local current detection signal of the power supply unit PSU I -PSU N , i.e., the design of the second current signal S I21 -S I2N  and the droop compensation voltage V DROOP1 -V DROOPN . For the droop current unit  13 , it only receives the second current signal S I21 -S I2N  provided by the local current bus I LB1 -I LBN , and does not involve the first current signal S I1  of the current sharing bus I SB . Also, according to the built-in (designed) droop slope of the power supply unit PSU 1 -PSU N  itself, the magnitude of the output voltage that changes due to the variation of the load can be adjusted (adjusted). Therefore, the droop current sharing can improve the response speed of dynamic load transient current sharing. 
     As shown in  FIG.  4   , the integration calculation unit  14  receives the compensation voltage V COMP1 -V COMPN , the average voltage V AVG1 -V AVGN , and the droop compensation voltage V DROOP1 -V DROOPN . Further, the integration calculation unit  14  generates a reference voltage V OUT_REF1 -V OUT_REFN  to control the output voltage V OUT_SENSEI -V OUT_SENSEN  of the average voltage V AVG1 -V AVGN  according to the compensation voltage V COMP1 -V COMPN , the average voltage V AVG1 -V AVGN , and the droop compensation voltage V DROOP1 -V DROOPN  so as to dynamically current share the output currents I OUT1 -I OUTN  of the power supply units PSU I -PSU N . 
     Please refer to  FIG.  5   , the power supply unit PSU I -PSU N  further includes a control signal generation unit  15 . The control signal generation unit  15  includes an output voltage comparison unit  151  and a control signal generator  152 . Specifically, the reference voltage V OUT_REFI -V OUT_   REFN  generated from the integration calculation unit  14  and the output voltage V OUT_   SENSEI -V OUT_   SENSEN  of the power supply unit PSU I -PSU N  are provided to the output voltage comparison unit  151 , and the output voltage comparison unit  151  compares the output voltage V OUT_SENSE1 -V OUT_SENSEN  with the reference voltage V OUT_REFI -V OUT_REFN  (i.e., the voltage subtraction between the output voltage V OUT_   SENSEI -V OUT   _   SENSEN  and the reference voltage V OUT_   REFI -V OUT_   REFN ) to acquire an output voltage difference V OUT_   DIF . The control signal generator  152  receives the output voltage difference V OUT_DlF  to generate a control signal PWM according to the output voltage difference V OUT_   DIF , and the control signal PWM is provided to control at least one switch component (not shown) of the switched power converter  106  (shown in  FIG.  2   ) through the switch drive circuit  105  so as to control the output voltage V OUT_ of the switched power converter  106 , i.e., the output voltage V OUT  of the power supply unit PSU I -PSU N , thereby achieving continuous and fast dynamic current sharing for the output current of the load. 
     In summary, the present disclosure has the following features and advantages:
     1. The active current-sharing control, the average current difference compensation control, and the droop current-sharing control are integrated/combined to acquire the advantages of each current sharing control, that is, achieving continuous and fast dynamic current sharing for the output current of the load, and increasing voltage compensation speed and current sharing accuracy so that the output currents of the parallel-connected power supply units are approximately equal (for example, the average error between two output currents is less than 5% of the total output current) to implement the optimized current-sharing effect.   2. The active current-sharing control is used to increase the output voltage by acquiring the current difference between the current of the current-sharing bus and the current of the local current bus.   3. The average current difference compensation control is used to help parallel-connected power supply units to compensate the average voltage error caused by the current detection and the active current-sharing delay in the continuous dynamic load, thereby achieving more accurate current-sharing effect according to the compensated average voltage.   4. The droop current-sharing control is used to improve the response speed of dynamic load transient current sharing.   

     Although the present disclosure has been described with reference to the preferred embodiment thereof, it will be understood that the present disclosure is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the present disclosure as defined in the appended claims.