ADAPTIVE IMPEDANCE TRACKING

Abstract

Current sharing in a power system having multiple PSUs comprises generating and supplying a first power and a second power to a load, and sensing a remote voltage value received by the load based on an accumulation of the first and second powers. The method further comprises determining, by the first PSU, local voltage and current values of the first power, a real impedance value of the first PSU based on the remote voltage value and the local voltage and current values of the first power, and a virtual impedance value of the first PSU based on the real impedance value of the first PSU and a reference impedance value. The method further comprises controlling generation of the first power by the first PSU based on the virtual impedance value of the first PSU.

Claims

1. A method for supplying power comprising: generating a first power by a first PSU; supplying the first power to a load; determining, by the first PSU: a real impedance value of the first PSU based on the first power and a remote voltage value received by the load; a virtual impedance value of the first PSU based on the real impedance value of the first PSU and a target impedance value; and controlling generation of the first power by the first PSU based on the virtual impedance value of the first PSU.

2. The method of claim 1, wherein the target impedance value is greater than the real impedance value.

3. The method of claim 1 further comprising: generating a second power by a second PSU; supplying the second power to the load; determining, by the second PSU: a real impedance value of the second PSU based on the second power and the remote voltage value; and a virtual impedance value of the second PSU based on the real impedance value of the second PSU and the target impedance value; and controlling generation of the second power by the second PSU based on the virtual impedance value of the second PSU.

4. The method of claim 3, wherein the real impedance value of the second PSU is different than the real impedance value of the first PSU.

5. The method of claim 3 further comprising determining the remote voltage value received by the load based on an accumulation of the first power and the second power.

6. The method of claim 1, wherein controlling generation of the first power by the first PSU comprises: determining an integrator of adjusting voltage (IOAV) value based on the virtual impedance value of the first PSU; determining a command voltage value based on a reference voltage value and the IOAV value; providing the command voltage value to a controller; and controlling the first PSU by the controller based on the command voltage value to generate the first power.

7. The method of claim 6 further comprising adjusting a subsequent IOAV value based on the virtual impedance value of the first PSU in response to a current value of the first power being greater than a current threshold.

8. The method of claim 7 further comprising adjusting the subsequent IOAV value based on a reducing factor in response to the current value of the first power being less than the current threshold and the IOAV value being greater than zero.

9. A power system comprising: a first power generation device; and a first controller configured to control the first power generation device to: generate a first power; supply the first power to a load; determine a real impedance value of the first PSU based on a received voltage value and the first power; determine a virtual impedance value of the first power generation device based on the real impedance value and a target impedance value; and control the first power generation device based on the virtual impedance value to generate the first power.

10. The power system of claim 9, wherein the first controller is further configured to determine the real impedance value by: calculating a difference between a voltage value of the first power and the received voltage value; and dividing the difference by a current value of the first power.

11. The power system of claim 10, wherein the first controller is further configured to determine the virtual impedance value by subtracting the real impedance value from the target impedance value.

12. The power system of claim 9 further comprising: a second power generation device; and a second controller configured to control the second power generation device to: generate a second power; and supply the second power to the load; determine a real impedance value of the second power generation device based on the received voltage value and the second power; determine a virtual impedance value of the second power generation device based on the real impedance value of the second power generation device and the target impedance value; and control the second power generation device based on the virtual impedance value of the second power generation device to generate the second power.

13. The power system of claim 12, wherein the target impedance value is greater than the real impedance values of the first and second power generation devices.

14. The power system of claim 12, wherein the virtual impedance value of the second power generation device is different than the virtual impedance value of the first power generation device.

15. The power system of claim 12, wherein the load is configured to determine the received voltage value based on receiving the first power and the second power; and wherein the first controller is configured to receive the received voltage value from the load via a first communication bus.

16. The power system of claim 15 further comprising determining the remote voltage value received by the load based on an accumulation of the first power and the second power.

17. A method comprising: supplying, by a first power supply unit (PSU), a first power to a load, the first power comprising a first voltage and a first current; determining a real impedance value, Z.sub.real, of the first PSU via the equation: $Z_{\mathrm{real}}=\frac{V_{\mathrm{local}}-V_{\mathrm{remote}}}{I_{\mathrm{psu}}},$ where V.sub.local is the first voltage, V.sub.remote is a voltage value of the first voltage received at the load, and I.sub.psu is the first current; determining a virtual impedance value, Z.sub.virtual, of the first PSU via the equation: $Z_{\mathrm{virtual}}=Z-Z_{\mathrm{real}},$ where Z is a constant reference impedance; and controlling generation of the first power based on the virtual impedance value, Z.sub.virtual.

18. The method of claim 17 further comprising determining a current value of a voltage adjustment, IOAV.sub.current, via the equation: ${\mathrm{IOAV}}_{\mathrm{current}}={\mathrm{IOAV}}_{\mathrm{previous}}+\left(I_{\mathrm{psu}}*Z_{\mathrm{virtual}}-{\mathrm{IOAV}}_{\mathrm{previous}}\right)*\mathrm{KF},$ where IOAV.sub.previous is a previous value of the voltage adjustment and KF is a filter gain.

19. The method of claim 18 further comprising determining at least a portion of a voltage command, V.sub.command, used to control the generation of the first power via the equation: $V_{\mathrm{command}}=V_{\mathrm{ref}}-{\mathrm{IOAV}}_{\mathrm{current}}H,$ where H corresponds with a feedback control.

20. The method of claim 19 further comprising: setting the current value of the voltage adjustment, IOAV.sub.current, equal to zero based on the first current being less than a predetermined current threshold and based on the previous value of the voltage adjustment, IOAV.sub.previous being equal to zero; and setting the current value of the voltage adjustment, IOAV.sub.current, equal to the previous value of the voltage adjustment, IOAV.sub.previous multiplied by a reducing value based on the first current being less than the predetermined current threshold and based on the previous value of the voltage adjustment, IOAV.sub.previous being greater than zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings illustrate embodiments presently contemplated for carrying out the invention.

[0010] In the drawings:

[0011] FIG. 1 illustrates a multi-PSU system according to an embodiment.

[0012] FIG. 2 is a schematic diagram illustrating a portion of the multi-PSU system of FIG. 1 according to an embodiment.

[0013] FIG. 3 illustrates different impedances of multiple PSUs according to an embodiment.

[0014] FIG. 4 illustrates a flowchart for adjusting a control voltage for a single PSU of the multi-PSU system of FIG. 1 according to an embodiment.

[0015] FIG. 5 illustrates a control diagram for a single PSU of the multi-PSU system of FIG. 1 according to an embodiment.

[0016] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure. Note that corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0017] Examples of the present disclosure will now be described more fully with reference to the accompanying drawings. The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0018] Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0019] Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

[0020] FIG. 1 illustrates a multi-power supply unit (PSU) system 100 according to an embodiment. A plurality of PSUs 101, 102, 103 are coupled to a system load 104 and are configured to supply individual power outputs to the system load 104. The individual power outputs are paralleled so that each PSU 101-103 supplies a portion of the total current to be provided to the system load 104. In a preferred embodiment, each PSU 101-103 provides an equal share of current so that the output current is balanced among all of the power supplies. For example, in a multi-PSU system having three PSUs, each PSU provides one-third of the total current received at the system load 104. Embodiments of this disclosure address impedance variances among the multiple PSUs to maintain substantially equal current sharing and to avoid one of the PSUs from taking over all of the current supply needs, leading to a shutdown of the overachieving PSU.

[0021] As illustrated in FIG. 1, each PSU 101-103 supplies its own output power to the system load 104 including an output voltage (V.sub.local) 105 and an output current (I.sub.psu) 106. Due, in part, to varied component tolerances, circuit impedances, cables, and the like, the output voltages of the PSUs 101-103 are not equal. Accordingly, the voltage 107 received by the system load 104 can be different from the voltage produced by the individual PSU 101-103. The voltage at the system load 104 is typically less than the voltages produced by the PSUs 101-103 such that a real impedance is experienced between the PSUs 101-103 and the system load 104. A resistor 108 illustrated in phantom is shown in FIG. 1 to graphically illustrate the results of the real impedance. The impedance resistor 108 is not a physical resistor, but its impedance is determinable via Equation 1 below:

[00001]$\begin{array}{cc}{Z}_{\mathrm{real}}=\frac{V_{\mathrm{local}}-V_{\mathrm{remote}}}{I_{\mathrm{psu}}}.& \left(\mathrm{Eqn}.1\right)\end{array}$

In Equation 1, Z.sub.real is the impedance of the virtual impedance resistor 108 illustrated in FIG. 1. It is determined by subtracting the voltage (V.sub.remote) sensed at the remote system load 104 from the output voltage (V.sub.local) sensed at the PSU 101-103. The difference is then divided by the output current (I.sub.psu) to determine the real impedance experienced between the PSU 101-103 and the system load 104. As explained herein, the real impedance is used to encourage full current sharing among the PSUs 101-103.

[0022] FIG. 2 is a schematic diagram illustrating a portion of the multi-PSU system 100 of FIG. 1 according to an embodiment. FIG. 2 illustrates additional details with respect to PSU 101 not illustrated in the blocks for PSUs 102, 103 to simplify the drawing of FIG. 2. However, it is understood that PSUs 102, 103 may include the same details described for PSU 101.

[0023] The PSU 101 includes a voltage conversion plant 200 configured to convert an input voltage 201 into output voltage 105 for delivery to the system load 104. The plant 200 may be any type of voltage converter such as a forward converter, an LLC converter, a buck/boost converter, or the like in a single, multi-interleaved, or multi-parallel configuration according to the design needs of the PSU 101. A controller 202 coupled to the plant 200 is configured to control one or more switches (not shown) in the plant 200 to convert the input voltage 201 into the output voltage 105.

[0024] The paralleled PSU 101 supplies its output voltage 105 through an ORing switch 203 such as a diode or a MOSFET. A measurement point 204 coupled to the output of the plant 200 is configured to provide a measurement of the output voltage 105 to obtain the local voltage (V.sub.local) of the PSU 101. In one embodiment, a current sense resistor 205 in series with the output power delivered through a power output 206 to the system load 104 is provided to sense the output current 106. Measurement points 207, 208 allow the voltage across the current sense resistor 205 to be measured, which can be used to calculate the output current 106 based on a known value of the impedance of the current sense resistor 205. In one embodiment, the controller 202 receives the locally measured voltage and current to be used in the calculations described hereinbelow.

[0025] The system load 104 includes an input power node 209 that receives the output voltages 105 and output currents 106 of all PSUs 101-103. A combined input voltage (V.sub.remote) of the output powers supplied by the PSUs 101-103 is measured at a measurement point 210 by ADC channel of the PSUs 101-103. In one embodiment, the PSU 101 includes a communication controller 212 coupled with the PMBus 211 for sensing remote voltage by the system load 104. The communication controller 212 in turn communicates with the controller 202 to provide the sensed remote voltage. In another embodiment, communication controller 212 is not provided, and the controller 202 may itself sense the sensed remote voltage in a single-controller arrangement. With the local voltage, remote voltage, and output current values known, the controller 202 may calculate the real impedance (Z.sub.real) of the PSU 101 using Eqn 1.

[0026] According to embodiments of this disclosure, a constant, reference impedance Z is determined as a reference for impedance tracking by the individual PSUs 101-103. As illustrated in FIG. 3, the reference impedance Z 300 is a combination of a real impedance (Z.sub.real) 301, 302 and a virtual impedance (Z.sub.virtual) 303, 304. The difference between a PSU's real impedance and the reference impedance Z is the PSU's virtual impedance. For example, Eqn. 2 illustrates calculation of the virtual impedance (Z.sub.virtual) of an individual PSU 101-103.

[00002]$\begin{array}{cc}{Z}_{\mathrm{virtual}}=Z-Z_{\mathrm{real}}& \left(\mathrm{Eqn}.2\right)\end{array}$

As illustrated in FIG. 3, the real impedance 301 of the PSU 101 is greater than the real impedance 302 of the PSU 102. However, both real impedances 301, 302 are below the reference impedance Z 300. Accordingly, each PSU 101, 102 has its corresponding virtual impedance 303, 304. According to embodiments of this disclosure, the value of the reference impedance Z 300 is chosen or selected such that each PSU in the multi-PSU system 100 has some amount of virtual impedance. Choosing the reference impedance Z 300 in this manner promotes equalized current sharing among the PSUs 101-103.

[0027] FIG. 4 illustrates a control voltage adjustment procedure 400 for adjusting the control voltage of a single PSU of the multi-PSU system of FIG. 1 according to an embodiment. The procedure 400 may be implemented by the controller 202 of each PSU 101-103 to adjust the control of the plant 200 based on equalizing current sharing among the PSUs 101-103.

[0028] The procedure 400 determines (STEP 401) whether the output current 106 is less than a predetermined current threshold (I.sub.threshold). The current threshold may be a small value such as 0.5 amps, 0.2 amps, or the like. STEP 401 helps the controller 202 to determine whether any output current 106 is being produced by the plant 200. If the output current is above the threshold (402), the calculation (STEP 403) of a current value of a voltage adjustment (integrator of adjusting voltage, IOAV.sub.current) is begun based on Eqns. 1 and 2 above. STEP 403 employs Eqns. 1 and 2 to calculate the virtual impedance (Z.sub.virtual) of the PSU to which the controller 202 belongs.

[0029] The current value of the voltage adjustment (IOAV.sub.current) is thereafter calculated using the virtual impedance (Z.sub.virtual), the output current (I.sub.psu), a previous value of the IOAV (IOAV.sub.previous), and a filter gain (KF) as illustrated in Eqn. 3.

[00003]$\begin{array}{cc}{\mathrm{IOAV}}_{\mathrm{current}}={\mathrm{IOAV}}_{\mathrm{previous}}+\left(I_{\mathrm{psu}}*Z_{\mathrm{virtual}}-{\mathrm{IOAV}}_{\mathrm{previous}}\right)*\mathrm{KF}& \left(\mathrm{Eqn}.3\right)\end{array}$

Using the calculated current value of the voltage adjustment (IOAV.sub.current), at least a portion of the voltage command (V.sub.command) used by the controller 202 to control the plant 200 is calculated (STEP 404) via Eqn. 4.

[00004]$\begin{array}{cc}{V}_{\mathrm{command}}=V_{\mathrm{ref}}-{\mathrm{IOAV}}_{\mathrm{current}}H,& \left(\mathrm{Eqn}.4\right)\end{array}$

where H corresponds with feedback control appropriate for the type of plant 200 used in the PSU 101-103. H, for example, may be PID control used to adjust the voltage command based on the actual voltage produced.

[0030] Returning to STEP 401, if the output current 106 is less than the predetermined current threshold (405), the previous value of the IOAV is checked to see if its value is zero (STEP 406). If the value is zero (407), the current value of the IOAV is set to zero (STEP 408), and control passes to STEP 404 for calculation of the voltage command (V.sub.command). If the previous value of the IOAV is not zero (409), the current value of the IOAV is set (STEP 410) to the previous value of the IOAV multiplied by a reducing value (e.g., 0.9 as illustrated in FIG. 4). This helps to reduce abrupt or dramatic changes in the V.sub.command signal, especially during transient loading conditions. Control then passes to STEP 404 for calculation of the voltage command (V command).

[0031] FIG. 5 illustrates a control diagram 500 employable by the controller 202 for generating the output power according to an embodiment. As described above with respect to FIG. 4 and Eqn. 4, a voltage reference 501 is modified by a feedback loop H 502 appropriate for the type of plant 503 used in the PSU 101-103 and modified by a current value of the IOAV 504. As a result, the output power 505 generated by the plant 503 includes an output current that is closely matched with the output currents produced by the other PSUs in the multi-PSU system 100.

[0032] Embodiments of this disclosure provide for equal current distribution among the multiple PSUs used such that no one PSU assumes the task of providing all of the current to the system load. In this manner, each PSU provides its equalized share of total output current of 1/N, where N is the number of PSUs in the multi-PSU system.

[0033] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description but is only limited by the scope of the appended claims.