GB2570357A

GB2570357A - Load balancing of phases of a power distribution unit

Info

Publication number: GB2570357A
Application number: GB1809596.8A
Authority: GB
Inventors: Paakkunainen Teemu
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2018-06-12
Filing date: 2018-06-12
Publication date: 2019-07-24
Also published as: GB201809596D0

Abstract

A power distribution unit 100 comprising a multi-phase power supply input 102, several power supply sockets 1040-1052 each for supplying a device 1060-1072 with single-phase power, several multi-phase controllable switches 1080-1092 to connect the phase of each socket to one of the phases of the multi-phase input, a power load monitor 110 for monitoring the load of each phase of the multi-phase input by devices connected to and supplied by the sockets and/or the power load of the sockets, and a switch controller 112 for controlling the switches and changing the load of each phase of the multi-phase power supply input and/or each power supply socket. The controller may control the switches so that the load of each phase is equally distributed. This may be done by determining the phases with the highest and lowest loads and controlling the switches to connect a socket connected to the highest load to the lowest load in an iterative process.

Description

TECHNICAL FIELD

This specification relates to load balancing of phases of a power distribution unit (PDU).

BACKGROUND

PDUs are for example applied in datacenters and racks housing multiple information technology (IT) equipment such as servers for supplying the IT equipment with electric power. A PDU may receive electrical power from a multiphase, particularly a three-phase power supply input from a grid. Each of the three phases are then wired in in the PDU as single-phase power supply to receptacles with which IT equipment such as servers are connected.

Typically, the load in racks is added in small amounts, basically by installing new servers in a rack. A user must then make the decision from which of the incoming power supply phases a server should be supplied. Most often this is not a conscious decision but just a task of finding the closest receptacle of a PDU of a rack, which may incur unbalancing of the power supply phases with in most cases one phase more loaded than the other phases and in the worst case overloaded.

Fig. 4 shows an example of a standard PDU 400 with a three-phase power supply input 402 and fourteen power supply sockets 4040-4066, each of which is connected to one of the phases LI, L2, L3. Seven servers 4080-4092 are randomly connected to different sockets 4040, 4042, 4046, 4052, 4058, 4062, and 4064 incurring an unbalanced power load on the three phases LI, L2, L3 in that phase LI supplies 5 servers 4080, 4084, 4086, 4088, and 4092, while phases L2 and L3 each only supply one server 4082 and 4090, respectively. In Fig. 4, a neutral line is not shown.

Solutions for phase balancing in datacenters and server racks are known from the US patent US 9,218,033 Bl and the US patent application US 2017/0242469 Al. Power load balancing by phase switching is known from the international patent application

WU2015/134494A2 and the US patent applications US2017/0160711A1 and US2012/0316691A1.

SUMMARY OF INVENTION

This specification describes a PDU being capable of load balancing of phases.

According to an aspect of this specification, a PDU is disclosed, which comprises a multiphase power supply input, several power supply sockets each being provided for supplying a device with single-phase power, several multi-phase controllable switches to connect the single-phase of each power supply socket to one of the phases of the multi-phase power supply input, a power load monitor for monitoring the power load of each phase of the multi-phase power supply input by devices connected to and supplied by the power supply sockets and/or the power load of the power supply sockets, and a switch controller provided for controlling the multi-phase controllable switches and allowing to change the monitored power load of each phase of the multi-phase power supply input and/or each power supply socket. The application of this PDU for example in a datacenter, particularly in racks housing servers may result in better manageable electrical infrastructure allowing a higher utilization rate. Particularly, the required electrical overhead due to load balancing may be reduced. Furthermore, a lower neutral current may be obtained due to the balanced loads. Also, a user does not need to know in which outlet or power supply socket of the PDU a load such as a server should be connected to obtain a balanced load.

The switch controller may be configured to control the multi-phase controllable switches to connect the single-phases of the power supply sockets to phases of the multi-phase power supply input such that the power load of each phase of the multiphase power supply input is as equally distributed as possible. Thus, an automatic load balancing may be achieved and no manual interaction may be required.

The switch controller may be particularly configured to perform the following the steps for obtaining a more equally distributed load of the phases of the multi-phase power supply input: determining the phase of the multi-phase power supply input having the highest load of all phases, determining the phase of the multi-phase power supply input having the lowest load of all phases, and controlling the multi-phase switches of a power supply socket, which is connected to the phase having the highest load, such that the power supply socket is connected to the phase having the lowest load. Furthermore, the switch controller may be configured to iteratively perform the steps until the load difference between the phase of the multi-phase power supply input having the highest load of all phases and the phase of the multi-phase power supply input having the lowest load of all phases is below a predetermined threshold value. Thus, load balancing may be performed as often as required, also when the load balance changes for example due to a server utilization rate.

The multi-phase switches may comprise semiconductor switches, particularly silicon controlled rectifiers, and/or contactors. The multi-phase switches may be configured such that a switchover of the single-phase of a power supply socket from one phase to another phase of the multi-phase power supply input takes less than 5 milliseconds. This may allow to avoid a downtime during a load balancing since the interruption of the power supply of a load is so short that for example a server may not require a shut down.

The switch controller may be further configured for controlling the multi-phase controllable switches such that a switchover of the single-phase of a power supply socket from one phase to another phase of the multi-phase power supply input is asynchronously controlled in such a way that it occurs at or close to a zero crossing of the voltage of the one phase. This may reduce the stress on the switches during a switchover.

One multi-phase controllable switch may be assigned to each power supply socket or to a group of power supply sockets. While the first allows a finer tuning of the load balancing, the later reduces the implementation efforts since less switches are employed.

The switch controller may be further configured in case of an outage on a phase of the multi-phase power supply input to control the multi-phase controllable switches to connect the single-phases of the power supply sockets being connected to the phase having an outage to other phases of the multi-phase power supply input. This allows to protect loads against single phase outages.

A further aspect of this specification relates to a rack comprising at least one PDU as disclosed in this specification. The rack may particularly be provided for housing IT equipment such as servers and designed for application in datacenters with dozens of IT equipment housed in such racks.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

Fig. 1 shows a block diagram of an embodiment of a PDU with a three-phase power supply input and being capable of load balancing of phases;

Fig. 2 and 3 show the PDU in an unbalanced condition and a balanced condition; and

Fig. 4 shows an example of a standard PDU with a three-phase power supply input.

DETAILED DESCRIPTION

In the following, functionally similar or identical elements may have the same reference numerals. Absolute values are shown below by way of example only and should not be construed as limiting.

Fig. 1 shows a PDU 100, which can be for example applied in a server rack for power supply of servers. The PDU 100 comprises a three-phase power supply input 102, which can be connected to a three-phase power supply line of a grid. The neutral connector is not shown in Fig. 1. For supplying IT equipment, the PDU 100 comprises seven power supply sockets 1040,1042,1044,1046,1048,1050, and 1052, each of which is provided to supply connected devices such as servers 1060, 1062, 1064, 1066, 1068, 1070, and

1072 with single phase power.

The PDU 100 further comprises seven multi-phase controllable switches 1080, 1082, 1084, 1086, 1088,1090, and 1092, each of which is assigned to one of the power supply sockets 1040,1042,1044,1046,1048,1050,1052. Each multi-phase controllable switch 1080, 1082, 1084, 1086, 1088,1090, 1092 comprises three semiconductor switches, each of which is connected between one of the three phases LI, L2, L3 and the phase connector of the respective power supply sockets 1040, 1042, 1044, 1046, 1048, 1050, 1052. The semiconductor switches may be implemented by antiparallel connected SCRs. Control inputs of the semiconductor switches of the multi-phase controllable switches 1080,1082, 1084, 1086,1088, 1090,1092 are connected via a bus to a switch controller 112.

The switch controller 112 receives as input signals power load measurements from a power load monitor 110, which may contactless detect the power load on each phase LI, L2, L3 and/or on each of the single-phases of the power supply sockets 1020, 1042, 1044, 1046, 1048, 1050, 1052 (shown by the dotted-lines). Depending on the phase power load measurements, the switch controller 112 can turn the semiconductor switches of the of the multi-phase controllable switches 1080, 1082, 1084, 1086, 1088, 1090, 1092 on or off and in that way control, with which phase LI, L2 or L3 the phases of the power supply sockets 1040, 1042, 1044, 1046, 1048, 1050, 1052 are connected. The switch controller 112 is configured to turn on only one of the three semiconductor switches of each multi-phase controllable switch and to turn off the other two semiconductor switches so that only one of the phases LI, L2, L3 is connected to the phase of a power supply socket.

The switch controller 112 may be for example implemented by a microcontroller configured by a program, which processes the received phase power load measurements and generates depending on the processing control signals for the semiconductor switches, which are transmitted via the bus to the switches.

Fig. 2 shows the PDU 100 in an unbalanced load condition. The turned-on semiconductor switches of the multi-phase controllable switches 1080, 1082, 1084,

1086, 1088, 1090, 1092 are marked with thicker black lines in Fig. 2. In the shown situation, servers 1060, 1064, 1066, 1068, and 1072 are supplied via the sockets 1040, 1044, 1046, 1048, and 1052 with power from phase LI, while the server 1062 is supplied via the socket 1042 with power from phase L2 and the server 1070 is supplied via the socket 1050 with power from phase L3. This leads to a load unbalancing with five servers supplied from phase LI, one server supplied from phase L2, and one server supplied from phase L3. Phase LI thus faces a very high load which could with a standard PDU as shown in Fig. 4 require an intervention from a user to improve the load balancing between the three phases.

The PDU 100 can however assist a user in balancing the loads between the three phases as will be described in the following: the unbalanced condition as shown in Fig. 2 is measured by the power load monitor 110, which transmits the phase load measurements to switch controller 112. The switch controller 112 detects from the received measurements a much higher load on phase LI compared to the load on phases L2 and L3. The switch controller 112 then decides to switch two of the servers from phase LI to phase L2 and L3, respectively, to better balance the load among the three phases. The switchover may be handled by the switch controller 112 asynchronously by first turning off the semiconductor switches connecting servers 1064 and 1068 to phase LI at or close to a zero crossing of the voltage on phase LI, and then turning on the semiconductor switches connecting servers 1064 and 1068 to phase L3 and L2, respectively. The entire switchover may take less than 5 milliseconds so that an interruption of the power supply of the servers 1064 and 1068 is too short for a shutdown of the servers. The short switchover may be achieved by fast semiconductor switches or fast contactors (if used instead of semiconductor switches).

The switch controller 112 may also be configured to implement a certain load balancing strategy, such as for example by determining the phase of the multi-phase power supply input 102 having the highest load of all phases (phase LI in the situation shown in Fig. 2), determining the phase of the multi-phase power supply input 102 having the lowest load of all phases (both phases L2 and L3 in the situation shown in Fig. 2), and controlling the multi-phase switches 1084 and 1088 of the power supply sockets 1044 and 1048, respectively, which are connected to the phase LI with the highest load to switchover the power supply sockets 1044 and 1048 to the phases L3 and L2, respectively, which both have a lower load. This results in a more equally distributed load of the three phases LI, L2, and L3 with three servers supplied from phase LI, two servers supplied from phase L2, and two servers supplied from phase L3. Phase LI thus does no longer face the very high load as in the situation shown in Fig. 2.

It should be noted that the switchover handled by the switch controller 112 can be either automatically initiated by the controller 112 or by a manual interaction from a user, who for example may control the switchover by programming the switch controller 112 via a respective input, for example from a user terminal.

The switch controller 112 may be also configured to initiate a switchover in case of an outage on a phase of the multi-phase power supply 102. For example, when the switch controller 112 detects from the received power load measurements of the phase LI, L2, and L3 a voltage outage on phase LI, it may initiate an emergency transfer from loads connected to phase LI to one of phases L2, L3, assuming that the phases L2 and L3 have sufficient capacity for the loads to transfer safely. If transferring all loads from LI is not possible due to a lack of capacity in phases L2 and L3, a certain priorities scheme can be assigned to loads connected allowing the most critical loads to be transferred to healthy power supply phases and non-critical to be left un-transferred

In the situation shown in Fig, 3, the switch controller 112 would in case of a voltage outage on phase LI switchover the power supply sockets 1040,1046, and 1052 to one of the phases L2 and L3, for example power supply sockets 1040 and 1046 each to phase L3, and power supply socket 1052 to phase L2 such that load is balanced between the phase L2 and L3 and no load is connected to phase LI, which is now protected. Thus, the up-time and reliability of the PDU 100 may be increased on a rack level.

Claims

1. A power distribution unit (100) comprising • a multi-phase power supply input (102), • several power supply sockets (1040-1052) each being provided for supplying a device (1060-1072) with single-phase power, • several multi-phase controllable switches (1080-1092) to connect the single-phase of each power supply socket (1040-1052) to one of the phases of the multi-phase power supply input (102), • a power load monitor (110) for monitoring the power load of each phase of the multi-phase power supply input by devices (1060-1072) connected to and supplied by the power supply sockets (1040-1052) and/or the power load of the power supply sockets (1040-1052), and • a switch controller (112) provided for controlling the multi-phase controllable switches (1080-1092) and allowing to change the monitored power load of each phase of the multi-phase power supply input (102) and/or each power supply socket (1040-1052).

2. The power distribution unit of claim 1, wherein the switch controller (112) is configured to control the multi-phase controllable switches (1080-1092) to connect the single-phases of the power supply sockets (1040-1052) to phases of the multi-phase power supply input (102) such that the power load of each phase of the multi-phase power supply input (102) is as equally distributed as possible.

3. The power distribution unit of claim 2, wherein the switch controller (112) is configured to perform the following steps for obtaining a more equally distributed load of the phases of the multi-phase power supply input (102):

• determining the phase of the multi-phase power supply input (102) having the highest load of all phases, • determining the phase of the multi-phase power supply input (102) having the lowest load of all phases, and • controlling the multi-phase switches (1080-1092) of a power supply socket (1040-1052), which is connected to the phase having the highest load, such that the power supply socket (1040-1052) is connected to the phase having the lowest load.

4. The power distribution unit of claim 3, wherein the switch controller (112) is configured to iteratively perform the steps until the load difference between the phase of the multi-phase power supply input (102) having the highest load of all phases and the phase of the multi-phase power supply input (102) having the lowest load of all phases is below a predetermined threshold value.

5. The power distribution unit of any of the preceding claims, wherein the multiphase switches (1080-1092) comprise semiconductor switches, particularly silicon controlled rectifiers, and/or contactors.

6. The power distribution unit of claim 5, wherein the multi-phase switches (1080-1092) are configured such that a switchover of the single-phase of a power supply socket (1040-1052) from one phase to another phase of the multi-phase power supply input (102) takes less than 5 milliseconds.

7. The power distribution unit of any of the preceding claims, wherein the switch controller (112) is configured for controlling the multi-phase controllable switches (1080-1092) such that a switchover of the single-phase of a power supply socket (1040-1052) from one phase to another phase of the multi-phase power supply input (102) is asynchronously controlled in such a way that it occurs at or close to a zero crossing of the voltage of the one phase.

8. The power distribution unit of any of the preceding claims, wherein one multi-phase controllable switch (1080-1092) is assigned to each power supply socket (1040-1052) or to a group of power supply sockets.

5

9. The power distribution unit of any of the preceding claims, wherein the switch controller (112) is configured in case of an outage on a phase of the multi-phase power supply input (102) to control the multi-phase controllable switches (1080-1092) to connect the single-phases of the power supply sockets (1040-1052) being connected to the phase having an outage to other

10. A rack comprising at least one power distribution unit (100) of any of the preceding claims.

Intellectual Property Office

Application No: GB1809596.8 Examiner: Jonathan Huws

Claims searched: 1-10 Date of search: 26 November 2018

Patents Act 1977: Search Report under Section 17

Documents considered to be relevant:

Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-10 WO2016/003410 Al SCHNEIDER ELECTRIC IT CORP See figures 2 and 3, abstract, page 8 line 13-page 14 line 28 X 1-10 US7898104B1 VERGES See figures 5, 6 and 7, abstract, column 4 line 33-column 5 line 39 X 1-10 US2017/0185121 Al FLUMAN et al See figures, abstract and paragraphs 41-49 in particular X 1-10 US2014/0031997 Al MUKHERJEE See figures 1 and 2, abstract, paragraphs 27-32 in particular X 1-10 US2013/0063280 Al PAMULAPARTHY et al See figures, abstract, paragraphs 28-49 X 1-10 US9820406B1 ERRATO JR et al See figures, abstract, column 6 line 28 - column 7 line 58

10 phases of the multi-phase power supply input (102).