English:
[0001] This application claims the benefit of U.S. Provisional Patent Application No. 60/595,446, filed on July 6, 2005, which is incorporated by reference.
[0003] Uninterruptible power supplies are designed to provide continuous power to a critical load in the event of a temporary failure of utility power. In some systems, a plurality of UPS modules are connected together in parallel to supply the critical load. Each UPS module generally includes a rectifier, a battery, and an inverter. In the event of an interruption of utility power, the critical load will be supplied by DC power from the batteries in the UPS modules. This DC power is converted to AC power by the inverters on the UPS modules before being passed to the critical bus. One disadvantage of a system using parallel UPS modules is that the load is distributed evenly across each of the batteries in the UPS modules. There is no guarantee, however, that the batteries will have the same energy delivery capabilities. For example, one battery may be relatively new and able to deliver twice as much runtime as another battery that is relatively old. So the UPS with the "old" battery may terminate operation due to an earlier End of Discharge ("EOD") before the UPS with the new battery. In a system with multiple UPS modules, the module with the weakest battery may shut down first, followed by the next weakest, and so on. Each time a UPS module shuts down, the remaining modules experience an increased share of the load. This diminishes the runtime available for the remaining batteries and may overload the remaining UPS modules. The present application addresses these shortcomings and provides other advantages that will be apparent to those skilled in the art.
[0005] Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
[0006] Figure 1 is a schematic diagram of a parallel UPS system according to an embodiment of the invention.
[0007] Figure 2 is a schematic diagram of a control loop for adjusting the output of an inverter according to an embodiment of the invention.
[0009] Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
[0010] Figure 1 illustrates an uninterruptible power supply system according to an embodiment of the invention. The system includes a plurality of UPS modules 10. Each UPS module in this example has a rectifier 16, a battery 18, an inverter 20, and a controller 22. The rectifier 16 converts AC power received by the module 10 to DC power. The AC power received by the module 10 may come from utility power or other AC power sources such as generators. The inverter 20 converts the DC power to a regulated conditioned AC power. The battery 18 provides reserve DC power in the event there is a failure of the AC power source.
[0011] The UPS modules 10 are coupled to a communication bus 12. The communication bus 12 allows the UPS modules 10 to exchange information and commands necessary to operate the UPS modules, such as the battery voltage of each UPS module 10 in the system. The communication bus 12 is preferably a digital communication bus, such as a Control Area Network ("CAN") bus, but other conventional digital buses, such as Ethernet could be substituted as a matter of design choice. Alternatively, an analog bus could be substituted as a matter of design choice as long as the bus can be shared between the UPS modules 10 to facilitate load sharing and other parallel system operations.
[0012] The outputs of the UPS modules 10 are coupled to the critical bus 14. The critical bus 14 delivers power to the critical load (not shown). The critical load is any load that is intended to be protected from power interruptions, and typical examples include computer and medical equipment and the like. The UPS modules 10 may be coupled to the critical bus 14 by conventional means, such as a bypass static switch. The bypass static switch may be common, or each UPS module 10 may be provided with its own bypass static switch. In the event of an interruption of utility power, the critical load will be supplied by DC power from the batteries 18 in the UPS modules 10. This DC power is converted to AC power by the inverters 20 on the UPS modules 10 before being passed to the critical bus 14.
[0013] The controllers 22 in each UPS module adjust the load supplied by the module 10 to the critical bus 14. It is advantageous that the controllers 22 are PID controllers that include a feedback control loop, but other controllers may be substituted as a matter of design choice. The controllers 22 depicted in the embodiment shown in Fig. 1 are PID controllers that have been implemented in software on a microprocessor and use digital signal processing ("DSP") techniques.
[0014] According to one embodiment of the invention, the feedback control loop adjusts the load of each UPS module based on the average battery voltage. With reference to Fig. 1, the average battery voltage is given by the equation: Vbatt_average = (Vbatt_l + Vbatt_2 + Vbatt_3 ... + Vbattji) / n where n is the number of modules on-line. The battery voltage of each battery is communicated over the CAN bus to the other UPS modules in the system. The average battery calculation can be made at a central processor and then passed over the CAN bus, or each UPS module can make the calculation individually.
[0015] According to one embodiment of the invention, the feedback loop, depicted in Fig. 2, will increase the load on an individual battery in a UPS module if the battery's voltage is greater than the average battery voltage and decrease the load if the battery voltage is less than the average battery voltage. As shown in Fig. 2, a signal representing the average battery voltage ("Vbatt_average") is summed with a signal representing the battery voltage of the battery in the particular UPS module. The result of the summation is provided as an error signal to the controller. The controller then sends a signal to the inverter to increase or decrease the amount of energy supplied by the battery in the UPS modules. If the critical bus is an AC bus, then the phase angle of the power supplied by the inverter is advanced with respect to the phase angle of the power on the critical bus to increase the load on the inverter and, hence, decrease the battery voltage relative to the average battery voltage. Conversely, the relative phase angle is decreased to lower the load on the inverter and raise the battery voltage. In this way, the load will be distributed across all the UPS modules that are on battery such that the battery voltage of each battery is adjusted to Vbatt_average, plus or minus a small amount of error that may be present in the control loops. Of course, the accuracy and speed of the control loops is a matter of design choice. Those of skill in the art will recognize that a similar control could be used in a system in which the critical bus is a DC bus, except, of course, that there is no phase angle to adjust and the output voltage of the inverter is adjusted so that it will provide more or less power depending on the battery voltage.
[0016] According to another embodiment of the invention, if one or more of the UPS modules looses utility power and switches to battery operation, the modules can coordinate together to handle the load in an efficient manner. In this embodiment, the UPS module (or modules) that is on battery power first reduces its share of the critical load to zero. By reducing the load to zero, the battery of the UPS module need only supply enough energy to make up for the inverter losses and, therefore, can run for an extended period of time. Reducing its share of the load to zero, however, could overload one or more of the inverters in the remaining UPS modules. The inverters, however, are typically designed to operated in an overload condition for a brief period of time, for example, ten minutes. A signal representing the overload condition is passed over the CAN bus to the module or modules that are on battery. The UPS module(s) will start to provide power to the critical load from its battery, increasing the amount of power provided until the remaining UPS modules are not overloaded.
[0017] According to another embodiment of the invention, the UPS modules may shift load between each other depending on the estimated battery runtime left for their various batteries balanced against the overload runtime. This embodiment is particularly advantageous if one (or more) UPS modules looses utility and operates from battery, and the battery runtime is less than the overload runtime of the remaining modules. Typically, inverters are as designed to run at 125% for 10 minutes. If, for example, a UPS module is within 10 minutes or less of its End of Discharge ("EOD"), then it may be advantageous to reduce the load on that UPS module and allow other modules in the system to temporarily operate in an overload condition, thus preserving battery life for as long as possible. Thus, for example, in a two module system, if the first UPS module is near EOD and has 50% load, then it could give up 25% to the second UPS module, that might have 100% for example, hence placing that module in overload. This would extend the battery run time and keep the critical load protected. Of course, this embodiment is operable with any number of UPS modules. In this case, the UPS module (or modules) that is on battery reduces the power it is supplying thus causing the remaining UPS modules to become overloaded. The control loop balances the estimated battery runtime with the overload runtime. Those of skill in the art will be familiar with methods for estimating the battery runtime, which will depend on the batteries being used and other factors unique to the specific implementation.
[0018] The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Consequently, all such similar applications are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

中文:
[0001]本申请请求于2005年7月6日提交的美国临时专利申请号为60/595,446的申请的优先权,其结合于本文中作为参考。
[0003]不间断电源设计成在市电(utility power)发生临时故障的情况下为关键负载连续供电。在一些系统中,多个UPS模块被并联在一起以向关键负载供电。每个UPS模块一般包括整流器(rectifier)、电池和逆变器(inverter)。在市电发生中断时,关键负载将由来自UPS模块中的电池的直流电供电。此直流电在传送到关键总线(critical bus)前被UPS模块的逆变器转换为交流电。使用并联UPS模块的系统的一个缺点是负载在UPS模块中的各电池之间均匀分配。然而,不能保证电池具有相同的能量输出性能(energy delivery capability)。例如,相对较新的电池能够输出能量的运行时间是另一个相对旧的电池的两倍。所以,具有“旧”电池的UPS可能在具有新电池的UPS之前由于较早的放电结束(“EOD”)而终止操作。在具有多个UPS模块的系统中,具有最弱电池的模块可能首先关断,紧接着是具有次弱电池的模块,依次类推。每次UPS模块关断,剩余模块就要分担更多的负载。这减少了剩余电池可用的运行时间并且可能使剩余的UPS模块过载。本申请解决这些缺点并且提供对本领域技术人员来说很明显的其它优点。
[0005]通过理解以下的详细说明并通过参考附图,本发明的其它目的和优点将变得明显,其中:
[0006]图1是根据本发明的实施例的并联UPS系统的示意图。
[0007]图2是根据本发明的实施例的用于调整逆变器的输出的控制环的示意图。
[0009]以下说明本发明的说明性实施例。为了清楚,不是所有实际实施方式的特性都在本说明书中进行描述。可以理解,在对任何这样的实际实施例的开发中,必须做出多个指定实现的决定,以实现开发者的指定目标,例如遵守与系统相关和业务相关的限制,其随着实施方式的不同而不同。此外,可以认识到,此开发的努力可为复杂的和耗费时间的,但对于利用本公开的优点的那些本领域的普通技术人员,将为例行任务。
[0010]图1示出根据本发明的实施例的不间断电源。系统包括多个UPS模块10。此实例中的每一个UPS模块具有整流器16、电池18、逆变器20和控制器22。整流器16将由模块10接收的交流电转换为直流电。由模块10接收的交流电可来自于市电或例如生成器的交流电源。逆变器20将直流电转换为符合规定条件的交流电。电池18在交流电源发生故障时提供储存的直流电。
[0011]UPS模块10被连接到通信总线12。通信总线12允许UPS模块10交换操作UPS模块所必需的信息和命令,例如系统中的每一个UPS模块10的电池电压。通信总线12优选地为数字通信总线,例如控制局域网络(Control Area Network,“CAN”)总线,但其它常规数字总线,例如以太网可代替作为设计的选择。可替换地,只要总线可在UPS模块10间被共享以促进负载分担和其它并行系统操作时,模拟总线可代替作为设计上的选择。
[0012]UPS模块10的输出被连接到关键总线14。关键总线14将电功率传送到关键负载(未显示)。关键负载是希望能被保护而避免遭受电源中断的任何负载,并且典型实例包括计算机和医疗设备等。UPS模块10可通过例如旁路静态开关的常规装置连接到关键总线14。旁路静态开关可以是共用的,或每个UPS模块10可配备有其自身的旁路静态开关。在市电发生中断时,关键负载将由来自UPS模块10中的电池18的直流电供电。此直流电在传送到关键总线14前被UPS模块10上的逆变器20转换为交流电。
[0013]每个UPS模块中的控制器22调整由模块10供应到关键总线14的负载。控制器22为包括反馈控制环的PID控制器是有利的,但其它控制器也可代替作为设计的选择。在图1所示实施例中绘出的控制器22为已在微处理器上的软件中实现的PID控制器并且使用数字信号处理(“DSP”)技术。
[0014]根据本发明的一个实施例,反馈控制环根据平均电池电压调整每个UPS模块的负载。参照图1,平均电池电压由下式给出:Vbatt_average=(Vbatt_1+Vbatt_2+Vbatt_3...+Vbatt_n)/n,其中n为在线模块的数目。每个电池的电池电压通过CAN总线上传送到系统中的其它UPS模块。平均电池计算可在中央处理器处进行并且随后通过CAN总线传送,或每个UPS模块可单独进行计算。
[0015]根据本发明的一个实施例,图2中所绘的反馈环将在单个电池的电压大于平均电池电压时增加该电池的负载,并且在电池电压小于平均电池电压时减少负载。如图2中所示,表示平均电池电压(“Vbatt_average”)的信号与表示特定UPS模块电池的电池电压的信号相加。相加的结果作为误差信号提供给控制器。控制器随后发送信号给逆变器以增加或减少由UPS模块电池供应的能量大小。如果关键总线为交流总线,则相对于关键总线上的电功率的相位角增加由逆变器供应的电功率的相位角以增加逆变器上的负载,从而相对于平均电池电压减小电池电压。相反,相对的相位角被减小以降低逆变器上的负载并且提升电池电压。通过这种方式,负载将这样分布在所有用电池作为电源的UPS模块中以致使每个电池的电池电压被调整到Vbatt_average,加上或减去可在控制环中出现的误差量。当然,控制环的准确性和速度为设计选择的一个事项。本领域的技术人员将认识到类似的控制可在其中关键总线为直流总线的系统中使用,当然除了没有相位角被调整并且逆变器的输出电压被调整以使可提供取决于电池电压的更大或更小的电功率。
[0016]根据本发明的另一个实施例,如果一个或多个UPS模块释放市电并且转向电池操作,则模块可共同协作使得以有效方式处理负载。在此实施例中,利用电池电源的单个UPS模块(或多个模块)首先将其对关键负载的分担减小到零。通过将负载减小到零,UPS模块的电池仅需要供应足够的能量以补偿逆变器的损失,并且,因此,可运行的时间延长。然而,通过将其对负载的分担减小到零,可使剩余UPS模块中的一个或多个逆变器过载。然而,逆变器一般被设计成能在短时间内例如10分钟内在过载条件下运行。表示过载条件的信号通过CAN总线传送到利用电池作为电源的一个模块或多个模块。UPS模块将开始从其电池供电给关键负载,增加提供的电功率大小直到剩余UPS模块不过载。
[0017]根据本发明的其它实施例,UPS模块可根据它们的多个电池的估计剩余电池运行时间相对过载运行时间的权衡来在彼此之间转移负载。如果一个(或多个)UPS模块释放市电并且利用电池来运行,并且电池运行时间小于剩余模块的过载运行时间,则此实施例特别有利。一般情况下,逆变器被设计为在125%下运行10分钟。如果,例如UPS模块还在这10分钟内或还没到其放电结束(“EOD”)时间,则减小该UPS模块上的负载并且允许系统中的其它模块临时在过载条件下操作可能是有利的,这样就使电池寿命保持到尽量长的时间。这样,例如,在具有两个模块的系统中,如果第一个UPS模块接近EOD并且具有50%的负载,则其可将25%的负载放弃给第二个UPS模块,该第二UPS模块例如可能具有100%的负载,由此将该模块置于过载的。这将延长电池运行时间并且保持关键负载受到保护。当然,此实施例可在具有任何数目的UPS模块的条件下进行操作。在此情况下,利用电池作为电源的单个UPS模块(或多个模块)减小其正在供应的电功率,这样,导致剩余的UPS模块变得过载。控制环使估计的电池运行时间与过载运行时间相平衡。本领域的技术人员对估计电池运行时间的方法是熟悉的,电池运行时间将取决于正在使用的电池和对指定实施方式唯一的其它因素。
[0018]以上公开的特定实施例仅为示例性的,因为本发明可以对具有本文所述内容的优点且对于本领域技术人员来说很明显的不同但等价的方式进行修改和实践。此外,除了权利要求中所述内容之外,没有对此处显示的构造或设计的细节的限制。因此,很明显,以上公开的特定实施例可被改变或修改,并且所有这些改变被认为在本发明的范围和精神内。因此,所有这些类似的应用被认为在本发明的范围和精神内。因此,本文所寻求的保护在权利要求中进行阐述。