Multi-mode UPS system with an improved energy saver mode

An uninterruptible power supply (UPS) system operable in an energy saver mode includes: a static bypass switch connected between an input connector and an output connector of the UPS system and being activatable to operate the UPS system in the energy saver mode; a plurality power modules, each of the plurality of power modules being connected between the input connector and the output connector of the UPS system and at least some of the plurality of power modules being controllable for a reactive power compensation; and a controller for controlling one or more of the controllable power modules depending on a data input related to a reactive power compensation. The controller controls one or more of the controllable power modules depending on the data input such that a reactive power flow via the UPS system is adjusted.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2018/064963, filed on Jun. 7, 2018, and claims benefit to British Patent Application No. GB 1709695.9, filed on Jun. 19, 2017. The International Application was published in English on Dec. 27, 2018 as WO 2018/234046 under PCT Article 21(2).

FIELD

This specification relates to a multi-mode UPS (Uninterruptible Power Supply) system, which can be operated in an energy saver mode.

BACKGROUND

FIG. 1shows a block diagram of a typical multi-mode UPS system10comprising a rectifier12, an inverter13, a battery converter14, and a silicon controlled rectifier (SCR)11. The UPS system10comprises an input connector for connecting it to a power supply system such as a grid15, a battery connector for coupling the UPS system10to one or more rechargeable batteries16, and an output connector for connecting it to a load17. The input connector and the output connector can be provided either for one, 3-phase or generally a multi-phase power supply. Power supply fed to the input connector can come from separate power sources or from a shared power source.

The UPS system10can be operated in several different modes.

In a double conversion mode, the rectifier12generates a DC (direct current) link voltage from the voltage supplied to the input connector, and the inverter13generates an output AC (alternate current) voltage from the DC link voltage. The battery converter14uses the DC link voltage to charge the one or more batteries16. During a power outage, the battery converter14maintains the DC link voltage while the inverter13continues to operate like in double conversion mode.

The UPS system10can also be put on bypass for maintenance purposes or because of a failure. In this so-called bypass mode, the UPS system10provides mains current directly to the load17through the SCR11. In bypass mode, the load17is however not protected from power outages.

The UPS system10can also support an energy saver mode. In such mode, the UPS system10provides mains current directly to the load17through the SCR11, and the DC link voltage is taken from the output connector. The inverter13and the rectifier12are commanded off to save power. However, when the bypass voltage goes out of its limits or there is some other condition preventing switching the UPS system10into the energy saver mode, the UPS system10immediately transfers back to double conversion mode to protect the load17. The main reason for using the energy saver mode is the improved operation efficiency.

The input power factor of the UPS system10may incur a problem in the energy saver mode. In the double conversion mode, the rectifier12can control the input power factor and depending on the design of the UPS system10, the amount of reactive current can be close to zero. In the energy saver mode, the UPS system10has no control over the power factor, and the load17connected to the UPS output, which may draw reactive power, may cause a lower power factor on the UPS input connector. Capacitors at the input of the rectifier12and at the output of the inverter13may also draw reactive current and, thus, may contribute to a lower power factor of the UPS system10.

The international patent application WO2014201309A1 discloses a multi-mode UPS system, which is operable in an economy mode like the above described energy saver mode. In the economy mode, at least one of the rectifier and the inverter of the UPS system is activated, and that at least one of the rectifier and the inverter is operable to perform at least one of DC voltage regulation, reactive power compensation, and active damping.

The U.S. Pat. No. 6,295,215 B1 relates to power supply apparatus and methods of operation thereof, and more particular, to AC power supply apparatus and methods. Disclosed is a power supply apparatus which includes a multi-mode DC/AC converter circuit that provides a first component of power, for example, a real power component, while a bypass circuit provides a second component of power, for example, a harmonic power component and/or a reactive power component, to the load from an AC power source. The DC/AC converter circuit may include a current mode controlled inverter that provides reactive and harmonic currents to the load such that the bypass circuit predominantly transfers real power between the AC source and the load. In this manner, power factor and other power quality parameters at the AC source may be maintained at desired levels.

The US patent application US 2005/043859 A1 relates to a modular uninterruptible power supply system and control method thereof, in particular to a system of parallel UPS modules all with full uninterruptible power supply capabilities, and identical control logic and functional capabilities for initiating role detection dynamically and electing a virtual master through the arbitration process to control the parallel operation of UPS modules. The system design has incorporated the characteristics of both centralized control and distributed processing by dispensing with a dedicated control module, and is able to operate with one or more UPS modules in parallel, providing fault tolerance and maximum redundancy, and reducing the risks of system-level single point failure to minimum possibility to the emergent and sensitive load.

The US patent application US 2012/181871 A1 relates generally to control of an uninterruptible power supply. Disclosed is an uninterruptible power supply (UPS) that may include an inverter, a controller, and a bypass switch. In a bypass mode of operation, the controller operates the bypass switch to provide power at the uninterruptible power supply output from an input power source via the bypass switch. The controller can also operate the inverter during online operation to regulate the inverter output voltage and to provide output voltage from the inverter at the UPS output when bypass operation is interrupted. The controller can also operate the inverter during bypass and other operation modes to provide, among other things, power factor correction, harmonic current distortion control, and active power to charge a backup power source. In some embodiments, the controller operates the inverter to provide reactive power control and power factor correction.

SUMMARY

In an embodiment, the present invention provides an uninterruptible power supply (UPS) system operable in an energy saver mode, comprising: a static bypass switch connected between an input connector and an output connector of the UPS system and being activatable to operate the UPS system in the energy saver mode; a plurality power modules, each of the plurality of power modules being connected between the input connector and the output connector of the UPS system and at least some of the plurality of power modules being controllable for a reactive power compensation; and a controller configured to control one or more of the controllable power modules depending on a data input related to a reactive power compensation, the controller being configured to control one or more of the controllable power modules depending on the data input such that a reactive power flow via the UPS system between a power supply connected to the input connector and a load connected to the output connector is adjusted according to a required reactive power compensation when the UPS system is operated in the energy saver mode, the controller being configured to determine a required reactive power compensation based on the data input and to determine a number of active power modules for obtaining the required reactive power compensation.

DETAILED DESCRIPTION

In an embodiment, the present invention provides an improved multi-mode UPS system.

According a first aspect, an improved UPS system being operable in an energy saver mode comprises several power modules each being connected between the input connector and the output connector of the UPS system and at least some of the power modules being controllable for a reactive power compensation. The reactive power compensation may be performed depending on a data input related to a reactive load compensation.

According to a first embodiment, a UPS system operable in an energy saver mode is disclosed. The system comprises a static bypass switch being connected between an input connector and an output connector of the UPS system and being activatable to operate the UPS system in the energy saver mode, several power modules each being connected between the input connector and the output connector of the UPS system and at least some of the power modules being controllable for a reactive power compensation, and a controller being configured to control one or more of the controllable power modules depending on a data input related to a reactive power compensation,

the controller being configured to control the one or more of the controllable power modules depending on the data input such that a reactive power flow via the UPS system between a power supply connected to the input connector and a load connected to the output connector is adjusted according to a required reactive power compensation when the UPS system is operated in the energy saver mode.

the controller being configured to determine the required reactive power compensation based on the data input and to determine a number of active power modules for obtaining the required reactive power compensation.

In some embodiments, the controller may be configured to determine the number of active power modules by rounding up the result of the following equation to the next integer value: number of active power modules=required reactive power compensation/maximum reactive power compensation per power module.

In some embodiments, the data input may comprise one or more of the following data: a configured reactive load compensation requirement; a defined UPS system equivalent capacitance; a reactive power on the input side of the UPS system and/or a power factor.

In some embodiments, the controller may be configured to calculate a required reactive power compensation based on one or more of the data comprised by the data input.

In some embodiments, at least one of the controllable power modules may comprise reactive power compensation device being controllable by the controller.

In a specific embodiment, the reactive power compensation device may comprise a rectifier and an inverter being connected in series between the input connector and the output connector of the UPS system, and at least one of the rectifier and the inverter being controllable by the controller.

In some embodiments, the system may comprise measurement unit for measuring the reactive power flow via the UPS system and/or the power factor of the system comprising the UPS system and a load connected to the output connector of the UPS system.

According to a second aspect, a method for operating a UPS system in an energy saver mode is disclosed, the method comprising the steps of obtaining data for determining a required reactive power compensation, determining the required reactive power compensation depending on the obtained data, determining a number of power modules of the UPS system for the determined required reactive power compensation, and controlling the determined number of power modules for achieving the determined required reactive power compensation.

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. 2shows a block diagram of a multi-mode UPS system comprising two parallel connected UPS systems100,100′ for supplying a load170, for example server racks in a datacenter, being connected to the output connectors of the UPS systems100,100′. The input connectors of both UPS systems100,100′ are connected to power supply means such as the grid150.

Both UPS systems100,100′ may be identically implemented, i.e. may comprise identical elements. In the following, only the implementation of the UPS system100is described in detail since the implementation of system100′ is identical.

UPS system100comprises a SCR110, and two or even more power modules connected in parallel to the SCR110between the input connector and the output connector of the UPS system100. Each power module may comprise a series connection of a rectifier120,121and an inverter130,131. The connection point between the rectifier120,121and the inverter130,131comprises a branch connection to a battery and/or battery converter like in the UPS system10shown inFIG. 1.

At least some of the power modules of both UPS systems100,100′ are controllable, which means that they can be at least partly commanded off, particularly when the UPS system100,100′ is operated in the energy saver mode. The at least partly commanding off may be implemented in that the rectifiers120,121and/or inverters130,131of the power modules can be activated or deactivated by means of a respective control signal.

Either a rectifier or an inverter or even both can be used for a reactive power compensation.

The control of the rectifiers and/or inverters of the controller power modules of UPS systems100,100′ is performed by a controller180. The controller180may be an element external to or separated from the UPS systems100,100′, or it may be implemented as an internal element of one or more of the UPS systems100,100′. The controller180may be for example implemented by a stationary or mobile computing device being configured to perform control of the power modules and comprising a data communication connection with the UPS systems100,100′, for example wired or wireless LAN connection, a USB connection, or a Bluetooth connection. The controller180may be also for example integrated in an internal control electronic of the UPS systems100,100′, particularly it may be integrated together with the power modules in an integrated circuit implementing a power electronics of the UPS system. The controller180may be implemented by a standard processor as it is applied for example in personal computers or a microcontroller and configured by a computer program implementing a control algorithm for performing the controller tasks required for a reactive power compensation. The controller180may also be implemented by an ASIC or a FPGA.

When the UPS system100,100′ is operated in the energy saver mode, the SCR110,110′ is activated so that electrical power from the grid150is directly supplied to the load170. As explained in the introductory part, the power modules of both UPS systems100,100′ are normally commanded off in this mode to save energy. The load170or the UPS system100,100′ itself, particularly the input and/or output capacitors of the power modules, may however draw reactive power Q in the energy saver mode. A goal of the reactive power compensation is to eliminate the drawn reactive power Q so that ideally only active power P flows in the input of the UPS system, which would mean an ideal power factor of 1.

For reactive power compensation, a number of the power modules is determined by the controller180, which are not completely commanded off, but either remain activated or are merely partly commanded off, for example by deactivating the inverter or the rectifier of a power module.

The number of the power modules used for reactive power compensation versus the number of all power modules of a UPS system may depend on the following data input:the (amount of) reactive power compensation required in the energy saver mode may be a setting that can be modified according to customer's needs; the reactive power compensation may then be constant and may try to match this predetermined setting; and/orthe (amount of) reactive power compensation required in the energy saver mode may be determined depending on the reactive power drawn by the load and/or the UPS system itself, the reactive power on the UPS input, and/or the power factor of the UPS system in the energy saver mode; andthe maximum reactive power compensation that can be achieved by one power module (maximum compensation per power module).

The number of the power modules required for the reactive power compensation can be calculated from the data input using the following formula:
number of active power modules=reactive power compensation/maximum compensation per power module

The result of the above formula can be rounded up to the next integer value. The maximum compensation per power module may be a configurable quantity, which may be set depending on the type of power module and is known by the algorithm. Particularly, it may be a value predefined in the algorithm and defining the maximum compensation which is possible per power module.

Power modules are commanded on or off according to the result of the calculation. If it is for example calculated that two power modules are needed for the compensation, the first and the second power module of a UPS system may be commanded on while the other power modules are commanded off. A rotation function for commanding on and off power modules according to a predetermined scheme can also be used to reduce the stress for individual power modules. For example, the reactive power compensation can be switched from one power module to another, for instance monthly. For example, so that if power module one and two handled the compensation in January power module two and three will do it in February, power module three and four in March and so on.

In energy saver mode, also the input power factor of the UPS system can be controlled by adjusting the level of reactive power compensation. The UPS system may constantly monitor the power factor and adjust the level of compensation trying to achieve an optimal power factor. The number of active power modules can be calculated using the formula described above. The number of power modules commanded on can change as the reactive power drawn by the load may change. A similar power module rotation function as above described can be used.

Next, an algorithm for controlling a reactive power compensation in energy saver mode of the UPS system100,100′ is explained in detail with reference to the flowchart shown inFIG. 3.

In step S10, the algorithm checks whether the energy saver mode of the UPS system100,100′ is activated.

If the UPS system operates in the energy saver mode, the algorithm loads in step S12as data input a configured reactive load compensation requirement if a corresponding setting has been input for example by a user.

In the following step S14, the algorithm loads as further data input a defined UPS equivalent capacitance which particularly corresponds to the sum capacitance of all power modules of the UPS system, particularly the sum capacitance of the input and output capacitors of the rectifiers and inverters comprised by the power modules.

The algorithm may further determine in step S16as data input the reactive power on the input side of the UPS system and/or the power factor of the UPS system, for example by obtaining measurements of the reactive power and/or power factor as data input from measurement unit, which may be part of the entire system.

It should be noted that two of the data inputs obtained in steps S12to S16may be optional, which means that only one data input is required for a reactive power compensation. It should also be noted that the steps S12to S16can be processed in another order or even simultaneously by the algorithm.

After obtaining the data inputs in steps S12to S16, the algorithm determines in step S18the required reactive power compensation.

If the required reactive power compensation was input as a user setting in step S12, the algorithm can directly use the setting.

If in step S14, a defined UPS equivalent capacitance was input, the algorithm may derive therefrom the required reactive power compensation incurred by the equivalent capacitance. The derivation could be for example calculated with the following formula: Q=C*2*pi*f*U{circumflex over ( )}2, where Q is the reactive power to be compensated (in Var), C is the equivalent capacitance (in F), f is the input frequency of the UPS power supply (in Hz), and U is the input voltage of the UPS power supply (in Volts). Since the input voltage and frequency can vary slightly, an actual measurement of the input voltage and frequency should be used in the calculation. For example, the input voltage and frequency can be constantly measured and the required reactive power compensation can be adjusted accordingly. So, the amount of the reactive power compensation based on the equivalent capacitance is not constant but almost since the UPS system usually only allows small variations in voltage and frequency. In an alternative approach, the required reactive power compensation could be calculated based on the nominal voltage and frequency of the UPS system, for example 230 V @ 50 Hz in Europe and use a constant compensation based on this.

If the algorithm determined in step S16the actual reactive power and/or power factor, it can deduce the required reactive power compensation from these values or measurements.

In step S20, the algorithm determines the number of power modules, which are required for achieving the determined required reactive power compensation, particularly by calculating it with the above described formula by using the data input from steps S12to S16.

The algorithm can use anyone of the data inputs obtained in steps S12, S14, and S16. Particularly, the algorithm may determine the usage of data input depending on whether it obtained in steps S12, S14, and S16, as will be explained in the following:

If the algorithm obtained no data input in step S16, but in steps S12and S14, it may use the data input obtained in the later steps for the determination of the number of power modules to be used for reactive power compensation. The number of power modules determined in this way may be constant.

If the algorithm obtained a data input in step S16, and also in steps S12and S14, the data inputs obtained in steps S12and S14may be used as a starting points for the reactive power compensation, i.e. the algorithm may calculate an initial number of power modules to be used for an initial reactive power compensation from the data inputs obtained in steps S12and S14and may further adjust the number of modules and the reactive power compensation based on the data input obtained in step S16, for example based on actual measurements of the reactive power and/or power factor.

If the algorithm obtained only a data input in step S16and no data inputs in steps S12and S14, it may start with an initial configuration, where all power modules are commanded off and no reactive power compensation is performed by the power modules. Then, the algorithm may determine a number of power modules to be used for reactive power compensation and activate the determined number of power modules. The number of power modules may thereafter be adjusted depending on the actual data input obtained in step S16.

Finally, the algorithm controls in step S22the determined number of power modules, particularly inverters and/or rectifiers of the determined number of power modules for the compensation. For example, the algorithm may generate control signals in step S22to activate the rectifiers and deactivate the inverters of the determined number of power modules. However, it is also possible to active both the rectifiers and inverters of the determined number of power modules, or to deactivate the rectifiers and to activate the inverters.

At least some of the functionality may be performed by hard- or software. In case of an implementation in software, a single or multiple standard microprocessors or microcontrollers may be used to process a single or multiple algorithms.