Claims

[Claim 1] An uninterruptible power supply system (UPS system) (1) comprising a plurality of uninterruptible power supplies (UPS)

(2a to 2e) coupled in parallel between a main input (4) configured to be coupled to a power source (13) and receive input power, and a main output (12) configured to be coupled to a load (14) and providing output power to the load (14) derived from at least the input power, each UPS (2a to 2e) comprising:

- an input (3) coupled to the main input (4),

- an output (11) coupled to the main output (12), and

- a bypass line (5) coupled between the input (3) and the output (11) via a bypass switch (10) configured to be closed in a first mode of operation, coupling said input (3) to said output (11) via the bypass line (5), and to be opened in a second mode of operation, decoupling said input (3) from said output (11),

characterized in that each UPS (2a to 2e) of the UPS system (1) comprises a control unit (20) in communication with the control unit (20) of all the other UPSs of the UPS system ( 1), the control unit (20) of each UPS (2a to 2e) comprising:

- a first block (22) comprising a first unit (220) configured to monitor a current signal flowing in the branch line of its UPS and determine a root mean square (RMS) value, i.e. an effective value , the current intensity of said current signal, a second unit (224) configured to collect the RMS values ​​of its UPS and of the other UPSs of the UPS system (1) for which the bypass switch is closed, and for defining an RMS reference value corresponding to the lowest RMS value collected, and a third unit (226) configured to determine an activation delay for closing the bypass switch of its UPS, the activation delay being equal to zero if the RMS value of its UPS is equal to the RMS reference value and the activation delay being different from zero otherwise, and

- a second block (24) comprising a fourth unit (246) configured to control the bypass switch (10) of its UPS according to the activation delay transmitted by the third unit (226), the bypass switch (10) being held closed if the activation delay is zero, otherwise the bypass switch being open for a certain time corresponding to the activation delay and then closed.

[Claim 2] A UPS system (1) according to claim 1, wherein the first block (22) is configurable to operate at a first frequency and the second block (24) is configurable to operate at a second higher frequency at the first frequency, the ratio between the second frequency and the first frequency being proportional to the accuracy of the control requested.

[Claim 3] A UPS system (1) according to claim 1 or 2, wherein the first unit (220) of each control unit (20) comprises an AC-DC converter (221) for sampling the monitored current signal and an RMS calculation module to determine the RMS value of the current sample.

[Claim 4] A UPS system (1) according to one of claims 1 to 3, wherein the second unit (224) of each control unit (20) comprises a real-time communication module.

[Claim 5] UPS system (1) according to one of Claims 1 to 4, in which the third unit (226) of each control unit (20) comprises a comparator (227) calculating the difference between the RMS value current signal of its UPS and the reference RMS value, and a delay unit (228) configured to calculate said activation delay after which the bypass switch (10) of said UPS can be closed.

[Claim 6] UPS system (1) according to one of Claims 1 to 5, in which the delay unit (228) comprises an integral corrector

proportional to have zero error at stable state.

[Claim 7] UPS system (1) according to one of the claims 1 to 6, in which the activation delay (28) determined by the third unit (226) is an angle of delay with respect to an angle of phase, and the third unit (226) further comprises a saturation module (229) configured to limit the delay angle of the activation delay between a minimum delay angle of 0° and a maximum delay angle depending on the number of UPS of said UPS system (1).

[Claim 8] A UPS system (1) according to one of claims 1 to 7, wherein the second block (24) further comprises an extraction unit (240) configured to extract fundamental harmonics from the current signal , a phase locked loop (PLL) (242) configured to determine a phase angle of the current signal and detect zero crossing of the current signal, and a comparator (244) comparing the phase angle of the current signal detected by the PLL (242) with the activation delay determined by the third unit (226) of the first block (22), the fourth unit (246) of the second block (22) controlling the bypass switch (10) according to this comparison.

Description

Title of Invention: Dynamic Bypass Power Sharing Uninterruptible Power Supply System

Technical area

The invention relates generally to uninterruptible power supplies (UPS), and more particularly to an automatic bypass system of the shared power supply in an installation comprising a plurality of uninterruptible power supplies electrically coupled in parallel.

Prior technique

The invention can be applied to all uninterruptible power supplies with a static bypass switch independently controlled phase by phase, that is to say with a silicon-controlled rectifier technology, referred to in English as "Silicon Controlled Rectifier". (CRS).

An uninterruptible power supply (UPS) is an electrical device capable of supplying power to a load despite variations in the quality and/or availability of power supplied by public utilities.

A classic online UPS rectifies the input power supplied by an electrical network using a power factor correction circuit, called "Power Factor Correction Circuit" (PFC), in order to supply a bus direct current (DC). The rectified DC voltage is typically used to charge a battery when mains is available, as well as to power the DC bus. In the absence of mains power, the battery powers the DC bus. From the DC bus, an inverter generates an AC output voltage to the load.

Since the DC bus is powered by the mains or the battery, the output power of the inverter remains uninterrupted in the event of a mains failure and if the battery is sufficiently charged. Conventionally known online UPSs can also operate in so-called bypass mode, where unconditioned power with basic protection is supplied directly to a load by an alternating current (AC) power source via a line of derivation. The AC power source used in bypass mode can be the same as that used for the rectifier or a separate (auxiliary) source.

An uninterruptible power supply system (UPS system) thus has a bypass circuit, or bypass path, which is a power path bypassing the UPS, i.e. bypassing the rectifier, the inverter and the direct current (DC) power supply such as the battery which form an uninterruptible power supply unit (UPS unit). An automatic bypass circuit can be used by the UPS unit to switch its load to utility power if the UPS system is overloaded or fails internally. A manual, maintenance or service bypass circuit will allow the user to isolate, maintain or remove the UPS unit without interrupting power to the load by switching the load to mains through the derivation.

Thus, a bypass switch is a non-essential addition to a UPS system which, although not integral to the operation of an uninterruptible power supply, is clearly useful in the event of maintenance or repair. In the event of a problem or if a unit needs to be removed for repair, a bypass switch ensures that power continuity is maintained in the event of a fault.

There are two main types of bypass switches that perform similar but distinct functions. These are static bypass switches and external maintenance bypass switches.

The static bypass switch, or static bypass, is used as a fail-safe for the UPS. If the inverter fails, the load will automatically drop to the main power input, ensuring continuous power. This switch fits almost any online UPS system, providing an added safety measure to ensure power continuity.

The external maintenance bypass switch, or external maintenance bypass, is connected to the outside of a UPS system and is sometimes referred to as a "wraparound bypass". This bypass is used to continue power flow while the UPS is isolated and easily removed for repair.

The alternative is to shut down the entire network in order to remove the UPS, which for some companies can mean several hours of downtime and cost them considerable sums. Additionally, in the unlikely event that the UPS system should itself fail, this switch will ensure that the load is transferred safely and allows the unit to be easily removed and replaced.

To improve scalability and/or redundancy, two or more UPSs can be electrically connected to form a single parallel UPS system with one output. In such a system, the combination of several UPSs can increase the power supply capacity of a load connected to the UPS system in parallel. Moreover, if one of the paralleled UPS fails, the other paralleled UPS can make a backup copy for the faulty UPS.

Typically, a parallel UPS system operating in bypass mode cannot actively control the current flowing through the various bypass paths.

This is because in a parallel UPS system, successful (i.e. equal) load sharing between parallel coupled online UPSs is achieved in online or battery mode by running the UPS of each online UPS in order to correctly regulate the power supplied to each online UPS at the single output (coupled to the load). However, successful load sharing between parallel coupled online UPSs is much more difficult to achieve in bypass mode, where unconditioned power is supplied from each UPS to the single output. Specifically, even though on-line UPSs of the same class are coupled in parallel to a single output and each supply one output (i.e. the load) in bypass mode, the manufacturing differences of the components of each UPS and differences in the cables coupling each UPS to the single output can result in uneven load distribution between each UPS coupled in parallel.

For example, in the case where two UPSs have their branch circuit electrically coupled in parallel with each other. If the branch circuit impedance of each UPS is the same as the other, each UPS will have exactly 50% of the load. However, any mismatch in the branch circuit impedance will cause a different power sharing between the two UPSs.

And, if the load coupled to the facility uses almost 100% of the power that the facility can supply, i.e. close to 100% of the load rate, the impedance mismatch can cause the operation of one of the UPSs overloaded while the other is not, thus creating a potential malfunction of the entire system.

This is because if a load is shared unequally between on-line UPSs coupled in parallel and operating in bypass mode, one of the UPSs can be overloaded, which can lead to damage to UPS components. Unequal sharing of a load between on-line UPSs coupled in parallel can also result in the creation of an upstream protection circuit (a circuit breaker, for example) when one of the UPSs trips, resulting in the transfer its share of the load to the other UPSs connected in parallel. The additional load transferred to the other UPSs may cause an upstream protection circuit to trip in another of the UPSs and transfer its load to the other UPSs connected in parallel. As the circuit breaker tripping/load transfer process continues to other UPSs, the later UPSs may no longer be able to support the load and the load may be abandoned.

In general, the power mismatch is directly proportional to

impedance mismatch and indirectly to impedance. For this reason, and also considering the impedance properties of the cables, high power inverters are more affected by the power sharing problem.

the bypass power supply.

A common technique for dealing with uneven load sharing between parallel UPSs operating in bypass mode is to identify the real part of the load that each UPS bears (i.e. the load sharing part) coupled in parallel and adjusting the impedance between each UPS and the load in an attempt to evenly distribute the load on the UPS. The impedance between each UPS and the load can be configured by adjusting the length of the cable connecting each UPS to the load and/or adding an inductor, i.e. an inductor also called a bypass sharing inductor, between a UPS and the load.

However, such a solution can only mitigate the impedance imbalance and therefore cannot guarantee a high level of bypass power sharing. This is because perfect sharing is very difficult to achieve, normally ±10%, due to inductive sharing imbalance.

In addition, this hardware solution also has the disadvantage of increasing the total cost, reducing efficiency, reducing reliability, increasing the size of the installation and increasing the weight.

For example, it is generally accepted that, despite adjusting lengths and/or adding snubbers to cables coupling UPSs in parallel to a load, a maximum number of four online UPSs, or units of UPSs, operating in dice mode 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closed to ensure a direct path between the main input and the main output of the UPS system.

The UPS system according to the invention thus comprises an electrical structure comprising a plurality of control units distributed over each of the UPSs of the UPS system. As indicated above, this electrical architecture is produced without a master-slave relationship between the control units of the different UPSs, unlike the system described in the state of the art such as for example in document US 2017/0163086 which always has at least at least one main controller or a main controller managing the different UPSs or the controllers of the UPS.

The structure of the present invention using distributed control units on each of the UPSs eliminates the criticality of the single point of failure and therefore creates a current sharing structure suitable for a real parallel system. With this distributed structure, a failing control unit of a UPS can be ruled out with limited compromise of bypass power balancing.

This solution eliminates the concept of increasing the physical impedance used in the state of the art and therefore all the drawbacks associated with it and which relate to cost, efficiency, reliability, size and weight.