FIELD

[0001] The present invention generally relates to electrical power systems, and in particular to an electrical power system and method incorporating an energy storage system. While the present invention will be described with reference to its application in wind turbine installation vessels, it is to be appreciated that the invention is not restricted to this application, and that other applications are also envisaged.

BACKGROUND

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the invention.

[0003] Wind turbine installation vessels (WTIV) typically utilise a very large number of electric motors in their operation. A WTIV may for example require between 96 to 120 AC motors to allow for the jacking up or down of the vessel hull. The AC motors used for this application are known as ‘jacking’ motors. Furthermore, many other AC motors are required to operate other ancillary equipment such as the stabilisers and cargo elevators of the WTIV, these AC motors being referred to as ‘non-jacking’ motors. Therefore, an elaborate electrical power system is required to control and supply all these AC motors with electric power.

[0004] During the lowering of the hull or leg of the WTIV, the jacking motors will effectively operate as an AC generator thereby providing regenerative energy back into the electric power system. This regenerative energy has however generally been dissipated as heat using a resistive load. This regenerative energy could however be reutilized to power the jacking and non-jacking motors. Systems have therefore been developed that include arrangements to capture and store the regenerative energy produced by the motors, and to subsequently feed that energy back into the power supply to supplement the power generated to run the motors thereby leading to energy savings.

[0005] Such a system is shown in U.S. Patent 10797510 (Keppel Offshore & Marine Technology Centre Pte Ltd et. Al.) which describes a power storge and supply system used for drilling rigs, the system being provided with energy storge systems (ESS) that can be charged by the regenerative energy produced by the jacking motors. The design shown in this patent does not however allow the use of Variable Frequency Drive (VFD) control of these jacking motors due to the direct connection of the AC jacking motors to the AC Bus described in this patent which will in practice mean that the jacking motors must operate at a fixed speed. The use of VFD control of the jacking motors allows them to be soft started with reduced starting current, controlled torque and operated at varying speeds which can lead to reduction in mechanical stress to the jacking system components and greater efficiencies in the power usage of the jacking motors.

[0006] It would be advantageous to provide an electric power and power storage system and method that can be optimised to minimise operational losses and initial capital expenditure.

SUMMARY

[0007] According to an aspect of the present disclosure, there is provided an electrical power and energy storage system for a wind turbine installation vessel including: a DC Bus; at least one energy storage module connected to the DC Bus; and at least one motor module connected to the DC Bus, the or each motor module including an AC jacking motor, an AC non-jacking motor, a DC to AC motor inverter module (MIV) for providing variable frequency drive (VFD) control of the AC jacking motor and AC non-jacking motor, and a change-over switch for alternatively connecting the MIV to the AC jacking motor or the AC non-jacking motor, the MIV being adapted to alternatively provide VFD control of the AC jacking motor or the AC non-jacking motor when connected thereto by the change-over switch; wherein regenerative energy generated by the AC jacking motor or AC non-jacking motor of the or each motor module is transferable though the MIV of the motor module to the DC Bus, and subsequently to the or each energy storage module.

[0008] In some embodiments, the energy storage module includes an Energy Storage System (ESS), and a DC to DC Converter connecting the ESS to the DC Bus.

[0009] In some embodiments, the system includes at least one DC power source connection for connecting the DC Bus to an external MIV for VFD control.

[0010] In some embodiments, the system further includes at least one DC to AC power connection including a DC to AC inverter for connecting the DC Bus to an external VFD control.

[0011] In some embodiments, the system further includes at least one DC to AC connection for connecting the DC Bus to an AC ship services consumer, the DC to AC connection including a DC to AC Inverter and a transformer.

[0012] In some embodiments, the DC Bus is configured as a ring Bus.

[0013] In some embodiments, the system includes an AC Bus, and one or more generators connected to the AC Bus, wherein the AC Bus is connected to the DC Bus by at least one bus connection including a jacking transformer and a bidirectional AC to DC Converter Module connected to the DC Bus.

[0014] In some embodiments, the system further includes at least one AC Bus connected energy storage modules including an energy storage system (ESS), DC to AC Inverter and transformer.

[0015] According to another aspect of the present disclosure, there is provided a method of controlling an electrical power and energy storage system for a wind turbine installation vessel, the system including: a DC Bus; at least one energy storage module connected to the DC Bus; and at least one motor module connected to the DC Bus, the or each motor module including an AC jacking motor, an AC non-jacking motor, a DC to AC motor inverter module (MIV) for providing variable frequency drive (VFD) control of the AC jacking motor and AC non-jacking motor, and a change-over switch for alternatively connecting the MIV to the AC jacking motor or the AC non-jacking motor, the MIV being adapted to alternatively provide VFD control of the AC jacking motor or the AC non-jacking motor when connected thereto by the change-over switch; the method including: connecting the MIV within the or each motor module to either the AC jacking motor or AC non-jacking motor depending on the motor that is being used at the time to thereby provide Variable Frequency Drive (VFD) control to the connected AC jacking motor or AC non-jacking motor; and further enabling regeneration energy generated by the AC jacking motor or AC non jacking motor of the or each motor module to be transferred though the MIV of the motor module to the DC Bus, and subsequently to the or each energy storage module.

[0016] In some embodiments, the system includes an AC Bus, and one or more generators connected to the AC Bus, wherein the AC Bus is connected to the DC Bus by at least one Bus connection including a jacking transformer and at least one bidirectional AC to DC Inverter connected to the DC Bus, and at least one AC Bus connected Energy Storage Module including an energy storage system (ESS), DC to AC Inverter and transformer; wherein the method includes storing energy delivered from the AC Bus to the or each AC Bus connected Energy Storage Module during a low load period of the system, and supplying the stored energy from the AC Bus connected Energy Storage Module during a peak load period of the system. [0017] In some embodiments, the method includes storing energy delivered from the AC Bus to the or each DC Bus connected Energy Storage Module during a low load period of the system via the Bus connection, and supplying the stored energy from the or each DC Bus connected Energy Storage Module to the AC Bus during a peak load period of the system via the Bus connection.

[0018] Other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the figures, which illustrate, by way of example only, embodiments of the present invention,

[0020] Figure 1 shows a first part of a single line diagram (SLD) of an electric power and energy storage system according to the present disclosure; and

[0021] Figure 2 shows a second part of a single line diagram (SLD) of an electric power and energy storage system of Fig. 1 ; and

[0022] Figure 3 shows a third part of a single line diagram (SLD) of an electric power and energy storage system of Fig. 1 .

DETAILED DESCRIPTION

[0023] Throughout this document, unless otherwise indicated to the contrary, the terms “comprising”, “consisting of”, “having” and the like, are to be construed as non- exhaustive, or in other words, as meaning “including, but not limited to”.

[0024] Furthermore, throughout the specification, unless the context requires otherwise, the word “include” or variations such as “includes” or “including” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0025] Figs. 1 to 3 respectively show different parts of a partial single line diagram (SLD) of an electric power and energy storage system 1 according to the present disclosure that is suitable for use in a WITV. Figs. 1 to 3 therefore together show the complete SLD of the system 1 when joined together, with the SLD part shown Fig. 1 being joined to the left of the SLD part shown in Fig. 2, and SLD part of Fig. 2 being joined to the left of the SLD part shown in Fig. 3.

[0026] The electric power and energy storage system 1

[0027] The electric power and energy storage system 1 generally comprises a DC Bus 102 connected to a jacking motor electrical variable speed drive system. The jacking system comprises one or more motor modules 2, each motor module 2 comprising a DC to AC Motor Inverter Module (MIV) 200 connected via a change over switch 201 to an AC jacking motor 202 and AC non-jacking motor 203. One or more energy storage modules 3 are also connected to the common DC Bus 102, each energy storage module 3 comprising an energy storage system (ESS) 301 connected via a bidirectional DC to DC converter 302 to the DC Bus 102. The ESS 301 can receive and store regenerative braking energy from the AC jacking motor 202 or AC non-jacking motor 203 of the motor module 2 for later consumption. The system 1 is also provided with a main AC bus 105 to which is connected one or more generators 106, which may typically be diesel generators. The AC Bus 105 is connected to the DC Bus 102 via one or more jacking transformers 404 108 respectively connected to one or more bidirectional AC to DC converter 400 402 which are in turn connected to the DC Bus 102.

[0028] Motor Module 2

[0029] The MIV 200 of each motor module 2 provides variable frequency drive (VFD) control for both the jacking motor 202 and non-jacking motor 203 when connected thereto. The change-over switch 201 can be electrically or manually operated to switch the MIV 200 to provide an AC power supply to alternatively drive the jacking motor 202 or the non-jacking motor 203. The MIV 200 can store parameters in relation to both the jacking and non-jacking motors 202, 203. The appropriate pre-stored motor parameters will be applied to the appropriate jacking or non-jacking motor 202, 203 through the selection of the change-over switch position selected for that motor. When the jacking motor 202 is selected through the selection of the change-over switch 201 , the MIV 200 together with the associated jacking motor 202 can be arranged to operate together in a jacking group. When the non jacking motor 203 is selected through selection by the change-over switch 201 , the MIV 200 together with the associated non-jacking motor 203 can be arranged to operate in a non-jacking group. Alternatively, the MIV 200 together with its associated non-jacking motor 203 can also be arranged to operate as an individual non-jacking motor 203 with MIV 200.

[0030] The motor module 2 provides several advantages. When the jacking motors 202 are in operation, the non-jacking motors 203 are generally not required to operate and vice versa. The provision of a change-over switch 201 eliminates the need for a separate MIV 200 for the non-jacking motor 202. This can lead to a substantial reduction in capital expenditure for the system 1. Furthermore, the elimination of the MIV 200 for the non-jacking motors 203 reduces the amount of expensive room space required on the WITV. In addition, the maintenance and spare parts costs for a separate non-jacking motor MIV is eliminated. This can also lead to a reduction in the steel structure cost for the system 1 leading to an overall reduction in the dead weight tonne of the WITV. There is also a reduction in the height for the centre of gravity in the overall WITV leading to a more stable vessel.

[0031] Energy Storage Module 3

[0032] Because the energy storage modules 3, each comprising an ESS 301 and a bidirectional DC to DC converter 302, are connected to the DC Bus 102, regenerative energy generated by the jacking or non-jacking motors 202, 203 from each motor module 2 can flow and be stored within the ESS 301 of the or each energy storage module 3. The regenerative energy generated by the jacking or non jacking motor 202, 203 passes though the MIV 200 to the DC Bus 102, and then flows from the DC Bus 102 through the bidirectional DC to DC converter 302 to the ESS 301 of the or each Energy Storage Module 3. It is envisaged that the ESS 301 be a battery, super capacitor or other type of energy storage device

[0033] As VFD control is used for each jacking and non-jacking motor 202,203, this facilitates the recovery of regenerative braking energy that can be harvested and stored in the ESS 301 . Commercially available VFD controllers are typically based on a voltage source Pulse Width Modulation (PWM) principle, and therefore by necessity require an inherent stage of a dc supply within its VFD configuration due the need to convert from ac to dc and then from dc to ac in order to achieve variable voltage with variable frequency output to the ac motor. This requirement of a DC supply within a VFD controller, makes recovery of motor regenerative power easily achievable. During the lowering of the hull or legs of the WITV, the jacking motors 202 operate as a generators, regenerating power and energy back to the DC Bus 102 through the MIV 200, converting ac from the ac motor to dc onto the DC Bus 102 for the Jacking System. The non-jacking motors 203 may also generate regenerative energy in particular motor applications.

[0034] By comparison, in other known jacking systems using VFD control for their jacking motors, they are provided with a dc-to-dc converter or a dc-to-ac converter with a braking resistor to dissipate the regenerative energy thereby wasting this energy as heat which is dissipated into water or air. In the system 1 according to the present disclosure, this regenerative energy is stored in the ESS 301 for later consumption. This will result in fuel cost savings, and lower carbon footprint for the present system 1 when compared with other systems that dissipate this energy into wasted heat.

[0035] DC Power Source Connection 5

[0036] The electric power and energy storage system 1 according to the present disclosure may also provide a DC Power Source Connection 5 to allow external machinery including VFD for cranes to be connected to the DC Bus 102 as shown in Fig. 1.

[0037] Some major crane manufacturers produce cranes complete with their own VFD complete with dc-to-dc converter with braking resistor for dissipation of regenerative energy from the crane motor MIV. This arrangement is provided to protect the proprietary crane control software used within their cranes. Therefore, in order to comply to the crane manufacturer’s power supply requirements, the vessel has to provide one or more AC circuit breaker feeders, and at least one or more step down transformers rated for the high kW crane motor load and its secondary circuit breaker feeder. The crane manufacturers therefore also need to supply an AC to DC rectifier and a crane motor MIV to provide VFD control of the crane motors.

[0038] In the system according to the present disclosure, the DC Power Source Connection 5 provides one or more dc power supply sources to the crane manufacturer’s crane motor MIV. The crane manufacturer can eliminate the need for their own AC to DC rectifier which has no intelligence in its crane control system. The crane manufacturer can now take in a dc power supply source and supply only the crane MIV. This allows the crane manufacturer to keep their proprietary crane control software within their crane motor MIV without exposing that software to other vendors.

[0039] The benefit to the WTIV owner include cost and space savings in not requiring another separate AC circuit breaker feeder for crane VFD, its step down transformer, its AC to DC inverter and its dc to dc converter with braking resistor. The benefit for the system 1 according to the present disclosure is that regenerative braking energy from the crane motor MIV can be fed back to the DC Bus 102 and be recovered as stored energy within the ESS 301 .

[0040] DC Bus 102

[0041] The DC Bus 102 can be a fully closed ring bus. It is however also envisaged that the DC Bus 102 be a partially open ring bus with one or more bus tie breakers 104 open, or a fully open ring bus in an independent island mode. One or more Energy Storage Modules 3 can be connected to the DC Bus to recover regenerative energy for later consumption as previously discussed.

[0042] This flexibility in ring bus connection combined with the winding design of the jacking transformer 108 can operate as a multi-pulse (at least 12 pulse or more) or a pseudo multi-pulse system (at least 12 pulse or more) to mitigate harmonics without having to install expensive and room space occupying harmonics filter nor to worry about high harmonics content.

[0043] A ring bus configuration of the DC Bus 102 provides benefits including high redundancy, reliability and flexibility in operation. This ring bus connection can allow for continuous jacking operation and continuous VFD operation for the MIVs 200 connected to the DC Bus 102. This therefore allows the operation to continue without disruption even if one AC feeder or jacking transformer is lost due to a fault condition, the other remaining quantity of healthy jacking transformers with its connected healthy jacking VFD continue to operate without disruption.

[0044] Low harmonics content is expected and guarantee to meet marine class certification requirement for harmonics content without installation of any harmonics filter.

[0045] DC to AC Power Connection 6

[0046] A DC to AC Power Connection 6 can also be connected to the DC Bus 102 as shown in Fig. 2. The DC to AC Power Connection 6 includes a DC to AC inverter 601 located between and connected to the DC Bus 102, and a crane or other motor 602. This integrated approach with one or more pieces of crane MIV (601) saves space for any crane or other heavy load consumer using VFDs to drive their motors. The benefits achieved by this DC to AC Power Connection is similar to that provided by the DC Power Source Connection 5.

[0047] DC to AC Power Supply 7

[0048] The system 1 according to the present disclosure may also be provided with one or more DC to AC Power Supply connections 7 connected to the DC Bus 102 as shown in Fig. 7. Each DC to AC Power Supply connection 7 includes a DC to AC fixed frequency inverter 701 and a transformer 702 for connection to provide power supply to a AC Ship Services consumer 703.

[0049] During light load conditions, for example in a port, energy stored within ESS 301 connected on DC Bus 102 can provide energy to the AC Ship Services consumer 703. These ESS 301 can operate alone without any generator or operate in parallel with a Harbour Generator or Ship Service Transformer.

[0050] The benefit of this arrangement is that it allows flexibility for the energy stored within ESS 301 to be consumed through any MIV load connected onto DC Bus 102 or to be consumed by AC Ship Services consumers 703.

[0051] AC Bus connected Energy Storage Module 8

[0052] The system 1 according to the present disclosure may also be provided with one or more AC Bus connected Energy Storage Modules 8 connected to the AC Bus 105 as shown in Figs. 1 and 3. Each AC Bus connected Energy Storage Module 8 includes an ESS 801 connected via a bidirectional DC to AC Inverter 803 to a stepdown transformer 803 which is then connected to the AC Bus 105. It is envisaged that the ESS 801 be a battery, super capacitor or other type of energy storage device.

[0053] These ESS 801 can cater for spinning reserve or allow operation of the main diesel engine generators 106 to operate at as close to its full load as possible through a reduction in quantity of one or more main engine generators 106, using the ESS 801 to supply the peak load and for peak load shaving on the generation load or for spinning reserve.

[0054] During low generation load period, the ESS 801 is charged and stored with energy delivered from the AC Main bus 106 to the ESS 801. During peak load conditions with a higher kW load rating beyond that each main diesel engine generator 106 could generate, the Energy Supply Module 8 will supply the energy from the ESS 801 to the AC Main Bus 105 through the bi-direction DC to AC inverter 802. This can allow for a reduction in number of main diesel engine generator 106 that need to operate in parallel operation thereby saving fuel and reducing the carbon footprint of the system 1 .

[0055] The benefits in using the AC Bus connected Energy Storage Modules 8 include cost savings in diesel fuel by running a lesser number of generators 106 than otherwise required to operate for at high loads. Furthermore, the generators 106 can operate at a higher efficiency because they are operating at a higher loading point of operation. There will also be a reduction in the maintenance cost and spare part costs of the diesel engine generators 106 due to the reduction in the number of generators operating in parallel.

[0056] Bus Connection 4

[0057] AC power from the AC Bus 105 can flow to the DC Bus 102 though one or more Bus connections 4 including a jacking transformer 108 and at least one bidirectional AC to DC convertor 400, with two such inverters being shown in Fig. 1 . These bidirectional Power Flow AC to DC convertor 400, commonly known as Active Front End (AFE), can be connected to the DC Bus 102.

[0058] In conventional power systems, single direction AC to DC inverters are installed to convert the AC power from an AC Bus to DC power for a DC Bus, with DC power being provided to the MIV of the motors in combination with a DC to DC converter and Braking Resistor connected onto the DC Bus to dissipate regenerative energy from the MIV of the jacking motor.

[0059] The system 1 according to the present disclosure may use bidirectional AC to DC convertor 400 for converting AC power from the AC Bus 105 to DC power for the DC Bus 102. The advantage of using bidirectional AC to DC Inverters 400 is that it allows the Energy Storage Modules 3 connected to the main DC Bus 102 to also be utilized to provide those functions provided by the previously described AC Bus connected Energy Storage Modules 8. These functions include the generation of a peak shaving and spinning reserve through reverse power flow from ESS 301 through the Jacking Transformers 108 to supply energy to Main AC Bus 105. The ESS 301 installed on the DC Bus 102 can be designed an additional energy source to supplement the ESS 801 installed on the AC Bus 105 to reduce the rating for ESS 801 installed on the AC Bus 105. Alternatively, the ESS 301 installed on the DC Bus 102 can also be designed to serve as a complete vessel ESS energy storage source to eliminate the need for installation of the ESS 801 installed on the AC Bus 105. The benefits of this arrangement include greater flexibility in the energy storage operation of the system 1 , and potential cost reductions or cost elimination of an AC Bus ESS. [0060] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by a skilled person to which the subject matter herein belongs.

[0061] It should be appreciated by the person skilled in the art that the above invention is not limited to the embodiment described. It is appreciable that modifications and improvements may be made without departing from the scope of the present invention.

It should be further appreciated by the person skilled in the art that one or more of the above modifications or improvements, not being mutually exclusive, may be further combined to form yet further embodiments of the present invention.